• 소음진동
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• 제7권6호
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• pp.975-984
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• 1997

A direct boundary element method (DBEM) is developed for thin bodies whose surfaces are rigid or compliant. The Helmholtz integral equation and its normal derivative integral equation are adoped simultaneously to calculate the pressure on both sides of the thin body, instead of the jump values across it, to account for the different surface conditions of each side. Unlike the usual assumption, the normal velocity is assumed to be discontinuous across the thin body. In this approach, only the neutral surface of the thin body has to be discretized. The method is validated by comparison with analytic and/or numerical results for acoustic scattering and radiation from several surface conditions of the thin body; the surfaces are rigid when stationary or vibrating, and part of the interior surface is lined with a sound-absoring material.

• 대한조선학회지
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• 제24권4호
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• pp.19-36
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• 1987

In this research the coupling problem between the elastic structure and the fluid, specially the hydroelastic harmonic vibration problem, is studied. In order to couple the domains, i.e., the structural domain and the fluid domain, the boundary integral method(direct boundary integral formulation) is used in the fluid domain in combination with the finite element method for the structure. The boundary integral method has been widely developed to apply it to the hydroelastic vibration problem. The hybrid boundary integral method using eigenfunctions on the radiation boundaries and the boundary integral method using the series form image-functions to replace the even bottom and free surface boundaries in case of high frequencies have been developed and tested. According to the boundary conditions and the frequency ranges the different boundary integral methods with the different idealizations of the fluid boundaries have been studied. Using the same interpolation functions for the pressure distribution and the displacement the two domains have been coupled and using Hamilton principle the solution of the hydroelastic have been obtained through the direct minimizing process. It has become evident that the finite-boundary element method combining with the eigenfunction or the image-function method give good results in comparison with the experimental ones and the other numerical results by the finite element method.

• 소음진동
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• 제8권2호
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• pp.274-282
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• 1998

A systematic procedure for designing a direct-radiator-type loudspeaker has been developed, based on the numerical vibro-acoustic analysis and the Taguchi method. The finite-element model of the speaker cone has been used to calculated the vibration response of the cone excited by the voice coil. The vibration displacement of the speaker cone has been converted into the vibration velocity and used as a boundary condition for the acoustic analysis. The acoustic frequency characteristics of the loudspeaker have been calculated by the boundary element method. The numerical results have been verified by the experiments carried out in an anechoic chamber. Some design parameters have been selected by using the Taguchi method, and the variations of the acoustic characteristics due to the changes of the parameter values have been examined using the numerical model.

• 한국산학기술학회논문지
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• 제11권7호
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• pp.2328-2333
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• 2010

직접경계요소법은 음향방사문제 해석에 널리 적용되는 수치해석기법중 하나이지만, 외부 음향방사 문제에 있어서는 방사면 내부공간의 고유주파수 근방에서 비유일성이 나타나게 된다. 이를 해결하기 위한 방법으로 CHIEF 방법이 일반적으로 적용되어 왔으며, 최근 들어서는 ICA-Ring 방법과 같은 새로운 기법이 제안되어 해의 정확도 향상에 기여하고 있다. 본 논문에서는 앞서 언급한 두 가지 비유일성 회피기법들의 특성을 살피고, 각각의 기법 구현을 포함한 직접경계요소법 기반의 수치해석 코드를 작성한다. 또한, 법선방향 균일속도로 진동하는 구의 음향방사문제에 대한 수치해석을 수행하고 그 결과를 해석 해와 비교하여 각각의 기법들에 대한 비유일성 회피 성능을 고찰한다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권2호
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• pp.282-296
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• 2014

In this paper, an iterative boundary element method (IBEM) was proposed to solve for a wing-in-ground (WIG) effect. IBEM is a fast and accurate method used in many different fields of engineering and in this work; it is applied to a fluid flow problem assessing a wing in ground proximity. The theory and the developed code are validated first with other methods and the obtained results with the proposed method are found to be encouraging. Then, time consumptions of the direct and iterative methods were contrasted to evaluate the efficiency of IBEM. It is found out that IBEM dominates direct BEM in terms of time consumption in all trials. The iterative method seems very useful for quick assessment of a wing in ground proximity condition. After all, a NACA6409 wing section in ground vicinity is solved with IBEM to evaluate the WIG effect.

