bluuebunny/crossref_metadata_2025_split huggingface dataset:
An accelerated Boundary‐Domain Integral Method for three‐dimensional fluid flow analysis
Authors: Tibaut Jan , Ravnik Jure 
Published: November 2019

AbstractThe rapid growth of computer power enables performing of more and more complex numerical simulations. However, the need to develop efficient numerical algorithms is always present. In this study, we propose an acceleration of an algorithm to solve the nonlinear system of Navier‐Stokes equations. We present an accelerated Boundary‐Domain Integral method (BDIM). The BDIM is a boundary element method (BEM) based method, thus its computational demands scale as 𝒪(N2), where N is the number of grid nodes. This is due to the fact that the discretization procedure leads to fully populated matrices. However, the computational demands can be reduced to a linear‐logarithmic 𝒪(N log N) complexity, with the implementation of an approximation procedure. In this study, we solve the velocity‐vorticity formulation of the Navier‐Stokes equations and develop an accelerated algorithm for determination of the boundary vorticity in 3D based on ℋ‐matrix and the adaptive cross approximation (ACA) method. We test the algorithm using coupled nanofluid flow and heat transfer. As expected results show that, the acceleration (matrix compression rate) has a negative influence on the solution accuracy.
Kinematics of finite‐dimensional mechanical systems on Galilean manifolds
Authors: Winandy Tom , Eugster Simon R. , Capobianco Giuseppe 
Published: November 2019

AbstractIn a coordinate‐free description of time‐independent finite‐dimensional mechanical systems the configuration manifold plays a central role. In the case of time‐dependent mechanical systems, time needs to be included in the space on which the related physical theory is formulated. In this respect, we show that a so‐called Galilean manifold not only provides a ‘generalized space‐time’ but that it allows the coordinate‐free presentation of a physical theory for time‐dependent finite‐dimensional mechanical systems. The motion of a mechanical system is interpreted as an integral curve of a second‐order vector field on the state space related to the Galilean manifold of the system. Second‐order vector fields, which are the coordinate‐free equivalent of second‐order differential equations, are in one‐to‐one correspondence with the action forms introduced by Loos [4,5]. Because of this bijective relation, the kinetic part of the theory can be formulated by postulating the action form governing the motion of a finite‐dimensional mechanical system.
Rate‐dependent fracture simulation of viscoelastic material by the phase‐field method
Authors: Yin Bo , Kaliske Michael 
Published: November 2019

AbstractThe phase‐field method has been studied for fracture analysis during the last decade. Based on the classical GRIFFITH‐type brittle fracture, good agreements are obtained by comparing to other numerical methods as well as experiments. Furthermore, phase‐field modelling does not depend on any explicit criterion and gets rid of discontinuous displacement tracing. Regarding most elastomers exhibiting both elastic and viscous behaviour simultaneously, it yields a rate‐dependent mechanical response. Investigated by experiments, the fracture process is shown to be rate‐dependent as well. In this work, a viscoelastic rheological model based on REESE & GOVINDJEE [1] is coupled to the phase‐field approach to investigate rate‐dependent fracture evolution within elastomers. The fracture mechanism is based on the volumetric‐isochoric split and the driving force for fracture is defined to be the elastic strain energy potential by both the equilibrium and the non‐equilibrium branches. Representative numerical models are simulated and related findings and potential subsequent perspectives are summarized to close the paper.
Capillary Rise ‐ Jurin's Height vs Spherical Cap
Authors: Gründing Dirk , Fricke Mathis , Bothe Dieter 
Published: November 2019

AbstractWhen liquid rises in a capillary, the interface has a shape close to a spherical cap when the Eotvos number is sufficiently small. This assumption is typically used when computing the stationary rise height of the liquid. Considering a continuum mechanical approach it can be shown that the exact shape of a spherical cap is not a solution to the rise problem yet a good approximation. Consequently, the assumption of a spherical cap used in Washburn‐type rise models is justified only for small Eotvos numbers. In this limit, Jurin's height has the largest error.
Thermo‐Mechanical Modeling of Pre‐Consolidated Fiber‐Reinforced Plastics for the Simulation of Thermoforming Processes
Authors: Ziegs Jean-Paul , Weck Daniel , Gude Maik , Kästner Markus 
Published: November 2019

