bluuebunny/crossref_metadata_2025_split huggingface dataset:
A numerical study of the influence of inclusion geometries in heterogeneous dielectric elastomers
Authors: Klassen Markus , Klinkel Sven , Müller Ralf 
Published: December 2018

AbstractThe 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

AbstractSelection 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

AbstractAnalytical 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

AbstractProjection‐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

AbstractThis 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractOpen‐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

AbstractOne 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

AbstractThe 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

AbstractData 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

AbstractIf 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

AbstractIn 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

AbstractUltrasonic 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.
Phase‐field predictive model for setting of fresh self‐compacting concrete
Authors: Huang Haiqin , Zilian Andreas 
Published: December 2018

AbstractThe initial setting of fresh concrete is mainly caused by the dissolution of cement grains and the precipitation of calcium‐silicate‐hydrates during cement hydration. Progressing hydration drives the transition from a dense suspension to a porous solid phase. Fresh mixture of self‐compacting concrete (SCC) can be considered as a phase‐changing multi‐component material and can be described as a continuum at the macro scale, interacting with a set of transport‐reaction‐diffusion processes which in turn are driven by phenomena at the level of the microstructure. This contribution focuses on a predictive model for the setting of fresh SCC where the liquid‐solid phase transition is captured by a phase‐field variable using the Ginzburg‐Landau type free energy function. Hydration‐related chemical reactions together with heat and mass transfer are volume‐coupled with the mechanical behaviour and determined by the environmental conditions. The weak form of the predictive model is discretised using the finite element method and implemented with the FEniCS computational framework.
An investigation on residual stresses in gas tungsten arc welding
Authors: Ali Baharin Rahim Ali , Nguyen An Danh , Markert Bernd 
Published: December 2018

AbstractIt is known that the gas tungsten arc welding (GTAW) generates high and localised heat gradients in the welded components, leading to the formation of weld bead and residual stresses that affect their fatigue life. In this work, a finite element model of GTAW is presented to estimate the temperature and stress induced by GTAW. The heat and fluid flow (HFF) approach using the enthalpy‐porosity model and the finite element multiphase modelling allows us to simulate the rapid melting and solidification. Moreover, the Marangoni effect, due to a thermally caused surface tension gradient, is also studied. The performance of the proposed finite element model is demonstrated via a simulation of the GTAW process with appropriate boundary conditions on temperature and velocity fields. The model can be extended for further residual stress and distortion analyses.
Analytical investigation of non‐local deformation‐mediated magneto‐electric coupling
Authors: Rambausek Matthias , Keip Marc‐André 
Published: December 2018

AbstractThe research on magneto‐electric materials is concentrated on multi‐ferroics and hard‐matter composites. However, rather recently soft composites also exhibiting pronounced magneto‐electric coupling entered the scene. Such composites are straight‐forward to manufacture and have cheap constituents compared to classical approaches. This contribution is concerned with an analytical estimation of a particular non‐local magneto‐electric coupling effect that exists regardless of the composite nature but relies on the softness of a magneto‐electric material.
Analysis of the nonlinear chaotic behavior of an inverted flexible pendulum system affected by impulses
Authors: Kahar Hartiny , Söffker Dirk 
Published: December 2018

AbstractIn this contribution, the effect of impulses realized by non‐perfect feedback to an inverted flexible pendulum system is studied. Using experimental data from chaotic jumping in an inverted flexible pendulum, several techniques of signal processing and time‐frequency representation are carried out. These methods are used to observe the changes in the nonlinear dynamic properties and time behavior of the system before and during the jumping between equilibrias. The evaluation of the experimentally realized inverted flexible pendulum system for specific control parameters shows that ’chaotic’ jumping behavior between the three equilibrias (with different attraction regions) are depending on the existence of impulses. The results from detailed analysis shows that this is caused by feedback imperfectness. Considering the time‐frequency‐based analysis conducted, it can be stated that the (uncontrolled) impulses causing a temporarily disturbance in the energy distribution between the ’modes’/frequency bands the system vibrates with, which finally leads to a new and more stable distribution in energy, followed by related jumping between the equilibrias.
Optimization based muscle wrapping in biomechanical multibody simulations
Authors: Penner Johann , Leyendecker Sigrid 
Published: December 2018

AbstractIn musculoskeletal simulations muscle lengths and muscle force directions imply the characteristics of muscles acting around joints. Typically, the anatomical structure of the human body forces muscles to wrap around bones and neighboring tissue, thus most muscle paths cannot be represented adequately as straight lines. Therefore, biomechanical simulations require methods to compute musculotendon paths, their lengths, and their rates of length change to determine the muscle forces. This work focuses on a mechanical analogue to find the shortest path on general smooth surfaces, using a discrete variational principle. In this context, the geodesic path is reinterpreted as the constrained, force‐free motion of a particle in n dimensions. The muscle path is then a G1‐continuous combination of geodesics on adjacent obstacle surfaces [1,3,4].
Comparison of experimental data and FEM simulation for a multiferroic nanocomposite
Authors: Lemke Veronica , Webers Samira , Labusch Matthias , Schröder Jörg , Wende Heiko 
Published: December 2018

AbstractThe combination of ferromagnetic and ferroelectric materials, so‐called multiferroic composites, increases the opportunities for technical sensors and data storage devices, see [1]. The magnetic and electric constituents have the property to affect each other e.g. an applied electric field modifies the magnetization of the magnetic phase. In nature also single‐phase materials exist with magneto‐electric properties. Though, the interoperation of the magnetization and the polarization is exclusively activated at very low temperature. Therefore, they are not favorable for most of the known technical applications. Considering this, the magneto‐electric (ME) composites can be seen as a good option since their synergy of the magneto‐electric properties is active at room temperature [2] and can be differentiated in two different effects, the direct and the converse ME effect. We will focus on (1‐3) nanocomposite grounded on the experiments made in [3] and [4]. In the experiments, cobalt ferrite nanopillars, embedded in a barium titanate matrix, are characterized. Then, for the numerical FEM‐simulations the material coefficients from [5] and [6] are taken. The change of the strain‐induced in‐plane polarizations of the ferroelectric matrix around one cobalt ferrite nanopillar is calculated. These computed results are compared to the ones of the experimental measurement outcomes.
A data‐driven model order reduction approach for Stokes flow through random porous media
Authors: Grigo Constantin , Koutsourelakis Phaedon‐Stelios 
Published: December 2018

AbstractDirect numerical simulation of Stokes flow through a random, impermeable rigid body matrix by finite elements requires meshes fine enough to resolve the pore‐size scale and is thus a computationally expensive task. It is well known that on a larger scale, Stokes flow can accurately be approximated by Darcy's law [1] with an effective diffusivity field depending on viscosity and the matrix phase topology. We propose a fully probabilistic Darcy type reduced‐order model which, based on only a few tens of full‐order model runs, is capable to learn a fine‐scale topology to effective diffusion map which is maximally predictive for fine‐scale response. After training, the model provides sharp predictive distributions based on repeated evaluation of the much cheaper Darcy equation only.