bluuebunny/crossref_metadata_2025_split huggingface dataset:
Automatic generation of material laws based on rheological models using a genetic algorithm
Authors: Wulf Hans , Kießling Robert , Gypstuhl Richard , Ihlemann Jörn 
Published: November 2019

AbstractDeveloping material laws based on rheological models is an established method in the field of material modelling. Here, the identification of an appropriate rheological model fitting a given set of experimental data is often a challenging task. This contribution presents an automated method for searching such rheological models. To this end, a tree representation for rheological models is defined first. Then, a generic material law, that can implement any rheological model given by a model tree, is introduced. Based on this, a genetic algorithm is used to generate rheological models, which are subsequently evaluated by fitting to measurements. This methods allows to search for a global optimum in the space of material models. Successful applications to both synthetic and actual experimental data are demonstrated.
Application of Artificial Neural Network accelerating a porous media FE2 homogenization scheme
Authors: Bartel Florian , Ricken Tim , Schröder Jörg , Bluhm Joachim 
Published: November 2019

AbstractMultiscale techniques, which include information of discrete lower level substructures of real material, are state of the art methods of current researches. This technology has the advantage of achieving more accurate results, by imaging the real geometry information from the microscopic level. In addition, it provides the opportunity to design a certain microstructure which fulfills the specific requirements at a macroscopic level. The drawback lies on the increasing computational effort. Simulation of a 3‐dimensional, nonlinear, time‐dependent, coupled, two‐scale problem with industrial relevance, could cause unacceptable runtimes. There are several strategies to overcome this disadvantage, such as parallelization, analytical derivatives and various surrogate models. This contribution shows the feasibility of storing microstructural information in an Artificial Neural Network, in order to reduce computational runtime.
Reduced‐order FFT‐based homogenisation by tensor approximation
Authors: Liu Dishi , Vondřejc Jaroslav , Ladecký Martin , Matthies Hermann 
Published: November 2019

AbstractWe enhanced the efficiency of Fast Fourier transform (FFT) based Galerkin methods on numerical homogenisation problems by exploiting low‐rank tensor approximations in canonical, Tucker, and tensor train formats. This leads to a significant reduction in computational complexity and memory requirement. The advantages of the approach are demonstrated in a numerical example of a model homogenisation problem with stochastic heterogeneous material coefficients.
On VOIGT and KELVIN Matrix Notations of Second‐Order Tensors
Authors: Schlebusch Rainer 
Published: November 2019

AbstractThe implementation of constitutive models into a computer software necessitates the conversion of abstract tensors into real numbers that can be processed by a computer. This is accomplished (1) by introducing a basis, and (2) by arranging the scalar tensor components into matrices. In literature, such conversion processes are often used ad hoc without any rigorous mathematical derivation or justification. Probably most prominent are the VOIGT and KELVIN matrix notations. These matrix notations use existing symmetries of the tensors and allow to remove any redundant information from the matrix representations. Thus, in this special but very common case, the effective size of the matrices are significantly reduced and with this the computational effort.In this contribution, the mathematical background for the two mentioned conversion processes is explained. It is shown that VOIGT and KELVIN matrix representations are not restricted to orthonormal bases, and with this not to Cartesian tensors. Moreover, it is demonstrated that the value of a duality pairing is invariant with respect to the conversion process.
Differences and similarities between reinforcement learning and the classical optimal control framework
Authors: Gottschalk Simon , Burger Michael 
Published: November 2019

AbstractIn this contribution , we discuss Reinforcement Learning as an alternative way to solve optimal control problems. Especially for biomechanical models, well‐established classical techniques can become complex and time‐consuming, because biomechanical models have often much more actuators than degrees of freedom. Furthermore, the solution of such a technique is normally only applicable to this specific setting. This means, that a slightly change of the initial value of the model or the desired end position does make the computed solution useless. We give a short overview to Reinforcement Learning and apply it to an optimal control problem containing the above mentioned challenges. We use an algorithm, which updates the weights and biases of a neural network, which takes the role of a controller, using simulated trajectories of the model generated by the current neural network.
On the application of a greedy reduced basis scheme to the multi‐frequency solution of acoustic boundary element equations
Authors: Jelich Christopher , Baydoun Suhaib Koji , Marburg Steffen 
Published: November 2019

