Home About us Contact
|
Home About us Contact | ||
|
|
||
Different Boundary Conditions (different + boundary_condition)
Selected AbstractsChemInform Abstract: MoV2O2+4 Directs the Formation and Subsequent Linking of Potential Building Blocks under Different Boundary Conditions: A Related Set of Novel Cyclic Polyoxomolybdates.CHEMINFORM, Issue 47 2001Achim Mueller Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Finite-element analysis of a combined fine-blanking and extrusion processINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2006P. F. Zheng Abstract This paper presents the characteristics of the combined fine-blanking and extrusion process and gives a detailed analysis of the process with the finite-element method. To carry out the simulation step by step and avoid the tendency to diverge in the calculations, the remeshing, tracing and golden section methods were developed and introduced into the finite-element program. Different boundary conditions were used in the simulation; the mesh distortion, field of material flow, and the stress and strain distributions were obtained. From the simulated results, the deformation characteristics under different boundary conditions were revealed. An experiment was also carried out to verify the simulated results. A large strain analysis technique was chosen to determine the effective strain distribution based on the experiment. The effective strain distributions from the simulation are in accordance with the effective strain distributions and the hardness distributions from the experiment. Copyright © 2005 John Wiley & Sons, Ltd. [source] Chain length effects on nonlinear excitation transitions in trans-polyacetyleneINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2008Pedro Henrique de Oliveira Neto Abstract We investigate the nonlinear excitation transitions in a trans-polyacetylene chain. The Su,Schrieffer,Heeger model was used. The chain length was successively changed so that this modification effects could be explored. The system is composed of a polyacetylene chain initially with a charged polaron. An electron ionization is then simulated and the formation of a couple of solitons took place. It was observed that the chain length influences the spectra, raising concerns about the proper chain length to simulate very long chains. Different boundary conditions were also investigated, and as a result we found that steady chain edges are more appropriate to model long chains, when transitions take place. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Assessment of Protection Systems for Buried Steel Pipelines Endangered by RockfallCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2005Bernhard Pichler First, a gravel-based protection system (GBPS) is investigated, that is, a pipeline buried in sandy gravel is considered. To assess the load-carrying behavior of this structure when subjected to rockfall, a finite element (FE) model has been developed. The development and the validation of this structural model are strictly separated, that is, they are based on two physically and statistically independent sets of experiments. Subsequently, scenarios of rockfall onto a gravel-buried steel pipe are analyzed considering different boundary conditions and structural dimensions. Following the conclusions drawn from these numerical analyses, an enhanced protection system (EPS) is proposed. It consists of gravel as an energy-absorbing and impact-damping system and a buried steel plate resting on walls made of concrete representing a load-carrying structural component. The potential and the limitations of both protection systems are discussed in detail. [source] Full-scale study on combustion characteristics of an upholstered chair under different boundary conditions,Part 1: Ignition at the seat centerFIRE AND MATERIALS, Issue 6 2009Q. Y. Xie Abstract The objective of this work is to investigate the effects of boundary conditions on the combustion characteristic of combustible items in a room. A series of full-scale experiments were carried out in the ISO 9705 fire test room with an upholstered chair at four typical locations, i.e. at the middle of side wall, at the center of the room with the seat toward the door, at the center of the room with the seat toward inside of the room, at the room corner, respectively. Ignition was achieved through a BS No.7 wooden crib at the geometric center of the seat surface for each test. Besides the heat release rate (HRR), four thermocouple trees were placed around the chair to monitor detailed temperature distributions during the combustion process of an upholstered chair. The results indicated that the boundary conditions had some effects on the combustion behavior of a chair in a room. It was shown that there were clearly two main peak HRRs for the cases of a chair being clung to the side wall or at the corner. However, there was only one main peak HRR when the chair was placed at the center of the room, either outwards or inwards. In addition, the results of the two cases of chairs being at the center indicate that the maximum HRR (about 829,kW) for the chair seat toward the door was relatively larger than the maximum HRR (about 641,kW) for the chair seat toward inside of the room. It was suggested that the