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This work presents a novel formulation of the Boundary Element Method (BEM) with the Radial Integration Method (RIM) to calculate the critical loads of the plate buckling problem with shear deformation. An alternative formulation is adopted where the effect of the geometric non-linearity is described by using the first derivative of the function for the out-of-plane displacements. The RIM is developed for this problem and used to convert the resulting domain integrals into equivalent boundary integrals. The results are compared with other results available in the literature and with the results obtained with the Dual Reciprocity Method (DRM). The advantages of using the RIM are discussed at the end of this work.

Steel plate shear walls (SPSWs) are among the most desirable load-bearing systems, which have been used wildly in various structures. Recently, designers have tended to SPSWs with only beam connections showing several problems. In the present research, several SPSWs with various types of connection conditions between infill plate and boundary elements, and various stiffness of boundary elements have been studied. The result illustrates that by having the full connection between infill plate and boundary elements, at least a 33% interconnected infill plate to columns could eliminate the significant loss of fundamental factors in SPSWs connected to beam only. Furthermore, increasing the stiffness of columns has more effect on the performance of SPSWs in comparison with beams.

The buckling problem represents a way to evaluate the effect of in-plane forces in the behaviour of plates. The effect is distributed along the plate domain, and thus the Boundary Element Method (BEM) formulation of the problem requires domain integration. Several techniques can be used in the numerical implementation of the BEM to replace the domain integral with equivalent boundary integrals. This study adopted the Dual Reciprocity Method (DRM) to obtain a formulation without domain integrals. The bending model considered the effect of the shear deformation for better assessment of the relationship between the buckling load and the plate thickness. The analyses considered in-plane forces distributed in one or in both directions of the plate (normal forces), as well as in the tangential direction to the plate side (shear forces). The numerical results obtained for square and rectangular plates are compared with those available in the literature.

Made available in DSpace on 2019-10-06T15:24:54Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-02-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) A boundary element formulation to obtain the constitutive response of heterogeneous microstructures is proposed, considering a RVE-based multiscale theory. The sub-region technique is adopted to model the RVE (Representative Volume Element), where voids and inclusions can be defined inside the matrix and different elastic properties and constitutive models can be assumed for each phase. Triangular cells are adopted to approximate the dissipative forces over the RVE domain, where they are assumed constant. After a strain vector is imposed to the microstructure boundary, its elastic forces field is obtained and the respective strain field computed. Then, according to the RVE-based multiscale theory, the RVE equilibrium problem must be solved what requires an iterative procedure to find the displacement fluctuations field that auto-equilibrates the microstructure stress field. After the RVE solution, the boundary tractions must be recalculated to consider the displacement fluctuations field as well as the dissipative forces. Then, from the boundary tractions the homogenized stress vector can be computed. The homogenized constitutive tensor is evaluated considering the constitutive tensors of all cell nodes and also the consistent tangent operator. To validate the proposed model, the homogenized responses of different microstructures are compared to the responses obtained via finite element model. Civil Engineering Department Federal University of Goiás (UFG) – Regional Catalão, Av. Dr. Lamartine Pinto de Avelar, 1120, Setor Universitário- CEP Civil Engineering Department São Paulo State University – UNESP, Al. Bahia, 550 Civil Engineering Department São Paulo State University – UNESP, Al. Bahia, 550 CNPq: 302841/2014-8

Sometimes boundary value problems have isolated regions where the solution changes rapidly. Therefore, when solving numerically, one needs a fine grid to capture the high activity. The fine grid can be implemented as a composite coarse-fine grid or as a global fine grid. One cheaper way of obtaining the composite grid solution is the use of the local defect correction technique. The technique is an algorithm that combines a global coarse grid solution and a local fine grid solution in an iterative way to estimate the solution on the corresponding composite grid. The algorithm is relatively new and its convergence properties have not been studied for the boundary element method. In this paper the objective is to determine convergence properties of the algorithm for the boundary element method. First, we formulate the algorithm as a fixed point iterative scheme, which has also not been done before for the boundary element method, and then study the properties of the iteration matrix. Results show that we can always expect convergence. Therefore, the algorithm opens up a real alternative for application in the boundary element method for problems with localised regions of high activity.

Made available in DSpace on 2022-04-28T19:07:07Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-02-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) A BEM formulation to perform elastic analysis of heterogeneous microstructures is proposed in the context of multi-scale analysis. The microstructure, also denoted as RVE (Representative Volume Element), is modeled as a zoned plate where voids or inclusions can be considered inside a matrix. Thus, each sub-region represents either the matrix or an inclusion, where different values of Poisson's ratio and Young's modulus can be defined. The RVE equilibrium equation is solved in terms of displacement fluctuations according to the formulation proposed in de Souza Neto and Feijóo (2006). Only elastic behavior is considered for matrix and inclusions, although the proposed model can be extended to consider dissipative phenomena. To make the micro-to-macro transition necessary in a multi-scale analysis, the homogenized values for stress and constitutive tensor have to be computed adopting homogenization techniques. Some numerical examples of heterogeneous microstructures are presented and compared to a FEM model to show the accuracy of the proposed model. FEIS – Faculdade de Engenharia de Ilha Solteira, Av. Brasil Sul, 56 - Centro, Ilha Solteira - Civil Engineering Department Federal University of Goiás (UFG) – Regional Catalão, Av. Dr. Lamartine Pinto de Avelar, 1120, Setor Universitário CNPq: 302841/2014-8 CAPES: BEX 0602/11-6

The paper deals with the direct time domain calculation of a transient electric field generated by a ground penetrating radar (GPR) dipole antenna and transmitted into the lossy half-space. The space–time dependent current along the dipole is governed by the Hallen integral equation which is numerically solved by means of the Galerkin–Bubnov scheme of the Indirect Boundary Element Method (GB-IBEM). Provided that the current distribution along the GPR antenna is determined, one may compute the related electromagnetic field transmitted into the lossy ground by solving the field integral formulas. Some illustrative computational examples related to the transmitted field into the lower half-space are reported in this paper.

