bluuebunny/crossref_metadata_2025_split huggingface dataset:
Trajectory‐based computational study of coherent behavior in flows
Authors: Padberg‐Gehle Kathrin , Schneide Christiane 
Published: March 2018

AbstractThe 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

AbstractIn 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

AbstractA 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

AbstractNowadays, 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

AbstractPhase‐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

AbstractLiquid 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

AbstractThe 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

AbstractClassic 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

AbstractThe 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

AbstractCable 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

AbstractThis 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

AbstractA 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

AbstractA 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

AbstractPulling 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

AbstractThe 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

AbstractIt 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

AbstractClassical 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

AbstractWith 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

AbstractIn 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

AbstractA 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)