special complex structure of a chair was also a considerable factor for the effect of boundary conditions on the combustion behavior of a chair in an enclosure. Furthermore, the measured temperature distributions around the chair also illustrated the effects of boundary condition on the combustion behavior of a chair in a room. It was suggested that although HRR was one of the most important fire parameters, HRR mainly represented the comprehensive fire behavior of a combustible item. In order to develop more suitable room fire dynamic models, more detailed information such as the surrounding temperature distributions measured by the thermocouple trees are useful. Copyright © 2009 John Wiley & Sons, Ltd. [source] An ellipticity criterion in magnetotelluric tensor analysisGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2004M. Becken SUMMARY We examine the magnetotelluric (MT) impedance tensor from the viewpoint of polarization states of the electric and magnetic field. In the presence of a regional 2-D conductivity anomaly, a linearly polarized homogeneous external magnetic field will generally produce secondary electromagnetic fields, which are elliptically polarized. If and only if the primary magnetic field vector oscillates parallel or perpendicular to the 2-D structure, will the horizontal components of the secondary fields at any point of the surface also be linearly polarized. When small-scale inhomogeneities galvanically distort the electric field at the surface, only field rotations and amplifications are observed, while the ellipticity remains unchanged. Thus, the regional strike direction can be identified from vanishing ellipticities of electric and magnetic fields even in presence of distortion. In practice, the MT impedance tensor is analysed rather than the fields themselves. It turns out, that a pair of linearly polarized magnetic and electric fields produces linearly polarized columns of the impedance tensor. As the linearly polarized electric field components generally do not constitute an orthogonal basis, the telluric vectors, i.e. the columns of the impedance tensor, will be non-orthogonal. Their linear polarization, however, is manifested in a common phase for the elements of each column of the tensor and is a well-known indication of galvanic distortion. In order to solve the distortion problem, the telluric vectors are fully parametrized in terms of ellipses and subsequently rotated to the coordinate system in which their ellipticities are minimized. If the minimal ellipticities are close to zero, the existence of a (locally distorted) regional 2-D conductivity anomaly may be assumed. Otherwise, the tensor suggests the presence of a strong 3-D conductivity distribution. In the latter case, a coordinate system is often found, in which three elements have a strong amplitude, while the amplitude of the forth, which is one of the main-diagonal elements, is small. In terms of our ellipse parametrization, this means, that one of the ellipticities of the two telluric vectors approximately vanishes, while the other one may not be neglected as a result of the 3-D response. The reason for this particular characteristic is found in an approximate relation between the polarization state of the telluric vector with vanishing ellipticity and the corresponding horizontal electric field vector in the presence of a shallow conductive structure, across which the perpendicular and tangential components of the electric field obey different boundary conditions. [source] Role of lateral mantle flow in the evolution of subduction systems: insights from laboratory experimentsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004Francesca Funiciello SUMMARY We present 3-D laboratory experiments constructed to investigate the pattern of mantle flow around a subducting slab under different boundary conditions. In particular we present a set of experiments, characterized by different conditions imposed at the trailing edge of the subducting plate (that is, plate fixed in the far field, plate detached in the far field, imposed plate motion). Experiments have been performed using a silicone slab floating inside a honey tank to simulate a thin viscous lithosphere subducting in a viscous mantle. For each set, we show differences between models that do or do not include the possibility of out-of-plane lateral flow in the mantle by varying the lateral boundary conditions. Our results illustrate how a subducting slab vertically confined over a 660-km equivalent depth can be influenced in its geometry and in its kinematics by the presence or absence of possible lateral pathways. On the basis of these results we show implications for natural subduction systems and we highlight the importance of suitable simulations of lateral viscosity variations to obtain a realistic simulation of the history of subduction. [source] A computational model for fracturing porous mediaINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2007R. Al-Khoury Abstract This paper presents a new computational model for simulating a fracturing process in a porous medium using the finite element method. Two independent numerical techniques are used for describing this process. The partition of unity method is used for describing the fracturing