bluuebunny/crossref_metadata_2025_split huggingface dataset:
Coarse‐Grid‐CFD for a Wire Wrapped Fuel Assembly
Authors: Viellieber Mathias , Dietrich Philipp , Class Andreas G. 
Published: November 2013

AbstractComputational fluid dynamics (CFD) simulations of complete nuclear reactor core geometries requires exceedingly large computational resources. However, in most cases there are repetitive geometry‐ and flow patterns allowing the general approach of creating a parameterized model for one segment and composing many of these reduced models to obtain the entire reactor simulation. Traditionally, this approach lead to so‐called subchannel analysis codes that are relying heavily on transport models based on experimental and empirical correlations. With our method, the Coarse‐Grid‐CFD (CGCFD), we intend to replace the experimental or empirical input with CFD data. Our method is based on detailed and well‐resolved CFD simulations of representative segments. From these simulations we extract and tabulate volumetric source terms. Parameterized data is used to close an otherwise strongly under resolved, coarsely meshed model of a complete reactor setup. In the previous formulation only forces created internally in the fluid are accounted for. The Anisotropic Porosity (AP) formulation wich is subject of the present investigation adresses other influences, like obstruction and flow guidance through spacers and in particular geometric details which are under resolved or ignored by the coarse mesh. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
ALE‐FEM for Two‐Phase Flows
Authors: Hahn Andreas , Held Kristin , Tobiska Lutz 
Published: November 2013

AbstractWe present a finite element method for the flow of two immiscible incompressible fluids in two and three dimensions. Thereby the presence of surface active agents (surfactants) on the interface is allowed, which alter the surface tension. The model consists of the incompressible Navier‐Stokes equations for velocity and pressure and a convection‐diffusion equation on the interface for the distribution of the surfactant. A moving grid technique is applied to track the interface, on that account a Arbitrary‐Lagrangian‐Eulerian (ALE) formulation of the Navier‐Stokes equation is used. The surface tension force is incorporated directly by making use of the Laplace‐Beltrami operator technique [5]. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A hybrid level set / front tracking approach
Authors: Basting Steffen , Weismann Martin , Prignitz Rodolphe 
Published: November 2013

AbstractIn finite element simulations of fluid flows with free boundaries, the representation of boundaries and interfaces plays an essential role. Common approaches can be categorized into two groups, interface tracking and interface capturing methods, each with individual pros and cons. The proposed approach provides a hybrid description of the interface. The main ingredient is a mesh optimization technique that aligns a given triangulation to the geometry which is implicitly represented by a level set function. Resulting triangulations are of optimal quality while connectivity of the mesh is retained. Consequently, finite element spaces defined on the aligned triangulations can be efficiently modified to account for solution specific properties such as discontinuities across interfaces.We outline an ALE‐based finite element method which can be used in various application scenarios. We briefly demonstrate the benefits of the method by applying it to two applications: The first application is concerned with a finite element method for particulate flows for which we provide an a priori error estimate. The estimate indicates that by using the proposed approach, h2 convergence can be obtained on aligned meshes, while a sharp h1/2 results holds for non‐aligned meshes. The second application is concerned with a fully coupled two‐phase flow benchmark problem. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical analysis of wave propagation in fluid‐filled deformable tubes
Authors: Uribe David , Steeb Holger , Saenger Erik H. , Kurzeja Patrick , Ruiz Oscar 
Published: November 2013

