Browsing by Author "Eberhard, Peter"

Now showing 1 - 20 of 48

Open Access
3D FEM simulation of titanium alloy (Ti6Al4V) machining with harmonic endmill tools
(2023) Kalu-Uka, Abraham; Ozoegwu, Chigbogu; Eberhard, Peter
Usually, 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.
Open Access
Analysis of mixed uncertainty through possibilistic inference by using error estimation of reduced order surrogate models
(2022) Könecke, Tom; Hose, Dominik; Frie, Lennart; Hanss, Michael; Eberhard, Peter
In the context of solving inverse problems, such as in statistical inference, an efficient repeated evaluability of a system can be achieved through methods of model order reduction. However, quantifying and adequately representing the emerging reduction error requires special techniques for combining different sources of uncertainty. In this paper, parametric finite element models are reduced through parametric model order reduction. The induced approximation error, an epistemic uncertainty, is reasonably estimated with the help of modern estimators for formulating statistical statements about the parameters to be identified. Measurement noise is also taken into account as a source of aleatory uncertainty. As a novel extension to analyzing a single source of uncertainty, the construction of a basic workflow for parameter identification in the face of both epistemic and aleatory uncertainties is presented, combining efficient error estimation techniques and possibilistic inference. The general applicability of this procedure is highlighted by two illustrative applications.
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.
Open Access
Analyzing and optimizing multibody systems
(1992) Bestle, Dieter; Eberhard, Peter
Optimization of holonomic as well as non-holonomic multibody systems is presented as a nonlinear programming problem that can be solved with general-purpose optimization codes. The adjoint variable approach is used for calculating design derivatives of a rather general integral type performance measure with respect to design parameters. The resulting equations are solved by numerical integration backward in time. A multi-step integration algorithm with order and step-size control is adapted for this application by including an interpolation scheme. Numerical experiments and a comparison to the common approach of approximating the gradient of the performance measure by finite differences show that high efficiency, accuracy, and reliability are achievable.
Open Access
Anomalously acting agents : the deployment problem
(2024) Wenger, Ingeborg; Ebel, Henrik; Eberhard, Peter
Detecting intentionally antagonistic behavior in robot swarms brings challenges that exceed identifying merely erroneous behavior. We investigate a data-based approach to recognize anomalous and, in particular, antagonistic behavior in robots executing a deployment task. The task requires a robot swarm of variable size and starting positions to be optimally distributed within an arbitrary convex surveillance area. Combining a long short-term memory neural network and a normalizing flow, our approach learns to approximate the probability of a robot action. Thus, actions with low probability density values can be categorized as anomalous. The applicability of the proposed approach is validated on simulated runs containing benevolent, antagonistic, and erroneous robots. Both antagonistic and erroneous robots are detected with more than 90 percent accuracy.
Open Access
Automated approach for optimizing dynamic systems
(1994) Bestle, Dieter; Eberhard, Peter
The optimal design of nonlinear dynamic systems can be formulated as a multicriteria optimization problem. On the basis of a multibody system model integral type objective functions are defined evaluating the dynamic behavior of the system under consideration. Multicriteria optimization methods reduce the problem to nonlinear programming problems which can be solved with standard algorithms like the SQP method. The gradients required for such an efficient optimization procedure are computed by solving, additional differential equations resulting from an adjoint variable approach. The whole design process can be highly automated by using computer algebra packages.
Open Access
Beyond uncertain material properties : possibility-based uncertainty propagation in computational modal analysis
(2025) Könecke, Tom; Kaupp, Lars; Cillo, Pierfrancesco; Ziegler, Pascal; Hanss, Michael; Eberhard, Peter
Modal analysis relies on computational models that approximate experimental systems through the identification of material and geometry parameters. However, beyond these properties, the model creation process itself involves other critical choices, such as solver schemes, reduction order, element type, mesh density, and boundary conditions, that are typically treated as fixed choices rather than uncertain parameters. This study presents a widened perspective that treats these modeling choices as additional uncertain parameters alongside traditional material and geometry properties. Using possibility theory for forward uncertainty propagation, we quantify uncertainty without requiring probabilistic distributions over modeling choices. That is, instead of treating all choices as equally likely, possibility theory captures the range of feasible modeling options while incorporating quantitative information where available, particularly for material properties. We apply this framework to evaluate eigenfrequency predictions under imprecise input parameters, yielding uncertain output ranges rather than point estimates. A critical innovation is the accurate matching of results from varying parameters to corresponding eigenfrequencies using modal assurance criterion (MAC) clustering. The methodology is demonstrated through a case study of a guitar soundboard model, showing how possibility theory provides a robust framework for uncertainty quantification in structural dynamics without requiring probabilistic assumptions about modeling choices.