The buckling of square perforated plates is analysed with the effect of shear deformation in the bending model. The relationship between the buckling load and the plate thickness is better assessed with this bending model instead of the classical model. The simply supported condition at all sides was adopted in the buckling problem such that opposite sides of the plates were uniformly compressed in one direction. The plates had a thickness to length ratio between 1/1000 and 1/5. This study adopted the dual reciprocity method (DRM) to obtain a formulation without domain integrals. The numerical results obtained were compared with those available in the literature.

Finite-element techniques in geomechanic calculations to assess strain-stress state in rock have shown insufficient flexibility towards varying geometry of computational schemes and necessity to set a large number of the unknown in solving space problems. Numeric calculation of stress intensity factor at the fracture tip by finite element analysis is a very demanding task in dimensional geomechanic simulation. Domain partition by irregular grid significantly expands the length of rigidity matrix bandwidth, which also largely depends on element enumeration approach. When computational scheme geometry considerably exceeds the size of the area of the detailed exploration of strain-stress state application of traditional methods of finite elements and geometric immersion is not feasible. The paper suggests to apply a potentially more accurate computational scheme for assessing strain-stress state of three-dimensional piecewise-homogeneous elastic environment on the basis of indirect method of boundary elements. In developing potassium beds by pillar system displacement discontinuity method as a variation of boundary element method appears to be a convenient tool to compute strain-stress state, which allows taking account of relation between the top and soil of the longwall space. Based on the indirect method of boundary elements, a software package was developed that offers a computational scheme to solve the problem of evaluating strain-stress state of piecewise-homogeneous linear-elastic environment. The results of solving test problems are given that prove adequacy of the computational scheme to evaluate strain-stress state of rock.

Inverse scattering acoustics find practical appli- cations in the detection and imaging of objects embedded in continuous media as well as in finding the optimum geomet- ric configuration of an object to produce a given radiation per- formance. This work introduces a boundary element method (BEM) approach for the solution of acoustic identification and optimization problems via a topological-shape sensitiv- ity method. The devised optimization tool takes advantage of the inherent characteristics of BEM to effectively solve the forward and adjoint acoustic problems arising in the topolog- ical derivative formulation and to deal with infinite domains. The objectives for the identification and optimization prob- lems are to achieve a prescribed sound pressure at a given region of the problem domain. The locus giving extreme val- ues for the topological derivative indicates the optimum posi- tions for the placement of sound-hard scatterers in order to minimize the cost function. The proposed implementation has the ability to deal with initially empty design spaces as well as with design spaces containing pre-existent scatterers. The capabilities of the method are demonstrated by solving a number of identification and optimization problems. Fil: Sisamón, Agustín. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina Fil: Beck, Silja C.. Technische Universität Braunschweig; Alemania Fil: Langer, Sabine C.. Technische Universität Braunschweig; Alemania Fil: Cisilino, Adrian Pablo. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina

In humans over 15% of X-linked genes have been shown to 'escape' from X-chromosome inactivation (XCI): they continue to be expressed to some extent from the inactive X chromosome. Mono-allelic expression is anticipated within a cell for genes subject to XCI, but random XCI usually results in expression of both alleles in a cell population. Using a study of allelic expression from cultured lymphoblasts and fibroblasts, many of which showed substantial skewing of XCI, we recently reported that the expression of genes lies on a contiunuum between those that are subject to inactivation, and those that escape. We now review allelic expression studies from mouse, and discuss the variability in escape seen in both humans and mice in genic expression levels, between X chromosomes and between tissues. We also discuss current knowledge of the heterochromatic features, DNA elements and three-dimensional topology of the inactive X that contribute to the balance of expression from the otherwise inactive X chromosome.

This work describes a setup for the experimental and theoretical study of the mass transport of a penetrant through a two-dimensional model-material microstructure consisting in a homogeneous matrix with slender obstacles. Experiments were performed using polydimethylsiloxane (PDMS) specimens with a controlled pattern of randomly distributed laser-ablated microscopic slender holes that mimic the obstacles to the diffusion of the penetrant, 1-octadecanol (ODOL). Mass transport of ODOL throughout the patterned PDMS matrix was monitored by means of Confocal Raman microscopy. Rigorous numerical simulations of ODOL transport in transient regime were performed using the Boundary Element Method for exactly the same model-material microstructure topology used in the experimental tests. It was found that both, experiments and BEM simulations very well capture local barrier effects of the obstacles to the ODOL transport. The whole strategy provides a valuable base for validation and experimental verification of theoretical models of mass transport through heterogeneous membranes with complex barrier structure. Fil: Dondero, Marco. Universidad Nacional de Mar del Plata. Facultad de Ingenieria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina Fil: Cisilino, Adrian Pablo. Universidad Nacional de Mar del Plata. Facultad de Ingenieria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina Fil: Tomba, Juan Pablo. Universidad Nacional de Mar del Plata. Facultad de Ingenieria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina

