bluuebunny/crossref_metadata_2025_split huggingface dataset:
Topology Optimization with Isogeometric Analysis and Phase Field Modeling
Authors: Muench Ingo , Klassen Markus , Wagner Werner 
Published: November 2019

AbstractWe use a Phase Field Model (PFM) for the evolution of load‐bearing structures on base of the equivalent stress criterion. Similar to Evolutionary Structural Optimization, the equivalent stress from all integration points is collected to evaluate a threshold. The approach couples density and stiffness to the phase field variable. The topology evolves from homogeneously filled regions by nucleation of holes. In numerical examples we compare results using standard Finite Elements (FEM) and Isogeometric Analysis (IGA), respectively. Latter allows for higher continuity between elements, which is essential to avoid the well‐known mesh‐pinning effect.
On the relaxation of continuity conditions for finite element schemes based on a least‐squares approach
Authors: Igelbüscher Maximilian , Schröder Jörg 
Published: November 2019

AbstractThe proposed contribution is based on the idea of the relaxation of continuity conditions and an enforcement of these continuity constraints for the considered fields via Lagrange multipliers. Therefore, a stress‐displacement least‐squares formulation

is considered, which is defined by the squared

‐norm applied to the first‐order system of differential equations, given by the balance of momentum and the constitutive equation, compare for the case of linear elasticity e.g. [1], as well as an additional (mathematically redundant) residual for enforcement of the stress symmetry condition. In general the assumptions for the continuity conditions are related to the conforming discretization of the individual fields. The conforming discretization, which demands continuity of the displacements and normal continuity of the stresses, is given by polynomial functions of Lagrange type for the displacements, i.e.

, and a stress approximation with Raviart‐Thomas functions, i.e.

. A non‐conforming discretization of the stresses considering discontinuous Raviart‐Thomas approximation functions with

yield to a relaxation of the continuity conditions. However the fulfillment of these relaxed constraints is enforced by the introduction of Lagrange multiplier within the underlying least‐squares formulation.
Numerical study of nonlinear elastic wave propagation in locally damaged engineering structures
Authors: Ankay Benjamin , Zhang Chuanzeng 
Published: November 2019

AbstractIn this paper, the two‐dimensional (2‐D) ultrasonic wave propagation problem in an elastic half‐space with a localized damaged zone is numerically simulated by a mapped Chebyshev pseudo‐spectral collocation method [1]. The considered damaged zone, which is embedded in an undamaged host medium, is modelled by a nonlinear elastic and viscoelastic constitutive law. Classical nonlinear elastic and nonclassical hysteretic material behaviors are separately considered and evaluated. In particular, the classical nonlinear elasticity theory of Murnaghan [2] is implemented, while the hysteretic material behavior is modelled by the Duhem‐model. To transfer the constitutive relations from the one‐dimensional (1‐D) to the 2‐D case the Kelvin decomposition method is used. Furthermore, Convolutional Perfectly Matched Layers (CPML's) are used to simulate the semi‐infinite elastic half‐space. The computed time‐domain signals are transformed to the frequency‐domain and subsequently analyzed for different degrees of the wave attenuation and nonlinearity in the damage zone. The applications of the nonlinear ultrasonic technique are discussed based on the numerical results.
A degenerate Cahn‐Hilliard model as constrained Wasserstein gradient flow
Authors: Matthes Daniel , Cances Clement , Nabet Flore 
Published: November 2019

AbstractExistence of solutions to a non‐local Cahn‐Hilliard model with degenerate mobility is considered. The PDE is written as a gradient flow with respect to the L2‐Wasserstein metric for two components that are coupled by an incompressibility constraint. Approximating solutions are constructed by means of an implicit discretization in time and variational methods.
Towards deep learned constitutive models based on two‐dimensional strain fields
Authors: Hillgärtner Markus , Linka Kevin , Abdolazizi Kian P. , Itskov Mikhail 
Published: November 2019

