• 한국해양학회지
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• 제15권2호
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• pp.112-122
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• 1980

A two-dimensional non-linear tidal model has been established to calculate the M$\_$2/ tide of Inchon Bay in the west coast of Korea. Cartesian coordinates are used for the derivation of the governing equations and account is taken of extensive drying boundaries (tidal flats) which are exposed at low tides. The tidal amplitudes and phases computed from the model agree well with those known from observation lying within bounds 5cm in amplitude and 5 in phase relative to the observed results. The work represents a further stage in the development including extensive sea measurements capable of application in various coastal engineering problems encountered in Inchon Bay area.

• 대한조선학회지
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• 제25권2호
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• pp.1-10
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• 1988

An axially marching numerical method is developed for the simulation of the internal waves produced by translation of a submersed vehicle in a density-stratified ocean. The method provides for the direct solution of the primitive variables [$\upsilon,\;p,\;\rho$] for the nonlinear and steady state three-dimensional Euler's equation with a non-constant density term in the vehicle-fixed cartesian co-ordinate system. By utilizing a known potential flow around the vehicle for an estimate of the axial velocity gradient, the present parabolic algorithm local upstreamwise disturbances and axial velocity variation.

• Journal of Advanced Marine Engineering and Technology
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• 제22권4호
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• pp.436-444
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• 1998

Applicability of the RNG k-$\varepsilon$ model to the analysis of unsteady axisymmetric turbulent flow of a reciprocating engine including port/valve assembly is studied numerically. The governing equations based on non-orthogonal including port/valve assembly is studied numerically. The governing equations based on a non-orthogonal coordinate formulation with Cartesian velocity components are used and discretised by the finite volume method with non-staggered variable arrangements. The predicted results using the RNG k-$\varepsilon$ model of the unsteady axisymmetric turbulent flow within a cylinder of reciprocating model engine including port/valve assembly are compared to these from the modified k-$\varepsilon$ model and experimental data. Using the RNG k-$\varepsilon$ model seems the have some potential for the simulations of the unsteady turbulent flow within a port/valve-cylinder assembly over the modified k-$\varepsilon$model.

• 한국항공우주학회지
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• 제31권8호
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• pp.19-26
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• 2003

비정상 Euler 방정식 틀에서 동안정 미계수의 정상 예측 방법을 제안하였다. 새로운 접근방법은 비정상 지배방정식을 수정하지 않고 정상 예측방법을 적용하도록 해 준다. 제안된 방법을 통해 lunar 코닝운동 및 나선운동을 사용하여 피치감쇠 계수 합과 개별 값을 계산하였다. ANSR 형상과 Basic Finner 형상에 대한 계산결과는 PNS 계산결과, 실험치, 그리고 비정상적 예측방법을 사용한 결과와 잘 일치하고, 직교좌표계에서 정상적 예측 방법이 피치감쇠 계수의 예측에 성공적으로 적용될 수 있음을 보여준다.

• 대한기계학회논문집B
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• 제23권2호
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• pp.198-209
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• 1999

This study reports the selection of dependent variables for momentum equations in general curvilinear coordinates. Catesian, covariant and contravariant velocity components were examined for the dependent variable. The focus of present study is confined to staggered grid system Each dependent variable selected for momentum equations are tested for several flow fields. Results show that the selection of Cartesian and covariant velocity components intrinsically can not satisfy mass conservation of control volume unless additional converting processes ore used. Also, Cartesian component can only be used for the flow field in which main-flow direction does not change significantly. Convergence rate for the selection of covariant velocity component decreases quickly as with the increase of non-orthogonality of grid system. But the selection of contravariant velocity component reduces the total mass residual of discretized equations rapidly to the limit of machine accuracy and the solutions are insensitive to the main-flow direction.

