bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of the fractal properties of silica aerogels using diffusion‐limited aggregation
Authors: Abdusalamov Rasul , Itskov Mikhail , Milow Barbara , Rege Ameya 
Published: January 2021

AbstractSilica aerogels are highly porous solids with very low densities and thermal conductivities. Their high porosity results in a fractal morphology which has a strong influence on mechanical properties. In this work, the diffusion‐limited cluster aggregation (DLCA) method is implemented to model silica aerogel aggregates. A preliminary model based on this approach demonstrates good agreement with experimental data [1]. The influence on the fractal properties of different input parameters as for example the particle size is investigated. Moreover, the resulting geometries are compared to fractal features of silica aerogels determined by experimental data from small angle X‐ray scattering (SAXS). The mechanical response of these aggregation models is analyzed by a finite element analysis (FEA) for the generated representative volume elements (RVE). The effect of varying densities on the mechanical properties, for e.g., Young's modulus, is further elucidated.
Modeling the microstructure of biopolymer aerogels using Voronoi tessellation method
Authors: Chandrasekaran Rajesh , Hillgärtner Markus , Rege Ameya , Milow Barbara , Itskov Mikhail 
Published: January 2021

AbstractThe bulk properties of biopolymer aerogels depend on their microstructure, which can be tailored by different synthesis and drying methods. Biopolymer aerogels are characterized by a fibrillar morphology having a cellular‐like network. The recently proposed constitutive modeling approach by Rege et al. [1] has shown good predictive capabilities in describing the mechanical behavior of such aerogels. Although the model describes the cellular nature and adheres to the cell‐size distributions of aerogels, it is based on the assumption that the network is made up of idealized square‐shaped cells. In this contribution, the diversified cellular morphology of aerogels is described computationally using a Laguerre‐Voronoi tessellation based approach [2]. The pore‐size distribution (PSD) data obtained from experiments accounts for the random cell sizes within the network. Accordingly, Voronoi tessellations are generated to create periodic representative volume elements (RVEs) resembling the microstructural properties of the cellular network. This work is an extension of our previous Voronoi tessellation‐based 2‐d description of biopolymer aerogels [3].
Identifying equivalent transversely isotropic material parameters for full‐surface bonded sheet‐layered lamination stacks
Authors: Baloglu Maximilian Volkan , Willner Kai 
Published: January 2021

AbstractThe accurate prediction of the structural properties of sheet‐layered lamination stacks in rotors and stators of electric motors is a challenging task due to the special layer design. The joining technology has a major influence on the individual sheet interactions and on the macroscopic quantities. Here, full‐surface bonded lamination stacks are considered for which equivalent linear transversely isotropic material parameters are determined by modeling the bonding varnish using Zero‐Thickness interface elements. It is shown that this procedure delivers comparable results to those obtained with traditional methods, like the rule of mixture or by modeling the adhesive layer with 3D continuum elements.
Topology and material optimization of anisotropic materials including a filter to smooth fiber pathways
Authors: Jantos Dustin Roman , Hackl Klaus , Junker Philipp 
Published: January 2021

AbstractA three‐dimensional topology optimization of anisotropic materials including the optimization of the local material orientation based on thermodynamic principles is presented. To this end, the topology is parameterized by a continuous density variable with penalization of intermediate densities (SIMP) [1]. The material orientation is defined by the rotation of a given anisotropic base material and the rotation is parameterized by a set of three Euler angles. A novel filtering technique is presented to provide a smoothing of the material orientation, i.e. the fiber paths. The influence of the filter parameter on the maximum allowed fiber path curvature is shown. The constraint on the maximum fiber curvature also influences the results for the optimal topology. Corresponding numerical results for the simultaneous optimization of the topology and local material optimization for the two‐dimensional and three‐dimensional case will be presented.
GPU‐accelerated simulation of a non‐local conservation law
Authors: Göttlich Simone , Müller Jann , Weissen Jennifer 
Published: January 2021

