bluuebunny/crossref_metadata_2025 huggingface dataset:
Trajectory‐based computational study of coherent behavior in flows
Authors: Padberg‐Gehle Kathrin , Schneide Christiane
Published: March 2018

The notion of coherence in time‐dependent dynamical systems is used to describe mobile sets that do not freely mix with the surrounding regions in phase space. In particular, coherent behavior has an impact on transport and mixing processes in fluid flows. The mathematical definition and numerical study of coherent structures in flows has received considerable scientific interest for about two decades. However, mathematically sound methodologies typically require full knowledge of the flow field or at least high resolution trajectory data, which may not be available in applications. Recently, different computational methods have been proposed to identify coherent behavior in flows directly from Lagrangian trajectory data, such as obtained from particle tracking algorithms. In this context, spatio‐temporal clustering algorithms have been proven to be very effective for the extraction of coherent sets from sparse and possibly incomplete trajectory data. Inspired by these recent approaches, we consider an unweighted, undirected network, in which Lagrangian particle trajectories serve as network nodes. A link is established between two nodes if the respective trajectories come close to each other at least once in the course of time. Classical graph algorithms are then employed to analyze the resulting network. In particular, spectral graph partitioning schemes allow us to extract coherent sets of the underlying flow. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Discontinuous Galerkin (DG) method in 3D linear elasticity with application in problems with locking
Authors: Bayat Hamid Reza , Kastian Steffen , Wulfinghoff Stephan , Reese Stefanie
Published: March 2018

In the present work, a three‐dimensional discontinuous Galerkin (DG) formulation is presented and investigated for linear elastic problems, with special emphasis on locking phenomena. Among different variations of DG methods, the incomplete interior penalty Galerkin (IIPG) method is applied here, where the symmetry term is absent and the approach is stable through the application of a penalty term. Different examples are calculated to investigate the locking behavior of the DG method compared to continuous Galerkin (CG) method. Additionally, A locking‐free 3D element formulation based on reduced integration and hourglass stabilization (Q1SP) is applied to compare and evaluate the results of the DG formulation in both shear and volumetric locking‐dominated problems. Due to the discontinuity of the DG elements, a new meshing approach is applied in the finite element analysis program FEAP. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
POD‐based multiobjective optimal control of PDEs with non‐smooth objectives
Authors: Beermann Dennis , Dellnitz Michael , Peitz Sebastian , Volkwein Stefan
Published: March 2018

A framework for set‐oriented multiobjective optimal control of partial differential equations using reduced order modeling has recently been developed [1]. Following concepts from localized reduced bases methods, error estimators for the reduced cost functionals are utilized to construct a library of locally valid reduced order models. This way, a superset of the Pareto set can efficiently be computed while maintaining a prescribed error bound. In this article, this algorithm is applied to a problem with non‐smooth objective functionals. Using an academic example, we show that the extension to non‐smooth problems can be realized in a straightforward manner. We then discuss the implications on the numerical results. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polymorphic uncertainty quantification for stability analysis of fluid saturated soil and earth structures
Authors: Henning Carla , Ricken Tim
Published: March 2018

Nowadays, numerical simulations enable the description of mechanical problems in many application fields, e.g. in soil or solid mechanics. During the process of physical and computational modeling, a lot of theoretical model approaches and geometrical approximations are sources of errors. These can be distinguished into aleatoric (e.g. model parameters) and epistemic (e.g. numerical approximation) uncertainties. In order to get access to a risk assessment, these uncertainties and errors must be captured and quantified. For this aim a new priority program SPP 1886 has been installed by the DFG which focuses on the so called polymorphic uncertainty quantification. In our subproject, which is part of the SPP 1886 (sp12), the focus is driven on quantification and assessment of polymorphic uncertainties in computational simulations of earth structures, especially for fluid‐saturated soils. To describe the strongly coupled solid‐fluid response behavior, the theory of porous media (TPM) will be used and prepared within the framework of the finite element method (FEM) for the numerical solution of initial and boundary value problems [2, 3]. To capture the impacts of different uncertainties on computational results, two promising approaches of analytical and stochastic sensitivity analysis will enhance the deterministic structural analysis [6–8]. A simple consolidation problem already provided a high sensitivity in the computational results towards variation of material parameters and initial values. The variational and probabilistic sensitivity analyses enable to quantify these sensitivities. The variational sensitivities are used as a tool for optimization procedures and capture the impact of different parameters as continuous functions. An advantage is the accurate approximation of the solution space and the efficient computation time, a disadvantage lies in the analytical derivation and algorithmic implementation. In the probabilistic sensitivity analysis from the field of statistics, the expense only increases proportionally to the problems dimension. Instead of a constant value, the model parameters are defined as probability distribution, which provides random values. Thus, a set of solution data is built up by several cycles of the simulation. Different approaches of the Bayes statistics will enable to receive accurate information with just a few simulations. The overall objective is the development of more efficient methods and tools for the sizing of earth structures in the long‐run. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A phase‐field approach to pneumatic fracture
Authors: Bilgen Carola , Kopaničáková Alena , Krause Rolf , Weinberg Kerstin
Published: March 2018

