• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.1
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• pp.33-39
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• 2015

This paper describes test result of the Supersonic Wing Structure and the utility of thermal test equipment, which is possible to heat rapidly and continuously above $1,000^{\circ}C$, the durability and reliability of which are improved compared with the existing equipment. Through the test, we could predict the amount of strength reduction of the wing due to aerodynamic heating, caused by exposure of high temperature. Recently the aerodynamic heating temperature of the supersonic flying object is rapidly increased. It is possible to carry out the High Temperature Strength Test on the hypersonic speed flying object with the newly designed thermal test equipment. Because of that, we can upgrade the High Temperature Strength Structure Test technique and test reliability.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.437-440
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• 2004

HMS(Hull Mounted Sonar) 운용 시 수중음속구조의 영향에 의한 음파가 경계면(해저면, 해수면)의 반사를 통해서 근거리 음영구역(short range shadow zone)을 발생시킨다(그림 1). 따라서 본 논문에서는 다양한 수중음파탐지 무기체계 가운데 특히 단상태 (monostatic) 조건일 때 HMS에 의해 발생하는 근거리 음영구역을 최소화하는 방안을 연구하였다. 즉, 2차원 수중공간 (수심-거리)에서 빔형성기법 (beamforming)을 이용한 HMS Vertical Scanning (HMS Verscan) 기법을 제안하여 수치 실험을 수행하였다. 수치실험을 위해 HMS 운용환경에 근접한 고주파 음선모델(BELLHOP)과 잔향음 모델(HYREV)을 이용하였다. 그 결과 HMS Verscan 기법은 수평방향의 음파방사에 의해 주로 발생하는 근거리 음영구역으로 해저반사를 통하여 음파를 전달시켰고, 근거리 음영 구역에 숨어있는 표적의 탐지가능성을 높였다. 또한 실제 산란환경을 고려한 수치실험 결과에서도 부분적으로 표적이 탐지가 됨으로써 HMS Verscan 기법의 근거리 음영구역의 감소효과를 확인하였다.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.4
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• pp.12-19
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• 2007

In this study, nonlinear flow-induced vibration(flutter) analyses of a 2-DOF launch vehicle airfoil have been conducted in supersonic and hypersonic flow regimes. Advanced aeroelastic analysis system based on computational fluid dynamics and computational structural dynamics is successfully developed and applied to the present analyses. Nonlinear unsteady aerodynamic analyses considering strong shock wave motions are conducted using inviscid Euler equations. Aeroelastic governing equations for the 2-DOF airfoil system is solved by the coupled integration method with interactive CFD and CSD computation procedures. Typical wedge type airfoil shapes with initial angle-of-attacks are considered to investigate the nonlinear flutter characteristics in supersonic(15). Also, the comparison of detailed aeroelastic responses are practically presented as numerical results.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.303-306
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• 2008

After the successful flight test of X-43A, U.S. Airforce is developing missile-type X-51A SED (Scramjet Engine Demonstrator-Wave Rider). X-51A using PWR (Pratt and Whitney Rocketdyne) X-1 hydrocarbon fueled scramjet engine will have a ground test in 2008 and flight test in 2009. Technologies established though the X-51A program will be transferred to DARPA's Falcon program developing HTV (Hypersonic Test Vehicle)-3X and HCV (Hypersonic Cruise Vehicle). Present paper is an overview of propulsion core technologies of X-51 such as regenerative cooling of engine structures and combustion using liquid/supercritical JP-7 fuel.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.2
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• pp.107-115
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• 2003

Nondestructive testing was carried out in order to evaluate the structural integrity and construction quality of the slurry wall of the underground LNG storage tank. 9 test points were selected, and the wall thickness, rebar spacing, and compressive strength of the slurry wall were evaluated by stress wave impact-resonance method, GPR, sonic velocity, and rebound testing, respectively. As results, the wall thickness, rebar sparing and estimated compressive strength satisfy the design criteria.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.6
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• pp.559-566
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• 2011

