bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mixed/Hybrid finite elements for finite deformations of quasi‐incompressible materials with non‐constant bulk moduli
Authors: Schneider Patrick , Schönherr Josef Arthur , Mittelstedt Christian 
Published: January 2021

AbstractTechnical elastomers are usually quasi‐incompressible. For simulations they are, therefore, often modeled as ideal incompressible or a linear relation between the hydrostatic pressure and the (volumetric) dilation is assumed, i.e., a constant bulk modulus. However, for strongly compressed structural components, like sealings or damper elements, a nonlinear material model for the compression behavior is required in order to achieve accurate results.In general, the numerical ill‐posedness of irreducible (purely displacement‐based) finite element (FE) formulations for quasi‐incompressible materials demands for a hybrid/mixed finite element implementation. State of the art hybrid/mixed elements still suffer from numerical stability issues that can be greatly amplified by the usage of nonlinear compression models. In the talk, a versatile mixed/hybrid finite element family for finite deformations is introduced that can readily be used in combination with any invariant‐based hyperelastic material model. The numerical stability is assessed by a benchmark test and compared to other established hybrid elements. The presented finite element family is way robuster than comparable hybrid elements implemented in the commercial FE‐code Abaqus Standard, Simulia (Dassault Systèmes).
Prediction of changes in local quantities of interest due to structural modifications
Authors: Materna Daniel 
Published: January 2021

AbstractIn this contribution a method for the prediction of the change in a quantity of interest due to structural modifications is considered. The approach is based on a goal‐oriented method by using the primal and dual problems. The method can be used in order to reduce the overall computational cost in the numerical simulation. Furthermore, the proposed method is easily to implement in existing finite element programs, because no derivatives with respect to the design variables are necessary.
Modeling of Single‐Slip Finite Strain Crystal Plasticity via the Virtual Element Method
Authors: Böhm Christoph , Hudobivnik Blaž , Aldakheel Fadi , Wriggers Peter 
Published: January 2021

AbstractThis work addresses an efficient low order virtual element method (VEM) for the modeling of single‐slip crystal plasticity system undergoing finite deformations. VEM has been attracting attention as a novel scheme within the field of computational mechanics. A key advantage of VEM is the ability of constructing an arbitrary element shapes that can be non‐convex [1]. Another important aspect is that VEM fits the grain shapes of crystal plasticity within polycrystalline aggregates perfectly. Contrary, classical finite element (FE) approaches request a fine mesh‐size at possibly sharp geometric regions, i.e. complex shaped grain boundaries.
A thermomechanical simulation method for fused deposition modeling
Authors: Oelsch Erik , Landgraf Ralf , Ihlemann Jörn 
Published: January 2021

Abstract3D printing is a complex manufacturing method with completely new challenges. One of them is the simulation of the whole process. In this contribution the building process of the 3D printed part is thermomechanically coupled simulated with step by step element activation along a path from a slicer program. Thereby a hyperelastic material model and material parameters from literature are used. Simulation results of an exemplifying building process are in good agreement with corresponding experiments.
Phase‐Field Simulation of Crack Propagation at Adhesive Interfaces in Brittle Materials
Authors: Dammaß Franz , Hansen-Dörr Arne Claus , Kästner Markus 
Published: January 2021

AbstractWhen it comes to failure of a heterogeneous material, the adhesive interfaces linking the different constituents can crucially influence its mechanical behavior. In this contribution, a diffuse description of interfaces in the context of the phase‐field approach to brittle fracture is outlined. Two‐ and three‐dimensional simulations of crack phenomena are presented and serve for validation of the model against LEFM.
Preconditioning of a FETI‐solver for a nonlinear asynchronous time‐integrator applied to structural dynamics
Authors: Seibold Andreas S. , Rixen Daniel J. 
Published: January 2021

AbstractIn this work we construct a Dirichlet‐type preconditioner for a FETI‐solver in a nonlinear version of the BGC‐macro asynchronous time‐integrator. This preconditioner is then tested on a simple beam‐model with six substructures and an impact load.
A computational framework for gradient‐enhanced damage – implementation and applications
Authors: Schulte Robin , Ostwald Richard , Menzel Andreas 
Published: January 2021

