bluuebunny/crossref_metadata_2025 huggingface dataset:
Networks in economics and finance in Networks and beyond: A half century retrospective
Authors: Nagurney Anna
Published: November 2019

This paper presents a panoramic view of research on economic and financial networks in the journal Networks, since its inception half a century ago. This paper focuses on both the breadth and depth of the journal articles, and within the context of earlier contributions, as well as more recent related ones in other scientific publications. From network optimization to game theory and a plethora of equilibrium concepts, along with novel dynamical systems frameworks, the journal has led the way in advancing economic and financial network models, algorithms, and applications. Moreover, Networks has helped to attract researchers in a variety of disciplines to the science of networks and the formulation and solution of associated problems drawn from the real world.
A discrete maximum principle for the weak Galerkin finite element method on nonuniform rectangular partitions
Authors: Liu Yujie , Wang Junping
Published: November 2019

This article establishes a discrete maximum principle (DMP) for the approximate solution of convection–diffusion–reaction problems obtained from the weak Galerkin (WG) finite element method on nonuniform rectangular partitions. The DMP analysis is based on a simplified formulation of the WG involving only the approximating functions defined on the boundary of each element. The simplified weak Galerkin (SWG) method has a reduced computational complexity over the usual WG, and indeed provides a discretization scheme different from the WG when the reaction terms are present. An application of the SWG on uniform rectangular partitions yields some 5‐ and 7‐point finite difference schemes for the second order elliptic equation. Numerical experiments are presented to verify the DMP and the accuracy of the scheme, particularly the finite difference scheme.
Corporate policy entrepreneurship and cross‐boundary strategies: How a private corporation champions mobile healthcare payment innovation in China?
Authors: He Alex Jingwei , Ma Liang
Published: November 2019

The private nature of corporate actors does not necessarily preclude them from contributing to public interest. When business strategies and genuine public motivation are favorably aligned, corporate actors from the private sector can also drive public sector innovations. For a private corporation, policy entrepreneurship inherently entails crossing not only the public–private boundary but also various policy domains. This study formulates five propositions to characterize the cross‐boundary strategies of corporate policy entrepreneurship, a distinct form of policy entrepreneurship in a developing authoritarian state. The case study of mobile healthcare payment innovation in China finds that the corporate entrepreneur used a series of cross‐boundary strategies adeptly that eventually made the innovation not only adopted in one locality but also rapidly diffused nationwide. These strategies were not used in isolation or in a pure stepwise fashion but appeared to be recursive and interactive, suggesting the dynamic nature of corporate policy entrepreneurship in a multilevel governance system. More studies could be done to further examine strategies and processes of other forms of policy entrepreneurship in various national and sectoral settings.
High‐temperature torsion of aluminum bars
Authors: Piao Yinguang , Le Khanh Chau
Published: November 2019

This paper studies high‐temperature torsion of aluminum bars within the simplified thermodynamic dislocation theory that ignores the excess dislocations. Employing a small set of physics‐based parameters, we are able to fit experimental torque‐twist curves for five different twist rates. The thermal softening effect is shown to be essential at high twist rates.
High‐order shape functions for interior acoustics
Authors: Duvigneau Fabian , Duczek Sascha
Published: November 2019

The acoustic behavior of structures has lately been in the focus of industrial applications, due to the fact that the acoustic emission of a product is one major parameter which significantly influences the customer perception with respect to comfort and functionality. In this context, the numerical simulation of vibroacoustic problems needs to provide reliable information in order to be able to evaluate the acoustic behavior of new products already in an early stage of the product development cycle. With the help of a suitable simulation model expensive experimental studies can be reduced and acoustically improved designs can be developed. However, there are already commercial software tools available which offer the opportunity to solve coupled vibroacoustic problems. These tools are typically based on conventional low‐order finite element methods (h‐FEM) for solving the governing partial differential equations (PDEs) of the problem. In this contribution, the advantages of high‐order finite element methods, such as a possibly exponential rates of convergence, will be exploited. Based on this approach a similar accuracy compared to classical h‐FEM simulations using significantly less degrees of freedom (dof) can be achieved. Consequently, the computational time required for the analysis can be notably reduced for a given error threshold. Reducing the computational effort is of special importance when investigating complex structures of practical relevance. Even today, the overall efficiency of the simulation process is still an issue, despite the ever growing computational power. To exploit the described advantages, high‐order FEMs have to be extended to acoustical problems. In this contribution the developed high‐order simulation approach is discussed and the obtained results are compared to commercial finite element solutions focussing on the accuracy and the computational effort of the different approaches.
Size effect caused by excess dislocations in twisted micro‐wires
Authors: Le Khanh Chau , Piao Yinguang
Published: November 2019

This paper applies thermodynamic dislocation theory to simulate the torque‐twist curves of copper micro‐wires subjected to torsion. The size effect due to the pile‐up of excess dislocations is essential for wire's radii in micron range.
Efficient Simulations for Contamination of Groundwater Aquifers under Uncertainties
Authors: Litvinenko Alexander , Logashenko Dmitry , Tempone Raul , Wittum Gabriel , Keyes David
Published: November 2019

