bluuebunny/crossref_metadata_2025 huggingface dataset:
Multilevel Monte Carlo Method for Stochastic Analysis of Fluid‐Structure Interaction
Authors: Kodakkal Anoop , Wüchner Roland , Bletzinger Kai‐Uwe
Published: December 2018

Abstract: Uncertainty quantification for multi‐physics problems like fluid‐structure interaction (FSI) is challenging in terms of the required computational effort and complexity of physics involved. A Multilevel Monte Carlo (MLMC) approach for stochastic analysis of FSI problems is presented in the current study. An overall reduction in computational cost is achieved by variance reduction in MLMC method. The efficacy of MLMC algorithm for expensive problems like FSI is compared with classical Monte Carlo(MC) method and MLMC is found to achieve the required accuracy at a significantly reduced computational cost. An FSI benchmark test case with uncertain inputs is presented here. The possibility of uncertainty quantification for FSI systems with a plausible computational cost using MLMC is demonstrated.
Galerkin‐based mixed time finite elements for structural dynamics
Authors: Ströhle Timo , Betsch Peter , Schiebl Mark
Published: December 2018

Numerically stable and accurate time integration methods are important in structural dynamics. We propose such a method based on a mixed variational formulation of the underlying semi‐discrete equations of motion. The newly developed scheme relies on a specific combination of the so‐called continuous Galerkin (cG(k)) method and the discontinuous Galerkin (dG(k)) method. We refer to [2] for an introduction of the original cG(k) and dG(k) methods for ODEs (see also [1]). The mixed approach relies on polynomial approximations of degree k on the level of each time finite element. In particular we make use of hierarchical interpolation polynomials. The present approach is closely related to Hellinger‐Reissner type mixed variational formulations for elastodynamics. The mixed method yields implicit time‐stepping schemes with order of accuracy equal to 2k for the displacements and velocities. In addition to that, the method is capable of conserving the energy in the case of conservative mechanical systems. Numerical examples are presented which highlight the numerical properties of the newly proposed mixed approach.
Scaled boundary isogeometric analysis of large deformations in solids
Authors: Chasapi Margarita , Klinkel Sven
Published: December 2018

The so‐called scaled boundary isogeometric analysis combines the advantages of the isogeometric analysis and the scaled boundary finite element method. Here, the parameterization of the solid follows the idea of the scaled boundary finite element method (SB‐FEM), where the boundary of the domain is scaled in respect to a specified scaling center inside the domain. In the framework of isogeometric analysis (IGA), the NURBS functions that describe the geometry also interpolate the unknown displacement field. Such a combined approach is advantageous for three‐dimensional solids, as a radial scaling parameter describes the interior of the solid and only the geometry of the boundary is required for the analysis. The motivation is therefore to fit the idea of the boundary representation modeling technique, which is the way solids are designed in CAD –namely only by their boundary surfaces. Our contribution introduces a formulation for geometrical nonlinear 2D problems. The derived formulation addresses hyperelastic material behavior for large deformations and plane strain conditions for the two‐dimensional domain. We solve the boundary value problem by applying the weak form of equilibrium in both radial scaling and circumferential direction of the boundary. Thereafter, the nonlinear deformation behavior requires a linearization and the application of the Newton‐Raphson iterative scheme. Finally, we study the performance of this approach on a numerical problem by comparison to the standard finite element method.
Hyperbolicity‐preserving stochastic Galerkin method for hyperbolic systems with uncertainties
Authors: Schneider Florian , Schlachter Louisa
Published: December 2018

Uncertainty Quantification through stochastic spectral methods is rising in popularity. We derive a modification of the classical stochastic Galerkin method that ensures the hyperbolicity of the underlying hyperbolic system of partial differential equations. The modification is done using a suitable linear scaling limiter, based on similar ideas in the context of kinetic moment models. We apply the resulting modified stochastic Galerkin method to the compressible Euler equations. Our numerical results show that it can compete with other UQ methods like the intrusive polynomial moment method while being computationally inexpensive and easy to implement.
Approximation of Periodic and Quasi‐Periodic Motions of a Rotor System with Visco‐elastic Seal Support by Using a Fourier‐Galerkin‐Method
Authors: Bäuerle Simon , Hetzler Hartmut
Published: December 2018

