bluuebunny/crossref_metadata_2025_split huggingface dataset:
Global weak solutions for coupled transport processes in concrete walls at high temperatures
Authors: Beneš M. , Štefan R. 
Published: June 2013

AbstractWe consider an initial‐boundary value problem for a fully nonlinear coupled parabolic system with nonlinear boundary conditions modeling hygro‐thermal behavior of concrete at high temperatures. We prove a global existence of a weak solution to this system on any physically relevant time interval. The main result is proved by an approximation procedure. This consists in proving the existence of solutions to mollified problems using the Leray‐Schauder theorem, for which a priori estimates are obtained. The limit then provides a weak solution for the original problem. A practical example illustrates a performance of the model for a problem of a concrete segment exposed to transient heating according to three different fire scenarios. Here, the focus is on the short‐term pore pressure build up, which can lead to explosive spalling of concrete and catastrophic failures of concrete structures.
Higher order accurate discontinuous and continuous p‐Galerkin methods for linear elastodynamics
Authors: Gleim T. , Kuhl D. 
Published: June 2013

AbstractThe present paper is concerned with the numerical integration of linear structural dynamics by means of different higher order accurate Galerkin time integration schemes. Firstly the single field discontinuous and continuous p‐Galerkin schemes are developed in a generalized fashion using arbitrary polynomial degrees. In a further step the two field discontinuous and continuous p‐Galerkin schemes are derived. In both algorithmic classes continuous Galerkin schemes are obtained by the strong enforcement of the continuity condition as special case of the discontinuous Galerkin schemes. The related time integration schemes are conditioned in an algorithmic set‐up in such a manner that the implementation is similar to the classical Newmark scheme and its α derivates. Selected benchmark examples demonstrate the excellent dissipation and dispersion behavior and the robustness of the present Galerkin integration schemes. Furthermore, an error analysis, based on the analytical solution and the real local time integration error, verifies the order of accuracy of Galerkin time integration schemes controlled by the chosen polynomial degree. In particular the order of accuracy for each class of Galerkin integration schemes is specified. The comparison of the numerical effort for the classical Newmark scheme and the family of Galerkin schemes indicates advantages for Galerkin schemes: For a prescribed error level higher order Galerkin schemes are more effective than the Newmark scheme.
Infiltration processes in cohesionless soils
Authors: Schaufler A. , Becker C. , Steeb H. 
Published: June 2013

AbstractIn this paper, a thermodynamically consistent four‐phase continuum model in the framework of the mixture theory is presented describing infiltration processes of suspensions in cohesionless granular material. The paper focuses on the distinct form of the constitutive relation for the volume production term of the fluidized particles and its consequences on the infiltration process. To this end a constitutive equation describing infiltration phenomena is proposed which includes only one material parameter. Therefore we study numerically a boundary value problem, which is characterized by a homogeneous field of the hydraulic gradient in the reference configuration at the time t0 = 0. Infiltration is affecting the distribution of the hydraulic properties and illustrates the consequences of the proposed constitutive equation for specific parameter choices. Furthermore it is shown how the material parameter can be estimated without explicit numerical calculations.
On the instability of equilibrium position of a mechanical system with singular constraints
Authors: Čović V. , Mitrović Z. , Rusov S. , Obradović A. 
Published: June 2013

AbstractThe Lyapunov first method generalized to the case of nonlinear differential equations is applied to the study of the instability of the equilibrium position of a mechanical system, whose motion is constrained by singular nonholonomic constraints. Starting from the results of S. D. Furta (On the instability of equilibrium position of constrained mechanical systems) three theorems on the instability are formulated. The first theorem considers the case of nonholonomic constraints that do not satisfy the condition of weak nonholonomity. The other two theorems are related to the case of weakly nonholonomic systems. In each of the formulated theorems it is shown that the minimum form of Maclaurin series for the potential energy has not a local minimum. Thus, a contribution has been made to the inversion of Lagrange's theorem.
Difficulties arising from different definitions of tortuosity for wave propagation in saturated poroelastic media models
Authors: Cowin S.C. , Cardoso L. 
Published: June 2013

AbstractThe multiple definitions of permeability and tortuosity employed by investigators modifying the basic equations of dynamic poroelasticity pose a problem as some resulting analyses produce results conflicting with those of other investigators. When the same words are used to describe different definitions of different concepts, the problem is compounded. These problems were highlighted in recent applications of acceleration wave analyses of dynamic poroelasticity. Wilmanski [40] and Coussy [14] applied acceleration wave analysis to their own systems of dynamic poroelastic equations and found contradictory results. In one case the wave speed depends upon tortuosity and in the other case a dependence upon permeability (and tortuosity) was not allowed. This means that acceleration waves in the Wilmanski [40] analysis cannot exhibit dispersion at lower frequencies. Harmonic wave analyses applied to the same systems of dynamic poroelastic equations predict a dependence of wave speed upon permeability. The acceleration wave analysis of a system of dynamic poroelastic equations is dependent upon the definitions of tortuosity used by the investigators. Wilmanski [40] and Coussy [14] each used their own definition of tortuosity.
On the temporal behaviour in the bending theory of porous thermoelastic plates
Authors: Ghiba I.D. 
Published: June 2013

