bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bioreactor development for regenerative tissues of the locomotor system
Authors: Stoffel Marcus , Dursun Gözde , Nachtsheim Julia , Fuhrmann‐Nelles Nadine , Markert Bernd 
Published: December 2018

AbstractIn biomedical engineering it is an important challenge to predict the mechanical behaviour of living biological tissues under dynamic loading conditions. As a basis for theoretical models, experimental set‐ups are necessary to trace evolutive processes, such as remodelling and growth, in biological materials. However, in order to mimic in‐vivo situations most realistically, in‐vitro bioreactor systems with physiologically enhanced loading conditions have to be developed. The present study deals with a set of bioreactor systems covering a wide range of applications for investigating remodelling behaviour of biological tissues, such as cartilage replacement materials in knee joints, tendons, and intervertebral discs.
On the modal analysis of flexible multibody systems with singular mass and stiffness matrices
Authors: Hente Christian , Gebhardt Cristian G. , Hofmeister Benedikt , Rolfes Raimund 
Published: December 2018

AbstractA complex mechanical system can be described as a combination of individual rigid and/or flexible components and a set of kinematical constraints. The restrictions can be either internal, which come on the scene in the case of parameterizing the configuration manifold of a system with a number of parameters larger than its intrinsic dimension, e.g. by employing three directors to describe the Lie Group SO(3) (basically for rigid bodies and beams) or by employing a single unit director to describe the two dimensional sphere with unit radius embedded in the three‐dimensional Euclidean space, i.e. S2 1 , (basically for inextensible shells, in which the component of the Green‐Lagrange strain tensor E33 is set to be zero at every time), or external ones, which come on the scene in the case of constraining bodies by means of joints, connections or supports. The linearized form of the resulting governing equations possesses usually singular mass and stiffness matrices. This fact represents an issue when the calculation of natural frequencies and natural modes for the whole system is needed. The classical modal analysis (solving directly the generalized eigenvalue problem from the stiffness and mass matrices) is no longer applicable. To overcome this difficulty, it is firstly necessary to utilize the linearized constraint equations that complete the missing information at the level of the mass and stiffness matrices and secondly, to redefine the eigenvalue and ‐vector problem within a suitable framework. In the current work, we set the focus on the development framework for the modal analysis able to deal with singular matrices.
On the construction of a triangular Mixed Finite Element based on the principle of Hellinger‐Reissner
Authors: Viebahn Nils , Steeger Karl , Schröder Jörg 
Published: December 2018

AbstractA low order finite element based on a Hellinger‐Reissner formulation with weak enforcement of the stress symmetry is presented. The novel element gets along without any additional degrees of freedom beside the displacements and stresses. Therein, lowest order Raviart‐Thomas interpolation is utilized for the stresses and a C0 continuous polynomial interpolation of first order is adopted for the displacements. This combination leads to a very efficient and robust element formulation which will be depicted on a couple of numerical examples.
FFT‐based Homogenization in nonlinear Electroelasticity
Authors: Göküzüm Felix Selim , Nguyen Lu Trong Khiem , Keip Marc‐André 
Published: December 2018

AbstractElectroactive polymers (EAPs) are a group of materials that is able to respond with large strains to applied electric fields, making them candidates for applications such as artificial muscles or smart fins. The present contribution addresses the computational homogenization of electroactive materials based on fast‐Fourier‐transforms. The focus lies on the formulation of a coupled Lippmann‐Schwinger equation with respect to the deformation gradient as well as the electric displacement, where the reference medium introduced in the Lippmann‐Schwinger equation is also fully coupled. As the reference medium is acting as a preconditioner on the system, this has an impact on the convergence rate and stability of the iterative solver. We provide an algorithmically consistent coupled tangent operator as alternative to finite‐difference based approaches.
Investigation of the laminate free‐edge effect by means of the scaled boundary finite element method
Authors: Dölling Sebastian , Hell Sascha , Becker Wilfried 
Published: December 2018