AbstractIn this work, a greedy reduced basis scheme for the multi‐frequency solution of linear time‐harmonic acoustic problems is investigated. The scheme allows to express the approximate solution within a frequency range of interest as a linear combination of a few basis vectors. These basis vectors are given by the solutions of the underlying frequency dependent linear system at iteratively chosen frequency samples within the frequency band. In each step of the algorithm, the next basis vector is evaluated at a frequency point for which the solution is worst approximated by the current reduced basis. In order to approximate the solution between the frequency points, a least square solver is used and an a posteriori error estimator is applied for assessing the quality of the approximation. The boundary element method is used for discretizing the underlying Helmholtz problem and an iterative solver is applied for the solution of the high‐fidelity system. In view of medium to large‐scale problems, a data sparse representation of the system matrix based on the ℋ2‐format is introduced. This reduces both the memory requirements of the scheme as well as the computational effort of the matrix‐vector products. The performance of the proposed scheme is shown based on interior and exterior acoustic problems. Comparisons to conventional multi‐frequency strategies verify the efficiency of the method.
Comparison of different Excitation Strategies in Operational Modal Analysis (OMA)
Authors: Gille Max , Berninger Tobias F. C. , Rixen Daniel J. 
Published: November 2019

AbstractDifferent ways of exciting a structure for the use in Operational Modal Analyisis (OMA) are compared and evaluated on a simple structure. As in OMA the exact excitation is unknown, some assumptions about the excitation have to be made and it is very hard or even impossible to meet all theoretical requirements, such as randomness of the excitation in time and space. As a result, compromises have to be made. Therefore, multiple techniques are evaluated to give a recommendation for those who want to perform OMA measurements themselves.Classical Experimental Modal Analysis (EMA) is performed as a reference, and we compare these results with those of OMA with different types of excitation. These are: tipping with fingers on the structure, brushing, and acoustic excitation with noise and different styles of music through a loudspeaker. The experimental results are evaluated using the Polymax algorithm for both EMA and OMA.
Comparison of MRI measurements and CFD simulations of hemodynamics in intracranial aneurysms using a 3D printed model ‐ A benchmark problem
Authors: Giese Daniel , Heinlein Alexander , Klawonn Axel , Knepper Jascha , Sonnabend Kristina 
Published: November 2019

AbstractA benchmark for the comparison of MRI (Magnetic Resonance Imaging) measurements and CFD (Computational Fluid Dynamics) simulations for blood flow in intracranial aneurysms is presented. The benchmark setting is designed to allow for CFD simulations that are completely independent of the MRI measurements. This facilitates a fair comparison of both methods. Furthermore, results showing the good agreement of MRI and CFD are presented.
Locating the extremal entries of the Fiedler vector for rose trees
Authors: Gernandt Hannes 
Published: November 2019

AbstractIn this note we locate the extremal entries of the Fiedler vector for the class of rose trees, which consists of paths with a star graph attached to it. We derive directly from the eigenvector equation conditions to characterize in which cases the extremal values are located either at the end points of the path or on the pendant vertices of the star graph.
Computational Modeling of Drying Shrinkage in Early‐Age Concrete
Authors: Ghasabeh Mehran , Göktepe Serdar 
Published: November 2019

