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Institute: search.filters.UBSInstitut.Institut für Technische und Numerische MechanikSubject: search.filters.subject.670

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Now showing 1 - 7 of 7
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    On shift selection for Krylov subspace based model order reduction : an iterative greedy approach combined with singular value decomposition
    (2023) Frie, Lennart; Eberhard, Peter
    Mechanical systems are often modeled with the multibody system method or the finite element method and numerically described with systems of differential equations. Increasing demands on detail and the resulting high complexity of these systems make the use of model order reduction inevitable. Frequently, moment matching based on Krylov subspaces is used for the reduction. There, the transfer functions of the full system and of the reduced system are matched at distinct frequency shifts. The selection of these shifts, however, is not trivial. In this contribution we suggest an algorithm that evaluates an increasing number of shifts iteratively until a reduced model that approximates the full model in a subspace with very low approximation error is found. Thereafter, the projection matrix that spans this subspace is decomposed with singular value decomposition and only most important directions are retained. In this way, small reduced models with good approximation properties that do not exceed a predefined error bound can be found or low-error models for a given reduced order can be generated. The evaluation of more shifts than necessary and further reduction by means of singular value decomposition is the novelty of this contribution. In this paper, this novel approach is extensively studied and, furthermore, applied to the numerical example of an industrial helicopter model.
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    A physically based material model for the simulation of friction stir welding
    (2020) Panzer, Florian; Shishova, Elizaveta; Werz, Martin; Weihe, Stefan; Eberhard, Peter; Schmauder, Siegfried
    A physically based material model, taking into account the interdependence of material microstructure and yield strength, is presented for an Al 5182 series aluminum alloy for the simulation of friction stir welding using continuum mechanics approaches. A microstructure evolution equation considering dislocation density and grain size is used in conjunction with a description of yield stress. In order to fit experimental stress-strain curves, obtained from compression tests at various strain rates and temperatures, phenomenological relationships are developed for some of the model parameters. The material model is implemented in smoothed particle hydrodynamic research code as well as in the commercial finite element code Abaqus. Simulations for various strain rates and temperatures were performed and compared with experimental results as well as between the two discretization methods in order to verify the material model and the implementation. Simulations provide not only an accurate approximation of stress based on temperature, strain rate, and strain but also an improved insight into the microstructural evolution of the material.
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    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.
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    Vibration analysis on newly designed painting supports for the Cranach exhibition 2022 at Herzogin Anna Amalia Bibliothek
    (2023) Hartlieb, Eva; Ziegler, Pascal; Eberhard, Peter
    The effect of vibration on the condition of sensitive works of art continues to be of great importance to museums. Vibrations contribute to irreversible changes in the complex materiality of art and cultural heritage. In cooperation with the Klassik Stiftung Weimar, the Institute of Engineering and Computational Mechanics at the University of Stuttgart accompanied an exhibition setup. The museum and partners designed free‐standing columns in the exhibition hall to support valuable works of art. Due to their original design, these are susceptible to vibrations. Thus, the question arises as to what extent these columns should be modified in order to reduce these vibrations. In this study, measurements were taken on the floor and on the columns using a variety of measuring techniques. It was investigated which excitations from the environment propagate to the artwork. It was confirmed that vibrations from the environment, such as road traffic and museum visitors in the exhibition room, are sources of excitation. Experimental modal analysis was used to identify the characteristic vibration behaviour of these columns. By using finite element methods, a simulation model was set up allowing to investigate modifications to the columns in order to predict the change in vibration behaviour. Based on the simulation modifications, structural changes were made to the system through stiffening of individual components and redistribution of masses.
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    Investigation of chip jamming and drill breakage in deep-hole drilling using Smoothed Particle Hydrodynamics
    (2024) Baumann, Andreas; Eberhard, Peter
    Single-lip deep hole drilling is characterized by a high-quality hole and a high level of productivity achieved. It is performed using high feed rates in a single pass, and, therefore, chips must be removed by the cooling liquid. However, chip jamming is a significant problem when chips wrap around the tool, leading to marks on the borehole wall and an increased drilling torque, potentially causing sudden tool failure. The Smoothed Particle Hydrodynamics method is applied to simulate the challenging fluid flow and elastic bodies. A first approach is developed to model the effects of chip jamming and the possible consequence of drill breakage for a deeper understanding of the process behavior.
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    Reproduction of transport-induced vibration of paintings based on a multi-channel FxLMS controller
    (2023) Gao, Yulong; Ziegler, Pascal; Hartlieb, Eva; Heinemann, Carolin; Eberhard, Peter
    Monitoring the vibration of the painting canvas during transport is of great significance to protect paintings from damage. However, limited to the narrow structure of the transport crate, the lack of an inertial reference, and the limitations to attach sensors to the canvas, this is a difficult task. For this reason, based on vibration data measured on the strainer that is easily obtained during transport, this contribution proposes to reproduce these with high accuracy in the laboratory. There, the resulting vibration of the canvas can be conveniently observed in a controlled environment with respect to an inertial reference. A real-time simulation platform based on the multi-channel Filtered- x Least Mean Square (FxLMS) algorithm controls four actuators simultaneously and reproduces the vibration of the strainer obtained from a real transport experiment. The vibration of the canvas is then measured by a laser Doppler vibrometer without contact. The experimental results show that the vibration reproduction system has sufficient reproduction accuracy for the vibration response. Even though some overshoot in the reproduced acceleration can be observed in some cases, the overall reproduction is very good. A long-term reproduction experiment verifies its stable reproducibility. Therefore, the designed vibration reproduction system provides a reference for the unknown canvas response during transport, and further helps art conservators to evaluate the transport process of the painting.
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    Modeling and mitigation of vortex formation in ejector deep hole drilling with smoothed particle hydrodynamics
    (2024) Baumann, Andreas; Gerken, Julian Frederic; Sollich, Daniel; Rupasinghe, Nuwan; Biermann, Dirk; Eberhard, Peter
    Ejector deep hole drilling achieves high-quality boreholes in production processes. High feed rates are applied to ensure a high productivity level, requiring reliable chip removal from the cutting zone for a stable process. Therefore, a constant metalworking fluid flow under high volume flow rates or high pressure is required. Experimental results show a vortex formation at the outer cutting edge. This vortex can lead to delayed chip removal from the cutting zone, and ultimately, it can lead to chip clogging and result in drill breakage due to increased torque. This paper investigates modified drill head designs using the smoothed particle hydrodynamics method. The investigated modifications include various designs of the chip mouth covering. Besides graphical analysis based on flow visualizations, flow meters are placed at the tool’s head to evaluate the impact of the modifications on the flow rate and possible increased resistance and relocation of the fluid flow from the outer cutting edge to other parts of the tool. The simulation results for the reference design show the experimentally observed vortex formation, validating the simulation model. By adding the tool’s rotation in the SPH simulation, which is not included in the experiments for observation reasons, the vortex formation is positively influenced. In addition, some designs show promising results to further mitigate the vortex formation while maintaining a sufficient fluid flow around the cutting edges.