AbstractThe theory of Biot describing wave propagation in fluid saturated porous media is a good effective approximation of a wave induced in a fluid‐filled deformable tube. Nonetheless, it has been found that Biot's theory has shortcomings in predicting the fast P‐wave velocities and the amount of intrinsic attenuation. These problems arises when complex mechanical interactions of the solid phase and the fluid phase in the micro‐scale are not taken into account. In contrast, the approach proposed by Bernabe does take into account micro‐scopic interaction between phases and therefore poses an interesting alternative to Biot's theory. A Wave propagating in a deformable tube saturated with a viscous fluid is a simplified model of a porous material, and therefore the study of this geometry is of great interest. By using this geometry, the results of analytical and numerical results have an easier interpretation and therefore can be compared straightforward. Using a Finite Difference viscoelastic wave propagation code, the transient response was simulated. The wave source was modified with different characteristic frequencies in order to gain information of the dispersion relation. It was found that the P‐wave velocities of the simulations at sub‐critical frequencies closely match those of Bernabe's solution, but at over‐critical frequencies they come closer to Biot's solution. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of optimal metal flow in incremental sheet forming
Authors: Bambach Markus , Grzibovskis Richards 
Published: November 2013

AbstractSheet metal forming processes are manufacturing processes in which a piece of sheet metal is shaped to a specified geometry, e.g. a car door. A promising new forming process is incremental sheet metal forming, in which the deformation is imposed by a progressive, localised plastic deformation induced by a pin‐like forming tool that moves under numerical control along a pre‐defined trajectory. This process offers the possibility to control the metal flow by adjusting the trajectory of the forming tool. Mathematically, sheet metal forming processes can be considered as a mapping between the initial, undeformed sheet metal and the final, deformed state. In most applications the surface area of the sheet metal is enlarged during the deformation. In this case, an ideal mapping would produce a homogeneous stretching of the sheet metal such that the final sheet thickness is the same everywhere. In this work, we analyze the following question: for each point in the initial configuration, what must be its location on the final geometry such that the thickness is the same everywhere? We construct a special type of surface evolution that combines flow along the surface normal with appropriate tangential velocity corrections, and show that the flow yields a constant sheet thinning on a sheet metal. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Treatment Planning Optimization for Radiotherapy
Authors: Barnard Richard C. , Frank Martin , Herty Michael 
Published: November 2013

AbstractWe study the problem of treatment planning in radiotherapy. We use an energy‐dependent Boltzmann‐based particle transport model as a partial integro‐differential constraint for a convex optimization problem. We solve the resulting optimal control problem using a minimum entropy moment closure. Numerical results for problems on patient data are presented. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variation of friction drag via spanwise transversal surface waves
Authors: Meysonnat Pascal , Klumpp Stephan , Meinke Matthias , Schröder Wolfgang 
Published: November 2013

AbstractThe turbulent wall shear stress can be influenced through the introduction of spanwise velocity components in the near‐wall flow field. The underlying physical mechanisms for the drag reduction still remains to be fully understood. Two distinct wave configurations are analyzed and compared to an unactuated turbulent boundary layer to obtain further inside of the drag reducing mechanism using the dynamic mode decomposition. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the dynamics of the vortex structures generated by plasma DBD actuator
Authors: Procházka Pavel , Uruba Václav , Antoš Pavel 
Published: November 2013

AbstractThe plasma actuator is used to generate pseudo‐periodical vortices moving almost parallel to the wall under various settings of high‐voltage high‐frequency power AC. Low‐frequency amplitude modulation is desired to generate vortices, otherwise wall‐jet‐like flow is present. It will be shown how the dynamics of generated coherent vortices alternates depending on generator setting, frequency spectrum will be introduced in dependency on frequency of amplitude modulation and duty cycle. Measurements will be performed using TR‐PIV technique or HW anemometry across wall‐jet flow. The generated flow patterns are to be applied for control of boundary layers. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Armstrong‐Frederick Plasticity model with Cosserat effects
Authors: Chełmiński Krzysztof , Neff Patrizio , Owczarek Sebastian 
Published: November 2013

