• Journal of Ship and Ocean Technology
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• 제12권2호
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• pp.41-52
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• 2008

The development of a high-lift rudder is needed because low speed full ships such as the VLCC(Very Large Crude oil Carrier) have difficulty for obtaining enough lifting force from a common rudder. The rudder of a ship is generally positioned behind the hull and propeller. Therefore, rudder design should consider the interactions between hull, propeller, and rudder. In the present study, the FLUENT code and body fitted mesh systems generated by the GRIDGEN program are adopted for the numerical simulations of flow characteristics around a rudder that is interacting with hull and propeller. Sliding mesh model(SMM) is adopted to analyze the interaction between propeller rotation and wake flow behind hull. Several numerical simulations are performed to compare the interactions such as hull-rudder, propeller-rudder, and hull-propeller-rudder. Also, we consider relationships between the interactions. The results of present numerical simulations show the variation of flow characteristics by the interaction between hull, propeller, and rudder, and these results are compared with an existing experimental result. The present study demonstrates that numerical simulations can be used effectively in the design of high-lift rudder behind low speed full ship.

• 한국전산유체공학회지
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• 제6권1호
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• pp.1-13
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• 2001

The natural convection heat transfer and solidification in a stratified pool are studied. The flow and heat transfer characteristics in a heat generating pool are compared between single-layered and double-layered pools. And local Nusselt number distributions on outer walls are obtained to consider thermal loads on a vessel wall. The cooling and solidification of Al₂O₃/Fe melt in a hemispherical vessel are simulated to study the mechanism of heat transfer and temperature distribution. A unstructured mesh is chosen for this study because of the non-orthogonality originated from the boundaries of double-layered pool. Interface between the layers is modeled to be fixed. With this assumption mass flux across the interface is neglected, but shear force and heat flux are considered by boundary conditions. The colocated cell-centered finite volume method is used with the Rhie-Chow interpolation to compute cell face velocity. To prevent non-physical solutions near walls in case body force is large the wall pressure is extrapolated by the way to include body force. The numerical solutions calculated by current method show that averaged downward heat flux of the double-layered pool increases compared to single-layered pool and maximum temperature occurs right below the interface of the layers.

• 한국항해학회지
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• 제23권2호
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• pp.29-42
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• 1999

An accurate method of estimating ship maneuverability needs to be developed to evaluate precisely and improve the maneuverability of ships according to the water depth. In order to estimate maneuverability by a mathematical model. The hydrodynamic forces acting on a ship hull and the flow field around the ship in maneuvering motion need to be estimated. The ship speed new the berth is very low and the fluid flow around a ship hull is unsteady. So, the transient fluid motion should be considered to estimate the drag force acting on the ship hull. In the low speed and short time lateral motion, the vorticity is created by the body and grow up in the acceleration stage and the velocity induced by the vorticity affect to the body in deceleration stage. For this kind of problem, CFD is considered as a goof tool to understand the phenomena. In this paper, the 2D CFD code is used for basic consideration of the phenomena to solve the flow in the cross section of the ship considering the ship is slender and the water depth is large enough. The flow fields Added and hydrodynamic forces for the some prescribed motions are computed and compared with the preliminary experiment results. The comparison of the force with measurement is shown a fairly good agreement in tendency. The 3D Potential Calculation based on the Hess & Smith Theory is employed to predict the surge, sway added mass and yaw added moment of inertia of hydrodynamic coefficients for M/V ESSO OSAKA according to the water depth. The results are also compared with experimental data. Finally, the sway added mass of hydrodynamic coefficients for T/S HANNARA is suggested in each water depth.

• Structural Engineering and Mechanics
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• 제70권4호
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• pp.479-497
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• 2019

In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world's tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.

• 한국공작기계학회논문집
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• 제10권3호
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• pp.68-74
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• 2001

In the drawing of large size automotive panels, elastic deflection of die components is induced by the contact force between them. The deflection is nonuniform and locally distributed, and results in nonuniform material flow. In order to arrange such a nonuniform die gap, a correcting operation, so called die spotting, is inevitable, which requires trial and error works and consuming time. A prediction of the bending deflection prior to a try-out must be useful to reduce the die spotting time. In this study, drawing process of a front fender is simulated first. and the deflection of the blank holder is calculated from the contact force imposing on th blank holder. The balance block heights ensuring a uniform deflection are optimized by the analysis and design of experiments.

• 한국물환경학회지
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• 제21권1호
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• pp.79-83
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• 2005

Foraging behaviour of false dace, Pseudorasbora parva, was investigated in water flowing at various velocities with the existence of a cavity for rest. The pursuit comprised three succeeding processes such as, approaching, chasing and attacking. Angles between the fish body and the water flow direction and swimming speeds increased in the latter stages of approaching, chasing and attacking. All pursuit angles, swimming speeds and distances increased with flow velocity and peaked at the flow velocity of 7 cm/sec. At higher velocities, however, the fish avoided the use of much energy against the large drag force. The probability of capture and the feeding rate steadily decreased with increasing flow velocity. Under the fast flow, the fish adjusted their swimming speed to get the optimum velocity relative to the flowing water for the energetic budget. Fish spent more time in the cavity as flow velocity increased to avoid the energy expenditure necessitated by the high velocity.

