Wave Force Analysis of the Three Vertical Cylinders in Water Waves

김남형,Tan Ngoc Than Cao 한국항해항만학회 2008 한국항해항만학회지 Vol.32 No.7

The diffraction of waves by three bottom‐fixed vertical circular cylinders is investigated by using the boundary element method. This method has been successfully applied to the isolated vertical circular cylinder and now is used to study the interaction between waves and multiple vertical cylinders. In this paper, a numerical analysis by the boundary element method is developed by the linear potential theory. The numerical analysis by the boundary element method is based on Green’s second theorem and introduced to an integral equation for the fluid velocity potential around the vertical circular cylinders. To verify this method, the results obtained in present study are compared with the results computed by the multiple scattering method. The results of the comparisons show strong agreement. Also in this paper, several numerical examples are given to illustrate the effects of various parameters on the wave‐exciting force such as the separation distance, the wave number and the incident wave angle. This numerical computation method might be used broadly for the design of various offshore structures to be constructed in the future. The diffraction of waves by three bottom‐fixed vertical circular cylinders is investigated by using the boundary element method. This method has been successfully applied to the isolated vertical circular cylinder and now is used to study the interaction between waves and multiple vertical cylinders. In this paper, a numerical analysis by the boundary element method is developed by the linear potential theory. The numerical analysis by the boundary element method is based on Green’s second theorem and introduced to an integral equation for the fluid velocity potential around the vertical circular cylinders. To verify this method, the results obtained in present study are compared with the results computed by the multiple scattering method. The results of the comparisons show strong agreement. Also in this paper, several numerical examples are given to illustrate the effects of various parameters on the wave‐exciting force such as the separation distance, the wave number and the incident wave angle. This numerical computation method might be used broadly for the design of various offshore structures to be constructed in the future.

이차원 탄성 정적 문제를 위한 유한요소법과 경계요소법의 근사 결합 방법

송명관(Myung-Kwan Song) 한국지반신소재학회 2021 한국지반신소재학회 논문집 Vol.20 No.3

본 논문에서는 유한요소법과 경계요소법을 결합하여 기하학적으로 급변 부위가 있는 이차원 탄성 정적 문제에 대하여 효율적이고 정확한 해석 결과를 얻기 위한 유한요소법과 경계요소법의 근사 결합 방법을 제시한다. 이차원 문제의 유한요소로서는 3절점, 4절점 평면응력 요소를 적용하고, 이차원 문제의 경계요소로는 3절점 경계요소를 적용한다. 모델링 단계에서는 우선 전체 해석 대상을 유한요소로 모델링한 후에 기학학적 급변 부위를 경계요소로 모델링 하는데, 유한요소의 모델링을 위하여 정의된 절점을 이용하여 경계요소를 정의한다. 해석 단계에서는 전체 해석 대상에 대하여 유한요소 해석을 우선적으로 수행하고, 이후에 경계요소 해석을 자동으로 수행하는데, 경계부에서의 경계조건은 유한요소 해석 결과인 변위 조건과 응력 조건을 적용한다. 수치예제로서 이차원 탄성 정적 문제인 균열이 있는 평판에 대한 해석 결과를 제시하고 고찰한다. In this paper, the approximately coupled method of finite element method and boundary element method to obtain efficient and accurate analysis results is proposed for a two-dimensional elasto-static problem with a geometrically abruptly changing part. As the finite element of a two-dimensional problem, three-node and four-node plane stress element is applied, and as the boundary element of a two-dimensional problem, three-node boundary element is applied. In the modeling stage, firstly, an entire analysis target object is modeled as finite elements, and then a geometrically abruptly changing part is modeled as boundary elements. The boundary element is defined using the nodes defined for modeling finite elements. In the analysis stage, finite element analysis is firstly performed on a entire analysis target object, and boundary element analysis is automatically performed afterwards. As for the boundary conditions at boundary element analysis, displacement conditions and stress conditions, which are the results of finite element analysis, are applied. As a numerical example, the analysis results for a two-dimensional elasto-static problem, a plate with a crack, are presented and investigated.