Phase‐field methods for brittle fracture employ a variational framework and have proven to predict complex fracture patterns in two and three dimensional examples. This contribution focuses on a phase‐field approach for a coupled field model of brittle pneumatic fracture. Two different challenges are tackled in this contribution: First, we have to deal with pressure‐driven processes within the proposed phase‐field ansatz, second, we have to consider the numerical effort of the simulations.

Our phase‐field formulation is based on elasticity and a suitable operator split to take only the tensile parts into account. Furthermore, a prescribed pressure is coupled with the phase‐field parameter to consider crack propagation induced by pneumatic pressure. To keep the numerical effort as small as possible we apply a specifically developed multigrid method for three‐dimensional problems. The accuracy and the robustness of the solution method will be demonstrated with a series of numerical examples. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetohydrodynamic flows in liquid metal blankets for fusion reactors
Authors: Mistrangelo Chiara , Bühler Leo
Published: March 2018

Liquid metal blankets will be tested in the experimental fusion reactor ITER. Three main concepts are currently under development. In the water‐cooled and in the helium‐cooled lead lithium blankets the PbLi alloy serves only as breeder material for producing the fuel component tritium used to generate the magnetically confined fusion plasma. The fusion heat is removed by a separated water or helium cooling system and therefore the liquid‐metal could be practically at rest. However, for tritium extraction and liquid metal purification a weak circulation (1 mm/s) is required. Instead in the dual coolant lead lithium blanket the liquid metal serves both to produce tritium and to remove the volumetric heat deposited in the breeding zone, while helium is employed to cool first wall and blanket structure. In this concept PbLi has to flow faster (10 cm/s) than in the separately cooled blanket designs to allow efficient cooling of the breeding zone.

In all liquid metal blankets there are issues related to the specific characteristics of the liquid metal. The interaction of the electrically conducting fluid with the strong magnetic field induces electric currents and electromagnetic forces that influence velocity and pressure distribution in the blanket. Lorentz forces are balanced by pressure gradients and these additional magnetohydrodynamic (MHD) pressure losses are proportional to the electric current density induced in the fluid. The electrical coupling of adjacent fluid domains that results from the presence of leakage currents crossing common conducting walls, has also to be taken into account. Two examples of MHD flows typical in fusion blankets are discussed in this paper. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The DRESDYN project: planned experiments and present status
Authors: Stefani Frank , Eckert Sven , Gerbeth Gunter , Giesecke André , Gundrum Thomas , Räbiger Dirk , Seilmayer Martin , Weier Tom
Published: March 2018

The Dresden sodium facility for dynamo and thermohydraulic studies (DRESDYN) is a platform for large‐scale liquid sodium experiments devoted to fundamental geo‐ and astrophysical questions as well as to various applied problems related to the conversion and storage of energy. Its most ambitious part is a precession driven dynamo experiment, comprising 8 tons of liquid sodium supposed to rotate with up to 10 Hz and to precess with up to 1 Hz. Another large‐scale set‐up is a Tayler‐Couette experiment with a gap width of 0.2 m and a height of 2 m, whose inner cylinder rotates with up to 20 Hz. Equipped with a coil system for the generation of an axial field of up to 120 mT and two different axial currents through the center and the liquid sodium, this experiment aims at studying various versions of the magnetorotational instability and their combinations with the Tayler instability. We discuss the physical background of these two experiments and delineate the present status of their technical realization. Other installations, such as a sodium loop and a test stand for In‐Service‐Inspection experiments will also be sketched. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimized simulation of multiscale problems on high‐performance computers
Authors: Schlottke‐Lakemper Michael , Yu Hans , Berger Sven , Meinke Matthias , Schröder Wolfgang
Published: March 2018

Classic hybrid computational fluid dynamics ‐ computational aeroacoustics simulations rely on disk I/O to exchange large volumes of data between the flow solver and the aeroacoustics solver, which considerably limits the scalability of the overall scheme. A direct‐hybrid method is presented that eliminates this restriction by executing both solvers simultaneously on a joint hierarchical Cartesian mesh. Simulation results for a pair of co‐rotating vortices show the parallel efficiency of the approach. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Challenges in Modeling Flexible Bodies based on Experimental Data with Utilization in Elastic Multibody Simulation
Authors: Lein Claudius , Beitelschmidt Michael , Woller Johannes
Published: March 2018