AbstractWe propose an extension of equations formulated by Armstrong and Frederick which includes micropolar effects. We study existence of solutions to the quasistatic Armstrong‐Frederick model with Cosserat effects which is still of non‐monotone type. It was shown that the limit in the Yosida approximation process satisfies the energy inequality. The limit functions have a better regularity than it could be found in the literature, where the original Armstrong‐Frederick model was studied. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some Poincaré type inequalities for quadratic matrix fields
Authors: Bauer Sebastian , Neff Patrizio , Pauly Dirk , Starke Gerhard 
Published: November 2013

AbstractWe present some Poincaré type inequalities for quadratic matrix fields with applications e.g. in gradient plasticity or fluid dynamics. In particular, an application to the pseudostress‐velocity formulation of the stationary Stokes problem is discussed. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cavitation and Singular Solutions in Nonlinear Elastodynamics
Authors: Giesselmann Jan 
Published: November 2013

AbstractBased on works of Ball (1982) and Pericak‐Spector and Spector (1988), we investigate singular solutions to the compressible nonlinear elastodynamics equations. These solutions have discontinuous displacement fields and describe fracture or cavitation. We explore a definition of singular solution via approximating sequences of smooth functions. We employ these approximating sequences to investigate the energy of such solutions, taking into account the energy needed to open a crack or hole. We show that the existence of singular solutions and the finiteness of their energy is strongly related to the behavior of the stress response function for infinite stretching. We outline our findings in one space dimension. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gamma‐convergence for Ginzburg‐Landau functional with degenerate 3‐well potential in one dimension
Authors: Raguž Andrija 
Published: November 2013

AbstractWe consider the Ginzburg‐Landau functional in one dimension, endowed with epsilon‐dependent 3‐well potential which degenerates as small parameter epsilon tends to zero. By using the approach in G. Alberti, S. Muller: A new approach to variational problems with multiple scales, Comm. Pure Appl. Math. 54, 761‐825 (2001), we obtain Gamma‐convergence as small parameter epsilon tends to zero. We also recover the underlying geometric properties shared by all minimizing sequences. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evolutional contact with Coulomb's friction on a periodic microstructure
Authors: Orlik Julia , Shiryaev Vladimir 
Published: November 2013

AbstractWe consider the elasticity problem in a heterogeneous domain with an ε‐periodic micro‐structure, ε ≪ 1, including a multiple micro‐contact in a simply connected matrix domain with inclusions completely surrounded by cracks, which do not connect the boundary, or a textile‐like material. The contact is described by the Signorini and Coulomb‐friction contact conditions. In the case of the Coulomb friction, the dissipative functional is state dependent, like in [2]. A time discretization scheme from [2] reduces the contact problem to the Tresca one (with prescribed frictional traction or state independent dissipation) on each time‐increment. We further look for the spatial homogenization. The limiting energy and the dissipation term in the stability condition were obtained for the contact with Tresca's friction law in [4] for closed cracks and can be extended to textile‐like materials. Using these results and the concept of energetic solutions for evolutional quasi‐variational problems from [2], for a uniform time‐step partition, the existence can be proved for the solution of the continuous problem and a subsequence of incremental solutions weakly converging to the continuous one uniformly in time. Furthermore, the irreversible frictional displacements at micro‐level lead to a kind of an evolutional plastic behavior of the homogenized medium. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A PDE constraint formulation of Open Pit Mine Planning Problems
Authors: Strogies Nikolai , Griewank Andreas 
Published: November 2013

AbstractThe modeling of open pit mine schedules employing continuous functions [1] yields several difficulties regarding the optimization process. Besides the dynamic capacity constraint one of the most challenging problems is a proper way of ensuring the physical stability of the obtained profile functions of an excavation schedule. This paper shows, that under certain suitable assumptions the physically stable excavation path is the solution of a certain Hamilton Jacobi equation. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parallel solvers for flow control based on domain decomposition
Authors: Ketelaer Eva , Heuveline Vincent , Heinkenschloss Mathias 
Published: November 2013