• 한국산업융합학회 논문집
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• 제4권3호
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• pp.295-304
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• 2001

The hydrodynamic impact problem was studied from 1929 to recent. Especially, Impact pressure is important for the design of the ships and offshore structure and spacecrafts, and under weapons. A ship traveling at high speed or in heavy sea has its bow and bottom damaged by high pressure caused by impact with and detachment from the water surface. Considerable impact may also occur when large waves hit the cross member or deck plate of an offshore structure within the splash zone. Many engineering cases require consideration of impact pressure, the movement of objects and change of the flow field. This study was obtained the pressure distribution of a falling body that is deadrise angle $0^{\circ}$ and deadrise angle $5^{\circ}$ upon a water surface by the experiment with the impact machine. The theoretical equation was obtained the air region and the interface and the water region which devide 3 parties between the body and the water surface for an investigation of the complete phenomena. Pressure distributions and histories compare favorably with available experimental data. The numerical results are similar to the experimental results for the impact force type with Fo(1+$cos{\pi}t/tc$).

• Wind and Structures
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• 제35권1호
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• pp.67-81
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• 2022

While the aerodynamics of solid bluff bodies is reasonably well-understood and methodologies for their reliable numerical simulation are available, the aerodynamics of porous bluff bodies formed by assembling perforated plates has received less attention. The topic is nevertheless of great technical interest, due to their ubiquitous presence in applications (fences, windbreaks and double skin facades to name a few). This work follows previous investigations by the authors, aimed at verifying the consistency of numerical simulations based on the explicit modelling of the perforated plates geometry and their representation by means of pressure-jumps. In this work we further expand such investigations and, contextually, we provide insight into the flow arrangement and its sensitivity to important modelling and setup configurations. To this purpose, Unsteady Reynolds-Averaged Navier-Stokes (URANS) and Large-Eddy Simulations (LES) are performed for a 5:1 rectangular cylinder at null angle of attack. Then, using URANS, porosity and attack angle are simultaneously varied. To the authors' knowledge this is the first time in which LES are used to model a porous bluff body and compare results obtained using the explicit modelling approach to those obtained relying on pressure-jumps. Despite the flow organization often shows noticeable differences, good agreement is found between the two modelling strategies in terms of drag force.

• 대한한의학원전학회지
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• 제10권
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• pp.450-493
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• 1997

