bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural and material optimization based on thermodynamic principles
Authors: Jantos Dustin Roman , Hackl Klaus , Junker Philipp 
Published: November 2019

AbstractIn our previous work, we developed a variational approach for topology optimization based on thermodynamic principles, i.e. Hamilton's principle for dissipative processes. Hamilton's principle yields a closed set of differential equations for a variety of problems in continuum mechanics, which include microstructural processes described by internal variables (e.g. plasticity, damage modeling, crystallographic transformations, etc.). These internal variables can also be used to describe design variables for an optimization, i.e. structural compliance minimization. The resulting differential equations yield evolution equations as known from material modeling that can be used as update scheme for an iterative optimization procedure.With this method, we derived differential equations for different design variables: 1) the topology, which is described by a continuous density distribution with penalization of intermediate densities (SIMP); 2) the local material orientation of a anisotropic base material, for which we introduce a filtering technique to control the fiber path smoothness; 3) the material distribution for tension and a compression affine materials, e.g. steel and concrete, in which tension affine material is applied in regions predominant to tension and compression affine material in regions predominant to compression.
Mixed‐primal Discontinuous Galerkin approximation of flows in fractured porous media on polygonal and polyhedral grids
Authors: Facciolà Chiara , Antonietti Paola Francesca , Verani Marco 
Published: November 2019

AbstractWe propose a formulation based on discontinuous Galerkin methods on polygonal/polyhedral grids for the simulation of flows in fractured porous media. We adopt a model for single‐phase flows where the fracture is modelled as a (d − 1)‐dimensional interface in a d‐dimensional bulk domain and the flow is governed by the Darcy's law in both the bulk and the fracture. The two problems are then coupled through physically consistent conditions. We focus on the numerical approximation of the coupled bulk‐fracture problem, discretizing the bulk problem in mixed form and the fracture problem in primal form. We present an priori h‐ and p‐version error estimate in a suitable (mesh‐dependent) energy norm and numerical tests assessing it.
On the robustness of stress integration algorithms for finite single crystal (visco)‐plasticity
Authors: Prüger Stefan , Kiefer Björn 
Published: November 2019

AbstractThe accurate determination of the slip activity in single crystal plasticity models is crucial to predict the mechanical response and the reorientation of the crystal. Therefore, a comparison of two rate‐independent and two rate‐dependent formulations of single crystal plasticity is carried out, subject to homogeneous proportional and non‐proportional deformation histories. From the simulation results it is concluded that the robustness of the corresponding stress‐integration algorithm depends on the complexity of the hardening law.
A physically and geometrically nonlinear formulation for isogeometric analysis of solids in boundary representation
Authors: Chasapi Margarita , Klinkel Sven 
Published: November 2019

AbstractThis contribution concerns a physically and geometrically nonlinear formulation for isogeometric analysis of solids in boundary representation. The parametrization of the proposed approach is inspired by the scaled boundary finite element method, where the geometry of the boundary is sufficient to define the entire solid surface. This suits perfectly the boundary representation modeling technique, which is commonly employed for the design of solids in CAD. In order to provide a boundary‐oriented approach, the solid surface is parametrized by a radial scaling parameter emanating from a scaling center and a parameter in the circumferential direction of the boundary. According to the idea of isogeometric analysis, NURBS basis functions define the geometry of the boundary and approximate the solution on the boundary. We also employ NURBS to approximate the solution in the scaling direction in the interior of the domain. This enables a straightforward treatment of nonlinear problems while preserving the exact geometry of the boundary. The approximation in scaling direction is in principle flexible and requires for coupling of adjacent patches inside the domain. The Galerkin method is employed for the solution in both parametric directions and a linearization is derived which is used within an iterative Newton‐Raphson scheme. We consider nonlinear problems in solid mechanics including elasto‐plastic material behavior and large deformations as well as complex geometries commonly employed in engineering applications. In this paper we study a numerical example of a complex geometry in order to evaluate the performance of the proposed approach.
3D Dynamic Crack under Cyclic Loading using XFEM: Numerical Treatment
Authors: Lyu Tengfei , Löhnert Stefan , Wriggers Peter 
Published: November 2019

