bluuebunny/crossref_metadata_2025_split huggingface dataset:
Noise reduction for DIC measurements
Authors: Reis Martin , Diebels Stefan , Jung Anne 
Published: November 2019

AbstractDigital image correlation (DIC) is well known as a contact‐less, full‐field strain and displacement measuring method. The use of the method is widely spread in experimental mechanics. Nevertheless, there are error sources such as light settings, speckle pattern and noisy images, which strongly affect measurement quality, but often stays uninvestigated. Therefore, this work outlines a simple routine to identify errors and enhance the accuracy of DIC measurements. A calibration sample adapted to the specifications of the setup using the beam theory to link machine displacement, DIC measurements and forces. All evaluations are done in the commercial software ISTRA4D. The noise in the measurements is reduced to an error of under two per cent. The routine allows estimating the quality of the images before performing the experiments. Furthermore, the routine is transferable to all experimental setups. The calibration of the setup allows getting reliable experimental results with a known error. With this estimated stochastic error, the advantages of DIC can be used to evaluate mechanical experiments such as three‐point bending tests on single struts of an open cell metal foam.
Interfacial energies depending on curvature: the drastic loss of elastic coupling on small scales and its impact on multiphase mechanics
Authors: Kurzeja Patrick 
Published: November 2019

AbstractInterfacial energies are often assumed to be well approximated by a constant surface tension. This assumption however fails at very small radii, e.g., for fluid bubbles or lipid layers. Below a cut‐off radius, the interface elasticity can even turn negative and interface resonance vanishes, diminishing the resonance spectrum and dispersion.
Sensor positioning in the context of wave‐based damage identification in dams
Authors: Reichert Ina , Alalade Muyiwa , Lahmer Tom 
Published: November 2019

AbstractDams and their adjourning reservoirs play an important role in the drinking water supply as well as in the flood defense. Their world‐wide use and possible massive devastation due to dam failures make the monitoring of the structural health of these huge structures imperative. Therefore, it is necessary to identify faults/damages in the dams' structure non‐invasively in order to proceed with the current use. Additionally, monitoring of these huge structures is very complex, time‐consuming and costly. To circumvent the aforementioned challenges, an inverse analysis, here an enhanced, regularized, cyclic full‐waveform inversion is proposed based on wavelengths between seismic and ultrasonic waves. Parameters of the dam material, such as stiffness, density and permeability, are estimated in synthetic experiments. Having this, an optimal design of experiment approach is used to identify the most informative sensor positions regarding the reconstruction quality. An optimized sensor layout may further improve the efficiency of the solution of the inverse problem.
An anisotropic creep model for continuously and discontinuously fiber reinforced materials
Authors: Hohe Jörg , Fliegener Sascha 
Published: November 2019

AbstractThe present study is concerned with the formulation, implementation and validation of anisotropic creep laws for neat thermoplastic matrix materials, discontinuously long fiber reinforced thermoplastic (LFT) composite materials with process dependent fiber preference directions as well as unidirectionally fiber reinforced thermoplastic tapes. Based on a simple three term Kelvin‐Voigt approach, an anisotropic model is formulated and implemented into a finite element program. The model is validated against an experimental data base of creep experiments on continuously and discontinuously fiber reinforced materials.
Gradient Recovery for the BEM‐based FEM and VEM
Authors: Seibel Daniel , Weißer Steffen 
Published: November 2019

AbstractIn this article, we propose new gradient recovery schemes for the BEM‐based Finite Element Method (BEM‐based FEM) and Virtual Element Method (VEM). Supporting general polytopal meshes, the BEM‐based FEM and VEM are highly flexible and efficient tools for the numerical solution of boundary value problems in two and three dimensions. We construct the recovered gradient from the gradient of the finite element approximation via local averaging. For the BEM‐based FEM, we show that, under certain requirements on the mesh, superconvergence of the recovered gradient is achieved, which means that it converges to the true gradient at a higher rate than the untreated gradient. Moreover, we propose a simple and very efficient a posteriori error estimator, which measures the difference between the unprocessed and recovered gradient as an error indicator. Since the BEM‐based FEM and VEM are specifically suited for adaptive refinement, the resulting adaptive algorithms perform very well in numerical examples.
Structural optimization of electrically charged anodes
Authors: Homberger Stefanie , Werner Marek , Weinberg Kerstin 
Published: November 2019