AbstractWe sketch a non‐overlapping domain decomposition method (DDM) for a linear quadratic optimal control problem governed by the Oseen equations. The DDM is applied to the system of necessary and sufficient optimality conditions. The approach extends balanced Neumann Neumann DDMs from single partial differential equations (PDEs) to the optimization control context, and it extends previous work on balanced Neumann Neumann DDMs for the optimal control of scalar elliptic PDEs to the optimal control of the Oseen equations. This extension requires a careful handling of the incompressibility constraint and resulting compatibility conditions, as well as a careful handling of the advection term. The DDM is used to parallelize the matrix‐vector operations for the optimality system, as well as to parallelize the preconditioner. We present two approaches. One tackles the global optimality system directly, the other forms the Schur complement corresponding to variables on the subdomain interfaces. We present numerical experiments which clearly show the potential of the approaches. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Iterative solution of inconsistent systems of linear inequalities
Authors: Carp Doina , Popa Constantin , Serban Cristina 
Published: November 2013

AbstractIn 1980 S.P. Han proposed a finitely terminating (in exact arithmetic) algorithm for solving an inconsistent system of linear inequalities in a least squares sense. This algorithm uses a singular value decomposition of a submatrix of the problem matrix on each iteration, making it impractical for all but only smaller problems. In this paper we show that a modification of Han's algorithm allows us to introduce an iterative approximation to the singular value decomposition solution. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Diagonal scaling in eigenvalue localization for the Schur complement
Authors: Cvetković Ljiljana , Nedović Maja 
Published: November 2013

AbstractGeršgorin theorem is a well‐known result in eigenvalue localization area. In this paper, using diagonal scaling method, we obtain more Geršgorin‐type localizations for the eigenvalues of the Schur complement using the entries of the original matrix instead of the entries of the Schur complement. We deal with classes of matrices with some form of diagonal dominance. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Backward error analysis of an inexact Arnoldi method
Authors: Kandler Ute , Schröder Christian 
Published: November 2013

AbstractWe investigate the behavior of Arnoldi's method for Hermitian matrices in the case of inexact vector operations. A special purpose variant of Gram Schmidt orthogonalization is introduced which computes a nearly orthogonal Krylov subspace basis and additionally implicitly provides an exactly orthogonal basis. In the second part we perform a backward error analysis and show that the exactly orthogonal basis satisfies a Krylov relation for a perturbed system matrix. The norm of the backward error is shown to be on the level of the accuracy of the vector operations. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Convection‐diffusion‐reaction problems on a B‐type mesh
Authors: Brdar Mirjana , Zarin Helena 
Published: November 2013

AbstractOne‐dimensional singularly perturbed problems with two small parameters are considered. Numerical methods for such problems are discussed in several papers, but on a Shishkin‐type mesh. The first optimal result of convergence in an energy norm on a Bakhvalov‐type mesh for one‐dimensional convection‐diffusion problem was given by Roos in [9]. In this paper we analyze Galerkin finite element method on a Bakhvalov‐type mesh for two‐parameter convection‐diffusion‐reaction problems. In the interpolation error analysis, instead of the usual interpolation operator in the finite element space we use a quasi‐interpolant with improved stability properties. We prove that the finite element method for these problems is uniformly convergent in the energy norm. Numerical results confirm our theoretical analysis and show first‐order convergence rate. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Verification of Functional A Posteriori Error Estimates for Obstacle Problem in 1D
Authors: Harasim Petr , Valdman Jan 
Published: November 2013

AbstractWe verify functional a posteriori error estimates of numerical solutions of a obstacle problem proposed by S. Repin. The simplification into 1D allows for the construction of a nonlinear benchmark for which an exact solution can be derived and also an exact quadrature can be applied. Quality of a numerical solution obtained by the finite element method is compared with the exact solution to demonstrate the sharpness of the studied error estimated. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Making the semi‐implicit space‐time conservation‐element solution‐element method of Jerez et al. more explicit
Authors: Niessner Herbert 
Published: November 2013