The Elastic Multi‐Body Simulation (EMBS) is the state‐of‐the‐art method when dealing with elastic deformations of components in complex mechanical systems. But the required FE‐model representing the elastic structure contains several uncertainties concerning geometry, local and directional stiffness as well as damping phenomena. A mandatory Model Order Reduction (MOR) embodies further approximation errors. Due to the drawbacks of the conventional procedure, a novel approach is suggested, where the data of the elastic body model is directly gained from the results of an Experimental Modal Analysis (EMA). Therefore, the measured data is transferred to the Standard Input Data (SID) format by means of the software MORPACK (Model Order Reduction PACKage). The novel approach yields several challenges for which adequate solutions are presented. The feasibility is demonstrated at the example of an U‐section. The accuracy in the higher frequency range can be increased, which is especially important for vibro‐acoustic simulations. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Real‐time Trajectory Tracking of a Cable‐driven Parallel Robot Using Servo‐constraints
Authors: Otto Svenja , Seifried Robert
Published: March 2018

Cable robots are widely applicable for various industrial tasks, where accurate trajectory tracking of the end‐effector is an essential control objective. This is especially challenging for underactuated cable robots since they possess less actuators than degrees of freedom. Trajectory tracking can be achieved by using an inverse model based on servo‐constraints. It is possible to solve the DAE problem in real‐time, which makes an implementation on experimental setups straightforward. Stabilization of the tracking error can be achieved by a feedback controller which augments the feedforward loop in a two degree of freedom control structure. Effectiveness of the described method is shown in experiments on a cable robot test bench. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parameter Identification of Non‐Holonomic Omnidirectional Vehicles using a Redundantly Parameterized Model
Authors: Stöger Christoph , Gattringer Hubert , Müller Andreas
Published: March 2018

This paper presents a method for the identification of inertia parameters of non‐holonomic omnidirectional (NHO) vehicles. NHO vehicles use several centered steerable standard wheels for their movement. They are omnidirectional in the sense that they are able to drive in each direction but may have to steer the wheels before starting the motion. A precise knowledge of the inertia parameters of such vehicles is e.g. mandatory for the application of model‐based control approaches. The presented identification approach enhances a classic strategy consisting of the following steps: formulate the motion equations linear w.r.t. inertia parameters, determine uniquely identifiable (base) parameters, and plan an optimal excitation trajectory for the experiment, that is applicable to mobile robotic systems with non‐holonomic (NH) constraints and locomotion limits. The overall approach is validated by experiments and yields promising results. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A robot inspired by a non‐smooth point mass model of a worm
Authors: Winandy Tom , Eugster Simon R. , Bergold Markus
Published: March 2018

A non‐smooth point mass model which mimics the locomotion of an earthworm is presented. The planar model consists of a chain with five elements on a rough ground. The distance between each pair of neighbouring elements is restricted by unilateral constraints. The contacts between the elements and the ground are subjected to anisotropic Coulomb friction. First, the equations of motion governing the impact‐free motion are derived. Then, the impact equations are formulated which, together with the generalized Newton's impact law, describe the dynamics at instantaneous impacts. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Assessment of the high‐cycle fatigue performance of a PEEK‐based spinal dynamic instrumentation using numerical simulation and experimental data
Authors: Beckmann Agnes , Ma Songyun , Stoffel Marcus , Markert Bernd
Published: March 2018

A lumbar spine model with a PDSD was created using CT data and validated with experimental results of the same specimen. The material parameters of the spine and the stabilisation device were taken from literature and calibrated using experimental data. A fatigue model accounting for notch effect and cyclic plastic deformation was used to predict the fatigue life of the device regarding high‐cycle loading and material softening of PEEK. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A key to high‐amplitude movement synthesis: the muscle lever arm
Authors: Hammer Maria , Günther Michael , Haeufle Daniel F. B. , Schmitt Syn
Published: March 2018

Pulling actuators play an important role in biomechanical simulations. In most animals, muscles are the actuators exerting torques onto the joints. These torques highly depend on the muscle line of action or, in other words, muscle lever arms. Common methods focus either on single‐joint movements, on two‐dimensional problems, or on imitating physiological lever arms only in a small working range. However, especially in complex multibody simulations, where reduced descriptions of muscles as massless, visco‐elastic, active bands are used, a correct representation of lever arms is mandatory for a large range of joint angles for all degrees of freedom. To address these issues, we developed a new design and computational algorithm for modeling the path of linear pulling actuators. The method is based on finding the shortest muscle path while the actuator is lead through a small number of two‐dimensional shapes. It allows for multiple degree of freedom and high‐amplitude movements as well as combinations of both, ensuring reasonable lever arms at all possible joint configurations even for muscles spanning more than one joint. We applied this method to a multibody model of the human musculoskeletal system. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Method for the Development of Realistic Boundary Conditions for the Simulation of Non‐Contact Tonometry
Authors: Muench Stefan , Balzani Daniel , Roellig Mike , Spoerl Eberhard
Published: March 2018