AbstractIn order to calibrate material models, experimental stress‐strain curves are usually compared with model predictions under the same loading conditions. While this approach guarantees good results for one specific loading type, the resulting model is not generally able to properly predict other loading scenarios. Therefore, a variety of mechanical tests can be conducted, amongst which uniaxial tension, uniaxial compression, pure‐shear and equibiaxial tension tests are the most commonly used ones. Multi‐axial loading often cannot be adequately predicted solely based on test data from one such experiment. Therefore, the material model can be fitted against several mechanical test data sets simultaneously in order to increase the prediction quality, which requires a considerable amount of experiment work.This contribution aims to create phenomenological material models which are directly fitted against an experimental force response and the corresponding two‐dimensional strain field obtained from arbitrary loading. To this end, a deep learning framework based on a multilayer‐perceptron (MLP) approach [2] is proposed which identifies suitable strain‐energy functions and their corresponding derivatives. These can be utilized in a commercial finite element code via a user defined material subroutine in order to compare the quality of the approximation with the reference data. This approach avoids the above mentioned idealized experiments and simplifies the process of phenomenological modeling by exploiting the capabilities of deep neural networks.
Stabilization of underactuated nonlinear systems to non‐feasible curves
Authors: Grushkovskaya Victoria , Zuyev Alexander 
Published: November 2019

AbstractThis paper focuses on the development of stability conditions for systems of nonlinear non‐autonomous ordinary differential equations and their applications to control problems. We present a novel approach for the study of asymptotic stability properties for nonlinear non‐autonomous systems based on considering a parameterized family of sets. The proposed approach allows to state asymptotic stability conditions for a family of sets representing the level sets of a time‐varying Lyapunov function and to estimate the rate of convergence of solutions to a prescribed neighbourhood of the given curve. The obtained stability results are applied to the trajectory tracking problem for a class of nonholonomic systems.
Computational modeling of adhesive contact between a virus and a cell during receptor driven endocytosis
Authors: Wiegold Tillmann , Klinge Sandra , Gilbert Robert P. , Holzapfel Gerhard A. 
Published: November 2019

AbstractThe present contribution deals with the viral entry into a cell dictated by the change of the receptor density. While the receptors of the virus are considered to be fixed on its surface, the ones of the cell are mobile within its membrane. Upon contact, a locally increased receptor density of the cell is required, which causes it to diffuse towards the virus. The membrane inflicts and forms an envelope around the virus in the contact zone. The described problem is simulated on the basis of the assumption that the differential equation typical of the heat transport is suitable to describe the diffusion of receptors. Furthermore, two boundary conditions are proposed. The first condition deals with the balance of fluxes on the front of the adhesion zone, where the velocity is supposed to be proportional to the gradient of the chemical potential. The second condition represents the energy balance equation with contributions due to the binding of receptors, the free energy of the membrane, its curvature and the kinetic energy due to the motion of the front. The selected numerical example shows the change of the receptor density over the membrane as well as the motion of the front of the adhesion zone. Special attention is paid to the mobility of the receptors.
A finite fracture mechanics approach for interlaminar crack initiation using the scaled boundary finite element method
Authors: Dölling Sebastian , Bremm Sophia , Hell Sascha , Becker Wilfried 
Published: November 2019

AbstractIn the present study, crack initiation induced by the free‐edge effect in symmetric angle‐ply laminates is investigated. For this purpose, the coupled stress and energy criterion within the framework of finite fracture mechanics is used. In order to obtain the required quantities efficiently the semi‐analytical scaled boundary finite element method is implemented. The obtained effective failure stresses are compared to experimental findings from literature.
Phase field modeling with IGA and FEM: Error surveillance in the transition zone
Authors: Klassen Markus , Muench Ingo , Klinkel Sven 
Published: November 2019