AbstractMulti‐material design aims at the targeted combination of materials with different characteristics in order to meet technical requirements. Especially the combination of metals and fiber‐reinforced plastics (FRP) has led to innovative lightweight structures with high loading capacity and ductility in recent years. The process chain required to produce such structures is characterized by a variety of process parameters which have a significant influence on the quality of the manufactured workpiece. In order to treat the thermoforming process numerically, we present constitutive models for the metal and composite part to simulate the deformation behavior of these components. In addition, experimental setups are described to identify the required material parameters. Simulations of the manufacturing process will indicate correlations between material as well as process parameters and possible defects of the final structure that may occur during manufacturing.
Oscillations in a system of two coupled self‐regulating spool valves with switching properties
Authors: Schröders Simon , Fidlin Alexander 
Published: November 2019

AbstractIn hydraulic systems, valves can be considered as fundamental components. They serve as control elements to regulate hydraulic power transmission. In order to minimize control effort, self‐regulating spool valves enjoy great popularity. However, their disadvantage is a possible loss of stability, caused by the coupling between hydraulic and mechanical degrees of freedom via pressure feedback areas. So far, the self‐excited oscillations, evoked from the operating point's loss of stability, have mostly been investigated using minimal models of individual valves. In real world applications, for example in automotive transmissions, typically several valves are employed which are coupled by hydraulic pipes. Here, it is expected, that dynamical phenomena occur, which cannot be portrayed by simple models of individual valves. Within this contribution, the oscillatory behaviour of a system employing two coupled self‐regulating valves is discussed. The resulting non‐stationary solutions are characterized by using Floquet theory and computing Lyapunov‐Exponents.
Coupled thermomechanical model for strain‐induced crystallization in polymers
Authors: Aygün Serhat , Klinge Sandra 
Published: November 2019

AbstractCrystallization in certain polymers, like natural rubber, is characterized by the specific geometrical arrangement of atoms in macromolecules caused by high strains. Starting from crystallization nuclei, polymer chains leave their natural entangled structure, stretch out, fold back and stack. Eventually, they build regions with a regular structure, also called lamellae. The process must be taken into consideration when planning manufacturing processes since it significantly influences mechanical and thermal properties of the final product. The present contribution deals with the thermomechanical model for crystallization of unfilled polymers, which involves displacements and temperature as global degrees of freedom, and the degree of network regularity as an internal variable. The mechanical part of the model uses the dissipation potential with two special features: Firstly, the thermodynamically consistent framework is developed to simulate the reduction of the network regularity during the unloading phase. Secondly, the microstructure evolution under the cyclic tensile load is visualized. The thermal part of the model is based on the solution of the heat equation. The resulting, coupled thermomechanical problem is solved in a monolithic way. Finally, selected numerical examples are compared with experimental data of natural rubber without fillers.
External Vibration Damping of a Robot Manipulator's TCP Using Acceleration Feedback
Authors: Berninger Tobias F. C. , Rixen Daniel J. 
Published: November 2019

AbstractThere are multiple possible applications, which demand high accuracy from industrial robot arms. The usual approach to improve the path accuracy of these robot manipulators is to make the mechanical design as stiff as possible and to employ high fidelity joint controllers, which compensate path inaccuracies with well‐identified models of the manipulator system. These methods are, however, only available to the robot manufactures themselves during their development phase. Companies designing tools for specific high accuracy tasks generally cannot change the design of a given robot manipulator and are bound to its precision. An alternative concept to further increase the path accuracy of a robot manipulator, without making changes to its design itself, might be to employ traditional Active Vibration Damping techniques by adding a supplementary proof‐mass actuator to the robots tool center point with collocated acceleration sensor feedback. This paper explores the feasibility of this idea within a multi body simulation of a simple robot manipulator, which consist of rigid links, flexible joints and is actuated by cascaded joint controllers. The performance of an acceleration feedback controller employed on the robots TCP is evaluated by a test trajectory.
A mixed least‐squares finite element formulation within the framework of the theory of porous media
Authors: Schwarz Alexander , Averweg Solveigh , Bluhm Joachim , Schröder Jörg 
Published: November 2019

