CHAIR OF

MULTIBODY

DYNAMICS

The project aims to implement a digital twin in the powertrain area and combines various methodological preliminary work in the area of component development (interaction between structural and electrodynamics as well as acoustics in e-components) with overall system considerations. The main focus of the work is on simulation models for constant velocity joints in the drivetrains, which are subject to different loads as a result of e-mobility.
Questions relating to the identification of excitation mechanisms in the constant velocity joints and process parameters for influencing them are being investigated. The necessary experimental investigations are carried out on a cardan shaft test bench and a road-to-rig test bench.
The relevant work packages can be summarized as follows:

• Recording of measurement data (forces, torques, deflection angles, vibrations) of the drivetrain in cooperation with the Institute for Competence in AutoMobility (IKAM) & the Center for Method Development (CMD)
• Development of a detailed calculation method for the drivetrain with a focus on the constant velocity joints
• Reduction of the degree of complexity for implementing the method in the typical development process

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The Modular Peristaltic Surface Conveyor (MPSC) is an entirely new device that conceptually enables the separation and sorting of flexible small packages (polybags) for the first time, providing an alternative to costly manual processing. For the first time, alongside the development of the actual MPSC, an AI-based Digital Twin (DT) is to be developed, which, based on AI-optimized simulation models, will allow predictions of system behavior and automated parameterization of the actuators and sensor data processing.

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The DFG-funded research project aims to increase the numerical prediction capability for technical systems by implementing a holistic simulation methodology that enables efficient coupling between a multi-body simulation and a non-linear FE model. An extension of the physically motivated dynamic flocculation model is used to fully and precisely map the non-linear material behavior of elastomeric bearing elements. The focus here is primarily on the changes in the properties of the bearings under multi-axial loading, which are often neglected in current modeling approaches at . Since the integration of a detailed FE model leads to an increase in the necessary computing resources, different levels of detail of the solver coupling are implemented and analyzed in this project with the aim of allowing a reduction in computing time with an acceptable loss of accuracy. The resulting different levels of complexity of the developed methodology are comprehensively compared with conventional modeling strategies. The individual coupling strategies are evaluated with regard to the implementation and parameterization effort as well as the physical interpretability and the required computing resources. The developed and validated FE models based on the DFM are also examined with regard to their suitability, to what extent and with what reliability certain material parameters can be transferred once to other geometries and load scenarios. Finally, the accuracy of all investigated strategies for coupling the FEM and MBS is assessed with the aid of test results from real applications. The FEM is integrated into the MBS both directly via various solver couplings and indirectly by generating a characteristic map or a surrogate model with the aid of the FE model for use within the MBS. The first application example is a laboratory centrifuge, whose vibration amplitudes and operating resonances are measured and compared with the numerically obtained results of the respective coupling strategies. Furthermore, the developed methodology is applied and validated in the context of a vibration analysis of chassis components of an electric vehicle.
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The Fatigue Damage Spectrum (FDS) is a popular method used in industry to execute accelerated vibration testing for mechanical components and structures. This method uses compressed test signals in time domain to derive vibrational velocity which in turn is used for obtaining induced mechanical stresses. Taking the SN-curve properties (slope and intercept) of the material and linear damage accumulation model (Palmgren/Miner) in account, the damage for the component is derived in frequency domain. The core of the process now comes into action by reducing the time of the test signal and preserving the damage content in each frequency band constant. The accelerated signal is converted back into time signal from frequency domain using a distribution function. This process ensures keeping the damage content in each frequency band constant while accelerating testing times on testbenches.
The process uses the relationship between vibrational velocity and mechanical stress to deduce the damage. Other vibrational parameters like acceleration for the dependency of mechanical stresses has also been investigated in recent times. However, the choice of parameters is the sole responsibility of the user. This study aims to aid the user in the choice of parameter by conducting experiments on an electrodynamic shaker and analysing the dependency of mechanical stresses on various vibrational parameters.
Additionally, the question arises how would the results of FDS change if SN-curve parameters are varied for the same material (e.g. from FKM Guidelines, MIL standard or even from an experimentally determined SN-curve). The limits of FDS are investigated in this scenario.
The transformation of the accelerated signal from frequency to time domain is undertaken with the help of a distribution function (often assumed to be Gauss) and a random phase distribution of the load amplitudes. In reality, loads are more often than not, non-Gaussian. From a new perspective, consideration of distribution functions like Lalanne, Dirlik as well as higher statistical moments like skewness and kurtosis are proposed for the reconstruction of the accelerated time signal. The research question arises here to which extent is the general assumption of a distribution function valid and if necessary which additional information is required to achieve a better consensus between simulated and experimental results.
Experiments are conducted on an electrodynamic shaker with samples of structural steel and electro-grade copper. In parallel, FEM simulations as well as spectral methods of damage calculation are used to compare experimental results.

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Modern, shoulder arthroplasties with stemless implants (figure a) help to preserve larger parts of the original bone substance and to reduce potential risks of conventional implants. Their shape allows newly formed bone structures to grow directly through the implant. However, it is not fully explained how an optimal fixation of the implant can be achieved or stimulated.

In this context, the project aims to simulate the mechanical loading in the humerus during the operation using the finite element method. The results are used to investigate whether one or more mechanical parameter, e.g. stresses or elastic/plastic strains, can be correlated with measurement data of cell activity in the bone, which is available in the form of SPECT/CT data.
The derived workflow consists of the following steps:

1. Derive the relevant bone geometries as well as the exact location of the implant from SPECT/CT data (figure b) .
2. Transform the geometries as well as the measurement data to a reference position for the simulation.
3. Generate a finite element model from the data (3D point cloud and corresponding intensity from the CT measurement (figure a) .
4. Conduct FEM-Simulation with suitable material models and material data (figure d) .
5. Evaluation of the simulation results and correlation with measured cell activity in vicintiy of the implant.

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The rotordynamic properties of systems with hydrodynamic bearings are affected crucially by the nonlinear bearing forces. Regarding fast-rotating, lightly-loaded rotors, this causes subsynchronous self-excited oscillations with potentially high amplitudes, which can reduce the durability of the components, cause critical noise emissions, and affect the energy efficiency of the machine. To reduce expensive test bench experiments and time-consuming iterations in the product development process, the design has to be based on precise simulative analyses of the operating behavior under consideration of the nonlinear interactions between the bearing forces and the shaft vibrations. To this end, the equation of motion of the elastic shaft is incorporated into a time integration scheme and coupled with the Reynolds equation, which describes the pressure generation in hydrodynamic bearings. Hence, each time step of the simulation includes a solution of the Reynolds equation, for which numerical methods, analytical approximations, and look-up tables are employed. While numerical methods lead to considerable and often inacceptable computational times, analytical solutions are only possible in conjunction with substantial simplifications. The look-up table approach, to some extent, offers a tradeoff between these two extremes, while the modeling depth is usually limited, since the interpolation effort increases with every considered physical effect.

A promising basis for the development of a novel, numerically efficient solution without the substantial limitations of analytical methods or look-up table techniques is the semi-analytical Scaled Boundary Finite Element Method (SBFEM). The fundamentals for solving the Reynolds equation with the SBFEM have been derived in preliminary work, but the potential of the approach has not been exploited yet, which is the objective of this project. In order to further reduce the numerical effort, high-order shape functions need to be employed in combination with an automatic, adaptive mesh refinement as well as coarsening and a transformation of the Reynolds equation in a manner that smoothens the solution is analyzed. Another strategy worth investigating is to avoid the repeated solution of eigenvalue problems within the time integration scheme. This requires that the eigenvalue problem is differentiated with respect to the parameters of the shaft displacement and developed into a series prior to the rotordynamic simulation. In order to improve the modeling depth of the SBFEM solution compared to the preliminary work, strategies for incorporating mass-conserving cavitation models as well as shaft tilting need to be investigated. In the last step, the developed methodology is to be verified and analyzed with regard to its efficiency. To ensure a realistic context, this is done within the framework of a rotor dynamics or MBS formulation, whereby complex technical overall systems can also be simulated.

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Screws are often used for the assembly of machines, which enable non-destructive disassembly. An important parameter for bolted connections is the preload force and the torque required to set this force in the fastener. The calculation of a bolted joint can usually be carried out analytically if the stiffness of the components to be bolted is known, whereby the preload force can be maintained by a long bolt shank even when the components are set or moved. This principle is implemented in practice with expansion bolts.
It becomes problematic if there are additional thermal expansions due to different temperatures or different coefficients of thermal expansion in the materials of the connection, which can lead to a rapid drop in preload. Due to the thermomechanical coupling and the usually indeterminate bearing, numerical simulations must be used at this point.
The project examines a machine in which parts of the screw connection become very hot. On the real component, the longitudinal strain and thus the longitudinal force under real temperatures and other loads are recorded by operating forces using strain gauges.
For detailed analysis, a thermomechanical FE model of the entire machine with all screw elements (statically indeterminate bearing) is created in order to calculate the influence of the change in preload force due to temperature.
In addition to the preload force, the stress distribution in the remaining part of the machine can also be determined in the FE model. These analyses are relevant because a preloaded bolt in a warm state contracts when it cools down and the preload force then increases. This means that the permissible stresses in the bolt and also in the components can quickly be exceeded.
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The sacroiliac joint (SIG) is the articulated connection between the sacrum and the ilium, whereby the joint is characterized by a composite structure and is tight and only slightly mobile as a result of various attaching ligaments. In many dogs, this joint stiffens further with age, causing pain during movement. So far, too little information is known about the degree of stiffening and the actual range of movement for treatment.
Consequently, recording the range of motion of different individuals (healthy and diseased) is a necessary step towards a better understanding of the so-called SIG syndrome.
The basic examination of the mechanical properties of the SIG is carried out post mortem. To determine the mobility of the joint, the sacrum is fixed and a movement is forced on the ilium using actuators. The forces required for this and the resulting spatial movement of the ilium and sacrum are measured. In principle, the translational and rotational stiffnesses of the SIG can be determined from the ratio of the kinematic and dynamic variables determined in this way.
As it is not possible to impose directed loads on the ilium to specifically stress the individual ligaments of the joint, the elastic parameters of the ligaments are determined using heuristic methods from the previously determined measurement data. This method is validated by simulation using a multi-body model that includes the ilium, the ligaments and the actuators of the test stand with their spatial orientation.
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In refrigeration systems, gaseous media are compressed by a compressor and thereby liquefied. The refrigerant is then transported in pipes to other components such as heat exchangers or dryers. The rotary motion of the compressor causes vibration excitation of the pipe system, whereby resonance excitation is also possible depending on the speed and operating point, which can lead to large deformations and system failure, especially in the often weakly damped pipes.
In the project, the vibrations of a piping system are determined experimentally and a 3D FE model of the actual state is created. After validation, design changes in the fastening and mounting of the pipes can be examined for their influence on the stresses acting in the material. Particularly in complex refrigeration systems, the pipelines are very long and angled, which is why an analytical approach is no longer possible.
This development step allows critical pipe vibrations to be determined and suitable design changes to be implemented in the calculation model. In practice, virtual product development saves the construction of prototypes and reduces the final test to a few preferred variants that can be derived from the calculation model.
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Simulation-based and sensor-based functionalized housing design

