Universität Stuttgart
Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1
Browse
14 results
Search Results
Item Open Access 3D FEM simulation of titanium alloy (Ti6Al4V) machining with harmonic endmill tools(2023) Kalu-Uka, Abraham; Ozoegwu, Chigbogu; Eberhard, PeterUsually, end milling operations have been carried out using conventional uniform helix tools with fixed helix angles. Thus, many studies have been conducted to study the effects of these tools on the thermomechanical properties of a milling process. Recently, there have been works that point to the benefits of using harmonic endmills. Harmonic endmills consist of cutting edge profiles that have continuously harmonically varying helix angles. The variation is described using a harmonic function of axial position (elevation) of points on the cutting edge. In this work, a 3D finite element simulation using ABAQUS, is carried out for the complex milling process of Titanium alloy Ti6Al4V. The envelope of the harmonic tool is first generated using a set of MATLAB codes and stored in a Standard Triangle Language (.stl) format. The machine tool is introduced into an FEM program which has been designed to provide for dynamic effects, thermo‐mechanical coupling, material damage law and the criterion for contact associated with the milling process. A Johnson‐Cook material constitutive equation which combines the effects of strain hardening, strain softening, and temperature softening is used. To account for the chip separation criterion, the Johnson Cook damage evolution equation is used. The milling process simulation for Ti6Al4V is then carried out. In the end, the stress distribution and the cutting forces are obtained.Item Open Access Inverse fuzzy arithmetic for the quality assessment of substructured models(2015) Iroz, Igor; Carvajal, Sergio; Hanss, Michael; Eberhard, PeterThe dynamical analysis of complex structures often suffers from large computational efforts, so that the application of substructuring methods has gained increasing importance in the last years. Substructuring enables dividing large finite element models and reducing the resulting multiple bodies, yielding a reduction of, in this case, complex eigenvalue calculation time. This method is used to predict the appearance of friction-induced vibrations such as squeal in brake systems. Since the method is very sensitive to changes in parameter values, uncertainties influencing the results are included and identified. As uncertain parameters, standard coupling elements are considered and modeled by so-called fuzzy numbers, which are particularly well suited to represent epis- temic uncertainties of modeled physical phenomena. The influence of these uncertainties is transferred to undamped and damped eigenfrequencies of a substructured model by means of direct fuzzy analyses. An inverse fuzzy arithmetical approach is applied to identify the uncertain parameters that optimally cover the undamped reference eigenfrequencies of a non-substructured, full model. If a validity criteria is defined, a positive decision in favor of the most adequate model can be performed.Item Open Access Ride Comfort Transfer Function for the MAGLEV Vehicle Transrapid(2018) Zheng, Qinghua; Dignath, Florian; Eberhard, Peter; Schmid, PatrickIn order to predict the ride comfort for the MAGLEV vehicle Transrapid TR09 for various scenarios, e.g. for higher vehicle speeds than hitherto travelled, a transfer function from the excitations given by the guideway position to the relevant car body acceleration is calculated by two different methods. Method A is based on a mechatronic simulation model of the Transrapid TR09 which describes a two- dimensional lateral cross section of the vehicle. The simulation model consists of a 2D multibody system describing the mechanical part, four network models of the electro-magnets - two levitation magnets and two guidance magnets - and a signal model of each magnet controller. These signal models contain a representation of the authentic C-Code of the control law used within the actual magnet control units within the vehicle TR09. The overall model can be exploited to calculate the accelerations of the car body for given excitations at the interfaces between guideway and vehicle. Moreover, it is possible to generate a model-based transfer function in the frequency domain from the guideway excitations to the car body accelerations. For method B, measurement results of test runs of the Transrapid TR09 at the test track TVE in Northern Germany are exploited which were recorded for vehicle dynamics analysis and ride comfort evaluation in 2009. From these measurement results two characteristic quantities are generated for several different velocities of the vehicle: Firstly, the position of the guideway is reconstructed by using an integration of the absolute accelerations of the magnets and the signals of the magnet's sensors for the air gap. Secondly, the relation between the accelerations at the car body of the vehicle and the guideway position is calculated as a transfer function in the frequency domain. For this, the measurement data and the reconstructed guideway position are both transformed into the frequency domain by a Fast Fourier Transformation (FFT). The resulting