bluuebunny/crossref_metadata_2025_split huggingface dataset:
A novel approach to mode‐tracing in SBFEM‐simulations: Higher‐order Taylor‐ and Padé approximation
Authors: Krome Fabian , Gravenkamp Hauke 
Published: October 2015

AbstractThis contribution presents the study of strange phenomena in wave mode representations of waveguides. For this study the waveguides are computed by means of the Scaled Boundary Finite Element Method (SBFEM). Different approaches of mode tracing are used to identify the characteristics of the resulting wave modes. Higher order differentials of the underlying eigenvalue problem are the basis for these approaches.The main idea behind this mode tracing approach is to reduce the cubic computation time to solve the eigenvalue problem for each frequency of interest. This study identifies potentially critical frequency regions and attempts to formulate a solution process. The fascinating effects at critical frequencies are displayed and a suggestion for a stabilization for the solution process is made. This study bases its conclusion on a numerical viewpoint. Main aspects in this study include high order differentials of the eigenvalue problem and the corresponding Taylor and Padé approximations for the eigenvalue problem as a whole. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Forward and Inverse Viscoacoustic Modelling in a Tunnel Environment
Authors: Musayev Khayal , Hackl Klaus , Baitsch Matthias 
Published: October 2015

AbstractIn this work, the goal is to model forward acoustic waves in a tunnel environment with attenuation and to do full waveform inversion. In reality, there is no material without attenuation. Some materials, such as rocks, have so low attenuation that, in a small domain, the waves are almost not damped at all. At the same time, there are materials with high attenuation. In an environment with such materials, the attenuation has to be taken into account in order to model the waves properly. In this study, attenuation effect is integrated into acoustic equation by using Kolsky‐Futterman model ( [1], [2]) which only replaces velocity field with a complex‐valued field in frequency domain. Apart from attenuation, another objective is to consider an inhomogeneous density field. Mainly, acoustic equation with a constant density field is referred to in many studies. In many cases, it may suffice to model waves appropriately. However, in reality, the density field of ground can be highly inhomogeneous. The objective is to investigate the effect of the inhomogeneity in waves, and to search for density field ρ and attenuation parameter Q as well as pressure wave velocity c using full waveform inversion. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Calculation of Acoustic Sources for the Landing Gear of Aeroplane during Take‐off and Landing
Authors: Rašuo Boško , Jazarević Vladimir 
Published: October 2015

AbstractIn this paper we present Orthogonal Sub‐grid scale stabilized method with static subscales applied on turbulent flow around landing gear of aircraft during take‐off and landing. Numerical results of proposed method are compared with famous LES Smagorinsky method for turbulent flow and it is shown how obtained results affect allocation of acoustic sources and then propagation of acoustic waves in computational domain. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Calculation of the effective speed of sound in corrugated pipes by multiple scales
Authors: Russo Serena , Fabre David , Giannetti Flavio , Luchini Paolo 
Published: October 2015

AbstractThe flow through corrugated pipes is known to lead to strong whistling tones which may be harmful in many industrial appliances. The mechanism is known to originate from a coupling between vortex shedding at the edges of the cavities forming the wall of the tube and the acoustical modes of the pipe. The latter depend upon the effective velocity of sound ceff within the corrugated pipe. The purpose of this paper is to compute accurately this effective velocity of sound through an asymptotic calculation valid in the long‐wave limit. Results are given for a number of geometries used in previous works, and compared with a simple model in which the effective speed of sound is function of the geometry of the pipe. The latter is found to work best for short cavities but significant disagreement is found for longer cavities. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical modeling of a sub‐sonic moving load front along a rod's skin
Authors: Weber Wolfgang E. , Balzani Daniel , Fangye Yannick F. , Zastrau Bernd W. 
Published: October 2015

AbstractIn this contribution the dynamical behaviour of a semi‐infinite rod subjected to a longitudinal load moving along the rod's skin is investigated both analytically and numerically. By means of the analytical results the numerical model is validated and thus can be used for more advanced studies e. g. concerning dynamic fibre pull‐out phenomena. These forthcoming studies involve spatially moving boundary conditions which are also modeled within the present model in a first step. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Potential flow simulations of Peregrine‐type deep water surface gravity wave packets
Authors: Wenzel Arne , Bünte Dennis , Hoffmann Norbert P. 
Published: October 2015

AbstractApplying a higher order spectral method for potential flow we numerically determine the time evolution of non‐linear deep water wave packets originating from initial conditions derived from the Peregrine breather solution of the non‐linear Schrödinger equation (NLS). The spatio‐temporal evolution of the wave packets qualitatively agrees well with what would be expected from lowest order weakly nonlinear estimates (NLS). Some quantitative discrepancies do, however, exist: The maximum wave envelope amplification appears retarded with respect to the NLS predictions. The amplification factor slightly exceeds the factor known from the NLS solution. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Laminate structures in plastic composite materials with rigid layers
Authors: Christowiak Fabian , Kreisbeck Carolin 
Published: October 2015

