• Title/Summary/Keyword: 고차경계요소법

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Isogeometric Shape Design Optimization of Structural Systems Subjected to Design-dependent Loads (설계의존형 하중조건을 갖는 시스템의 아이소-지오메트릭 형상 최적설계)

  • Koo, Bon-Yong;Ha, Seung-Hyun;Cho, Seon-Ho
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2010.04a
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    • pp.512-515
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    • 2010
  • 본 논문에서는 등기하 해석법을 이용하여 설계의존형 하중조건을 갖는 구조물에 대한 형상 최적설계를 수행하였다. 유한요소법 기반 형상 최적설계는 CAD 모델과 해석 모델의 차이로 인해, 설계영역 매개변수화에 어려움이 있다. 등기하 해석법은 CAD 모델과 동일한 NURBS 기저 함수와 조정점을 해석에 이용함으로써 설계의 기하학적 변화를 해석모델에 직접적으로 표현할 수 있는 장점을 가진다. 하중조건이 설계 영역이 변화함에 따라 변하는 최적설계 문제의 경우, 정확한 설계 영역 표현은 법선 벡터, 즉 변화하는 하중의 방향과 곡률과 같은 고차항의 정보를 정확하게 표현할 수 있고, 따라서 목적함수를 최소 또는 최대화시키는 최적의 해로 이끌어 낸다. 유한요소법 또는 밀도법을 이용한 형상 최적설계에서 설계의존형 하중조건을 갖는 구조물의 문제를 푸는 경우, 최적설계가 진행됨에 있어 변화하는 경계의 부정확성 때문에 정확한 설계민감도를 얻기가 어려운 점이 있다. 본 논문에서는, 수치 예제를 통해 등기하 해석 기반의 형상 최적설계 방법론이 설계의존형 하중조건을 갖는 구조물 문제에서 수월성을 가짐을 확인하였다.

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Numerical Analysis of Wave-induced Motion of Floating Pendulor Wave Energy Converter (부유식 진자형 파력발전 장치의 파랑운동 수치해석)

  • Nam, Bo-Woo;Hong, Sa-Young;Kim, Ki-Bum;Park, Ji-Yong;Shin, Seung-Ho
    • Journal of Ocean Engineering and Technology
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    • v.25 no.4
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    • pp.28-35
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    • 2011
  • In this paper, the wave-induced motion characteristics of a floating pendulor are investigated numerically. A floating pendulor is a movable-body-type wave energy converter. This device consists of three main parts (floater, pendulum, and damping plates). In order to obtain the hydrodynamic coefficients and wave exciting forces acting on floating bodies, a higher-order boundary element method (HOBEM) using a wave Green function is applied to the present problems. The hinged motion of a pendulum is simulated by applying the penalty method. In order to obtain a more realistic motion response for a pendulor, numerical body damping is included. First, the wave force and motion characteristics of just a floater are observed with respect to different shape parameters. Then, a coupled analysis of a floater, pendulum, and damping plates is carried out. The relative pitch velocity and wave forces acting on the floating pendulor are compared with those of a fixed pendulor.

On the Solution Method for the Non-uniqueness Problem in Using the Time-domain Acoustic Boundary Element Method (시간 영역 음향 경계요소법에서의 비유일성 문제 해결을 위한 방법에 관하여)

  • Jang, Hae-Won;Ih, Jeong-Guon
    • The Journal of the Acoustical Society of Korea
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    • v.31 no.1
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    • pp.19-28
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    • 2012
  • The time-domain solution from the Kirchhoff integral equation for an exterior problem is not unique at certain eigen-frequencies associated with the fictitious internal modes as happening in frequency-domain analysis. One of the solution methods is the CHIEF (Combined Helmholtz Integral Equation Formulation) approach, which is based on employing additional zero-pressure constraints at some interior points inside the body. Although this method has been widely used in frequency-domain boundary element method due to its simplicity, it was not used in time-domain analysis. In this work, the CHIEF approach is formulated appropriately for time-domain acoustic boundary element method by constraining the unknown surface pressure distribution at the current time, which was obtained by setting the pressure at the interior point to be zero considering the shortest retarded time between boundary nodes and interior point. Sound radiation of a pulsating sphere was used as a test example. By applying the CHIEF method, the low-order fictitious modes could be damped down satisfactorily, thus solving the non-uniqueness problem. However, it was observed that the instability due to high-order fictitious modes, which were beyond the effective frequency, was increased.

An Efficient Matrix-Vector Product Algorithm for the Analysis of General Interconnect Structures (일반적인 연결선 구조의 해석을 위한 효율적인 행렬-벡터 곱 알고리즘)

  • Jung, Seung-Ho;Baek, Jong-Humn;Kim, Joon-Hee;Kim, Seok-Yoon
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.38 no.12
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    • pp.56-65
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    • 2001
  • This paper proposes an algorithm for the capacitance extraction of general 3-dimensional conductors in an ideal uniform dielectric that uses a high-order quadrature approximation method combined with the typical first-order collocation method to enhance the accuracy and adopts an efficient matrix-vector product algorithm for the model-order reduction to achieve efficiency. The proposed method enhances the accuracy using the quadrature method for interconnects containing corners and vias that concentrate the charge density. It also achieves the efficiency by reducing the model order using the fact that large parts of system matrices are of numerically low rank. This technique combines an SVD-based algorithm for the compression of rank-deficient matrices and Gram-Schmidt algorithm of a Krylov-subspace iterative technique for the rapid multiplication of matrices. It is shown through the performance evaluation procedure that the combination of these two techniques leads to a more efficient algorithm than Gaussian elimination or other standard iterative schemes within a given error tolerance.