transfer function gives the relevant accelerations for the ride comfort for given excitations of the vehicle as calculated by Method A above. The two transfer functions from Method A and B are compared for validation. Then, a smoothed version of the validated transfer function is applied for estimating the ride comfort for travelling scenarios which have not yet been measured in practical operation, e.g. for higher velocities of the vehicle.Item Open Access Methods of model order reduction for coupled systems applied to a brake disc‐wheel composite(2023) Matter, Fabian; Iroz, Igor; Eberhard, PeterIn this contribution, investigations on model order reduction for coupled systems composed from components of a passenger car are shown. In today's development processes, the simulation of mechanical components is indispensable and large Finite Element models are often used for this purpose. For the calculation of time‐domain or frequency‐domain analyses, for example, a lot of computing power is required. However, with the application of model order reduction methods, this effort can be reduced, but this results in a trade‐off between the reduction error and the computational time. Since the computation of reduction bases for complete systems can be computationally expensive, it is of interest to be able to reduce components individually and then assemble them into a reduced overall model. This can result in both, a saving of computational effort when creating the bases, as well as a saving of the required memory space. Furthermore, there are many possible combinations of components in the modular systems of today's automotive industry, which emphasizes the model order reduction by parts and not by assemblies. In this work, methods of model order reduction for coupled systems are presented and will be tested on components in the chassis of a sports car. Therefore, an assembly consisting of a brake disc and wheel rim together with the wheel hub are investigated. For this purpose, the eigenmodes and transfer functions of the overall model, the reduced overall model and the assembly built from individual reduced bodies are compared.Item Open Access Hybrid modeling of multibody systems : comparison of two discrepancy models for trajectory prediction(2024) Wohlleben, Meike; Röder, Benedict; Ebel, Henrik; Muth, Lars; Sextro, Walter; Eberhard, PeterThis study focuses on hybrid modeling approaches that combine physical and data‐driven methods to create more effective dynamical system models. In particular, it examines discrepancy models, a type of hybrid model that integrates a physical system model with data‐driven compensation for inaccuracies. The study applies two discrepancy modeling methods to a multibody system using discrepancies in the state vector and its time derivative, respectively. As an application example, a four‐bar linkage with nonlinear damping is investigated, using a simplified conservative system as a physical model. The comparative analysis of the two methods shows that the continuous approach generally outperforms the discrete method in terms of accuracy and computational efficiency, especially for velocity prediction and prediction horizon. However, scenarios, where input signals for training and testing differ, present nuanced findings. When the continuous method is trained on complex signals (sine) and tested on simpler ones (stair), it struggles to deliver satisfactory results, exhibiting notably higher root mean square error (RMSE) values, particularly in angular velocity prediction. Conversely, training on simple signals (stair) and testing on complex ones (sine) surprisingly yields low RMSE values, indicating the continuous method's adaptability. While the discrete method aligns more closely with expectations and performs better in certain scenarios, its results are consistently moderate, neither exceptional nor particularly poor. The study also introduces a selection framework for choosing the most suitable algorithm based on the specific characteristics of the modeling task. This framework provides guidance for researchers and practitioners in leveraging hybrid modeling effectively. Finally, the study concludes with an outlook on future research directions.Item Open Access Modeling of the Transrapid’s electromagnets and the application to large mechatronic vehicle models(2022) Schmid, Patrick; Schneider, Georg; Kargl, Arnim; Dignath, Florian; Liang, Xin; Eberhard, PeterThis work gives an overview of a general approach for modeling the electromagnets of a magnetic levitation (Maglev) vehicle based on electromagnetic suspension. The method intends to map the magnets’ static and dynamic behavior in a frequency range relevant for use in mechatronic simulation models and Maglev control or observer design. The methodology starts with setting up the equivalent magnetic circuit considering magnetic reluctances, fringing and leakage flux, magnetic saturation, and eddy currents. Then, the resulting equations are coupled with the magnet’s electric circuits using Ampère’s law and Faraday’s law of induction. Further, a numerical model reduction technique is sketched, which yields a simplified version of the previously derived magnet model with nearly the same input-output structure and input-output