AbstractThis contribution is concerned with the computational modeling of durability problems related to drying shrinkage. The associated formulations are conducted by developing a coupled constitutive modeling approach, which is furnished by the robust computational tools within the framework of poroviscoelasticity. In contrast to the existing studies, we employ a physically motivated technique where the pore pressure is obtained as a function of the water content that is determined using sorption‐desorption equations for a given value of the local relative humidity. Therefore, the proposed model accounts for the hygro‐chemo‐mechanical cross coupling effects between the shrinkage‐induced strain development due to the pressure evolution through humidity variations and the stress concentrations in hardening and hardened viscoelastic concrete. The comparison of the numerical examples with experiments demonstrates excellent predictive capacity of the proposed model.
Parameter identification for constitutive models of innovative textile composite materials using digital image correlation
Authors: Hofmann Justin Felix , von Boyneburgk Claudia , Tunger Sophie , Heim Hans-Peter , Kuhl Detlef 
Published: November 2019

AbstractThis contribution focuses on an innovative composite material consisting of textile layers made from continuous wooden fibers embedded in a thermoplastic matrix. A finite element simulation of potential use‐cases is planned to support the development process and to study the suitability of the material in an architectural context. The simulation is based on a constitutive model assuming homogenous orthotropic elastic behavior and will be expanded to include multiscale modeling in future research. The material parameters used in such models can often be determined based on a small number of local measurements during experiments like tensile tests, which assume classical one dimensional load scenaria at least in parts of the specimen. However, this is not sufficient for non‐homogeneous materials, especially when dealing with non‐isotropic materials in off‐axis configurations and the need for full‐field measurements like digital image correlation (DIC) arises. Experimental results of uniaxial on‐ and off‐axis tensile tests using DIC are presented and used in the identification of the material parameters of the given model. Results of simulations and experiments are compared and the suitability of the material model is discussed.
Adaptive isogeometric discretizations for diffuse modeling of discontinuities
Authors: Hennig Paul , Maier Roland , Peterseim Daniel , Kästner Markus 
Published: November 2019

AbstractIn this contribution, we discuss the modeling of discontinuities using non‐conforming meshes. For weak discontinuities we propose to regularize the sharp material interface over a characteristic length scale. To define the material properties in the transition region, homogenization assumptions are used that fulfill the kinematic compatibility across the interface and the static equilibrium at the interface. For strong discontinuities we use a phase‐field model that is able to account for failure of adhesive interfaces and extend it to general heterogeneous materials. To improve the efficiency of the approach, adaptive isogeometric analysis is used to discretize the computational domain.
On Aerodynamic Load Transfer to the Flexible Car‐Body of a High Speed Train
Authors: Dou Weiyuan , Zhang Lele , Stichel Sebastian 
Published: November 2019

AbstractInvestigating the influence of aerodynamic loads on the flexible car‐body of high speed trains (HST) , a method to investigate the elastic vibrations of the car‐body modeled as a dynamic system, induced by aerodynamic‐loads during operation, was developed based on an equivalent force system. A reduced degree of freedom model was developed by considering master nodes in the full‐scale model. The results demonstrate the feasibility of our proposed method which introduces aerodynamic‐loads as input to analyze the aerodynamic performance of a HST with a flexible car‐body. The new method can also reduce the time consumption in the multi‐body dynamics calculation and provide more information of the elastic vibration of a car‐body.
Soil modeling with a DEM Lookup approach
Authors: Jahnke Jonathan , Steidel Stefan , Burger Michael 
Published: November 2019

AbstractWe consider an efficient, data‐driven approximation approach for the prediction of soil‐tool interaction forces. In a time‐consuming offline phase, we perform a set of Discrete Element Method basis simulations. In each simulation, we consider a different tool state, process the acquired data and save it into a data structure, which we call a Lookup Table. In an online phase, when performing arbitrary tool maneuvers, we obtain tool forces and moments from the Lookup Table, based on the current tool state. In other words, we generate a data base of tool maneuver forces and access it efficiently.
Incorrect Estimates by the Four Wave Interaction(FWI) system for the Fermi‐Pasta‐Ulam(FPU) System
Authors: Sunny Danish Ali , Farooq Sarfraz 
Published: November 2019

AbstractRecently it was proved in [9] that the nonlinear Schrödinger equation fails to predict accurately the dynamics of an original system because of unstable resonances. By extending the ideas in [9], we prove a similar result for the Four Wave Interaction System.
Model order reduction for space‐adaptive simulations of Navier‐Stokes
Authors: Gräßle Carmen , Hinze Michael , Lang Jens , Ullmann Sebastian 
Published: November 2019

