• Title/Summary/Keyword: Non-Cartesian

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Tidal Computations For Inchon Bay

  • Choi, Byung Ho
    • 한국해양학회지
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    • v.15 no.2
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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.

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An Axially Marching Scheme for Internal Waves

  • In-Joon,Suh
    • Bulletin of the Society of Naval Architects of Korea
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    • v.25 no.2
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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.

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Flow Analysis with a Port/Valve Assembly and Cylinder Using a RNG k-$\varepsilon$ Model (RNG k-$\varepsilon$모델을 이용한 포트/밸브계 및 실린더내의 유동해석)

  • 양희천
    • Journal of Advanced Marine Engineering and Technology
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    • v.22 no.4
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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.

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Computation of Dynamic Damping Coefficients for Projectiles using Steady Motions (정상 운동을 이용한 발사체의 동적 감쇠계수 계산)

  • Park,Su-Hyeong;Gwon,Jang-Hyeok
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.8
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    • pp.19-26
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    • 2003
  • A steady prediction method of dynamic stability derivatives is presented in the unified framework of the unsteady Euler equations. New approach does not require any modification of the governing equations except addition of non-inertial force terms. The present methods are applied to compute the pitch-damping coefficients using the lunar coning and the lunar helical motions in the Cartesian coordinate frame. The results for the ANSR and the Basic Finner are in good agreement with the PNS data, range data, and the results using the unsteady prediction method. The results show that the steady approach using the unified governing equations in the Cartesian coordinate frame can be successfully applied to predict the pitch-damping coefficients.

A Study on the Selection of Dependent Variables of Momentum Equations in the General Curvilinear Coordinate System for Computational Fluid Dynamics (전산유체역학을 위한 일반 곡률좌표계에서 운동량 방정식의 종속변수 선정에 관한 연구)

  • Kim, Won-Kap;Choi, Young Don
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.2
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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.

NUMERICAL SIMULATION OF THREE-DIMENSIONAL INTERNAL WAVES USING THE FDS SCHEME ON THE HCIB METHOD (FDS 기법과 HCIB법을 이용한 3차원 내면파 수치 모사)

  • Shin, Sang-Mook
    • Journal of computational fluids engineering
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    • v.17 no.1
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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.

A Fundamental Study for the Numerical Simulation Method of Green Water Occurrence on Bow Deck (선수부 갑판침입수의 수치시뮬레이션에 대한 기초연구)

  • Jeong, Kwang-Leol;Lee, Young-Gill;Kim, Nam-Chul
    • Journal of the Society of Naval Architects of Korea
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    • v.47 no.2
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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.

Development of an Enhanced 8-node Hybrid/Mixed Plane Stress Element : HQ8-14βElement (8절점 Hybrid/Mixed 평면응력요소)

  • Chun, Kyoung Sik;Park, Won Tae;Yhim, Sung Soon
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.2A
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    • pp.319-326
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    • 2006
  • A new enhanced 8-node hybrid/mixed plane stress elements based on assumed stress fields and modifed shape functions has been presented. The assumed stress fields are derived from the non-conforming displacement modes, which are less sensitive to geometric distortion. Explicit expression of shape functions is modifed so that it can represent any quadratic fields in Cartesian coordinates under the same condition as 9-node isoparametric element. The newly developed element has been designated as 'HQ8-$14{\beta}$'. The presented element is compared with existing elements to establish its accuracy and efficiency. Over a wide range of mesh distortions, the element presented here is found to be exceptionally accurate in predicting displacements.

Fundamental theory of curved structures from a non-tensorial point of view

  • Paavola, Juha;Salonen, Eero-Matti
    • Structural Engineering and Mechanics
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    • v.7 no.2
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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.

IMMERSED BOUNDARY METHOD FOR COMPRESSIBLE VISCOUS FLOW AROUND MOVING BODIES (이동하는 물체 주위의 압축성 유동에 대한 가상경계법)

  • Cho, Yong;Chopra, Jogesh;Morris, Philip J.
    • Journal of computational fluids engineering
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    • v.13 no.3
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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.