AbstractThe eXtended Finite Element Method (XFEM) is a special numerical method to handle arbitrary discontinuities in the displacement field independent of the finite element mesh. This is advantageous during crack initiation, growth and propagation processes. In the range of continuum damage mechanics, gradient‐enhanced damage models can be used to model damage and fracture without spurious mesh dependencies. Gradient‐enhanced damage models have been investigated extensively in the context of quasi‐brittle and elasto‐plastic materials. To avoid fracture and failure of materials, modelling the component under cyclic loading is significant for fatigue lifetime prediction. The focus of this contribution is set on algorithmic issues. The numerical treatment of 3d cracks under cyclic loading is investigated. The domain is discretized with ten‐node tetrahedral elements. Discrete cracks are captured using XFEM and updated by level set methods. In oder to take advantage of the explicit time discretization scheme, a modified differential equation for the gradient‐enhanced damage is presented and the central difference explicit time stepping method is employed to obtain 2nd oder accuracy of the solved equations.
Influence of thermal boundary conditions on the parameter identification in thermodynamics
Authors: Rose Lars , Menzel Andreas 
Published: November 2019

AbstractFinite‐Element based identification schemes, such as the FEMU‐method, are a powerful tool for the (quantitative) adjustment of material models to an observed material behaviour. A relative sparingly explored segment of this field, however, is the identification of thermal material parameters based on full field temperature measurements. Hence, the focus of this contribution lies on the influence of thermal boundary conditions on the result of such an identification. More precisely, the impact of the convection and conduction coefficient is analysed by simply performing several identifications, each with different values prescribed. Results suggest that some parameters are indeed very sensitive to the choice of coefficients.
Topology optimization combined with element‐by‐element solution techniques
Authors: Sala Ramses , Kuhn Charlotte , Sator Christian , Müller Ralf 
Published: November 2019

AbstractTopology optimization approaches are commonly used for design problems involving physical phenomena related to solid mechanics, acoustics, electromagnetism, fluid mechanics, and combinations thereof. In computational models of these physical phenomena, the field variables are commonly approximated using spatial discretizations within the domain using the Finite Element Method. Even for topology design problems in which the field variables must only satisfy linear state equations, the storage and solution of the resulting global system of equations can become a computational bottleneck. In this contribution, we investigate a topology optimization approach in which the Solid Isotropic Material with Penalization (SIMP) method is combined with element‐wise solution approaches, in order to reduce computational memory requirements.
Two‐Grid hp‐DGFEMs on Agglomerated Coarse Meshes
Authors: Congreve Scott , Houston Paul 
Published: November 2019

AbstractWe generalise the a priori error analysis of two‐grid hp‐version discontinuous Galerkin finite element methods for strongly monotone second‐order quasilinear elliptic partial differential equations to the case when coarse meshes consisting of general agglomerated polytopic elements are employed.
Experiment on wave propagation in soft resins
Authors: Aghayan Sam , Bieler Sören , Reppel Thomas , Weinberg Kerstin 
Published: November 2019

AbstractThe wave propagation in a group of soft resin based (3d printed) materials is investigated by using a Split Hopkinson Bar test. The principal assumptions and the role of pulse shaping, as an approach to achieve constant strain rates and dispersion reduction, is discussed. The experimental stress‐strain curves, gained by aluminium Split Hopkinson bars, are presented and indicates that tough and white standard resins have a dynamic elastic modulus of almost 3 GPa.
Particle Finite Element Simulation of Fresh Cement Paste – Inspired by Additive Manufacturing Techniques
Authors: Reinold Janis , Meschke Günther 
Published: November 2019

AbstractThe properties of hardened concrete structures, fabricated by novel additive manufacturing techniques with fresh concrete, are significantly influenced by the manufacturing process. A numerical framework for the simulation of extrusion processes in additive manufacturing techniques based on layered extrusion is proposed. The flow behavior of fresh concrete is approximated with a regularized Bingham model and in order to deal with large deformation, governing equations are solved via the Particle Finite Element Method.
A comparison between the performance of different Mindlin's theory based strain gradient models in local singularities
Authors: Makvandi Resam , Juhre Daniel 
Published: November 2019

AbstractThe classical continuum mechanics theories are originally supposed to determine deformations in ranges from millimeter to meter, the so‐called macroscopic scale. In fact, these theories are approximations of physical systems neglecting the underlying microstructure. For instance, a Cauchy continuum, i.e. a continuum with an elastic energy determined as a function of the gradients of its macroscopic displacement, can only approximate the behavior of a physical system sufficiently as long as the microstructure has a much smaller length‐scale than the macrostructure [1]. Although these models were exploited in studies for large and small scales, experiments have shown that the classical models are not able to properly cover the smaller scales; in particular, problems in micron‐ and nano‐dimensions are frequently observed. Size‐effects, which cannot be captured exploiting these theories, seem to be the source of this issue. On top of that, the appearance of local singularities at the crack tips (or more broadly, in the presence of point and line loads) is one of the known limitations of the classical continuum mechanics theories. Generalizing these models by introducing additional kinematic terms to consider the underlying microstructure effects at macroscopic levels is one way of overcoming the already mentioned problems. In this contribution, we will focus on the Mindlin's theory of elasticity with microstructures [2] and its different forms. Therein, it is shown that for the first strain gradient theory, five additional parameters must be introduced. However, in practice, due to the complexities of measuring the new parameters, various simplified versions of the theory are being exploited, among them we name Altan et al. [3] and Reiher et al. [4]. Our aim here is to compare the performance of these simplified theories in removing the local singularities of the conventional continuum mechanics theory.
Model Reduction for Second‐Order Dynamical Systems Revisited
Authors: Beddig Rebekka S. , Benner Peter , Dorschky Ines , Reis Timo , Schwerdtner Paul , Voigt Matthias , Werner Steffen W. R. 
Published: November 2019