The ZIM network INSTANT is primarily concerned with medical issues. Within the network, the COCOON R&D project focuses on reducing noise pollution during diagnostic and interventional image-guided procedures.
Various medical studies show that persistently high noise levels can lead to poor concentration, stress, impaired memory, a general reduction in performance and other symptoms, including burnout syndrome. Such stress and anxiety situations are detrimental to the recovery of patients and lead to longer treatment times and therefore increased costs. On the part of clinical/medical staff, noise pollution can lead to loss of concentration and treatment errors, for example during interventions lasting several hours or several consecutive interventions.
In many machines, the generation of loud noises cannot be prevented or can only be prevented by interfering with the existing structure. However, technical measures can be taken to hinder the propagation and transmission of noise and thus minimize the disturbing noise emissions. The COCOON project is researching methods for designing and manufacturing acoustically optimized housings for large medical devices, which also results in very high standards with regard to approval and the materials used.
Furthermore, the ambitious approach of researching a "diagnostic system" for recording the status of product functionality is being pursued. The early alerting of malfunctions is intended to minimize device failures and can thus contribute to product monitoring after the product has been placed on the market.
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The sport of hammer throwing is a very technical discipline in which the execution of the movement significantly influences the result, i.e. a high throwing distance. There are many approaches for supporting technical training that are based on metrological data and image acquisition. The accelerations and locus curves of the athlete and hammer are recorded and can be compared with target data. Multi-body simulation of the hammer throw, in which the kinematics of the hand movement are described by means of a parameterized synthetic trajectory, allows the movement of the hammer and thus the final throwing distance to be simulated. Scalar parameters in the approach allow the trajectory to be changed and thus the direct analysis of changes in movement. Using heuristic methods, the parameters of the hand movement can thus be optimized for a maximum throwing distance and the motion sequences derived from this can then be used to improve training.
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The aim of the research project is to increase the simulation quality of rotordynamic systems with regard to the influence of the non-linear damper characteristics of squeeze oil dampers (QOED), taking transient load conditions into account, and to derive suitable design criteria for improved response and damping behavior.
As part of the previous project "Squeeze oil dampers - elements of an optimized external bearing support", a tool was developed for the transient simulation of QOED, taking into account axial seals, fluid inertia effects and cavitation using a two-phase model. The focus of the current project is a consistent extension of the tool to include the effects of fluid turbulence and transient bubble growth. Furthermore, the influence of acting contact forces between the damper sleeve and the locking bolts will be analyzed and the fluid dynamics in the area of the feed geometry of the QOED will be examined more closely. Due to the non-linear interactions of the fluid, contact and rotor dynamics, a holistic approach is pursued, which provides for a direct evaluation of the Reynolds differential equation as part of a transient multi-body dynamics simulation. The results are validated directly using practical test data from the participating industrial partners.
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Due to the necessary high performance requirements, agricultural commercial vehicles are often equipped with large diesel engines that drive numerous units. During the operation of such a vehicle, the engine generates very dominant structure-borne and airborne noise emissions, which is why working next to a running large diesel engine is usually not possible without hearing protection. For this reason, modern driver's cabs in current vehicles are heavily encapsulated so that the driver is protected from airborne noise. However, technical modifications to the engine can lead to a subjective increase in sound amplitudes in a limited frequency range, which is perceived as disturbing in the driver's cab.
As part of the experimental study, the cause of the noise is narrowed down and specific conversion measures on the cabin are evaluated. In addition to the vibration acceleration on engine parts, the sound pressure outside and inside the cabin is recorded and evaluated audiologically, among other things.
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This project builds on two previous publicly founded projects, which focused on detailed models for hyrodynamic bearings to calculate the complex dynamic behaviour of rotors, which are supported by hydrodynamic bearings. In this context, it is essential to simulate the non-linear behaviour of the bearings as accurately as possible. This non-linear bearing behaviour is characterised by non-linear stiffness and damping properties, cavitation processes and a non-linear dependence of the lubricant viscosity on the operating temperature. This modelling is done by transient solving the differential equations, which describe the lubricating film: the Reynolds PDE and the energy equation.
Three aspects are analysed in more detail in the current project:

1. Precise calculation of the fluid flow in gap height direction. The velocity of this flow is usually very small because of the small gap heights (order of magnitude: <100 µm), but it can still have a big impact on heat transfer mechanisms in the lubricating film. This is especially true for thrust bearings at high rotational speeds and loads (figure 1). Because there is more heat transfer in gap height direction, more heat is carried over the segment, which means an increased temperature niveau in the lubricating film
2. Investigation of the centrifugal term in the Reynolds PDE for thrust bearings, which is often not implemented completely, but only up to the order h³. At high rotational speeds, this can also lead to inaccuracies. In the analysed load cases, the inertial influence is overestimated by up to 15% due to the simplified implementation.
3. Investigation of suitable temperature boundary conditions at the segment inlet of hydrodynamic bearings.

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A key point in the design of rotordynamic systems is the bearing. Compared to conventional bearing concepts such as plain and roller bearings, gas or foil bearings have significantly lower power losses, which is mainly due to the low viscosity and the associated shear stresses of the fluid used (air). As a result of the low viscosity, a low clearance is required to ensure an adequate load carrying capacity. In order to compensate for the temperature rise and the centrifugal force development of the shaft, the bearing shell is designed to allow elastic deformation, which is usually realized by a system of metal foils, e.g. in the form of a top and underlying bump foil. The relative movement between the foils also provides additional damping. During the design process, dynamic simulations of the rotor must be performed to predict the amplitudes due to unbalance and subsynchronous vibrations, the latter defining the stability limit of the system.
The aim of the project is to implement bump-type foil bearings in a rotordynamic simulation in order to be able to perform Campbell diagrams taking into account the non-linearity of the bearings as well as non-linear run-up analyses. The procedure includes an online numerical solution of the Reynolds equation applied to the ideal gas law and combined with different models for the film deformation. A common approach is to use a 1d discretization in the circumferential direction assuming stationary conditions, for which an analytical formulation of the bump film stiffness or a finite element model of the top film is often used. This approach is initially extended to a 2d approach in order to take into account misalignment or tilting of the shaft. To additionally describe the damping of the foil structure in a suitable way, the time-dependent deformation behavior of the foil is mapped, which requires the inclusion of inertial properties and a friction model. This is initially realized by a displacement-dependent structural damping with superimposed Rayleigh damping.
Due to the time dependence, the described formulation leads to further state space equations, which are solved by a Newmark algorithm and are embedded in the time integration of the rotor's equation of motion.
The comparison of the simulation results with the measurements available in the literature shows a high modeling quality of the extended approach, which cannot be realized with quasi-stationary simulations or simplified foil models, resulting in a significant added value in the design of non-linear rotor systems with foil bearings.
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The increasing variety of products in the automotive industry, combined with considerable time and cost constraints in the development process, requires the increasing use of computer-aided simulations. As a means of increasing driving safety and comfort, the scope and importance of active chassis control systems in vehicles is constantly growing. Since these active control systems have a considerable influence on component loads and service life, an important task and challenge for the simulation is the accurate representation of the interaction. Therefore, possible simulation strategies for the integration of active control systems into the multi-body simulation of vehicles are developed and evaluated as part of the research activities.
The corresponding methods are analyzed using the example of the brake control system, whereby quality criteria are first defined on the basis of a statistical evaluation of driving measurements in order to evaluate the minimum required simulation accuracy as well as various coupling strategies and control models.
In addition to modelling the original control system, a simplified parameterizable control system model was developed for this purpose. Furthermore, a methodology for modeling the controlled systems using neural networks was developed, whereby the optimal methods are to be identified depending on the project phase and the accuracy requirements.
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In recent years, electrical machines have been developed and optimized at OVGU in various research projects (ELISA, KEM - Kompetenz in Elektromobilität). The basic design is a permanently excited synchronous motor with an air gap winding, which requires particularly little copper. The current design is an external rotor, i.e. the stator is inside and the outer part rotates. The advantage of this design is a higher torque due to the large diameter of the air gap, which means that a gearbox is not required to connect the motor to the wheel or the propeller.
While the central element of the investigations as part of the KEM research project was the optimization of the thermal and acoustic properties of the motor, current and future projects are investigating an adapted design to make the manufacturing process more efficient, as well as the adaptation to corresponding applications.
After an early version of the motor had already been installed in an e-glider, test drives revealed a need for further optimization, primarily with regard to the construction of the fuselage shell. The second version of the e-glider is characterized by consistent lightweight construction, which is realized with an extremely light fuselage shell by FVK Dessau. In addition, the drivetrain is being adapted with the electric motor with air gap winding, which was optimized as part of the research project and will become part of an outboard drive.

Technical data: E-glider Adelheid 2

• Propulsion: outboard motor
• Motor: optimized electric motor with air gap winding and 12 kW continuous power, water-cooled - electrically limited to 10 kW
• Traction battery: 3x2 kWh 48 V LiIo
• Motor controller: 1x Hersi HST350 air-cooled
• Empty weight: approx. 250 kg

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The aim of the joint project DampedWEA is to increase the acceptance of wind turbines. The aim is to open up new areas for wind turbines, particularly in the vicinity of inhabited areas. This requires a reduction in the radiated noise level. In this joint project, the focus is on monofrequency emissions, which are increasingly coming to the fore as a result of the successful optimization of aeroacoustic emissions and can pose a problem. In order to reduce these sufficiently, innovative concepts for vibration and noise reduction are used. The generator can be a significant source of disturbing noise, as the vibrations from the generator propagate through the bearings and the drive train or through the generator support structure into the entire wind turbine and are ultimately emitted as sound. Noise with a limited frequency range is particularly critical for public acceptance, as it is perceived as much more disturbing than broadband noise.

