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Analysis of Multiple Inclusion Potential Problems by the Adaptive Cross Approximation Method
Get PDFOver recent years the rapid evolution of the computational power has motivated the development of new numerical techniques to account for engineering solutions. The Boundary Element Method (BEM) has shown to be a powerful numeric tool for the analysis and solution of many physical and engineering problems. However, BEM fully populated and non-symmetric system matrices implies in higher memory requirements and solution times. This work analyze the application of hierarchical matrices and low rank approximations, applying the Adaptive Cross Approximation - ACA, to multiple inclusion potential problems. The use of hierarchical format is aimed at reducing the storage requirement and the computational complexity arising in the BEM. First, the use of hierarchical matrices and low rank approximation on multidomain potential problems is depicted. Finally, a numerical example is performed to show the applicability of using ACA in largescale multidomain problems. Moreover, the application of ACA to multidomain problems showed to be an important option in future multiscale problem analyses
Application of Different Variants of the BEM in Numerical Modeling of Bioheat Transfer Problems
Get PDFHeat transfer processes proceeding in the living organisms are described by the different mathematical models. In particular, the typical continuous model of bioheat transfer bases on the most popular Pennes equation, but the Cattaneo-Vernotte equation and the dual phase lag equation are also used. It should be pointed out that in parallel are also examined the vascular models, and then for the large blood vessels and tissue domain the energy equations are formulated separately.
In the paper the different variants of the boundary element method as a tool of numerical solution of bioheat transfer problems are discussed. For the steady state problems and the vascular models the classical BEM algorithm and also the multiple reciprocity BEM are presented. For the transient problems connected with the heating of tissue, the various tissue models are considered for which the 1st scheme of the BEM, the BEM using discretization in time and the general BEM are applied.
Examples of computations illustrate the possibilities of practical applications of boundary element method in the scope of bioheat transfer problems
Magnetorheological fluids particles simulation through integration of Monte Carlo method and GPU accelerated technology
No full textIn order to study the rheological characteristics of magnetorheological fluids, a simulation approach through integration of Monte Carlo method and GPU accelerated technology was proposed and the three-dimensional micro-structure of magnetic particles in different strength magnetic fields were simulated. The Monte Carlo method to magnetic particles of magnetorheological fluids and its key steps such as particle modeling, magnetic energy equations calculating and system state updating were elaborated. Moreover, GPU accelerated technology was applied to the simulation of magnetorheological fluids to reduce computational time and a flowchart for the proposed approach was designed. Finally, a physics experiment was carried out and the three-dimensional simulation examples were provided. The comparison results indicated that proposed approach was feasible, efficient and outperforming others
Effect of Interface Energy on Size-Dependent Effective Dynamic Properties of Nanocomposites with Coated Nano-Fibers
Get PDFIn nanocomposites, coated nano-fibers are often used to obtain good performance, and the high interface-to-volume ratio shows great effect on the macroscopic effective properties of nanocomposites. In this study, the effect of interface energy around the unidirectional coated nanofibers on the effective dynamic effective properties is explicitly addressed by effective medium method and wave function expansion method. The multiple scattering resulting from the series coating nano-fibers is reduced to the problem of one typical nano-fiber in the effective medium. The dynamic effective shear modulus is obtained on the basis of the derived imperfect interface conditions. Analyses show that the effect of the interface properties on the dynamic effective shear modulus is significantly related to the coating layer, the nano-fiber, and the wave frequency. Due to the existence of softer coating layers, the effect of the interfaces around the layers increases greatly. Comparison with the existing results is also illustrated in the numerical examples
EM Analysis of Metamaterial Based Radar Absorbing Structure (RAS) for MillimeterWave Applications
Get PDFThe EM performance analysis of a multilayered metamaterial based radar absorbing structure (RAS) has been presented in this paper based on transmission line transfer matrix (TLTM) method for millimeter wave applications. The proposed metamaterial-RAS consists of cascaded DPS and MNG layers of identical configurations. It exhibits extremely low reflection (< 42 dB) at 95 GHz and absorbs more than 95% power of incident wave over the frequency range of 90.4- 100 GHz without metal backing for both TE and TM polarizations. In view of aerospace applications, the reflection, transmission, and absorption characteristics of the proposed metamaterial-RAS are also studied at different incident angles (0°, 30°, and 45°) for both polarizations
Broadbanding of A-sandwich Radome Using Jerusalem Cross Frequency Selective Surface