In this contribution a Fourier‐Galerkin method is used to calculate the periodic and quasi‐periodic motions of a rotor‐seal system. The system consists of a classical Laval‐rotor, a visco‐elastically supported rigid seal rigid and a turbulent fluid flow through the seal gap. The Fourier‐Galerkin method uses one‐ and two‐dimensional Fourier series to approximate steady‐state periodic solutions due to rotor mass unbalance and quasi‐periodic solutions due to unbalance and self‐excitation stemming from the seal fluid forces. The method is applied to continue solution‐branches of the rotor‐seal system which show periodic/ quasi‐periodic solutions, resonance, multiple Neimark‐Sacker bifurcations as well as synchronisation (Torus‐breakdown).
Constitutive modelling of sheet‐layered lamination stacks
Authors: Baloglu Maximilian Volkan , Willner Kai
Published: December 2018

Sheet‐layered lamination stacks found in electric motors as rotor and stator are a challenging task in structural mechanics due to their special design. The manufacturing process determines the nature of the microstructure resulting in the presence of bonding varnish or frictional contact between the individual metal sheets. For the latter case, a penalty method in normal and tangential direction can be used to capture the contact interactions of single plates. In combination with homogenization techniques, a transversely isotropic surrogate material model with a corresponding strain energy density can be identified. In this paper, the focus lies on the influence of the penalty parameters on the elastic quantities of the constitutive equation.
Implicit forming simulations for “Die‐Less‐Hydroforming”‐structures
Authors: Metzger Andreas , Ruff Daniel C. , Ummenhofer Thomas
Published: December 2018

FEM forming simulations are often performed using an explicit solver, which usually requires time‐scaled and often mass‐scaled simulation approaches. Explicit simulation with the commercial software LS‐DYNA also provides very good results for the forming simulation of the innovative process of “"Die‐Less‐Hydroforming” when time‐scaling and relatively very strong mass‐scaling are used. Nevertheless, this paper presents an implicit forming simulation for “Die‐Less‐Hydroforming” using LS‐DYNA, which can be used on the one hand (in addition to costly experimental investigations) as comparison and verification of the explicit simulation. On the other hand, the simulation of the forming process, which in reality is quasi‐static, corresponds more precisely with regard to the mapping of its process time, since neither time‐scaling nor mass‐scaling are required when using the implicit solver in comparison to the calculation with the explicit solver.
Kirchhoff‐Love shell theory based on Tangential Differential Calculus
Authors: Schöllhammer Daniel , Fries Thomas‐Peter
Published: December 2018

We propose a parametrization‐free reformulation of the classical Kirchhoff‐Love shell equations in terms of tangential differential calculus. An advantage of our approach is that the surface may be defined implicitly, and the resulting shell equations and stress resultants lead to a more compact and intuitive implementation. Numerical tests are performed and it is confirmed that the obtained approach is equivalent to the classical formulation based on local coordinates.
Linear Low‐Rank Parameter‐Dependent Fluid‐Structure Interaction Discretization in 2D
Authors: Weinhandl Roman , Benner Peter , Richter Thomas
Published: December 2018

Fluid‐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

In 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

We 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

In 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

In 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.
On the reduced solution of the earthquake‐induced pounding problem
Authors: Shi Jianye , Bamer Franz , Markert Bernd
Published: December 2018

The present contribution deals with the improvement of the computational efficiency of earthquake‐induced dynamic pounding problems based on hierarchical substructure techniques.
Stability Analysis of Numerically Approximated Quasiperiodic Motions
Authors: Fiedler Robert , Hetzler Hartmut
Published: December 2018

This 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

Electrical 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

Simulation 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

Nowadays 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

We 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

The 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

In 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

We 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

The 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

A 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

In 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

Using 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

Technical 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

An 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.
On an optimal control problem for non‐smooth wave phenomena
Authors: D. Maldonado André , Yousept Irwin
Published: December 2018

The optimal control problem for a hyperbolic evolution system is considered. The presence of non‐smooth nonlinearities in the governing PDE system constitutes the main difficulty of this problem. An existence result and an optimality system of Bouligand‐type are presented.
Application of the Stochastic Field Method to Multi‐Fluid Flow
Authors: Raquet Martin R. , Class Andreas G. , Edelbauer Wilfried
Published: December 2018