AbstractThe model under consideration is a non‐local conservation law in two space dimensions that might be used to model material or pedestrian flow. We accelerate the simulation of the non‐local model using parallelization of the non‐local terms in the programming language Haskell. The implementation allows for the computation of the solution to the conservation law with a finite volume method at reasonable computational cost even for large domains and fine discretizations.
Daily Precipitation Generation using a Hidden Markov Model with Correlated Emissions for the Potomac River Basin
Authors: Kroiz Gerson C. , Majumder Reetam , Gobbert Matthias K. , Neerchal Nagaraj K. , Markert Kel , Mehta Amita 
Published: January 2021

AbstractA daily precipitation generator based on a hidden Markov model with Gaussian copulas (HMM‐GC) is constructed using remote sensing data from GPM‐IMERG for the Potomac river basin on the East Coast of the USA. Daily precipitation over the basin from 2001–2018 for the wet season months of July to September is modeled using a 4‐state HMM, and correlated precipitation amounts are generated from a mixture of Gamma distributions using Gaussian copulas for each state. Synthetic data from a model using a mixture of two Gamma distributions for the non‐zero precipitation is shown to replicate the historical data better than a model using a single Gamma distribution.
Plate theories: A mixed Vekua and consistent approximation approach
Authors: Meyer-Coors Michael , Kienzler Reinhold , Schneider Patrick 
Published: January 2021

AbstractBy the use of Taylor series expansion, we arrive from the three‐dimensional theory of linear elasticity at the exact two‐dimensional plate problem which consists of infinitely many equations and unknowns. Applying the approximation approach of Vekua or the consistent‐approximation approach to this exact problem leads to hierarchical PDE‐systems. For the latter approach a modular structure of the displacement coefficients is assumed and proved for several orders. With this modularity we show that “fully” reducible PDE‐systems, so called complete plate theories, can be obtained by using a special schema. The results of the complete plate theories coincide with the classical theories and also fulfill several local conditions. When proving the existence of “fully” reducible PDE‐systems for an Nth order complete plate theory, Hilbert‐type matrices appear. We calculate the determinant for these matrices and present a sketch of evidence.
The Invention of the Eigenstress Calculation in Plasticity
Authors: Bruhns Otto T. 
Published: January 2021

AbstractAlmost one hundred years ago, Heinrich Hencky, in a work published in German and probably for this reason less noticed, laid the essential foundations for today's calculation methods of elastic‐plastically deformed structures. In short remarks the importance of this work for several of today's commonly used methods is underlined.
Towards a stochastic model for electrohydrodynamic turbulence with application to electrolytes
Authors: Klein Marten , Schmidt Heiko 
Published: January 2021

AbstractWe investigate turbulent Couette flows of dilute, weakly‐conducting electrolytes by utilizing the stochastic one‐dimensional turbulence (ODT) model. The flow is driven by relative motion of the top and bottom wall and affected by an electric field between these walls that is prescribed by a voltage difference. The electrolytes considered have zero bulk charge and consist of two ion species with the same mobility, valence, and initial concentration. The stochastic model predicts a decrease of the mean streamwise velocity when an external voltage is applied provided that both Schmidt (Sc) and Reynolds (Re) numbers are sufficiently large, that is, Sc ≥ 30 for Re = 12000 investigated. The effect observed is relevant for flow control, but the mechanism awaits clarification. Present ODT results may help to develop this understanding or design laboratory experiments.
A thermomechanical‐phase‐field approach for modeling of residual stresses in fusion welding
Authors: Ali Baharin Rahim Ali , Heider Yousef , Markert Bernd 
Published: January 2021