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A Time Domain Analysis for Hydroelastic Behavior of a Mat-type Large Floating Structure in Calm Water under Dynamic Loadings by Mode Superposition Method (모드중첩법을 이용한 정수중의 매트형 거대부유구조물의 동하중에 대한 시간영역 유탄성 해석)

  • D.H. Lee;K.N. Jo;Y.R. Choi;S.Y. Hong;H.S. Choi
    • Journal of the Society of Naval Architects of Korea
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    • v.38 no.4
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    • pp.39-47
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    • 2001
  • In this paper, the hydroelastic behavior of a mat-type large floating structure is analyzed in time domain by using mode superposition method. The time-memory function is estimated by Fourier transforming the wave damping coefficients, which are computed by a higher-order boundary element method based on potential theory. Meanwhile, the structural response is obtained by time integrating the eigenmodes of the structure. Numerical examples are made for three test cases on the scaled model of a mat-type large floating structure ; weight pull-up case, weight drop case and weight moving case. In all three cases, the numerical results coincide well with experimental data.

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Time-Domain Analysis of Nonlinear Wave-Making Phenomena by a Submerged Sphere Oscillating with Large Amplitude (대진폭 조화 운동을 하는 잠수구에 의한 비선형 조파현상의 시간영역 해석)

  • Kim, Yong-Jig;Ha, Young-Rok
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2006.11a
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    • pp.382-385
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    • 2006
  • A high-order spectral/boundary-element method is newly adapted as an efficient numerical tool. In this method, the velocity potential is expressed as the sum of surface potential and body potential. Then, surface potential is solved fly using the high-order spectral method and body potential is solved fly using the high-order boundary element method. Through the combination of these two methods, the wave-making problems fly a submerged sphere moving with the large amplitude oscillation are solved in time-domain. With the example calculations, nonlinear effects on free-surface profiles and hydrodynamic forces are shown and discussed.

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Numerical Calculation of the free-Surface Flows around a Submerged Body (잠수체 주위 자유표면 유동의 수치계산)

  • 김용직;하영록;홍사영
    • Journal of the Society of Naval Architects of Korea
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    • v.40 no.2
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    • pp.11-20
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    • 2003
  • In this paper, the high-order spectral/boundary-element method is developed to calculate the 3-dimensional water waves generated by a submerged body. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated Tn time-domain. Three-dimensional free-surface flows generated by a submerged sphere which is moving under the free-surface are calculated. Through example calculations, nonlinear effects on free-surface profiles and hydrodynamic forces are shown. Comparisons with others' results show good agreements.

A Study on the Sloshing of Cargo Tanks Including Hydroelastic Effects (유탄성을 고려한 탱크내 슬로싱에 대한 연구)

  • Dong-Yeon Lee;Hang-Shoon Choi
    • Journal of the Society of Naval Architects of Korea
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    • v.35 no.4
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    • pp.27-37
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    • 1998
  • The sloshing is very important in a safe transport of the liquid cargo by a ship. With the increasing number of supertanker and LNG carriers, this problem has become increasingly more important. In order to study the magnitude and characteristics of impact pressures due to sloshing, experiments ware performed with a rectangular tank and compared with numerical results. Structural responses of tank wall under impulsive pressures were measured. Structural vibrations induced by the sloshing load were analysed by including hydroelastic erects in terms of added mass and damping. To check the validity of the numerical model, the natural frequencies of plate in air and water were compared with measurements, and a good agreement was found. In the case that a plate vibrates under impulsive loads, the pressure on the flexible plate is larger than that on the rigid plate without hydroelastic effects, which was confirmed experimentally. The frequency of oscillatory pressure as well as accel%pion coincides with the natural frequency of plate in water.

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Time-Domain Analysis of Nonlinear Wave-Making Problems by a Submerged Sphere Oscillating with Large Amplitude (대진폭 조화 운동을 하는 잠수구에 의한 비선형 조파문제의 시간영역 해석)

  • Kim, Yong-Jig;Ha, Young-Rok
    • Journal of Ocean Engineering and Technology
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    • v.20 no.6 s.73
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    • pp.67-74
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    • 2006
  • A high-order spectral/boundary-element method is newly adapted as an efficient numerical tool. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated and hydrodynamic forces also can be calculated in time-domain. In this method, the velocity potential is expressed as the sum of surface potential and body potential. Then, surface potential is solved by using the high-order spectral method and body potential is solved by using the high-order boundary element method. By the combination of these two methods, the wave-making problems by a submerged sphere oscillating with large amplitude under the free~surface are solved in time-domain. Through the example calculations, nonlinear effects on free-surface profiles and hydrodynamic forces are shown and discussed.

A Study of Numerical Wave Tank for 3-Dimensional Free Surface Wave Simulation (3차원 자유표면파 모사를 위한 수치 파수조에 관한 연구)

  • Ha, Y.R.;Kim, Y.J.
    • Journal of Power System Engineering
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    • v.15 no.6
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    • pp.27-34
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    • 2011
  • The increasing capabilities of the computers enable us to utilize various numerical schemes for the time-domain simulations concerned with 3-dimensional free-surface wave problems. There are still difficulties to solve such kind of problems, however. That's because long time simulations with large computational domain are needed in time-domain analysis. So, we need faster and more efficient numerical schemes to get the solutions practically for these problems. In this paper, a high-order spectral/boundary-element method is used for the numerical investigation of physics involved in wave-body interaction. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated and hydrodynamic forces also can be calculated in time-domain. To get the robust study in these topics, various numerical tests are performed and compared with others' works.