AbstractIn the present study, a coupled stress and energy criterion within the framework of finite fracture mechanics is used to predict interlaminar crack onset in composite laminates induced by the free‐edge effect. In order to obtain the required quantities for the evaluation of the coupled criterion the scaled boundary finite element is implemented. This semi‐analytical approach reduces the numerical effort significantly in comparison to standard finite element method. To assess the reliability of the obtained results a comparison to a finite element model is presented.
On a relaxation‐based and time‐incremental approach to damage modeling
Authors: Schwarz Stephan , Hackl Klaus , Junker Philipp 
Published: December 2018

AbstractDamage models, which are characterized by softening effects, suffer from ill‐posed boundary value problems that result in mesh‐dependent finite‐element results. Regularization strategies counteract these problems by taking into account the non‐local behavior such as realized by the gradient‐enhanced formulation presented in [1]. Two variational equations are resulting at the expense of numerical effort but, however, mesh‐independent finite‐element results are provided. In contrast, we present a novel approach to the regularization of damage processes based on relaxed energies of two‐state models that are formulated in a time‐incremental way. The energies within each time step remain convex but the overall behavior is non‐coercive in order to maintain the characteristic stress‐behavior of damage models. Therefore, mesh‐independent results with less numerical effort are achieved.
A modified plate model for an efficient analytical treatment of stress concentrations at notches
Authors: Felger Julian , Becker Wilfried 
Published: December 2018

AbstractIn the present work, a modified plate model is proposed lying in‐between the established Kirchhoff‐Love and first‐order shear deformation plate theories. The resulting system of partial differential equations can be solved using a complex potential approach which allows for tackling complex geometries such as sharp or rounded notches. Using the proposed model, the singular stress field in the vicinity of a sharp notch can be obtained explicitly and the influence of the notch opening‐angle on the singular behaviour is investigated. It is shown that resulting bending moments and transverse shear forces match with asymptotic solutions according to first‐order shear deformation plate theory and are in very good agreement with numerical results.
A fluid model for the simulation of fluid‐structure interaction in the Scaled Boundary Finite Element Method for prismatic structures
Authors: Wasmer Paul , Krome Fabian , Bulling Jannis , Prager Jens 
Published: December 2018

AbstractThe Scaled Boundary Finite Element Method is known as an efficient method for the simulation of ultrasonic wave propagation. As to investigate acoustic wave behavior in case of fluid‐structure interaction, a fluid model is implemented in the SBFEM for prismatic structures. To omit coupling terms a displacement‐based formulation is used. Spurious modes, which occur in the solution, are suppressed using a penalty parameter. To verify this formulation dispersion curves obtained with Comsol Multiphysics are compared to results of SBFEM. The results of both methods are in very good agreement.
Numerical Simulation of Wind Turbine Considering the Soil‐Structure‐Interaction
Authors: Schauer Marco 
Published: December 2018

AbstractWhenever vibrations are emitted to soil, they induce waves traveling through the ground. This work is focused on the Soil‐Structure‐Interaction effects on the dynamic behavior of operating wind turbines. Two different mechanical problems have to be addressed and to be solved simultaneously. There is the near‐field, containing the structure of the wind turbine and its foundation as well as parts of the soil modeled by the Finite Element Method (FEM), and the far‐field, the surrounding infinite half‐space discretized by the Scaled Boundary Finite Element Method (SBFEM) [1]. Both domains are discretized separately in order to reduce the effort of the preprocessing. This leads to non‐matching meshes in general. To overcome this issue state projection methods are utilized to exchange state variables at the common interface while solving the coupled FEM‐SBFEM approach.
A quantitative comparison of two‐ and three‐dimensional modeling approaches for magnetorheological elastomers
Authors: Metsch Philipp , Kalina Karl Alexander , Brummund Jörg , Kästner Markus 
Published: December 2018