AbstractThe welding process of metallic components, such as using gas tungsten arc welding (GTAW), is often accompanied by detrimental deformations and residual stresses, which affect the strength and functionality of these welded components. In this work, a phase‐field model, usually used to track the state of the phase‐change materials, is embedded in a thermo‐elasto‐plastic finite element model in order to simulate the welding process and the residual stresses. The phase‐field method (PFM) enables us to track the melting front of the metal, due to the welding heat source, and to split the analysis domain into soft and solid regions. In this way, temperature and phase‐field‐dependent material properties can properly be assigned to different regions in the domain. The phase‐field evolution is governed by Allen‐Cahn equation and relies on specification of the free energy density function as the main driving force for the phase change. Having a coupled thermomechanical process during the welding heating‐cooling cycle, the onset of residual stresses is associated with plastic deformations and can be observed after cooling to the ambient temperature. The plasticity model considers J2 plasticity with isotropic hardening. The coupled nonlinear system of equations is solved in the open‐source FE package, FEniCS, with time discretization based on the finite difference method.
A transfer operator based computational study of mixing processes in open flow systems
Authors: Klünker Anna , Padberg-Gehle Kathrin 
Published: January 2021

AbstractWe study mixing by chaotic advection in open flow systems, where the corresponding small‐scale structures are created by means of the stretching and folding property of chaotic flows. The systems we consider contain an inlet and an outlet flow region as well as a mixing region and are characterized by constant in‐ and outflow of fluid particles. The evolution of a mass distribution in the open system is described via a transfer operator. The spatially discretized approximation of the transfer operator defines the transition matrix of an absorbing Markov chain restricted to finite transient states. We study the underlying mixing processes via this substochastic transition matrix. We conduct parameter studies for example systems with two differently colored fluids. We quantify the mixing of the resulting patterns by several mixing measures. In case of chaotic advection the transport processes in the open system are organized by the chaotic saddle and its stable and unstable manifolds. We extract these structures directly from leading eigenvectors of the transition matrix.
A lattice Boltzmann study on the effect of fluid viscosity contrast on the retention behavior of two‐fluid flow in porous media
Authors: Chaaban Mohamad , Heider Yousef , Markert Bernd 
Published: January 2021

AbstractIn this contribution, the Shan‐Chen (SC) two‐phase flow model of the lattice Boltzmann method (LBM) is numerically implemented to simulate multiphase fluid flow on microtomography (µ‐CT) data of a sphere packing. From the model, the saturation degrees of the fluid phases, i.e. invading and displaced fluids, are extracted from the computed lattice density distribution functions. Several simulations are run with different degrees of kinetic viscosity contrast between the fluid phases within increasing increments of capillary pressure. At each increment, the relative permeability regarding each fluid phase is computed as a function of the saturation degree. The motivation of this study is to (1) investigate the effect of the kinetic viscosity contrast between the fluid phases on the retention behavior, (2) analyze the range of validity of the van Genuchten relation according to the computed retention data and (3) propose an extension towards an upscaling micro‐to‐macroscopic hierarchic scheme for the simulation of multiphasic fluid flow in unsaturated porous media.
On the non‐uniqueness of marginally separated boundary layer flows
Authors: Stojanovic Ivo , Braun Stefan 
Published: January 2021

AbstractA stationary or time dependent, laminar flow with a locally separated boundary layer is considered. The Navier‐Stokes equations are analysed with the method of matched asymptotic expansions. The resulting integro‐differential equation, known as the fundamental equation of marginal separation, is solved numerically by means of a spectral method based on Chebyshev polynomials. The critical value of the parameter controlling the magnitude of the adverse pressure gradient is associated with a bifurcation of the stability characteristics of the locally separated shear layer. The solution behaviour of the integro‐differential equation in the corresponding parameter space is investigated. Special emphasis is placed on the observed non‐uniqueness of solutions and the associated branch points.
Orthogonal projections for image quality analyses applied to MRI
Authors: Breger Anna , Ramos Llorden Gabriel , Vegas Sanchez-Ferrero Gonzalo , Hoge W. Scott , Ehler Martin , Westin Carl-Fredrik 
Published: January 2021