AbstractThe present contribution compares the solution of a phase field problem by the finite element method (FEM) with isogeometric analysis (IGA). For the sake of simplicity, the coupling to additional fields is neglected. Thus, the phase field variable appears as the only unknown in the boundary value problem. The numerical solutions are compared to the analytical solution, elaborated by Falk, of the Allen‐Cahn equation. In this model, the Ginzburg‐Landau free energy density combines a free Landau energy of sixth order with a quadratic gradient energy. The benchmark consists of a simple quadrilateral geometry with boundary conditions for the phase field variable which allows to solve static unidirectional phase transitions. For the FEM, the mesh is refined uniformly in space by h‐ and p‐refinement. In IGA, the refinement is realized by the knot insertion and order elevation algorithms from computer aided design (CAD) which is known as k‐refinement. Furthermore, IGA allows for a higher continuity between the elements which enhances the gradient of the phase transition variable.
Role of diameter and percentage of SMA bars as reinforcement in strength and residual displacement of concrete beams
Authors: Molod Mohammad Amin , Barthold Franz-Joseph , Spyridis Panagiotis 
Published: November 2019

AbstractShape memory alloy (SMA) is a smart material that is currently used in reinforced concrete members. This preliminary research aims to numerically investigate the role of diameter and percentage of SMA as the main reinforcement of concrete beam in increasing stiffness and reduction of residual displacement. To do so, eight beams with same geometry and boundary condition reinforced with superelastic SMA under two cycle of four‐point bending loading in Ansys APDL have been simulated. Results showed that enhancement of ratio of SMA in the beams will reduce residual displacement and increase stiffness of the beams. Furthermore, for beams with same percentage of SMA bars, more number of bars with thinner diameters leaded to less residual displacement compared to less number of bars with thicker diameters.
Model adaptivity on mean‐field and full‐field homogenization methods considering hierarchical unit cells
Authors: Ju Xiaozhe , Mahnken Rolf 
Published: November 2019

AbstractThe increasing use of heterogeneous materials like composites in the industrial praxis has made the finite element (FE) simulation using homogenization techniques a well‐accepted and often even inevitable tool. For a reliable simulation, both discretization and model error need to be controlled. Aiming at a user‐defined target functional called quantity of interest, error estimators are derived using duality arguments. Model adaptivity is established on the macro scale, towards an economic model distribution that exploits the advantages of mean‐field and computational homogenization methods based on unit cells of increasing size. This is achieved by using the same philosophy of adaptive finite element method (FEM) for an economic mesh, which applies simultaneously to model adaptivity. A numerical example shows the effectiveness of the adaptive approach.
Parameter Study of Turbulent Drag Reduction by Spanwise Traveling Transversal Surface Waves
Authors: Albers Marian , Meysonnat Pascal S. , Fernex Daniel , Semaan Richard , Noack Bernd R. , Schröder Wolfgang 
Published: November 2019

AbstractLarge‐eddy simulations of spanwise traveling transversal surface waves in turbulent boundary layer flow are conducted. The parameter space of period, amplitude, and wavelength is investigated by 80 simulations. A maximum decrease of the averaged drag by 26 percent is obtained and an approximate scaling law for the decrease of the skin friction is found.
Optimisation of Diffusion Driven Degradation Processes
Authors: Waschinsky Navina , Barthold Franz-Joseph , Menzel Andreas 
Published: November 2019

AbstractNature strives for optimal processes in order to prevent early damage or failure, for example bones which regulate the tissue in high stress areas or the optimal shape of trees. Many materials in nature are highly complex as they are designed for long duration. Taking nature itself as a role model means taking its complexity into account, especially when considering materials which suffer from chemical attacks and the degradation of materials. From this point of view, we create an algorithm which considers degradation processes triggered by chemical substances which depend on diffusion conditions in a finite element (FE) framework. In addition, we perform design optimisation with stress restrictions by taking evolutionary processes as a role model.
Development of a simulation model for the automatic optimization of tools for multi‐dimensional tube forming
Authors: Derr Ralf , Jung Anne , Diebels Stefan 
Published: November 2019