The 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

Coalescing 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

Biphasic 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.
A numerical study of the influence of inclusion geometries in heterogeneous dielectric elastomers
Authors: Klassen Markus , Klinkel Sven , Müller Ralf
Published: December 2018

The investigation and study of dielectric elastomers has emerged as an important research field in the last years with regard to the development of so called dielectric elastomer actuators (DEAs). The main advantage of this technology lies in the possibility of the design of soft actuators which are capable of large deformations. The main drawback is given by the high electric fields, which are necessary to drive such actuators. This drawback emerges from the reduced relative permittivity of dielectric elastomers, which leads to a low electromechanical coupling. In order to improve this handicap, a heterogeneous material structure, consisting of an elastomer matrix with barium titanate inclusions, is suggested. This contribution is concerned with the numerical analysis of the heterogeneous material including the electromechanical coupling for the dielectric elastomer. A mixed finite element formulation is employed to account for the nearly incompressibility of the dielectric elastomer. The numerical results show that the proposed material inclusions are capable to improve the stretch ratios of the elastomers. Different geometries of the inclusion are investigated with respect to the actuator deformation range.
Experimental and Numerical investigation of a Nozzle at different operating conditions for a Clean in Place System
Authors: Sivaramakrishnan Anand Sivaram , Abubaker Harish , Münsch Manuel , Delgado Antonio , Murcek Roman , Boye Andre
Published: December 2018

Selection and optimization of a Clean In Place (CIP) system is a complex process. The CIP nozzles used in the system plays a huge role in the efficiency of the entire system. Therefore, numerical investigations are widely employed by many industrial processes, especially in the hygiene critical industries, such as Food, Beverage and Pharmaceutical industries. An enormous quantities of cleaning agent and water are consumed on a daily basis during their cleaning processes. Finding a reliable and efficient design and operating condition of the cleaning nozzle based on understanding the internal and external flow properties and their optimization is a priority for these industries. This paper presents the comparison between experimental measurement and the numerical prediction of the flow characteristics of a currently available CIP nozzle which are widely used for the industrial cleaning in place application. The flow features are measured experimentally using the optical measurement technique, Phase Doppler Anemometry (PDA) system which is then numerically compared. Computations of the CIP nozzle system were conducted using a finite volume based commercial computational fluid dynamics (CFD) solver, StarCCM+ V12.04. The Eulerian based unsteady multiphase simulation is carried out using different numerical solvers and the best suitable and efficient one is presented here. The achievement of good agreement between the numerical predictions and the experimental results has presented the opportunity to understand the flow behaviour in unsteady state conditions. Based on these studies further optimization will be carried out with the help of some evolutionary algorithms or artificial neural networks.
Comparison of a numerical versus an analytical approach to calculate 1D impact problems of non‐uniform cross sections
Authors: Burgert Jens , Seemann Wolfgang
Published: December 2018

Analytical solutions for the wave propagation of impacting partners can only be found for certain shapes of the cross section by applying a modified exponential approach. For arbitrary cross sections, numerical methods have to be chosen. In this contribution, an analytical approach is applied and presented in the field of rock drilling. It is shown that the comparison of the numerical and analytical solutions yields good agreement.
Randomized nonlinear model order reduction methods for large dynamical problems with explicit time integration
Authors: Bach C. , Bartol J. , Ceglia D. , Song L. , Duddeck F.
Published: December 2018

Projection‐based nonlinear model order reduction (MOR) often involves the computation of a truncated singular value decomposition (SVD) of a snapshot matrix A ∈ ℝm×n, m≥n, computed from training simulations, where only the first k basis vectors are retained. A can however become very large in case of detailed models with a large number of degrees of freedom (DoFs), or when many snapshots are present. This is often the case for explicit FEM simulations of industrial problems. Computing the SVD can then become problematic, as most widely used SVD algorithms for MOR have an asymptotic complexity of 𝒪(mn2 ) [1]. Randomized algorithms can alternatively be used to compute only the k most significant basis vectors. Such methods only scale with 𝒪(mnk) or even 𝒪(mn log(k)) [2]. We present a modified hybrid randomized incremental algorithm for efficient reduced basis (RB) computation with low memory requirements, and apply the method to a large‐scale example problem. The results show that the hybrid algorithm is capable of efficiently computing a RB even for very large problems at a manageable computational effort.
Thermodynamical consistency of an anisotropic meanfield damage model for SMC composites
Authors: Görthofer Johannes , Schemmann Malte , Seelig Thomas , Hrymak Andrew , Böhlke Thomas
Published: December 2018