AbstractIn this paper we consider the bending theory of Mindlin type thermoelastic plates with voids. We study the temporal behaviour of the solution of the boundary‐initial value problem of this theory. Assuming that the internal energy density is positive definite, relations describing the asymptotic behaviour of the Cesáro means of various parts of total energy are established. An extension of the results to a large class of thermoelastic materials with voids is given.
Yielding of two‐layer curved bars under pure bending
Authors: Arslan E. , Sülü İY. 
Published: June 2013

AbstractYielding of a curved bar consisting of two layers subject to pure bending is investigated. It is assumed that both layers of the bar are in a state of plane stress and Tresca's yield criterion is used to detect onset of plasticization. Analytical expressions are obtained for the bending moments corresponding to the elastic limit leading to plastic flow. The results show that, depending on material properties and dimensions of the layers, different cases for plastic deformation may occur. Yielding may emerge at the inner or outer surface of the bar or at the interface between two layers. Furthermore, a critical case in which yielding commences at the outer and interface surfaces simultaneously was observed. Numerical results for real engineering materials are presented in graphical form.
Dynamic response of a cracked magnetoelectroelastic layer sandwiched between two elastic layers
Authors: Hu Keqiang , Chen Z. 
Published: June 2013

AbstractThe dynamic response of a cracked magnetoelectroelastic layer sandwiched between dissimilar elastic layers under anti‐plane shear and in‐plane electric and magnetic impacts is investigated by the integral transform method. Fourier transforms and Laplace transforms are applied to reduce the mixed boundary value problem of the impermeable crack to simultaneous dual integral equations, which are then expressed in terms of simultaneous Fredholm integral equations of the second kind. The stress field, electric field and magnetic field near the crack tip are obtained asymptotically, and the corresponding field intensity factors are further determined. Numerical results show that the stress intensity factors are influenced by the material properties, the electric and magnetic loadings, and the geometry. The crack initiation can be enhanced or retarded depending on the electric and magnetic loading, and the crack may propagate along its original crack line when the criterion of maximum hoop stress is applied.
Index reduction for operator differential‐algebraic equations in elastodynamics
Authors: Altmann R. 
Published: June 2013

AbstractIn space semi‐discretized equations of elastodynamics with weakly enforced Dirichlet boundary conditions lead to differential algebraic equations (DAE) of index 3. We rewrite the continuous model as operator DAE and present an index reduction technique on operator level. This means that a semi‐discretization leads directly to an index‐1 system. We present existence results for the operator DAE with nonlinear damping term and show that the reformulated operator DAE is equivalent to the original equations of elastodynamics. Furthermore, we show that index reduction and semi‐discretization in space commute if the discretization schemes are chosen in an appropriate way.
Microstructure and effective behavior of materials
Authors: Dolzmann G. 
Published: June 2013

AbstractTailor‐made materials often take advantage of surprising material behavior which is related to special effects and structures on small length scales. In order to achieve the design goals, a precise understanding of the underlying mechanisms in a mathematical model is indispensable. This contribution presents modern methods in the calculus of variations which are available for the analysis and numerical simulation of systems with multiple scales and illustrates their use in two characteristic model examples.
A perturbative model for predicting the high‐Reynolds‐number behaviour of the streamwise travelling waves technique in turbulent drag reduction
Authors: Belan M. , Quadrio M. 
Published: June 2013

