• International Journal of CAD/CAM
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• 제11권1호
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• pp.11-17
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• 2011

A new method has been developed in this paper for automatic quadrilateral mesh generation for a two-dimensional domain. The method is named 'centering method' because it centers a point at the domain and then divides it into sub-domains using cutting lines from the center point. Each of the cutting lines is selected based on the criterion using the angles between the boundary of the domain and the cutting line. The decomposition of the domain into sub-domains is repeated until every subdomain has four or six nodes. Pre-defined splitters are used to divide six-node domains into quadrilateral elements depending on their configuration and presence on the boundary of the initial domain. Arbitrary domains are meshed as examples to verify the robustness of the new method.

• 한국전산유체공학회지
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• 제20권4호
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• pp.44-50
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• 2015

The computational efficiency of flow simulations with Multi-resolution analysis (MRA) was enhanced via the boundary treatment of the computational domain. In MRA, an adaptive dataset to a solution is constructed through data decomposition with interpolating polynomial and thresholding. During the decomposition process, the basis points of interpolation should exceed the boundary of the computational domain. In order to resolve this problem, the weight coefficients of interpolating polynomial were adjusted near the boundaries. By this boundary treatment, the computational efficiency of MRA was enhanced while the numerical accuracy of a solution was unchanged. This modified MRA was applied to two-dimensional steady Euler equations and the enhancement of computational efficiency and the maintenance of numerical accuracy were assessed.

• 대한기계학회논문집A
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• 제32권10호
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• pp.836-843
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• 2008

An efficient domain/boundary decomposition method is applied for heat transfer problems with non-linear thermal radiation boundaries. The whole domain of solids or structures is considered as set of subdomains, an interface, and radiation interfaces. In a variational formulation, simple penalty functions are introduced to connect an interface or radiation interfaces with neighboring subdomains that satisfy continuity conditions. As a result, non-linear finite element computations due to the thermal radiation boundaries can be localized within a few subdomains or radiation interfaces. Therefore, by setting up suitable solution algorithms for the governing finite element equations, the computational efficiency can be improved considerably. Through a set of numerical examples, these distinguishing characteristics of the present method are investigated in detail.

• 한국CDE학회논문집
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• 제8권4호
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• pp.270-277
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• 2003

In two dimensional mechanical design analysis, quadrilateral element mesh is preferred because it provides more accurate result than triangular element mesh. However, automation of quadrilateral element mesh generation is much more complex because of its geometrical complexities. In this study, an automatic quadrilateral element mesh generation algorithm based on the boundary normal offsetting method and the boundary decomposition method is developed. In so doing, nodes are automatically placed using the boundary normal offsetting method and the decomposition method is applied to decompose the designed domain into a set of convex subdomains. The generated elements are improved by relocation of the existing nodes based on the four criteria - uniformity, aspect ratio, skewness and taper degree. The developed algorithm requires minimal user inputs such as boundary data and the distance between nodes.

• Structural Engineering and Mechanics
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• 제32권1호
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• pp.37-53
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• 2009

In this paper the problem of calculating the probability that the responses of a wind-excited structure exceed specified thresholds within a given time interval is considered. The failure domain of the problem can be expressed as a union of elementary failure domains whose boundaries are of quadratic form. The Domain Decomposition Method (DDM) is employed, after being appropriately extended, to solve this problem. The probability estimate of the overall failure domain is given by the sum of the probabilities of the elementary failure domains multiplied by a reduction factor accounting for the overlapping degree of the different elementary failure domains. The DDM is extended with the help of Line Sampling (LS), from its original presentation where the boundary of the elementary failure domains are of linear form, to the current case involving quadratic elementary failure domains. An example involving an along-wind excited steel building shows the accuracy and efficiency of the proposed methodology as compared with that obtained using standard Monte Carlo simulations (MCS).