behavior, suitable for large simulation models and control design. The approach’s capabilities and strengths are shown by the agreement to measurements and by implementing the resulting models in large mechatronic vehicle models of the Transrapid.Item Open Access Analysis of the SPH interpolation moments matrix with regard to the influences of the discretization error in adaptive simulations(2021) Heinzelmann, Pascal; Spreng, Fabian; Sollich, Daniel; Eberhard, Peter; Williams, John R.Item Open Access Simulation of a high-speed maglev train on an elastic guideway of infinite length(2022) Schneider, Georg; Schmid, Patrick; Kargl, Arnim; Liang, Xin; Dignath, Florian; Eberhard, PeterSimulations of the coupled vehicle/guideway dynamics are an essential part in the development of high-speed magnetic levitation (maglev) systems with higher speed than traveled so far. In this contribution, a two-dimensional rigid multibody model mapping the heave-pitch motion of the vehicle is presented and used for dynamics simulations of the vehicle traveling along an infinite elastic guideway. The concept of moving system boundaries is applied for the guideway model to efficiently implement an infinite series of elastic Euler-Bernoulli beams while keeping the number of system states small. Guideway deflection interpolation and computation of equivalent nodal forces and torques are realized using Hermite polynomials. Together with a physically advanced magnet model and a model predictive control scheme, the coupled system is applied for vehicle and guideway dynamics analysis for different vehicle speeds and guideway elasticities.Item Open Access Geometry modifications of single-lip drills to improve cutting fluid flow(2022) Baumann, Andreas; Oezkaya, Ekrem; Biermann, Dirk; Eberhard, PeterFor single-lip drills with small diameters, the cutting fluid is supplied through a kidney-shaped cooling channel inside the tool. In addition to reducing friction, the cutting fluid is also important for the dissipation of heat at the cutting edge and for the chip removal. However, in previous investigations of single-lip drills, it was observed that the fluid remains on the back side of the cutting edge, and accordingly, the cutting edge is insufficiently cooled. In this paper, a simulation-based investigation of an introduced additional drainage flute and flank surface modifications is carried out using smoothed particle hydrodynamics as well as computational fluid dynamics. It is determined that the additionally introduced drainages lead to a slightly changed flow situation, but a significant flow behind the cutting edge and into the drainage flute cannot be achieved due to reasons explained in this paper. Accordingly, not even a much larger drainage flute with unwanted side-effect of a decrease tool strength is able to archive a significant improvement of the flow around the cutting edge. Therefore, major changes to the cooling channel, like the use of two separate channels, the modification of their positions, or modified flank surfaces, are necessary in order to achieve an improvement in lubrication of the cutting edge and heat dissipation.Item Open Access Interpolation‐based parametric model order reduction of automotive brake systems for frequency‐domain analyses(2023) Matter, Fabian; Iroz, Igor; Eberhard, PeterBrake squeal describes noise with different frequencies that can be emitted during the braking process. Typically, the frequencies are in the range of 1 to 16 kHz. Although the noise has virtually no effect on braking performance, strong attempts are made to identify and eliminate the noise as it can be very unpleasant and annoying. In the field of numerical simulation, the brake is typically modeled using the Finite Element method, and this results in a high‐dimensional equation of motion. For the analysis of brake squeal, gyroscopic and circulatory effects, as well as damping and friction, must be considered correctly. For the subsequent analysis, the high‐dimensional damped nonlinear equation system is linearized. This results in terms that are non‐symmetric and dependent on the rotational frequency of the brake rotor. Many parameter points to be evaluated implies many evaluations to determine the relevant parameters of the unstable system. In order to increase the efficiency of the process, the system is typically reduced with a truncated modal transformation. However, with this method the damping and the velocity‐dependent terms, which have a significant influence on the system, are neglected for the calculation of the eigenmodes, and this can lead to inaccurate reduced models. In this paper, we present results of other methods of model order reduction applied on an industrial high‐dimensional brake model. Using moment matching methods combined with parametric model order reduction, both the damping and the various parameter‐dependent terms of the brake model can be taken into account in the reduction step. Thus, better results in the frequency domain can be obtained. On the one hand, as usual in brake analysis, the complex eigenvalues are evaluated, but on the other hand also the transfer behavior in terms of the frequency response. In each case, the classical and the new reduction method are compared with each other.