AbstractA gradient‐enhanced damage model is combined with finite viscoelasticity and implemented in an Abaqus user subroutine, exploiting the heat equation solution capabilities for the damage regularisation, in order to simulate soft polymers. This regularised damage approach provides the advantage of mesh independent results and avoids localisation effects. In this work, a self‐diagnostic poly(dimethylsiloxane) (PDMS) elastomer is chosen as an example. To this end, an efficient two‐step parameter identification framework is developed to calibrate the corresponding model parameters.
Practical Economic MPC
Authors: Zanon Mario , Faulwasser Timm , Gros Sébastien 
Published: January 2021

AbstractAs opposed to tracking Model Predictive Control (MPC), economic MPC directly optimizes a given performance objective rather than penalizing the distance from a reference. On the one hand this typically improves performance. On the other hand, however, this also poses challenges in terms of stability and computational burden. In order to make economic MPC implementable in practice, we recently proposed some techniques that address both issues. In this contribution, we give a brief overview on economic MPC and the related literature and discuss how to exploit existing results in order to apply economic MPC in practice. Finally, we present a new promising research direction towards data‐driven economic MPC: the use of reinforcement learning to obtain optimality for the real system, rather than for the (unavoidably inaccurate) model used by MPC.
Aerodynamic‐thermal/structural design optimization of missile fin configuration during supersonic flight condition
Authors: Rašuo Boško , Vidanović Nenad , Kastratović Gordana , Mirkov Nikola 
Published: January 2021

AbstractThe main goal of this paper is to expand previously conducted study and consequently to upgrade the proposed multi‐modular numerical environment developed for fluid‐structure interaction simulation (FSI) and multi‐disciplinary design optimisation (MDO) purposes, in a manner that thermally induced structural responses in a current study are taken into consideration. The present study concerns with a broader observation of critical multi‐point flight conditions and represents a more realistic scenario which presents one contribution more in a scope of fluid‐thermal‐structure interaction (FTSI) numerical modelling and optimisation. This means that thermo‐mechanical effects of the missile fin structure are observed and implemented into established numerical environment. Numerical modelling of FSI/FTSI and MDO within an industry‐accepted design tool was resulted in powerful monolithic environment which with adopted multi‐point regimes and multi‐criteria settings is used for aerodynamic‐thermal/structural optimisation. The multi‐disciplinary shape optimisation, with respect to predefined objectives and constrains, was carried out in order to achieve global improvement of missile initial aerodynamic and to prevent aerothermally‐induced critical responses of the fin configuration.
Actuation of an elastic membrane by the use of an electrorheological valve
Authors: Schomberg Thomas , Gerland Florian , Wünsch Olaf , Rütten Markus 
Published: January 2021

AbstractThe dynamic response of a fluidic actuator is investigated on the basis of numerical simulations. With this actuator a membrane is excited to oscillate by means of an electrorheological valve. For this purpose the solid and fluid domains are coupled. Furthermore, the constitutive equation of the fluid is coupled to the electric field. The dynamic response is discussed on the example of a variable stiffness of the membrane. Actuators of this type offer the potential to delay the transition of a boundary layer.
Modeling inelastic‐anisotropic damage behavior of concrete considering lateral deformation
Authors: Stein Timo , Gafoor Ajmal , Dinkler Dieter 
Published: January 2021

