• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.12
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• pp.1675-1682
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• 2012

Weight reduction is increasingly being considered very important in light of air pollution and the exhaustion of resources. As a result, many automotive components are being replaced by Al and Mg alloys, and studies are increasingly focusing on the same. However, the use of Mg alloys is limited because they have higher material cost and lower productivity owing to the difficult forming conditions compared with Al alloys. In this study, the tube extrusion process conditions of an automotive bumper back beam were analyzed using FEA. Material tests were performed to determine the properties, and experiments and analyses for a simple shape were performed to define the data for heat generation during plastic deformation. Then, the analyses of the product were carried out by considering various temperatures and ram speeds. The conditions were then established, and a product without surface defects was extruded successfully.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.529-534
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• 2002

유도초음파는 얇은 판재와 다층재료를 평가하는데 널리 사용되는데, 이를 정량적으로 이용하기 위해서는 위상 및 군속도의 분산선도는 필수적이다. 본 연구에서는 후방복사 리키 램파를 이용하여 위상속도 분산곡선과 군속도를 측정하였다. 물에 잠긴 판재에 입사각을 변화 시키면서 판재에서 발생하는 후방복사 초음파 신호를 측정하였고, 후방복사된 초음파 신호는 유도초음파의 분산특성을 지님을 보였다. 입사각도와 수신된 파형의 주파수 분석을 통하여 램파의 위상속도 분산선도를 구하였다. 또한, 특정한 입사각에서 입사점을 변화시키면 서 론 파형의 시간대역 이동으로부터 군속도를 측정하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.1
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• pp.51-56
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• 2007

Flow characteristics in a liquid fuel ramjet combustor were investigated using the PIV method. The combustor has two rectangular inlets that form a $90^{\circ}$ angle each other. Three cases of test combustors are made in which those inlet angles are $30^{\circ},\;45^{\circ}\;and\;60^{\circ}$. The experiments were performed in a water tunnel test with the same Reynolds number as Mach 0.3 at the inlet. PIV software was developed to measure the characteristics of the flow field in the combustor. A large and complex recirculating flow was measured in the dome area with 4 different dome size. Experimental results shows that 1/3 dome size of combustor diameter is suitable and smaller inlet angle provide large recirculation flow at the dome of combustor as a frame holder in this experimental ranges but need to consider secondary recirculation flow in a junction region to optimize the configuration of ramjet combustor.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.6
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• pp.29-34
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• 2006

This study experimentally investigates the characteristics of Lamb wave propagating in a composite plate of varied thickness. In practical aerospace structures, there are so many parts that have varied thickness. Therefore, in order to employ the Lamb wave in a structural health monitoring of those parts, it is necessary to understand correctly the characteristics of Lamb wave for the structure with thickness variation. Thin surface-bonded piezoelectric transducers, which have great potential in integrated monitoring systems for structural health, were used to generate and receive Lamb waves. The predicted propagation velocity under the assumptions of ideal mode conversions was compared with the experimentally measured one. The validity of the results was supported by the frequency analysis of the signals. Consequently, the results show that the transient region is occurred when Lamb waves propagate across the region that thickness variation over some gradient exists.

• 발명특허
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• v.10 no.8 s.114
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• pp.64-64
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• 1985

금성반도체(대표 : 구자두)는 미국, 일본에 이어 세계 3번째로 첨단반도체제품인 CMOS 64K SRAM을 자체개발하는데 성공했다. 국내 최초로 개발된 금성반도체의 CMOS 64K SRAM은 우리나라의 반도체 기술수준을 선진국 수준으로 성큼 다가서게 했다. CMOS 64K SRAM은 NMOS의 256K DRAM에 비해 작동속도가 2배이상 빠를 뿐만 아니라 재충전이 필요없는 완전한 스태틱(static) RAM으로 대용량$\cdot$고속$\cdot$고신뢰성을 요하는 고성능 컴퓨터, 통신장비등 첨단 산업용 기기의 기억장치에 주로 사용된다.