Accurate modeling of contamination in subsurface flow and water aquifers is crucial for agriculture and environmental protection. Here, we demonstrate a parallel method to quantify the propagation of the uncertainty in the dispersal of pollution in density‐driven flow. We solve an Elder‐like problem, where we use random fields to model the limited knowledge on the porosity and permeability. The uncertain solution, mass fraction, is approximated via low‐cost generalized polynomial chaos expansion (gPCE). Parallelization is done in both the physical and parametric spaces.
Numerical Analysis of Vibration Patterns in Hydropower Units
Authors: Sperber Christian , Weber Wilhelm , Eberhard Peter
Published: November 2019

Every manufactured hydropower rotor shows some degree of unbalance and other imperfections that cause vibrations. In this contribution, a non‐linear dynamic model is used to calculate the lateral vibrations of vertical rotors in hydropower units due to generator unbalance and coupling misalignment. The vibrations are analyzed and distinguishing features are identified. Using the identified features, it is possible to diagnose the vibration cause from vibrational data for the described model. This can be done even when some model parameters like bearing properties are not known with high accuracy.
Logistic regression for potential modeling
Authors: Kost Samuel , Rheinbach Oliver , Schaeben Helmut
Published: November 2019

Regression or regression‐like models are often employed in potential modeling, i.e., for the targeting of resources, either based on 2D map images or 3D geomodels both in raster mode or based on spatial point processes. Recently, machine learning techniques such as artificial neural networks have gained popularity also in potential modeling. Using artificial neural networks, decent results in the prediction of the target event are obtained. However, insight into the problem, e.g., about importance of specific covariables, is difficult to obtain. On the other hand, logistic regression has a well understood statistical foundation and works with an explicit model from which knowledge can be gained about the underlying problem. However, establishing such an explicit model is rather difficult for real world problems. We propose a model selection strategy for logistic regression, which includes nonlinearities for improved classification results. At the same time, interpretability of the results is preserved.
Perimetric blowing at the rear of a bluff body: consequences on the wake dynamics and drag reduction
Authors: Lorite-Díez Manuel , Jiménez-González José-Ignacio , Martínez-Bazán Carlos , Cadot Olivier , Pastur Luc
Published: November 2019

In a perspective of active flow control of the bistable wake of a square‐back Ahmed body, we show that the steady blowing through a perimetric slit at the rear of the body is not equivalent to a material rear perimetric cavity, the latter being able to suppress the bistable dynamics and symmetrize the wake flow, while the former cannot achieve any of the two targets, indicating that the steady perimetric blowing has no control authority on the symmetric unstable steady solution of the system.
Palmgren, Gaßner and the challenges of fatigue behavior of components at variable amplitudes
Authors: Wächter Michael , Hinkelmann Karsten , Esderts Alfons , Zenner Harald
Published: November 2019

The focus of this contribution is on the work of the German engineer Ernst Gaßner. He invented the first fatigue tests at variable amplitude loading and introduced the field of “Betriebsfestigkeit” to the engineering community.
A variational material model for shape memory alloys under thermal cycling
Authors: Waimann Johanna , Hackl Klaus , Junker Philipp
Published: November 2019

Due to their special material behavior– namely the superelasticity as well as the one‐way and two‐way effect– shape memory alloys are very attractive materials for industrial applications. The solid/solid phase transformation between austenite and martensite is however accompanied by a formation of dislocations which influence the cyclic behavior of this special class of smart materials. For mechanical cycling, the formed dislocations favor the transformation from austenite to martensite and delay the reverse transformation. But for thermal cycling, they have the opposite effect and thus result in a decrease of the transformation temperature and in a delayed transformation from austenite to martensite.

We present a material model which is able to show both effects and hence displays microstructural evolution for a mechanically and thermally cycled material. Based on the variational method of the principle of the minimum of the dissipation potential, we model the so called effect of functional fatigue by storage of the transformation history of the observed material. In addition to that and for numerical efficiency, we use an evolving orientation distribution function to account for the polycrystalline structure of shape memory alloys, see [2]. Finally, we present first numerical results which verify the micromechanical model's functionality.
A thermomechanical modelling framework for selective laser melting based on phase transformations
Authors: Guschke Isabelle , Bartel Thorsten , Menzel Andreas
Published: November 2019

SLM (selective laser melting) is one of many processes belonging to the additive manufacturing sector, where a laser beam completely melts the particles of the manufactured part layer by layer. In contrast to common models, this framework is based on the minimisation of the free energy density where the phase transformation from powder to molten pool to re‐solidified material is modelled explicitly. The goal is to develop a more sophisticated model which is based on the material behaviour itself rather than on the use of temperature dependent material parameters. The following model is adapted from phase transformations in shape memory alloys, cf. [1]. With this at hand, more insight into the process is gained and the deformation as well as the residual stresses are predictable.
Multi‐dimensional Sum‐Up Rounding using Hilbert curve iterates
Authors: Manns Paul , Kirches Christian
Published: November 2019

