Yoo-Chul Kim

Development of a Numerical Method for the Evaluation of Ship Resistance and Self-Propulsion Performances

A RANS(Reynolds averaged Navier-Stokes) based numerical method is developed for the evaluation of ship resistance and self-propulsion performances. In the usability aspect of CFD for the hull form design, the field grid around practical hull forms is generated by solving a grid Poisson equation based on the hull surface grid generated from station offsets and centerline profile. A body force technique is introduced to model the effects of the propeller in which the propeller loads are obtained from potential flow analysis using an unsteady lifting surface method. The free surface is captured by using a two-phase level-set method and the realizable model is used for turbulence closure. The hull attitude in vertical plane, i.e., trim and sinkage, is calculated by using a quasi-steady method and then considered in the computation by translating and rotating the grid system according to the values. For the validation of the proposed method, the numerical results of resistance tests for KCS, KLNG, and KVLCC1 and of self-propulsion test for KCS are compared with experimental data.

Production of a hepatoprotective cerebroside from suspension cultures of Lycium chinense

Abstract Suspension cultures derived from Lycium chinense Miller seedlings produced significant amounts of a hepatoprotective cerebroside. Callus was induced from the stem of aseptic seedlings of L. chinense and maintained on MS solid media supplemented with 1.0 ppm 2,4-D and 0.1 ppm kinetin. Suspension cultures were established, and the cells were grown in the same liquid media in the dark. Lyophilized cells were extracted with a combined reagent of chloroform and methanol (2:1, v/v). An aqueous suspension of the evaporated cell extract was partitioned with chloroform, and the chloroform layer was subjected to silicic acid column chromatography followed by semi-preparative reverse phase C8 high pressure liquid chromatography. The purified compound showed hepatoprotective activity comparable to that shown by silymarin, and the structure was identified as 1-O-(β-d-glucopyranosyl)-(2S,3R,4E,8Z)-2-N-2′-hydroxy-(palmitoyl)-4,8-sphingadiene on the basis of spectral data. The content of the compound in cultured cell was tenfold higher than that of the fruit of L. chinense. The biosynthesis of the compound in cultured cell systems appears to parallel cell growth.

Numerical Prediction of Ship Motions in Wave using RANS Method

This paper provides the structure of a Reynolds Averaged Navier-Stokes(RANS) based simulation method and its validation results for the ship motion problem. The motion information of the hull computed from the equations of motion is considered in the momentum equations as the relative fluid motions with respect to a non-inertial coordinates system. A finite volume method is used to solve the governing equations, while the free surface is captured by using a two-phase level-set method and the realizable k- model is used for turbulence closure. For the validation of the present numerical approach, the numerical results of the resistance and motion tests for DTMB 5415 at two ship speeds are compared against available experimental data.

Design of Propeller Geometry Using Blade Sections Adapted to Surface Streamlines

In this paper, we suggest a design concept of defining the propeller geometry by stacking up the blade sections aligned with propeller surface streamlines. Numerical and experimental propeller open water(P.O.W.) characteristics of a newly designed propeller are presented. The surface streamlines for a propeller are obtained by using the panel method. Redefinition of the blade sections aligned with the streamlines is provided together with 8-spline modeling, by which we manufacture model propellers. We carried out the P.O.W, tests in a towing tank in order to show the effect of the present method on P.O.W. characteristics.

Development of Algorithm for Stereoscopic PIV using Normalized Cross-correlation

Contrary to the conventional single-point measuring devices such as LDV, pitot-tube, hot-wire, etc., it would be possible to measure instantaneously 3-D flow fields with a stereoscopic PIV system. In this paper, we present an analysis algorithm for a stereoscopic PIV system using the normalized cross-correlation (NCC) and a 3 -D calibration based reconstruction method. The evaluation method based on NCC is one of the most accurate correlation-based methods. We validated the developed algorithm through a benchmarking comparison with 3-D artificial SPIV images and calibration target images.