The aim of this project is to investigate transmission paths where research into the potential for noise reduction is promising. In addition, many different concepts will be tested, some of which go far beyond the current state of the art. The project is being carried out in a consortium consisting of WRD/Enercon with the research partners DLR, Fraunhofer IFAM, Otto von Guericke University Magdeburg and Leibniz University Hanover.
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The aim of the joint project DampedWEA is to increase the acceptance of wind turbines. The aim is to open up new regions for wind turbines, particularly in the vicinity of inhabited areas. This requires a reduction in the radiated noise level. In this joint project, the focus is on tonal emissions, which are increasingly coming to the fore due to the successful optimization of aeroacoustic emissions and now pose a problem. In order to reduce these sufficiently, innovative concepts for vibration and noise reduction are used. The main source of tonal noise is the generator, as the vibrations from the generator propagate via the bearings and the drive train or via the generator support structure into the entire wind turbine and are ultimately emitted as sound. Tonal noises are particularly critical for public acceptance, as they are perceived as much more annoying than broadband noise.

The aim of this project is to investigate transmission paths where research into the potential for noise reduction is promising. In addition, many different concepts will be tested, some of which go far beyond the current state of the art. The project is being carried out in a consortium consisting of WRD/Enercon with the research partners DLR, Fraunhofer IFAM, Otto von Guericke University Magdeburg and Leibniz University Hanover.
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The declared aim of the project is the continuous implementation of the models created in the project: Friction-welded hybrid joints made of aluminum and steel: experimental investigation and phenomenological modeling. A simulation platform is being developed specifically for this purpose, in which the calculations for the process, material and structural simulation (virtual tensile test) converge incrementally. The modeling method is then critically evaluated by validating the simulated load-bearing capacity with corresponding experimental data. After successful validation, the load-bearing capacity of the hybrid joint is to be improved through targeted process optimization.
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As part of the KEM - Competence in Electromobility research project, a modular battery pack based on 48V was developed, which is characterized above all by good dismantlability and temperature control of the cells. However, these functions require a complex structure that must be able to withstand the dynamic loads (depending on the application) during operation.
To ensure functionality under dynamic conditions, a vibration test was carried out in accordance with ECE R100-R2, whereby a 10 kN shaker including a suitable vibration control system was used due to the forces required (as a result of the high mass to be moved). In order to check all hose connections for leaks during the vibration test, the battery module was continuously flushed with cooling medium.
As a result, the battery module tested showed no structural damage or leaks after several cycles (sine sweep 7-50 Hz; 1-0.2 g peak).
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As part of a collaboration with the Alfred Wegener Institute (AWI), lattice structures (lattice arrangements of individual small strings) that are used as bearings in machines were investigated. Previous studies have shown that the arrangement of the strings has a significant influence on the stiffness of the structures and that irregular designs are preferable in this context. Since the vibration behavior of technical systems is determined by the damping behavior, especially with regard to the amplitudes near resonance, the current project investigated whether the damping can also be increased by artificially disordering the topology.
The first step was to identify the parameters of existing additively manufactured lattice structures. The modulus of elasticity, density and damping constants were determined. The identified model was used to build a parameterized FE model of the lattice structures, which enabled an automated adjustment of the topology and the lattice structure. Using heuristic optimization methods, the topology with the highest damping or the highest loss factor could be determined simulatively.
A key result of the investigation is that disorder in the grating can lead to both an increase and a decrease in attenuation. Irregular structures are therefore not per se more damped. In addition, a change in the lattice structure primarily changes the stiffness, which means that the damping itself must always be considered relative to the stiffness. A useful measure for this is the loss factor, which relates the loss work of a period to the deformation energy.
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The use of composite structures has long been state of the art in many areas. Due to various factors, however, this is almost never the case for two-wheelers. As part of a model study, various test rigs were therefore set up to analyze the strength properties of the frame of a CFRP scooter (kick bike) in order to derive optimization potential for the composite structure from the results.
The frame was loaded in its main directions and the strains and deformations were measured using various methods. First, optical measurements were taken (using a GOM Aramis system) at several points on the frame in order to determine hotspots of strain and stress in the component. Strain gauges were then applied to these hotspots in order to record the data at the most highly stressed points during the subsequent fracture test and field test with the roller. The fracture test of the scooter frame was carried out at the IKAM technical center in Barleben on a hydraulic punch test bench. As the strains were recorded using strain gauges and optically with the GOM Aramis, measurement errors were eliminated due to data redundancy and the overall quality of the measurement was increased. The strains determined in this way can be used as limit values for use in the field. Another roller was equipped with strain gauges and a data logger so that the strains occurring in the structure during use can be measured.
This makes it possible to determine the degree of utilization and identify oversized areas. Finally, the results of the experimental study can be used to perform a multi-criteria optimization of the structure.
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This project is a cooperation between the Chair of Multibody Dynamics and the Chair of Computational Mechanics with one research assistant from each partner. The core objective of the project is the development of a practical simulation methodology for calculating the noise emissions of engines and their psychoacoustic evaluation. This makes it possible to directly trace the effects of structural modifications (stiffness, mass distribution) and tribological system parameters (bearing clearances, viscosity, deaxialization and filling level) back to the excitation mechanisms and the internal structure-borne sound paths and to preventively combat them in terms of acoustic optimization through design and tribological measures. This purely virtual engineering approach is intended to do entirely without real prototypes and thus enable an acoustic evaluation early on in the engine development process. In this way, design measures to improve acoustic quality can be implemented in coordination with the development groups of adjacent subject areas without negatively influencing other important design criteria such as performance, pollutant emissions or total mass.
In contrast, passive measures to combat noise emissions through insulation, for example, are generally cost-intensive, as they require additional material as well as additional assembly steps and therefore have an impact on the production process. At the same time, this runs counter to the idea of lightweight construction, reduced consumption and environmental friendliness and leads to additional installation space being required, which is usually a very scarce resource in the development of modern engines and automobiles. The fundamental problem with these insulation measures, which are being used more and more frequently these days, is their symptomatic approach, which combats the effect but ignores the causes of the acoustic disturbance.
The holistic methodology that is the focus of this project, on the other hand, makes it possible to directly analyze and combat the cause of the disruptive noise emissions. In addition, the psychoacoustic evaluation of the sound emission allows it to be categorized into disturbing and less disturbing sound emissions. In this way, the design can be specifically modified so that the resulting noise is classified as more pleasant by people; after all, a quiet noise can still be perceived as more disturbing than a loud one.
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Since, in addition to the inertia properties of a structure, it is primarily the stiffness and damping parameters of the bearing that influence its vibration behavior, precise knowledge of these influencing variables is of crucial importance when designing dynamic systems. These parameters are dependent on the vibration frequency and temperature, which must be taken into account for a valid description. Machines that are operated over a long period of time usually heat up, which leads to a drop in damping. Possible consequences are the occurrence of unstable vibrations, the consequences of which can extend to sudden machine failure due to structural or bearing element failure.
A rheological equivalent model can be used to determine an equivalent stiffness and damping resistance at a defined frequency. The energy balance of a full harmonic oscillation of a spring-damper system is used to calculate the parameters, which can then be implemented as characteristic maps in the numerical simulation. The elastomer mounts under investigation are tested using an electrodynamic shaker (max. 440 N sine amplitude), whereby the force between the shaker and the elastomer mount is measured using a piezoelectric load cell (±450N). To determine the deflection, a laser triangulation sensor is used, which records the path between the shaker and the elastomer bearing, from which the force-path relationship follows.
The measurements are carried out for several frequencies under harmonic excitation, whereby the elastomer bearings are also thermally preconditioned with a heating element in the installation position. This allows the dynamic properties to be measured in a small time window after the heating element has been removed.
As a result, various elastomer bearings could be compared in terms of their temperature and frequency-dependent damping (and stiffness), which is very important for use in dynamic machines, as this is the only way to estimate the damping for all operating conditions and identify unstable areas.
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The aim of this project is to develop an efficient methodology for mapping the non-linear properties of hydrodynamic journal bearings in transient rotor dynamics simulations. This requires an efficient solution of the Reynolds equation, for which the semi-analytical Scaled Boundary Finite Element Method (SBFEM) is used. In this way, the calculation times are to be reduced compared to conventional, numerical methods, without the need to simplify the boundary conditions as in analytical approximations.

The operating behavior of high-speed plain bearing rotor systems is significantly influenced by the non-linear bearing properties. A typical example of this is the occurrence of self-excited, sub-harmonic vibrations. These can impair the service life of the components and lead to increased power loss and critical noise emissions and must therefore be taken into account in the design. This requires a precise analysis of the dynamic behavior, which is often only carried out at a late stage of the product development process using test bench tests. If this reveals defects that require changes to the product to be rectified, the development time is extended and additional costs are incurred. To avoid this, dynamic simulations are increasingly being integrated into the product development process, which allow the operating behavior to be examined even before a prototype is manufactured. The decisive factor here is the realistic representation of the non-linear relationships between the dynamic and hydrodynamic subsystems in the simulation model. For this purpose, the equations of motion are embedded in a time-step method and coupled with the Reynolds equation, which describes the hydrodynamic pressure build-up in the journal bearing. The Reynolds equation is usually solved numerically or based on characteristic maps, as closed analytical solutions are only known for highly simplified cases. A two-dimensional discretization of the lubrication gap is required for the numerical solution, which, in conjunction with the high number of time steps, entails a considerable computational effort. In turn, the map approach is only possible or useful with a limited modeling depth, as each physical effect taken into account increases the interpolation effort. In order to create an efficient alternative to conventional methods, a semi-analytical solution is being developed in this project. The resulting reduction in computing times should contribute to time and cost savings in industrial and scientific applications. The developed methodology is based on the SBFEM and, in contrast to the numerical solution methods, only requires a one-dimensional discretization. The original partial differential equation is converted into an ordinary differential equation system, which can be solved using an exponential approach. To further improve efficiency, the SBFEM solution is combined with various strategies to reduce the required number of degrees of freedom.
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This project is a cooperation between the Junior Professorship of Fluid-Structure Coupling in Multibody Systems and the Chair of Computational Mechanics with one research assistant per partner. The core objective of the project is the development of a practical simulation methodology for the calculation of noise emissions from engines and their psychoacoustic evaluation. This makes it possible to directly trace the effects of structural modifications (stiffness, mass distribution) and tribological system parameters (bearing clearances, viscosity, deaxialization and filling level) back to the excitation mechanisms and the internal structure-borne sound paths and to preventively combat them in terms of acoustic optimization through design and tribological measures. This purely virtual engineering approach is intended to do entirely without real prototypes and thus enable an acoustic evaluation early on in the engine development process. In this way, design measures to improve acoustic quality can be implemented in coordination with the development groups of adjacent subject areas without negatively influencing other important design criteria such as performance, pollutant emissions or total mass.
In contrast, passive measures to combat noise emissions through insulation, for example, are generally cost-intensive, as they require additional material as well as additional assembly steps and therefore have an impact on the production process. At the same time, this runs counter to the idea of lightweight construction, reduced consumption and environmental friendliness and leads to additional installation space being required, which is usually a very scarce resource in the development of modern engines and automobiles. The fundamental problem with these insulation measures, which are being used more and more frequently these days, is their symptomatic approach, which combats the effect but ignores the cause of the acoustic disturbance.
The holistic methodology that is the focus of this project, on the other hand, makes it possible to directly analyze and combat the cause of the disruptive noise emissions. In addition, the psychoacoustic evaluation of the sound emission allows it to be categorized into disturbing and less disturbing sound emissions. This allows the design to be specifically modified so that the resulting noise is perceived as more pleasant by people; after all, a quiet noise can still be perceived as more disturbing than a loud one.
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The eMobility Competence Center project addresses the structural challenges and develops solutions in key areas as part of a newly established competence center, which will significantly strengthen cooperation between SMEs and university research and teaching. The knowledge can be transferred directly to the affected supplier industry, where it can help to successfully manage structural change and exploit new economic opportunities. In addition to the primary objective of building up and transferring core know-how, the main focus is on the long-term anchoring of the knowledge gained in economic structures that create jobs.
Based on a multi-patented, globally unique lightweight engine concept from OVGU, the work in the DRIVE TRAIN research area focuses on the further development and prototypical presentation of the new engine technology, its integration into the drive train and its operation in accordance with given safety and comfort requirements (driving dynamics). At the same time, there are further innovative steps in the area of basic research to increase the performance of the engine technology, which are to be developed and implemented in prototypes during this funding period.