AbstractAlthough isotropic damage models are considered for a first approximation to simulate the deformation behavior of concrete, micro‐cracking of concrete occurring due to the sequential and multi‐directional loads necessitates an anisotropic description of damage for a reliable representation of damage in concrete. The present paper discusses modeling aspects of mechanical degradation behavior of concrete based on continuum damage theory. The model characterizes the distinct behavior of concrete in tension and compression using using multi‐loading surfaces. The principal strains govern the growth of damages in principal directions. The damage effect tensors are based on the principal tensile or compressive damages. Crack‐opening/closure effects and permanent strains are described through inelastic crack strains under tension and compression. The effect of tensile/compressive damage evolution on the Poisson's ratio is incorporated to capture large strains in the lateral directions during tension‐compression loadings. The numerical results of several test cases exhibit good agreement with experimental results.
Contribution of Large and Very Large Scale Motions to the Turbulent Kinetic energy in Turbulent Pipe Flow
Authors: Hallol Zeinab , Merbold Sebastian , Egbers Christoph 
Published: January 2021

AbstractIn the present investigation in turbulent pipe flow we study the contribution of turbulent structures, such as Large scale motion (LSM) and very large scale motion (VLSM) to the turbulent kinetic energy. Hence, the streamwise velocity fluctuation is measured using a single hot wire anemometer in the Cottbus Large Pipe Facility test facility (CoLaPipe) at Brandenburg University of Technology Cottbus‐Senftenberg (BTU) for Reynolds numbers Reτ = 1.3 × 104 and 1.9 × 104, where Reτ is the Reynolds number based on the friction velocity (Uτ) and the pipe diameter (D). By the use of pre‐multiplied power spectra of the streamwise velocity, we aim to understand the influence of the LSM and VLSM onto the turbulent momentum budget at different wall normal locations.
A potential‐based formulation of the classical and relativistic Navier‐Stokes equations
Authors: Scholle Markus , Marner Florian , Gaskell Philip H. 
Published: January 2021

AbstractAnalogies drawn to Maxwell's equations in tandem with complementary viscous flow theory, involving the introduction of a tensor potential, has been used to achieve exact integration of the Navier‐Stokes equations. The same methodology facilitates the derivation of an elegant four‐dimensional Lorentz‐invariant first‐integral formulation of the energy‐momentum equations for viscous flow assuming a flat space‐time, consisting of a single tensor equation. It represents a generalisation of corresponding Galilei‐invariant theory associated with the classical incompressible Navier‐Stokes equations, with the key features that it: (i) takes the same form as its two‐ and three‐dimensional incompressible counterparts; (ii) applies to any physical model, in that it does not depend at outset on the constitutive fluid relationship forming the energy‐momentum tensor, other than that the latter is taken as being symmetric. The new general theory is applied to the problem of propagating acoustic waves, with and without viscous damping, and shown to recover the well‐known classical expressions for sound speed and damping rate consistent with those available in the open literature.
Simulation of guided waves in cylinders subject to arbitrary boundary conditions for applications in material characterization
Authors: Itner Dominik , Gravenkamp Hauke , Dreiling Dmitrij , Feldmann Nadine , Henning Bernd 
Published: January 2021

AbstractMaterial characterization of viscous polymers is typically carried out as quasi‐static or in the low‐frequency range. However, some applications require excitation in the high‐frequency range, and subsequently adequate elastic properties capable of describing such specific behavior. The FEM may be used to solve the elastic wave equations, however three‐dimensional simulations in the ultrasound regime require considerable computational resources. The computational time can be reduced by combining the scaled boundary finite element method with the Fourier finite element method for cylindrical domains: then, only the radial direction is discretized. We present such an axisymmetric formulation, which is extended to allow the definition of circumferential as well as arbitrarily shaped dynamic boundary conditions. It is shown that the results are in good agreement with standard FEM procedures, while greatly reducing computational time.
Fourier Analysis of DG Schemes for Advection‐Diffusion
Authors: Ortleb Sigrun 
Published: January 2021

AbstractThis work compares the wave propagation properties of discontinuous Galerkin (DG) schemes for advection‐diffusion problems in particular with respect to the discretization of diffusion terms. Extending previous investigations, the advection discretization now additionally varies between the choices of central or upwind fluxes. The results show that a previously recognized better performance of central schemes for well‐resolved problems only hold for even polynomial degrees and that upwind‐type discretizations also perform better on Gauss‐Lobatto nodes.
A priori reduced order model of steady Navier‐Stokes equations for low Reynolds number
Authors: Hoareau Christophe , Shang Lan , Zilian Andreas 
Published: January 2021