열원 입력과 비드 생성 방법이 원통형 다층 금속 용접 과정의 유한요소해석에 미치는 영향

박원동(Won Dong Park),반치범(Chi Bum Bahn),김지훈(Ji Hoon Kim) 대한기계학회 2017 大韓機械學會論文集A Vol.41 No.6

본 논문에서는 원통형 다층 이종 금속 용접부를 대상으로 유한요소 해석을 수행하여, 열원 입력 방법과 용접 비드 생성 방법이 용접 잔류 응력 분포에 미치는 영향을 고려하였다. 열원 입력 방법은 열속 입력 방법과 온도 경계조건 입력 방법으로 나누어 비교하였고, 용접 비드 생성 방법은 요소망 생성 방법과 평온 요소망 방법으로 나누어 비교하였다. 두 열원 입력 방법에 따른 열 해석 결과는 차이가 있었으나, 응력 해석 결과는 유사하였다. 이것은 고온(약 1000 ℃ 이상)에 노출되었던 영역이 비슷하고, 고온에서 재료의 강도가 매우 낮아 용접 비드의 온도가 용접잔류응력에 미치는 영향이 미미하기 때문이다. 두 용접 비드 생성 방법의 용접 잔류응력 분포는 유사하였지만 요소망 생성 방법 적용 시 용접 비드 경계에서 겹침과 들뜸이 발생하였다. 대변형이 발생하는 모델의 용접부 형상을 정확하게 모사하기 위해서는 평온요소망이 더 적합하다고 판단된다. In this study, a finite element analysis of a cylindrical multi-pass weldment for dissimilar metals was performed. The effects of the heat input method and weld bead generation method were considered. We compared two heat input methods: the heat flux method and the temperature method. We also compared two weld bead generation methods: the element birth method and the quiet element method. Although the results of the thermal analysis show deviations between the two heat input methods, the welding residual stresses were similar. Because the areas exposed to high temperature were similar and the strength of the material was very low in high temperature (above the 1000 ℃), the effects of the weld bead temperature were insignificant. The distributions of the welding residual stress were similar to each other. However, gaps and overlaps occurred on the welding boundary surfaces when the element birth method was applied. The quiet element method is more suitable for a large deformation model in order to simulate a more accurate weld shape.

Influence of Modeling Errors in the Boundary Element Analysis of EEG Forward Problems upon the Solution Accuracy

Kim, Do-Won,Jung, Young-Jin,Im, Chang-Hwan The Korean Society of Medical and Biological Engin 2009 의공학회지 Vol.30 No.1

Accurate electroencephalography (EEG) forward calculation is of importance for the accurate estimation of neuronal electrical sources. Conventional studies concerning the EEG forward problems have investigated various factors influencing the forward solution accuracy, e.g. tissue conductivity values in head compartments, anisotropic conductivity distribution of a head model, tessellation patterns of boundary element models, the number of elements used for boundary/finite element method (BEM/FEM), and so on. In the present paper, we investigated the influence of modeling errors in the boundary element volume conductor models upon the accuracy of the EEG forward solutions. From our simulation results, we could confirm that accurate construction of boundary element models is one of the key factors in obtaining accurate EEG forward solutions from BEM. Among three boundaries (scalp, outer skull, and inner skull boundary), the solution errors originated from the modeling error in the scalp boundary were most significant. We found that the nonuniform error distribution on the scalp surface is closely related to the electrode configuration and the error distributions on the outer and inner skull boundaries have statistically meaningful similarity to the curvature distributions of the boundary surfaces. Our simulation results also demonstrated that the accumulation of small modeling errors could lead to considerable errors in the EEG source localization. It is expected that our finding can be a useful reference in generating boundary element head models.

A Study on Plate Bending Analysis Using Boundary Element Method

손재현,김유일 한국해양공학회 2022 韓國海洋工學會誌 Vol.36 No.4

This study presents a method for level ice-structure interaction analysis to estimate the fatigue damage of arctic structures by applying plate theory to the behavior of level ice. The boundary element method (BEM), which incurs a lower computational cost than the finite element method (FEM), was introduced to solve the plate bending problem. The BEM formulation was performed by applying the BEM to plate theory. Finally, to check the validity of the proposed method, the BEM results and FEM results obtained using the ABAQUS commercial software were compared. The response results of the BEM analysis agreed well with those of the FEM analysis. Based on the results of the analysis, the BEM approach is considered to be very powerful in level ice-structure interaction analysis for estimating level ice-induced fatigue damage. Further work is being conducted to perform level ice fracture analysis based on the stress field calculated using the boundary element method.

Boundary element method to estimate the time-varying interfacial boundary in horizontal immiscible liquids flow using electrical resistance tomography

Khambampati, Anil Kumar,Kim, Kyung Youn,Lee, Yeon-Gun,Kim, Sin Elsevier 2016 Applied mathematical modelling Vol.40 No.2

