• 대한기계학회논문집B
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• 제39권12호
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• pp.913-919
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• 2015

초공동 수중비행체는 수중에서 시속 300 km 이상의 속력을 가진다. 초공동 수중비행체는 로켓추진을 동력으로 사용하기 때문에 초공동 수중비행체의 수치해석은 물과 수증기, 배기가스로 이루어진다상 유동을 다루게 된다. 배기가스가 수중비행체에 미치는 영향은 초공동 수중 비행체 성능연구에 중요한 부분이다. 본 연구에서는 초공동 수중비행체 주변의 유동장에 대한 수치해석을 통하여 배기가스가 비행체의 항력에 어떠한 영향을 미치는지 알아보았다. 배기가스가 없는 경우, 수중비행체를 둘러싼 초공동으로 물이 유입되는 재유입현상에 의해 수중비행체 항력의 변화가 발생한다. 추진체가 있는 경우 배출되는 가스는 재유입현상에 의한 영향을 감소시킨다. 또한 배기가스는 마하디스크를 생성하며 그 영향을 받아 항력 변화가 발생한다.

• 한국해양공학회지
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• 제10권1호
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• pp.75-80
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• 1996

The importance of the impact force on the vertical offshore circular structure member in the surf zone due to the breaking wave has been recognized recently. In this paper characteristics of breaking wave forces and the corresponding estimation procedures for them are investigated. For the characterization of the wave forces, three parts, drag force, inertia force, impact force are categorized and identified, respectively. Among them the impact force is maimly studied and the concise form of the force is proposed with the application scheme for the design of offshore circular structure member. The resulting form porposed here for impact force is well coincided with former research results by other people. Except the impact force, so called Morison equation can be employed for the common offshore structure design. The drag force and inertia force are represented as convertionally for the profile except the breaking part. In the numerical example, for thpical sea condition and the member size, the proposed procedures for the breaking wave forces calculation are demonstrated. It is found that the impact force is the most deminant one comparing with inertia and drag forces in the surf zone.

• 한국해양공학회지
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• 제23권1호
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• pp.48-53
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• 2009

Autonomous Underwater Vehicles (AUV's) provide an important means for collecting detailed scientific information from the ocean depths. The hull resistance of an AUV is an important factor in determining the power requirements and range of the vehicle. This paper describes a design method that uses Computational Fluid Dynamics (CFD) to determine the hull resistance of an AUV under development. The CFD results reveal the distribution of the hydrodynamic values (velocity, pressure, etc.) of an AUV with a ducted propeller. This paper also discusses the optimization of the AUV hull profile to reduce the total resistance. This paper demonstrates that shape optimization in a conceptual design is possible by using a commercial CFD package. Optimum design work to minimize the drag force of an AUV was carried out, for a given object function and constraints.

• Journal of Advanced Marine Engineering and Technology
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• 제26권5호
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• pp.596-606
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• 2002

The three-dimensional unsteady compressible Euler equation solver with ALE, CFD code, PAM-FLOW based on FEM method has been applied to analyze the flow field around the high speed train which is entering into a channel. From the present study, the pressure and flow transients were calculated and analyzed. The generation of compression wave was observed ahead of train and the high pressure in the gap between the train and the tunnel was also found due to the blockage effects. It was found that abrupt fluctuation in pressure exists in the region from train nose to shoulder of train corresponding to 10％ of total length of train during tunnel entry. Computed time history of aerodynamic forces of train during tunnel entry show that drag coefficient rapidly rises and saturates at about non-dimensional time 0.31. The total increase of drag coefficient before and after tunnel entry is about 1.1%. Transient profile of lift force shows similar pattern to drag coefficient except abrupt drop after saturation and lift force in the tunnel increases 0.08% more than that before tunnel entry.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.38-42
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• 2004

The optimal design for a leading car considering the aerodynamic resistance is required on the high-speed train due to increasing of ratio of drag force with proportion for the square of velocity. The aerodynamic analysis using CFD in the stage of concept design offers more economical analysis method which is used to estimate the influence of flow and pressure around the leading car than the experimental method using the Mock-up. In this study, we want to assist the artistic design with aerodynamics analysis in order to get the optimal design for leading car made of composite material. The results of aerodynamic analysis for two leading car models, which one is expressed with lineal beauty and the other is with curvaceous beauty, are compared with each other and offer the proposal of modification for two models in order to decrease be drag force. The shape of curvaceous model is better for the pressure force but slightly worse for the viscous force than the other. The Fluent software is used for the calculation of flow profile in this study.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2003년도 추계학술대회 논문집(III)
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• pp.351-357
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• 2003

