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Kim, Yoo-Chul,Kim, Kwang-Soo,Kim, Jin,Kim, Yoonsik,Park, Il-Ryong,Jang, Young-Hun The Society of Naval Architects of Korea 2017 International Journal of Naval Architecture and Oc Vol.9 No.6
The KVLCC2 and its modified hull form were investigated in regular head waves using Unsteady Reynolds Averaged Navier-Stokes (URANS) methods. The modified KVLCC2 (named KWP-bow KVLCC2) is designed for reducing wave reflection from the bow. Firstly, the original KVLCC2 is studied for verification of the present code and methodology and the computed time history of total resistance and 2DOF motions (heave and pitch) for the selected two wave length conditions are directly compared with the results obtained from KRISO towing tank experiment under the identical condition. The predicted added resistance, heave and pitch motion RAOs show relatively good agreement with the experimental results. Secondly, the comparison of performance in waves between KVLCC2 and KWP-bow KVLCC2 is carried out. We confirmed that newly designed hull form shows better performances in all the range of wave length conditions through both the computation and the experiment. The present URANS method can capture the difference of performance in waves of the two hull forms without any special treatment for short wave length conditions. It can be identified that KWP-bow KVLCC2 gives about 8% of energy saving in sea state 5 condition.
Yoonsik Kim,Donghoon Shin,Chung Choo Chung 제어로봇시스템학회 2014 제어로봇시스템학회 국제학술대회 논문집 Vol.2014 No.10
In this paper, we propose nonlinear adaptive speed control under three-phase voltage unbalance of permanent magnet synchronous motors. An adaptive control applied in a-b-c frame dynamics is proposed to compensate three-phase voltage unbalance by different values of resistance. At this method can estimate actual resistances. For velosity tracking, it is proven that the tracking error is globally asymptotically stable via Lyapunov theorem. The proposed method is performed to validate via the simulation.
Kim, Jeong Bae,Hong, Sokjin,Lee, Won-Chan,Lee, Yong-Woo,Kim, Hyung Chul,Cho, Yoonsik The Academy 2015 Journal of environmental biology Vol.36 No.2
<P>To assess the spatiotemporal changes in phytoplankton community composition in relation to the environment of Masan Bay, a semi-enclosed bay on the southern coast of Korea, photosynthetic pigments and environmental variables were analyzed in seawater, every month between March and November 2010. The level of dissolved inorganic nutrients was highest between July and September when the freshwater influx was at its peak, whereas chlorophyll a level was highest in April and August. Phosphate concentration was low in April (average: 0.22 +/- 0.17 microM), indicating the role of phosphate as a growth-limiting factor for phytoplankton. The results of pigment analysis indicate that dinoflagellate blooms occurred under favorable conditions, where competition with diatoms occurred. Fucoxanthin- and chlorophyll b-containing phytoplankton dominated the surface layer of Masan Bay from July to September. The composition of phytoplankton community in Masan Bay changed dramatically each month according to variations in the amount and composition of nutrients introduced through surface runoff.</P>
다중 격자 Navier-Stokes 해석을 위한 수렴 특성 연구 : Ⅰ. 상류 차분 기법
김윤식(Yoonsik Kim),권장혁(Jang Hyuk Kwon) 한국항공우주학회 2004 韓國航空宇宙學會誌 Vol.32 No.3
본 연구에서는 다중 격자 Navier-Stokes 방정식 해석의 수렴성 향상을 위하여 상류 차분기법들의 주파수 영역에서의 특성 해석을 수행하였다. 1차 상류 차분 기법에 기반한 내재적 연산자의 예조건화 특성 향상을 위하여 다차원적인 효과를 갖는 2차 상류 차분 기법이 전통적인 2차 상류 차분 기법에 비하여 우수한 예조건화 특성을 가지는 이유를 제시하였다. 주파수 영역에서의 해석 결과에 대한 검증을 위하여 완전 성김 다중 격자 기법과 예조건화된 다단계 시간 전진 기법을 적용하였다. 비 점성 유동장 및 Spalart-Allmaras 난류 모델을 이용한 난류 유동장 해석을 수행하였으며, 주파수 영역해석의 결과와 일치하는 우수한 수렴 특성을 가짐을 확인하였다. This study concentrates on the upwind schemes for convergence acceleration of the multigrid method for the Navier-Stokes equations. Comparative study of the upwind schemes in the Fourier space has been performed to identify why the second-order upwind scheme with enlarged stencil can be preconditioned better than the classical second-order upwind scheme. The full-coarsening multigrid method with implicit preconditioned multistage scheme has been implemented for verification of analysis. Numerical simulations on the inviscid and turbulent flows with the Spalart-Allmaras turbulent model have been performed. The results showed consistent trend with the analysis.
다중 격자 Navier-Stokes 해석을 위한 수렴 특성 연구
김윤식(Yoonsik Kim),권장혁(Jang Hyuk Kwon) 한국항공우주학회 2004 韓國航空宇宙學會誌 Vol.32 No.6
본 연구는 다중 격자 Navier-Stokes 방정식 해석의 수렴성 향상을 그 목적으로 한다. 다중 격자 기법의 성능 향상을 위해 최근 많이 사용되고 있는 예조건화된 다단계 시간 전진 기법의 효율성 향상을 위한 연구를 수행하였다. 압축성 유동장 해석시 자주 이용되는 ADI 예조건자와 DDADI 예조건자의 수렴 특성 비교 연구를 수행하였다. 2차원 압축성 난류 유동장 해석에 적용함으로써 DDADI 예조건자가 ADI 예조건자에 비해 우수한 수렴특성을 가짐을 확인하였고, 이를 통하여 Fourier 해석을 통한 예조건화 특성 연구와 일치하는 수렴 특성을 확인하였다. Spalart-Allmaras(S-A) 난류 모델과 Baldwin-Lomax(B-L) 난류 모델의 적용을 통해 난류 모델에 따른 수렴성 비교를 수행하였다. The objective of this study is convergence acceleration of multigrid Navier-Stokes solvers. This study has been performed to enhance the performance of preconditioned multi-stage time stepping method which is a popular smoother for the multigrid Navier-Stokes solvers. Comparative study on the convergence characteristics of the ADI and DDADI preconditioners has been conducted. It is shown that the DDADI preconditioner has better performance than the ADI by numerical tests on the 2-D compressible turbulent flows past airfoils. The Spalart-Allmaras turbulent model and the Baldwin-Lomax turbulent model have been compared with the multigrid calculations.