Open Access
Comparison of distributed model predictive control approaches for transporting a load by a formation of mobile robots
(2017) Ebel, Henrik; Sharafian Ardakani, Ehsan; Eberhard, Peter
This paper investigates and discusses two different distributed formation control approaches based on model predictive control (MPC). Specifically, the presented control schemes are used to govern the motion of omnidirectional mobile robots that shall maintain a given formation shape while following a path through a previously unknown environment. The setup of the control schemes accounts for the requirements of transporting an elastic plate purely by normal and friction forces. The intricacy of this task motivates the choice of model predictive control since it allows to explicitly constrain the movements of the robots. The two schemes analyzed in this contribution are fundamentally different in their optimization and communication strategies. The performance of the schemes is carefully examined in various simulations. These include situations in which the robots have to shrink the formation in order to squeeze through narrow passages. An exemplary experimental result involving real robot hardware is also presented.
Open Access
Comparison of local and global approaches for parametric model order reduction for systems with distributed moving loads
(2017) Fröhlich, Benjamin; Eberhard, Peter
In order to ensure a numerically efficient simulation of elastic multibody systems, model order reduction has to be employed for reducing the complexity of the underlying Finite-Element-Models. Elastic multibody systems with moving loads can be modeled as parameter dependent systems for which methods from parametric model order reduction have to be applied. In this contribution, two local and a global approach from parametric model order reduction are investigated. A comparison is made with respect to their approximation quality in frequency domain and time domain and their numerical cost in transient simulations. As a numerical example, a linear drive with a distributed moving load is considered.
Open Access
Cooperative search by combining simulated and real robots in a swarm under the view of multibody system dynamics
(2013) Tang, Qirong; Eberhard, Peter
This paper presents a new approach for cooperative search of a robot swarm. After modeling the robot, the mechanical Particle Swarm Optimization method is conducted based on physical robot properties. Benefiting from the effective localization and navigation by sensor data fusion, a mixed robot swarm which contains both simulated and real robots is then successfully used for searching a target cooperatively. With the promising results from experiments based on different scenarios, the feasibility, the interaction of real and simulated robots, the fault tolerance, and also the scalability of the proposed method are investigated.
Open Access
Coupled vehicle-guideway dynamics simulations of the Transrapid with discretized levitation magnet forces
(2022) Schneider, Georg; Schmid, Patrick; Dignath, Florian; Eberhard, Peter
Magnetic levitation (maglev) is a promising technology for high-speed transportation systems, as shown by the Transrapid line in Shanghai operating successfully for nearly 20 years. Currently, a new high-speed train based on this technology is being developed, driven by China's Ministry of Science and Technology. Magnets are one of the key components of a maglev vehicle's suspension system. Attractive magnet forces ensure the contactless coupling of the vehicle to the guideway. Electromagnets are usually described using finite element (FE) models, electromagnetic circuit models, or simple analytical models for simulation purposes. However, FE magnet models are computationally often overwhelming, especially for transient studies, and thus too slow to use them in large vehicle models for vehicle dynamics simulations. Moreover, the parameterization of FE models often is non-trivial. Therefore, less detailed but fast-computable models are used in such simulations, often providing only a coarse discrete distribution of magnet forces along the vehicle. In this contribution, the coupled vehicle-guideway dynamics is investigated regarding different discretizations of levitation magnet forces. A two-dimensional model of the maglev vehicle Transrapid moving along an infinite elastic guideway is used, considering the heave-pitch motion of the vehicle and the vertical guideway bending. Simulations are performed using either a coarse distribution with two magnet forces per magnet or a fine distribution with twelve magnet forces per magnet, i.e., one magnet force at each magnet pole. It is shown that the simplification of two magnet forces per levitation magnet is valid for vehicle dynamics simulations. The model is parameterized with data from the Transrapid TR08 and uses a self-developed model predictive control (MPC) scheme to control the magnets.