Description of the sub-project:
For electrical machines, a constant magnetic field that is as free of interference as possible is of great importance. The smallest changes in the air gap lead to changes in the magnetic field compared to the designed ideal geometry and thus to changes in both the resulting torque and the resulting vibration excitation, which in turn can lead to acoustic abnormalities in the unit. Local and global asymmetrical gap changes due to load- and operation-dependent deformations of the stator and rotor are particularly problematic. Such deformations are caused on the one hand by the electromagnetically excited structural vibrations and on the other hand by the rotordynamic loads. For these reasons, it is essential to consider the magnetic circuit and the structural dynamics together. At present, no commercial software tool offers the possibility of considering the interactions between the magnetic circuit and structural vibrations in terms of feedback. In addition, there is also no possibility to consider the feedback effect of the rotor dynamics on the magnetic circuit in a modern multi-body program. Both issues are essential for the development of electric motors in terms of performance, reliability, reliability and noise emissions. For this reason, the proposed project aims to develop software solutions that enable the magnetic circuit to be considered holistically in combination with both vibroacoustics and rotor dynamics. As part of the rotor dynamics considerations, the correct mapping of the bearings and their loads as well as the non-linearities that occur naturally also play a decisive role. The outlined software developments are carried out for both rolling and plain bearing systems in order to be able to realistically record and evaluate different concepts of electric motors. As part of the holistic vibroacoustic approach, different strategies for controlling the excitation current will also be implemented and analyzed with regard to their effect.
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The aim of the research project is to improve the existing calculation methodology for high-speed exhaust gas turbochargers (ATL) with hydrodynamic bearings. While the previous project focused on radial bearings in the form of floating bush bearings (shown in blue), the current project addresses the modeling of axial bearings (shown in red; simple and floating disk bearings). The influences of the thrust bearings on the rotor dynamics as a result of their non-linear tilting rigidity and the coupling of the thrust bearings to the radial bearings are to be investigated. This also includes practically relevant counter-rotation excitations, e.g. due to engine vibrations.
The movement of the shaft results in dynamic misalignment of the track disk and, if applicable, the floating disk. The resulting small gaps lead to high shear stresses and thus to a significant heat input into the system. At the same time, there are interactions between the temperatures and the hydrodynamic properties (thermal expansion, viscosity), which is why the transient temperature development of the bearing partners and the oil must be modeled. In addition, radial and axial bearings are connected to each other via the oil supply lines, the influence of which must be recorded thermodynamically and hydrodynamically.
The individual aspects are mapped in a holistic simulation model, which includes rotor, hydrodynamics and thermodynamics, and the underlying differential equations are solved numerically within the framework of time integration, whereby the results of the previous project are consistently developed further.
Ultimately, the reliable simulation of subharmonic vibrations in frequency and amplitude should be made possible, as these cause safety-relevant issues (rubbing processes) as well as having drastic effects on the power loss and service life of the bearings
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Friction welding is an established joining process that is used in many areas of mechanical engineering to produce hybrid structures made of aluminum and steel. The decisive factor for the serviceability of hybrid joints is above all the material-appropriate design of the joint. Due to the dependence of the welded joint on the shape, type and continuity of the intermetallic diffusion layer, the microstructure and the material bonding, the development of friction-welded hybrid structures with optimum properties is often time-consuming and cost-intensive. For kmU in particular, it is therefore almost impossible to develop such hybrid structures economically. The declared aim of the project is to set up and test a simulation for the design of friction-welded hybrid joints made of aluminum and steel. For this purpose, corresponding friction welding tests are carried out, whereby the process parameters are systematically varied. These tests provide the data basis for the experimental analysis of the macroscopic, mesoscopic and microscopic influences on the load-bearing capacity of the structure. At the same time, the tests serve as a validation basis for the simulation of the welding process itself. With the help of the process simulation, the effects of the process parameters on the process variables and thus on the material and structural properties can be derived. Based on this, corresponding phenomenological models are developed in order to map the relevant influences. These results are then used as initial conditions for the simulation of the load-bearing capacity (virtual tensile test) of the hybrid joint.
For kmU in particular, the simulation creates the economic possibility of predictively evaluating the joint depending on the selected process. Complex friction welding tasks can be analyzed in advance of the test and optimized accordingly.
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In addition to the elastic and inertia properties of the rotor and the external loads, the vibration behavior of rotor systems is primarily determined by the bearing. Due to the advantageous mechanical and thermal characteristics as well as the low costs, plain bearing designs are often used. On the one hand, this applies to radial plain bearings, which have a dominant influence on bending vibrations; at the same time, axial plain bearings are used for axial securing or for absorbing axial loads. Due to their respective stiffness and damping parameters, both bearing types make a significant contribution to system behavior, which has a drastic effect on the resulting vibrations and stability. Continuous further developments and increasing requirements require a successively higher mapping quality of the transient system behavior, which is why detailed modeling of the system properties of the rotor system, the bearing and their interactions is necessary.
For transient investigations, the use of established quasi-stationary solutions in the field of coupled rotor-bearing simulation is not adequately possible. While the solution of a non-linear system of equations is sufficient for quasi-stationary considerations of the bearing situation, time integrations must be carried out for transient questions, taking into account the rotor dynamics. A correspondingly detailed representation of the bearing situation requires the evaluation of Reynolds' differential equation in each step of the time integration, taking into account the time-variant cavitation state.
In the previous project, a modified cavitation algorithm according to Elrod was developed for radial bearings, which is now to be transferred to axial bearings. In this context, in addition to the simple thrust bearing, there are various other designs that can be divided into combined bearings (radial/axial composite plain bearings), floating disk bearings and tilting pad bearings. Hydraulic couplings between axial and radial lubrication films as well as mechanical couplings to the components of the rotor-bearing system under the influence of cavitation must be taken into account. With the extended simulation model, relevant vibration phenomena (subharmonic vibrations, counter-rotation excitations due to external loads, tilting pad vibrations) are to be validly predicted in terms of frequency and amplitude.
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Vibration testing in the automotive sector is of crucial importance for vehicle approval. For this purpose, vibration measurements are first carried out on the individual components installed in the vehicle. The measured loads are reproduced on a vibration table and extrapolated to the required service life. The loads are scaled accordingly in order to obtain a time lapse.
The state of the art is testing on uniaxial excitation vibration tables, which all relevant industry standards in the automotive sector are based on. The subject of current research is the prototype of a new vibration table that can excite all three axes simultaneously. The motivation for this is to achieve a more realistic test condition for simulating the same type of damage. Furthermore, the more precise prediction of reliability contributes to the more efficient design of future structures. As part of the investigations, a methodology for the design of 3D vibration tests is to be developed. On the one hand, this includes the definition of relevant measured variables and measurement positions on the component. On the other hand, existing methods for evaluating the damage potential of different excitation profiles will be reviewed and expanded.
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Regardless of the type of drive - conventional, hybrid or electric - drive shafts in motor vehicles are an essential component for transmitting drive power to the wheels. The testing of drive shafts currently relies primarily on endurance wear and functional tests, which analyze the condition of the system as an integral part. The mechanisms inside the joint, especially the transitions from rolling to sliding of the rolling elements, which are largely responsible for the potential wear of the system, are not or only indirectly recorded.

The project aims to develop a multimodal measurement method and a measurement system based on it, which records the movement behavior of the individual rolling elements in the drive shaft in detail and allows a specific statement on the tendency to damage. With regard to the necessary robustness for valid analysis under real boundary conditions, partially redundant measurement methods are therefore combined and implemented in a near-series prototype system.
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In addition to the usual design criteria for chain drives, wear is a significant parameter that must be taken into account as early as the design phase in order to ensure an acceptable service life and to define the necessary maintenance intervals. For this reason, a physical wear model for chain drives in car engines is to be developed as part of the doctorate, which takes the special requirements into account.
First of all, the main factors influencing chain wear must be identified and incorporated into the model, whereby common wear models (e.g. according to Archard and Fleischer) take into account the influence of surface hardness, sliding distance, normal force and friction coefficient in the contact area. Further measurements using radionuclide technology (RNT) show a further influence of surface roughness in the contact area on chain wear, which requires a modification of the common wear models for engine operation.
To validate the model to be derived, the condition of the chain links is examined using defined surface measurements both in the initial state and on running timing chains with different mileages, resulting in a time parameter curve for the wear model:

