• Journal of Navigation and Port Research
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• v.28 no.6
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• pp.557-564
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• 2004

The WAM wave model has been widely used for wave hindcasting in the ocean by many domestic and foreign researchers due to its relative simplicity and high accuracy. As this model was originally developed for the condition of deepwater and comparatively coarse grid size covering wide area, it might produce in a fault result caused by the improper distribution of directional spreading. We extensively investigated involved problems based on WAM Cycle 4 model and suggested the improved WAM model so that it is applicable to both shallow water sea and fine mesh wave simulation The modified W AM model is verified here by comparing the computed result with and the observed data at Ieodo Ocean Research Station for September of 2003.

• Journal of the Korea Society of Computer and Information
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• v.25 no.4
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• pp.55-61
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• 2020

In this paper, we present a novel approach to efficiently control the location of NPC(Non-playable characters) in the interactive virtual world such as game, virtual reality. To control the NPC's movement path, we first calculate the main trajectory based on the user's path, and then move the NPC based on the weight map. Our method constructs automatically a navigation mesh that provides new paths for NPC by referencing the user trajectories. Our method enables adaptive changes to the virtual world over time and provides user-preferred path weights for smartagent path planning. We have tested the usefulness of our algorithm with several example scenarios from interactive worlds such as video games, virtual reality. In practice, our framework can be applied easily to any type of navigation in an interactive world.

• Journal of the Korea Society for Simulation
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• v.14 no.3
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• pp.21-31
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• 2005

In state-of-the-art games, characters can move in a goal-directed manner so that they can move to the goal position without colliding obstacles. Many path-finding methods have been proposed and implemented for these characters and most of them use the A* search algorithm. When .the map is represented with a regular grid of squares or a navigation mesh, it often takes a long time for the A* to search the state space because the number of cells used In the grid or the mesh increases for higher resolution. Moreover the A* search on the grid often causes a zigzag effect, which is not optimal and realistic. In this paper we propose to use visibility graphs to improve the search time by reducing the search space and to find the optimal path. We also propose a method of taking into account the size of moving characters in the phase of planning to prevent them from colliding with obstacles as they move. Simulation results show that the proposed method performs better than the grid-based A* algorithm in terms of the search time and space and that the resulting paths are more realistic.

• Journal of Navigation and Port Research
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• v.44 no.2
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• pp.53-64
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• 2020

This paper discusses the hydrodynamic characteristics of a catamaran at low speed. In this study, the Delft 372 catamaran model was selected as the target hull to analyze the hydrodynamic characteristics by using the RANS (Reynold-Averaged Navier-Stokes) numerical method. First, the turbulence study and mesh independent study were conducted to select the appropriate method for numerical calculation. The numerical method for the CFD (Computational Fluid Dynamic) calculation was verified by comparing the hydrodynamic force with that obtained experimentally at high speed condition and it rendered a good agreement. Second, the virtual captive model test for a catamaran at low speed was conducted using the verified method. The drift test with drift angle 0-180 degrees was performed and the resulting hydrodynamic forces were compared with the trends of other ship types. Also, the pure rotating test and yaw rotating test proposed by Takashina, (1986) were conducted. The Fourier coefficients obtained from the measured hydrodynamic force were compared with those of other ship types. Conversely, pure sway test and pure yaw test also were simulated to obtain added mass coefficients. By analyzing these results, the hydrodynamic coefficients of the catamaran at low speed were estimated. Finally, the maneuvering simulation in low speed conditions was performed by using the estimated hydrodynamic coefficients.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.329-334
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• 2006

Rail clamps are mechanical components installed to fix the container crane to its bottoms from wind blast or slip. Rail clamps should be designed to survive the harsh wind loading condition. In this study, the jaw structure that is one part of wedge-typed rail clamp is optimized, considering strength under the severe wind loading condition. According to the classification of structural optimization, the structural optimization of a jaw belongs to shape optimization. In the conventional structural optimization methods, they have difficulties in defining complex shape design variables and preventing mesh distortions. To overcome the difficulties, the metamodel using kriging interpolation method is introduced, replacing true response by approximate one. This research presents the shape optimization of a jaw using iterative kriging interpolation models and simulated annealing algorithm. The new kriging models are iteratively constructed by refining the former kriging models. This process is continued until the convergence criteria are satisfied. The optimum results obtained by the suggested method are compared with those obtained by the DOE (design of experiments) and VT (variation technology) methods built in ANSYS WORKBENCH.