AbstractIn this contribution, a qualitative and quantitative comparison of two‐ and three‐dimensional finite element simulations for magneto‐rheological elastomers is presented. Based on a continuum formulation, a microscopic modeling approach is applied. To understand basic deformation mechanisms, the differences between simplified two‐dimensional and realistic three‐dimensional simulations are initially shown for the example of chain‐like structures with different arrangements of the particles. Subsequently, a numerical homogenization is used to connect microscopic and macroscopic quantities: different two‐ and three‐dimensional microstructures are compared with regard to their effective magneto‐mechanical behavior.
Convergence properties of the enriched Scaled Boundary Finite Element Method in fracture mechanics
Authors: Bremm S. , Hell S. , Becker W. 
Published: December 2018

AbstractThe standard Finite Element Method (FEM) yields optimal rates of convergence for smooth domains. The presence of cracks, corners or notches within the considered domain leads to low rates of convergence which are independent of the polynomial degree of the employed trial functions. In order to regain full rates of convergence, an appropriate adaptation and a skilful choice of test and trial space of the FEM is necessary. The Scaled Boundary FEM (SBFEM) has turned out to be an appropriate method for the treatment of 2D crack problems, in which the singularity is entirely located within the considered domain. However, in 3D problems, singularities are still present at the meeting points of the crack front and the discretized boundary. Then, the SBFEM suffers from the same drawbacks as the standard FEM. In order to dispel this inconvenience, an extension of the trial space with asymptotic crack tip displacement solutions is considered resulting in improved rates of convergence.
Finite volume based multigrid preconditioners for discontinuous Galerkin methods
Authors: Versbach Lea Miko , Birken Philipp , Gassner Gregor J. 
Published: December 2018

AbstractOur aim is to construct efficient preconditioners for high order discontinuous Galerkin (DG) methods. We consider the DG spectral element method with Gauss‐Lobatto‐Legendre nodes (DGSEM‐GL) for the 1D linear advection equation. It has been shown in [4] that DGSEM‐GL has the summation‐by‐parts (SBP) property and an equivalent finite volume (FV) discretization is presented in [3]. Thus we present a multigrid (MG) preconditioner based on a simplified FV discretization.
A Simplification of the RitzGenEO Recycling Strategy for Adaptive Multi‐Preconditioned FETI Applied to Multiple Right‐Hand Sides
Authors: Leistner Michael C. , Gosselet Pierre , Rixen Daniel J. 
Published: December 2018

AbstractIn this article, a method to accelerate the solution of multiple right‐hand side problems when using the adaptive multi‐preconditioned finite element tearing and interconnecting algorithm is presented. This is done by deflating the conjugate gradient algorithm by means of a coarse space, which is built by a simplification of the recently published RitzGenEO method. While the proposed method no longer requires to solve local eigenproblems, it is able to maintain a significant part of the reduction in computational cost. Numerical results show a comparison of the methods and appropriate applications for either method are discussed.
In‐situ and ex‐situ micro mechanical testing of open‐cell metal foams
Authors: Jung Anne , Luksch Jutta , Bleistein Thomas , Adrien Jerome , Maire Eric 
Published: December 2018

AbstractMetal foams are cellular materials with structural features resembling to lightweight load‐bearing materials such as bones. Their high stiffness‐to‐weight‐ratio coupled with their long flat stress‐strain response make them ideal candidates as energy absorbers. Their macroscopic properties are strongly influenced by both the struts and their structure at the microscopic length‐scale based on a strong structure‐property relationship. Whereas macroscopic mechanical characterisation is widespread, micromechanical characterisation and assessment of parameters on single struts is very limited. Micromechanical characterisation of individual struts is very challenging but an emerging field of research. The present contribution deals with the mechanical characterisation of open‐cell foams on the meso and micro scale. In‐situ and ex‐situ micro tensile tests were conducted on individual struts. There is a large scattering in the micro material parameters deduced from individual struts. X‐ray computed tomography (CT) scans during micro tensile testing and ex‐situ micro tensile tests performed on struts, where the local microstructure (blowholes, pores, cracks and intermetallic inclusions) was previously determined in CT scans, were performed. The scattering in the material parameters is largely connected to the occurring defects in the microstructure of individual struts.
Investigating incompressible temporally developing turbulent boundary layers using One‐Dimensional Turbulence
Authors: Rakhi  , Schmidt Heiko 
Published: December 2018