This contribution investigates the thermodynamic consistency of a meanfield damage model published by the authors [1]. The model is based on an empirical description of the fiber orientation distribution function (FODF). Due to a combination of matrix damage and fiber‐matrix interface debonding, the model is able to predict the inhomogeneous and anisotropic evolution of the overall behavior of the considered Sheet Molding Compound (SMC) composite.
Diffusive fluid‐driven brittle fracture in saturated porous media
Authors: Heider Yousef
Published: December 2018

The aim in this research work is to develop a numerical model of fracturing of saturated, brittle porous materials. Different sources of the energy dissipation can be distinguished in this process, such as the crack propagation, the injection fluid flow in the crack and the fluid flow the surrounding porous domain (e.g. due to leak‐off). In this study, the phase‐field modelling (PFM) scheme together with the continuum mechanical theory of porous media (TPM) are applied. The proposed TPM‐PFM modelling framework accounts for the crack nucleation and propagation, deformation of the solid matrix and the different types of fluid flow in the porous domain and the crack. Additionally, an open system with possible fluid mass production from external source is assumed, where special focus is on the description of pressure time history at the injection location during the crack propagation. A major factor that influences the pressure history profile is the fluid viscosity, giving rise to the toughness‐dominated and viscous‐dominated responses. Therefore, the effect of the fluid type in the fracturing processes will be discussed in a numerical example.
Effect of grain orientations on the thermal grain boundary grooving in a three‐dimensional setting
Authors: Khan Asim Ullah , Hackl Klaus , Baitsch Mattias
Published: December 2018

The objective of this work is to study the effect of grain orientation on the thermal grooving by surface diffusion. Hackl et al. [1] have presented a finite element model for thermal grooving in three‐dimensions. This variational model involves surface energy, grain boundary energy, external and internal triple line energy. In this study, We use an orientation dependent surface energy. For {1 0 0} grain orientation in the normal direction, we have self‐similar groove profiles for increasing extent of anisotropy of the surface energy. For {1 1 0} and {1 1 1} orientations, there are formation of facets for critical anisotropic cases. These formations are due to so‐called missing orientations concerning the shape of an unconstrained crystal in equilibrium. The rate of grooving varies with change in the extent of surface free energy anisotropy. Flux along the triple line is also important in determining the groove root shape. Triple line energy and its mobility lead to deviate from a typical t1/4 scaling law. For all theses simulations, grain boundary energies are constant, satisfying Herring's relation. Comparisons are made for different values of mobilities for groove shape and its growth rate, using different grain orientations.
A flexible two‐surface gradient‐extended damage‐plasticity model for large deformations with nonlinear kinematic hardening
Authors: Brepols Tim , Wulfinghoff Stephan , Reese Stefanie
Published: December 2018

A novel ‘two‐surface’ gradient‐extended damage‐plasticity model for large deformations is discussed which can be considered the geometrically nonlinear version of a corresponding model for small deformations developed recently [1, 2]. The ‘two‐surface’ approach makes the model flexible in the sense that it can be adapted to various situations in which the considered material's behavior is either (quasi‐)brittle‐like, ductile‐like or possibly something in between. Nonlinear kinematic and isotropic hardening as well as nonlinear damage hardening are accounted for by the model which is finally formulated in terms of symmetric internal variables only, being advantageous not only from the computational point of view. Selected theoretical and numerical aspects are briefly discussed and a numerical example practically illustrates the model's functionality.
Topological analysis of open‐pore structures
Authors: Bogunia Lukas , Weinberg Kerstin
Published: December 2018

Open‐cell structures like open‐pore foams have several applications, e.g. as acoustic damping material in civil engineering. Most models for such materials capture the static but not the dynamic behavior correctly. In order to develop a model which is able to describe the static and the dynamic properties, an analysis of the microstructure is required. Three dimensional micro computer tomography (µCT) scans allow studying the relevant material features. Suitable methods summarized in [1] and [2] are used to determine the topological parameters of open‐pore PUR foam. Simplified models based on the extracted structural parameters are studied here.
Error Estimation for the Simulation of Elastic Multibody Systems
Authors: Fehr Jörg , Grunert Dennis , Bhatt Ashish , Haasdonk Bernard
Published: December 2018