• Journal of Korean Port Research
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• v.13 no.1
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• pp.175-182
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• 1999

The ocean wave is hydrodynamically investigated to get more reliable solution. To improve the computational accuracy more fine grids are used with relatively less computer storage on the free surface. One element of the free surface is discretized into more fine grids because the free-surface waves are much affected by the grid size in the finite difference scheme. Here the multi-grid method is applied to confirm the efficiency for the S103 ship model by solving the Navier-Stokes equation for the turbulent flows. According to the computational result approximately 30% can be improved in the free surface generation, Finally the limiting streamlines show numerical result is similar to the experiment by twin tuft.

• Journal of Korean Port Research
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• v.13 no.1
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• pp.167-174
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• 1999

Numerical analysis of two-fluid flows for both water and air is carried out. Free-Surface flows with an arbitrary deformation have been simulated around two dimensional submerged hydrofoil. The computation is performed using a finite volume method with unstructured meshes and an interface capturing scheme to determine the shape of the free surface. The method uses control volumes with an arbitrary number of faces and allows cell-wise local mesh refinement. the integration in space is of second order based on midpoint rule integration and linear interpolation. The method is fully implicit and uses quadratic interpolation in time through three time levels The linear equation systems are solved by conjugate gradient type solvers and the non-linearity of equations is accounted for through picard iterations. The solution method is of pressure-correction type and solves sequentially the linearized momentum equations the continuity equation the conservation equation of one species and the equations or two turbulence quantities.

• Proceedings of the Korean Information Science Society Conference
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• 1999.10b
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• pp.559-561
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• 1999

구형 파노라믹 영상은 영상기반의 가상현실 시스템에서 가상환경을 구축하기 위해 널리 이용되고 있다. 이러한 구형 파노라믹 영상은 카메라를 회전시켜 실세계를 촬영하고 각 영상들을 정렬(image alignment)을 거쳐 구에 사상시킴으로써 얻어진다. 실세계로부터 직업 입력된 영상을 가상환경으로 표현하기 때문에 기하학적 기반의 가상환경에 비해 현실감이 뛰어나다. 그러나 고정된 시점에서 카메라의 회전에 대해서만 가상환경의 영상이 복원 가능하므로 가상환경의 항해(navigation)에 있어서 제약을 받는다. 본 논문에서는 시점의 이동 운동에 따른 운동시차(motion parallax)를 제공하기 위해 구 파노라믹 영상의 특정 부분에 TIP(Tour Into the Picture)기법을 이용하여 spidery mesh 인터페이스를 제공하는 방법을 제안한다. 본 논문에서 제안하는 가상환경 저작 기술은 보다 나은 사용자 상호 작용(interaction)을 제공하는 영상기반 가상 환경 구축에 활용될 수 있다.

• Journal of Korean Port Research
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• v.11 no.1
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• pp.121-128
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• 1997

To analyze the ocean wave more efficiently, more fine grids are used with relatively less computer memory. Each element of free surface is discretized into more fine grids because the ocean waves are much influenced by the mesh used in the finite difference scheme. According to the flow analysis, remarkable improvements could be seen in the free surface generation. The multi grid is applied to confirm the validity of scheme. The Baldwin Lomax turbulence model is used for the analysis of S103 Inuid ship. Finally some discussion on experiments was made for the physical phenomena of the viscous

• Journal of Korean Neurosurgical Society
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• v.37 no.2
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• pp.154-156
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• 2005

We present a case of chondroblastoma in the thoracic vertebra. A 40-year-old patient with upper back pain and lower extremity weakness was admitted to our clinic. On neurological examination, the patient exhibited lower extremity spastic paraparesis. Magnetic resonance imaging revealed a mass infiltrating the 7th thoracic vertebra and its adjacent structures with concomitant compression of the epidural space. After right upper lung tuberculoma was resected through the transthoracic approach, T7 total corpectomy was done with anterior stabilization using a MESH cage and T7 rib bone graft. Two weeks after the first operation, remained part of vertebra was removed and posterior stabilization was performed using a pedicle screw fixation and cross linkage bar with the assistance of the navigation system. The final pathologic diagnosis of the vertebral lesion was benign chondroblastoma.