AbstractSecond‐order control systems are used to describe the dynamics of mechanical and vibrational systems, and in particular, their response to excitations. In this article, we discuss model order reduction (MOR) of such systems. A particular focus is on preserving the second‐order structure and physical properties such as stability and passivity.
On grasp based objectives in human grasping simulation
Authors: Phutane Uday , Roller Michael , Leyendecker Sigrid 
Published: November 2019

AbstractWe solve optimal control problems to perform predictive human grasping simulation for a two‐finger rigid multibody model. The quality of the grasp is strongly influenced by the choice of the objective function. We investigate the quality of the grasp using objectives based on grasp matrix and the hand Jacobian. We compare the performance of optimal control grasping simulations by minimising objectives based on these grasp quality measures for a lateral grasp activity.
Automatic analysis of the stress‐strain response of rheological models
Authors: Schultz Timm , Müller Ralf 
Published: November 2019

AbstractViscoelastic material behaviour can be represented by rheological models combining elastic and viscous rheological elements. These combinations can be serial and parallel connections of such elements as well as combinations of both. A method based on transfer functions formulated in the Laplace domain allows the calculation of constitutive equations of serial and parallel connections by a simple summation.Furthermore the use of a breadth‐first search algorithm for the analysis of complex systems of rheological elements is explained. By using this search algorithm a hierarchy of nested connections in a system can be found. This hierarchy guarentees dependencies are satisfied during the calculation of constitutive equations and signal propagation through the system.
Macroscopic modeling of open cell foams
Authors: Kirchhof Stephan , Ams Alfons 
Published: November 2019

AbstractOpen cell foams are widely used in engineering which includes an application in areas, where vibration excitations can act on the structures. Therefore dynamical properties as eigenfrequencies and natural modes are of great interest. We will discuss the description of the dynamic behavior of open cell foams by stochastic macroscopic models. These are based on a computed tomography scan of the foam, which gives access to parameters and the power spectral density needed for the generation of the stochastic process. The simulation results shall be used to get an estimate of the natural frequencies.
Sensitivity analysis of elastoplastic structures and application to optimal specimen design
Authors: Liedmann Jan , Barthold Franz-Joseph , Gerke Steffen , Brünig Michael 
Published: November 2019

AbstractThis paper is concerned with the shape improvement of novel specimens for biaxial experiments in terms of optimal stress states, characterized by the stress triaxiality. For this, gradient based optimization strategies are utilized and the needed sensitivities are obtained using a variational approach. Considering elastoplastic material behavior, the deformation history as well as its sensitivity has to be taken into account. In a first step, the material parameters have to be identified for the given material (AlCuMgSi). With the identified parameters, a chosen specimen is numerically analyzed and optimized with the aim to achieve a preferably homogeneous stress triaxiality distribution in the relevant part of the specimen.
How Housing Dynamics Affect the Monitoring of Rotor Unbalance: A Case Study
Authors: Krügel Samuel , Maierhofer Johannes , Wagner Christian , Thümmel Thomas , Rixen Daniel J. 
Published: November 2019

AbstractWhen monitoring faults in a rotating system, the rotor support and housing have an important effect on the measured dynamic response. Within this contribution, we show the effect of stiffness orthotropy in the supports when monitoring the unbalance of a rotor. The study is illustrated with an industrial case, namely a cooling blower for a drive system. The considered application was evaluated in a new and a defective state by measurements using radially distributed accelerometers to answer two questions: 1. May a suspected unbalance be detected at different operating conditions by measuring on the housing? 2. Which problem can appear in estimating the rotor unbalance when the support has orthotropic stiffnesses?Thereby, we figured out that the suspected unbalance can be well detected only between global resonance frequencies of the application. The correlating modes superimpose the acquired signals, initially evoked by unbalance excitation. Due to these modes, a phase shift of the measured unbalance signals in correlating measurement directions occurs. Thus, forward and backward whirl expresses themselves within the rotational frequency in the sensor signals. Due to these effects, the knowledge of global modes is a requirement for unbalance monitoring. Keywords: Orthotropic‐elastic rotor support, unbalance, vibration‐based monitoring
Coupled physics solvers for analysing the magneto‐thermal behaviour of a permanent magnet synchronous machines
Authors: Lotfi A. , Marcsa D. , Horvath Z. , Prudhomme C. , Chabannes V. 
Published: November 2019