Maxwell's equations are considered with transparent boundary conditions, with initial conditions and inhomogeneity having support in a bounded, not necessarily convex three-dimensional domain or in a collection of such domains. The proposed computational scheme only involves the interior domain and its boundary. The transparent boundary conditions are imposed via a time-dependent boundary integral operator that is shown to satisfy a coercivity property. The stability of the numerical method relies on this coercivity. The method proposed here uses a discontinuous Galerkin method and the leapfrog scheme in the interior and is coupled to boundary elements and convolution quadrature on the boundary. The method is explicit in the interior and implicit on the boundary. Stability and convergence of the spatial semidiscretization are proven, and with a computationally simple stabilization term, this is also shown for the full discretization.

The three-dimensional eddy current time-dependent problem is considered. We formulate it in terms of two variables, one lying only on the conducting domain and the other on its boundary. We combine finite elements (FEM) and boundary elements (BEM) to obtain a FEM–BEM coupled variational formulation. We establish the existence and uniqueness of the solution in the continuous and the fully discrete case. Finally, we investigate the convergence order of the fully discrete scheme.

The paper deals with two different approaches to the assessment of the transient impedance of a horizontal grounding electrode: frequency domain boundary element analysis, based on the straight thin wire antenna model (AM) and generalized telegrapher’s equations combined with inverse Fast Fourier Transform (FFT) ; and time domain finite element analysis based on the transmission line model (TLM) and standard telegrapher’s equations. Extensive numerical experiments have been undertaken and some of illustrative numerical results are presented in this paper.

We investigate the use of the Multipole-accelerated Boundary Element Method (BEM) and of the Singularity Method for studying the interaction of many bubbles rising in a volcanic conduit. Observation shows that the expression of volcanic eruption is extremely variable, from slow release of magma to catastrophic explosive manifestation. We investigate the application of the Fast Multipole Method to the solution of (i) the Boundary Element Formulation of the Stokes flow and of (ii) the particle formulation using the Stokeslets, the Green Function of the Stokes flow law, as a particle kernel. We show how these implementations allow for the first time to numerically model in a dynamic setting a very large number of bubbles, i.e few thousands with the BEM models, allowing investigating the feedback between the single bubble deformation and their collective evolution, and few hundred of thousands of bubbles with the particle approach. We illustrate how this method can be used to investigate the intense interaction of a large number of bubbles and suggest a framework for studying the feedback between many bubbles and a complex thermal nonlinear magmatic

Traditionally only the static bearing capacity and stiffness of the ground is considered in the design of wind turbine foundations. However, modern wind turbines are flexible structures with resonance frequencies as low as 0.2 Hz. Unfortunately, environmental loads and the passage of blades past the tower may lead to excitation with frequencies of the same order of magnitude. Therefore, dynamic soil-structure interaction has to be accounted for in order to get an accurate prediction of the structural response. In this paper the particular problem of a rigid foundation on a layered subsoil is discussed. Based on the Green's function for a stratified half-space, the impedance of a surface footing with arbitrary shape is computed. A wind turbine foundation is analysed in the frequency range 0 to 3 Hz. Analyses show that soil stratification may lead to a significant changes in the impedance related to both rocking and translation at frequencies close to the first resonance frequency of an offshore wind turbine.

International audience; The numerical solution of the free boundary Bernoulli problem is addressed. An iterative method based on a level-set formulation and boundary element method is proposed. Issues related to the implementation, the accuracy and the generality of the method are discussed. The efficiency of the approach is illustrated by numerical results

Analytical integrations, in the framework of linear elastic problems modelled by means of boundary integral equations, have been considered in a previous publication (Int. J. Numer. Methods Eng. 2002; 53(7):1695–1719): the present note aims at extending the subject to linear elastic fracture mechanics. In such a context, special shape functions have been recently proposed (SIAM J. Appl. Math. 1998; 58: 428–455) in order to increase accuracy in stress intensity factors approximation: the closed form solution for ‘integrals’ that arise from the boundary element method is a goal of the present work. Exploiting the analytical integrations, asymptotical analysis around the crack tip are made possible, with the purpose of formulating a coherent and accurate correlation between approximated stress intensity factors and crack opening displacements over the crack tip straight special elements. Copyright © 2006 John Wiley & Sons, Ltd.

Operator preconditioning offers a general recipe for constructing preconditioners for discrete linear operators that have arisen from a Galerkin approach. The key idea is to employ matching Galerkin discretizations of operators of complementary mapping properties. If these can be found, the resulting preconditioners will be robust with respect to the choice of the bases for trial and test spaces. I survey the application of operator preconditioning to finite elements and boundary elements.