Mixed‐integer optimal control problems can be reformulated by means of partial outer convexification, which introduces binary‐valued switching functions for the different realizations of a discrete‐valued control variable. They can be relaxed naturally by allowing them to take values in [0, 1]. Sum‐Up Rounding (SUR) algorithms approximate feasible switching functions of the relaxation with binary ones. If the controls are distributed in one dimension, the approximants are known to converge in the weak∗ topology of L∞. We show that this still holds true for controls that are distributed in more than one dimension if an appropriate grid refinement strategy that is coupled with a deliberate ordering of the grid cells is chosen. This condition is satisfied by the iterates of space‐filling curves, e.g. the Hilbert curve.
Continuum Limit and Homogenization of Stochastic and Periodic Discrete Systems – Fracture in Composite Materials
Authors: Lauerbach Laura , Neukamm Stefan , Schäffner Mathias , Schlömerkemper Anja
Published: November 2019

The limiting behaviour of a one‐dimensional discrete system is studied by means of Γ‐convergence. We consider a toy model of a chain of atoms. The interaction potentials are of Lennard‐Jones type and periodically or stochastically distributed. The energy of the system is considered in the discrete to continuum limit, i.e. as the number of atoms tends to infinity. During that limit, a homogenization process takes place. The limiting functional is discussed, especially with regard to fracture. Secondly, we consider a rescaled version of the problem, which yields a limiting energy of Griffith's type consisting of a quadratic integral term and a jump contribution. The periodic case can be found in [8], the stochastic case in [6,7].
Analytical investigation of the motion of lapping particles
Authors: Bilz Raphael , de Payrebrune Kristin M.
Published: November 2019

Lapping is a machining process that improves technical surfaces that require a high level of precision and accuracy. Smooth surfaces can be very important to avoid cracks in components exposed to high loads. During lapping, the workpiece is placed on the lapping plate with a complex relative movement between both parts. In the gap between both parts, the lapping fluid with abrasive particles is placed. The moving particles can deform or cut the material of the workpiece, and iteratively smooth its surface. With appropriate operating parameters, as fluid and particle material, size and proportion, very high quality surfaces can be achieved.

To describe lapping processes, it is essential to understand the kinematics of the particles that influence the outcome of the manufacturing process, which can be accomplished by experiments, numerical studies and analytical approaches. Here we will investigate the kinematics of lapping particles analytically. Using a straightforward model, geometry‐dependent threshold values for the coefficient of friction can be found that significantly influence the system behavior. We expect that the findings will contribute to extending the knowledge of the underlying physics in the lapping process so that we can adapt it to specific requirements.
A Novel Two‐Step Model to Investigate Turbulent Gas Flows Shearing Thin Liquid Films
Authors: Bender Achim , Stroh Alexander , Frohnapfel Bettina , Stephan Peter , Gambaryan-Roisman Tatiana
Published: November 2019

In this work a two‐step model to investigate a thin liquid film sheared by a turbulent gas flow is presented. In a first step, a direct numerical simulation of the gas phase is conducted. The turbulent shear stress at the lower wall is stored and used as a boundary condition for the long‐wave evolution of the liquid film, which is calculated in a second step. Results show that the turbulent shear stress fluctuations have to be considered when evaluating turbulent‐two‐phase channel flows.
High‐performance modeling of concrete ageing
Authors: Habera Michal , Zilian Andreas
Published: November 2019

Long‐term behaviour of concrete structural elements is very important for evaluation of its health and serviceability range. The phenomena that must be considered are complex and lead to coupled multiphysics formulations. Such formulations are difficult not only from physical perspective, but also from computational perspective.

In this contribution attention to computational efficiency and effective implementation is payed. Presented model for concrete ageing is based on microprestress‐solidification (MPS) theory of Bazant [1], Kunzel's model for heat and moisture transport [2] and Mazars model for damage [3]. Ageing linear viscoelastic response, which is immanent to MPS theory and concrete creep, leads to ordinary differetial equation for internal variables solved for every quadrature/nodal point. Numerical structure of the finite element discretisation is examined. Few simplifications on physical model lead to a very efficient linear algebra problem for which standard preconditioned Krylov solvers are reviewed. In parallel, weak and strong scaling tests are performed. All results are produced within open‐source finite element framework FEniCS [4].