AbstractThe background of this work is the problem of reducing the aerodynamic turbulent friction drag, which is an important source of energy waste in innumerable technological fields (transportation being probably the most important). We develop a theoretical framework aimed at predicting the behaviour of existing drag reduction techniques when used at the large values of the Reynolds numbers Re which are typical of applications. We focus on one recently proposed and very promising technique, which consists in creating at the wall streamwise‐travelling waves of spanwise velocity (M. Quadrio, P. Ricco, and C. Viotti, J. Fluid Mech. 627, 161–178, 2009). A perturbation analysis of the Navier‐Stokes equations that govern the fluid motion is carried out, for the simplest wall‐bounded flow geometry, i.e. the plane channel flow. The streamwise base flow is perturbed by the spanwise time‐varying base flow induced by the travelling waves. An asymptotic expansion is then carried out with respect to the velocity amplitude of the travelling wave. The analysis, although based on several assumptions, leads to predictions of drag reduction that agree well with the measurements available in literature and mostly computed through Direct Numerical Simulations (DNS) of the full Navier–Stokes equations. New DNS data are produced on purpose in this work to validate our method further. The method is then applied to predict the drag‐reducing performance of the streamwise‐travelling waves at increasing Re, where comparison data are not available. The current belief, based on a Re‐range of about one decade only above the transitional value, that drag reduction obtained at low Re is deemed to decrease as Re is increased is fully confirmed by our results. From a quantitative standpoint, however, our outlook based on several decades of increase in Re is much less pessimistic than other existing estimates, and motivates further, more accurate studies on the present subject.
Classical plate buckling theory as the small‐thickness limit of three‐dimensional incremental elasticity
Authors: Steigmann D.J. , Ogden R.W. 
Published: June 2013

AbstractClassical plate buckling theory is obtained systematically as the small‐thickness limit of the three‐dimensional linear theory of incremental elasticity with null incremental data. Various a priori assumptions associated with classical treatments of plate buckling, including the Kirchhoff–Love hypothesis, are here derived rather than imposed, and the conditions under which they emerge are stated precisely.
Drug release from collagen matrices including an evolving microstructure
Authors: Ray N. , van Noorden T. , Radu F.A. , Friess W. , Knabner P. 
Published: June 2013

AbstractBiodegradable collagen matrices have become a promising alternative to traditional drug delivery systems. The relevant mechanisms in controlled drug release are the diffusion of water into the collagen matrix, the swelling of the matrix coming along with drug release, and enzymatic degradation of the matrix with additional simultaneous drug release. These phenomena have been extensively studied in the past experimentally, via numerical simulations as well as analytically. However, a rigorous derivation of the macroscopic model description, which includes the evolving microstructure due to the degradation process, is still lacking. Since matrix degradation leads to the release of physically entrapped active agent, a good understanding of these phenomena is very important. We present such a derivation using formal twoscale asymptotic expansion in a level set framework and complete our results with numerical simulations in comparison with experimental data.
Optimization of concrete shells using genetic algorithms
Authors: Bertagnoli G. , Giordano L. , Mancini S. 
Published: June 2013

AbstractIn structural design, structures are often modeled using the finite elements method (FEM). One of the most common element type is the shell, which is used to model surfaces in a three dimensional space as far as the surface thickness is smaller than the other two dimensions. Many decisions must be taken during the design process, and many physical and loading constraints must be satisfied. Designers are generally interested in providing a solution that respects all the problem constraints, without trying to further improve it. In fact optimization is not trivial, even if it could yield a huge benefit both from the economic and the construction point of view. Additionally, saving materials is one of the fundamental criteria for the sustainable approach to the design. In this paper, we address the Skew Reinforcement Design in Reinforced Concrete Two Dimensional Elements (SRD2D). It consists of determining the minimum reinforcement required to respect all the constraints given by the geometric properties and the internal actions working on it. As this problem is strongly nonlinear and non‐convex it cannot be easily solved using exact methods, while heuristics and meta‐heuristics are suitable to this purpose. We propose a Genetic Algorithm (GA) and an enhanced version of it, a memetic algorithm, in which we apply an intensification heuristic to the solution obtained by the GA, where each variable is separately optimized by applying a first improvement based on local search strategy. We report computational results showing both the effectiveness of the proposed method, and the benefit of combining GAs with intensification methods.
Approximating the vanishing capillarity limit of two‐phase flow in multi‐dimensional heterogeneous porous medium
Authors: Andreianov B. , Brenner K. , Cancès C. 
Published: June 2013

AbstractNeglecting capillary pressure effects in two‐phase flow models for porous media may lead to non‐physical solutions: indeed, the physical solution is obtained as limit of the parabolic model with small but non‐zero capillarity. In this paper, we propose several numerical strategies designed specifically for approximating physically relevant solutions of the hyperbolic model with neglected capillarity, in the multi‐dimensional case. It has been shown in [Andreianov & Cancès, Comput. Geosci., DOI: 10.1007/s10596‐012‐9329‐8, 2013] that in the case of the one‐dimensional Buckley‐Leverett equation with distinct capillary pressure properties of adjacent rocks, the interface may impose an upper bound on the transmitted flux. This transmission condition may reflect the oil trapping phenomenon. We recall the theoretical results for the one‐dimensional case which are used to motivate the construction of multi‐dimensional finite volume schemes. We describe and discuss a coupled scheme resulting as the limit of the scheme constructed in [Brenner & Cancès & Hilhorst, HAL preprint no.00675681, 2012] and two IMplicit Pressure – Explicit Saturation (IMPES) schemes with different level of coupling. We finally provide numerical evidences of the good behavior of the fully decoupled version of the IMPES scheme.
Liquefaction phenomena in fluid‐saturated soil based on the Theory of Porous Media and the framework of elasto‐plasticity
Authors: Ehlers W. , Schenke M. , Markert B. 
Published: June 2013