The aim of the study presented here, is to understand and characterize the air puff generated by a non‐contact tonometer (NCT). Therefore, we propose a method to experimental calibrate a computational fluid dynamic (CFD) model of an eye examined with a Corvis ST. The time dependence of the nozzle pressure was found to be equal to the pressure measured by a device intern sensor. However, the maximum pressure identified at the nozzle inlet reaches approximately 25 kPa. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards a virtual mechanical human brain
Authors: Wagner Arndt , Fink Davina , Schröder Patrick , Ehlers Wolfgang
Published: March 2018

It is supposed that the vision of an integrated Overall Human Model (OHM) can be realised by the combination of isolated models. By this means, a so‐called OHM‐toolbox contains these models, which need to be extended and/or linked to each other depending on the chosen application. However, this implies the need to bridge over several length and time scales as well as to combine different physical effects and numerical approaches. In this regard, the proposed contribution is related to the description of one part of this toolbox, namely, the overall mechanical behaviour of human brain tissue. As an application‐driven organ model, it can substantially contribute to a holistic understanding of various complex processes, such as the study of brain‐tumour treatment. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Molecular dynamics simulations of the cooling rate influence on the tensile strength of silica glass
Authors: Ebrahem Firaz , Markert Bernd
Published: March 2018

Classical molecular dynamics (MD) simulations are performed to study the stress‐strain behaviour of armorphous silica glass (a‐SiO2) at small time and length scales. Various amorphous states are generated by quenching molten SiO2 using a two‐body and a three‐body interaction potential. This quenching process is carried out for different cooling rates. The structural properties of a‐SiO2 are validated through a comparison with other numerical and experimental results. Finally, tensile tests are performed on a‐SiO2 until fracture occurs, and the cooling rate influence on the tensile strength is analysed. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A phase‐field approach to fracture coupled with mass transport for the simulation of environmentally‐assisted damage
Authors: Falkenberg Rainer
Published: March 2018

With the introduction of a mass transport mechanism the entire problem is subjected to a time frame that dictates the time‐dependent action of soluted species on mechanical properties. A numerical framework within the phase‐field approach is presented with an embrittlement‐based coupling mechanism. The underlying functionals are expressed in terms of the displacement, mass concentration and crack phase‐field. Within the phase‐field approach the modelling of sharp crack discontinuities is replaced by a diffusive crack model facilitating crack initiation and complex crack topologies without the requirement of a predefined crack path. The isotropic hardening of the elasto‐plastic deformation model and the local fracture criterion are affected by the species concentration. This allows for embrittlement and leads to an accelerated crack propagation. An extended mass transport equation for hydrogen embrittlement, accounting for mechanical stresses and deformations, is implemented. For stabilisation purposes a staggered scheme is applied to solve the system of partial differential equations by a multi‐field finite‐element method. A thermodynamically consistent coupling relation that accommodates the required mechanisms is presented. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental and numerical study of glass fracture using J‐integral and phase‐field modelling approaches
Authors: Li Ziyuan , Heider Yousef , Markert Bernd
Published: March 2018

In this contribution, an experimental study and FE simulations based on J‐integral theory and the phase‐field modelling approaches are presented in order to systematically study the temperature and strain‐rate dependency of glass fracture behaviour. First, a series of three‐point bending tests are successfully carried out under different stain‐rates and temperatures. Secondly, numerical modelling of the bending tests with the introduction of a micro crack yields the stress‐strain response, which serves to the calculation of J‐integral values, in order to describe the glass fracture resistance in terms of energy. At the end, the critical energy release rate serves as a bridge connecting the J‐integral theory with the phase‐field modelling, where a dynamic fracture model with crack propagation is realised as a new direction for further researches. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
3D Fracture Modeling by Extended Finite Element Method and Gradient Enhanced Damage
Authors: Pezeshki Mahmoud , Loehnert Stefan , Wriggers Peter
Published: March 2018

A combined continuous‐discontinuous approach to fracture is presented to model crack propagation in 3D. The damage evolution governs the discrete crack advancement and the direction of the crack propagation. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Implementation of a dissipation based path‐following method and its application to the simulation of nonlocal quasi‐brittle damage
Authors: Prüger Stefan , Balzani Daniel
Published: March 2018

The implementation of a path‐following method for the simulation of quasi‐brittle failure is discussed, which employs a constraint function based on the overall dissipation increment associated with the softening material. Spurious mesh‐dependency is avoided by a nonlocal integral formulation of the isotropic damage model. The performance of the method is illustrated for a one‐dimensional bar problem in which snap‐back behavior is observed immediately after damage initiation. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromechanical Damage Modeling of Long Fiber Reinforced Composites With the Parametric Method of Cells
Authors: Schmerbauch Mario , Erler Felix , Matzenmiller Anton , Levi‐Sasson Aviad , Haj‐Ali Rami , Aboudi Jacob
Published: March 2018