AbstractMeasuring digital image quality is of importance in numerous applied research fields, such as image acquisition, image processing or image reconstruction. Subjective evaluation, i.e. assessment by human beings, is often too time‐consuming, expensive and inconsistent in complicated tasks such as medical imaging. In order to better understand the relation between objective image quality assessment measures, we compare a selection in an experimental setup. It is well known that L2 error estimation, i.e. computing the mean squared error (MSE) between two images, does not correspond well to the perceptual evaluation by the human visual system. Here, we illustrate on the example of MRI data the interaction of the MSE with the signal to noise ratio (SNR), the variance and subjective evaluation. We use random coverings of the space of orthogonal projections for coil combination to enable a comprehensive correlation analysis.
Efficient Solution of Distributed MIP in Control of Networked Systems
Authors: Liu Zonglin , Stursberg Olaf 
Published: January 2021

AbstractCertain classes of optimization‐based control problems stated for networked systems involving hybrid dynamics and logical constraints can be cast into Mixed‐Integer Programming (MIP) problems. Since these belong to the complexity class NP‐hard, the motivation arises to find approximations of the optimal solution by distributed solution efficiently. For the cases that the cost functional is linear or quadratic and the constraints are linear, this paper proposes an alternative to the standard centralized schemes, by employing dual decomposition into a set of local problems of moderate size which can be solved in parallel. Numerical examples demonstrate that the scheme can efficiently approximate the global solution.
Formal Calculation of Positive Invariant Sets for the Lorenz Family Combining Lyapunov Approaches and Quantifier Elimination
Authors: Röbenack Klaus 
Published: January 2021

AbstractThe Lorenz family is a class of dynamic systems which is parameterized in one variable and includes both the classic Lorenz system and the Chen system. Both systems (and therefore the Lorenz family) can show chaotic behaviour. For different questions of system analysis, e.g. for the estimation of various types of dimensions, it is helpful to be able to determine bounds on the attractor. One typical approach ist the usage of Lyapunov functions to describe positive invariant sets. However, this approach usually requires a good knowledge of the system to perform the necessary calculations. For polynomial systems, these calculations can be carried out using a computation technique known as quantifier elimination. In this contribution we describe this approach and employ it to calculate bounds on the Lorenz family.
An Overset Grid (Chimera) Method for a Discontinuous Galerkin Discretization of the Navier‐Stokes Equations
Authors: Genuit Fabian , Keßler Manuel , Krämer Ewald 
Published: January 2021

AbstractThe discontinuous Galerkin (DG) method, a high‐order method in space, is applied to discretize the compressible Navier‐Stokes (NS) equations. The temporal discretization is realized using an implicit backward differentiation formula. Furthermore, an overset grid method is employed to enable rigid relative movements of flow bodies in the numerical setup. The Magnus effect serves as a test case and reveals promising results compared to reference values in literature.
Damage and fracture of the optimized X0‐specimen
Authors: Gerke Steffen , Liedmann Jan , Brünig Michael , Barthold Franz-Joseph 
Published: January 2021

AbstractThe paper deals with numerical and experimental results of the gradient based optimized biaxial X0‐specimen. The original, engineering based design has been optimized under producibility restrictions for two different loading conditions to gain a distinct (high or low) stress triaxiality maintaining a sufficiently homogeneous distribution in the notched regions of the specimen. Specimens with the initial and the two load case dependent optimized geometries have been fabricated of aluminum alloy sheets and biaxially tested. Here the corresponding results with respect to biaxial tension loading are presented and the numerical results clearly indicate the higher stress triaxialities and the experimental results demonstrate elevated void growth as leading damage mechanism.
Consideration of accelerations within the Theory of Porous Media
Authors: Bergmann Julia Nicolina , Bluhm Joachim , Schröder Jörg 
Published: January 2021