AbstractLiquefaction phenomena are encountered in many engineering applications, especially, in geomechanics and earthquake engineering. Drawing our attention to fluid‐saturated granular materials with heterogeneous microstructures, the modelling is carried out within a continuum‐mechanical framework by exploiting the macroscopic Theory of Porous Media (TPM) together with thermodynamically consistent constitutive equations. In this regard, the solid skeleton of the water‐saturated soil is described as an elasto‐plastic material with isotropic hardening and a stress‐dependent failure surface. The underlying equations are discretised and implemented into the coupled porous‐media finite‐element solver PANDAS and linked to the commercial finite‐element package Abaqus via a general interface. This coupling allows the definition of complex intial‐boundary‐value problems through Abaqus, thereby using the sophisticated material models of PANDAS. To reveal the capabilities of this approach, two types of simulations have been carried out. At first, in order to get a detailed understanding of the porous‐media soil model under transient loading conditions, a cyclic torsion benchmark is computed. In a second step, specific liquefaction phenomena are addressed, where the underlying initial‐boundary‐value problems are inspired by practically relevant scenarios.
A new direct time integration method for the equations of motion in structural dynamics
Authors: Katsikadelis J.T. 
Published: June 2013

AbstractA direct time integration method is presented for the solution of the equations of motion describing the dynamic response of structural linear and nonlinear multi‐degree‐of‐freedom systems. It applies also to large systems of second order differential equations with fully populated, non symmetric coefficient matrices as well as to equations with variable coefficients. The proposed method is based on the concept of the analog equation, which converts the coupled N equations into a set of single term uncoupled second order ordinary quasi‐static differential equations under appropriate fictitious loads, unknown in the first instance. The fictitious loads are established from the integral representation of the solution of the substitute single term equations. The method is simple to implement. It is self starting, unconditionally stable and accurate and conserves energy. It performs well when large deformations and long time durations are considered and it can be used as a practical method for integration of the equations of motion in cases where widely used time integration procedures, e.g. Newmark's, become unstable. Several examples are presented, which demonstrate the efficiency of the method. The method can be straightforward extended to evolution equations of order higher than two.
Accounting for differential swelling in the multi‐physics modelling of the diffusive behaviour of polymers
Authors: Sar B.E. , Fréour S. , Davies P. , Jacquemin F. 
Published: June 2013

AbstractThe purpose of this paper is to take into account the derivative by moisture content of polymer volume in order to establish a diffusion law within the so‐called “thermodynamical approach” for a polymer material which experiences a hygro‐mechanical load. In this study, the specific case corresponding to the existence of unsymmetrical hygroscopic boundary conditions was investigated.
Stability of the rotating compressed nano‐rod
Authors: Atanackovic T.M. , Zorica D. 
Published: June 2013

AbstractWe study stability of a rotating compressed nano‐rod clamped at one and free at the other end. By using the Euler method of adjacent equilibrium configuration, we determine critical values for angular speed and compressive force. Post‐critical shape of the rod is obtained by solving the non‐linear system of equilibrium equations for several values of parameters.
Asymptotic decomposition in the problem of joined elastic beams
Authors: Kolpakov A.G. , Andrianov I.V. 
Published: June 2013

AbstractThe analysis of problem of joined elastic beams is presented in comparison with the engineering and asymptotic approaches. Our analysis is based on three‐dimensional elasticity theory model and recently developed method of local perturbation (Gaudiello and Kolpakov, 2011), which seems to be an effective tool for analysis of fields in the vicinity of joint. We demonstrate that the method of local perturbation developed in (Gaudiello and Kolpakov, 2011) for scalar Laplace equation can be modified for vectorial elasticity theory problem. We demonstrate that the elasticity theory problem in joined domains of small diameter can be decomposed into one‐dimensional problem describing global deformation of a system of joined beams and three‐dimensional problems describing local deformation of singular joints in uniform fields. The first problem is the classical one, which ignores individual properties of joint absolutely. The second problem initiates reminiscence about the cellular problem of the homogenization theory for periodic structure. In spite of some similarities, the mentioned problems differ significantly. In particular, the joint of normal type (the joint similar in dimensions and material characteristics to the joined beams) does not manifest itself on global level. Due to the strong localization of perturbation of solution, computation of local strains and stresses in the vicinity of joint can be realized with standard FEM software.