• Journal of Advanced Marine Engineering and Technology
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• 제28권1호
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• pp.124-135
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• 2004

An experimental study is performed turbulent flow behind a square cylinder by using 2-D PIV technique. The Reynolds number investigated are 10.000. 30.000 and 50,000. The mean velocity vector, time mean axial velocity turbulence intensity. kinetic energy and Reynolds shear stress behind the cylinder are measured, The numerical method used this study is a CFD code, STAR-CD. The numerical results are compared with these of experimental.

• 한국수자원학회논문집
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• 제44권5호
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• pp.363-376
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• 2011

하천 홍수해석 분야에서 가장 널리 이용되고 있는 1차원 동수역학 수치모형의 입력자료는 상하류단 경계조건, 조도계수, 하도단면 등이며, 계산 시간간격 및 거리간격의 선정은 계산결과의 정확성, 안정성, 효율성 확보를 위한 핵심 요소이다. 본 연구에서는 기존 단면간격 선정기법의 이론적 배경을 검토하였고, 매 시간단계별로 도출되는 흐름특성을 반영하여 계산거리간격을 추정하는 가변 계산거리간격 추정 기법을 제안하였다. 제안된 기법을 1차원 부정류 수치모형과 연계하여 Teton 댐 붕괴 및 한강 홍수 사상에 대해 적용함으로써 기존 고정 계산거리간격 추정 기법에 의한 해석결과와 비교하였다. 더 많은 내삽단면이 사용될 경우, 수치 수렴성 실험 결과는 수치해의 정확성과 안정성이 높아짐을 나타내었고, 본 연구에서 제안된 기법은 기존 고정 계산거리간격 추정기법보다 적은 단면개수로 동일한 정도의 정확도를 나타냄으로써 계산 효율성을 크게 향상시켰다. 본 연구에서 개발된 기법의 실무적용을 통해 정확성과 안정성뿐만 아니라 높은 효율성을 갖는 하천 홍수해석이 가능할 것으로 판단된다.

• 한국정밀공학회지
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• 제20권6호
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• pp.105-112
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• 2003

This paper presents the numerical design technology of a passive orifice fluid damper system especially for the characteristics between the damper piston velocity and the damping force. Numerical analysis with the visual interfacial modeling technique was applied into the analysis of the damper system's dynamics. A prototype orifice fluid damper was manufactured and experimentally tested to validate the numerical simulation results. The performances of various damper system schemes were investigated based on the verified numerical simulation model of orifice fluid damper.

• Journal of applied mathematics & informatics
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• 제24권1_2호
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• pp.17-30
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• 2007

A new scheme for solving the Vlasov equation using a compactly supported wavelets basis is proposed. We use a numerical method which minimizes the numerical diffusion and conserves a reasonable time computing cost. So we introduce a representation in a compactly supported wavelet of the derivative operator. This method makes easy and simple the computation of the coefficients of the matrix representing the operator. This allows us to solve the two equations which result from the splitting technique of the main Vlasov equation. Some numerical results are exposed using different numbers of wavelets.

• Structural Engineering and Mechanics
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• 제38권5호
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• pp.619-631
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• 2011

This paper provides a complex variable BIE for solving the periodic notch problems in plane plasticity. There is no limitation for the configuration of notches. For the periodic notch problem, the remainder estimation technique is suggested. In the technique, the influences on the central notch from many neighboring notches are evaluated exactly. The influences on the central notch from many remote notches are approximated by one term with a multiplying factor. This technique provides an effective way to solve the problems of periodic structures. Several numerical examples are presented, and most of them have not been reported previously.

• Journal of Theoretical and Applied Mechanics
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• 제3권1호
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• pp.16-33
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• 2002

A concept of hierarchical modeling, the newest modeling technology. has been introduced early In 1990. This nu technology has a goat potential to advance the capabilities of current computational mechanics. A first step to Implement this concept is to construct hierarchical models, a family of mathematical models which are sequentially connected by a key parameter of the problem under consideration and have different levels in modeling accuracy, and to investigate characteristics In their numerical simulation aspects. Among representative model problems to explore this concept are elastic structures such as beam-, arch-. plate- and shell-like structures because the mechanical behavior through the thickness can be approximated with sequential accuracy by varying the order of thickness polynomials in the displacement or stress fields. But, in the numerical analysis of hierarchical models, two kinds of errors prevail: the modeling error and the numerical approximation errors. To ensure numerical simulation quality, an accurate estimation of these two errors Is definitely essential. Here, a local a posteriori error estimator for elastic structures with thin domain such as plate- and shell-like structures Is derived using element residuals and flux balancing technique. This method guarantees upper bounds for the global error, and also provides accurate local error Indicators for two types of errors, in the energy norm. Comparing to the classical error estimators using flux averaging technique, this shows considerably reliable and accurate effectivity indices. To illustrate the theoretical results and to verify the validity of the proposed error estimator, representative numerical examples are provided.