AbstractThe latest battery developments focus on the design of the anode and try to ensure a safe charging of the electrical device. Here an anode is studied which is made of graphite or silicon and subjected to several physical effects like thermal expansion, electrical current conductivity, and mechanical deformation. Typical design objectives like compliance or conductivity are competing against each other. On the one hand, the compliance is adapted as a design objective and is subjected to a minimization condition by applying external mechanical loads. On the other hand, the conductivity is aimed to be maximized. As a consequence, there is no global optimum structure. Therefore, an univariate optimization of certain objectives is investigated at first. Next, for a bivariate optimization Pareto optimality is used and finite element based numerical simulations are performed. The resulting structures will be used for a simulation of the charging process involving multi‐field physics.
Sparse discretization of sparse control problems
Authors: Herberg Evelyn , Hinze Michael , Schumacher Henrik 
Published: November 2019

AbstractWe consider optimal control problems that inherit a sparsity structure, especially we look at problems governed by measure controls. Our goal is to achieve maximal sparsity on the discrete level. We use variational discretization of the control problems utilizing a Petrov‐Galerkin approximation of the state, which induces controls that are composed of Dirac measures. In the parabolic case this allows us to achieve sparsity on the discrete level in space and time. Numerical experiments show the differences of this approach to a full discretization approach.
On a simple nonlinear system with circulatory forces
Authors: Barakat Ahmed A. , Hagedorn Peter 
Published: November 2019

AbstractSelf‐excited vibrations in mechanical system have been always gathering attention since being problematic for various applications, including brake squeal, aerodynamic flutter, machining chatter, and galloping transmission lines, or in some cases beneficial as in some musical instruments (ex. violin) or resonant MEMS. These vibrations can have different origins, such as ‘negative damping’ (such as in the classical Van der Pol oscillator) and/or circulatory forces (i.e. ‘follower forces’, non‐conservative positional forces). Both the negative damping and the circulatory forces can have different physical origins. It is well known that frictional forces generated between bodies in sliding contact can generate circulatory terms as well as damping and other types of forces. In particular, if one of two bodies in frictional contact moves with a constant speed or angular velocity, the other one being capable to oscillate, this implies an energy source for the oscillating part of the system. This has been identified as the cause for many self‐excited vibrations. In this presentation a very simple nonlinear two‐degree‐of‐freedom system of this general type is examined in some detail. It has recently been proposed in the literature as a paradigm for frictionally generated circulatory forces, for which the equations of motion can be derived from first principles. Other related systems have been presented in the literature before, but this newer system seems to be much simpler than the earlier ones and presents a great wealth of dynamic behavior. The nonlinear equations of motion of this 2‐DoF system always have the trivial solution and, depending on the system's parameters, also non‐trivial stationary solutions. The stability of the different stationary solutions is discussed in some detail. It was interesting to note that the increase of the friction parameter drives the system towards instability. This does however not happen, if the stiffness of both springs are identical, which practically can't be guaranteed.
Thin liquid film formation on hemispherical and conical substrate
Authors: Scholle Markus , Marner Florian , Gaskell Philip H. 
Published: November 2019

AbstractThe deposition and coating of thin films onto curved rigid substrate, involving displacement of air by a liquid, has numerous applications within the technology sectors but faces two major challenges: (i) control of the local film thickness; (ii) ensuring that the coating remains stable. The work reported here investigates the full coverage of three‐dimensional curved geometries, of hemispherical and conical shape, by a continuously fed, gravity‐driven, thin liquid layer. The modelling approach adopted utilises a first integral formulation [1,2] of the Navier‐Stokes equations leading to a variational formulation in the case of steady flow and an advantageous re‐formulation of the dynamic boundary condition at the free surface [3]. Asymptotic analysis, underpinned by the long‐wave approximation, enables analytic solutions for the local film thickness to be obtained.
Towards multifield discrete element modeling of concrete structures
Authors: Flack Christian , Dinkler Dieter 
Published: November 2019