AbstractIn the present contribution a mixed least‐squares finite element method (LSFEM) based on the Theory of Porous Media (TPM) is presented. In detail, we investigate an incompressible binary model consisting of the phases solid and liquid. The main idea is based on the modeling of saturated porous structures. The resulting finite element is a four‐field formulation in terms of solid displacements, liquid pressure, mixture stresses and a new variable related to the pressure gradient. The conforming discretization of the unknowns in the spaces H(div) and H1 is realized by vector‐valued Raviart‐Thomas and standard Lagrange functions. Finally, a numerical example for liquid saturated porous structures considering an incompressible, linear elastic material behavior at small deformations, demonstrates the applicability of the LSFEM approach to the TPM.
Artificial Neural Network forecasting for monomorphic and polymorphic uncertainty models and comparison with experimental investigations
Authors: Gruhlke Robert , Drieschner Martin , Eigel Martin , Hömberg Dietmar , Petryna Yuri 
Published: November 2019

AbstractTools from probability or possibility in terms of fuzzy sets are usable for the description and quantification of uncertainties within numerical simulations. In this work, different monomorphic and polymorphic uncertainty models are applied on linear elastostatic structures with non‐periodic perforations in order to analyze the individual expressiveness. The first principal stress is used as an indicator for structural failure which is evaluated and classified. Artificial Neural Networks are used as surrogate model to compare and assess the uncertainty models with regard to the numerical predictions. Real experiments of perforated plates under uniaxial tension are validated with the help of various uncertainty models.
Thermo‐Mechanical Analysis of a Steam Turbine rotor
Authors: Eisenträger Johanna , Naumenko Konstantin , Kostenko Yevgen , Altenbach Holm 
Published: November 2019

AbstractIn power plants, high temperatures prevail during long holding times. Furthermore, power plants are often started and shut‐down in order to account for gaps or oversupplies in energy production. These loading conditions induce both creep and fatigue loads. Due to their excellent thermo‐mechanical properties, such as high tensile strength and elevated corrosion resistance, heat‐resistant steels are established materials for power plant components. Nevertheless, these steels tend to soften under deformation, which should be accounted for by a constitutive model.The contribution at hand analyses the thermo‐mechanical behavior of a steam turbine rotor. For this purpose, a unified phase mixture model is introduced. This constitutive model accounts for rate‐dependent inelasticity, hardening, as well as softening by employing an iso‐strain approach with a soft and a hard constituent. While the soft constituent represents areas with a low dislocation density, such as the interior of subgrains, the hard constituent refers to regions with a high dislocation density, i.e. the subgrain boundaries. Furthermore, two internal variables are introduced: a backstress tensor of Armstrong‐Frederick type and a scalar softening variable. The model results in a coupled system of three evolution equations with respect to the inelastic strain, the backstress, and the softening variable.To allow for the analysis of real power plant components, the model is implemented into the finite element method such that the evolution equations are integrated based on the backward EULER method. The applicability of the model is demonstrated by conducting a thermo‐mechanical analysis of a steam turbine rotor with complex geometry under realistic boundary conditions. In a first step, the instationary temperature field in the rotor is computed in a heat transfer analysis. Thereby, typical steam temperatures in power plants and the corresponding heat transfer coefficients are prescribed. As a next step, the structural analysis is conducted based on the phase mixture model and the obtained temperature field as input. In addition, the time‐dependent rotational frequency and steam pressure are taken into account. Note that the influence of different start‐up procedures such as a cold or a hot start is examined in detail. As a result, the structural analysis provides the stress‐strain hystereses, which constitute the basis for further fatigue and damage assessment.
Characterizing Materials in the Frequency Domain: Validation Experiments
Authors: Katzmann (né Sauer) Josef , Musialak Jana , Steeb Holger 
Published: November 2019