One important issue in the development of complex technical system is the use of rapid simulations to evaluate substructures / surrogate models for system level simulations. For safety‐critical simulations, it is essential to know the error introduced by model order reduction (MOR) used to create the surrogate models to decide whether the simulation can be trusted or not. Typically, a‐priori error estimates, e.g., the sum of neglected singular values in balanced truncation are used. They deliver upper bounds for the error – independently of the applied excitation. By contrast, the error estimates from the reduced basis community deliver a‐posteriori error bounds, which account for the current excitation. These error bounds use the residual between the reduced and original model to derive an error bound. In this work, we review the error bounds used in elastic multibody system (EMBS) described in the floating frame of reference formulation.
An Approach for Stable Time Integration of Dual Craig‐Bampton Reduced Systems
Authors: Gille Max , Gruber Fabian M. , Rixen Daniel J.
Published: December 2018

The dual Craig‐Bampton method, a substructuring method that employs free interface normal modes, rigid body modes and attachment modes, yields reduced systems with negative eigenvalues making a stable time integration impossible. A way to overcome this problem through a subsequent modal reduction of dual Craig‐Bampton reduced systems is presented and investigated by a simple numerical example. Furthermore, the beneficial effect of additional static modes in the systems' reduction bases is demonstrated.
Efficient Conditional Reliability Updating with Sequential Importance Sampling
Authors: Ehre Max , Papaioannou Iason , Straub Daniel
Published: December 2018

Data on the performance of engineering systems can and should be used to learn system parameters and update the system reliability estimate. This can be achieved in a Bayesian framework. In order to capture the dependence of the reliability estimate on the data used, we consider the probability of failure conditional on the updating variables, i.e. those variables on which data is available. Thus, the probability of failure becomes a random variable itself. In practice, the distribution of the conditional probability of failure may be obtained by solving a reliability problem at several samples from the updating variable space which causes a considerable increase in required computational effort. To address this challenge, we devise a procedure for the fast re‐computation of failure probabilities within a sequential sampling method. We exploit the similarity of reliability problems with small distance in a suitable norm by sequentially initializing computations with failure samples of similar problem solutions.
A sructure‐preserving numerical method for the dynamic optimization of flexible mechanical systems
Authors: Schneider Simeon , Betsch Peter
Published: December 2018

If an optimal control problem has symmetries, associated generalized momentum maps are preserved quantities along an optimal path, as can be seen by the extension of Noether's theorem to optimal control problems. These symmetries on the control level are inherited from the underlying mechanical system. The presented discretization method does respect the symmetries on both levels, the mechanical system and the optimal control problem, and preserves the generalized momentum mapping.
A computational study on the cyclic softening and fatigue behaviour of medical PEEK
Authors: Beckmann Agnes , Ma Songyun , Zhang Le , Stoffel Marcus , Markert Bernd
Published: December 2018

In the underlying study, a computational method to predict the cyclic plastic deformation and the fatigue life of medical PEEK is proposed. The OHNO‐WANG plasticity model was implemented as an Abaqus® user subroutine. The SMITH‐WATSON‐TOPPER criterion was implemented as a postprocessing Python script to predict the fatigue failure of PEEK. The validation of the OHNO‐WANG model with the five effective cyclic stable stress‐strain hysteresis curves show a very good agreement. The fatigue model was calibrated with a good final goodness of fit.
A thermo‐mechanical model of ultrasonic metal welding process with the focus on the mating interface
Authors: Mostafavi Shimaalsadat , Heider Yousef , Markert Bernd
Published: December 2018

Ultrasonic welding (USW) of metals is counted as a solid state consolidation of the involved parts, in which the growing interface temperature is far below the melting point of the material. This type of welding is a joining technique, in which a combined effect of the applied pressure and the ultrasonic frictional vibrations on the surface of the mating parts causes the formation of the bond. This contribution is devoted to study the coupled effect of the process parameters, namely the applied pressure and the amplitude of the ultrasonic vibrations on the interface temperature rise. Finally the result of the proposed thermo‐mechanical model are compared with the results from experiments in ultrasonic wire bonding.