AbstractConcrete structures are built extensively all over the world. The prediction of the lifetime of a structure is very important in terms of costs and usability. A numerical modeling concept is presented that can describe concrete on the mesoscale. The focus of the model development is on the coupling of mechanics, heat conduction and chemical reactions. The Discrete Element Method (DEM) is used to describe the aggregates with spherical bonded particles. A voronoi tessellation provides access to the free space between the aggregates and leads to a pore network model (PNM) approach accounting for transport phenomena. Chemical reactions are handled within a processzone which couples the DEM and PNM. In the scope of this framework the sulfate attack on concrete is modeled and computed. The local deterioration in the concrete matrix is directly captured and the impact on the macroscopic behavior is presented.
Numerical approaches for the simulation of the yeast distribution in a fermentation tank
Authors: Klembt Daniel , Meironke Heiko 
Published: November 2019

AbstractIn recent years, in addition to the experimental investigation of a flow phenomena, numerical investigation has become increasingly established. Especially in investigations where conventional flow measurement techniques such as PIV or LDA fail, numerical computation can offer new possibilities. Models for the simulation of the natural convection flow in a fermentation tank and in second step a superposition of the natural convection by gas bubbles have already been presented in earlier publications. Based on these results, this paper examines the simulation of yeast using the Euler‐Lagrange model. The aim is to extend the existing simulation, which is based on the Eulerian‐Eulerian time‐averaged model and to validate it with measurements from real experiments with the Ultrasonic Doppler Velocimetry (UDV). Starting point is the Dense Discrete Phase Model (DDPM), which is based on the Kinetic Theory of Granular Flow (KTGF). Especially the physical interaction models, for example the lift force, virtual mass force and collision models, play an important role. These fundamental studies must be conducted because the behaviour of the real yeast is really complex. During real fermentation, the yeast increases over time and also combines with other yeast particles. As a result, the proportion of yeast in the process increases and the equivalent particle size also increases due to the combination of the yeast. The goal of this paper is a numerical simulation of the flow processes in the fermentation tank, based on the Eulerian‐Eulerian model with the additional DDPM as realistic as possible, taking into account the natural convection flow and the actual bubble behaviour as well as the yeast distribution.
An ISS characterization for discontinuous discrete‐time systems
Authors: Geiselhart R. , Noroozi N. 
Published: November 2019

AbstractInput‐to‐state stability (ISS) is an important concept to study robustness properties of nonlinear control systems. The ISS property can be, in particular, characterized by ISS Lyapunov functions. For discrete‐time nonlinear control systems two different forms of ISS Lyapunov functions (implication‐form and dissipation‐form) are known to be equivalent if the dynamics are continuous. However, for discontinuous dynamics the equivalence is no longer satisfied. In this work, we discuss this phenomenon and, eventually, give a complete characterization of ISS in terms of ISS Lyapunov functions.
A penalization scheme for the numerical solution of optimal control problems with control complementarity constraints
Authors: Clason Christian , Deng Yu , Mehlitz Patrick , Prüfert Uwe 
Published: November 2019

AbstractWe suggest a simple penalty method for the numerical solution of optimal control problems with control complementarity constraints which is based on the famous Fischer–Burmeister function. The distinct advantage of this approach is the resulting smoothness of the penalty term and the unconstrainedness of the associated penalized surrogate problems. A numerical example from elliptic PDE control is presented as well.
On boundary conditions and constraints for representative volume elements of a two‐scale shell formulation
Authors: Zoller Jan , Gruttmann Friedrich 
Published: November 2019