AbstractHigh Performance Concrete (HPC) and Ultra High Performance Concrete (UHPC) achieve an effective stiffness or strength which allows constructing highly stressed buildings. Following, we present a mechanical characterization technique for HPC and UHPC, using harmonic excitations from 0.1 Hz up to 1 kHz and displacement amplitudes in the micrometer range. The small‐amplitude excitations are performed by a high‐performance piezo‐electric actuator. To validate the experimental workflow, we characterize the mechanical behaviour of Polymethylmethacrylat (PMMA). In this contribution, we present results gained with two different cylindrical sample sizes. By this comparison we shall ensure that geometrical scaling of samples has no influence on the rheological results of the experiments, apart from a change in Signal‐to‐Noise ratio.
A Priori Error Estimates for an Optimal Control Problem Governed by a Variational Inequality of the Second Kind
Authors: Meyer Christian , Weymuth Monika 
Published: November 2019

AbstractWe consider an optimal control problem governed by an elliptic variational inequality of the second kind. The problem is discretized by linear finite elements for the state and a variational discrete approach for the control. We derive nearly optimal a priori error estimates based on L∞‐error estimates for the variational inequality and a quadratic growth condition. Our error analysis yields a convergence rate of order 1 − ϵ for the L2‐norm of the control.
Damage simulation of fiber reinforced composites using mean‐field homogenization methods
Authors: Lenz Peter , Mahnken Rolf 
Published: November 2019

AbstractOur work presents a two‐scale mean‐field homogenization framework for constitutive multiscale (meso‐macro) modeling of fiber reinforced composites (FRC) including damage. The FRC is decomposed into three distinct linear thermo‐chemo‐elastic material phases. The three phases are unidirectional fibers surrounded by an interface, which is surrounded by a matrix material. Different mean‐field homogenization methods can be used to determine the effective properties. For the damage a distinction is made between four different damage modes namely matrix damage, fiber damage, interface damage and a simultaneous damage of the matrix and the fiber called matrix‐fiber damage. An element deletion algorithm is used to simulate a crack propagation. A representative example demonstrates the different types of damage and a resulting crack propagation in an FRC.
Specimen design for extreme uniaxial tension‐compression tests of rubber materials
Authors: Kanzenbach Lars , Schlomka Clemens , Gelke Sören , Ihlemann Jörn 
Published: November 2019

AbstractIn this contribution a new measurement strategy is presented, which enables in combination with an optimized specimen‐setup the investigation of strains up to a compression level of −70%. The specimen‐setup itself consists of a slender dumbbell structure and a mounting geometry. The main idea of the new measurement strategy is, that for almost incompressible materials the average strain in the symmetry plane can be derived from the tangential strain at the surface. For this, the new measurement strategy is derived, simulated and experimentally tested. Finally, phenomenological characteristics of rubber, like Payne effect, Mullins effect, permanent set, relaxation and creep can be investigated at such extreme compression levels.
A phase field model for thermo‐oxidative aging in cracked polymers
Authors: Voges Jannik , Juhre Daniel 
Published: November 2019

AbstractWhen dealing with polymers, the behavior of aging processes is of great interest in many applications in engineering, as the usually very complex mechanisms can result in a drastic reduction of the lifetime of machine parts. In addition, those single mechanisms are coupled, which results in even more complexity. A crack creates new surfaces deeper inside the material and thus enables oxidation processes beyond the original surface. Once being oxidized, the crack resistance might be reduced, which may result in further crack propagation, which, again, enables oxidation even deeper.In the present work, a new approach for diffusion limited oxidation is introduced. The approach is based on the phase field method, which has become an important and versatile tool to model different phase evolutions in materials. An evolution equation is underlain by a gradient energy term to capture an interface energy and by a second term, which corresponds to the phase change representing the oxidation state. A diffusion equation controls the amount of available oxygen which is able to trigger the phase change. The phase change, in turn, drains a specific amount of oxygen in the coupled system of differential equations. In this work, cracks are able to expedite the oxidation process deeper into the specimen. The model has been implemented into the FE code FEAP and investigated by means of two academic examples.
Local Fourier analysis of multigrid smoothers for the Stokes problem
Authors: Bolten Matthias , Claus Lisa 
Published: November 2019