The macroscopic behaviour of unidirectional fibre-reinforced-composite materials is strongly dependent on the strength of the fibre/matrix adhesion. The stress concentrations around the fibres lead to micro-crack initiation, which will grow along a ply to become a complete transverse crack. In this paper a boundary element methodology for the three-dimensional analysis of bimaterial interface cracks is presented. Fracture mechanics parameters, namely J-integral and stress intensity factors, are computed along the crack front using the Energy Domain Integral and the M1-integral methodologies. The devised numerical tool is employed to analyse the problem of a fibre/matrix interface crack under transverse loading in order to assess the three-dimensional character of the problem, and to evaluate the representatives of the results obtained from two-dimensional models. Obtained results show the key role played by the relative elastic properties of the fibre, the matrix and the laminate on the state of mixed mode fracture. Fil: Cisilino, Adrian Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Ortiz, Jhonny E.. Universidad Nacional de Trujillo; Perú

We analyze a least squares formulation for the numerical solution of second-order lineartransmission problems in two and three dimensions, which allow jumps on the interface. In a bounded domain the second-order partial differential equation is rewritten as a first-order system; the part of the transmission problem which corresponds to the unbounded exterior domain is reformulated by means of boundary integral equations on the interface. The least squares functional is given in terms of Sobolev norms of order -1 and of order 1/2. These norms are computed by approximating the corresponding inner products using multilevel preconditioners for a second-order elliptic problem in a bounded domain @? and for the weakly singular integral operator of the single layer potential on its boundary @[email protected]?. As preconditioners we use both multigrid and BPX algorithms, and the preconditioned system has bounded or mildly growing condition number. Numerical experiments confirm our theoretical results.

The changes in the seismic response due to the presence of an irregular elastic seabed, and/or the presence of a water-filled inclusion located under the elastic seabed surface, in the presence of a dilatational spatially harmonic line source, is assessed. The seabed surface deformations and the water-filled inclusions are bi-dimensional. The solution is obtained using the Boundary Elements Method for a wide range of frequencies and spatially harmonic line sources, which are then used to compute the time series by means of fast inverse Fourier transforms.

The dual reciprocity method (DRM) is a technique to transform the domain integrals that appear in the boundary element method into equivalent boundary integrals. In this approach, the nonlinear terms are usually approximated by an interpolation applied to the convective terms of the Navier-Stokes equations. In this paper, we introduce a radial basis function interpolation scheme for the velocity field, that satisfies the continuity equation (mass conservative). The proposed method performs better than the classical interpolation used in the DRM approach to represent such a field. The new scheme together with a subdomain variation of the dual reciprocity method allows better approximation of the nonlinear terms in the Navier-Stokes equations.

An isogeometric boundary element method based on NURBS is used to find solutions to the Helmholtz equation. The method is extended in a partition-of-unity sense, multiplying the NURBS functions with families of plane waves; this new method is called the eXtended Isogeometric Boundary Element Method (XIBEM). When compared to non-enriched boundary element simulations, using XIBEM significantly reduces the number of degrees of freedom required to obtain a solution with a given error. The extension used here (and in similar Tretz methods) requires a set of wave directions to be specified. Ideally, these directions are uniformly spaced points over the unit-sphere. Simple schemes (e.g. latitude/longitude and discretised cube methods) have been proposed previously. However, while these schemes provide adequate spacing of wave directions, they do not allow an arbitrary number of wave directions to the be chosen. The authors use a novel algorithm, based on a physical analogy of charged particles held in static equilibrium on a spherical surface. The XIBEM formulation will be described, including a focus on the novel method of choosing a uniformly spaced set of plane wave directions for the enrichment. Numerical results show the reduction in degrees of freedom required to obtain approximations of engineering accuracy.

The publication is available http://dx.doi.org/10.1137/S0036142998335364 [Abstract] We use a version of the FEM--BEM method introduced by Costabel [ Boundary Elements IX, Vol. 1, C. A. Brebbia et al., eds., Springer-Verlag, 1987] and Han [ J. Comput. Math., 8 (1990), pp. 223--232] to discretize an exterior quasilinear problem. We provide error estimates for the Galerkin method and propose a fully discrete scheme based on simple quadrature formulas. Furthermore, we show that these numerical integration schemes preserve the optimal rates of convergence. Finally, we present results of numerical experiments involving our discretization method.

We consider the classical Fredholm linear integral equation of the first kind with logarithmic kernel on a smooth Jordan open arc. Applying the well-known cosine change of variable, the arc is reparametrized and the problem is transformed into a new integral equation. We investigate the existence of an asymptotic expansion for the error of the Galerkin method with splines on a uniform mesh as test-trial functions. We also analyse a full discretization of the method based on the Galerkin collocation method using high order integration formulae to keep the optimal error estimates of the Galerkin method in weak norms. Asymptotic expansions of the error for this method are provided. Finally, we show how these expansions extend to the computation of the potential. The expansions of the error in powers of the discretization parameter are useful to obtain a posteriori estimates of the error and to apply Richardson extrapolation for acceleration of convergence. © 1999 Elsevier Science Ltd. All rights reserved.

The concept of isogeometric analysis, whereby the parametric func- tions that are used to describe CAD geometry are also used to approx- imate the unknown fields in a numerical discretisation, has progressed rapidly in recent years. This paper advances the field further by outlin- ing an isogeometric Boundary Element Method (IGABEM) that only re- quires a representation of the geometry of the domain for analysis, fitting neatly with the boundary representation provided completely by CAD. The method circumvents the requirement to generate a boundary mesh representing a significant step in reducing the gap between engineering design and analysis. The current paper focuses on implementation details of 2D IGABEM for elastostatic analysis with particular attention paid towards the differences over conventional boundary element implementa- tions. Examples of Matlab R{\deg} code are given whenever possible to aid understanding of the techniques used.