These models are usually a basis for more involved thermo‐hygro‐chemo‐mechanical (THCM) models with migrating chemical species. It is anticipated, that presented results will help practitioners or other structural engineerers with the choice of suitable and efficient methods for long‐term concrete modeling.
Application of different plasticity models to PC/ABS blends within micromechanical approaches
Authors: Hund Jonas , Seelig Thomas
Published: November 2019

Rubber‐toughened thermoplastic polymers such as PC/ABS blends exhibit a non‐monotonic dependence of fracture toughness on composition, e.g. [6]. The key parameters determining the mechanical response of PC/ABS are the PC vs. ABS ratio and the rubber content in ABS. In this contribution, two micromechanical modeling approaches (single particle unit cell models, random representative volume elements) are considered to investigate this behavior. Thereby, different visco‐plasticity models are utilized to capture the specific deformation behavior of each phase. Computational studies of both micromechanical modeling approaches are compared to each other as well as to experimental data.
On phase field modeling in the context of cyclic mechanical fatigue
Authors: Schreiber Christoph , Kuhn Charlotte , Müller Ralf
Published: November 2019

In this work the phenomenon of cyclic fatigue is integrated within a phase field model for brittle fracture by means of an additional contribution in the internal energy formulation in order to achieve a dependency of the crack evolution on the number of load cycles. Results of numerical fatigue crack growth simulations are presented.
Coupled atomistic‐continuum simulation of the mechanical properties of single‐layered graphene sheets
Authors: Zheng Qige , Wackerfuß Jens
Published: November 2019

The purpose of this work is the multiscale modeling of a single‐layered graphene sheet. The model is divided into three parts. One is an atomistic domain which is simulated with the atomic‐scale finite element method (AFEM). Another is a continuum domain. In this domain, the mechanical properties are investigated by using a finite element based on a nonlocal continuum shell model with a high order strain gradient. To be exact, it is a 4‐node 60‐generalized degree of freedom (DOF) Mindlin–Reissner finite shell element with a second order strain gradient. In the third part, a new transitional finite element is developed for smoothing the transition between the atomistic domain and continuum domain.
Motivating the development of a virtual process chain for sheet molding compound composites
Authors: Görthofer Johannes , Meyer Nils , Pallicity Tarkes Dora , Schöttl Ludwig , Trauth Anna , Schemmann Malte , Hohberg Martin , Pinter Pascal , Elsner Peter , Henning Frank , Hrymak Andrew , Seelig Thomas , Weidenmann Kay , Kärger Luise , Böhlke Thomas
Published: November 2019

This contribution presents a physical process chain and the corresponding virtual process chain for sheet molding compound (SMC) composites. Here, focus lies on the physical process chain as a motivation for the virtual process chain as discussed in the authors' publication [1]. The key steps of the virtual process chain are the identification of initial and boundary conditions, the compression molding simulation, the mapping of data and the structural simulation. The so established virtual process chain is validated via experimental investigations on a demonstrator structure. Both, the predicted results of the compression molding simulation, as well as the results of the structural simulation are in good accordance with the experiments.
On the electro‐chemo‐mechanical modelling of stomach smooth muscle contraction
Authors: Klemm Lisa , Seydewitz Robert , Morales-Orcajo Enrique , Böl Markus
Published: November 2019

During the ingestion of a meal the activation of smooth muscle cells (SMC) in the stomach wall lead to different types of contraction and relaxation processes, enabling the stomach to perform its main functions, which are the storage, mixing and transport of food. A three‐dimensional multi‐field and multi‐scale model of the gastric smooth muscle contraction is presented and its ability is tested in simulations performed on a tissue strip as well as on the whole organ.
An FFT‐based solver for brittle fracture on heterogeneous microstructures
Authors: Ernesti Felix , Schneider Matti , Böhlke Thomas
Published: November 2019

The description of material failure as an energy minimization problem, i.e., the Francfort–Marigo model, has been studied widely in recent years. The approximation of the crack surface as a phase field, i.e., smeared interface, enjoys great popularity, as it allows describing fracture as a set of partial differential equations. In numerical homogenization, FFT‐based solution methods have been established over the past two decades. Their purpose is to compute the overall response of a heterogeneous microstruture w.r.t. a macroscopic loading and can be applied to a variety of nonlinear materials. The benefits lie in a fast implementation and the possibility to use image data like CT‐scans as input without further need for meshing. Based on the results of the master thesis of the first author, we investigate phase field crack propagation on heterogeneous microstructures using FFT‐based solvers.
Lattice Boltzmann Simulation of the Dynamic Behavior of Solids
Authors: Reinirkens Thomas , Schlüter Alexander , Müller Ralf , Kuhn Charlotte
Published: November 2019

The Lattice Boltzmann Method (LBM) is a numerical method that is mainly used to simulate fluid flows but it can be applied to structural problems as well. In this work, different LBMs for solids subject to antiplane shear deformation are investigated with regard to their convergence and energy conservation behavior. In particular, the two‐dimensional models of Guangwu [1] and Chopard et al. [2] are analyzed. To compare the two models, the evolution of the total energy and theL2norm of a global error measure are analyzed.
A posteriori error analysis for the mixed Laplace eigenvalue problem: investigations for the BDM‐element
Authors: Bertrand Fleurianne , Boffi Daniele , Stenberg Rolf
Published: November 2019

A posteriori error estimates for the mixed numerical approximation of the Laplace eigenvalue problem can be derived using a reconstruction in the standard