• SEM measurement to record the surface structure
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• Measurement with a confocal laser for 3D measurement of the surface with regard to surface topography
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• White light interferometer for measuring surface roughness with resolution in the nano range
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• Measurements of surface hardness using the mechanical Vickers method and UCI method
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The measured surface topographies are transferred to the model and adapted for the numerical method.
To determine the necessary loads (chain forces) of the motor, MKS simulations are used, which are compared with tests and from which the contact normal forces in the chain link can be calculated. The modified wear model can be calibrated using the corresponding wear parameters from the RNT measurements and the operating point-dependent internal friction values of the chain (measurement of chain friction on a reduced chain test bench including the influence of aged engine oil).
Finally, chain drives are to be optimized depending on the cycle, which represents a significant added value compared to the current state of research, particularly due to the variable load spectrum.
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The central aim of this project is to develop a CT platform that has open interfaces for hardware and software and is also modular in design. This modularity relates to both the internal CT structure (e.g. interchangeable electronic modules for processing high-speed signals) and the peripherals (connection of additional modalities such as optical 3D imaging). This high degree of flexibility will enable rapid adaptation to different requirements and application scenarios. The open interface structure plays a central role here, allowing future users to develop and use their own extensions - both hardware and software. This is particularly important for research institutions and companies aiming to develop their own enhancements. Thanks to the planned open structure and the core component of multimodality, completely new approaches - e.g. for artifact and dose reduction - can be pursued and implemented. In the area of dose reduction and shortening scan times, innovative methods will be implemented, some of which have already been developed at the STIMULATE research campus in Magdeburg. Derived from the extended possibilities and the open structure of the CT platform, questions regarding the dynamics of the system are also to be investigated, which require a detailed analysis of the vibration behavior.
The OI-CT project focuses on pediatrics as an exemplary clinical application. Here, CT offers irreplaceable diagnostic added value for polytrauma and pulmonary and congenital diseases, as well as for diseases of the osseous system. Innovations to reduce the radiation dose should therefore be driven forward for this field of application. Existing methods must be adapted to the physical conditions of children. The concepts envisaged for this include significantly higher accelerations of the rotating CT element, which is why the resulting excitations must be determined and design adjustments made to the structure so that the diagnostic added value is not reduced by superimposed vibrations and inaccurate positioning.
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The aim of the research project is to increase the simulation quality with regard to the influence of squeeze oil dampers (QÖD) on the rotordynamic system behavior, taking transient load conditions into account. This applies in particular to the low-frequency vibrations that occur during engine and foot-point excitations compared to the rotor speed, with regard to which design criteria for an effective improvement of the response and damping behavior are to be developed on the basis of simulations.
Of particular interest here is the reliable mapping of the non-linear damping characteristics of the QÖD, which affects the vibration amplitudes of the rotor system. For this purpose, significant influences such as design boundary conditions (seal), inertia effects of the oil as a result of the size and cavitation behavior (bubble formation) must be taken into account. The latter should allow the transient development of the bubble concentration to be mapped, which affects the viscosity and thus the damping properties. Due to the non-linear interactions with the rotor dynamics, a holistic approach is pursued, which provides for a direct evaluation of the Reynolds differential equation within the framework of a time integration of the rotor system. After validation of the simulation results with regard to the rotor dynamics, a calibrated software tool is available that maps the complex relationships of turbomachinery with QÖD.
As a result, their effective operational safety can be increased and the risk of malfunctions and damage reduced.
can be reduced. The resulting increase in design reliability is of particular interest to SMEs, which can use the derived design criteria to carry out system optimizations in addition to increasing efficiency. This helps to strengthen SMEs in their position as a competent partner for the mostly larger machine manufacturers and releases innovation potential.
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As part of the overall design of machine components, the damping behavior of the structure is of great importance due to its significant impact on noise emissions. As part of the project, the damping effect for two different aluminum alloys is to be investigated on a housing.
The evaluation is based on an experimental vibration analysis using a laser scanning Doppler vibrometer in the entire acoustically perceptible frequency range. The data is provided in both sound and one-third octave bands in order to identify the advantages and disadvantages of each variant.
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The acoustic emissions of the combustion engine contribute a main part to the pass by noise of a passenger car, which is the main focus of associated NVH activities.
An adequate simulation model of a crank drive with piston liner contact will be developed. The main bearings and lower con-rod bearings will be modeled as HD-contact, which means hydrodynamic contact without local elasticity. The resulting Reynolds equation will be solved numerically in every step of time integration including all effects due to tilting etc. The crankshaft can be modeled with its global elasticity. The connection from the con-rod to the piston will be modeled using linear stiffness and damping. In later steps this connection can be modeled with the elasticity of the piston pin and hydrodynamic effects. The main focus of the developed model is the piston liner contact modeled as EHD contact, which includes hydrodynamic effects and local elastic deformations of the piston and the cylinder.
After the parameter variation, all variants will be analysed due to the vibration of the crank housing, bearing forces and hydrodynamic condition of the piston linear contact.

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The acoustic emissions of the combustion engine contribute a main part to the pass by noise of a passenger car, which is the main focus of associated NVH activities.
Starting from an initial model of the crank shaft at first the CAD data has to be adapted for each variant (given in the analysis matrix). Afterwards an adapted finite element model will be generated including a suitable reduction process. As the setup of the MBS model was realized in previous projects, the adapted crank shafts representations can be implemented directly.
After model setup of all defined variants a nonlinear time integration to the steady state condition for a given speed will be performed. As a result, the bearing forces are present w.r.t. the changed parameters of the crankshaft.
Furthermore the strain energy of the elastic crank shaft model is analysed. The results are averaged (and peak hold) for one load cycle to allow for an overall statement, which regions are sensitive concerning the NVH behavior (due to large strain energy). For reasons of further investigations also the contribution of each eigenmode to the strain energy is calculated and weighted with the participation factor.
After the parameter variation, which is performed in time domain, the bearing forces, which are assumed to affect the NVH behaviour dominantly, are transferred into frequency domain including the resulting phase angle with respect to the crank shaft angle and the different variants are compared.

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The aim of the project is to improve the mapping quality of rotor systems with plain and floating bush bearings, taking into account high speeds and variable dynamic loads. A particular focus is on the mapping of transient effects, which can have a massive influence on the system behavior.
For the consideration of these problems, there is no generally valid approach that includes the non-linear effects of the hydrodynamic bearings in the time domain, taking into account a mass-conserving cavitation algorithm. The binary behaviour of the discretization, which is necessary for the solution of the descriptive Reynolds differential equation (assignment is either to the cavitation or to the pressure region), is to be regularized in order to improve on the current status. This means that individual elements can be part of both the cavitation and pressure domains, enabling a continuous transition independent of the elementization.
While pure plain bearing concepts are often used for technical applications with moderate speeds, concepts with floating bush bearings are largely used in the high speed range, whose tendency to subharmonic vibrations is to be investigated in connection with rotordynamic issues and the cavitation algorithm to be regularized.
The project offers the opportunity to increase system understanding in the simulation of rotor systems with sliding and floating bush bearings. Due to the absolutely stable convergence properties of the extended modeling method, a transient investigation of the mechanical system including all dominant hydrodynamic effects can be implemented.
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The design of the bearings is a key element in the overall design of rotor systems. For cost reasons and due to a large number of advantageous properties, plain bearing elements are predominantly used. However, this is offset by a relatively complex design process, as the movement behavior of the rotor relative to the plain bearings exhibits a highly non-linear behavior. Due to the asymmetrical stiffness and damping properties, self-excited vibrations can occur, which often lead to unstable running of the rotor and are known as oil whirl or oil whip.
In this context, the predictive simulation of rotor behaviour is of key importance in order to minimize cost-intensive prototype tests. In addition, model-based variations of boundary conditions that are difficult to access experimentally, such as the unbalance distribution, can be carried out in order to be able to evaluate the expected vibration behavior a priori.
Since an increase in the degree of modeling is usually accompanied by an increase in computing times and this counteracts the goal of a fast design process, an adequate compromise must be found between the accuracy of the simulation and the resulting effort in the context of the necessary model quality, which also entails parameter variations in modeling.
The aim of the project is to analyze two exhaust gas turbochargers with a different radial bearing concept. While the reference turbocharger is equipped with a semi-floating floating bushing bearing, the new development should manage without a second lubricating film, which is referred to as a compact bearing. The expected vibration behavior and the tribologically relevant bearing parameters in the context of manufacturing tolerances and the transient load must also be investigated, which finally enables an evaluation of the new bearing concept
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In friction welding, the necessary heat is generated by a relative movement and the application of a normal pressure directly in the joining zone, which allows a material-locking connection between materials that cannot be achieved with conventional welding processes. However, particularly with delicate lightweight components, it should be noted that high forces and torques are generated compared to other joining processes, which can have a negative effect on residual stresses and component distortion. Both are primarily formed during cooling, after the actual welding process, and cannot be evaluated using existing simulation models due to the use of fluid formulations.
Finally, an extension of the simulative approach to qualitatively predict the residual stresses enables more precise geometry and process recommendations.
For this purpose, the material model used is able to differentiate between elastic, thermal and plastic strains. Furthermore, structural transformations can be included, whereby an empirical model is implemented to determine the phase fractions. Based on
on the phase composition, both the flow behavior of the material is modified and
volume expansions due to the changed grid structure are also taken into account.
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The aim of the research project is to improve the existing calculation methodology for high-speed ATL with floating bushing bearings on the basis of elastic MBS formulations. The subsynchronous vibrations occurring in ATL as well as unstable system states during turbocharger run-up are to be mapped reliably in frequency and amplitude values even for high speeds by reducing the thermal uncertainties.
This requires an extension of the existing calculation methods to include a holistic view of the thermodynamics of the ATL. For the desired solution of the energy equation, a solution of Reynolds' differential equation must be realized that allows the degree of gap filling to be determined. For this purpose, the two-phase model, which enables an efficient numerical implementation of the JFO boundary conditions, is to be used.
As a result, the three-dimensionally variable temperature and viscosity distribution in the lubrication gap can then be determined from the 3D energy equation.
This extension requires that additional thermal state variables (temperatures of the bearing surfaces) and material parameters are taken into account. In addition to the mechanical results (forces and torques), this results in additional heat flows acting on the rotor, floating bushing(s) and housing.
This is associated with an adequate description of the thermal bodies, which must be implemented as part of the higher-level MBS algorithm (rotor dynamics). The components to be considered as thermal bodies (shaft, floating bushings, housing) allow the heat flows to be modeled both in their time dependence and the thermal interactions between the bearings as well as the heat flows from the turbine to the compressor to be mapped.
Finally, due to the different time scales between the thermal and mechanical systems, the use of hybrid integration algorithms is investigated in order to keep the simulation times within practicable orders of magnitude despite the increase in modeling depth.
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The aim of the project is to derive a general procedure for investigating the fluid-solid interaction that combines the existing calculation methods of the finite element method (FEM) and smoothed particle hydrodynamics (SPH). An experimentally investigated system in which the interactions between the fluid and the surrounding structure must necessarily be mapped is the oil pan. As a result of the oil filling, there is a shift in the natural frequencies and a change in the vibration amplitudes, which above all has a significant influence on the sound radiation.
The SPH method is a macroscopic simulation method in which the fluid is approximated by discrete points. The movement behavior of these points, which each represent partial volumes of the total fluid, is described using the Navier-Stokes equation. This method is named after the smoothing of the particle properties, in which the effect of the neighboring particles on a particle depends on their distance. In this way, each particle is only influenced by the particles in its immediate vicinity. This results in a large number of small systems of equations, which are easy to parallelize and can be solved with little numerical effort. The flexible and robust Lagrangian meshless method, which is particularly suitable for multiphase flows and large deformations but is also used in the simulation of welding processes, is often used for mapping due to the movement of the fluid particles among each other.
In contrast to the SPH, the FEM is a numerical method which, in addition to other physical problems, is mainly used in the field of strength and deformation investigations.
While many small systems of equations are solved in the SPH, a large system of equations is solved in the FEM, which represents a significant numerical effort. In return, however, there is no need for complex search operations, which are necessary with the SPH due to the formulation.
The general concept of coupling the FEM with the SPH is realized in a first step by a co-simulation of both sub-elements, whereby both methods are executed alternately and transfer information such as position and pressure of the particles or nodes is exchanged. In the further course of this investigation, a complete coupling of the methods is aimed at, in which only one solver is used, which enables a holistic representation of the cause-effect relationships.
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Automatic ball balancers (ABB) can be applied to rotating machinery in order to reduce the effective unbalance excitation and resulting deflections. The passive working mechanism does not necessitate active components such as sensors, control units and actuators. In an ABB several balls are enclosed in a cylindrical cavity and can orbit freely on a circular track positioned centrically to the axis of rotation of the equipped rotor. As inherent to the functional principle, the rotating speed has to exceed the first critical frequency for the balls to be positioned beneficially and counterbalancing the primary unbalance. During the transient phase prior to the rotor reaching the final operating speed and the balls adopting their final stationary resting position relative to the rotor system, the movement of the balls is strongly dependent on the environing fluid in the cavity. From gaseous environments to highly viscous oils a wide scope is available to design the ABB.
In current research a carbon fiber reinforced plastic rotor for medical centrifuges is equipped with an ABB and the ideal range for the density and viscosity of the fluid in the balancer is explored experimentally as well as by means of multi-body simulations incorporating the fluid structure interaction in the ABB.