Micromechanical damage modeling is presented with the parametric high‐fidelity generalized method of cells for a long fiber reinforced composite. Two models for a planar single fiber repeating unit cell, including damage, are proposed. The first one, implemented with the spatial continuum damage mechanics, is based on the idea that volumetric defects occur in the material phases. The other one, modeled with the interface damage mechanics, is founded on the view that cracks as surface‐like de‐ fects cause the stress degradation. The potential and ability of both approaches to predict damage in first‐order homogenization is shown by comparing the simulation results with each other as well as with test data under uniaxial and biaxial stress loading. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A continuum model for intralaminar damage progression and delamination in layered composites
Authors: Höwer Daniel , Stier Bertram , Bednarcyk Brett A. , Fish Jacob , Reese Stefanie , Simon Jaan‐Willem
Published: March 2018

The accurate prediction of progressive damage is one of the key challenges in the design of layerd composites. To this end, a continuum damage model has been proposed recently, which can account for both inter‐ and intralaminar damage. This is accomplished by a modification of the damage interaction parameters. The procedure is applied to the example of a [0/90/0] carbon fiber reinforced cross‐ply. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of crack growth under mixed‐mode loading in 1D piezoelectric quasicrystals
Authors: Wang Zhibin , Ricoeur Andreas
Published: March 2018

Lacking translational symmetry in particular directions, quasicrystals (QC) are a new class of materials besides crystals and amorphous solids, where 1D means the atomic arrangement is quasiperiodic in one direction. Since the very first discovery in 1982, QCs have been implemented in many fields due to their peculiar properties. This work adopts the generalized linear elastic framework of fracture theory in quasicrystals and develops numerical tools to compute fracture quantities and crack growth paths. Under the intrinsic mixed‐mode loading, crack growth in several specimens is simulated and the influences of the phonon‐phason coupling effect as well as the electric field are investigated. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermally loaded elastic‐plastic shrink fit with FGM‐hub
Authors: Apatay Tunç , Arslan Eray , Mack Werner
Published: March 2018

Subject of the investigation is an elastic‐plastic shrink fit with solid inclusion and functionally graded hub in a state of generalized plane strain. It is shown that by appropriate grading a substantial weight reduction while maintaining a satisfactory performance at elevated temperature during operation can be achieved. In particular, numerical results are given for a steel/aluminum FGM‐hub. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Advanced Rebar Formulation within a Thermo‐Mechanically Coupled Tire Simulation
Authors: Berger Thomas , Kaliske Michael
Published: March 2018

As shown in various experiments, coupling between the thermal and the mechanical field of a rolling tire in contact with a rigid surface can be observed. An increase of its temperature over time when rolling with a constant velocity can be seen. This phenomenon is caused by the viscoelastic material properties, where the dissipated energy will lead to a heating of the rubber. Also the constitutive behaviour will change, when the temperature increases. A nonlinear viscoelastic material model is chosen to model an amplitude dependency of the time dependent behaviour of the rubber, proposed by Bergström and Boyce [1].

Another important part of a tire are the reinforcements, which are embedded inside the rubber. These consist mostly of steel or polyester. These materials are not known for a dissipative behaviour and will not contribute to the heating of the tire. However, they also change their properties with increasing temperature and have a significant influence on the overall tire properties. Even without a contribution to the heating, the reinforcements will change its conductivity and have to be taken into account.

For an accurate and efficient way to model the thermo‐mechanical coupling, an in‐house framework [2] will be presented, by use of the Arbitrary Langrangian Eulerian formulation and a commercial code. It is assumed, that the temperature in circumferential direction will stay constant and instant coupling effects are negligibly small. Therefore, the problem is split into a thermal and a mechanical part, and the coupling quantities (dissipated energy and temperature) are updated in a sequential manner.

A common practise to model the reinforcements in tires is to use smeared layers, which leads to some difficulties. First of all, the modelling is only valid for a really small spacing between the bars. Another problem is, that the smeared layers have to fit with the nodes of the rubber matrix. Because of that, the mesh has to be refined, which leads to an increasing computation time and can cause numerical difficulties, due to too small elements.