AbstractWe consider model order reduction with proper orthogonal decomposition (POD) for simulations of incompressible, laminar flow governed by the Navier‐Stokes equations. The major goal in reduced‐order modeling is to replace expensive high‐fidelity systems by low‐order approximations while ensuring a good approximation quality. In this work, the reduced‐order model is constructed from snapshots which are space‐adapted finite element solutions. In order to guarantee stability of the POD surrogate model, we either use a projection onto a common divergence‐free space or utilize a supremizer enrichment of the reduced velocity space. In a numerical experiment, we compare the accuracy of the resulting reduced solution with the standard approach using a static, uniform snapshot discretization.
Global proper orthogonal decomposition for parametric model reduction of geometrically nonlinear structures
Authors: Meyer Christian H. , Rixen Daniel 
Published: November 2019

AbstractFinite element simulations of structures that undergo large deformations can imply long simulation times due to the nonlinearity of the resulting equations of motion and a high number of degrees of freedom. Especially for design studies, where the equations of motion must be solved several times, it is highly desired to reduce the simulation time.The simulation time can be reduced by nonlinear model reduction. Nonlinear model reduction is carried out in two steps: First, the dimension of the problem is reduced by projecting the equations of motion onto a low‐order subspace that is defined by a reduction basis. Second, the evaluation of the nonlinear restoring force term, that originates from large deflections, is accelerated through hyperreduction.The first step can be challenging for design studies spanning large parameter intervals. For those studies, the calculated reduction basis either must be updated several times or must provide a subspace that captures the solution vectors for the whole parameter space. The latter option can be performed by sampling the parameter space, building local reduction bases at these sampling points and then applying a proper orthogonal decomposition on their concatenation.This contribution shows how this procedure is used for parametric model reduction of geometrically nonlinear structures. It demonstrates its accuracy and computation time on a shape‐parameterized beam structure that undergoes large deflections. It turns out that the success of the proposed method is highly dependent on the implementation of the shape parameterization.
Wear mechanisms of hard phase containing materials
Authors: Röttger Arne 
Published: November 2019

AbstractWear affects the service life of tools and counteracts an economic operation of a tunneling project. Because of wear, tools must be replaced to ensure adequate penetration, which means downtime. Targeted planning of replacement intervals requires knowledge of precise wear prediction models. In these predictive models the abrasiveness of the soil has to be regarded, which can be evaluated by experimental experiments such as the LCPC test for soil and the CAI test for solid rock. However, the forecast models developed provide only a rough guide value and often do not correlate with the real wear conditions of the tools during a tunneling project. The main reason here is to mention the disadvantage that in the previous work not the overall tribological system has been considered sufficiently. Thus, the wear occurring on the tool is not only dependent on the abrasiveness of the soil to be penetrated, but is also determined by the material properties of the tool, the loads acting on it and the presence of any intermediate and surrounding media. From this simple consideration, it can be seen that wear is not a sole property of the soil or of the tool material, but a system property. The motivation of this short report is to show the basics of tool wear of tools used for tunneling applications as well as to show basic boundary conditions for future experimental work and simulations in the field of tool wear. First, the tribological system and the four main wear mechanisms will be presented. In a further step, the damage mechanisms are focused on the dominant wear mechanisms abrasion and surface disruption of tunneling tools. Thereby, interaction of abrasive particles or crack propagation in hard phase materials at the microstructure level will be discussed.
Phase field modelling of stress assisted corrosion of biodegradable magnesium alloys
Authors: Ma Songyun , Zhang Dawei , Markert Bernd 
Published: November 2019