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To determine dynamic wheel forces, a measuring method is to be developed that allows the forces to be determined by measuring the load on the rim body. The disadvantages of commercial products are their limited applicability to special vehicles and the need to modify the wheel, in which the rim is split and reconnected using a cylindrical measuring adapter. The force transmitted through the measuring adapter is determined internally by several strain gages and transformed into the stationary system by an angle determined by the external rotary encoder. This method is not practicable for the application under consideration, and there are no suitable measuring adapters in the required size and load range. Therefore, a circular strain measurement is to be carried out on the original rim and the load state in the wheel is to be determined in rotation. Using a suitable rotary encoder (such as the ABS sensor) and an additional reference sensor that determines the absolute position of the wheel, the wheel-fixed load can be transferred to a vehicle-fixed coordinate system.
At the end of the project, a complete measuring wheel with measuring technology will be available. Furthermore, proof of functionality and documentation of the necessary steps for application to the real rim will be provided, whereby the process should be fully scalable.
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When designing differential gearboxes, acoustic behavior is a quality criterion in addition to pure functionality and high efficiency. Due to the large number of moving elements, their contacts with each other and the non-linear bearing properties, the multi-criteria design of the construction is usually only possible using numerical simulations and accompanying experimental investigations.
As part of the simulation, which can be advantageously implemented using multi-body systems due to the large reference movements, the excitation mechanisms on the one hand and the non-linear behavior of the overall system due to the plain bearing on the other must be correctly mapped. Significant influences arise from the elastic properties of the individual components and the behavior of the bearing. The latter is not trivial, especially for the thrust washer composite of the bevel gears, as spherical plain bearings with additional plastic elements are used here. A detailed mapping of the stiffness and damping influences as part of the overall simulation of the system behavior finally allows a holistic assessment of the design.
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The Competence in Mobility (COMO) research focus, a joint project within the OvGU's automotive research and transfer focus, deals with the electrification of motor vehicles in the broadest sense, including energy supply, energy conversion and drive technology as well as fundamentally new issues in connection with electromobility.
The sub-project "Complete vehicle: driving dynamics and wheel loads" is concerned with tuning the chassis dynamics, which is not only decisive for the load and service life of the chassis components, but also has a significant impact on ride comfort.
An axle model is built according to the available test vehicles and adapted to the requirements of the chassis set-up changed by the electrification. As part of the overall vehicle design, this procedure is used to determine the loads and movement characteristics of the unsprung vehicle components. For calibration, the incoming wheel loads are required, which can be measured directly on the vehicle using a 6-component measuring wheel. Only this correlation between incoming wheel loads and measured strains on the components of interest ensures the possibility of calibration and also validation with the developed simulation models.
By measuring the strains directly on the component to determine the cutting loads, load measurements can be carried out during operation. The measurement results obtained are essential for the design of the wheel hub motor. Alternatively, load cycles can only be derived from existing measurement series in the literature, the transfer of which to the actual vehicle would only allow a rough estimate.
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Extrusion is used to manufacture semi-finished products when processing copper. In this process, a pressed part heated to forming temperature is pressed through a die with a punch. In this specific application, heating is achieved by plastic deformation of the raw material on a rotary press. The deflecting friction wheel is fixed via an axial, hydraulically acting clamping device on a shaft that is supported by two roller bearings. A thread is provided for the clamping device in the bearing area, but this shows signs of failure during operation, which is reflected in shearing of the thread flanks and thus a loss of functionality.
In this context, the external loads acting on the machine and thus ultimately on the thread as a result of plastic deformation should first be measured. Due to the forces to be expected, it is not possible to measure the force directly; instead, indirect methods (strain gauges on the counter-holding bracket) must be used.
Once the external loads have been determined, the expected deflection of the shaft structure and the resulting normal bending stresses can be calculated from FE simulations and superimposed with the loads from the hydraulic prestressing to form the nominal total normal stress.
This information on the global stress curve can also be used to analyze the stress distribution in the thread contact using a detailed FE model and to determine the material stress that leads to failure of the structure in the specific application.
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The acoustic emissions of the combustion engine are one of the main contributors to the pass by noise of a passenger car, which is a main focus of current NVH activities.
In this context the crank drive has a dominant influence and has to be analyzed in detail to identify the most important design parameters concerning vibrations of the main bearings, which defines one excitation source of the engine's acoustic emission. Thereby, the main focus will be on design parameters, which can easily be changed in an already existing production line for mass production of passenger cars.
The deformation of the crank shaft, which was calculated with the previously defined MBS model under nominal conditions (two rotational speeds) is analyzed concerning the strain energy. The results are averaged for one load cycle to allow for an overall statement, which regions are sensitive concerning the NVH behavior (due to large strain energy). This approach neglects the non-linear interactions between the vibration behaviour of the crank shaft and the bearing parameter, but it allows for a determination of relevant geometrical parameters of the crank shaft. For reasons of further investigations also the contribution of each eigenmode to the strain energy is calculated and weighted with the participation factor.
After a parameter variation, which is performed in time domain, the bearing forces, which are assumed to affect the NVH behaviour dominantly, are transferred into frequency domain including the resulting phase angle with respect to the crank shaft angle. Furthermore, acoustic sensitivities for each bearing (from experimental or computational data) are used to compare different variants. In this context several aspects has to be taken into account: On the one hand vibration with different opposed phases vanish (phase cancel). On the other hand high bearing forces, which result from eigenvalues in the interesting frequency domain, can be shifted towards frequencies with low acoustic sensitivities, leading to a lower sound pressure (eigenvalue dispersion). The last point to mention is a mode control, so that specific modes are tuned to assure that the amplitudes in the bearings tend to zero.

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Today's engineering efforts in the field of product development are increasingly focused on the efficient use of energy and raw material resources. Against this background, the design principle of consistent lightweight construction is becoming increasingly important in mechanical and plant engineering. One possible approach is the targeted utilization of technological properties of different materials in hybrid structures. The declared aim of the project is to simulate the load-bearing capacity of such friction-welded hybrid joints made of aluminum and steel, taking into account local structural differences and inhomogeneities. For this purpose, corresponding friction welding tests are carried out, whereby the process parameters (friction pressure, friction time, spindle speed and upsetting pressure) are systematically varied. These tests provide the data basis for the experimental analysis of the macroscopic, mesoscopic and microscopic influences on the load-bearing capacity of the structure under tensile load. These influences include the characteristic bead formation (macroscopic), the expansion of the HAZ (mesoscopic) and the chemical composition of the joining contact plane or the local microstructure in the HAZ (microscopic in each case). At the same time, the tests serve as a validation basis for the simulation of the welding process itself. With the help of the process simulation, the effects of the process parameters on the process variables (heating and cooling rate, temperature distribution, plastic deformation, diffusion, etc.) and thus on the material and structural properties of the welded joint can be derived. Based on this, corresponding phenomenological models are developed in order to depict the relevant influences. Subsequently, these results are used as initial conditions for the simulation of the load-bearing capacity (virtual tensile test) of the hybrid joint, assuming large deformations and materially non-linear behavior.
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When designing laboratory centrifuges, in addition to performance parameters such as maximum speed and load, comfort features are also key criteria that have a significant influence on the customer's purchasing decision. One focus here is on high variability of the rotor and the simplest possible changeover. This requirement can be met with quick-locking concepts, although the functionality (connection of shaft and rotor) must be ensured under all circumstances despite simplified use and the dynamic behavior of the overall system, including acoustics, must not deteriorate.
Driven by constant competition and the associated cost pressure, such systems should only incur low additional costs and are therefore usually based on centrifugal force-driven concepts.
An analysis of such systems can be advantageously simulation-based in order to minimize the expected development costs and design modifications.
The aim of the project is to model such a locking mechanism and to test its functionality and the effects on the rotor dynamics on two centrifuges with different rotors and loads. The investigations will then allow an evaluation of the design and, if necessary, adjustments to the targeted design of the product.
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When designing rotor systems with rolling bearings, the design of the bearings is becoming increasingly important. Particularly when non-linear effects such as the load-dependent alternation of rolling and sliding are taken into account, vibration excitations occur which both reduce the service life of the system due to thermal and mechanical loads and cause undesirable noise emissions. By using multi-body models, the mechanical interactions can be mapped in more detail, whereby dynamic effects in transient operation can also be investigated as a result of the general non-linear description in contrast to quasi-stationary approaches.
The aim of the project is to analyze a preloaded angular contact ball bearing with regard to the slip of the rolling elements and the loads on the bearing cage. The main focus is on the influence of the lubricant and thus the friction and acceleration parameters during transient operation. On the basis of the investigations carried out, advantageous combinations are to be derived which, on the one hand, prevent slip-induced heating of the rolling bearing even at high accelerations and, on the other hand, realize a load on the bearing cage below the failure limit.
An improvement in the level of knowledge can be derived from the analysis of the internal cause-effect relationships in the rolling bearing, which also enables a more precise prediction of the non-linear vibration behavior and the associated effects for other applications.
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In addition to the radial bearings of rotors, their axial bearings also play an important role in the design of rotordynamic systems. Two thrust bearings acting against each other - the main bearing and the auxiliary bearing - are used for this purpose, particularly in the case of low or alternating axial loads. Due to the larger axial gap, the auxiliary bearing in particular is only partially filled, which results in lower frictional power compared to a fully filled bearing. Under transient conditions, the filling levels of both gaps depend on time and load and thus lead to variable pressure distributions in the segments and also to varying stiffness and damping properties of the overall bearing.
The aim of this project is therefore to simulate the described transient behavior and integrate it into a rotor dynamics model. The cavitation behaviour is implemented on the one hand based on a regularized variant of the Elrod algorithm and on the other hand using the two-phase model. First, a validation or verification under static loads is sought before corresponding transient investigations are carried out.
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The acoustic emissions of the combustion engine are one of the main contributors to the pass by noise of a passenger car, which is a main focus of current NVH activities.
In this context the crank drive has a dominant influence and has to be analyzed in detail to identify the most important design parameters concerning vibrations of the main bearings, which defines one excitation source of the engine's acoustic emission. Thereby, the main focus will be on design parameters, which can easily be changed in an already existing production line for mass production of passenger cars. For this purpose a multi-body-simulation model of the crank drive is build.
Beside the crankshaft, which will be modeled as an elastic body (using the floating frame of reference approach - elastic deformations are superimposed to the rigid body motion via a reduced FE-model), the remaining bodies are assumed as rigid. The bearings on the crank shaft are modeled by a transient solution of Reynolds PDE, which allows a detailed analysis of the bearing forces and the influence of bearing parameters. The exciting forces are determined by the transient combustion forces acting on the pistons. As it is assumed that a lower magnitude of excitation forces leads to lower acoustic emissions, the numerical results of interest are the forces in the main bearings, which can excite the crankcase and lead to a noticeable acoustic behaviour.