AbstractA variational model for composite materials with rigid horizontal layers is introduced within the framework of geometrically nonlinear single‐slip plasticity. Considering the orientation of the slip system, we discuss the effective material response in the case of vanishing layer thickness and give explicit examples of possible macroscopic deformations which are realized by simple laminate constructions. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A low volume‐fraction limit for martensic microstructures in shape‐memory alloys
Authors: Diermeier Johannes 
Published: October 2015

AbstractWe consider a variational model for the energy of deformations of shape‐memory materials. We restrict ourselves to a scalar‐valued, two dimensional simplification with two variants of martensite in which one of the variants has a much smaller volume fraction than the other one.We study the transition between a single phase and fine microstructures and compute the Γ‐limit for one volume fraction tending to zero. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the use of potential fields in fluid mechanics
Authors: Marner Florian , Scholle Markus 
Published: October 2015

AbstractIn classical fluid mechanics, potential fields have been employed to enable the integration of the equations of motion. As is well known, Bernoulli's equation is obtained as a first integral of Euler's equations in the absence of vorticity and viscosity if the velocity vector is perceived as the gradient of a scalar potential. The so‐called Clebsch transformation [1] involving three scalar potentials allows for a further extension to flows with non‐vanishing vorticity; the resulting equations turn out to be self‐adjoint, allowing for a variational formulation. All attempts in classic literature, however, are restricted to inviscid flows and the finding of a potential representation enabling the integration of the Navier‐Stokes equations remains desirable.Progress on this topic was reported by [3, 4] who constructed a first integral of the two‐dimensional incompressible Navier‐Stokes equations by making use of an auxiliary potential field and a representation of the fields in terms of complex coordinates. The new formulation proved to be useful in numerical applications and moreover, replacing the scalar potential by a tensor potential, the theory can be successfully generalised to encompass three‐dimensional Navier‐Stokes flow.Related to the first integral a finite element method was presented in [2] based on a formulation involving the velocities and the first order derivatives of the introduced potential. This way the dynamic boundary condition could be incorporated elegantly and the system of equations fitted into the first order system least‐squares methodology. However, a promising alternative approach results if one considers the streamfunction and a slightly modified potential field as independent variables. This new approach involves Laplacian operators rather than mixed derivatives and allows for a convenient embodiment of the Neumann conditions on the streamfunction that is in contrast to the original stream function / potential formulation [4]. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asymptotic sampling – a tool for efficient reliability computation in high dimensions
Authors: Bucher Christian 
Published: October 2015

AbstractMonte Carlo methods are most versatile regarding applications to the reliability analysis of high‐dimensional nonlinear structural systems. In addition to its versatility, the computational efficacy of Monte Carlo method is not adversely affected by the dimensionality of the problem. Crude Monte Carlo techniques, however, are very inefficient for extremely small failure probabilities such as typically required for sensitive structural systems. Therefore methods to increase the efficacy for small failure probability while keeping the adverse influence of dimensionality small are desirable.On such method is the asymptotic sampling method. Within the framework of this method, well‐known asymptotic properties of the reliability index regarding the scaling of the basic variables are exploited to construct a regression model which allows to determine the reliability index for extremely small failure probabilities with high precision using a moderate number of Monte Carlo samples. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Uncertainty quantification for linear elastic bodies with two fluctuating input parameters
Authors: Dridger Alex , Caylak Ismail , Mahnken Rolf 
Published: October 2015

AbstractIn this work, we present a numerical method for solving partial differential equations (PDEs) with stochastic coefficients for a linear elastic body. To this end, a stochastic finite element method is applied. We distinguish two different cases for an isotropic material with two fluctuating input parameters in order to analyse the optimal choice of input parameters. Using the GALERKIN projection, the final stochastic equation system is reduced to a system of deterministic PDEs. Subsequently, the solution is determined iteratively. Finally, a numerical example for a plate with a ring hole is presented. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Gaussian approximation of the strength of Daniels' bundle with brittle Weibull fibers
Authors: Sadílek Václav , Vořechovský Miroslav 
Published: October 2015

AbstractThe paper deals with the classical fiber bundle model with brittle Weibull fibers and equal load sharing. This model is significant for the strength of fibrous materials and composites, and the generally random strength of quasi‐brittle structures. The model is also relevant for the analysis of the reliability of various parallel systems (computer components, infrastructure etc.). An improved closed‐form Gaussian approximation of the standard deviation of bundle strength is presented and compared with accurate solution calculated by recursive formula proposed by Daniels. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Jump Phenomena and Bifurcations in Stochastic Vehicle‐Road Dynamics
Authors: Wedig Walter V. 
Published: October 2015