The boundary element method has its origins in the boundary integral equation method [1] and has, in the past two decades, become a well-established technique for the solution of problems in engineering and applied science. A significant amount of work has been focused on the development of computer programs, the vast majority of which have been written to run on sequential computers. However, the boundary element method exhibits inherent parallelisms which may be mapped onto a variety of parallel architectures. Over the past few years, boundary element researchers have started to realize the possibilities that parallel computing environments offer. Applications from elasticity, electromagnetics, fluid dynamics, etc., have had implementations on both fine-grained and coarse-grained architectures.

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2010, Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2010, Bu çalışmada, 154 kV hava hattı silikon kauçuk izolatör “Electro” programı ile modellenmiş; bu izolatörün üzerinde alternatif ve darbe gerilim şartlarında oluşan elektrik alan şiddetleri ve elektrik potansiyel değerleri incelenmiştir. Benzetimlerde izolatör etrafındaki korona halkası yerleşiminin izolatör üzerinde oluşan elektrik alan şiddeti ve potansiyel değerlerine etkisi incelenmiştir. İncelemelerde 3 temel unsur göz önünde tutulmuştur. Bunlar, korona halkasının izolatör alt ucundan yüksekliği, halka çapı ve et kalınlığı unsurlarıdır. Ayrıca program yardımıyla izolatör üzerine su halkaları yerleştirilerek oluşan alan şiddeti ve potansiyel değerleri, temiz durum değerleri ile karşılaştırılmıştır. Günümüzde darbe geriliminde oluşan anlık değerler deneysel yöntemler ile ölçülememektedir. Darbe gerilimi anında oluşan anlık değerleri ancak sayısal yöntemler ile elde edebilmekteyiz. Kullanılan bilgisayar programının çözüm tekniğindeki kısıtlamalardan dolayı, alternatif gerilim benzetimlerinde her iki yöntemin de kullanılabilmesine rağmen benzetimler sınır elemanları yöntemi ile darbe gerilimi benzetimlerinde ise sadece sonlu elemanlar yöntemi ile gerçekleştirilmiştir. Çalışmanın birinci bölümünde konu hakkında giriş yapılmış, ikinci bölümünde ise elektrik alan ifadeleri, sonlu elemanlar yöntemi ve sınır elemanları yöntemi hakkında genel bilgiler verilmiştir. Ayrıca model üzerinde alternatif gerilim kullanılarak hem sonlu elemanlar hem de sınır elemanları yöntemleri ile benzetim yapılıp, her iki yöntem ile ulaşılan sonuçlar karşılaştırılmıştır. Üçüncü bölümde ise kullanılan izolatörün modellemesinin nasıl yapıldığı ve benzetim sonuçlarında kullanılan bölgelerin tanımlamaları yapılmıştır. Dördüncü bölümde alternatif gerilim altında yapılan benzetim sonuçları verilmiştir. Beşinci bölümde ise darbe gerilimi ile yapılan benzetimlerin sonuçları verilmiştir. Çalışmanın sonucu olarak alternatif ve darbe gerilim benzetim sonuçları kullanılarak korona halkasının izolatör performansını en üst seviyeye çıkaracak yerleşimi belirlenmeye çalışılmıştır., In this study, 154 kV overhead line silicone rubber insulator is modelled with a computer program named Electro and electrical field and electrical potential values occurred under alternative and impulse voltage signals are investigated. In these analysis; the impact of the corona ring location to the electrical field and electrical potential values occurred on the insulator according to the corona ring diameter, height from energised end and tube diameter is also studied. Beside of these, electrical field and electrical potential values are analyzed in the existence of water rings on the insulator. It is not possible to determine exact values of electrical field and potentials with today’s experimental techniques. These values can only be determined by analytical techniques. In this study, in spite of the fact that both techniques can be used for alternative signal simulations, we prefer to use boundary element methods for alternative signal solutions. For the impulse signal simulations, we use finite elements method due to the methodological limitations of the software. In the first section of the study, a general introduction to the topic is made. In the second section, electrical field definitions, finite elements method and boundary elements method is briefly explained. Beside of these, the results of the boundary elements and finite element methods are compared by using alternative voltage signal upon the same model. In the third section, the method of modelling of the insulator is explained and critical areas used in the simulation results are defined. Simulation results under alternative voltage signal are enlisted in the fourth section. In the fifth section, simulation results done by impulse signal are mentioned. As the result of the study, the location of corona ring which leads the highest performance of insulator is concluded by using alternative and impulse signal simulation results., Yüksek Lisans, M.Sc.

The terminology "wave boundary elements" relates to boundary elements enriched in the Partition of Unity sense by a multiple plane wave basis for the analysis of the propagation of short wavelength waves. This paper presents a variant of this approach in which the plane wave basis is selected adaptively according to an error indicator. The error indicator is residual based, and exhibits useful local and global properties. Model improvement in each adaptive iteration is carried out by the addition of new plane waves with no h-refinement. The convergence properties of the scheme are demonstrated.