‐conforming space for the primal variable of the mixed problem. In the case of Raviart–Thomas finite elements of arbitrary polynomial degree the resulting error estimator constitutes a guaranteed upper bound for the error and is shown to be local efficient. This paper shows that the extension for the BDM‐element is not straightforward.
An experimental model for the analysis of energy dissipation in particle dampers
Authors: Meyer Niklas , Seifried Robert
Published: November 2019

Particle damping is a very promising passive damping technique, however, it is still rarely used in technical applications due to its complex dimensioning. An experimental model is developed in order to investigate the energy dissipation of the dampers regardless of the underlying structure. The testbed consists of a particle box with a free‐free boundary condition which is excited by an acceleration controlled shaker. The loss factor and the energy dissipation are obtained via the complex power. The particle damper can be analyzed over a wide frequency and acceleration range. Different particle numbers are used showing the high potential of particle dampers for different excitation ranges.
Optimal Control and Asymptotic Analysis of the Cattaneo Equation
Authors: Blauth Sebastian , Andres Matthias , Pinnau René , Totzeck Claudia
Published: November 2019

We compare the classical Fourier model for heat transfer to the Cattaneo model for delayed heat transfer. In particular, we consider the asymptotic behavior of the Cattaneo model for a vanishing delay time in the context of an optimal control problem with tracking type cost functional. It is possible to rigorously prove that both optimal controls and states for this problem constrained by the Cattaneo equation converge to the respective optimal control and state of the problem constrained by the heat equation (cf. [1]). Here, we present a short overview of the topic as well as some numerical results for the limit process.
A Hashin‐Shtrikman type semi‐analytical homogenization procedure
Authors: Jaworek David , Gierden Christian , Waimann Johanna , Wulfinghoff Stephan , Reese Stefanie
Published: November 2019

Heterogeneous materials are important for a vast amount of applications e.g. in automotive industry or in aerospace. For instance when producing components, it can be desired to use materials with a heterogeneous microstructure in order to achieve specific material properties. Thus, it is beneficial to take the materials' microscopic structure into account and couple its behavior to the macroscopic response. As multiscale methods (e.g. FE2, FE‐FFT) are computationally expensive, semi‐analytical homogenization procedures are investigated to account for the transition between different length scales. In this work, the focus lies on applying a Hashin‐Shtrikman type method to elasto‐plasticity.
Reduction of fuel consumption of small gas turbines at idling under combined operation with adjustable compressor inlet and turbine outlet guide vanes
Authors: Borchert Uwe
Published: November 2019

For the experimental verification of the effect of adjustable compressor inlet guide vanes combined with adjustable turbine outlet guide vanes for reducing the fuel consumption at idling, an 8 kW test gas turbine was designed and built up. The data of the experiments with the test gas turbine was compared with experimental data acquired by the author from another gas turbine. Additionally, experimental data was compared with external data of other heat engines. Using the newly introduced dimensionless Kruschik number, the test gas turbine, two series gas turbines and an internal combustion engine was compared in terms of their required heat supply at idling.
Dynamic selection limiter schemes for high density gradient simulations of supersonic rarefied gas flows
Authors: Groll Rodion
Published: November 2019

For modelling thrust and efficiency of micro propulsion sytems standard DSMC methods with static collision limiter schemes do not differentiate between regions with varying degrees of flow rarefaction and different DSMC particle densities. The discrete influence of multi‐level grid coarsening and different elongations of the numerical time step on the quality of predicted flow quantities show the advateges of the dynamic collision limitation.
Lagrangian perspectives on turbulent superstructures in Rayleigh‐Bénard convection
Authors: Klünker Anna , Schneide Christiane , Pandey Ambrish , Padberg-Gehle Kathrin , Schumacher Jörg
Published: November 2019

We analyze large‐scale patterns in three‐dimensional turbulent convection in a horizontally extended square convection cell by means of Lagrangian particle trajectories calculated in direct numerical simulations. Different Lagrangian computational methods, i.e. finite‐time Lyapunov exponents, spectral and density‐based clustering and transfer operator approaches, are used to detect these large‐scale structures, which are denoted as turbulent superstructures of convection.
A‐priori pole selection for reduced models in vibro‐acoustics
Authors: Aumann Quirin , Müller Gerhard
Published: November 2019

Large models of complex dynamic systems can be evaluated efficiently using model order reduction methods. Many techniques, for example the iterative rational Krylov algorithm (IRKA), rely on a set of expansion points chosen before the reduction procedure. The number and location of the expansion points has a major impact on the quality of the resulting reduced model and the convergence of the algorithm. Based on the system's geometry and material, the number of modes in a certain frequency range can be computed using wave equations. This mode count allows the choice of both a reasonable size for the reduced model as well as a reasonable distribution of initial expansion points, which improves the convergence of IRKA. Using the mode count in a specific frequency range, a reduced model approximating the full model only in this frequency range can be generated.
Drag Reduction of Transversal Surface Waves with Sweep Angle
Authors: Meysonnat Pascal S. , Albers Marian , Schröder Wolfgang
Published: November 2019