• Structural Engineering and Mechanics
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• 제8권5호
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• pp.513-529
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• 1999

A concept of hierarchical modeling, the newest modeling technology, has been introduced in early 1990's. This new technology has a great potential to advance the capabilities of current computational mechanics. A first step to implement this concept is to construct hierarchical models, a family of mathematical models sequentially connected by a key parameter of the problem under consideration and have different levels in modeling accuracy, and to investigate characteristics in their numerical simulation aspects. Among representative model problems to explore this concept are elastic structures such as beam-, arch-, plate- and shell-like structures because the mechanical behavior through the thickness can be approximated with sequential accuracy by varying the order of thickness polynomials in the displacement or stress fields. But, in the numerical, analysis of hierarchical models, two kinds of errors prevail, the modeling error and the numerical approximation error. To ensure numerical simulation quality, an accurate estimation of these two errors is definitely essential. Here, a local a posteriori error estimator for elastic structures with thin domain such as plate- and shell-like structures is derived using the element residuals and the flux balancing technique. This method guarantees upper bounds for the global error, and also provides accurate local error indicators for two types of errors, in the energy norm. Compared to the classical error estimators using the flux averaging technique, this shows considerably reliable and accurate effectivity indices. To illustrate the theoretical results and to verify the validity of the proposed error estimator, representative numerical examples are provided.

• 한국전산구조공학회논문집
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• 제19권4호
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• pp.441-447
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• 2006

이 논문은 구조해석에서 수치미분의 적용성에 관한 연구이다. 구조물 선형식의 미분은 구조물의 거동해석에서 반드시 필요한 수학적 계산 중의 하나이다. 아치와 같이 구조물의 선형식이 곡선인 경우에 미분식의 산출은 많은 시간과 노력을 필요로 한다. 이 연구에서는 구조해석에서 수치미분의 적용성을 아치의 자유진동 문제를 통하여 검증하였다. 전진 5차다항식으로부터 아치 곡률항의 미분값을 계산하고 이를 대수적으로 구한 곡률항과 비교하였다 이렇게 얻은 곡률항을 이용하여 최종적으로 산출한 아치의 고유진동수는 문헌해와 아주 우수하게 근접하였다. 이러한 결과로부터 구조해석에서 수치미분의 적용성과 그 결과의 정확성을 입증할 수 있었다.

• 한국항해항만학회지
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• 제37권1호
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• pp.1-7
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• 2013

본 연구에서는 개발된 선미부에 수직날개를 부착한 선박의 조파저항성능을 예측할 수 있는 수치해석기법의 검증에 관한 것이다. 수치해석기법은 비점성 유동장 해석기법인 랜킨소오스 패널법과 와류격자법을 사용하여 개발하였으며, 자유수면 경계조건의 비선형성은 반복해법을 사용하여 만족시켰고, 선박의 트림과 침하량을 구하는 알고리즘을 포함하고 있다. 수치해석을 위한 선체표면의 패널을 생성하기 위하여 패널절단법을 사용하였다. 4000TEU 컨테이너 운반선을 대상 선박으로 하여 선미부 6개소의 서로 다른 위치에 수직날개를 부착하여 수치해석을 수행하였으며, 수치해석기법의 타당성을 검증하기 위하여 상용 점성 유동장 해석 프로그램인 FLUENT를 사용하여 선체 주위의 점성 유동장을 계산하였고, 모형시험을 수행하여 얻은 실험 결과를 수치해석 결과와 서로 비교하였다.

• Wind and Structures
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• 제13권1호
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• pp.57-82
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• 2010

The 486m-long roof of Shenzhen Citizens Centre is one of the world's longest spatial lattice roof structures. A comprehensive numerical study of wind effects on the long-span structure is presented in this paper. The discretizing and synthesizing of random flow generation technique (DSRFG) recently proposed by two of the authors (Huang and Li 2008) was adopted to produce a spatially correlated turbulent inflow field for the simulation study. The distributions and characteristics of wind loads on the roof were numerically evaluated by Computational Fluid Dynamics (CFD) methods, in which Large Eddy Simulation (LES) and Reynolds Averaged Navier-Stokes Equations (RANS) Model were employed. The main objective of this study is to explore a useful approach for estimations of wind effects on complex curved roof by CFD techniques. In parallel with the numerical investigation, simultaneous pressure measurements on the entire roof were made in a boundary layer wind tunnel to determine mean, fluctuating and peak pressure coefficient distributions, and spectra, spatial correlation coefficients and probability characteristics of pressure fluctuations. Numerical results were then compared with these experimentally determined data for validating the numerical methods. The comparative study demonstrated that the LES integrated with the DSRFG technique could provide satisfactory prediction of wind effects on the long-span roof with complex shape, especially on separation zones along leading eaves where the worst negative wind-induced pressures commonly occur. The recommended LES and inflow turbulence generation technique as well as associated numerical treatments are useful for structural engineers to assess wind effects on a long-span roof at its design stage.