process, and the double porosity model is used for describing the resulting fluid flow. A key feature of the model is the coupling of these two independent numerical techniques, which provide the means for a better simulation of the involved physical and mechanical processes. The paper focuses on the numerical formulation of the model. The capability of the model is illustrated by means of numerical examples, which examine the behaviour of a 1D porous medium under different boundary conditions. The numerical results show that the very complicated physical and mechanical processes of the fracturing porous media can be simulated properly and efficiently. Copyright © 2006 John Wiley & Sons, Ltd. [source] Finite-element analysis of a combined fine-blanking and extrusion processINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2006P. F. Zheng Abstract This paper presents the characteristics of the combined fine-blanking and extrusion process and gives a detailed analysis of the process with the finite-element method. To carry out the simulation step by step and avoid the tendency to diverge in the calculations, the remeshing, tracing and golden section methods were developed and introduced into the finite-element program. Different boundary conditions were used in the simulation; the mesh distortion, field of material flow, and the stress and strain distributions were obtained. From the simulated results, the deformation characteristics under different boundary conditions were revealed. An experiment was also carried out to verify the simulated results. A large strain analysis technique was chosen to determine the effective strain distribution based on the experiment. The effective strain distributions from the simulation are in accordance with the effective strain distributions and the hardness distributions from the experiment. Copyright © 2005 John Wiley & Sons, Ltd. [source] Three-dimensional vibration analysis of rectangular thick plates on Pasternak foundationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2004D. Zhou Abstract The free-vibration characteristics of rectangular thick plates resting on elastic foundations have been studied, based on the three-dimensional, linear and small strain elasticity theory. The foundation is described by the Pasternak (two-parameter) model. The Ritz method is used to derive the eigenvalue equation of the rectangular plate by augmenting the strain energy of the plate with the potential energy of the elastic foundation. The Chebyshev polynomials multiplied by a boundary function are selected as the admissible functions of the displacement functions in each direction. The approach is suitable for rectangular plates with arbitrary boundary conditions. Convergence and comparison studies have been performed on square plates on elastic foundations with different boundary conditions. It is shown that the present method has a rapid convergent rate, stable numerical operation and very high accuracy. Parametric investigations on the dynamic behaviour of clamped square thick plates on elastic foundations have been carried out in detail, with respect to different thickness,span ratios and foundation parameters. Some results found for the first time have been given and some important conclusions have been drawn. Copyright © 2004 John Wiley & Sons, Ltd. [source] A meshless method for Kirchhoff plate bending problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2001Vitor M. A. Leitão Abstract In this work a meshless method for the analysis of bending of thin homogeneous plates is presented. This meshless method is based on the use of radial basis functions to build an approximation of the general solution of the partial differential equations governing the Kirchhoff plate bending problem. In order to obtain a symmetric and non-singular linear equation system the Hermite collocation method is used. To assess the formulation a series of plates with different boundary conditions are analysed. Comparisons are made with other results available in the literature. Copyright © 2001 John Wiley & Sons, Ltd. [source] The singular sources method for cracksMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 10 2007Morteza Fotouhi Abstract The singular sources method is given to detect the shape of a thin infinitely cylindrical obstacle from a knowledge of the TM-polarized scattered electromagnetic field in large distance. The basic idea is based on the singular behaviour of the scattered field of the incident point source on the cross-section of the cylinder. We assume that the scatterer is a perfect conductor which is possibly coated by a material and investigate two models with different boundary conditions. Also we give a uniqueness proof for the shape reconstruction. Copyright © 2006 John Wiley & Sons, Ltd. [source] Thermoelasticity with second sound,exponential stability in linear and non-linear 1-dMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 5 2002Reinhard Racke We consider linear and non-linear thermoelastic systems in one space dimension where thermal disturbances are modelled propagating as wave-like pulses travelling at finite speed. This removal of the physical paradox of infinite propagation speed in the classical theory of thermoelasticity within Fourier's law