Three-yum and three-yang(三陰三陽) is the change state of yum-yang(陰陽) which is caused by six gi(六氣). They mean the flow of six gi(六氣) which exist throughout the viscera, the channel(經絡), and the skin. But it is not easy to understand the meaning because the contents of the attribute of three-yum and three-yang(三陰三陽), the bolt-leaf-hanges(關闔樞) theory and large or small of gi-blood(氣血多少) which is the main clue that explain it in ${\ll}$Somun(素問)${\gg}$ and ${\ll}$Yeongchu(靈樞)${\gg}$ don't coincide with each other. I, the writer, tried to understand the uncertain meaning and the contents which are written about three points above differently in each of the books that are ${\ll}$Somun(素問)${\gg}$ and ${\ll}$Yeongchu(靈樞)${\gg}$. So, from that the course that the book, ${\ll}$Huangjenegeong(黃帝內經)${\gg}$ is handed down is so relatively simple in a wood block-printed book, that the ${\ll}$Huangjenegeongtaeso(黃帝內經太素)${\gg}$ has less wong-words than the Somun(素問) and the Yeongchu(靈樞), and from that Yangshangsun(楊上善) wrote the note in the ${\ll}$Huangjenegeongtaeso(黃帝內經太素)${\gg}$ by royal order about 100 years former than Wangbing(王氷), as making projects of Yangshangsun(楊上善)'s note and the original of the ${\ll}$Huangjenegeongtaeso(黃帝內經太素)${\gg}$ which has relation to the yum-yang(陰陽) attribute of three-yum and three-yang(三陰三陽), the bolt-leaf-hanges(關闔樞) theory, and the large or small of gi-blood(氣血多少) and researching the Yangshangsun(楊上善)'s theory. The result is summarized like this. First, wherease the order of the change of three-yum and three-yang(三陰三陽) which is explained by Yangshangsun(楊上善) consider the change of yangi(陽氣) in body most important, the order of the change gaeggi(客氣)'s three-yum and three-yang(三陰三陽) considers chungi(天氣) most important, and the order of jugi(主氣)'s three-yum and three-yang(三陰三陽) considers jigi(地氣)'s change of ohaeng(五行) most important. If the order of change three-yum and three-yang(三陰三陽) in the ${\ll}$Huangjenegeongtaeso(黃帝內經太素)${\gg}$ is considered, each of taeyang(太陽) and soyum(少陰) are expressed as the base of yum-yang(陰陽) and yangmeong(陽明) and taeyum(太陰) are expressed as the palmy days of yum-yang(陰陽), soyang(少陽) and gyolyum(厥陰) are expressed as pacemaker(樞杻) which controls the change of yum-yang(陰陽). Thus, each has something in common that is fettered by the inside and outside. In the flow of channel(經絡), taeyang(太陽) and soyum(少陰) take charge of the behind of body, yangmeong(陽明) and taeyum(太陰) take charge of the front of body and soyang(少陽) and gyolyum(厥陰) take of the side of body. Second, in Yangshangsun(楊上善)'s bolt-leaf-hanges(關闔樞) theory, three-yum(三陰) is regarded as inside, three-yang(三陽) as outside, so when bolt, leaf and hanges fulfil their duties in inside and outside, the life(life force) is thought to be revealed normally. It is impossible to understand the bolt-leaf-hanges with the conception of the inside and outside which divide three-yum and three-yang(三陰三陽) into taeyang-soyum(太陽-少陰), yangmeong-taeyum(陽明-太陰), soyang-gyolyum(少陽-厥陰) according to yum-yang(陰陽) attribute, hence it need the special conception that is taeyang(太陽)-taeyum(太陰), yangmeong(陽明)-gyolyum(厥陰), soyang(少陽)-soyum(少陰) which center on their duties in inside and outside. In the denunciation of the word open(開) and bolt(關), because Yangshangsun(楊上善) said that the duities of taeyang(太陽) and taeyum(太陰) are shutter(閉禁), bolt(關) is coincided with that significance. Third, with explaining the large or small of gi-blood(氣血多少) of three-yum and three-yang(三陰三陽), Yangshangsun(楊上善) expressed the inside and outside either in the same way or differently. Because the inside and outside is interior of body and exterior of body, it is the explanation that is noticed by the fact that the property of large or small of gi-blood(氣血多少) is either able to be same or different. In this viewpoint, if we unite the contents about large or small of gi-blood(氣血多少) of ${\ll}$Somun(素問)${\gg}$, ${\ll}$Yeongchu(靈樞)${\gg}$, we will find that the descriptions of large or small of gi-blood(氣血多少) of three-yang(三陽) in ${\ll}$Somun(素問)${\gg}$ ${\ll}$Yeongchu(靈樞)${\gg}$ correspond with the ${\ll}$Huangjenegeongtaeso(黃帝內經太素)${\gg}$, but in three-yum(三陰), the contrary presentations exit. The reason is that large or small of gi-blood(氣血多少) of three-yum(三陰) isn't only expressed as che(體) in the point of che-yong(體用), but as a point of yong(用) that is a phenomenon. As researching the original of ${\ll}$Huangjenegeongtaeso(黃帝內經太素)${\gg}$ and Yangshangsun(楊上善)'s notes as a center about three problems that are yum-yang(陰陽) attribute, the bolt-leaf-hanges(關闔樞) and large or small of gi-blood(氣血多少) of three-yum and three-yang(三陰三陽), I, the writer, tried to explain the part which is written differently or has uncertain conception in the book ${\ll}$Somun(素問)${\gg}$ and the book ${\ll}$Yeongchu(靈樞)${\gg}$, but the concrete result of the work like this will be judged according to the question how many theories are correspondent with real presence at a sickbed. Hence, the work to veryfy the theories in the future will be left as assignment.

• 한국추진공학회지
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• 제13권3호
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• pp.41-49
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• 2009

본 논문은 공기흡입식 추진기관의 고체 로켓 부스터 분리에 관한 수학적 모델링과 시뮬레이션 기법을 기술하였다. 비행체 및 부스터는 하나의 다물체(multi-body)로 고려하였고 부스터는 단지 비행체의 축 방향으로 움직이는 것으로 가정하였다. 비행체 및 부스터의 동적 운동은 Kane 방법에 의해 모델링 되었다. 다양한 부스터 위치에 따라 전체 시스템에 작용하는 공력은 DATCOM 소프트웨어를 사용하여 산출되었으며 부스터 분리 유효 작용면에 작용하는 내부 분리 압력은 일반적인 기체역학 및 Taylor-MacColl 관계식에 의해 산출되었다. 수치적 해석은 Mathworks사의 Matlab이 사용되었다. 해석 결과에 의하면 부스터 분리 동안 마하수 및 받음각 변화 등은 크지 않는 것으로 나타났으며, 실제 시험 장치를 이용한 부스터 분리 시험이 진행될 경우 자세 각 변화, 흡입 유동 특성 등은 무시할 만한 수치임을 확인할 수 있었다.