• 한국해양공학회지
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• 제25권4호
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• pp.1-6
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• 2011

The installation of a topside structure can be categorized into the following stages: start, pre-lifting, lifting, lifted, rotating, positioning, lowering, mating, and end of installation. The transfer of the module onto the floating spar hull occurs in the last three stages, from lowering to the end. The coupled multi-body motions are calculated in both calm water and in irregular waves with a significant wave height (1.52m). The effects of the hydrodynamic interactions between the heavy lifting vessel and the spar hull during the lowering and mating stages are considered. The internal forces caused by the load transfer and ballasting are derived for the mating phases. The results of the internal forces for the calm water condition are compared with those in the irregular sea condition. Although the effect of the pitch motion on the relative vertical motion between the deck of the floating structure and the topside module is significant in the mating phases, the internal force induced pitch motion is too small to have this influence. However, the effect of the internal force on the wave-induced heave responses in the mating phases is noticeable in the irregular sea condition because transfer mass-induced draught changes for the floating structure are observed to have higher amplitudes than the external force induced responses. The impacts of the module on the spar hull in the mating phase are investigated.

• 동력기계공학회지
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• 제16권1호
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• pp.65-71
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• 2012

A numerical procedure is described for predicting the dynamic structural responses of tension leg platforms(TLPs) in current and waves. The developed numerical approach is based on a combination of the three dimensional source distribution method and the dynamic structural analysis method, in which the superstructure of the TLPs is assumed to be flexible instead of rigid. The hydrodynamic interactions among TLP members, such as columns and pontoons, and the structural damping are included in the dynamic structural analysis. The equations of motion of a whole structure are formulated using element-fixed coordinate systems which have the origin at the nodes of the each hull element and move parallel to a space-fixed coordinate system. The dynamic structural responses of a TLP were analyzed in the case of including the current or not including the one in waves and the effects of current on the TLP were investigated.

• Wind and Structures
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• 제11권2호
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• pp.97-120
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• 2008

Wind and wave loadings have a predominant role in the design of offshore structures in general, and articulated tower in particular for a successful service and survival during normal and extreme environmental conditions. Such towers are very sensitive to the dynamic effects of wind and wind generated waves. The exposed superstructure is subjected to aerodynamic loads while the submerged substructure is subjected to hydrodynamic loads. Articulated towers are designed such that their fundamental frequency is well below the wave frequency to avoid dynamic amplification. Dynamic interaction of these towers with environmental loads (wind, waves and currents) acts to impart a lesser overall shear and overturning moment due to compliance to such forces. This compliancy introduces geometric nonlinearity due to large displacements, which becomes an important consideration in the analysis of articulated towers. Prediction of the nonlinear behaviour of these towers in the harsh ocean environment is difficult. However, simplified realistic mathematical models are employed to gain an important insight into the problem and to explore the dynamic behaviour. In this paper, various modeling approaches and solution methods for articulated towers adopted by past researchers are reviewed. Besides, reliability of articulation system, the paper also discussed the design, installation and performance of articulated towers around the world oceans.

• 대한기계학회논문집
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• 제18권7호
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• pp.1759-1772
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• 1994

In this study, we re-examined the Tate's modified Bernoulli equation to study penetration phenomena for long rod projectile into single or multi-layered finite thickness plates. We used the force equlibrium equation at mushroomed nose/target interface instead of conventional pressure equation at the stagnation point. In our penetration model, we considered the velocity dependent $R_t$ value for semi-infinite target and considered only the back face effect for finite target. To compensate for $R_t$ value according to target's thickness and back face effect, we used the spherical cavity expansion theory for semi-infinite plate and used the cylindrical cavity expansion theory for finite plate. Also we developed the experimental technique using make screen to measure the penetration duration time at each layered plate. In 3-layered laminated RHA/mild steel/ A1 7039 plate, we observed that spall had occured around the back face of A1 7039 plate by the stress wave interaction. Through the comparison between theoretical and experimental data including Lambert's results, we conform that our study has good confidences.