AbstractThe increasing number of vehicle components and the advancing lightweight construction in manufacturing processes increasingly require a more flexible design of the exhaust tube geometry. The use of process supplementary simulations is necessary, in order to meet these increasing requirements in the future.The aim of this study is the development of a software tool for the simulation of multi‐dimensional tube forming processes by tube bending and tube embossing. Therefore, a graphical user interface was developed to build‐up and simulate the tube forming processes. The required material parameters for the numerical modeling were determined by means of tensile tests. The simulation models were successfully validated by comparing the numerical results with the experimental results. The influence of the workpiece and the forming tools were numerically investigated on the basis of the validated simulation models. Batch‐related tolerances could be identified as a serious source of deviations. Furthermore, experimental forming errors could be numerically reproduced and corrected by modifying the parameter settings. The tool variation increased the process knowledge and provided the basis for a subsequent optimization. The embossing structure could be optimized satisfactorily by specifying user‐defined requirements.
A formulation for the dynamic analysis of multibody systems using non‐redundant unified local velocity coordinates
Authors: Holzinger Stefan , Gerstmayr Johannes 
Published: November 2019

AbstractIn this paper, we present a formulation for the dynamic analysis of multibody systems using non‐redundant unified local velocity coordinates. The motivation for the present work is the result of an earlier investigation of unified local velocity coordinates of Holzinger et al. [1]. The equations of motion presented by the authors allow the description of the rigid body motion in space by local, purely translational velocity coordinates. However, the earlier investigations are limited to the description of the spatial motion of a free rigid body. Therefore, constraints are incorporated in the present paper.
Shape optimization of a bended tube minimizing particle erosion
Authors: Hohmann Raphael , Leithäuser Christian 
Published: November 2019

AbstractThe transport of gas‐solid suspensions in bended pipes can lead to erosion of the walls due to particle impact. In this context the numerical prediction of the erosion rate is usually based on an Eulerian flow description in combination with Lagrangian particle tracking, which however does not lend itself straightforwardly to the continuous adjoint approach of shape optimization. In order to find a pipe design, which is less prone to erosion, we therefore use a one‐way coupled Eulerian particle model. Upon formally computing the shape derivative of the resulting PDE‐constrained shape optimization problem, we minimize the erosion rate for a three‐dimensional tube bend under laminar flow conditions using a gradient descent method.
Material modeling of hyperelastic silicone adhesives considering stiffness reduction
Authors: Toups Elisabeth , Seewald Robert , Schaaf Benjamin , Reisgen Uwe , Feldmann Markus , Reese Stefanie , Simon Jaan-Willem 
Published: November 2019

AbstractPredicting the hyperelastic behavior and the stiffness reduction of adhesive is essential for the economical dimensioning of load‐bearing bonds in the field of glass façade construction. The typical hyperelastic behavior can be modeled by using one of well‐known hyperelastic models. In addition, a new variable for modeling stiffness reduction was defined. A new material model based on the Ogden model for representing hyperelasticity and stiffness reduction was defined.
A juxtaposition of data driven and stochastic finite element analyses for problems with noisy material data
Authors: Korzeniowski Tim Fabian , Reppel Thomas , Weinberg Kerstin 
Published: November 2019

AbstractIn data driven modeling the constitutive model is replaced by a data set and therefore yields a model‐free computation. In this context the data set also can be the input for noisy material data and describe material uncertainty. This contribution presents a juxtaposition of different finite element trechniques to describe material uncertainties, namely the stochastic finite element method and a data driven finite element method.
BEM‐simulation of tubes using thin elements
Authors: Kreuzer Wolfgang , Weber Veronika 
Published: November 2019

AbstractThe boundary element method (BEM) is a commonly used tool in acoustics to calculate wave propagation and scattering. As for finite elements the stability of the BEM suffers if the thickness of the elements used in the discretization of the scatterer is very small. To deal with this problem special thin middle face elements have been designed. In this work we use these elements to model the acoustics of musical tubes (boomwhacker/Klangröhre), that are simple musical instruments for children. We briefly describe the integral equation for the thin elements and compare calculations using the BEM with thin elements with measurements of a tube tuned to the note ‘C’.
Proceedings in Fluid Design
Authors: Beckmann Tom , Reinke Peter , Schmidt Marcus 
Published: November 2019