• 한국전산유체공학회지
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• 제17권1호
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• pp.8-15
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• 2012

A code developed using the flux-difference splitting scheme on the hybrid Cartesian/immersed boundary method is applied to simulate three-dimensional internal waves. The material interface is regarded as a moving contact discontinuity and is captured on the basis of mass conservation without any additional treatment across the interface. Inviscid fluxes are estimated using the flux-difference splitting scheme for incompressible fluids of different density. The hybrid Cartesian/immersed boundary method is used to enforce the boundary condition for a moving three-dimensional body. Immersed boundary nodes are identified within an instantaneous fluid domain on the basis of edges crossing a boundary. The dependent variables are reconstructed at the immersed boundary nodes along local normal lines to provide the boundary condition for a discretized flow problem. The internal waves are simulated, which are generated by an pitching ellipsoid near an material interface. The effects of density ratio and location of the ellipsoid on internal waves are compared.

• 대한조선학회논문집
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• 제47권2호
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• pp.188-195
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• 2010

Green water load is an important parameter to be considered in designing a modern ship or offshore structures like FPSO and FSRU. In this research, a numerical simulation method for green water phenomenon is introduced. The Navier-Stokes equations and the continuity equation are used as governing equations. The equations are calculated using Finite Difference Method(FDM) in rectangular staggered grid system. To increase the numerical accuracy near the body, the Cartesian cut cell method is employed. The nonlinear free-surface during green water incident is defined by Marker-density method. The green waters on a box in regular waves are simulated. The simulation results are compared with other experimental and computational results for verification. To check the applicability to moving ship, the green water of the ship which is towed by uniform force in regular wave, is simulated. The ship is set free to heave and to surge.

• 대한토목학회논문집
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• 제26권2A호
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• pp.319-326
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• 2006

본 논문에서는 가정응력장과 수정된 형상함수를 이용한 새로운 8절점 hybrid/mixed 평면응력요소를 제시하였다. 가정응력장은 비적합 변위모드로부터 유도하였으며, 이는 요소의 찌그러짐에 대한 민감도를 완화시켜준다. 그리고 Cartesian 좌표계에서 9절점 등매개변수 요소와 동일한 조건하에서 2차 변위를 정확히 보간하도록 수정한 형상함수를 사용하였다. 제시한 8절점 hybrid/mixed 평면응력요소(HQ8-$14{\beta}$)의 수치해석에 대한 정확성과 효율성을 검증하기 위해 기존의 참고문헌들과 비교, 분석하였다. 그 결과 본 논문에서 제시한 요소는 요소가 왜곡된 경우를 포함하여 우수한 성능을 보였다.

• Structural Engineering and Mechanics
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• 제7권2호
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• pp.159-180
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• 1999

The present paper shows a new non-tensorial approach to derive basic equations for various structural analyses. It can be used directly in numerical computation procedures. The aim of the paper is, however, to show that the approach serves as an excellent tool for analytical purposes also, working as a link between analytical and numerical techniques. The paper gives a method to derive, at first, expressions for strains in general beam and shell analyses, and secondly, the governing equilibrium equations. The approach is based on the utilization of local fixed Cartesian coordinate systems. Applying these, all the definitions required are the simple basic ones, well-known from the analyses in common global coordinates. In addition, the familiar principle of virtual work has been adopted. The method will be, apparently, most powerful in teaching the theories of curved beam and shell structures for students not familiar with tensor analysis. The final results obtained have no novelty value in themselves, but the procedure developed opens through its systematic and graphic progress a new standpoint to theoretical considerations.

• 한국전산유체공학회지
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• 제13권3호
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• pp.35-43
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• 2008

A methodology for the simulation of compressible high Reynolds number flow over rigid and moving bodies on a structured Cartesian grid is described in this paper. The approach is based on a modified version of the Brinkman Penalization method. To avoid oscillations in the vicinity of the body and to simulate shcok-containing flows, a Weighted Essentially Non-Oscillatory scheme is used to discretize the spatial flux derivatives. For high Reynolds number viscous flow, two turbulence models of the two-equation Menter's SST URANS model and a two-equation Detached Eddy Simulation are implemented. Some simple flow examples are given to assess the accuracy of the technique. Finally, a moving grid capability is demonstrated.