In this contribution, a different way of modelling the rebars within a thermo‐mechanical coupled algorithm is presented without the assumption of a smeared layer and treat them as single rebars. In numerical examples, the advantages of the proposed method are presented and the difference to the classical approach is shown. Also, the influence of the reinforcements on the stiffness, heat generation and rolling resistance of the tire, will be discussed. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A machine‐learning approach to load‐monitoring based on guided waves
Authors: Hesser Daniel F. , Markert Bernd
Published: March 2018

The research field of structural health monitoring (SHM) describes the way to assess the structural integrity. The research objectives are broadly diversified, which are all addressing the improvement of SHM technologies. It is important to optimise the capability of sensor networks by applying intelligent signal processing models. These intelligent systems predict the health state based on acquired data in a real‐time environment. Piezoelectric sensor networks and guided‐wave based analyses are combined with machine learning to create an efficient load‐monitoring routine. This load‐monitoring approach is chosen to track any changes in the environmental conditions, which causes most of the problems in reference signal based damage detection. Therefore, the proposed load‐monitoring method can be used to compensate the influence of external changes on the acquired signals and improve the performance and robustness of future SHM systems. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the electromechanical coupling in rotordynamics of electrical machines
Authors: Boy Felix , Hetzler Hartmut
Published: March 2018

In this contribution the modelling of electromechanical interactions in electrical machines is revised and analysed. Based on Lagrange's equations of the second kind, approaches from literature are classified concerning the coupling between mechanical motion and electrical system behaviour. It is shown, that the modelling has a significant influence on the assessment of oscillations. This circumstance is shown investigating self‐excited oscillations in a 2‐pole asynchronous machine. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A note on a double‐serial switch‐spring‐parallel semi‐active connection element
Authors: Dahlmann Martin , Min Chaoqing , Sattel Thomas
Published: March 2018

Subject is a semi‐active connection element consisting of two identical subsystems in series. Each subsystem is composed of one spring and one switch in parallel. The switch can prevent spring movement when closed. Thus, the potential energy in the spring is stored. The use of two subsystems in series allows to direct power from extension and compression into different springs, yielding two spring forces with different directions. Due to the mass inertia, fast switching between the two spring forces controls the position of a connected mass. Thus, the semi‐active connection element behaves similar to an actuator with the limitation that the average work vanishes. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase Field Modeling of Ductile Fracture in Soil Mechanics
Authors: Aldakheel Fadi , Kienle Daniel , Keip Marc‐André , Miehe Christian
Published: March 2018

This work outlines a rigorous framework for the ductile failure of frictional materials in elastic‐plastic soil mechanics undergoing large strains. Describing soil crack formation can be achieved in a convenient way by recently developed continuum phase field approaches to fracture, which are based on the regularization of sharp crack discontinuities [1]. This avoids the use of complex discretization methods for crack discontinuities, and can account for complex crack patterns. For frictional materials, a non–associative Drucker–Prager‐type elastic‐plastic constitutive model suitable for a wide range of applications in soil mechanics is developed. It is linked to a failure criterion in terms of the elastic‐plastic work density that drives the fracture phase field. We demonstrate the modeling capabilities and algorithmic performance of the proposed formulation by a representative numerical example that describes soil crack formation using elastic‐plastic fracture mechanics. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phenomenological modelling of curing phenomena in a PU based adhesive
Authors: Landgraf Ralf , Ihlemann Jörn
Published: March 2018

In this contribution, the phenomenological material modelling of a polyurethane based adhesive including the curing process is considered. First, the underlying chemical process is regarded. To this end, differential scanning calorimetry experiments were carried out, models for the reaction heat and a so called degree of cure were formulated, and the corresponding model parameters were identified. Moreover, uniaxial tension tests with cyclic loading scenarios on the fully cured material were conducted and revealed typical behaviour of elastomers, like hysteresis, Mullins effect and permanent set. Based on the experimental results, a constitutive model has been formulated to capture the mechanical behaviour of the material in the fully cured state. Finally, an approach to capture changes of the mechanical behaviour during the curing process has been realized. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Automated modeling of nickel‐based superalloys
Authors: Munk Lukas , Beese Steffen , Reschka Silvia , Wriggers Peter
Published: March 2018

Throughout the last 60 years, nickel (Ni) based superalloys have been the standard high‐temperature material used in mobile and stationary gas turbines. The ever increasing temperatures necessitate further improvements of those alloys, foremost, enhancing their creep‐resistance. Creep denotes a macroscopic, permanent change of shape which, amongst other effects, stems from thermally and mechanically induced dislocation movement. The key microstructural feature of most modern alloys is a uniform distribution of particles of the L12‐ordered γ′ phase which are embedded into the nickel‐based matrix. Most importantly, these particles are impenetrable to matrix‐dislocations. This leads to numerous dislocation effects encountered in such microstructured alloys. A wealth of different material modeling‐approaches exists in the literature which try to capture creep behavior. Due to the multiscaled nature of the physical problem, most crystal plasticity approaches are phenomenological and, thus, rely on many parameters. Finding suitable constitutive equations that capture experimental results becomes a challenge. A large deformation crystal plasticity framework has been set up which allows for an efficient comparison of different material formulations. This has been achieved by the use of AceGEN. The analytically generated tangent‐subroutine is linked into a FEAP polycrystal plasticity model and thus, global quadratic convergence is reached. In future work, a variety of flow rules, dislocation density based (cross‐) hardening formulae and parameters can be studied in a unified way [6]. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical modeling of dynamic recrystallization in polycrystals
Authors: Nguyen Hai Van , Ebrahimzade Vahid , Hackl Klaus , Renner Jörg , Trinh Bach Tuyet
Published: March 2018