Open Access
End-effector trajectory tracking of flexible link parallel robots using servo constraints
(2022) Morlock, Merlin; Burkhardt, Markus; Seifried, Robert; Eberhard, Peter
We apply the concept of servo constraints to end-effector trajectory tracking control of parallel robots with structural link flexibilities. Such servo constraints deliver the inverse robot model where solution approaches via projections are proposed, which transform the resulting differential-algebraic equations to ordinary differential equations. The applicable solution process depends on the existence and stability of the internal dynamics. When using the exact end-effector of flexible link robots as output, this internal dynamics is usually unstable. Then a two-point boundary value problem is considered in the framework of stable inversion to obtain the noncausal solution offline. This solution is used as a feedforward control, which is initially combined only with actuator feedback control. To also account for errors within the link flexibility, the well-known linear-quadratic regulator is adapted to end-effector trajectory tracking based on differential-algebraic equations. Finally, we propose a systematic input-output feedback linearization approach, which uses servo constraints for flexible link parallel robots. Here a minimum phase system is obtained by tracking a redefined end-effector output, which is an approximation of the exact end-effector position. All control concepts are validated experimentally with a parallel robot having a highly flexible link. The results allow us to compare different control approaches and show the superior performance of controllers that rely on a flexible multibody model in contrast to classical rigid multibody modeling.
Open Access
Experimental investigations on impact transmission through a plate
(2013) Fischer, Christian; Eberhard, Peter
The concept of an impact actuated shift valve is presented. This valve concept can be actuated by different kinds of actuators, such as piezo stack actuators. A simplified model for the investigation of the impact process is created. The model consists of a plate, two spheres and a fluid-filled tank. Experiments are presented with and without fluids and different plates. The results are compared to simulations.
Open Access
Experimental research on the influence of modal nonlinearities of paintings under mechanical loads
(2022) Gao, Yulong; Ziegler, Pascal; Heinemann, Carolin; Hartlieb, Eva; Eberhard, Peter
In the traditional transportation of paintings and the design of the packaging systems, paintings are usually assumed to behave like a linear system. In order to verify this hypothesis, in this contribution, by means of a hammer experiment and a sweep excitation experiment to simulate the shock and vibration during transportation, respectively, the modal nonlinearities of two real paintings and a dummy painting are experimentally studied. The experimental results show that paintings can be treated as a linear system only when being subjected to shock, but the modal nonlinearities of paintings cannot be ignored when being subjected to vibration. The general behaviour of the paintings modal nonlinearities is then summarised based on experimental results, and their consequences for painting transportation are discussed. First of all, the offset of the resonance frequency is the most important problem which will lead to failure of the original vibration isolation measures. Further, the decrease in the resonance peak amplitude will increase the probability of the eigenmode being excited. Besides, it is also necessary to attenuate the harmonic vibrations of paintings. Lastly, the different modal characteristics obtained by a sweep with increasing and decreasing frequency make the analysis of different excitation schemes more complicated. Therefore, the identification of the paintings modal nonlinearities is necessary and important.
Open Access
Exploration-exploitation-based trajectory tracking of mobile robots using Gaussian processes and model predictive control
(2023) Eschmann, Hannes; Ebel, Henrik; Eberhard, Peter
Open Access
Force-based organization and control scheme for the non-prehensile cooperative transportation of objects
(2023) Rosenfelder, Mario; Ebel, Henrik; Eberhard, Peter
Open Access
Geometry modifications of single-lip drills to improve cutting fluid flow
(2022) Baumann, Andreas; Oezkaya, Ekrem; Biermann, Dirk; Eberhard, Peter
For 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.
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, Peter
This 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.
Open Access
Identification of confidence distributions for modal parameters in the face of measurement uncertainty
(2025) Könecke, Tom; Elangasinghe, Akila; Cillo, Pierfrancesco; Ziegler, Pascal; Hanss, Michael; Eberhard, Peter
While classical methods of modal analysis typically disregard measurement uncertainty and identify a single best-fitting set of modal parameters on the Fourier-transformed frequency response, this contribution presents a novel approach that models measurement uncertainty as an additive possibilistic error. A modified Fourier transform is applied to obtain imprecise frequency response functions, based on which an approach to imprecise modal parameter identification is presented. The applicability of the methodology is demonstrated on a simulated example of a damped harmonic oscillator and a real-world experiment of a wooden guitar soundboard.
Open Access
Improving accuracy in parametric reduced-order models for classical guitars through data-driven discrepancy modeling
(2024) Cillo, Pierfrancesco; Brauchler, Alexander; Gonzalez, Sebastian; Ziegler, Pascal; Antonacci, Fabio; Sarti, Augusto; Eberhard, Peter