• Proceedings of the Korean Information Science Society Conference
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• 2004.10a
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• pp.688-690
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• 2004

플래시 메모리는 롬(ROM)의 특성과 램(RAM)의 특성, 저전력 등의 이점을 바탕으로 임베디드 시스템의 저장 장치로 많이 사용되고 있다. 그러나 특성상 읽기와 쓰기 연산의 속도가 많이 다르고, 쓰기 연산을 한번 수행한 부분에 다시 쓰기 연산을 하기 위해서는 먼저 지우기 연산을 수행해야 하고, 지울 수 있는 회수도 제한되어 있는 단점을 가지고 있다. 따라서 본 논문에서는 이런 특성들을 고려하여 저장 장치로서 플래시 메모리를 사용할 때 운영교제에서 최적화할 수 있는 부분 중 가상 메모리 시스템의 페이지 프레임 회수 기법을 최적화하여 쓰기와 지우기 연산의 수를 줄일 수 있는 방법을 제시한다.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.271-275
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• 2001

Three dimensional flow characteristics in a liquid fuel ramjet combustor are investigated using PIV method. The combustors have two rectangular inlets that form 90 degree each other. Three guide vane is installed in each rectangular inlet to improve the flow stability. We made three cases of test combustors in which those inlet angles are 30 degree, 45 degree and 60 degree. Each combustor easily changes the size of combustor's recirculation zone with the replacement of combustors dome. The experiments are performed in the water tunnel test with the same Reynolds number in the case of Mach 0.3 at inlet. PIV software is developed to measure the flow field in the combustor and the accuracy of developed PIV program is verified with rotating disk experiment and standard data. The experimental results show that the two main streams from rectangular inlet collide near the plane of symmetry and generate two large longitudinal vortex, A large and complex three-dimensional recirculating flow is measured in the recirculation zone.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.59-63
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• 2005

The experimental study has been conducted to investigate the effect of the recirculation zone on the multi-slot film cooling in the ramjet combustor. The recirculation zone which is generated by the protrusion tip on the entrance of the coolant flow path affects on the first slot. Velocity fields, dimensionless temperature fields and adiabatic film cooling effectiveness on the downstream wall of the slot exit are measured. The results show that the film cooling performance is rapidly decreased after the slot exit by the share layer and high turbulence intensity between separated flows and coolant flows.

• Journal of the Korean Society of Visualization
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• v.3 no.1
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• pp.58-62
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• 2005

Flow characteristics at secondary recirculation zone in a liquid fuel ramjet combustor were investigated using CFD and Stereoscopic PIV method. The combustors have two rectangular inlets that form 90 degree each other. Three guide vanes were installed in each rectangular inlet to improve the flow stability. The tested angle of the air intakes was 60 degree. The experiments were performed in the water tunnel test with the same Reynolds number in the case of Mach 0.3 at inlet. The computational and experimental results showed that the secondary recirculation flow occurred at the front junction of inlet main stream and combustor chamber. The size of secondary recirculation regions are increased with approaching closer to the center of the combustor. Since the performance of combustor is closely dependent not only on the main recirculation in the dome region but also on the secondary recirculation flow in a junction region, the optimal angle of the air intakes should be considered the recirculation size as frame holder.

• Journal of the Korean Society of Combustion
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• v.5 no.1
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• pp.31-41
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• 2000

A numerical study was conducted to investigate the combustion phenomena of regular start and unstart processes based on ISL#s RAMAC 30 experiments with different diluent amounts in a ram accelerator. The initial projectile launching speed was 1800m/s which corresponded to the superdetonative speed of the stoichiometric $H_2/O_2$ mixture diluted with $5CO_2\;or\;4CO_2$. In this study, it was found that neither shock nor viscous heating was sufficient to ignite the mixture at a low speed of 1800m/s, as was found in the experiments using a steel-covered projectile. However, we could succeed in igniting the mixtures by imposing a minimal amount of additional heat to the combustor section and simulate the regular start and unstart processes found in the experiments with an aluminum-covered projectile. The numerical results matched almost exactly to the experimental results. As a result, it was found that the regular start and unstart processes depended on the strength of gas mixture, development of shock-induced combustion wave stabilized by the first separation bubble, and its size and location.