AbstractWhen vehicles ride on uneven roads, they are excited to vertical random vibrations whose stationary rms‐values (root‐mean‐square) strongly depend on the velocity of the vehicle. To investigate this vibration behavior, it is appropriate to introduce road models in way domain which are based on the theory of stochastic differential equations and transformed from way to time by means of velocity‐dependent way and noise increments.The random base excitations by roads are applied to nonlinear quarter car models. They lead to stationary rms‐values of the vertical vehicle vibrations which become resonant for critical velocities and show jump phenomena similar to those of the Duffing oscillator under harmonic excitations. In the stochastic case, jump phenomena are only observable for narrow‐banded road excitations. They vanish for increasing car damping and excitation bandwidth.For efficient simulations of the road‐vehicle model, the n state equations are utilized to derive n(n + 1)/2 stochastic covariance equations. For small step sizes, their numerical mean square solutions coincide with the nonlinear results of fix‐point iterations obtained when the noise terms of the covariance equations are omitted. It can easily be shown, that this deterministic approach leads to the correct stationary covariances in the linear case. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
About the design of morphing airfoils under uncertainties
Authors: Fusi Francesca , Quaranta Giuseppe , Guardone Alberto , Congedo Pietro Marco 
Published: October 2015

AbstractThe paper presents an optimization framework for dealing with morphing airfoils for helicopter rotor blades. With regard to the morphing strategy, a conformable camber line is considered to deal with variable flow conditions encountered in forward flight with the objective of increasing the aerodynamic performance on the advancing and retreating sides of the rotor. Another peculiarity of the method is that the optimal shape is sought to be minimally sensitive to uncertainty in the operating conditions. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of the double sided spiral groove thrust bearing: A comparison to approximate analytical solutions
Authors: Lehn Andreas , Schweizer Bernhard 
Published: October 2015

AbstractReliable high performance bearings are essential in rotordynamics. As speeds and loads are continuously increased the demands on bearing technology grow simultaneously. Optimization of bearing characteristics becomes more important under these circumstances. For hydrodynamic thrust bearings, recently a special design has been presented, which is supposed to enhance the load carrying capacity by 60% compared to the best known thrust bearing type. The bearing consists of two spiral grooved surfaces and is therefore called a double sided spiral groove bearing. Early calculations of the bearing performance base on approximate analytical methods.In order to verify those results, a detailed numerical model of the bearing is presented by the authors. With the help of a particle swarm optimization method, optimal bearing parameters are determined and a comparison is drawn to other thrust bearing designs. It is shown that previously published results overestimate the performance of the double sided spiral groove bearing severly. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A staggered approach to structural shape and topology optimization
Authors: Riehl Stefan , Steinmann Paul 
Published: October 2015

AbstractThis contribution is concerned with the design and evaluation of a staggered approach to computational shape and topology optimization. The main idea is to interrelate a classical boundary variation scheme based on the results from shape sensitivity analysis and an evolutionary‐type element removal procedure that relies on the topological sensitivity as a rejection criterion. The key ingredient in this perspective is to consider an advancing front algorithm that is gradually removing, from the evolving boundary of the domain, a number of finite elements based on the evaluation of the topological sensitivity.This process is repeated until the minimum topological sensitivity is no longer encountered at the boundary but in the interior of the domain, such that a topological change is to be considered for the current design layout. However, we first aim to establish a more accurate approximation of the true optimal shape of the newly established (zig‐zag representation) of the design boundary. This is achieved by the evaluation of the shape sensitivity and the accompanying boundary variations obtained by a basic descent algorithm. Only then, we create a hole in the interior of the domain by removing all cells that are adjacent to the nodal point that exhibits the minimum topological sensitivity and resume the advancing front algorithm to alter the newly established design boundary. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extended Hamiltonian Hessenberg Matrices arise in Projection based Model Order Reduction
Authors: Ferranti Micol , Mach Thomas , Vandebril Raf 
Published: October 2015

AbstractWe show that extended Hamiltonian Hessenberg matrices arise naturally in projection‐based model order reduction. Therefore we reduce a large dynamical system by projecting it on an extended Krylov subspace. The eigenvalues of the reduced order model can then be computed directly by applying the extended Hamiltonian QR algorithm. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A new Interpolatory Model Reduction Approach for Quadratic Bilinear Descriptor Systems
Authors: Ahmad Mian Ilyas , Benner Peter , Feng Lihong 
Published: October 2015