<P><B>Abstract</B></P> <P>Flow of immiscible liquids through horizontal pipe is observed in many industrial process applications. The flow is mainly characterized by its flow regime, relative phase velocities, liquid fraction and water holdup. Electrical resistance tomography (ERT) that provides a cross-sectional image of flow distribution is helpful in monitoring the process. In this paper, the moving interfacial boundary between the immiscible liquids of stratified flow is estimated based on the measured voltages on the pipe surface. Determining the time-varying shape and location of the interfacial boundary has a practical significance. It gives us the cross-sectional liquid fraction which is a key parameter to analyze the hydrodynamic properties of flow. The interfacial boundary shape and location is parameterized with discrete front points and the forward solution is formulated using analytical boundary element method (BEM). The analytic formulation of BEM is simple with less number of unknowns therefore it is computationally efficient. Moreover, BEM discretizes the boundaries alone and is therefore appropriate choice for interfacial boundary estimation. To estimate the time-varying boundary, conventional methods that assume no change in flow distribution within the measurement time of full frame of voltage data are inadequate. Dynamic imaging methods that use one or few sets of data can improve the temporal resolution and hence they are more accurate and practical in realistic situations. Inverse problem is treated as a state estimation problem where the front points are considered as state variables and are estimated using extended Kalman filter. Numerical simulations and phantom experiments are performed to validate the performance of the proposed method.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A numerical solution based on BEM is formulated for moving interfacial boundary. </LI> <LI> Boundary between immiscible liquids is parameterized using discrete front points. </LI> <LI> Analytic BEM is formulated for ERT boundary estimation problem. </LI> <LI> The moving front points that determine the boundary shape are estimated using EKF. </LI> <LI> Number of front points and contrast ratio of liquids affects estimation performance. </LI> </UL> </P>

A boundary radial point interpolation method (BRPIM) for 2-D structural analyses

Gu, Y.T.,Liu, G.R. Techno-Press 2003 Structural Engineering and Mechanics, An Int'l Jou Vol.15 No.5

In this paper, a boundary-type meshfree method, the boundary radial point interpolation method (BRPIM), is presented for solving boundary value problems of two-dimensional solid mechanics. In the BRPIM, the boundary of a problem domain is represented by a set of properly scattered nodes. A technique is proposed to construct shape functions using radial functions as basis functions. The shape functions so formulated are proven to possess both delta function property and partitions of unity property. Boundary conditions can be easily implemented as in the conventional Boundary Element Method (BEM). The Boundary Integral Equation (BIE) for 2-D elastostatics is discretized using the radial basis point interpolation. Some important parameters on the performance of the BRPIM are investigated thoroughly. Validity and efficiency of the present BRPIM are demonstrated through a number of numerical examples.

Virtual boundary element-equivalent collocation method for the plane magnetoelectroelastic solids

Yao, Wei-An,Li, Xiao-Chuan,Yu, Gui-Rong Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.22 No.1

This paper presents a virtual boundary element-equivalent collocation method (VBEM) for the plane magnetoelectroelastic solids, which is based on the fundamental solutions of the plane magnetoelectroelastic solids and the basic idea of the virtual boundary element method for elasticity. Besides all the advantages of the conventional boundary element method (BEM) over domain discretization methods, this method avoids the computation of singular integral on the boundary by introducing the virtual boundary. In the end, several numerical examples are performed to demonstrate the performance of this method, and the results show that they agree well with the exact solutions. So the method is one of the efficient numerical methods used to analyze megnatoelectroelastic solids.

역 문제에 대한 특이치 효율화

박성완(Sung-Oan Park) 한국생산제조학회 2012 한국생산제조학회지 Vol.21 No.2

This study proposed efficient method of singular value for inverse problem, linear approximation of contact position and loading in single and double meshing of transmission contact element, using 2-dimension model considered near the tooth by root stress. Determination of root stress is carried out for the gear tooth by finite element method and boundary element method. Boundary element discretization near contact point is carefully performed to keep high computational accuracy. The predicted results of boundary element method are good accordance with that of finite element method.

Wave Force Analysis of the Two Vertical Cylinders by Boundary Element Method

김남형,Tan Ngoc Than Cao 대한토목학회 2008 KSCE Journal of Civil Engineering Vol.12 No.6

The diffraction of waves by two bottom-fixed vertical circular cylinders is investigated by using boundary element method. This method has been successfully applied to the isolated vertical circular cylinder and now is used to study the interaction between waves and two vertical cylinders. In this paper, a numerical analysis by boundary element method is developed by using linear potential theory. The numerical analysis by boundary element method is based on Green뭩 theorem and introduced to an integral equation for the fluid velocity potential around the vertical circular cylinders. To verify this method, the wave-exciting forces on two transverse and tandem cylinders obtained in this study are compared with the results computed by the multiple scattering method. The comparisons show that the results of this study are strong agreement with their results. Also in this paper, several numerical examples are given to illustrate the effects of various parameters on the wave-exciting force such as the separation distance, the relative size of the cylinders and the incident wave angle. This numerical analysis developed by boundary element method will be applied for various offshore structures to be constructed in the future.