AbstractWe present a local Fourier analysis of the Stokes equations for a finite difference discretization on staggered grids. We compare the commonly used Vanka smoother with a non‐overlapping variant of the Vanka smoother. While the latter is computationally cheaper, the convergence depends severely on the order in which the unknowns are updated. In contrast, the convergence of the overlapping method is not affected by the order.
Aspects of the Particle Finite Element Method applied to contact problems
Authors: Schewe Markus , Menzel Andreas 
Published: November 2019

AbstractThe Particle Finite Element Method (PFEM) developed by [1] is designed to allow changes in the outer shape of a body while performing a Finite Element Analysis. This is achieved by repeated remeshing and shape detection of a particle cloud, which represents the body under consideration. The shape detection method creates new surfaces if formerly connected points on the surface move away from each other sufficiently. This method allows to model material separation, e.g. in metal cutting, see [2]. Details on advanced strategies to refine the detected shape are presented. Considering abrasive wear of surfaces, a mechanism‐based approach aims to model such separation of surface particles on a mesoscale. The basis of this approach consists of a contact algorithm that captures the interaction of solid bodies. This contribution presents a contact domain method [3] which is implemented in PFEM. The approach uses the abilities of the shape detection method as a contact search method. Furthermore, strategies for solving large strain boundary value problems using this contact model are discussed. Numerical examples show the abilities of the approach in an exemplary large strain contact problem.
On the calculation of a dry friction coefficient
Authors: Oestringer Lukas J. , Proppe Carsten 
Published: November 2019

AbstractNormal contact problems of rough surfaces have already been extensively investigated. For Gaussian surfaces, the normal force Fn is often found to be proportional to the real contact area A. Following the approach of Bowden and Tabor [1] for the tangential force Ft = τA, where τ denotes the yield shear stress of the softer surface, the friction coefficient µ = Ft/Fn , as ratio of tangential to normal force, is constant. This result is commonly used to justify Coulomb's friction law.Nevertheless, velocity dependent friction coefficients are widely used in many static and dynamic friction laws, although detailed simulative investigations on the physical background of the velocity dependence are missing. For these reasons, a halfspace simulation for rough surfaces subjected to sliding motion is presented here. The simulation includes temperature evolution as well as thermal expansion and their influence on contact forces, real contact area and friction coefficient. It is found that the frictional heat affects all of these variables and in particular leads to a velocity dependent friction coefficient.
Axisymmetric two‐phase flow simulations on space‐time meshes
Authors: Karyofylli Violeta , Kamaldinova Liubov , Simon Marek , Mokrov Oleg , Reisgen Uwe , Behr Marek 
Published: November 2019

AbstractFor reducing the dimensionality and consequently, the complexity of the dynamics related to bubble formation problems, this paper presents an axisymmetric space‐time interface capturing approach [1, 2]. For the description of the moving front, the level‐set method is used, because it is inherently able to account for topological changes of the interface [3], and is combined with a continuum surface force (CSF) model. Different benchmark cases from the literature are used for verifying our numerical approach, and the results are compared with those obtained using the commercial software, ANSYS CFX.
Waveform Iteration with asynchronous communication
Authors: Meisrimel Peter , Birken Philipp 
Published: November 2019

AbstractConsider the coupling of two multi‐physics systems of time‐dependent ODEs. We propose a new Waveform iteration type method for coupling which uses asynchronous communication to be both parallel in time and fast in convergence. Analytical results show convergence in the continuous setting and numerical results for two coupled head equations show good performance of this method, which is both parallel and converging fast.