AbstractIn this contribution a coupled two‐scale shell model with application of the FE2‐method based on the algorithm in [1] is presented. The representative volume element (RVE) is meshed with solid elements. In the RVE boundary effects can be reduced or even avoided using periodic boundary conditions. However, this requires proper constraints to prevent rigid body movements. For this purpose, the theory in [2] for beams, which considers the shape of normal stresses through the cross section, is transferred to the shell problem. Furthermore, the RVE reacts to shear deformations not only with shear stresses but also with bending stresses. This leads to a vanishing shear stiffness with an increase of the freely selectable in‐plane size. This dependence of the shear stiffness is eliminated by a further constraint on the normal stresses. Both constraints are incorporated using the method of Lagrange multipliers.
An Efficient Treatment of the Laplacian in a Gradient‐Enhanced Damage Model
Authors: Schwarz Stephan , Hackl Klaus , Junker Philipp 
Published: November 2019

AbstractAs is well‐known, softening effects that are characteristic for damage models are accompanied by ill‐posed boundary value problems. This arises from non‐convex and non‐coercive energies and results in mesh‐dependent finite element results. For that reason, regularization strategies, which somehow take into account the non‐local behavior, have to be applied in order to prevent ill‐posedness and to achieve mesh‐independence. Hereto, most commonly gradient‐enhanced formulations [1, 2] are considered, but also integral‐type [3,4] and viscous [5,6] regularization are well‐known.Gradient‐enhanced damage models such as [1,2], to what group our new model [7] basically belongs, come along with a field function acting on the non‐local level. Two variational equations are resulting and, however, usually the number of nodal unknowns is increased and consequently the numerical effort is increased as well.In contrast, we present an improved algorithm for brittle damage [7] combining finite element and meshless methods resulting in a quick update of the field function. Thereby, an efficient evaluation of the Laplace operator is applied as introduced in [8]. In the end, the numerical effort of the novel approach is almost comparable with an elastic problem while maintaining well‐posedness and therefore mesh‐independent results.
Artificial neural networks in structural dynamics
Authors: Stoffel Marcus , Bamer Franz , Markert Bernd 
Published: November 2019

AbstractThe aim of the present study is to investigate how structural models with inelastic material behaviour can be enhanced by means of artificial intelligence. To this end, artificial neural networks are proposed to replace continuum mechanical models in structural dynamics. This concerns predictions of shock wave‐loaded plates and finite element simulations with neural network enhanced material modelling. By comparison to experiments, the accuracy and the computational effort of the new approach is investigated.
The non‐real spectrum of a singular indefinite Sturm–Liouville operator with regular left endpoint
Authors: Behrndt Jussi , Schmitz Philipp , Trunk Carsten 
Published: November 2019

AbstractWe provide bounds on the non‐real spectra of indefinite Sturm–Liouville differential operators of the form (Af)(x) = sgn(x)(−f″(x) + q(x)f(x)) on the interval [a, ∞), −∞ < a < 0, with real potential q ∈ L1(a, ∞). The bounds depend only on the L1‐norm of the negative part of q and the boundary condition at the regular endpoint a.
Transformations and Enhancement Approaches for the Large Deformation EAS Method
Authors: Pfefferkorn Robin , Betsch Peter 
Published: November 2019

AbstractThe computer simulation of large deformation solid mechanics requires highly efficient finite elements. One widely used method enabling the construction of such elements is the enhanced assumed strain (EAS) method (cf. [1]). Within that framework, many transformations for the enhanced as well as the compatible deformation gradient have been used in previous publications (see e.g. [2]). We propose a new frame‐invariant alternative which fulfills the patch test and exhibits superior bending performance. Finally, novel mixed finite element methods based on the combination of mixed finite elements for polyconvexity [3] with the EAS method are presented. It is shown that this combination provides a promising framework for novel finite element methods.
Computationally effective spot‐weld fatigue life estimation for vehicle components
Authors: Zigo Milan , Arslan Eray , Mack Werner , Kepplinger Gerhard 
Published: November 2019