Large‐eddy simulations of oblique spanwise traveling transversal surface waves in turbulent boundary layer flow are conducted. The results show a minor dependence of the drag reduction on the wave angle for small angles and downstream traveling waves and a strong decrease of the drag for upstream traveling waves.
On the nullity of homogeneous linearized kinematic and equilibrium equations of a system of supported and connected rigid bodies
Authors: Flajs Rado
Published: November 2019

This paper deals with homogeneous linearized kinematic equations and the equilibrium equations of systems of supported and connected rigid bodies, the type of which were encountered during the undergraduate course of Statics within the first year of the study of Civil Engineering at the University of Ljubljana. In the paper the very fundamental relation

nullity(A) = nullity(BT)

is proven using the well‐known virtual work principle. Here, matrices A and B denote the matrix of the homogeneous linearized kinematic equations and the matrix of the equilibrium equations, respectively. Since the well‐known equilibrium equations

could potentially lack a physical interpretation [1], a new proof for a smaller set of the equilibrium equations, preferable in practical and pedagogical sense [2,3], is presented.
Computational study of ventricular fibrillation by considering a strongly coupled electromechanical rat heart model
Authors: Holz David , Duong Minh Tuan , Alkassar Muhannad , Dittrich Sven , Leyendecker Sigrid
Published: November 2019

Fully coupled electromechanical models of the heart have demonstrated the importance of computational models to better understand the cause, evolution and termination of ventricular fibrillation (VF). Especially these kinds of models are used to study the interplay between the mechanoelectrical feedback (MEF) and VF. In this study, we investigate the influence of the MEF in a strongly coupled excitation‐contraction model on the VF behaviour of a MRI based rat left ventricle (LV) by varying the maximum conductance of the stretch activated channels (SACs). We finally compare the action potential (AP) evolution and apex displacement under different strengths of the MEF.
Coherent vortex structure investigation behind the axial fan in pipe
Authors: Čantrak Ðorđe , Janković Novica , Nedeljković Miloš
Published: November 2019

Experimental investigation of the coherent vortex structure in pipe on the axial fan pressure side, by use of the velocity optical measurement techniques, is reported in this paper. Generated vortex structure, its velocity and turbulent statistical values are revealed and discussed.
Simulating plant‐cell dehydration using a double‐porosity formulation based on the Theory of Porous Media
Authors: Eurich Lukas , Shahmoradi Shahla , Wagner Arndt , Borja Ronaldo , Ehlers Wolfgang
Published: November 2019

Many living organisms, particularly plant tissues, exhibit very interesting features with regard to technical applications. For example, many plant tissues are frost resistant, which is mainly due to the dehydration of their tissue cells as one of the crucial mechanisms to cope with subzero temperatures. In this contribution, a fully coupled thermo‐hydro‐mechanical model based on the Theory of Porous Media is applied to assess the impact of ice formation on the water content of the tissue cells. Special attention is paid to the water exchange from the cells to the macro‐pore space.
Elasticity suppresses viscous fingering in a reactive Hele‐Shaw cell
Authors: Mokbel Dominic , Aland Sebastian
Published: November 2019

We consider a system of two liquids in a Hele‐Shaw cell that form a viscoelastic material layer between them by a chemical reaction. Is has been demonstrated that this system leads to a fingering instability, supposedly by the elasticity of the newly created material phase. To explore this mechanism we employ a novel phase‐field model [1], which can handle fluid‐structure interaction involving growing elastic materials. Assuming the newly created phase to be a viscoelastic Kelvin‐Voigt material, we find that this mechanism alone does not explain the experimentally observed fingering. Imposing a viscosity contrast between the materials, we even find the presence of elasticity to suppress any viscous fingering.
Multigrid‐reduction‐in‐time for Eddy Current problems
Authors: Friedhoff Stephanie , Hahne Jens , Schöps Sebastian
Published: November 2019

Parallel‐in‐time methods have shown success for reducing the simulation time of many time‐dependent problems. Here, we consider applying the multigrid‐reduction‐in‐time (MGRIT) algorithm to a voltage‐driven eddy current model problem.
Artificial intelligence control applied to drag reduction of the fluidic pinball
Authors: Cornejo Maceda Guy Y. , Noack Bernd R. , Lusseyran François , Deng Nan , Pastur Luc , Morzynski Marek
Published: November 2019

The aim of our work is to advance a self‐learning, model‐free control method to tame complex nonlinear flows—building on the pioneering work of Dracopoulous [1]. The cornerstone is the formulation of the control problem as a function optimization problem. The control law is derived by solving a nonsmooth optimization problem thanks to an artificial intelligence technique, genetic programming (GP). Metaparameters optimization of the algorithm and complexity penalization have been our main contribution and have been tested on a cluster of three equidistant cylinders immersed in a incoming flow, the fluidic pinball. The means of control is the independent rotation of the cylinders. GP derived a control law associated to each cylinder in order to minimize the net drag power and managed to outperform past open‐loop studies with a 46.0 % net drag power reduction by combining two strategies from literature. This success of MIMO control including sensor history is promising for exploring even more complex dynamics.
An Artificial Neural Network based Solution Scheme to periodic Homogenization
Authors: Göküzüm Felix Selim , Nguyen Lu Trong Khiem , Keip Marc-André
Published: November 2019