AbstractIn the beginning of the nineties a NASA‐group around S. C. Chang started to work on a new method for unsteady flow computation with seemingly good results. Thereby elements are space‐time domains. Within solution‐elements state and flux variables are linearized satisfying the underlying differential equation, within conservation‐elements space‐time flux is conserved. Proceeding this way for one‐dimensional pipe flow Jerez et al. include source terms with all cross‐section dependencies making the method semi‐implicit. We show that by taking simple measures as ‐ accounting for cross‐sections in state and flux variables of mass and energy or ‐ subtracting spatially integrated source terms from the fluxthe method may become more or completely explicit, particularly helpful when chemical species transport is involved. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Approximate solution of boundary integral equations for biharmonic problems in non‐smooth domains
Authors: Didenko Victor , Helsing Johan 
Published: November 2013

AbstractThis paper deals with approximate solutions to integral equations arising in boundary value problems for the biharmonic equation in simply connected piecewise smooth domains. The approximation method considered demonstrates excellent convergence even in the case of boundary conditions discontinuous at corner points. In an application we obtain very accurate approximations for some characteristics of two‐dimensional Stokes flow in non‐smooth domains. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
DG and hp‐DG for highly indefinite Helmholtz problems
Authors: Melenk Jens Markus , Parsania Asieh , Sauter Stefan 
Published: November 2013

AbstractWe develop a stability and convergence theory for a Discontinuous Galerkin formulation (DG) of a highly indefinite Helmholtz problem in ${\rm I\!R}^d, d \in \{2,3\}$. We prove that the DG‐method admits a unique solution under much weaker conditions than for conventional Galerkin methods. It is shown that for the case of hp‐DGFEM the optimal convergence order estimate can be obtained under the conditions that $kh/\sqrt{p}$ is sufficiently small and the polynomial degree p is at least O(log k). (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
About Some Boundary Value Problems for Fractional PDE and their Numerical Solution
Authors: Jovanović Boško , Delić Aleksandra , Vulkov Lubin 
Published: November 2013

AbstractA transmission initial‐boundary‐value problem in disjoint intervals for fractional in time diffusion equation is studied. Its well posedness in the corresponding Sobolev‐like spaces is proved. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bounds on the Solution of Linear Time‐Periodic Systems
Authors: Benner Peter , Denißen Jonas , Kohaupt Ludwig 
Published: November 2013

AbstractLinear time‐periodic systems have been an active area of research in the last decades. They arise in various applications such as anisotropic rotor‐bearing systems and nonlinear systems linearized about a periodic trajectory. Rigorous bounds support the transient analysis of these systems. Optimal constants are determined by the differential calculus for norms of matrix functions. Bounds based on trigonometric spline approximations of the solution are introduced and convergence results for the approximations are stated. Bounds are illustrated by means of an anisotropic rotor‐bearing system. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A meshless procedure for transient heat conduction in functionally graded materials
Authors: Mierzwiczak Magdalena 
Published: November 2013

AbstractA meshless numerical procedure is developed for analyzing the transient heat conduction problem in non‐homogeneous functionally graded materials. In the proposed method the time derivative of temperature is approximate by the finite difference. At each time step the original nonlinear boundary value problem is transform into a hierarchy of non‐homogeneous linear problem by used the homotopy analysis method. In this method a sought solution is presented by using a finite expansion in Taylor series, which consecutive elements are solutions of series linear value problems defining differential deformations. Each of linear boundary value problems with the corresponding boundary conditions is solved by using the method of fundamental solutions and radial basis functions which are used for interpolation of the inhomogeneous term. The accuracy of the obtained approximate solution is controlled by the number of components of the Taylor series, while the convergence of the process is monitored by an additional parameter of the method. Numerical experiments demonstrate the efficiency and accuracy of the present scheme in the solution of the heat conduction problem in nonlinear functionally graded materials. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)