This paper is devoted to developing a mathematical model of dynamic recrystallization phenomena based on the earlier work of K. Hackl and J. Renner [1] for polycrystalline materials. In this model a variational approach employing a distribution function for dynamic recrystallization processes of polycrystalline materials is presented. It is based on a marching algorithm at the microscale as well as a homogenization procedure to arrive at the macroscale. The newly proposed theory is now used to improve the variational approach. Then this theory is applied within the homogenization procedure. A comparison of the present model with existing phenomenological ones is given. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Modeling of Memristive Material Behavior in the Context of the Finite Element Method
Authors: Obst Jonathan , Franze Andreas , Balzani Daniel
Published: March 2018

Since HP‐Labs developed the first memristor as a technical device in 2008 (cf. [1]), electrical engineers are aware of its potential of revolutionizing electronics (cf. [2]). As analogies have a long tradition in various fields of science it is quite obvious to transfer the idea of the memristor in electric circuit theory to mechanics by electro‐mechanical analogies. This transfer already led to a generalized classification of devices for dynamical systems [3]. In particular, a mechanical memristor for a system with one single degree of freedom is a displacement‐dependent dashpot.

To investigate the behavior of continuous solids which show memristive properties, the development of suitable three‐dimensional material models is desired. Thus, this paper investigates the implementation of a memristive material model in the context of the Finite Element Method. Therefore, one‐dimensional memristive material models are analyzed and a continuum‐mechanical, memristive material model is developed based on an adaption of the KELVIN‐VOIGT‐Model. Example problems are simulated to verify the characteristics of this material class. In particular, the slipknot‐shaped hysteresis of the stress‐strainrate‐curve and the memory effect can be shown. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An explanation of damage and failure in cellulose aerogels: modeling approach
Authors: Rege Ameya , Itskov Mikhail
Published: March 2018

Cellulose aerogels can be considered as foam‐like materials and have recently been modeled using micro‐mechanical approaches. The proposed microcell based models describe the constitutive response of these aerogels based primarily on the bending of the cell wall fibrils, and show good agreement with experimental data. Under compression, the cell walls are considered to undergo nonlinear bending. On the other hand, under tension the deformation in the cell walls is attributed to both, bending and stretching. Accordingly, the total aerogel network energy is divided into a bending one and a tension one. The cell walls undergoing such combined loading fail after reaching a critical normal stress value, and are then considered to no longer contribute to the total network energy. Material constants in these models are obtained from experimental observations, like for example, the pore‐size data analysis, thus resulting into physically motivated models. Finally, the models are also shown to be effective in predicting the constitutive response of other polysaccharidic aerogels. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of large strain creep with static and dynamic recovery under cyclic loading conditions
Authors: Shutov Alexey , Larichkin Alexey , Shutov Valeriy
Published: March 2018

A new material model of finite strain metal creep is proposed. Transient effects occurring shortly after abrupt changes of the applied stress are captured by the model using the concept of nonlinear kinematic hardening. The evolution of the backstress tensor is affected by the static and dynamic recovery. In order to broaden the applicability range, the model includes the classical Kachanov‐Rabotnov damage evolution. Large strain kinematics is described using the assumption of a nested multiplicative split. The model is thermodynamically consistent, objective, and w‐invariant. The model is validated in MSC.MARC, basing on experimental data for the D16T aluminium alloy. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Grain boundary kinetics in polycrystalline material using orientation dependent interface energy
Authors: Khan Asim Ullah , Hackl Klaus , Baitsch Mattias
Published: March 2018

The Polycrystalline materials grain boundary structure, crystalline texture and grain surface morphology, each plays an important role in interface transport. Among the different surface evolution phenomenas, the objective of the current work is to study the kinetics of grooving by surface diffusion only. Most of the existing theoretical and computational models use two dimensional grooving with one dimensional surface evolution. Hackl, et al. [2] have presented a novel variational model of surface motion using a thermodynamic extremum principle for grooving and wetting under diffusion. This model is further extended to a three dimensional grain structure using two dimensional surface evolution [1].In this paper, the kinetics of grooving for a periodic polycrystalline aggregate is studied. An ansatz function for grain boundary energy is defined as a functional of grain orientation and boundary inclination. For such orientation dependent grain boundary energy, Herring's relation must be satisfied locally at each triple point of intersecting boundaries thus we have four equations at each node in a representative volume element(RVE). Such an overdetermined system is solved using a non‐linear optimization method with weak constraints for the grain boundary energies. The evolution of surface grooves is studied with isotropic surface energy and mobility. The effect of line mobility on surface evolution is also studied for the chosen RVE. A comparison is made between orientation dependent grain boundary energies and isotropic grain boundary energies. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of cyclic deformation behaviour of railway disc brakes under thermomechanical loading
Authors: Zhang Le , Ma Songyun , Markert Bernd
Published: March 2018

