bluuebunny/crossref_metadata_2025_split huggingface dataset:
Linear Low‐Rank Parameter‐Dependent Fluid‐Structure Interaction Discretization in 2D
Authors: Weinhandl Roman , Benner Peter , Richter Thomas 
Published: December 2018

AbstractFluid‐structure interaction problems involve material parameters such as the shear modulus of the solid and the dynamic fluid viscosity. In order to examine the behaviors of various solids and adapt the problems to different fluid configurations there is a need to vary such material parameters flexibly. This can be done by a parameter‐dependent fluid‐structure interaction discretization which yields a system matrix that has block diagonal structure. As also discussed in [2], the resulting equation is equivalent to a matrix equation which allows for a low‐rank approach where the iterate is represented by a tensor. A low‐rank GMRES variant similar to what was discussed in [1] can then be applied to such parameter‐dependent systems.
Simulation of upper and lower bainitic transformation with a coupled phase field/diffusion/deformation framework
Authors: Düsing Martin , Mahnken Rolf 
Published: December 2018

AbstractIn materials science one distinguishes between upper and lower bainite which grow due to different quenching processes. The temperature influences significantly the diffusion of carbon and therefore the resulting microstructure. The growth direction of the corresponding phase depends strongly on the eigenstrains of the transformation. In this work we describe this phase transformation process with different diffusion mechanisms and a coupling of the phase field method with deformations due to eigenstrains. Numerical examples demonstrate the expected behaviour.
Interacting Particles and Optimization
Authors: Pinnau René , Totzeck Claudia 
Published: December 2018

AbstractWe shed some light on the connection of dogs herding sheep and the optimization of interacting particle systems. Main goal is the control of a large crowd of individuals by a few external agents. This yields a high dimensional constrained optimization problem, which is solved by an instantaneous control approach applied to the mean‐field approximation of the state system.
A fluid‐structure interaction approach with inherently fulfilled coupling conditions
Authors: Schwarz Alexander , Averweg Solveigh , Nisters Carina , Schröder Jörg 
Published: December 2018

AbstractIn the present contribution a fluid‐structure interaction (FSI) approach based on a mixed least‐squares finite element method (LSFEM) is introduced. The LSFEM is a variational approach for constructing finite element formulations, see e.g. [1] and [2]. In this work, the proposed FSI method is based on the formulation of mixed finite elements in terms of stresses and velocities for both the fluid and the solid regime. The conforming discretization of the stresses and velocities in the spaces H(div) and H1, respectively, leads to the inherent fulfillment of the coupling conditions of a FSI method. The idea of the LSFEM based FSI scheme is the solution of the full problem consisting of both domains in one triangulation at the same time. The general idea on this was firstly annotated in [8]. A numerical example considering an incompressible, linear elastic solid at small deformations (compare to [3]) together with an incompressible laminar fluid flow demonstrates the applicability of the LSFEM‐FSI approach.
Generalised Convolution Quadrature with Runge‐Kutta methods for Acoustic Boundary Elements
Authors: Schanz Martin 
Published: December 2018

AbstractIn time domain boundary element formulations the convolution in time can be handled by analytical integration or the convolution quadrature method. Here, the generalised convolution quadrature method is applied based on Runge‐Kutta methods. This method allows a variable time step size and the usage of higher order methods in time. The example shows that the variable time step size preserves the convergence order for non‐smooth solutions. The order of convergence is restricted by the low order spatial discretisation.
Stability Analysis of Numerically Approximated Quasiperiodic Motions
Authors: Fiedler Robert , Hetzler Hartmut 
Published: December 2018

AbstractThis contribution deals with the stability analysis of flows on invariant manifolds based on the theory of LYAPUNOV‐exponents. The description using an invariant manifold for quasiperiodic motions allows an analysis of a finite p‐dimensional interval instead of an investigation through time integration of an one dimensional infinite interval. To demonstrate the use of this approach the LYAPUNOV‐exponents are calculated for a quasiperiodic motion of a forced VAN‐DER‐POL equation. The verification of the proposed method is carried out by comparing the results to an alternative approach based on a time integration using a continuous GRAM‐SCHMIDT orthonormalization.
Non‐linear Dynamics of Electrical Machines: A Kind of Electro‐Mechanical Sommerfeld Effect?
Authors: Boy Felix , Hetzler Hartmut 
Published: December 2018

AbstractElectrical machines in modern applications, as for example in electric mobility, are operated at high and rapidly changing rotational speeds. Under such conditions, lateral rotor oscillations due to unbalanced magnetic pull and modified flux linkage may affect the torque and rotational motion and thus the operational reliability. Such a scenario, which shows certain similarities to the SOMMERFELD‐effect in classical rotordynamics, is analysed within this paper using a computationally fast model, based on LAGRANGE‐MAXWELL equations and the permeance harmonic method.
Parameter Identification for Calcium Release in a Heart Cell with Modified Patankar–Runge–Kutta Schemes
Authors: Kopecz Stefan , Meister Andreas , Peercy Bradford E. , Gobbert Matthias K. 
Published: December 2018

