• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.78-84
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• 2001

In this paper, Power Flow Boundary Element Method(PFBEM) has been developed for one and two dimensional noise and vibration problems in the medium to high frequency ranges. Green functions used for PFBEM are the fundamental solutions of energy governing equations. Both direct and indirect methods of PFBEM have been formulated and numerically applied to predict the vibrational energy density and intensity distributions of simple beams, rectangular plates and L-type plates.

• Structural Engineering and Mechanics
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• 제20권2호
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• pp.225-239
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• 2005

Applications of the Trefftz boundary element method (BEM) to anti-plane electroelastic problems are presented in this paper. Both direct and indirect methods with domain decomposition are discussed in details. Each crack is treated as semi-infinite thin slit defined in a subregion, for which a particular solution of the anti-plane problem, satisfying exactly the crack-face condition, is derived. The stress intensity factors defined at each crack tip can be directly computed from the coefficients of the particular solution. The performance of the proposed formulation is assessed by two examples and comparison is made with results obtained by other approaches. The Trefftz boundary element approach is demonstrated to be suitable for the analysis of the anti-plane problem of piezoelectric materials.

• Structural Engineering and Mechanics
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• 제64권1호
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• pp.93-107
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• 2017

The article presents the vibration and acoustic responses of un-baffled doubly curved laminated composite panel structure under the excitation of a harmonic point load. The structural responses are obtained using a simulation model via ANSYS including the effect various geometries (cylindrical, elliptical, spherical and hyperboloid). Initially, the model has been established by solving adequate number of available examples to show the convergence and comparison behaviour of the natural frequencies. Further, the acoustic responses are obtained using an indirect boundary element approach for the coupled fluid-structure analysis in LMS Virtual.lab by importing the natural frequency values. Subsequently, the values for the sound power level are computed using the present numerical model and compared with that of the available published results and in-house experimentally obtained data. Further, the acoustic responses (mean-square velocity, radiation efficiency and sound power level) of the doubly curved layered structures are evaluated using the current simulation model via several numerical experimentations for different structural parameters and corresponding discussions are provided in detail.

• Geomechanics and Engineering
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• 제11권2호
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• pp.269-288
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• 2016

The jointed rock mass behavior often plays a major role in the design of underground excavation, and their failures during excavation and in operation, are usually closely related to joints. This research attempts to evaluate the effects of two basic geometric factors influencing tunnel behavior in a jointed rock mass; joints spacing and joints orientation. A hybridized indirect boundary element code known as TFSDDM (Two-dimensional Fictitious Stress Displacement Discontinuity Method) is used to study the stress distribution around the tunnels excavated in jointed rock masses. This numerical analysis revealed that both the dip angle and spacing of joints have important influences on stress distribution on tunnel walls. For example the tensile and compressive tangential stresses at the boundary of the circular tunnel increase by reduction in the joint spacing, and by increase the dip joint angle the tensile stress in the tunnel roof decreases.

• 한국소음진동공학회논문집
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• 제21권11호
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• pp.1029-1035
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• 2011

Pressure pulsation of exciting sources that generally occurs on the piping system connected to the discharge of BFP(boiler feed water pump) in power plants causes wave reflection, wave interference, resonance, standing wave and so on. But if the operating speed of the pump is changed, the state of the noise and vibration can be done because characteristics of the exciting source are changed. This paper is to investigate the cause of the noise and vibration occurring on the piping system when the operating speed of BFP is down in accordance with lowering of the power generation. It is approached to two points of view ; Firstly, it is examined whether the pulsation source impacts on the shell mode vibration that vibrates radially across the cross-section of the pipe. But it doesn't affect the shell mode as much as the resonance occurs. Secondly, to find the relation between the pulsation source and the acoustic mode of the piping system, analysis for the piping system by indirect BEM(boundary element method) is carried out. Therefore it is investigated that the mechanism of the noise and vibration relates with acoustic mode of the piping system.

• 소음진동
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• 제9권4호
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• pp.687-692
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• 1999

Digital holographic reconstruction method [W. A. Veronesi, et al, 1989, JASA, Vol. 85, pp. 588∼598] reconstructs a whole sound field by using measured sound pressure. This paper reports numerical errors of the method that occur at specific frequencies. The errors occur due to the truncation errors included in the calculation of transfer matrixes. The frequencies of the errors depend on the size of boundary element surfaces. Moreover, a modified calculation technique is proposed in the paper. The technique prevents the truncation errors by employing an indirect calculation procedure.

• International Journal of Aeronautical and Space Sciences
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• 제3권2호
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• pp.82-87
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• 2002

Aerodynamic analysis of NACA wings moving with a constant speed over guideways are performed using an indirect boundary element method (potential-based panel method). An integral equation is obtained by applying Green's theorem on all surfaces of the fluid domain. The surfaces over the wing and the guideways are discretized as rectangular panel elements. Constant strength singularities are distributed over the panel elements. The viscous shear layer behind the wing is represented by constant strength dipoles. The unknown strengths of potentials are determined by inverting the aerodynamic influence coefficient matrices constructed by using the no penetration conditions on the surfaces and the Kutta condition at the trailing edge of the wing. The aerodynamic characteristics for the wings flying over nonplanar ground surfaces are investigated for several ground heights.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1998년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring 1998
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• pp.98-105
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• 1998

In this study, the boundary element analysis in dynamics for the multilayered semi-infinite plane is developed using the fundamental solution for moving loads. Also the indirect method and superposition method are introduced to consider the multilayered systems and moving loads. At each layer the fundamental solution can be obtained by solving the governing equation which is transformed by the Fourier transform. The governing equation can be solved by three conditions; continuity conditions of displacement and stress, the traction free condition at the surface and the radiation condition at the surface and the radiation condition at the infinite distance. To verify the solution and the developed algorithm, the theoretical solution for the homogeneous layer and commercial FEM program is compared with the results of this study.

• Computers and Concrete
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• 제16권6호
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• pp.881-896
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• 2015

A simultaneous analytical, experimental and numerical analysis of crack initiation, propagation and breaking process of the Central Straight through Crack Brazilian Disk (CSCBD) specimens under diametrical compression is carried out. Brazilian disc tests are being accomplished to evaluate the fracturing process based on stress intensity factors (SIFs). The effects of crack inclination angle and crack length on the fracturing processes have been investigated. The same experimental specimens have been numerically modeled by a higher order indirect boundary element method (HDDM). These numerical results are compared with the existing experimental results proving the accuracy and validity of the proposed numerical method.

• 한국통신학회논문지
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• 제15권1호
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• pp.1-8
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• 1990

본 논문에서는 유전체 원통주의 전자파 과도 응답 산란 특성을 새로운 수치 해석 방법으로 연구하낟. 수치 해석에 사용하는 경계적분 방정식(BIE)의 기본 수식은 가중 잔차법으로 부터 시작된다. 경계 적분 방정식을 확장 경계 조건과 표면 경계 조건을 물체의 표면점 내부와 외부에 적용시켜 두개의 연립방정식을 만든다. 수치해석으로 경계요소법을 사용하고, 이 방법에는 직접법과 간접법 두 가지가 있다. 그래서 연산자를 메트릭스 역변환하는 간접법을 수치해석방법으로 사용한다. 결과값은 다른 연구 결과값과 좋은 일치를 보인다.