• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 춘계학술대회 논문집
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• pp.29-34
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• 2000

This paper describes a numerical study to make clear the characteristics of flow around a high speed catamaran hull advancing on calm water. The simulation is carried out at Froude number of 0.5 with a separation to length rations of 0.2 to 0.5. To simulate the flows, the Navier-Stokes solver is employed in which the free surface condition is included. Computations are performed in a rectangular grid system based grid system based on the Marker & Cell method. For the validation, the computation results are compared with the experiments.

• Structural Engineering and Mechanics
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• 제52권1호
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• pp.19-33
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• 2014

Structural robustness refers to the ability of a structure to avoid disproportionate consequences to the original cause. Currently attentions focus on the concepts of structural robustness, and discussions on methods of robustness based structural design are rare. Firstly, taking basis in robust $H_{\infty}$ control theory, structural robustness is assessed by $H_{\infty}$ norm of the system transfer function. Then using the SIMP material model, robustness based design of grid structures is formulated as a continuum topology optimization problem, where the relative density of each element and structural robustness are considered as the design variable and the optimization objective respectively. Generalized elitist genetic algorithm is used to solve the optimization problem. As examples, robustness configurations of plane stress model and the rectangular hyperbolic shell model were obtained by robustness based structural design. Finally, two models of single-layer grid structures were designed by conventional and robustness based method respectively. Different interference scenarios were simulated by static and impact experiments, and robustness of the models were analyzed and compared. The results show that the $H_{\infty}$ structural robustness index can indicate whether the structural response is proportional to the original cause. Robustness based structural design improves structural robustness effectively, and it can provide a conceptual design in the initial stage of structural design.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• 제26권1호
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• pp.1-14
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• 1998

Various numerical methods for the two dimensional shallow water equations have been applied to the problems of flood routing, tidal circulation, storm surges, and atmospheric circulation. These methods are often based on the Alternating Direction Implicity(ADI) method. However, the ADI method results in inaccuracies for large time steps when dealing with a complex geometry or bathymetry. Since this method reduces the performance considerably, a fully implicit method developed by Wilders et al. (1998) is used to improve the accuracy for a large time step. Finite Difference Methods are defined on a rectangular grid. Two drawbacks of this type of grid are that grid refinement is not possibile locally and that the physical boundary is sometimes poorly represented by the numerical model boundary. Because of the second deficiency several purely numerical boundary effects can be involved. A boundary fitted curvilinear coordinate transformation is used to reduce these difficulties. It the curvilinear coordinate transformation is used to reduce these difficulties. If the coordinate transformation is orthogonal then the transformed shallow water equations are similar to the original equations. Therefore, an orthogonal coorinate transformation is used for defining coordinate system. A multigrid (MG) method is widely used to accelerate the convergence in the numerical methods. In this study, a technique using a MG method is proposed to reduce the computing time and to improve the accuracy for the orthogonal to reduce the computing time and to improve the accuracy for the orthogonal grid generation and the solutions of the shallow water equations.

• 한국농공학회지
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• 제26권2호
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• pp.125-132
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• 1984

A physically-based, distributed, parametric hydrologic model PARK 10 is described and its test results with three agricultural watersheds are presented. The model uses a rectangular grid system to depict hydrologic characteristics of a watershed, and thus, has potentials of identifying the effects of changes in land uses and/or other activities. The model is being tested with small watersheds in the pennisula.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회 논문집
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• pp.532-537
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• 2005

The techniques of internally generating waves on a curve in a rectangular grid system are developed using the line source method. Numerical experiments are conducted using the extended mild-slope equations of Suh et al. (1997). For five different types of wave generation layout, numerical experiments are conducted in the cases of the propagation of waves on a flat bottom, and the refraction and shoaling of waves on a plane slope. The fifth type of wave generation, which consists of two parallel lines connected to a semicircle, shows the best solutions especially when the grid size is small enough.

• 한국분무공학회지
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• 제13권1호
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• pp.22-27
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• 2008

The false diffusion occurs generally when the flow is oblique to the grid lines and when there is a non-zero gradient of the dependent variable in the direction normal to the flow. This numerical problem can overestimate diffusion terms in the continuous phase, causing the numerical inaccuracy for the simulation of impinging sprays on inclined walls because most of spray calculation uses rectangular grid system. Therefore, the main objective of this article is to investigate numerically the influence of false diffusion on numerical simulation for spray-wall impingement on inclined walls. It is found that unlike the spray impingement normal to the wall, the numerical diffusion exists in the case when diesel sprays impinge on the inclined walls with different angles. The results show that the correction function should be considered for accurate prediction of spray penetration length and more elaborate numerical schemes should be utilized to reduce the false diffusion.