AbstractWe propose interpolation based projection techniques for model reduction of quadratic bilinear descriptor systems. The approach identifies projection matrices from the bilinear approximation of the original quadratic bilinear descriptor system and applies Petrov‐Galerkin projection to the original system to construct the required reduced quadratic bilinear descriptor system. Two different techniques of computing the projection matrices from the bilinear approximation are proposed. One is based on linear parametric model reduction and the other is the bilinear rational Krylov method. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Upwind Based Parameter Uniform Convergence Analysis for Two Parametric Parabolic Convection Diffusion Problems by Moving Mesh Methods
Authors: Das Pratibhamoy , Mehrmann Volker 
Published: October 2015

AbstractA parabolic two parametric convection‐diffusion reaction problem is considered for the moving mesh error analysis. The continuous problem is discretized by the first order upwind scheme on a non uniform mesh. A curvature based error monitor function is proposed to generate the layer adapted mesh. It is proved that the numerical solution converges to the exact solution on the mesh obtained by the equidistribution of the proposed monitor function. The convergence is first order accurate. The present analysis generalizes the results obtained in earlier publications [8,9]. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multigrid preconditioning for time‐periodic Navier–Stokes problems
Authors: Hupp Daniel , Obrist Dominik , Arbenz Peter 
Published: October 2015

AbstractWe propose to solve time‐periodic Navier–Stokes problems by a discrete Fourier transform in time. Truncating the Fourier series yields a nonlinear system of equations for the unknown Fourier coefficients. Its solution by Picard iteration requires to solve a sequence of linear systems of equations. The focus of this work is on an efficient method to solve these linear systems. We employ GMRES, complemented by an optimal block triangular preconditioner. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Using Schur complement for realtime automotive applications
Authors: Loderer Thomas , Bertsch Christian , Heuveline Vincent 
Published: October 2015

AbstractRealtime simulation of stiff physical models of mechatronic systems within electronic control unit software functions poses amongst others the challenge to solve linear systems of equations with minimal comutational effort. For this, one key approach is exploiting the model structure. In this paper, Schur complement based reformulations are examined for a tailored exploitation of the sparsity of a pipe model on the level of linear equations. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Error measurement and FEM benchmark for phase field modeling
Authors: Münch Ingo 
Published: October 2015

AbstractSolid‐state phase‐transformation often deals with coupled field variables like mechanical stress or electric potential on different scales compared to the size of phase transition. Further, highly nonlinear equations rule the phase parameter. Thus, required mesh density to approximate phase field variables is often higher than for coupled fields. Finite element techniques applying h‐ or p‐adaptivity can help to increase the efficiency of such simulations. Therefore, it is important to define a benchmark test to verify numerical approaches. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computation of state variables of one‐dimensional non‐stationary pipe flow at orifices on pipe ends
Authors: Niessner Herbert 
Published: October 2015

AbstractBoundary conditions of orifices in conjunction with the graphical method of characteristics given in [1] are reformulated and made ready to be used with finite difference methods. Orifice flow to the apparent narrowest cross‐section is assumed conserving entropy and energy, thereafter not recovering pressure without exceeding sound speed. These conditions allow to eliminate state variables at the narrowest cross‐section. Additional equations stem from mass conservation and a balance of the Riemann variable over the outgoing cross‐characteristic and either further energy conservation or a balance of entropy over the outgoing particle path. They permit to determine the state at the boundary of the computational grid for usual finite difference methods. A single nonlinear equation has to be solved only in case of outflow. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Online Parameter Identification for Traffic Simulation via Lagrangian Sensing
Authors: Thonhofer Elvira , Jakubek Stefan 
Published: October 2015

AbstractThis paper deals with parameter identification for traffic models. We present a method to estimate model parameters based on Lagrangian measurement data that can be used for online traffic simulation. In the context of Lagrangian sensing the sensor placement is reduced to the optimum choice of measurement vehicles currently moving with the traffic flow. Identifiability is investigated using the Fisher Information Matrix (FIM). Simulation results are presented and validated via simulation based on a car‐following‐model. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An Adaptive Local (AL) Basis for Elliptic Problems with Complicated Discontinuous Coefficients
Authors: Weymuth Monika , Sauter Stefan 
Published: October 2015

AbstractWe develop a generalized finite element method for the discretization of elliptic partial differential equations in heterogeneous media. In [5] a semidiscrete method has been introduced to set up an adaptive local finite element basis (AL basis) on a coarse mesh with mesh size H which, typically, does not resolve the matrix of the media while the textbook finite element convergence rates are preserved. This method requires O(log(1/H)d+1) basis functions per mesh point where d denotes the spatial dimension of the computational domain. We present a fully discrete version of this method, where the AL basis is constructed by solving finite‐dimensional localized problems, and which preserves the optimal convergence rates. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)