AbstractThe aim of this study is to present a thermal analysis of a permanent magnet synchronous machine based on the finite element method. The developed model can be used to predict temperature distribution inside the studied motor during the rated operation. Electromagnetic computation (EM) is carried out with the aid of two 2D finite‐element (FE) simulations on the cross‐section of the PM motor. To analyse the process of heat transfer (HT) in an electrical machine, empirical correlations are used to describe the convective (HT) from the different surfaces of the PM motor. The (HT) coefficient is determined using dimensionless numbers. The proposed numerical method to solve the coupled problem is based on independently and successively solving the (EM) and thermal problems and then transferring the results between the two sub‐problems. The results obtained by the model are compared with experimental results from testing the prototype electric motor.
Parameter Variation on Nonlinear Energy Sink attached to Multiple Degree of Freedom System
Authors: Jahn Martin , Panning-von Scheidt Lars , Wallaschek Jörg 
Published: November 2019

AbstractThe importance of lightweight structures has increased in the last years motivated by the goals of improving efficiency of vehicles and conserving resources. In most cases the loss of weight by using fewer or lighter materials is accompanied by a reduction of the structures stiffness having a strong effect on occuring vibrations. Even if the damping ratio of the structure remains unchanged, by reducing weight and stiffness the vibration amplitudes might increase if the vibration excitation stays the same. Damping elements might be introduced to the structure mitigating critical resonance gains of the structure to reduce these vibrations. In this work the dynamics of a linear multiple degrees of freedom structure with a nonlinear damping element are investigated. The damping element is chosen to have a nonlinear characteristic to allow for a situation adaptive design. Numerical parameter studies are carried out to optimize the resulting damping of the entire structure. The nonlinear equation of motion is solved by applying the Harmonic Balance Method. The evaluation of the performance of the nonlinear damping element is done by consideration of the nonlinear frequency response functions of the structure.
Numerical investigations of the hydrodynamics and the oxygen mass‐transfer in aerated tanks
Authors: Höffmann Ann Kathrin , Schmidt Johanna , Ehrhard Peter 
Published: November 2019

AbstractThe present work concentrates on numerical investigations of the hydrodynamics, the oxygen mass‐transfer, and the biochemical reactions in a pilot‐plant‐scale aeration tank, engaging the Euler‐Euler method and the Activated Sludge Model No. 1. The oxygen concentration, the ammonium concentration, and the nitrate concentration are discussed using results from the experimental investigations at the pilot‐plant‐scale aeration tank in the waste‐water‐treatment plant Ebersbach carried out by the HZDR.
A damage detection study of a bridge using bypassing vehicles and computational intelligence
Authors: Hesser Daniel Frank , Bamer Franz , Markert Bernd 
Published: November 2019

AbstractStructural integrity is an ubiquitous topic in research and daily living. Conventional monitoring strategies follow a preventive maintenance plan or require permanent installation of sensors. These steps are time and cost‐inefficient taking into account the high number of bridges to be monitored. In this study, a bridge structure is passively monitored using the acceleration signal of a bypassing vehicle. Thereby, the signal is measured on the vehicle. The health status of the bridge can be evaluated after each pass, which allows a continuous monitoring of the structure. A numerical model of a bridge and a bypassing car is carried out to prove the feasibility of this approach and to create a large database with different damage locations and vehicle velocities. Moreover, an artificial neural network is trained on that database to detect damaged bridge structures. The proposed method proves the feasibility of monitoring the structural integrity of bridges and supports conventional maintenance methods. Therefore, the combination of active and passive monitoring strategies paves the way to efficient and cheap infrastructure monitoring strategies.
Demand‐based coupling of the scales in the finite temperature CADD method
Authors: Wurm Patrick , Ulz Manfred H. 
Published: November 2019

AbstractConcurrent finite temperature atomistic‐to‐continuum models commonly use a fixed time interval coupling of the atomistic and continuum scale. With special focus on the continuum, this means, that its solution fields are updated in fixed intervals of time. However, in times, when the change in the continuum boundary conditions is negligible, these computations are unnecessary. We present the novel idea of a demand‐based coupling in this work, in which the continuum solution fields are only updated if needed, to save computational effort. To demonstrate the approach, we apply the coupling to a prototypical representative of the mentioned models, namely the coupled atomistic and discrete dislocation (CADD) model. We test the basic functionality of the approach in a 1‐dimensional pulse propagation problem.