AbstractWe investigate incompressible temporally developing turbulent boundary layers for the first time using the One‐Dimensional Turbulence (ODT) model. ODT is spatially fully resolved along the 1D domain, only turbulent advection is represented by stochastic mapping events. We compare the mean and root mean square velocity profiles with the Direct Numerical Simulations (DNS) results for bulk Reynolds numbers, Reb = 500 and 1000 (Reb = Ubd/ν, where ν is the kinematic viscosity, Ub is the velocity provided at the bottom wall and d is the trip wire diameter for experiments). The study demonstrates that ODT has the capability to systematically investigate developing boundary layers.
Towards a hybrid turbulent mixing model based on hierarchical parcel‐swapping and one‐dimensional turbulence
Authors: Pupo Sá da Costa Pedro , Schmidt Heiko 
Published: December 2018

AbstractOne‐dimensional turbulence (ODT) based models are able to generate good results for canonical flow problems compared to Direct Numerical Simulations. ODT has been successfully implemented as a sub‐grid scale model for LES problems (ODTLES) delivering promising results. However, due to the computational cost of the ODT model in this scope, there is a need for an even faster model for real world parameter regimes. The Hierarchical Parcel Swapping (HiPS) algorithm used in combination with the ODT model to simulate a channel flow recently provided results with an acceptable quality in a fraction of the time of an ODT simulation. HiPS uses a binary tree to define the fluid domain, and stochastic eddy events are sampled in this tree. A local instantaneous and complete mixing of the cells is performed when an eddy event happens at the Kolmogorov scale. The biggest limitation of this model is that the viscosity of the solution is implicitly defined by the number of cells in a mesh. Further development of HiPS is planned in order to create a computationally cheaper alternative for the ODT model to be used in ODTLES flow simulations.
Thermo‐mechanical modelling and finite element analysis of self‐piercing riveting processes
Authors: Nahrmann Marvin , Matzenmiller Anton 
Published: December 2018

AbstractIn this contribution, a thermo‐mechanical finite element analysis of the self‐piercing riveting process of two steel sheets is carried out taking into account the conversion of plastic work into heat. Thereby, a user defined constitutive model recently proposed by BRÖCKER and MATZENMILLER is applied considering the highly temperature and rate dependent characteristics of metals. All constitutive parameters are identified with test data of the microalloyed steel HX340LAD typically used for car body structures. The numerical results of the self‐piercing riveting process are compared to the according test data for model validation by means of the final joint geometry and the setting force.
Improving the Performance of Numerical Algorithms for the Bethe‐Salpeter Eigenvalue Problem
Authors: Benner Peter , Marek Andreas , Penke Carolin 
Published: December 2018

AbstractThe Bethe‐Salpeter eigenvalue problem arises in the computation of the electronic structure of many‐body physical systems. The resulting matrix is complex, admits a certain block structure and can become extremely large. This raises the need for structure‐preserving algorithms running in parallel on high performance compute clusters. In this paper we examine how a recently proposed direct method given in the BSEPACK library can be improved using eigenvalue solvers from the ELPA library. For large matrices a runtime reduction of up to 80% is achieved.
Extended Simulations of the Roll Bonding Process
Authors: Klinge Sandra , Aygün Serhat , Bambach Markus 
Published: December 2018

AbstractRoll bonding is a joining‐by‐forming process in which two or more layers of different metals are passed through a pair of flat rolls. Under the high pressure, a permanent bond between the metals is generated by plastic deformation. The main factors influencing this process and the creation of bond strength are the size of the surface area and the normal pressure in the interface. In order to numerically predict the bond strength the FE implementation of a contact algorithm is performed. Simultaneously, the physical mechanisms typical of plastic deformation are taken into consideration. The focus particularly lies on the micro‐mechanical modeling of strain hardening by dislocation slip. A first study is given on the effects of the chemical impurities on the dislocation density and motion.
Near‐critical turbulent open‐channel flow over wavy bottom
Authors: Müllner Markus 
Published: December 2018