An important cause of sound radiation from a submarine in the low frequency range is fluctuating forces at the propeller. The forces arise from the operation of the propeller in a non-uniform wake and are transmitted from the propeller to the submarine hull through both the shaft and the fluid. The sound radiated from the submarine is due to the combination of sound radiation caused by hull and propeller vibrations as well as dipole sound radiation from the propeller. To improve the stealth of a submarine, the radiated sound power can be reduced using passive and active noise and vibration control mechanisms. In this thesis, dynamic models of a submarine hull and propeller/shafting system are developed. To reduce the radiated sound fields, passive control is introduced using a hydraulic vibration attenuation device known as a resonance changer, which is implemented in the propeller/shafting system. Active control techniques are implemented using either tuned actuators or a control moment. To initially obtain the structural and acoustic responses of a submarine hull, an analytical model and fully coupled finite element/boundary element model are developed, for a simplified physical model of the hull. The submerged body under axial excitation is modelled as a ring-stiffened cylindrical shell with finite rigid end closures and separated by bulkheads into a number of compartments. Lumped masses are located at each end to maintain a condition of neutral buoyancy. In the low frequency range, only the axial hull modes in accordion motion and axial vibration of the propeller/shafting system are examined, which gives rise to an axisymmetric case. The frequency responses, axial and radial responses of the cylinder and the radiated sound pressure from both the analytical and computational models are compared. A dynamic model of the propeller/shafting system developed computationally and including the resonance changer is then coupled to the FE/BE model of the hull which is subject to both structural excitation from the propeller/shafting system and acoustic excitation from the propeller. The influence of tailcone properties on the structural and acoustic responses of the submarine are investigated. Passive control is implemented to attenuate the hull responses using a resonance changer. It is demonstrated that the performance of the resonance changer is negatively influenced at frequencies above the fundamental axial resonance of the hull by the effect of forces transmitted through the fluid. When the resonance changer is optimised to minimise excitation of the hull via the propeller shaft, the increased axial movement of the propeller results in an additional sound field that excites the submarine hull in a similar manner to the fluid forces that arise directly from the hydrodynamic mechanism. Cost functions that represent the submarine radiated sound power are developed, where the virtual stiffness, damping and mass of the resonance changer were chosen as design parameters. The minima of the cost functions are found by applying gradient based optimisation techniques. The adjoint operator is employed to calculate the sensitivity of the cost function to the design parameters. The influence of sound radiation due to propeller vibration on the optimisation of the resonance changer is investigated. The influence of the reduction in amplitude for higher harmonics of the blade passing frequency on the control performance is also examined. Different active control strategies are investigated, in which active control is applied to the propeller/shafting system and/or to the submarine hull. Active vibration control and discrete structural acoustic sensing based on the far field radiated sound power were considered in the development of the cost functions. In addition, the performance of a of a combined passive and active control system is investigated. Significant reduction of radiated sound power is achieved when an active control system using tuned actuators is combined with a resonance changer. The structural responses of a model scale, free flooded submarine tailcone are investigated computationally and experimentally. The tailcone is represented by a thin-walled conical shell attached to a stiff plate. The stiff plate represents the pressure hull end plate of the submarine and is subject to axial excitation correlated to propeller forces. Good agreement between the computational and experimental results are found for the tailcone in air as well as for the submerged tailcone.

Made available in DSpace on 2013-09-27T14:52:53Z (GMT). No. of bitstreams: 1 WOS000268277100004.pdf: 257892 bytes, checksum: cadcfe973fa5763a872cdcecc5fddebc (MD5) Previous issue date: 2009-01-01 Made available in DSpace on 2013-09-30T19:23:49Z (GMT). No. of bitstreams: 1 WOS000268277100004.pdf: 257892 bytes, checksum: cadcfe973fa5763a872cdcecc5fddebc (MD5) Previous issue date: 2009-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:34:18Z No. of bitstreams: 1 WOS000268277100004.pdf: 257892 bytes, checksum: cadcfe973fa5763a872cdcecc5fddebc (MD5) Made available in DSpace on 2014-05-20T15:34:18Z (GMT). No. of bitstreams: 1 WOS000268277100004.pdf: 257892 bytes, checksum: cadcfe973fa5763a872cdcecc5fddebc (MD5) Previous issue date: 2009-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) In this work, non-linear analyses of reinforced concrete plates are performed by using a BEM formulation, based on Kirchhoff's theory, which has already proved to be a robust technique to deal with plate problems. The non-linear behavior of concrete is modeled by the Mazars model, which is based on continuum damage mechanics (CDM) and has an easy parametric identification, while the reinforcement is governed by the uniaxial elasto-plastic model with constant hardening. Initially, the different types of damage models and their parametric identification are discussed and the Mazars model is presented. Then the BEM formulation is discussed, which is based on the initial moment technique, where the remaining domain integrals are evaluated by approaching the initial moment field over internal cells. The stress distribution over the plate thickness is obtained by using a Gauss scheme in which the adopted criterion is verified in each Gauss point defined along the plate. Then, the internal values of moments are approached by numerical integrals along the plate thickness. Finally, some numerical examples of reinforced concrete plates are analyzed, where the potentiality of the Mazars model is verified despite the difficulties of the parametric identification. Universidade Federal de Goiás (UFG), BR-75700000 Catalao, Goias, Brazil Univ Estadual Paulista, Fac Engn Ilha Solteira, São Paulo, Brazil Univ Estadual Paulista, Fac Engn Ilha Solteira, São Paulo, Brazil