AbstractThis work focuses on a priori reduced order model of the parameterised steady Navier‐Stokes equations for a Reynolds number lower than 100. The approach is based on the Proper Generalized Decomposition [1, 2] where the velocity and the pressure are expressed as series of separated function variables. Each term of the off‐line basis is computed progressively contrary to classical reduced order model techniques which necessitate snapshots of the problem before the reduction [3]. The curse of dimensionality could be overcome if the number of parameters increases. The approximation of the solution can be computed in real‐time once the terms of the reduced basis are known. Here, the Reynolds number µ and the position coordinate vector X are taken as parameters in the classical 2D lid‐driven cavity problem. The key points of the approach, which involve a succession of nonlinear problems expressed in a weak form, are briefly illustrated. Preliminary results, obtained with the use of the open source FEniCS software are presented. The velocity approximation is finally compared to a high fidelity solution. The results show that a small number of modes (fewer than 8) are necessary to obtain a velocity approximation with a global error lower than 1%.
Automatic model order reduction for vibro‐acoustic problems
Authors: Aumann Quirin , Müller Gerhard 
Published: January 2021

AbstractNumerical models of vibro‐acoustic systems require a fine spatial discretization to be valid also for high frequent vibrations. This results in large models with high memory consumption and a large computational cost. Model order reduction (MOR) methods reduce the size of such problems, allowing an efficient design process. However, the assumptions made prior to the reduction process, e.g. desired size of the reduced model or distribution of expansion points, heavily influence the quality of the reduced models. In this contribution, we investigate interpolation based MOR methods to automatically generate reduced order models of vibro‐acoustic systems valid in a limited frequency range not starting at zero.
A comparative study of numerical approaches for the computation of effective properties of micro‐heterogeneous materials
Authors: Assaf Rama , Scheunemann Lisa , Birk Carolin , Schröder Jörg , Ooi Ean Tat 
Published: January 2021

AbstractThe paper presents a comparative study of the finite element method (FEM) and the scaled boundary finite element method (SBFEM) for the numerical evaluation of the volume‐averaged stress of composites. Two‐dimensional meso‐scale models of concrete represented by digital images and discretized using an automatic mesh generation algorithm are considered. The different computational approaches are discussed and compared with respect to accuracy and efficiency for both scenarios.
Parameter estimation for orthogonal polynomial moments
Authors: Lorenz Dirk , Schneppe Felix 
Published: January 2021

AbstractProny's method recovers a Dirac ensemble μ = Σi=1M aiδxi with given sparsity level by separating the reconstruction of the unknown coefficients and positions. While it recovers the positions by examing the so called Prony polynomial, its reconstruction is heavily based on solving linear systems, which can be constructed by given monomial moments.The intention of this article is to propose a Prony‐like method to recover the Dirac ensemble with an upper bounded sparsity level from orthogonal polynomial moments.
Superstructures in turbulent boundary layers with pressure gradients
Authors: Bross M. , Eich F. , Schanz D. , Novara M. , Schröder A. , Kähler C. J. 
Published: January 2021

AbstractLarge‐scale coherent structures have been observed in various wall‐bounded turbulent flows. In turbulent boundary layers, streamwise elongated regions of high‐ and low‐momentum in the log‐law layer that can extent up to several boundary layer thicknesses are often referred to as superstructures. These structures contain a relatively large portion of the layer's turbulent kinetic energy and have been shown to interact with the near‐wall features. In the last few decades extensive research on zero‐pressure gradient turbulent boundary layers has been done, however by comparison, the structural characteristics for adverse pressure gradient turbulent boundary layer flows are much less studied. Therefore, the three‐dimensional dynamics of turbulent superstructures in a turbulent boundary layer flow is investigated in the Atmospheric Wind Tunnel Munich (AWM) measurement using a novel multi‐camera 3D time‐resolved Lagrangian particle tracking approach. In this study, the structural properties and dynamics of turbulent superstructures within a zero pressure gradient (ZPG) turbulent boundary layer at Reτ = 5000 or Reθ = 14000 that then flows over a curved plate subjected to a favorable (FGP) and strong adverse (APG) pressure gradient, which eventually separates, is considered. It was found that while the average superstructure topology is modulated by decelerating flow in the APG when compared to the ZPG region the basic shape and pattern is preserved.
A discrete element model for reinforced concrete
Authors: Kaschube Jan , Dinkler Dieter 
Published: January 2021