AbstractSimulation of calcium release in heart cells requires the solution of a complex three‐dimensional model, which involves a large number of parameters, whose values are crucial for a realistic simulation. To identify biophysically meaningful parameters, studying a one‐dimensional model for several hundred parameter values is instructive. The goal of this process is to capture the general model behavior and to maintain physical principles like positivity for all time step sizes. We use time adaptive modified Patankar–Runge–Kutta (MPRK) schemes to solve the one‐dimensional models for various parameter values. These schemes ensure unconditional positivity and capture the model behavior also for large time steps. The adaptive MPRK schemes are very efficient for crude tolerances, which enables fast and meaningful solutions of the one‐dimensional problems, and hence, fast parameter identifications.
Development of an internal physiological muscle controller within an open‐source Hill‐type material model in LS‐DYNA
Authors: Martynenko Oleksandr , Kempter Fabian , Kleinbach Christian , Schmitt Syn , Fehr Jörg 
Published: December 2018

AbstractNowadays automotive industry is paying more attention to vehicle safety systems with the aim to reduce the number of injuries and fatalities among road users. Simulations are used throughout the whole research and development process for such systems involving Finite Element Human Body Models (FE HBMs) and the multiphysics simulation software package LS‐DYNA. Because the safety of living (active) humans in traffic situations has to be assured, special material models are applied to generate reflexive or voluntary muscle reactions of the FE HBMs. These elements are governed by an application‐dependent controller, which produce individual activation signals for each of them. The current contribution presents the development of a physiologically inspired controller for muscle elements, enabling the simulation of voluntary or reflexive movements with the FE HBM. As a result, it is possible to control muscle elements internally without any additional superior controller level or complementary coding with LS‐DYNA keywords. A validation example with the calculation of appropriate muscle activation levels through optimization of the controller parameters is given.
Solving high‐dimensional Lyapunov inequalities to obtain linear port‐Hamiltonian systems
Authors: Pulch Roland 
Published: December 2018

AbstractWe investigate high‐dimensional linear dynamical systems. Each system can be converted into a port‐Hamiltonian formulation. A positive definite transformation matrix has to be identified, which satisfies a Lyapunov inequality. We apply a recent approach for the approximate solution of high‐dimensional Lyapunov equations, which guarantees the positive definiteness of an approximation. Results of numerical computations are presented using a benchmark.
On the impact of superimposed vibrations on the onset of friction‐induced oscillations
Authors: Kapelke Simon , Seemann Wolfgang 
Published: December 2018

AbstractThe reduction of effective frictional forces by superimposing vibrations is referred to as vibrational smoothing of dry friction and has been subject of numerous publications. Focussing on the impact of longitudinal vibrations and using simple Coulomb friction modelling, high‐frequency vibrations have been shown to change the non‐smooth characteristics of dry friction into a viscous‐like behaviour. Consequently, providing an appropriate excitation, friction‐induced vibrations due to decreasing friction‐velocity characteristics or non‐conservative coupling can be quenched. Among longitudinal excitation, also transverse vibrations have been shown to smooth the effective friction‐velocity characteristics. However, their influence on friction‐induced oscillations has not been discussed so far, such that the impact of superimposed transverse vibrations on decreasing friction‐velocity characteristics and non‐conservative coupling is investigated. Using an elasto‐plastic friction model, the influence of contact compliance and stiction on quenching friction‐induced vibrations is discussed, showing both quantitative and qualitative effects on the results.
A nonlinear Timoshenko beam formulation for modeling a tendon‐driven compliant neck mechanism
Authors: Eugster Simon R. , Deutschmann Bastian 
Published: December 2018

AbstractIn this paper, we consider the dynamical behavior of a tendon‐driven compliant neck mechanism which is used to actuate the head of a humanoid robot as proposed by [1, 2]. The neck is realized as a silicone block mounted onto the robot's torso. At the top end of the silicone block an aluminum plate interconnects the compliant neck with the head. At the same plate, tendons are attached whose actuation causes the soft and flexible block to deform thereby inducing a motion of the robot's head. For workspace design and control of the head's trajectory, a mechanical model is required which appropriately describes the entire neck‐head system. We present a dynamic model of the system in which the silicone block and the head are modeled as a planar nonlinear Timoshenko beam and a rigid body, respectively. The tendon actuations are included as external configuration‐dependent forces.
Convergence of a new FV‐discretization of the Fokker–Planck equation
Authors: Heida Martin 
Published: December 2018