A numerical tool for the design of foam-like microstructures with customized heat conduction properties is presented in this paper. The spatial variation of the local material properties is achieved via the optimization of the spatial distribution of the gas cells. A Genetic Algorithm (GA) is used for this purpose. Although very effective and versatile GAs are computationally expensive. This problem is tackled in two ways here: a Fast Multipole Boundary Element Method algorithm is used for the thermal analysis of the microstructures, and the GA is implemented in parallel using a cluster of PCs. Two examples illustrate the performance of the developped implementation. Fil: Dondero, Marco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Cisilino, Adrian Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Rodriguez Carranza, A.. Universidad Nacional de Trujillo.; Perú Fil: Stavroulakis, G.. Technical University of Crete; Grecia

An original approach to solve domain decomposition problems by the symmetric Galerkin boundary element method is developed. The approach, based on a new variational principle for such problems, yields a fully symmetric system of equations. A natural property of the proposed approach is its capability to deal with nonconforming discretizations along straight and curved interfaces, allowing in this way an independent meshing of non-overlapping subdomains to be performed. Weak coupling conditions of equilibrium and compatibility at an interface are obtained from the critical point conditions of the energy functional. Equilibrium is imposed through local traction (Neumann) boundary conditions prescribed on a subdomain situated at one side of the interface, and compatibility is imposed through local displacement (Dirichlet) boundary conditions prescribed on the other subdomain situated at the opposite side of the interface. No additional unknowns such as Lagrange multipliers are introduced. An SGBEM code for 2D elastic domain decomposition problems has been implemented. The effectiveness of the approach developed is documented by numerical examples involving non-matching linear boundary element meshes at the interfaces, where the accuracy is analyzed by comparing the numerical results obtained versus the analytical solutions and by evaluating the convergence rate of the error in the (discretized) integral L2-norm and maximum-normfor h-refinements of boundary element meshes. Finally, a theoretical analysis of a problem with an interior and an exterior subdomain is introduced to explain the observed behaviour of numerical results.

28th World Conference on Boundary Elements and other Mesh Reduction Methods (from 5/10/2006 to 5/12/2006), Skiathos, Greece, available, unclassified, unlimited

We considered a nonlinear parabolic equation in a bounded domain of R 2 coupled with the Laplace equation in the corresponding exterior region. This kind of problems appears in the modelling of quasi-stationary electromagnetic fields. We chose a regular artificial boundary containing the nonlinear region in its interior. Then, we applied a symmetric FEM-BEM coupling procedure including a parameterization of the artificial boundary. We used the backward Euler method for the time discretization and an exact triangulation of the finite element domain. Assuming that the nonlinear operator is strongly monotone and Lipschitz-continuous, we proved convergence and obtained optimal error estimates for the solution of the discrete problem. Finally, we proposed a fully discrete scheme with quadrature formulas of low order and, under some additional conditions on the nonlinearity, proved that the order of convergence remains optimal.

Boundary Elements XXVI, ISBN 1-85312-708-6 Three dimensional crack problems in transversely isotropic solids under static and time harmonic dynamic loading conditions are studied in this paper using a mixed BE approach. Hypersingular and strongly singular kernels appearing in the formulation are regularized prior to any discretization. Two different crack geometries are studied. Stress Intensity Factors are computed from the crack opening displacements at quarter-point quadratic elements. The results obtained in this paper show a good agreement with other results. The number of elements required is rather small. Ministerio de Ciencia y Tecnología DPI2000-1217-C02-01 Ministerio de Ciencia y Tecnología DPI2001-2377-C02-01

An accurate design of grounding systems is essential to assure the safety of the persons, to protect the equipment and to avoid interruptions in the power supply. In order to attain these targets, it is necessary to compute the equivalent electrical resistance of the system and the potential distribution on the earth surface in fault conditions. In this paper, a numerical approach for grounding analysis embedded in stratified soils and its implementation in a high-performance parallel computer are presented. The feasibility of this system is shown with its application to the grounding analysis in layered soils by using the geometry of real grounding grids.

Design of tunnels in rock mass require thought procedures in many ways different from other design projects, because the principal construction material is the rock mass itself rather than other engineered material. Resolving of problems related to the primary support carrying capacity usually follows the stress and strain analysis of the underground rock mass by the tunnel opening. Such problem could also be resolved by using an inverse method which means by assuming the ultimate limit state of the support elements and checking whether such reactive pressures of the support elements will retain the underground rock mass in stable state, namely does the underground rock mass meet the failure criteria. This would prove possible ultimate equilibrium in the primary support system - underground rock mass interaction. This is the principal advantage of the inverse method since an input material constant on which the results depend is reduced to a very small number. On the case of road tunnel driving, the method of boundary elements with the Hoek-Brown's failure criteria was used in computations. Computations have to be performed by choosing the mechanical rock characteristics in accordance with the categories of rocks and the assumed limit bearing capacities of appropriate support types. The problem is to determine the stresses and displacements around a tunnelexcavation of specified cross-section, given the primary support systems pressure and assumed fracture propagation in rock mass surrounding a tunnel opening. The upgraded boundary element program for two-dimensional stress, displacement and failure analysis conducts the stress and strain analysis for the area by the tunnel opening. This paper shows the results of an analysis for the tunnel Pod Vugles in the part from Zagreb to Rijeka motorway as a part of European Vb traffic corridor. The excavation of tunnel was performed by using the multi-phase New Austrian Tunnel Method. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. "Reprinted with permission from Elsevier".