This paper presents the flow passage design for a window cooling device, which have a conical poppet valve and an emissive orifice. Computational flow analysis and experiment are conducted according to the poppet strokes. The results show satisfactory flow characteristics that pressure is reduced enough to endure material strength and the flow does not choked inside window. The correction factor of discharge coefficients is found between 2-dimensional analysis and experiments, which is applied to control coolant flow rates of the window cooling device.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.12
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• pp.1057-1064
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• 2014

Recently, there has been a growing interest in sustainable energy. One method that has been used is an organic Rankine cycle using conventional turbine technology with a low-temperature waste heat source. A 200-kW organic Rankine cycle (ORC) system was designed for a waste heat recovery application using R245fa as the working fluid. A radial turbine running at 15,000 rpm was employed to generate more than 200 kW with an expansion ratio of nine. Because an ORC turbine uses a refrigerant as the working fluid, the ideal gas law was not employed to design the turbine. In addition, the complexity of the molecular structure of R245fa made it difficult to design the turbine. Because R245fa has an Ma value of one at a low velocity for the working fluid (about 1/3 of the speed of sound in air) at about $100^{\circ}C$, it easily reaches a supersonic flow condition with a small pressure expansion. To increase the efficiency of the turbine, a dual stage radial-type turbine with a subsonic speed was suggested. This paper will describe the design procedure and performance evaluation of the ORC turbine using R245fa.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.706-713
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• 2007

The jet structure issuing from a conventional convergent nozzle of variable expansion rate is compared with the result from the nozzle of a constant expansion rate using a normal type annular slit. In experiments, to investigate the jet characteristics between the two cases of jet, the mean velocity of nozzle exit is fixed to be 90m/s, the pressures along the jet axis and radial directions are measured by a scanning valve system moving with 3-axis auto-traverse unit, and the velocity distribution obtained by calculation from the measured static and total pressures is compared. Also to obtain the highly stable and convergence jets, it is turned out that the flow through a nozzle of constant expansion rate using the Coanda effect with an annular slit is the most preferable than that case through variable expansion rate nozzle. Furthermore, it is found that the pressure drop along the nozzle for the constant expansion rate nozzle is small relatively against to the case of variable expansion rate nozzle.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.2
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• pp.156-164
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• 2003

STS316L had been used as the structural material for energy environmental facilities, because austenite stainless steels like 316L have superior mechanical properties of which toughness, ductility, corrosion resistant and etc. However, those welded structures are receiving severe damage due to increasing of the aged degradation. Most studies until now have been carried out against fatigue behaviors of weldments, and were not well studied on nondestructive evaluation methods. In this study, the fatigue crack propagation behavior of STS316L weldment usually used for vessels of the nuclear power plant was investigated. Also, the degradation characteristics of 316L stainless steel weldments were evaluated by the ultrasonic parameter such as ultrasonic velocity, attenuation factor and time-frequency analysis. The results of this study can be used as a basic data for the prediction of the fatigue crack life of weldments structures without disjointing or stopping service of structures in service.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.78-86
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• 2000

The objective of this research is to understand the characteristics of a nonpremixed, turbulent, hydrogen jet flame which is stabilized in Mach 1.8 coflowing air flows. In order to investigate the flame structure, flame lengths and fuel trajectories were measured by using direct photography, acetone PLIF, Mie scattering techniques, and numerical simulation. Effect of increasing air velocity was investigated when fuel velocity is fixed. The subsonic flame length was decreased drastically, however the supersonic flame length was increased slowly Then the change of flame blow out characteristics was observed as varying fuel nozzle lip thickness. The flame stability can be increased when fuel nozzle lip thickness was increased, which indicates that the minimum fuel lip thickness ratio is required for the stable supersonic flames. Also, it is found that fuel jet is blocked by high pressure zone and low scattering zone is made. Then the fuel that was moving along the recirculation zone had longer residence time within the supersonic flames, which made partially premixed zone.