AbstractWe present a new finite volume discretization of the Fokker–Planck equation. The so called Squareroot Approximation (SQRA) scheme has recently been derived by several authors and shows a gradient structure that is asymptotically compatible with the Wasserstein gradient structure studied by Jordan, Kinderlehrer and Otto using methods from stochastic homogenization. We show that the SQRA scheme converges for Voronoi discretizations. In case the Voronoi cells are regular enough, the scheme converges even for unknown cell volumes, which makes it computationally feasible for high dimensional problems.
Multiscale characterisation and simulation of open cell metal foams
Authors: Bleistein Thomas , Jung Anne , Diebels Stefan 
Published: December 2018

AbstractThe complex microstructure of open cell metal foams results in beneficial global material properties like a good weight to stiffness ratio, which makes this special group of cellular materials interesting for several applications. Open cell metal foams are suitable for lightweight applications as well as for energy absorbing systems. The dependency of the entire samples' mechanical behaviour on their microstructure induces the demand of experiments and simulations on different scales. Hence, a couple of experiments are necessary to specify the material properties of open cell aluminium foams. On the macroscopic level, several tests with different load cases such as pure tension, pure compression or pure torsion and the superposition of these loading conditions are needed to obtain the yield surface for the different types of foams. The material parameters on the microscopic level can be identified by microtensile tests and inverse calculations using a 3D model of the strut. The deviation of the simulation results from the experimental data is minimised by an optimisation. Thus, the used material parameters in the simulations are changed until the numerical results match the experiments. This contribution focuses on the characterisation of open cell metal foams on different hierarchical levels. It introduces an approach to describe the macroscopic material behaviour with a homogeneous material model based on micromechanical experiments and material parameters.
On the phenomenological model for potato tuber tissue in relation to its anatomy
Authors: Trostorf Robin , Leichsenring Kay , Seydewitz Robert , Böl Markus 
Published: December 2018

AbstractA phenomenological constitutive model based on the principle of hyperelasticity for the perimedullary zone of the potato tuber is presented. The proposed constitutive model is controlled by an internal memory variable that is based on the strain history. Parameter identification is based on stress‐stretch relations obtained from single‐cycle uniaxial compression experiments on samples extracted from the perimedullary zone of potato tubers. The stress‐strain response of the tissue is characterized by a pronounced and reproducible hysteresis. This may be caused by the eviction of intracellular fluid as well as an inelastic cell wall response. Test on single cells from the perimedullary zone are used to identify the cause of hysteresis and plastic deformation as well as to connect the microstructure to the observed stress‐strain response.
Efficiency of parallel in time methods for coupled PDEs on moving domains
Authors: Naumann Andreas , Wensch Jörg 
Published: December 2018

AbstractIn recent years, several parallel in time methods have been developed. Amongst them are ParaReal, ParaExp and PFASST. In this talk, we apply these methods to the heat conduction problem of a coupled machine tool, which consists of several parts and materials. Neighboring parts are coupled at their common boundary with a robin type boundary condition. The challenging part comes from the fact that parts may move with respect to each other. We discretize the coupled PDE system on varying domains in space by finite elements. Due to the movement, we obtain a multi scale ODE containing the time scale of diffusion and the time scale of the movement. We apply different parallel in time methods on the resulting multi scale ODE and compare their parallel efficiency in numerical experiments.
Numerical Design for Primary Shaping Manufacturing Processes
Authors: Zwicke Florian , Schneppe Tobias , Hopmann Christian , Elgeti Stefanie 
Published: December 2018

AbstractUsing a mold or die, primary shaping manufacturing processes form material from an initially unshaped state (usually melt) into a desired shape. All of these processes have in common that the exact design of the mold cannot be determined directly and intuitively from the product shape. This is due to the non‐linear behavior of the material regarding the flow and solidification processes. Consequently, shape optimization as a means of numerical design can be a useful tool in mold development. The core of our optimization tool is the in‐house flow solver XNS, which is based on the finite element method with GLS stabilization. It is able to exploit the common communication interfaces for distributed‐memory systems. XNS has been coupled with an optimization framework. Furthermore, a geometry kernel has been developed, which internally describes the geometry of the mold in a CAD‐based fashion. The optimization tool has been applied to three melt‐based manufacturing processes: plastics profile extrusion, injection molding and high‐pressure die casting. This paper will focus on injection molding.
Gyrolog – Developing a Digital Collection of Gyro Instruments for Historical and Didactical Research
Authors: Niklaus Maria , Wagner Jörg F. 
Published: December 2018