Added Resistance and 2DOF Motion Analysis of KVLCC2 in Regular Head Waves using Dynamic Overset Scheme

2015년 IMO(International Maritime Organization)의 EEDI(Energy Efficiency Design Index) 지수의 규제 적용이 시작 되면서 선박 설계에 있어서 파랑중 부가저항에 대한 관심이 산업 계와 학계 등 관련분야에서 꾸준히 높아지고 있으며, 이에 대한 연구도 활발히 진행되고 있다. 파랑중 부가저항은 EEDI 지수의 날씨보정 계수와 관련이 있으며, 실제 해상에서 선박이 운행할 때, 파도에 의해 부가되는 저항 성분으로 선박의 실제 운항 효율 에 영향을 미치는 성분이다. 선박의 파랑중 부가저항을 예측하기 위한 방법으로는 실험적 방법과 수치 해석을 통한 방법으로 나눌 수 있다. 실험적 방법으 로 1973년 Storm-Tejsen et al. (1973)이 Series 60 선형에 대한 부가저항 실험을 시작으로, Journee (1992)의 Wigley 선형 실험, Hirota et al. (2004)의 Ax-bow와 Leadge-bow 효과 실험, Kuroda et al. (2012)의 STEP을 부착한 고속선형의 부가저항 실 험 등이 있었으며, 최근에는 HSVA 모델에 대한 Valanto and Hong (2015)의 연구, Park et al. (2015)의 ITTC 방법을 이용한 KVLCC2의 부가저항 불확실성 해석 등으로 이어지고 있다. 수치 해석을 이용한 방법으로는 크게 포텐셜 이론을 적용한 방법과 Navier-Stokes 방정식을 이용하는 Computational Fluid Dynamics(CFD) 방법으로 나눌 수 있다. 전통적으로 방사파 (radiation wave)의 영향을 잘 예측할 수 있는 포텐셜 기반의 방 법들이 많이 사용되어 왔으며, 최근에는 컴퓨팅 기술의 발전에 따른 수치유체역학 기법의 비약적인 발전에 힘입어 CFD를 이용 한 파랑중 부가저항 해석의 시도가 많이 이루어지고 있다. 포텐 셜 기법을 이용한 방법으로는 Salvesen (1978)과 Faltinsen et al. (1980)이 압력 직접적분법(near-field method)을 소개하였으 며, Maruo (1960)와 Gerritsma and Beukelman (1972)이 모멘 텀 보존법(far-field method)을 제안한 바 있다. 최근에는 Joncquez et al. (2008)이 BEM(Boundary Element Method)을 이용하여 Wigley, Series 60, 벌크선의 부가저항 계산을 소개하 였고, Kim and Kim (2011)이 시간영역 3차원 Rankine 패널법의 pISSN:1225-1143, Vol. 55, No. 5, pp. 385-393 October 2018

Numerical Prediction of Ship Hydrodynamic Performances using Explicit Algebraic Reynolds Stress Turbulence Model

In this study, Explicit Algebraic Reynolds Stress Model (EARSM) which is based on the existing   model has been applied to the flow field analysis around ship hulls. Existing transport equations for the turbulent kinetic energy and the dissipation rate are used in almost the same form and anisotropy terms of Reynolds stresses are newly considered. The well-known KVLCC2 and KCS hull forms are selected as validation cases, which were also used in 2010 Workshop on CFD in Ship Hydrodynamics. In case of KVLCC2 double model, comparison of mean velocity distribution, turbulent kinetic energy, and Reynolds stresses near the propeller plane has been carried out and wave elevation and wave profiles have been additionally studied for KCS and KVLCC2 with free surface models. Some improved results for mean velocity distribution at the propeller plane have been obtained while there is little change in free surface wave profiles.

Analysis of Viscous Flow Around an Impulsively Started Marine Propeller Using VIC(Vortex In Cell) Method

The 3-D unsteady viscous flow around an impulsively started rotating marine propeller is simulated using VIC(Vortex-In-Cell) method which is adequate to analyze the strong vortical flow around complicatedly-shaped body. The computational procedure is governed by the vorticity transport equation in Lagrangian form. In order to solve the equation, a regular grid which is independent to the shape of a body is introduced and each term of the equation is evaluated numerically on the grid by applying immersed boundary concept. In this paper, the overall algorithm including the formulation of governing equations and boundary conditions is described and some computational results are presented with discussing their physical validity.