This paper deals with the analysis of nonlinear elastic systems discretized by boundary elements in the presence of piecewise-linear material models. The problem is solved in the context of the ‘holonomic’ theory (or ‘deformation’ theory) of plasticity, plane-stress conditions only are dealt with and the implications of linearizing the relevant yield surface is briefly discussed. Piecewise-linear yield surfaces coupled with linear hardening lead to a linear complementarity problem, for which a step-by-step solution procedure is proposed. The paper gives details about the algorithm implemented and discusses its application with reference to the boundary element method. To illustrate the problem with reference to simple but still real systems, masonry walls are considered and a no-tension material model is assumed. Numerical results are presented and compared with those provided by programs that follow different approaches, but use the same assumptions (a no-tension material model with nonlinear, reversible behaviour): namely, a boundary element code based on a conventional ‘initial stress’ procedure and a finite element package.

This paper describes a method for the numerical solution of a Riabouchinsky cavity flow. Application of a boundary element method leads to a system of non‐linear equations. The mild singularity appearing at the separation point is treated with the introduction of a curved boundary element, which satisfies the exact behaviour of the free boundary in that neighbourhood. Copyright © 1988 John Wiley & Sons, Ltd 8 1 91 96 Cited By :8

In this paper an analytical integration scheme is described that is designed to reduce the errors resulting from the numerical evaluation of integrals with singular integrands. The analytical scheme can be applied to linear triangular elements for use in elastostatic problems and is particularly useful for predicting distortion, to high accuracy, close to surfaces. It is demonstrated that although the analytical scheme takes longer computationally than the usual quadrature approach it is quicker when element subdivision is required to achieve reasonable accuracy. Numerical tests are performed on a simple test problem to demonstrate the advantages of the analytical approach, which is shown to be orders of magnitude more accurate than standard quadrature techniques.

The Energy Boundary Element Method (EBEM) aims at the solution of acoustic high frequency problems, where the classic BEM becomes inefficient due to the large number of degrees of freedom (DOF) required. A transition to non-phased energetic state variables removes the correlation between the investigated frequency range and the element size. In the EBEM the number of DOF is thus determined primarily by the complexity of the geometry. In order to speed up the computation and to handle structures of very high geometric complexity, a fast multipole algorithm for the EBEM is investigated. It has a great potential to reduce the numerical effort in the Boundary Element Method (BEM). Helmholtz and Laplace problems have been solved very efficiently applying this algorithm. However, the kernels used in the EBEM require an adaptation of the algorithm. In this paper the development of a fast multipole formulation of the EBEM is presented.

The objetive of this work is to present the implementation of topologicalshape sensitivity formulation in a BEM analysis for simultaneous heat and mass transfer optimization problems. The proposed approach uses a topological derivative in order to estimate the sensitivity to create a hole in the domain of the problem. Thus, it is evaluated at internal points, and the ones showine the lowest values are used to remove material by opening a circular cavity. As the iterative process evolves, the original domain has holes progressively punched out until a given stop criteria is achieved. Since the sensitivities for each of the differential equations are different, a penalization-type approach has been used to weight the sensitives associated to each problem, This allows the imposition of district penalization factor for each problem, according to especified priorities. The result obtained showed good agreement with solutions avaliable in the literature. El objetivo de este trabajo es presentar la aplicación de una formulación para el análisis de sensibilidad de forma y topologia utilizando elemetos de contorno en problemas de optimización involucrando transferencia simultanea de calor y masa. El enfoque propuesto usa la derivada topológica para estimar la sensibilidad a criar un agujero en el dominio de definición del problema. De este modo, la misma se evalua en puntos internos y aquellos que presentan los valores más bajos se utilizan para eliminar material mediante la apertura de una cavidad circular. A medida que el proceso iterativo evoluciona, el dominio se modifica progresivamente con la incorporación de más agujeros hasta que se alcanza un criterio de parada determinado. Puesto que las sensibilidades de cada una de las ecuaciones diferenciales son diferentes, un enfoque tipo penalización ha sido utilizado para ponderar las sensibilidades asociadas a cada problema. Esto permite la imposición de factores de penalización distintos para cada problema, de acurdo a prioridades específicas. Los resultados obtenidos mostraron una buena concordancia con soluciones disponibles em la literatura.

Open trenches are an effective means of vibration mitigation, but they cannot be established in practice. When the trenches are covered by a concrete pavement, part of the efficiency may be lost. However, the present analysis indicates that barriers of this kind may still lead to a significant reduction of the horizontal and vertical vibrations caused by traffic at a nearby road or railway. Open trenches are an effective means of vibration mitigation, but they cannot be established in practice. When the trenches are covered by a concrete pavement, part of the efficiency may be lost. However, the present analysis indicates that barriers of this kind may still lead to a significant reduction of the horizontal and vertical vibrations caused by traffic at a nearby road or railway.