AbstractTechnical artefacts and instruments form an essential part of cultural heritage. If historically analysed and suitably explained, they provide insights into developments and objects that had and still have a significant influence upon our present civilization. Without any explanation and contextualization, however, these objects will remain stubbornly silent, especially if they are technically complex or highly encapsulated.Based on a gyroscope collection at the University of Stuttgart, the Gyrolog project intends to take these instruments out of their black boxes by digital means. These inconspicuous yet indispensable objects of many of today's key technologies (from automatic car navigation to handheld devices) are of prime interest to historians of technology as well as to technical didactics and to technical museums. The project will render the unique gyroscope collection at the University of Stuttgart digitally accessible and, moreover, will virtually unite it with smaller collections at other institutions.Apart from their importance for daily life technologies, gyroscopes have always been of prime military interest as well. Reproducing the artefacts digitally will therefore open further ways to science and technology studies of dual use technologies.Gyrolog aims at a basic digital representation of all gyroscopes found in German collections. At the centrepiece of the project, however, cutting edge imaging and digitalizing technologies will exhibit carefully selected objects literally in depth. By combining advanced animation and optical technologies, Gyrolog seeks to present a unique technical collection in digital format as well as an elaborated methodical approach for exploring complex small technical artefacts.
Modeling planar pantographic sheets using a nonlinear Euler–Bernoulli beam element based on B‐spline functions
Authors: Capobianco Giuseppe , Eugster Simon R. , Winandy Tom 
Published: December 2018

AbstractAn undeformed pantographic sheet consists of two orthogonal arrays of straight fibers interconnected by internal pins. In this paper, we model the fibers of this lattice‐like sheet as nonlinear Euler–Bernoulli beams and use B‐spline functions for their finite element discretization. Using the concept of one‐dimensional generalized force laws, we show how different models for the pins can be introduced in the model. Finally, the simulation of a tensile test is presented.
Application of the Stochastic Field Method to Multi‐Fluid Flow
Authors: Raquet Martin R. , Class Andreas G. , Edelbauer Wilfried 
Published: December 2018

AbstractThe Stochastic Field Method was originally derived in the field of combustion and firstly applied to a cavitation problem by our group [1]. Randomly distributed variables exist in both combustion and cavitating problems. Calculating strong nonlinear processes using mean values as input, leads to unphysical results. The consideration of the variable's probability density function (PDF) becomes mandatory. The Stochastic Field Method approximates this PDF by samples similar to methods of Lagrangian particles where imaginary particles are introduced to the flow. In contrast to Lagrangian particles methods, these samples are represented by Eulerian fields described by stochastic partial differential equations. This pure Eulerian interpretation makes the method attractive for CFD‐codes: A coupling of an Eulerian and a Lagrangian perspective becomes obsolete which results in efficient computation times ‐ especially in the presence of a vast number of bubbles. In contrast to other Eulerian methods, the calculation of an arbitrary PDF is possible at low computational cost. The representation of samples as fields allows the visualization of PDFs within every computational cell. The first implementation into a commercial CFD‐Code is presented. In addition, industrial examples, like cavitation in an automotive injection nozzle, are shown.
Numerical Investigation of Coalescing Filtration Process
Authors: Chaudhuri Jayotpaul , Ehrhard Peter 
Published: December 2018

AbstractCoalescing filtration is a mechanical process which is employed to remove dispersed aerosol particles from a gas stream. This kind of filtration is a depth‐filtration process and is widely used in process industries to remove particulate matter from exhaust gases or in compressed‐air applications to filter oil particles introduced during the compression process. Fibrous filters are often used due to low costs, high capture efficiency and low pressure drop. The droplets are first captured on the fibers, then coalesce, and eventually drain out. The performance of a filter medium is judged based on its capture efficiency and pressure‐drop characteristics. Estimating these parameters without setting up experimental investigations of each filter medium would be beneficial for choosing optimal filters. In the present study, numerical simulations are used to predict the behavior of a fully‐wetting fibrous filter using an Euler‐Euler formulation in ANSYS CFX. Different theoretical models to predict single fibre capture efficiencies are compared and a novel extrapolation scheme to predict the net capture of oil particles is presented. Pressure‐drop studies are carried out to find the pressure drop of a viscous fluid flowing through an array of fibers. A steady‐state multiphase simulation with the influence of gravity is set up, and the physical relevance of the results is examined.
Reduced order modeling of viscoelastic properties of asphalt concrete
Authors: Wingender Dennis , Fritzen Felix , Jänicke Ralf 
Published: December 2018

AbstractBiphasic asphalt concrete consists of mineral aggregates and a surrounding bituminous binding agent, of those material properties are known. To obtain the overall material behavior, we generate Statistical Volume Elements (SVE) of the asphalt concrete structure artificially. Afterwards, the Nonuniform Transformation Field Analysis (NTFA) is applied to homogenize them. This paper focuses on the stochastical differences of the microstructures of the SVEs and their influences on the macroscopic material behavior. Therefore, an indirect tensile test is simulated.