is achieved using Cattaneo's law for heat conduction. For different boundary conditions, in particular for those arising in pulsed laser heating of solids, the exponential stability of the now purely, but slightly damped, hyperbolic linear system is proved. A comparison with classical hyperbolic,parabolic thermoelasticity is given. For Dirichlet type boundary conditions,rigidly clamped, constant temperature,the global existence of small, smooth solutions and the exponential stability are proved for a non-linear system. Copyright © 2002 John Wiley & Sons, Ltd. [source] Pointwise estimates for Green's kernel of a mixed boundary value problem to the Stokes system in a polyhedral coneMATHEMATISCHE NACHRICHTEN, Issue 15 2005V. Maz'ya Abstract The paper deals with a mixed boundary value problem for the Stokes system in a polyhedral cone. Here different boundary conditions (in particular, Dirichlet, Neumann, free surface conditions) are prescribed on the sides of the polyhedron. The authors obtain regularity results for weak solutions in weighted L2 Sobolev spaces and prove point estimates of Green's matrix. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fast direct solvers for Poisson equation on 2D polar and spherical geometriesNUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 1 2002Ming-Chih Lai Abstract A simple and efficient class of FFT-based fast direct solvers for Poisson equation on 2D polar and spherical geometries is presented. These solvers rely on the truncated Fourier series expansion, where the differential equations of the Fourier coefficients are solved by the second- and fourth-order finite difference discretizations. Using a grid by shifting half mesh away from the origin/poles, and incorporating with the symmetry constraint of Fourier coefficients, the coordinate singularities can be easily handled without pole condition. By manipulating the radial mesh width, three different boundary conditions for polar geometry including Dirichlet, Neumann, and Robin conditions can be treated equally well. The new method only needs O(MN log2N) arithmetic operations for M × N grid points. © 2002 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 18: 56,68, 2002 [source] Imperfection Sensitivity and Limit Loads of Spherical Shells under Radial PressurePROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005Jens Pontow The evaluation of the imperfection sensitivity of shell structures and the estimation of their limit loads are widely discussed phenomena. The perturbation energy concept according to Dinkler et al. [1], [2] enables to assess the imperfection sensitivity of shell structures by means of an energy value, the perturbation energy. A buckling criterion may be developed from the comparison between the perturbation energy and experimental data. This paper focuses on the imperfection sensitivity and limit loads of spherical shells of revolution under radial pressure. The investigations include the influence of the meridional angle and different types of boundary conditions. By comparing the numerical results with the German design rule DIN 18800, critical values for the perturbation energy are derived to predict the limit loads. These critical values for the perturbation energy allow to judge whether the German design rule DIN18800 predicts the limit loads of spherical shells under external pressure with varying meridional angles and different boundary conditions with the same reliability in respect of the perturbation energy. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nutzung biogener Festbrennstoffe in Vergasungsanlagen,CHEMIE-INGENIEUR-TECHNIK (CIT), Issue 7 2004S. Osowski Dipl.- Ing. Abstract Aufgrund der knapper werdenden fossilen Rohstoffe gewinnen Biomassen als regenerative Energiequellen zunehmend an Bedeutung. Daher ist es für die Umsetzung von Biomasseprojekten und den verstärkten Einsatz von Biomasseanlagen wesentlich, geeignete thermische Verfahren für den Biomasseeinsatz zu identifizieren. Vor diesem Hintergrund muss die Bewertung verschiedener Vergasungstechnologien hinsichtlich unterschiedlicher Randbedingungen und Einsatzstoffe erfolgen. Da die Zusammensetzung des Produktgases mit Art und Form des Brennstoffs sowie der Vergaserbauart variiert, wird im Folgenden die Eignung für die Biomassenvergasung in ausgesuchten Vergasungsreaktoren mit ihren Vor- und Nachteilen analysiert. Utilization of Biogenic Solids in Gasifiers As a result of shrinking fossil fuels biomass as a regenerative energy source gains in importance. To realize biomass projects it is essential to investigate convenient thermal procedures. On this evidence an analysis and evaluation of diverse gasification technologies with different boundary conditions and diverse biomasses is indispensable. Form and kind of the biomass as well as the type of the gasification plant cause different compositions of the product gas. The gasifiers show advantages and disadvantages concerning the biomass and the produced gas quality, depending on reactor type, kind of heat supply, gasification medium, and the pressure ratio in the reactor. As the ideal gasifier for different biomass is presently not available it will be shown which biomass is suitable for fixed bed or fluidised bed gasifiers. [source] | ||||||||||||||||