Artificial neural networks (ANNs) have aroused research's and industry's interest due to their excellent approximation properties and are broadly used nowadays in the field of machine learning. In the present contribution, ANNs are used for finding solutions of periodic homogenization problems. The construction of ANN‐based trial functions that satisfy the given boundary conditions on the microscale allows for the unconstrained optimization of a global energy potential. Goal of the present approach is a memory efficient solution scheme as ANNs are known to fit complicated functions with a relatively small number of internal parameters. The method is tested for a three‐dimensional example using a global trial function and is qualitatively compared to a fast Fourier transform (FFT) based simulation.
Non‐linear vibrations in rotor systems with floating ring bearings induced by fluid‐structure interactions
Authors: Woschke Elmar , Nitzschke Steffen , Daniel Christian
Published: November 2019

Although the use of combustion engines will decrease in passenger cars due to ecological reasons, turbochargers (TC) as typical applications with floating ring bearings will furthermore be applied in other applications like combined heat and power plants, ships or emergency backup generators for data processing service center and similar systems. Thus, the development of TC concerning rotor‐ and hydrodynamics is an important task, which leads due to the non‐linear behaviour to the necessity of advanced simulations for improving the performance.
Geometric a‐priori evaluation of sample designs
Authors: Daum Rebecca
Published: November 2019

Highly complex FEM models for crash simulations require large computing capacities. A meaningful sample design is crucial for applications with large sensitivities. Latin Hypercube sampling techniques allow for a flexible number of sample points without specifying the required number of sample points for specific applications. We present an a‐priori technique for evaluating sample designs for highly sensitive applications.
A geometric nonlinear model for rotating cylindrical shells
Authors: Schmidt Rico , Ams Alfons
Published: November 2019

Shell structures are extensively used in engineering for constructions with light weight and high strength. Classical applications are covers in automotive industry, aero‐ and astronautics. For this purpose the dynamical behaviour is of interest for safety and comfort. The focus will be placed on rotating circumferential cylindrical shells.

Starting with the geometrical nonlinear kinematics for the strains, the HAMILTON's principle is evaluated. In the following‐up to the calculus of variation RITZ approach is used, to compute eigenfrequencies. Afterwards the results are discussed for certain examples and compared to FE‐solutions.
Modal Flatness Analysis of Thin Sheets
Authors: Gruber Peter , Löhe Klaus
Published: November 2019

Concerning the industrial process under investigation thin sheets are generated by squeezing material through a thin and actuated gap. Caused by improper settings or various disturbing control actions the sheets may exhibit residual stresses, and thus flatness defects. The aim of this work is to provide a modal analysis framework for visualization of these flatness defects.
Analysis of acoustic wave propagation in composite laminates via a spectral element method
Authors: Perras Elias , Zhang Chuanzeng
Published: November 2019

The analysis of the acoustic or elastic wave propagation phenomena in the time‐domain is computationally expensive. An often‐cited rule of thumb is to use at least ten nodes per wavelength if using quadratic shape functions, and even more nodes are necessary in order to achieve highly accurate numerical results. For large‐scale problems, this results in a large system of linear algebraic equations, which must be solved for several thousands of time‐steps. This requires a vast amount of the computing time. In this paper, a spectral element method (SEM), which is a variant of the finite element method (FEM) by using high‐order shape functions with non‐equidistant node distributions, is presented in order to investigate the acoustic wave propagation problems taking the fluid‐structure interaction into account with a minimum of required degrees of freedoms (DOFs). Hence, the computing time for solving the system of linear algebraic equations is reduced while maintaining a high accuracy. The element matrices are computed using the Lobatto quadrature method, which results in a diagonal element mass matrix. For fluid‐structure interaction problems in acoustics, a non‐symmetric sparse mass matrix is obtained. By using an explicit time‐integration scheme only the mass matrix becomes the coefficient matrix of the linear system and, due to its high sparsity, the solution process is very efficient. In this work, the SEM is implemented and applied for the analysis of the transient behavior of the laminated composite structures excited by acoustic waves. Numerical examples are presented and discussed to show the efficiency of the SEM in the time‐domain for applications in acoustic wave propagation problems considering the fluid‐structure interaction.
Reference material preconditioning for FFT‐based solvers
Authors: Ladecký Martin , Pultarová Ivana , Zeman Jan , Vondřejc Jaroslav
Published: November 2019

Problems of finding effective material properties discussed in the classical works on homogenisation [1, 2] originate from asymptotic analysis of elliptic partial differential equations with oscillating anisotropic data. In 1994, Moulinec and Suquet [3] introduced an iterative algorithm for efficient determination of effective properties. In spite of its popularity and a deep research interest in this method, there are still some opportunities for improving its numerical effectiveness. We focus on preconditioning of related linear systems, which is necessary for solving large problems by iterative solvers. We introduce a general scheme for construction of preconditioning matrices based on some appropriate approximation of original material data.
Block partitioning of sparse rectangular matrices
Authors: Dumitrasc Andrei , Leleux Philippe , Rüde Ulrich
Published: November 2019