The optimal design for a leading car considering the aerodynamic resistance is required on the high-speed train due to increasing of ratio of drag force with proportion for the square of velocity. The aerodynamic analysis using CFD in the stage of concept design offers more economical analysis method which is used to estimate the influence of flow and pressure around the leading car than the experimental method using the Mock-up. In this study, we want to assist the artistic design with aerodynamics analysis in order to get the optimal design for leading car with the operation speed at 180km/h. The results of aerodynamic analysis for two leading car models which one is expressed with lineal beauty and the other is with curvaceous beauty are compared with each other and they offer the proposal of modification for two models in order to decrease the drag force. The shape of curvaceous model is better for the pressure force but slightly worse for the viscous force than the other. The Fluent software is used for the calculation of flow profile in this study.

• International Journal of Naval Architecture and Ocean Engineering
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• 제4권1호
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• pp.44-56
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• 2012

Autonomous Underwater Vehicles (AUVs) provide a useful means of collecting detailed oceano-graphic information. The hull resistance of an AUV is an important factor in determining the power requirements and range of the vehicle. This paper describes a procedure using Computational Fluid Dynamics (CFD) for determining the hull resistance of an AUV under development, for a given propeller rotation speed and within a given range of AUV velocities. The CFD analysis results reveal the distribution of the hydrodynamic values (velocity, pressure, etc.) around the AUV hull and its ducted propeller. The paper then proceeds to present a methodology for optimizing the AUV profile in order to reduce the total resistance. This paper demonstrates that shape optimization of conceptual designs is possible using the commercial CFD package contained in Ansys$^{TM}$. The optimum design to minimize the drag force of the AUV was identified for a given object function and a set of constrained design parameters.

• 수산해양기술연구
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• 제30권2호
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• pp.109-115
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• 1994

This paper presents a new concept to reduce turbulent frictional drag by injecting micro-bubble into near the buffer layer of turbulent boundary layer on flat plate. The concentrations of micro bubble distribution in the boundary was calculater by eddy viscosity equations in the governing equations. When near region of the buffer layer of turbulent boundary layer is filled with micro-bulle of air and viscous of the region is kept low, the velocity profile in the near region should be changed substantially. Then the Reynolds stress in the region becomes less, which guide to lower velocity gradient there. It results in reduction of velocity gradient at the viscous sublayer, which gives the reduction of shear stress at the wall.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.71-74
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• 2008

This paper aims at studying the key design elements for the optimal ventilation system design, developing the design models and suggesting the design guidelines. The key elements include the basic exhaust emission rate, wall friction coefficient, vehicle drag coefficient and slip streaming effect, jet fan operating efficiency, natural ventilation force and installation scheme for jet fans and ventilation monitors in tunnel. The design models developed in this study are one-dimensional ventilation simulator to analyze the air flow, pressure profile and pollutant dispersion inside and outside tunnel, expert model to choose the optimal ventilation method, and the ventilation characteristic chart to evaluate the preliminary ventilation system. The study results are reflected in the design guideline for road tunnel ventilation system.

• 한국군사과학기술학회지
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• 제20권2호
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• pp.255-263
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• 2017

An infrared-guided missile has been emerging as a major threat against combat aircraft due to its passive guidance characteristics and with recent advances in stealth technology. Hence, the infrared stealth technology and its effectiveness-evaluation technique become more significant than ever before. In this study, we applied missile aerodynamics to lethal range calculation which allowed more precise prediction. CFD analyses were newly involved in estimating drag force characteristics of an infrared-guided missile. Velocity profiles during flight period of the missile were constructed utilizing these drag characteristics and then incorporated into our in-house code to predict corresponding lethal ranges. The results showed that the present method can predict lethal range more appropriately than the previous one with constant velocity profile. As one of the results, if a fighter gains altitude more which reduces less drag of the attacking missile, then the lethal envelope increases significantly more compared to the lock-on envelope.