• 대한토목학회논문집
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• 제7권3호
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• pp.121-132
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• 1987

우리나라 서남해안(西南海岸)에 공통적(共通的)인 감조하천체계(感潮河川體系)에서 하구조석(河口潮汐)은 상류부(上流部)로 파급(波及)됨에 따라 크게 변형(變形)된다. 이 변형양상(變形樣相)은 하상마찰(河床摩擦), 비선형이류효과(非線型移流效果), 수로(水路)의 기하학적형태(幾何學的形態)와의 상호작용(相互作用) 및 하천유량(河川流量)에 의해 좌우(左右)된다. 본고(本稿)에서는 금강감조구간(錦江感潮區間)에서의 하천유량(河川流量)의 증가(增加)에 따라 전파(傳播)되는 조석(潮汐)에의 영향(影響)을 1차원(次元) 동수역학(動水力學)모형에 의해 정량적(定量的)으로 평가(評價)하였다. 모형에 의해 산정(算定)된 유량(流量)의 증가(增加)에 따라 감조하천상류부(感潮河川上流部)의 조석(潮汐)의 진폭(振幅) 및 도달시각(到達時刻)과의 관계는 Godin(1985)에 의한 이론적(理論的)인 추론(推論)과도 잘 일치(一致)하였다.

• 대한조선학회논문집
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• 제34권2호
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• pp.90-103
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• 1997

본 논문에서는 3차원 특이점분포법, 파의 상호간섭이론 및 유한요소법을 결합한 Goo등[29]이 개발한 초대형 해양구조물의 동적응답 해석법과 스팩트럴 해석법을 이용하여 다수의 임의형상 지지부체간의 유체역학적 상호간섭을 고려한 다방향 불규칙파중의 초대형 해양구조물의 운동응답 및 구조응답의 유의치를 동시에 계산할 수 있는 동적응답 해석법을 개발하였으며, 반잠수식 Ring형상의 초대형 해양구조물을 수치계산 모델로 하여 구조물의 동적응답에 미치는 상호간섭과 다방향파의 영향을 평가하였다.

• 대한조선학회논문집
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• 제53권4호
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• pp.266-274
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• 2016

Many researchers have been trying to improve the propulsion efficiency of a propeller. In this study, the numerical analysis is carried out for the POW(Propeller Open Water test) performance of a propeller equipped with an energy saving device called PHVC(Propeller Hub Vortex Control). PHVC is aimed to control the propeller hub vortex behind the propeller so that the rotational kinetic energy loss can be reduced. The unsteady Reynolds Averaged Navier-Stokes(URANS) equations are assumed as the governing flow equations and are solved by using a commercial CFD(Computational Fluid Dynamics) software, where SST k-ω model is selected for turbulence closure. The computed characteristic values, thrust, torque and propulsion efficiency coefficients for the target propeller with and without PHVC and the local flows in the propeller wake region are validated by the model test results of KRISO LCT(Large Cavitation Tunnel). It is concluded from the present numerical results that CFD can be a good promising method in the assessment of the hydrodynamic performance of PHVC in the design stage.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.21-24
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• 2008

The present study numerically investigates the glottal airflow characteristics as well as acoustic features of phonation fully coupled with dynamic behavior of vocal folds. The vocal folds are described by a low-dimensional body-covered model characterized by bio-mechanical parameters such as glottal width, vocal folds stiffness, and subglottal pressure. The flow in the vocal tract is modeled as an incompressible, axisymmetric form of the Navier-Stokes equations (INS), while the acoustic field is predicted by the linearized perturbed compressible equations (LPCE). The computed result shows that a two-mass model of vocal folds is sufficient to reproduce temporal variations in oral airflow and glottis motion produced by female speakers. It is also found that i) the glottal width has a significant effect on the amplitude of glottal flow, and thus on the amplitude of acoustic wave in the vocal tract, ii) the vocal fold tension is the main control parameter for the fundamental frequency of phonation, iii) the subglottal pressure plays an appreciable role on reproduction of the self-sustained oscillation of vocal folds, and iv) the strength of pulsating airflow and vortical structures are primarily affected by glottal width and subglottal pressure, and are closely related to pitch, loudness, and voice quality. Finally, more comprehensive explanation about the difference between one- and two-mass models is presented with discussion of effectiveness of vocal folds oscillation and voice quality.