• Wind and Structures
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• 제5권2_3_4호
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• pp.379-392
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• 2002

Numerical flow computations around an aeroelastic 3D square cylinder immersed in the turbulent boundary layer are shown. Present computational code can be characterized by three numerical aspects which are 1) the method of artificial compressibility is adopted for the incompressible flow computations, 2) the domain decomposition technique is used to get better grid point distributions, and 3) to achieve the conservation law both in time and space when the flow is computed a with moving and transformed grid, the time derivatives of metrics are evaluated using the time-and-space volume. To provide time-dependant inflow boundary conditions satisfying prescribed time-averaged velocity profiles, a convenient way for generating inflow turbulence is proposed. The square cylinder is modeled as a 4-lumped-mass system and it vibrates with two-degree of freedom of heaving motion. Those blocks which surround the cylinder are deformed according to the cylinder's motion. Vigorous oscillations occur as the vortex shedding frequency approaches cylinder's natural frequencies.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
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• pp.575-582
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• 2002

A new coupling method of Element-Free Galerkin Method(EFGM) and Boundary Element Method(BEM) using the domain decomposition method is presented in this paper. This proposed methodology is that the problem domain is decomposed into sub-domains being modeled by the EFGM and BEM respectively and the respective EFGM and BEM domains share a partially overlapped region over an entire domain. Then, the each sub-domain is separately computed and the variables on common region are iteratively updated until converging. It is an important note that in the developed coupling method, there is no need to combine the coefficient matrices of EFGM and BEM sub-domains, in contrast with the other conventional coupling methods. In the first part of this paper, a theory of EFGM and BEM is summarized, and then a brief introduction of domain decomposition method is described. Then, a new coupling method is presented. Also, patch test and Some numerical examples are studied to verify stability, accuracy and efficiency of the proposed method, in which numerical performance of the method is compared with that of conventional method such as EFGM-BEM variational coupling method, EFGM and BEM.

• 음성과학
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• 제8권4호
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• pp.45-58
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• 2001

Modulated components of a speech signal are frequently used for speech coding, speech recognition, and speech synthesis. Time-frequency representation (TFR) reveals some information about instantaneous frequency, instantaneous bandwidth and boundary of each component of the considering speech signal. In many cases, the extraction of AM-FM components corresponding to instantaneous frequencies is difficult since the Fourier spectra of the components with time-varying instantaneous frequency are overlapped each other in Fourier frequency domain. In this paper, an efficient method decomposing speech signal into AM-FM components is proposed. A variable bandwidth filter is developed for the decomposition of speech signals with time-varying instantaneous frequencies. The variable bandwidth filter can extract AM-FM components of a speech signal whose TFRs are not overlapped in timefrequency domain. Also, amplitude and instantaneous frequency of the decomposed components are estimated by using Hilbert transform.

• 대한수학회논문집
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• 제16권3호
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• pp.487-508
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• 2001

We consider the Cauchy problem for Laplacian. Using the single layer representation, we obtain an equivalent system of boundary integral equations. We show the singular values of the ill-posed Cauchy operator decay exponentially, which means that a small error is exponentially amplified in the solution of the Cauchy problem. We show the decaying rate is dependent on the geometry of he domain, which provides the information on the choice of numerically meaningful modes. We suggest a pseudo-inverse regularization method based on singular value decomposition and present various numerical simulations.

• Coupled systems mechanics
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• 제1권1호
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• pp.19-37
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• 2012

In this work, the iterative coupling of finite element and boundary element methods for the investigation of coupled fluid-fluid, solid-solid and fluid-solid wave propagation models is reviewed. In order to perform the coupling of the two numerical methods, a successive renewal of the variables on the common interface between the two sub-domains is performed through an iterative procedure until convergence is achieved. In the case of local nonlinearities within the finite element sub-domain, it is straightforward to perform the iterative coupling together with the iterations needed to solve the nonlinear system. In particular, a more efficient and stable performance of the coupling procedure is achieved by a special formulation that allows to use different time steps in each sub-domain. Optimized relaxation parameters are also considered in the analyses, in order to speed up and/or to ensure the convergence of the iterative process.