AbstractSteady two‐dimensional turbulent free‐surface flow in a channel with mild baseline slope is considered. The shape of the channel bottom is assumed to be undular with a very small amplitude. Asymptotic expansions for large Reynolds numbers and Froude numbers slightly above the critical value 1, respectively, give for the surface elevation a differential equation of KdV‐type, with the additional terms representing turbulent dissipation and forcing due to the wavy bottom, respectively. No turbulence modelling is required. This asymptotic approach was used in [1] to describe stationary solitary waves in a channel with plain bottom and small variations in the bottom friction coefficient. It was shown recently [2,3] that there exist stationary single‐wave solutions of a different kind that are characterized by smaller wave amplitudes. In [4], both kinds of single stationary waves above single obstacles (bumps, ramps) are investigated theoretically and experimentally. In this paper, stationary space‐periodic surface waves for channel bottoms with undular shape are studied. First, a one‐parametric family of exact solutions for particular bottom shapes is derived. Remarkably, these particular solutions exist only in a narrow parameter range. The solutions are reproduced with a numerical solver to verify that the solver gives correct results. Secondly, a different type of asymptotic expansion is performed in order to describe solutions characterized by smaller wave amplitudes. The resulting linear differential equation is solved numerically. Both solutions are briefly discussed.
Pareto Front Interpolation Based on Parametric Sensitivity Analysis in a Bi‐Objective Setting
Authors: Berger Arne , Knauer Matthias , Büskens Christof 
Published: December 2018

AbstractThis paper shows how a discrete approximation of a Pareto front can be refined with polynomial interpolation. For this we exploit the information given by the discrete samples of the Pareto front and in addition we use parametric sensitivity information from these samples. The pararmetric sensitivities are afterwards used to ensure feasibility of the obtained interpolated solutions by applying an iterative self correction algorithm. Results are shown for an bi‐objective example.
Numerical material testing based on statistically similar representative volume elements for discontinuous fiber composites
Authors: Sasagawa Takashi , Tanaka Masato , Omote Ryuji , Balzani Daniel 
Published: December 2018

AbstractA computational method is proposed for the construction of statistically similar representative volume elements (SSRVEs) for discontinuous fiber composites (DFCs) in order to efficiently calculate material properties based on computational homogenization. The SSRVE is obtained by solving an optimization problem which minimizes differences between the power spectral density of a real target microstructure and the SSRVE. The target microstructure is obtained by means of computed tomography scanning of a DFC plate. As a result of a comparative study, the mechanical behavior of the SSRVE turns out to agree with that of the target microstructure. However, the SSRVE reduces extremely the computational costs of finite element analyses to derive macroscopic material properties of DFCs.
Staggered grid discretizations on Lie groups with applications in beam and shell theory
Authors: Hante Stefan , Arnold Martin 
Published: December 2018

AbstractWe will discuss staggered grid space discretizations for micropolar Cosserat models with nonlinear configuration spaces, that have Lie group structure. The discretization scheme is applied at the level of the variational principle, has second order truncation error and uses a staggered grid, where the spatial derivatives are discretized inbetween the discretization points of the material configuration.
An intelligent meta‐element for linear elastic continua
Authors: Koeppe Arnd , Bamer Franz , Markert Bernd 
Published: December 2018

AbstractLarge numbers of nodes and nonlinearities make the numerical solution of finite element models computationally expensive. We introduce “intelligent” elements for linear elastic continua, which use neural networks to reduce the number of nodes, and demonstrate their efficiency on two benchmark examples. It is shown, that models with “intelligent” meta‐elements accurately solve the boundary value problem and require a smaller number of nodes than conventional finite element models.
Variational Integrators for Parameter Identification of Mechanical Systems
Authors: Flaßkamp Kathrin , Schäfer Kai , Büskens Christof 
Published: December 2018

AbstractNumerical methods for parameter identification of dynamical systems are based on matching model outputs to measurements. Computing the model output requires numerical integration techniques, though. In this contribution, we study the role of integration methods for mechanical systems. Since mechanical systems have characteristic properties, using structure‐preserving integration methods suggests itself. First and second order methods are compared in the case study of a damped pendulum.