• Journal of computational fluids engineering
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• v.5 no.1
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• pp.14-21
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• 2000

A method of two and three dimensional orthogonal grid generation with control of spacing by using the covariant Laplace equation is presented. An important feature of the methodology is its ability to control effectively the grid spacing especially near the boundaries still maintaining good orthogonality in whole field. The method is based on the concept of decomposition of the global transformation into consecutive transformation of an approximate conformal mapping and an auxiliary orthogonal mapping to have linear and uncoupled equations. Control of cell spacing is based on the concept of reference arc length, and orthogonal correction is peformed in the auxiliary domain. It is concluded that the methodology can successfully generate well controlled orthogonal grids around bodies of 2 and 3 dimensional configurations.

• 한국전산유체공학회:학술대회논문집
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• 1995.10a
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• pp.82-89
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• 1995

In the present paper, a method of nearly orthogonal grid generation in an arbitrary simply-connected 3D domain will be presented. The method is a new direct and non-iterative scheme based on the concept of the decomposition of the global orthogonal transformation into consecutive mapping of a conformal mapping and an auxiliary orthogonal mapping, which was suggested by King and Leal [4]. In our numerical scheme. Kang and Leal's method is extended from 2D problems to 3D problems while the advantage of the non-iterative algorithm is maintained. The essence of the present mapping method is that an iterative scheme can be avoided by introducing a preliminary step. This preliminary step corresponds to a conformal map and is based on the boundary element method(BEM). This scheme is applied to generate several nearly-orthogonal grid systems which are orthogonal at boundaries.

• 한국전산유체공학회:학술대회논문집
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• 2000.05a
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• pp.99-106
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• 2000

A method of two and three dimensional orthogonal grid generation with control of spacing by using the covariant Laplace equation is Presented. An important feature of the methodology is its ability to control effectively the grid spacing especially near the boundaries still maintaining good orthogonality in whole field. The method is based on the concept of decomposition of the global transformation into consecutive transformation of an approximate conformal mapping and au auxiliary orthogonal mapping to have linear and uncoupled equations. Control of cell spacing is based on the concept of reference arc length, and orthogonal correction is performed in the auxiliary domain. It is concluded that the methodology can successfully generate well controlled orthogonal grids around bodies of 2 and 3 dimensional configurations.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.561-565
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• 1988

In the present study, a new method of generating a nearly orthogonal boundary-fitted coordinate systems with automatic grid spacing control is introduced. Applications of the method to a two dimensional simply-connected region is then demonstrated. The nearly orthogonal boundary-fitted method has the following features, (a) Strong grid control in the .eta.-direction can be made, (b) The generated boundary-fitted coordinates are nearly orthoronal, (c) Both the .xi.-and .eta.-direction control function are mathematically derived. Especially the .eta.-direction control function is derived under the assumption that the .eta.-direction grid spacing is by far smaller than the .xi.-direction grid spacing when the .eta.-direction grid line is strongly clustered. (d) The grid control functions are dynamically adjusted by the metric scale factors imposed on the boundary. The control function is fully automatic and eliminates the need of user manipulation of the control function.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.2038-2042
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• 2010

본 연구는 동해안 속초항에 정방형 직교격자체계(Regular Grid)와 직교-곡선 격자체계(Orthogonal Curvilinear Grid)를 이용하여 SWAN 모형에 적용시켜 각 격자체계에 따른 파랑변형의 특성을 비교하는데 목적이 있다. 본 연구결과 북방파제가 연장 중인 방파제 선단에서 회절현상이 관측 되었으며, 속초 해수욕장 인근에서의 해안선 형상에 따라 굴절 효과로 인하여 입사 파랑의 벡터들이 해안선에 수직하게 입사되는 현상이 관측 되었고, 특히, 조도 주변에서 파랑의 굴절 효과와 차단효과를 관찰할 수 있다. 정방형 직교 격자체계와 직교-곡선 격자체계의 계산결과는 유사하나 직교-곡선 격자체계가 해안선에서 보다 정밀한 계산 값을 얻을 수 있었다. 하지만 직교-곡선 격자체계는 계산시간이 최소 4배 이상 증가하는 단점을 가지고 있다.

• Composites Research
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• v.31 no.2
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• pp.69-75
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• 2018

In this study, a grid panel structure in which the woven CFRP composites were stacked in the orthogonal array was proposed and the mechanical properties were analyzed and studied. The grid parts were fabricated by cutting prepregs and laminating them. The grid panel structure was fabricated by co-curing with lower laminate plate in auto-clave process. The behavior of the proposed grid panel structure was evaluated by tests under tensile, compressive, shear, and bending loads. The effect of increasing the stiffness of the orthogonal grid structure was verified through these tests. In addition, the finite element model was constructed and compared with the test results, confirming the validity and reliability of the test and analysis.

• Journal of Power Electronics
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• v.15 no.1
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• pp.216-226
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• 2015

Grid synchronization is one of the key techniques for the grid-connected power converters used in distributed power generation systems. In order to achieve fast and accurate grid synchronization, a new phase locked loop (PLL) is proposed on the basis of the complex filter matrixes (CFM) orthogonal signal generator (OSG) crossing-decoupling method. By combining first-order complex filters with relation matrixes of positive and negative sequence voltage components, the OSG is designed to extract specific frequency orthogonal signals. Then, the OSG mathematical model is built in the frequency-domain and time-domain to analyze the spectral characteristics. Moreover, a crossing-decoupling method is suggested to decouple the fundamental voltage. From the eigenvalue analysis point of view, the stability and dynamic performance of the new PLL method is evaluated. Meanwhile, the digital implementation method is also provided. Finally, the effectiveness of the proposed method is verified by experiments under unbalanced and distorted grid voltage conditions.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.26 no.1
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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.

• 한국전산유체공학회:학술대회논문집
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• 2001.10a
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• pp.152-156
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• 2001

Three dimensional orthogonal grid generation is able to control effectively the grid spacing near the boundaries, but there are some difficulty to meshing complex geometry. The mesh complex geometry by orthogonal grid generation method must divide block of geometry It is required a careful skill, and long time. Its also difficulty to make unstructured mesh on complex geometry. Particularly, three dimensional geometry must have more time and effort. Recently, there have been growing interests in mesh generation of complex grometry, aslike an automobile headlamp, the heart. The method of easily meshing complex geometry is resarched to solve them. We suggest octree grid into one among these methods. As octrce grid is automaticaly adapted at the boundaries by determine the level operations to control the grid spacing near the boundaries are unnecessary. In this paper we showed throe dimensional mesh generation, and heat-flow analysis on the octree mesh.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.4
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• pp.256-265
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• 2019

In this paper, the progressive damage of an orthogonal grid shell fabricated with plain weave fabric CFRP under bending load was investigated. The orthogonal grids were cured with the bottom composite shell. Progressive damage analysis of an orthogonal grid shell under bending was performed using nonlinear finite element method with Hashin-Rotem failure criterion and Matzenmiller-Lubliner-Taylor(MLT) model. In addition, the three - point bending test for the structure was carried out and the test results were compared with the analysis results. The comparison results of the strain and displacement agreed well. The damage area estimated by the progressive damage analysis were compared with the visual inspection and ultrasonic non-destructive inspection.