AbstractThis report deals with Theory of Porous Media (TPM) calculations, which take the accelerations into account. Two concepts for a simplified binary model considering accelerations as well as the question when to include accelerations are discussed with the help of two numerical one dimensional examples. After a brief description of the basic equations, an infinite half space, presenting porous soil filled with water, with two distinct spatially constant load cases is simulated, showing the advantages and disadvantages of the approaches.
A polyhedral element formulation based on the scaled boundary method for the analysis of nonlinear problems in solid mechanics
Authors: Reichel Rainer , Klarmann Simon , Klinkel Sven 
Published: January 2021

AbstractIn this contribution a numerical element formulation for the nonlinear analysis of solids is proposed. The element is defined by a polyhedron with an arbitrary number of polygonal faces. It is based on the scaling concept, which is adopted from the so‐called scaled boundary finite element method (SBFEM). The SBFEM is a semi‐analytical formulation to analyze problems in linear elasticity. Within this method the fundamental concept is to scale the domain's boundary with respect to a scaling center in order to describe the interior domain. The present element formulation employs the scaling concept twice and in contrast to SBFEM, uses a numerical approximation for the displacement response in both scaling directions. This makes it suitable for the analysis of geometrically and physically nonlinear problems. The advantages of the proposed element formulation is its high flexibility in mesh generation. It avoids the hanging node problems as arbitrary element geometries are possible. For example, using Octree algorithms, a fast and reliable mesh generation can be achieved. In case of curved boundaries the element formulation allows a precise representation of the geometry even with coarse meshes. Some numerical examples are presented to evaluate the accuracy of the proposed numerical method against analytical solutions, and a comparison to standard element formulations is given as well.
An uncertainty model for the curing process of transversely fiber reinforced plastics
Authors: Penner Eduard , Caylak Ismail , Mahnken Rolf 
Published: January 2021

AbstractLightweight structures, such as fiber reinforced plastics (FRPs), become increasingly important due to their excellent mechanical and lightweight properties. During the manufacturing process, curing of the matrix is a dominant effect as it is highly temperature dependent and influences strongly the mechanical, thermal and chemical properties of FRPs. Variations in the manufacturing process, measurement errors and missing or incomplete information are typical causes of uncertainties. This contribution presents a framework for an uncertainty model for the curing process of transversely fiber reinforced plastics. As a key idea the overall effective properties of the cured matrix during the manufacturing process are calculated by uncertainty homogenization models.
Numerical simulation of cyclic deformation behavior of SLM‐manufactured aluminum alloys
Authors: Wiegold Tillmann , Klinge Sandra 
Published: January 2021

AbstractThe selective laser melting process has already been developed for many metallic materials, including steel, aluminum, and titanium. The quasi‐static properties of these materials have been found to be comparable or even better than their conventionally manufactured counterparts. However, for their reliable application in operational components, their fatigue behavior plays a critical role. This phenomenon is dominated by several process‐related features, such as surface roughness, remnant porosity, microstructure and residual stresses. The present contribution shows a model which relies on an assumption for the Helmholtz free energy and the dissipation potential. To be more precise: the phase‐field method is applied to simulate the damage evolution, whereas plastic effects are modeled in terms of the isotropic hardening. It is assumed that the damage evolution only occurs in the tension mode of a cyclic load, which is achieved by the decomposition of the stored energy. The numerical results give insight into the evolution of plastic deformations and of damage at a material point and for a chosen mesoscopic sample.
The influence of magnetic field on nanoparticle transport in a micro channel
Authors: Bavandi Mahrokh , Wünsch Olaf 
Published: January 2021

AbstractThe present study focuses on a new solver considering the effect of magnetic field on nanoparticles concentration in a micro size channel. To describe the multi component behavior of blood, the Euler‐Euler method is used. Particles are modeled by a concentration equation considering a magnetic drift. The influence of a realistic magnetic field on nanoparticles is investigated. A result for a test case is presented. It shows that the magnetic body force resulting from nanoparticles also influence the hematocrit distribution in the channel.