AbstractReinforced concrete structures are built all over the world. The development of cracks is an unavoidable appearance, based on the interaction of the concrete and the reinforcement. The crack pattern can have an significant influence at the ageing of the structure. The presented modelling concept describes the reinforced concrete on the mesoscale. For the description of the concrete the Discrete Element Method (DEM) is used. The plain concrete is discretised by spherical particles. Spherical particles, surrounded by an rigid hull, are also used to describe the reinforcement. For an interaction between concrete and reinforcement massless virtual particles are added inside the reinforcement. With this concept a resilient bond behaviour without sliding can be described.
Damage simulation of thermo‐chemo‐elasto‐plastic fibre reinforced composites using mean‐field homogenization methods
Authors: Lenz Peter , Mahnken Rolf 
Published: January 2021

AbstractThis work presents a three‐scale mean‐field homogenization framework for constitutive multiscale (micro‐meso‐macro) modelling of fibre reinforced composites (FRC) considering a curing process and damage. An FRC is decomposed into unidirectional fibres surrounded by an interface, which in turn is surrounded by a matrix material. Based on the Mori‐Tanaka mean‐field homogenization method effective properties are determined. In each material phase damage is considered, namely matrix damage, fibre damage and interface damage. Based on a curing process effective elastic, thermal, chemical and plastic properties of the matrix and the interface are determined in terms of a degree of cure.
Two applications of the asymptotic homogenization method
Authors: Sheshenin Sergey , Artamonova Nina , Klementyev Petr 
Published: January 2021

AbstractThe first part of the paper presents the application of the asymptotic averaging method for determining the effective moduli and stress concentrations in the B4C/2024Al composite using 2D and 3D x‐ray images of the internal structure. The second study concerns an application of asymptotic homogenization to metamaterials. Metamaterials may have unusual bahaviour such as tension–bending coupling or tension–torsion coupling. Most metamaterials have a periodic structure in Cartesian coordinates. Here it is important to formulate the question regarding the number of periodicity cells, which determines whether the metamaterial is really a material or it is just a structure. If some property remains to be true for infinite number of cells, then such a metamaterial is treated as real material. On contrary, the metamaterial must be treated just as a structure, if the same property is valid only for finite number of cells and vanishes when the number of cells increases.
A simple success check for delay differential‐algebraic equations
Authors: Ahrens Ines , Unger Benjamin 
Published: January 2021

AbstractSolutions of delay differential‐algebraic equations (DDAEs) may depend on derivatives and future evaluations of some of its equations. Structural analysis can be used to determine how often each equation needs to be differentiated and shifted. Unfortunately, these numbers are not always correct, such that a post‐processing step is required to validate the result. In this contribution, we present the first step towards a success check for DDAEs.
3D thermo‐mechanical dynamic crack propagation with the XFEM and gradient enhanced damage
Authors: Sun Jian , Löhnert Stefan 
Published: January 2021

AbstractThis work presents the application of the extended finite element method (XFEM) to dynamic crack propagation with thermo‐mechanical coupling. A gradient‐enhanced damage model is coupled that allows for a damage‐based propagation criterion. The transient thermal and dynamic mechanical fields, along with a gradient enhanced damage, are solved simultaneously for each time step by utilizing the Newmark‐beta method. The level set method enables the crack front to be implicitly tracked during crack propagation. The global crack tracking method is used to solve the extension of the propagation velocity more efficiently. The accuracy and robustness of the employed approach is assessed by means of some linear elastic fracture mechanics examples.