• 설비공학논문집
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• 제11권1호
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• pp.18-30
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• 1999

A heat transfer analysis for the two-dimensional (2-D) steady state using finite difference method (FDM) is performed to predict the thermal behavior of the primary first-wall (FW) system of fusion reactor under various geometric and thermo-hydraulic conditions, such as the beryllium (Be) armor thickness, pitch of cooling tube, and coolant velocity. The FW consists of authentic steel (type 316 stainless steel solution annealed) for cooling tubes, Cu for cooling tubes embedding material, and Be for a protective armor, based on the International Thermonuclear Experiment Reactor (ITER) report. The present 2-D analysis, the control volume discretized with hybrid grid (rectangular grid and polar grid) and Gauss-Seidel iteration method are adapted to solve the governing equations. In the present study, geometric and thermo-hydraulic parameters are optimized with consideration of several limitations. Consequently, it is suggested that the adequate pitch of cooling tube is 22-32mm, the beryllium armor thickness is 10-12mm, and that the coolant velocity is 4.5m/s-6m/s for $100^{\circ}C$ of inlet coolant temperature. The cooling tube should locate near beryllium armor. But, it would be better for locating the center of Cu wall, considering problems of material and manufacturing. Also, 2-D analysis neglecting the axial temperature distribution of cooling tube is appropriate, regarding the discretization error in axial direction.

• 한국공작기계학회논문집
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• 제14권5호
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• pp.55-61
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• 2005

In this paper, we propose the visual simulation system for virtual reality motion rider system. The visual simulation system can apply verity virtual reality system. This paper deals with programs on 3D automatic creation of terrain, road design, and a realtime rendering program for the virtual reality system. For the 3D automatic creation of terrain, DEM data and rectangular grid method are applied. We can make two different road object with the road design program. One of them includes road definition, and the other is obtained by using 'NURBS curve.' Visual simulation is consisted by additional modeling and real-time rendering. We can apply the programs made in this way to visual system of driving simulator.

• 전자공학회논문지
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• 제51권6호
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• pp.78-86
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• 2014

본 논문에서는 질량-스프링 구조를 이용한 새로운 광세기 기반 광섬유 진동센서를 제안하고 시뮬레이션과 부분 실험을 통하여 그 실현 가능성을 제시한다. 제안한 광세기 기반 광섬유 진동센서는 네 개의 구불구불하게 휘어지는 스프링과 질량체 안의 사각형 개구면(aperture)으로 구성된 질량-스프링 구조를 가진다. 광시준기(optical collimator)는 질량체 안의 사각형 개구면의 변위에 의해서 변조되는 광을 넓히는 데 이용된다. 제안한 광섬유 진동센서를 광학적인 면과 기계적인 면에서 해석하고 설계한다. 기계적인 부분의 설계는 이론적인 해석, 수학적인 모델링 및 3 차원 유한요소법 시뮬레이션을 이용한다. 기계적인 진동이 가해질 때 개구면의 상대적인 변위관계를 3차원 유한요소법 시뮬레이션을 이용하여 구하고, 개구면의 상대적인 변위에 따른 출력값을 실험을 통하여 측정한다. 이를 이용하여 진동에 따른 출력 특성을 파악한 결과 센서 민감도 $15.731{\mu}W/G$, 감지영역 ${\pm}6.087G$를 얻었다. 그리고 입력광원의 파워가 10 dB까지 변하더라도 참조광을 이용하여 0.75%의 상대오차를 보이는 매우 안정된 출력광 파워를 얻었다. 제안한 광섬유 진동센서는 간단한 구조, 저비용 및 다지점 측정 가능의 특징을 가지면서, MEMS (Micro-Electro-Mechanical System) 기술을 이용하여 소형으로 간편하게 제작할 수 있는 잠재력을 가진다.

• 한국방재학회 논문집
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• 제4권2호
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• pp.71-76
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• 2004

본 연구에서는 지진해일에 의한 원형섬 주변에서의 범람영역을 산정하기 위하여 사면구조(quadtree) 격자 기법을 이용한 수치모형을 개발하였다. 비선형 천수방정식을 지배방정식으로 사용하였으며, 적합화된 계층적사면구조 격자를 이용하여 leap-frog 기법으로 양해적으로 유한차분하였다. 원형섬 주위를 따라 적용된 사면구조 격자는 사각형 및 원형의 형상으로 세밀화 되었다. 본 모형에 의해 계산된 수치해석결과를 검증하기 위해 원형섬 주변의 처오름높이에 대한 수리실험결과와 비교하였으며, 본 연구의 결과는 수리실험결과와 양호하게 일치하였다.