Get PDFEnhancement of electromagnetic performance of A-sandwich radome using aperture-type Jerusalem cross frequency selective surface (FSS) is presented. The Jerusalem cross FSS array is embedded in the mid-plane of the core of Asandwich radome to enhance the EM performance parameters over the entire Xband. For modeling the Jerusalem cross FSS embedded radome panel and evaluation of its EM performance parameters, equivalent transmission line method in conjunction with equivalent circuit model is used. A comparative study of Jerusalem cross FSS embedded A-sandwich radome and A-sandwich radome of identical material and thickness (core and skin layers) indicate that the new wall configuration has superior EM performance as compared to the A-sandwich wall alone configuration. The excellent EM performance of Jerusalem cross FSS embedded A-sandwich radome makes it a desirable choice for the design of normal incidence radomes (hemispherical/ cylindrical), near-normal incidence radomes (paraboloidal) and highly streamlined airborne nosecone radomes
Effects of Non-Newtonian Ferrofluids on the Performance Characteristics of Long Journal Bearings
Get PDFOn the basis of the Shliomis ferrofluid model (1972) together with the micro-continuum theory of Stokes (1966), the influences of non-Newtonian ferrofluids on the steady-state performance of long journal bearings have been investigated in the present paper. Analytical solutions for bearing performances are obtained from the non-Newtonian ferrofluid Reynolds-type equation. Comparing with the Newtonian non-ferrofluid case, the effects of non-Newtonian ferrofluids with applied magnetic fields provide an increase in the zero pressure-gradient angle and the load capacity, and a decrease in the friction parameter, especially for a larger non-Newtonian couple stress parameter and magnetic Langevin’s parameter. For the long journal bearing lubricated with non-Newtonian ferrofluids and operating at larger couple stress parameter and magnetic Langevin’s parameter (for example, N=0.3, ξ =50), slight variation is observed for the friction parameter, but higher bearing loads are obtained with increasing values of the volume concentration parameter
Topology optimization of finite similar periodic continuum structures based on a density exponent interpolation model
No full textSimilar periodic structures have been widely used in engineering. In order to obtaining the optimal similar periodic structures, a topology optimization method of similar periodic structures with multiple displacement constraints is proposed in this paper. Firstly, in the proposed method, the design domain is divided into sub-domains. Secondly, a penalty term considering discrete conditions of density variables is introduced into the objective function, and the reciprocal density exponents of structural elements are taken as design variables. A topological optimization model of a similar periodic continuum structure with the objective function being the structural mass and the constraint functions being structural displacements is constructed in the proposed method. The optimization dual method is introduced and a set of iteration formula for Lagrange multipliers is built. Then, virtual sub-domain design variables are introduced to establish the relation of corresponding variables between all the sub-domains of the similar periodic continuum structure in order to enforce structurally similar periodic requirement. Three examples are provided to demonstrate that the proposed method is feasible and effective for obtaining optimal similar periodic structures
A finite-volume method based on compact local integrated radial basis function approximations for second-order differential problems
No full textIn this paper, compact local integrated radial basis function (IRBF) stencils reported in [Mai-Duy and Tran-Cong (2011) Journal of Computational Physics 230(12), 4772-4794] are introduced into the finite-volume / subregion - collocation formulation for the discretisation of second-order differential problems defined on rectangular and non-rectangular domains. The problem domain is simply represented by a Cartesian grid, over which overlapping compact local IRBF stencils are utilised to approximate the field variable and its derivatives. The governing differential equation is integrated over non-overlapping control volumes associated with grid nodes, and the divergence theorem is then applied to convert volume integrals into surface/line integrals. Line integrals are evaluated by means of the middle point rule (i.e. second-order integration scheme) and three-point Gaussian quadrature rule (i.e. high-order integration scheme). The accuracy of the proposed method is numerically investigated through the solution of several test problems including natural convection in an annulus. Numerical results indicate that (i) the proposed method produces accurate results using relatively coarse grids and (ii) the three-point integration scheme is generally more accurate than the middle point scheme
Compact Local IRBF and Domain Decomposition Method for solving PDEs using a Distributed termination detection based parallel algorithm
No full textCompact Local Integrated Radial Basis Function (CLIRBF) methods based on Cartesian grids can be effective numerical methods for solving partial differential equations (PDEs) for fluid flow problems. The combination of the domain decomposition method and function approximation using CLIRBF methods yields an effective coarse-grained parallel processing approach. This approach has enabled not only each sub-domain in the original analysis domain to be discretised by a separate CLIRBF network but also compact local stencils to be independently treated. The present algorithm, namely parallel CLIRBF, achieves higher throughput in solving large scale problems by, firstly, parallel processing of sub-regions which constitute the original domain and, secondly, accelerating the convergence rate within each sub-region using groups of CLIRBF stencils in which function approximations are carried out by parallel processes. The procedure is illustrated with several numerical examples of PDEs and lid-driven cavity problem using Message Passing Interface supported by MATLAB