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In addition to the conventional working principle of ram charging, the turbine of an exhaust gas turbocharger can alternatively be operated by means of shock charging. This variant utilizes not only the pressure differences across the turbine but also the kinetic energy of the exhaust gas, which results in efficiency advantages. However, due to the pulsating pressure in the exhaust gas, this leads to a transiently changing output torque of the turbine, which can result in vibrations of the impeller on the one hand and a change in run-up characteristics on the other. The specific effects on the rotordynamic behavior have not yet been conclusively investigated due to the strong non-linearity of the system behavior.
In this project, the influence of shock charging compared to conventional ram charging is investigated with regard to the rotor dynamics of the rotor and its radial bearing, which is designed as a floating bushing bearing. Adequate modeling of the bearing properties, which must reliably map typical non-linear effects such as oil whirl and oil whip in frequency and amplitude, is of essential importance, from which statements regarding the influence of the bearing on maximum speeds, instabilities, service life, etc. can be derived.
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Turbochargers are essential elements in the downsizing concept of recent combustion engines. One major development objective is to raise the maximum rotor speed to either increase the air-mass flow or decrease the design size. This causes, among mechanical strength issues, inadequate subsynchronous vibrations known as fluid-whirl and fluid-whip for turbochargers equipped with journal bearings. Another disadvantage of commonly used journal bearings is the rather high friction loss, which is a significant design parameter. To overcome these problems ball bearings concepts are most suitable for advanced designs.
In that context, the simulation of the rotor including the non-linear effects of ball bearings, (with additional squeeze film damper to assure sufficient damping) is essential for an apriori analysis of the system’s dynamics. For that purpose, a dynamic model of the ball bearings including the contact dynamics between the balls, the inner and outer bearing raise and the cage was established and is investigated in detail.
The ball bearings and the squeeze film dampers are implemented with high modelling depth, taking into account all relevant design parameters like initial load, contour of the ball bearings, seals of the squeeze film damper etc.. The system’s eigenbehaviour is investigated using a non-linear and a linearized approach for the stiffness and damping properties of the bearings.
Finally, the results in term of time dependent rotor displacements (under a given rotational frequency of the turbocharger) are examined and compared with measurements to validate the simulation model.

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To reduce the noise of vibrating components in automotive systems, foams are used that are applied to sound-emitting surfaces. The resulting sound insulation depends largely on the physical properties of the foam.
The studies carried out include the characterization of the foam material and the experimental determination of frequency-dependent stiffness and damping properties in the frequency range up to 2 kHz using a shaker.
Measurement methods based on different principles were compared:
a) A vertical setup in which the foam specimens are loaded by a rigid mass and excited to vibrate. By comparing the acceleration signals of the excitation and the sprung mass in relation to the expected magnification function of the linear oscillation system, the stiffness and the damping factor can be determined as a function of the resonance frequency using regression methods.
b) A horizontal setup in which the foam sample is positioned between a rigid counter bearing and the shaker and subjected to a monofrequency load. With the aid of a force sensor connected in series, the displacement-force diagram is recorded, from which the stiffness and the damping ratio can be derived.
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The aim of the project is to develop an externally toothed gear wheel in an Al-Fe mixed construction. The inner part of the gearwheel is to be made of aluminum and welded into the steel outer ring. A friction welded joint is to be realized on the circumferential surface to ensure the safe transmission of the highest possible forces and torques. Predictive methods of friction welding simulation are used for the design of the joint geometry, which enable the process parameters to be determined, on the basis of which a multi-criteria optimization of the joining process can be carried out.
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In ambulances, a rail system is used to secure the mobility-impaired persons to be transported on the vehicle floor, to which the necessary belts are attached. The rails are fixed to a metal sheet and a multiplex plate by means of screw connections via a threaded sleeve whose strength has to be analyzed. The sheet metal is in turn attached to the vehicle floor via an adhesive connection.
To determine the maximum loads on the threaded sleeve, the adjustability of the system and the associated load distribution on the individual fastening elements are modeled as an extreme value problem. The stresses resulting from the maximum loads are then analyzed using adapted FE models. Based on investigations by TÜV Rheinland, a corrosion-induced weakening of the load-bearing cross-section of the threaded sleeve is taken into account and the connection is evaluated with regard to its permissible loads.
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The metrological determination of component loads and stresses is an important aspect of mechanical engineering. These variables are used both for the design of technical systems and for the validation of simulations, which is why suitable determination is still the subject of research today. A common way of determining the forces and moments introduced into a component is to use strain gages. These are applied to the surface of the measurement object, whereby the strains occurring in the measurement object are imprinted on the strain gages. These strains cause a change in the electrical resistance, which is easy to measure. Strain gauges therefore measure the strain caused by the measured variables to be determined and thus allow conclusions to be drawn about the measured variables themselves.
In the field of vehicle development, the forces and torques that are introduced via the tires are of central importance. These external excitations are strongly dependent on driving behavior and the road surface and can be determined with commercial measuring wheels that use strain gages (CAEMAX, Kistler).
The high cost of these commercial measuring devices results in the desire for cost-effective alternatives. The expected strains can be determined simulatively as part of FEM analyses of the components to be tested and the positioning of the strain gauges can be optimized using problem-dependent criteria. This can improve the quality of the results or reduce the number of measuring points required.
The versatile measuring method of the inverse matrix method is examined using an automotive example, whereby the loads introduced into the chassis are determined using strain gages. In contrast to measuring wheels, these strain gages are applied to the wheel axle. The transmission behavior is calculated using FEM and a comparison of all selected position options is carried out. The transmission behaviour determined in this way must exhibit both high strains and good condition, which is why a Pareto approach is used to optimize these two criteria. Since this approach generates different solutions, an error analysis is carried out which includes the random and systematic errors occurring in the test. The applicability of the measurement method is investigated both on an axle test bench and on the vehicle.
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The frequency response of a generator with innovative air gap development was experimentally recorded as part of the operating vibration analysis in order to characterize the dynamic behaviour. The excitation is carried out as a foot-point excitation with a 10kN shaker, whereby the control was realized via a specially programmed signal generator, which can generate harmonic and non-harmonic signals and regulate them to a defined acceleration amplitude. A sliding sine or sine sweep was used to determine the frequency response. In contrast to conventional methods, which use excitation via impulse hammers, the large excitation forces that can be converted by the shaker also allow non-linear characteristics to be determined, which can occur, for example, as a result of playing fits. As a quintessence, it is thus possible to determine the transmission behavior taking into account the boundary conditions in real operation.
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As part of the project, a ZTR roadster was electrified and designed as a mobile battery test bench. For this purpose, the battery tray was designed in such a way that it can be changed in a short time (approx. 5 minutes). A key element of the new design is the rear swing arm, which was modified to accommodate a permanently excited synchronous motor, which also made it necessary to adapt the transmission ratio of the chain drive to the characteristics of the motor.
In addition to functioning as a mobile battery test bench, the ZTR Roadster offers the opportunity to demonstrate the steps required for electrification from the individual components to the complete vehicle and can be used for media-effective presentation of the work at OVGU in the context of electromobility.
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In addition to established systems, advanced passive concepts can also be used to reduce vibration and noise by filling cavities with granular media. The positive damping properties of granular materials are exploited and, using the example of an oil pan, it is shown that significant vibration reductions can be achieved without increasing the mass and without taking up additional installation space. Due to the unavoidable distribution of the granulate in a large cavity during operation and the associated significant influence on the vibration behavior of the structure, a structure with many small cavities was derived. Due to the advantageous stiffness-to-weight ratio, honeycomb structures can be used in this context, the optimal filling of which was derived.
Various alternative materials were then investigated, with granular rubber achieving the best results, as the deformation of the material acts as an additional source of dissipation. The resulting methods can be applied analogously to other problems, which leads to the definition of a
general methodology that can be used for both horizontal and vertical applications.
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Laboratory centrifuges are used to separate substances. At high speeds, large accelerations act on the material to be centrifuged, which leads to rapid sedimentation of the heavy components. The operation of centrifuges requires well-balanced rotors and even weight distribution of the samples in order to minimize imbalances.
The aim of the research project is to test and design a modular system that can automatically compensate for variable imbalances in laboratory centrifuges in order to prevent vibrations and consequential damage.
Our research has shown that purely fluid-based balancing units are not suitable for the desired dimensions of laboratory centrifuges, as the balancing effect is too small. With the aid of solids in the carrier fluid, the positive balancing effect could be demonstrated experimentally in a prototype and in a series sample as well as mathematically in multi-body simulations. The use of suitable raceway components and the resulting reduction in friction underline the potential achieved by the balancing unit on the series sample produced with a targeted design.
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The aim of the project is a detailed investigation of the non-linear behaviour of a semi-floating turbocharger for the whole operation range. For this task a model is necessary, which describe the eigenbehaviour of the rotor and further include a detailed bearing model as well as a suitable thermal model. In addition the simulations have to be compared with measurements. Finally, suggestions shall be stated to reduce the harmonic vibrations by change of geometrical parameters and by improvement of the balancing process always in the context of resulting friction power and subharmonic vibrations.