AbstractTo further speed up the frequency‐domain fatigue life estimation procedure for vehicle components with large numbers of spot‐welds, several measures are proposed. A two‐scale FE‐approach based on a pre‐processed library for various spot‐weld‐ / sheet‐geometries, applying the cutting plane method, and a priori stress estimations reduce the necessary CPU‐time considerably and allow for an efficient consideration of different load histories.
The Cauchy‐Riemann operator on smooth Fréchet‐valued functions with exponential growth on rotated strips
Authors: Kruse Karsten 
Published: November 2019

AbstractWe study the Cauchy‐Riemann operator

on spaces

of smooth functions on an open set

with values in a complex Fréchet space E which grow exponentially (γ = 1) on strips rotated by an angle θ. We state sufficient conditions for the surjectivity of

.
Numerical and experimental investigation on the flow behavior of liquids in narrow gaps
Authors: Luberto Luca , de Payrebrune Kristin M. 
Published: November 2019

AbstractLapping is one of the manufacturing processes with geometrically undefined cutting edges and is used to produce technical surfaces with high dimensional and shape accuracy. In order to predict the surface generation, a process model is developed that combines models of the material removal mechanism, the kinematics of the lapping particles and the flow of the lapping fluid. Due to many interactions in the process and the inhomogeneous flow of the lapping fluid (loose lapping particles in the fluid) a multiphysical model is needed. In a first step, only the flow behavior of the fluid without and with a simplified lapping particle (cuboid) is numerically and experimentally investigated. Particle Image Velocimetry is used to measure the flow field in the gap. The distance between the two plates, the velocity of the upper plate and the cuboid size can be varied. The experimental setup is simulated using a CFD model. Analogous to the experiment, the velocity of the upper plate and the cuboid size are also varied in the numerical study and the results agree well with the measured flow field. The CFD model helps to analyze further parameters, such as the influence of workpiece velocity on the flow. In the future, the model will be used to analyze the interaction between lapping particles and lapping fluid, which is very important for studying the mechanisms of material removal during lapping.
Comparative study of continuously differentiable Galerkin time discretizations for the wave equation
Authors: Bause Markus , Anselmann Mathias 
Published: November 2019

AbstractIn this work we compare numerically two families of space‐time finite element approximation schemes for wave equations. Continuously differentiable in time discrete solutions are provided by the schemes. The first family of schemes is based on a computationally cheap post‐processing of the continuous in space and time finite element approximation of the wave equation. The second family combines the variational approximation in time by finite element techniques with the concepts of collocation methods. Both families show equal order of convergence. The corresponding error constants are reviewed here.
Optimal periodic control of nonlinear chemical reactions with a time‐varying flow rate
Authors: Zuyev Alexander , Seidel-Morgenstern Andreas , Benner Peter 
Published: November 2019

AbstractThis paper deals with a mathematical model of a non‐isothermal chemical reaction described by nonlinear ordinary differential equations with two‐dimensional control. The control variables correspond to the possibility of manipulating the concentration of the input reactant and the total flow rate. We consider the task of maximizing the reactor performance as an isoperimetric optimal control problem with periodic boundary conditions. Necessary optimality conditions are derived by the Pontryagin maximum principle with Lagrange multipliers corresponding to the isoperimetric constraints.
Optimization Problems for Interacting Particle Systems and Corresponding Mean‐field Limits
Authors: Pinnau René , Totzeck Claudia 
Published: November 2019

AbstractWe summarize the relations of optimality systems for an interacting particle dynamic in the microscopic and in the kinetic description. In particular, we answer the question if the passing to the mean‐field limit and deriving the first order optimality system can be interchanged without affecting the results. The answer is affirmative, if one derives the optimality system on the kinetic level in the metric space (𝒫2, 𝒲2). Moreover, we discuss the relation of to the adjoint PDE derived in the L2‐sense. Here, the gradient can be derived as expected from the calculus in Wasserstein space.