AbstractThis work presents the process of designing a cavitating fluid for the lubricant flow in journal bearings. Hydrodynamic journal bearings are used in a wide range of technical and industrial applications because they provide low friction and minimal wear. The principal operational feature of these bearings is an eccentrically rotating shaft inside the bushing resulting in a convergent and divergent lubricating film of just a few micrometers in thickness between the shaft and the bushing. For the particular case of internal combustion engines the displacement of the shaft is transient with strong variations in eccentricity and displacement velocity. Hence, the flow inside the lubricating film is transient and three‐dimensional. Investigations of the flow inside journal bearings are technically challenging. The following geometrical and physical conditions have to be tackled: small lubricating film thickness, optical accessibility, Reynolds and cavitation similarity. The combination of these conditions requires a scaled journal bearing experiment with a special fluid that fulfills the cavitation condition. The most important component of the experimental setup is the fluid in order to create the desired flow conditions. The authors of this work have proven that a cavitating fluid can be designed to specification by applying the new approach to the cavitating Taylor‐Couette flow. The proper fluid design has to fulfill three criteria: physical compatibility, Reynolds analogy and cavitation number at the operating point. Physical compatibility stems from material specifications of the apparatus and the need to provide optical accessibility by providing identical refractive indices of fluid and housing. The fluid must be chemically compatible with acrylic glass of the apparatus preventing unwanted reactions. Laser‐optical measurements are the most suitable means to obtain significant data of the flow field inside the lubricating film. The relation of dynamic pressure at the operating point and mechanical dimensions of the apparatus defines the viscosity necessary to fulfill the Reynolds analogy. Finally, the cavitation number in relation to the combination of dynamic and static pressure provides the target vapor pressure of the special fluid. Thus, the present work describes the development of a special fluid applicable for journal bearings in model scale, which not only fulfills pressure and cavitation analogy but also features a favorable refractive index and a chemical suitability for the task. Furthermore, the work shows results of a cavitating flow in a small gap arrangement by means of the designed fluid.
A least‐squares finite element approach to model fluid‐structure interaction problems
Authors: Averweg Solveigh , Schwarz Alexander , Nisters Carina , Schröder Jörg 
Published: November 2019

AbstractIn this contribution an approach to model fluid‐structure interaction (FSI) problems with monolithic coupling is presented. The fluid as well as the structural domain are discretized using the least‐squares finite element method (LSFEM), whose application results in a minimization problem with symmetric positive definite systems also for non self‐adjoint operators, see e.g. [2]. In this study, the second‐order systems are reduced to first‐order systems by introducing new variables, which leads to least‐squares formulations for both domains based on the stresses and velocities as presented in e.g. [5] and [7]. A conforming discretization of the unknown fields in H1 and H(div) using Lagrange interpolation polynomials and vector‐valued Raviart‐Thomas interpolations functions, respectively, leads to the inherent fulfillment of the FSI coupling conditions. In more detail, a discretization in H1 ensures continuity of the velocity field and a discretization in H(div) results in continuity of the normal stress components at the interface.
A time‐adaptive Dirichlet‐Neumann waveform relaxation method for coupled heterogeneous heat equations
Authors: Monge Azahar , Birken Philipp 
Published: November 2019

AbstractWe introduce a time adaptive multirate method based on the Dirichlet‐Neumann waveform relaxation (DNWR) algorithm for the simulation of two coupled linear heat equations with strong jumps in the material coefficients across the interface. Numerical results are included to illustrate the advantages of the time adaptive approach over the multirate approach and the robustness of the multirate DNWR method with respect to its sibling, the multirate Neumann‐Neumann waveform relaxation (NNWR) method introduced in a previous work [3].