• 한국전산구조공학회논문집
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• 제25권5호
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• pp.413-420
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• 2012

본 논문은 2차원 선형탄성 직접 경계요소법에서 저매개변수 요소를 사용할 때 Kernel의 적분방법에 대하여 논의하였다. 일반적으로 등매개변수 요소의 경우 형상함수로 통칭되는 해의 기저함수와 요소의 적분을 위해 사용되는 사상함수를 동일하게 사용한다. 그러나 본 논문에서는 사상함수의 차수를 낮게 취하여 순수기저절점을 도입하고 그때 직접 경계요소의 Kernel을 적분하기 위한 방법이 모색되었다. 일반적으로 경계요소법의 적분 Kernel의 경우 Log수치적분과 코쉬주치(Cauchy principal value) 등을 통해 해결하는데, 본 논문에서는 대수적 조작을 통해 적분값의 정확도를 높일 수 있도록 새로운 수식을 유도하였다. 본 연구에서 저매개변수 기반의 직접 경계요소에 대한 강건성과 정확도를 검증하기 위해 2차원 타원형 편미분방정식으로 표현되는 평면응력과 평면변형문제에 대해 적용하였다. 적용 예제로는 단순연결영역(simple connected region)의 대표적 문제인 캔틸레버보와 다중연결영역(multiple connected region)의 대표적인 문제인 개구부가 있는 사각평면에 대해 각각 수치해석을 수행한 결과 대폭적인 자유도의 감소에 비해 정확도 측면에는 기존의 방법과 차이가 없음을 볼 수 있었다. 본 논문에서 제시된 방법은 기저함수 고차화 저매개변수 직접 경계요소법(subparametric high order boundary element)과 이에 기초를 둔 저매개변수 고차 이중경계요소법(subparametric high order dual boundary element)의 초석이 될 수 있을 것이다.

• International Journal of Safety
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• 제2권1호
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• pp.39-44
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• 2003

The present study deals with an approximate integral equation approach to finite deflection of elastic plates with arbitrary plane form. An integral formulation leads to a system of boundary integral equations involving values of deflection, slope, bending moment and transverse shear force along the edge. The basic principles of the development of boundary element technique are reviewed. A computer program for solving for stresses and deflections in a isotropic, homogeneous, linear and elastic bending plate is developed. The fundamental solution of deflection and moment is employed in this program. The deflections and moments are assumed constant within the quadrilateral element. Numerical solutions for sample problems, obtained by the direct boundary element method, are presented and results are compared with known solutions.

• Structural Engineering and Mechanics
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• 제17권6호
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• pp.735-749
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• 2004

This work presents a direct integration scheme, based on a fourth order finite difference approach, for elastodynamics. The proposed scheme was chosen as an alternative for attenuating the errors due to the use of the central difference method, mainly when the time-step length approaches the critical time-step. In addition to eliminating the spurious numerical oscillations, the fourth order finite difference scheme keeps the advantages of the central difference method: reduced computer storage and no requirement of factorisation of the effective stiffness matrix in the step-by-step solution. A study concerning the stability of the fourth order finite difference scheme is presented. The Finite Element Method and the Boundary Element Method are employed to solve elastodynamic problems. In order to verify the accuracy of the proposed scheme, two examples are presented and discussed at the end of this work.

• 터널과지하공간
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• 제4권1호
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• pp.17-23
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• 1994

This study consists of two procedures on back analysis and forward analysis which is a basic tool of the former. For a safe and economical construction of underground structures, it is required to identify the structural parameters and analyze the structural behavior as exactly as possible. In this paper, a boundary element method to analyze the behavior of multi-alyered underground structures is studied, in which body forces and initial stresses are considered. That is, each layer is discritized into subregions using infinite fundamental solutions, and terms of body forces and initial stresses are transformed into boundary integral where the applied direct integral method is used. And the system of equations containing body forces and initial stresses are considered. That is, each layer is discritized into subregions using infinite fundamental solutions, and terms of body forces and initial stresses are transformed into boundary integral where the applied direct integral method is used. And the system of equations containing body forces and initial stresses are composed, then the method to solve unknowns is used with applying compatibility and equilibrium conditions between interfaces. As well, the direct search method is applied in back analysis problems. By Powell's method as a technique to search unknown parameters, assuming displacements calculated from boundary element analysis as in-situ displacements, elastic moduli and initial stresses are presumed. As consequences of this study, the results of boundary element analysis of the behavior of multilayered structure considering body forces and initial stresses are agreed with those of finite element analysis. And results of back analysis of elastic moduli and initial stresses in each layers are agreed with exact values with a little difference. Therefore, it is known that this study can be efficiently applied for analyzing the behavior of underground structures including back analysis problems.

• 소음진동
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• 제10권2호
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• pp.319-324
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• 2000

This paper shows hot to model the submerged elastic structures and adequate analysis tools for modal behavior when using finite element and boundary element method. Four different cases are reviewed depending on the location of the water and air. First case is that structures are filled with air and water is located outside. Second case is opposite to case one. These cases are solved by direct approach using collocation procedure. Third case is that water is located both sides of structures. Last case is that air is located both sides. These cases are solved by indirect approach using variational procedure. As analysis tools harmonic frequency sweep analysis and eigenvalue iteration method are selected to obtain the natural frequencies of vibrating submerged structures depending on the cases. Results are compared with closed form solutions of submerged spherical shell.