AbstractBiodegradable magnesium alloys are regarded as promising biomaterials for orthopaedic fixation devices due to obvious advantages over conventional permanent implants. Experimental studies have shown that the stress state has a significant impact on the corrosion rate of biodegradable magnesium alloys. In the present work, the phase field modelling approach is used to simulate the stress assisted corrosion of biodegradable magnesium alloys with porous microstructures. The simulation results demonstrates effects of the porous microstructure on the degradation behaviour of biodegradable magnesium implants.
DIC‐measurement during tensile testing and its approach for the FEM‐simulation of "Die‐Less‐Hydroforming"
Authors: Metzger Andreas , Ruff Daniel C. , Ummenhofer Thomas 
Published: November 2019

AbstractDigital Image Correlation (DIC)‐measurement is an optical measurement method which enables contactless and area‐wide continuous acquisition of 3D‐geometry, deformation and surface strain during experimental investigations. Within Die‐Less‐Hydroforming, an increasing innovative forming technology, see [1] and [2], the DIC‐measurement may be used for two tasks at once: The forming process of Die‐Less‐Hydroforming can be investigated continuously within the scope of the classical application of DIC in terms of geometry and deformation acquisition. However, this paper focuses on the use of DIC during the uniaxial tensile test of sheet metal used for manufacturing the double‐layered Die‐Less‐Hydroforming‐blank. Using DIC during the tensile test facilitates to measure the current cross‐section area continuously which allows the determination of a true stress‐true plastic strain‐curve. This curve is required as input for FEM‐forming‐simulation to achieve significant results. But with conventional testing methods, for the case of flat tensile test specimens, it cannot be determined beyond uniform strain Ag. Therefore, the “true” values beyond Ag are often estimated by mathematical approximations.
Investigation of a centrifugal exciter with two coaxial unbalances on a carrier performing planar motion
Authors: Yüzbasioglu Tunc , Drozdetskaya Olga , Fidlin Alexander 
Published: November 2019

AbstractPassing through and capturing into the resonance of a centrifugal exciter is investigated. The current work is the continuation of [1], which considered a minimal model of a centrifugal exciter consisting of a carrier with one degree of freedom. The analysis is conducted using an averaging method for partially strongly damped systems. Additional stationary and periodic solutions in vicinity of the resonances of the carrier system have been found, which don't exist in the simpler system investigated previously.
A Model Problem for Optimal Control of a Parabolic PDE Fully Coupled to ODEs
Authors: Kimmerle Sven-Joachim 
Published: November 2019

AbstractIn many applications we encounter fully coupled systems involving a partial differential equation (PDE) and an ordinary differential equation (ODE). A particular class is the case in which the PDE is parabolic. This coupled optimal control problem is considered in theory in [1]. Here we consider a toy example with the heat equation and a second order ODE given by Newton dynamics. The acceleration in the ODE may be controlled and is subject to box constraints. We present numerical optimal control results for this toy example.
Kino‐Geometric Modeling: Insights into Protein Molecular Mechanisms
Authors: Budday Dominik , Leyendecker Sigrid , van den Bedem Henry 
Published: November 2019

AbstractProteins are dynamic macromolecules that perform an immense variety of biological functions on a broad range of spatio‐temporal scales. Their conformational ensemble is a fundamental determinant of functionality in health and disease. While computational advances have increasingly enabled the computation of atomically detailed trajectories from Molecular Dynamics (MD) simulations, there remain considerable drawbacks when aiming for fast, yet elaborate insights into the molecular mechanisms of function. Here, we explore the potential of kinematics and geometry based methods, inspired from traditional robotics, to study protein conformational dynamics. Using geometric tools, we demonstrate insights into molecular mobility from instantaneous rigidity and flexibility analysis on selected example systems. Resulting motions from kinematically sampling along collective degrees of freedom show qualitative and quantitative agreement with motions from MD simulations. Coupled to sophisticated motion planning strategies, our approach is capable of providing structural ensemble representations from sparse experimental data such as double electron‐electron resonance (DEER) that remain difficult to interpret otherwise. Overall, we establish our Kino‐Geometric Sampling tool KGS as an efficient alternative to obtain high‐level insights into molecular mechanisms across scales, with ample applications in protein design and human health.