Metallic materials of railway disc brakes exhibit viscoplastic deformation behaviour under cyclic thermomechanical loadings. In this study, a viscoplastic Chaboche model is applied to describe the inelastic deformation behaviour in the braking process incorporating the inhomogeneous variation of temperature. The rate‐dependent hardening behaviour of 28CrMoV5‐8 steel is modelled by employing combined nonlinear isotropic and kinematic hardening rules. Furthermore, a numerical integration algorithms of the constitutive model is developed by using the implicit backward Euler method. The constructed nonlinear algebraic equations are solved by coupling the improved Pegasus method [4] and Newton method. The proposed model is implemented in the finite element code ABAQUS via a user‐defined material subroutine (UMAT). Finally, finite element simulations including sliding friction and heat transfer between disc and pads are performed for the case of an emergency braking. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerische Strömungsanalyse von Kraftwerkstrennpfeilern unter Verwendung von RANS‐Turbulenzmodellen
Authors: Alfarra Anas , Seidel Christian , Ostermann Lars
Published: March 2018

Bei der Entwicklung von Wasserkraftanlagen ist die numerische Strömungsanalyse ein wichtiges Werkzeug für die Kraftwerksoptimierung. Auf Grund ihrer Effizienz und weitverbreiteten Anwendung im Wasserbau sind hierbei die numerischen Verfahren auf Basis von Flachwassergleichungen von besonderem Interesse. In [1] wurde das Potenzial solcher Verfahren bei der Optimierung der Strömung um Kraftwerkstrennpfeiler erfolgreich aufgezeigt und Optimierungskriterien herausgearbeitet sowie der Nachweis erbracht, dass die qualitative Formoptimierung mit Flachwassergleichungen möglich ist. Die Frage nach dem Turbulenzeinfluss stellt in diesem Kontext einen interessanten Aspekt dar, weshalb am Beispiel des Kraftwerktrennpfeilers dieser mittels eines RANS‐Turbulenzmodelles [2] für eine geschlossene Kanalströmung untersucht und mit den Ergebnissen in [1] und [4] verglichen wird. Die Unterschiede beider Modellansätze werden herausgearbeitet, der Einfluss der Turbulenz erklärt und die ermittelten Optimierungskriterien hinsichtlich ihrer Gültigkeit auch bei Berücksichtigung der Turbulenz überprüft sowie die durch den Turbulenzeinfluss verursachten Strömungsphänomene aufgezeigt. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary element and finite element analysis for the efficient simulation of fluid‐structure interaction and its application to mold filling processes
Authors: Harmel Maximilian , Sauer Roger A.
Published: March 2018

Metal casting and polymer molding are widely used for the economical shape processing of complex geometries. In these manufacturing processes, a liquid melt (metal, mineral or synthetic) is filled into a mold with a cavity of the desired shape. Cooling and solidification of the melt results in a product with almost the same shape as the cavity. Numerical simulations can be employed to increase the accuracy of the process. To this end, boundary element method for Stokes flow and a finite element formulation for liquid membranes are investigated in this work. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical study on the fluid‐structure interaction in a model aquatic canopy flow
Authors: Meller Richard , Tschisgale Silvio , Fröhlich Jochen
Published: March 2018

This work presents numerical simulations and selected results of the flow over aquatic canopies, consisting of artificial flexible rectangular blades, arranged in a well‐defined order. The results obtained with three different Reynolds and Cauchy numbers are compared with experimental data achieving good agreement. The considered range of Cauchy numbers represents three different types of canopies ranging from rigid up to highly flexible plants. The transient flow data and blade positions are statistically analyzed to gain deeper understanding of the complex physical processes for this kind of fluid structure interaction. For example, the correlation of role of large scale motion of the flexible blades in conjunction with coherent vortex structures of the flow is addressed. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and simulation of magnetorheological elastomers: A comparison of continuum and dipole approaches
Authors: Metsch Philipp , Romeis Dirk , Saphiannikova Marina , Kästner Markus
Published: March 2018

In the present work, a comparison of the results of a microscale continuum and a dipolar mean‐field approach with regard to their predictions for the magnetostrictive response of magnetorheological elastomers is presented. It turns out that – for random, isotropic microstructures – there is a very good agreement between both modeling strategies. This is in contrast to former comparisons of continuum and other dipole approaches, which have shown considerable deviations. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)