• BMB Reports
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• 제29권4호
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• pp.372-379
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• 1996

Components I and II (CI&II) are major phosphoproteins in the frog rod outer segments (ROS) of retina, whose phosphorylation is light- and cyclic nucleotide-dependent. Although it was reported that CI & II could be chemically cross-linked to ${\beta}{\gamma}-subunit$ of transducin (${\beta}{\gamma}_t$), it was not clear whether CI&II physically interact with ${\beta}{\gamma}_t$, under native conditions. CI&II extracted by hypotonic washing fo ROS membranes showed an overlapped migration with ${\beta}{\gamma}_t$, in sucrose density gradient centrifugation. The elution profile of CI&II in the peripheral membrane fractions from gel filtration chromatography also overlapped that of ${\beta}{\gamma}_t$. These hydrodynamic parameters indicate that the native molecular state of CI&II in the peripheral membrane fraction appears to be within a complex, most likely with ${\beta}{\gamma}_t$. CI&II coeluted with ${\beta}{\gamma}_t$, showed no phosphorylation by endogenous kinase which phosphorylates a serine of CI&II in other fractions. The purified CI&II were not able to inhibit trypsin-activated cGMP-phosphodiesterase, and CI&II were not recognized by a monoclonal antibody against the ${\gamma}-subunit$ of transducin, indicating that CI&II are not y-subunit of PDE or transducin. Thus, it is likely that native CI&II, which undergo a light-dependent phosphorylation/dephosphorylation cycle, can associate with ${\beta}{\gamma}$, in frog photoreceptor membranes, and the complex formation has an inhibitory effect on the endogenous phosphorylation of CI&II.

• 유변학
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• 제7권3호
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• pp.211-224
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• 1995

묽은 고분자 용액의선형 점탄성과 완화시간 스펙트럼에 대하여 비드수, 유체역학적 상호작용, 배제 부피와 비선형 스프링들의 영향을 비드-스프링 모델을 통하여 연구하였다. Fixman의 모델을 개량하였고, 비선형 스프링개념을 도입한후 선형점탄성에 관한 식들을 유 도하였다. 그중에서 주로 복고 점도의 크기와 위상차에 대한 BSM 파라미터들의 영향을 살 펴보았다. 실험데이터에서 진동수에 따른 위상차의 평평한 부분의 길이로부터 비드수를 Mark-Houwink 식의 지수 값으로부터 유체역학적 상호작용 파라미터를 그리고 fitting 파라 미터로써 배제 부피 파라미터와 비선형 스프링 파라미터의 함수형태로 표현되는 동적 확장 파라미터를 결정할수 있었다. 또한 광산란 실험등으로부터 배제 부피 파라미터를 결정하게 된다면 이로부터 비선형 스프링 파라미터도 결정할수 있음을 알수 있었다. 한편 불연속적인 현태인 BSM의 완화시간 스펙트럼에 미치는 BSM 파라미터들의 영향을 분석함으로써 각 파람터의 효과와 차이점을 분명히 알수 있었다. 본논문에서는 BSM에 비드수, 유체역학적 상호작용 배제 부피 그리고 비선형 스프링 효과를 동시에 적용하는 방법을 제시하였으며 이 방법을 통하여 묽은 고분자 용액의 선형 점탄성 실험 데이터를 정량적으로 설명할 수 있었다.