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For the transient simulation of centrifuges, which are often mounted on rubber buffers, the frequency-dependent stiffness and damping properties of the mounting in the three spatial directions represent a significant influence. These properties were measured using a shaker and a force sensor.
For this purpose, the rubber buffers were positioned between a rigid counter bearing and the shaker and subjected to a monofrequency load. The buffer displacement was recorded using a laser vibrometer. With the aid of a force sensor connected in series, the displacement-force diagrams were recorded, from which the stiffness and the degree of damping can be derived. The frequency-dependent rubber buffer characteristics can be determined efficiently by automatically scanning the frequency range.
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When optimizing transfer cases, it is necessary to analyse the forces acting on the individual components. Due to the complex kinematics (including large displacements) and the diverse contact conditions within torque-sensing plate differentials, a description using MBS algorithms is advantageous.
On the basis of the design parameters, a non-linear model is to be constructed, on which an analysis of the kinematics (contact behavior, locking effect) as well as a transient evaluation of the contact forces under different load conditions is possible.
This information forms the basis for further strength analyses with the aim of reducing costs by utilizing component reserves.
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During the development process of turbochargers, in addition to the flow and thermodynamic properties, the influences of the rotor dynamics and the design of the bearings are central points that are of great importance. Due to the diverse influences on the vibration behavior, an a priori estimation using simplified formulas is associated with many uncertainties. For this reason, a numerical model of the turbocharger to be developed is to be set up, which maps the rotor dynamic properties including the bearings.
The aim is to study the effects of design changes on subharmonic vibration components (whirl, whip), friction power and bearing forces.
Once a prototype has been implemented, the simulations are to be compared with the measurements carried out and the limiting bearing clearance combinations resulting from the manufacturing accuracy are to be examined with regard to their influence on the vibration behavior.
The work described is carried out analogously for two turbochargers (the design implementations vary as a result of the application in connection with gasoline or diesel engines).
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With the aim of investigating the strength properties of miniature rotors, a test rig is to be set up and put into operation that uses laser triangulation sensors to record the expansion of the winding on the rotor and its speed as a function of time. The background to the test rig is the maximum permissible speeds, which are difficult to estimate, especially for fiber-reinforced rotors, before the matrix-fiber connection fails and the rotor is destroyed.
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With the aim of investigating the dynamic properties of an exhaust system, the stiffness and damping coefficients of the mount are of great importance in addition to the structural properties of the design, as these have a significant effect on the natural frequencies and thus potential resonance points as well as the expected vibration amplitudes. Due to the elastomer design, there is a frequency dependency of the coefficients, which must be taken into account for a well-founded analysis.
To determine the frequency-dependent stiffness and damping coefficients, a test rig is to be set up and put into operation using laser triangulation sensors and a load cell, which also takes the preload into account via an adapted design. While the bracket is excited with a shaker at a defined frequency , the vibration velocities and the acting forces are recorded in parallel.
After integrating or differentiating the velocity signal, the associated spring stiffness can be calculated knowing the acting force. This information can also be used to determine the hysteresis losses, which can then be used to determine the damping coefficient.
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In the earlier project the influence of different parameter upon harmonic vibrations of a turbocharger rotor has already been analysed. As a result the unbalance distribution and the non-linear characteristics (mainly damping) of the bearings could be identified as significant factors.
The aim of the current project is a further detailed investigation of the system behaviour. For that task a model upgrade concerning eigenfrequencies of the rotor as well as an improved bearing and thermal model are necessary. In addition the simulations have to be compared with measurements. Finally suggestion of countermeasures shall be stated to reduce vibration amplitudes taking into account the current balancing process and the non-linearities of the bearings.

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Based on the knowledge gained in the previous projects "Turbocharger Benchmark" and "Instability of the Turbocharger Bearing" on the simulation of the dynamic behavior of turbochargers, the developed calculation routines are to be applied to another turbocharger. This relates on the one hand to the description of the rotor dynamics of the impeller, taking into account the non-linear bearing, and on the other hand to the reaction on the elastically mapped housing.
Due to a special bearing geometry, axial grooves and profiled bearing supports must be provided. This requires an adaptation of the algorithm with regard to discontinuous gap function curves and the resulting discretization problems.
In this context, parameter variations are performed to predict the effects on the subharmonic oscillations dominating the system behavior and their influences on the rotor dynamics and hydrodynamics.
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Subject to a confidentiality agreement .
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As part of the project, sliding friction welding is to be modeled using suitable simulation methods. An advantageous description of the temperature-dependent material properties, which are to be modeled continuously during the transition from solid to liquid phase, can be realized by a Carreau-fluid law. The simulation enables the material flow and temperature development in the joining zone to be mapped. Based on defined material parameters of the materials involved, the influence of various geometric and design parameters and their combinations can be investigated.
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During the development of turbochargers one design criterion involves the amplitudes of harmonic and subharmonic vibrations. When using semi-floating bearings often the harmonic vibrations are dominant and have to be reduced in order to get a beneficial acoustic behaviour.
One main influence upon the harmonic vibrations is the unbalance. Assuming a linear system, a reduction of the unbalance will lead to a reduction of the harmonic vibrations especially in the region of the eigenfrequencies.
During some experimental measurements an increase of the amplitudes in the second resonance was observed, although the unbalance of the rotor was decreased.
Beside the unbalance and its distribution also non-linear effects due to the floating ring bearings can be responsible for the described experimental results.
The aim of the project is to investigate the unexpected behaviour using a numerical model of the turbocharger under transient conditions including a non-linear description of the floating ring bearings.

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As part of technology optimization and cost minimization, sensors whose measurement data is also available for indirect determination are to be eliminated.
In this context, experimental studies have shown unexpected changes in friction performance depending on various parameters in certain constructive implementations of an oil pump.
A description of the dynamic behavior, including the hydrodynamic conditions and thus the resulting forces in the pump, is essential for investigating the mechanisms of action. For this reason, a hydrodynamic-mechanical coupled MBS model of the pump is set up and a simulative study is carried out depending on the design parameters.
In addition, the resulting loads make it possible to assess the load-bearing capacity of the main bearing.
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The aim of the project is to develop an FE-based method for the virtual parameter identification of elastomeric bearings with a focus on the stiffness behavior in the limit ranges that are difficult to represent experimentally.
After a literature research on hyperelastic material models and their application in FE simulation for large deformations and taking into account preloads, frictional influences and special geometries, a suitable hyperelastic material model is selected.
A simulation methodology is then developed to determine the spring characteristics for selected elastomer mounts in the operating and limit ranges, taking into account the required boundary conditions. Using this methodology, an optimization algorithm for the automated determination of the material model parameters is designed and implemented on the basis of the technical drawing.
Finally, the stiffness conditions can also be determined simulatively beyond the operating load range.
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For the design of turbochargers, it is necessary to describe the harmonic and subharmonic vibrations induced by the non-linear behavior of the floating bushing bearing over the entire operating speed range. The holistic, feedback coupling of rotor dynamics and hydrodynamics must be mapped in order to realize reliable simulation results.
Based on the knowledge gained in the previous project "Turbocharger Benchmark" on the simulation of the dynamic behavior of turbochargers, the developed calculation routines will initially be applied to another turbocharger in order to demonstrate the transferability of the method to other design implementations.
With regard to the comfort criterion "sound emission", a description of the elastic properties of the housing is implemented within the dynamic simulation, whereby the transmission behavior of the disturbance signal caused by the floating bushing bearings to the housing surface is mapped. The transmitted signal is the cause of the sound emission. A comparison with measured surface velocities makes it possible to evaluate the simulation results.
The aim of the project is to provide an improved level of knowledge for the dynamics of turbochargers, especially with regard to the influence of the bearings on maximum speeds, instabilities, service life, etc.
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When designing kinetic (intermediate) energy storage systems, high angular velocities and mass moments of inertia are required to achieve sufficient storage capacities.
This is accompanied by classical questions of rotor dynamics, which primarily concern the inherent behavior and the excitation due to the acting unbalance.
Deviating from the linear considerations, the non-linear, speed-dependent properties of the bearing arrangement, which is implemented here by roller bearings in conjunction with O-rings, must also be taken into account for safety reasons.
In the project, the stiffness and damping characteristics of the O-rings to be used will first be determined experimentally (this also includes investigations of the temperature dependency). In addition, an analysis of the system behavior will be carried out using the determined non-linear properties. The aim is a reliable prediction of the critical speeds including non-linear effects. % (generalized Campbell diagram).
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Due to the limited speeds of e-turbo units, which are often used in racing, rolling bearing designs are used to minimize friction, which are combined with additional squeeze oil damper elements to achieve sufficient damping values and due to the advantageous thermal properties. In addition to these positive characteristics of the squeeze oil dampers, however, there are also non-linear influences that must be described in combination with the dynamic behavior of the overall system in order to enable a reliable design of the overall system.
Based on the position and velocity vectors of the shaft and shell, the resulting restoring forces, which are determined by Reynolds' differential equation, can be determined. The influence of the Couette flow (shear flow) can be neglected due to the design restriction to purely translational movements of the shaft and shell.
As part of the project, a transient solution to the problem for implementation in ADAMS MSC will be realized using user-written force routines (g-force).
The descriptive differential equation is solved with the aim of an efficient numerical implementation (i.e. using a simplified cavitation algorithm) in the time domain, whereby freely definable oil supply conditions are to be realized.
Parallel to the numerical solution of Reynolds' differential equation, an approximate solution (short-bearing theory) is implemented, whereby initial design processes and the associated parameter studies can be realized with reasonable effort.
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