We present a means of reordering large, sparse rectangular matrices such that their nonzeros are closer to the diagonal. This enables a block‐partitioning which is useful in parallel contexts. We use the Reverse Cuthill‐McKee (RCM) algorithm on the adjacency matrix of the associated bipartite graph. The resulting, reordered matrix has a block bidiagonal structure.
FETI‐DP Solvers and Deal.II for Problems in Dislocation Mechanics
Authors: Köhler Stephan , Rheinbach Oliver , Sandfeld Stefan , Steinberger Dominik
Published: November 2019

FETI‐DP (Finite Element Tearing and Interconnecting Dual‐Primal) solvers and the deal.II adaptive finite element library are combined to solve dislocation eigenstrain problems in micromechanics. Computational results using adaptive finite elements with millions of unknowns and up to 3072 cores of the Taurus supercomputer at ZIH in Dresden are presented.
Permeability and flow through a packed bed of beads in a rectangular cross‐section affected by overlapping wall effects
Authors: Boettcher Konrad , Neumann Tim , Ehrhard Peter
Published: November 2019

The beads in a packed bed are usually distributed randomly. Therefore, on a macroscopic scale, a fluid flows uniformly through such a porous medium. For thin porous media, deviations are known near the regions of confinement. This so‐called wall effect is extensively investigated in literature for circular confinements. In this work, the wall effect and the flow through porous media in a rectangular domain is studied. This has great importance during the initial filling process of lithium‐ion batteries with the liquid electrolyte. Such batteries consist of collector foils, on which the porous electrodes are attached. Their thickness is only 5 – 10 times a particle diameter dP and may be modeled as a monodisperse bed of spheres. The filling flow is extremely slow and may be in the pre‐Darcy flow region, wherefore the validity of Darcy‘s law is experimentally checked. Then, the local porosity function depending on the distance to the wall is experimentally determined. For very thin porous media, the wall effect of each wall may overlap each other, which is taken into account by using an overlapping model from the literature. The widely used model of Carman‐Kozeny [1] relates the permeability with the porosity. Its validity in the near‐wall region is checked by comparing experimentally‐obtained mean pore diameters to those related to the model of Carman‐Kozeny. The flow through a porous media is computed and compared to experimental results from literature for circular confinement and preliminary optically‐matched PIV measurements.
Molecular dynamics simulation of ultrasonic metal welding of aluminum alloys
Authors: Mostafavi Shimaalsadat , Markert Bernd
Published: November 2019

In this study, molecular dynamics simulation of the ultrasonic welding of aluminum alloys is presented. Ultrasonic metal welding is counted as a solid state consolidation of the mating parts, in which the growing interface temperature is far below the melting point of the material and the energy consumption is relatively low compared to the common welding processes such as arc welding. The reciprocating motion of the sonotrode on the mating parts combined with the application of external pressure in the process of ultrasonic welding is the source of temperature rise and strong plastic deformations at the mating interface. This contribution is devoted to study the interactive effect of the process parameters on the interface temperature, deformation process of the mating parts and the diffusion behavior of the interface atoms.
An Explicit Nash Equilibrium to a Multi‐Leader‐Follower Game
Authors: Steffensen Sonja , Thünen Anna
Published: November 2019

The multi‐leader‐follower game (MLFG) is a generalization of the Stackelberg game which considers bilevel games with a single leader. Here, the individuals (players) are divided into two groups, namely leaders and followers, according to their position (role) in the game. Mathematically, this yields a hierarchical Nash game, where further minimization problems appear in the leaders' optimization problems as constraints. A Nash equilibrium is then given by a multistrategy vector of all players, where no player has the incentive to change his chosen strategy unilaterally.

We derive a Nash equilibrium for a quadratic multi‐leader‐follower game using the nonsmooth best response function of the follower. The existence and uniqueness of solutions are proven for an example and its Nash equilibrium is explicitly computed.
Gradient Enhanced Crystal Plasticity in Additive Manufacturing Identification of a Macroscopic Yield Criterion
Authors: Kergaßner Andreas , Mergheim Julia , Steinmann Paul
Published: November 2019

In this contribution the mechanical behavior of additively manufactured Inconel 718 (IN 718) is modeled on the meso and macro scale. Gradient enhanced crystal plasticity is utilized to capture the kinematics of crystallographic slips and grain boundaries on the meso scale. The material model is solved on a representative volume element (RVE) by means of the Finite Element Method. In order to represent additively manufactured material, the RVE is based on a numerical grain growth simulation of the solidification during additive manufacturing. Mesoscopic elastic behavior and the initial yield locus are transferred to the macro scale by numerical homogenization and used to identify the parameters for a quartic yield function which is able to capture the highly anisotropic material behavior.