• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.440-444
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• 2017

Two-dimensional hydrodynamic analysis was performed to analyze the attenuating characteristics of shock waves generated by the detonation of the bulkhead initiator. Through the interlocking analysis between HNS and HMX stacking initiator and STS bulkhead, we have precisely simulated detonation growth and pressure wave attenuation phenomena. The free surface velocity at the surface of the bulkhead was measured for quantitative comparison with the test data by VISAR. As a result, it was confirmed that the pressure attenuating pattern of the shock wave exponentially decreased according to the bulkhead thickness. The observed inflection point at the particle velocity measured over time is due to the subsequent propagation of the shock wave due to the rapid spallation of the interface between the detonator and the bulkhead.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.05b
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• pp.15-18
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• 2004

피뢰기에 뇌 또는 이상전압과 같은 정격이상의 고장전류가 유입되어 발생하게 되는 순간적인 열 충격과 내부압력 상승은 폭탄이 내부에서 터지는 것과 같은 엄청난 양의 충격에너지이다. 본 연구에 있어서 폴리머 피뢰기의 제조에 사용된 모듈용 브레이드 복합재료는 압력해소 및 폭발 비산하지 않도록 하는 기능을 수행하도록 설계되어있다. 기존의 폴리머 피뢰기에 적용된 복합재료보다 충격에너지를 흡수하는 구조물에 유리한 브레이드 복합재료를 피뢰기 모듈의 제조에 도입한 것은 매우 의미 있는 일이라 판단된다. 따라서 본 연구에서는 열경화성 브레이드 복합재료를 제조하기 위하여 프리폼을 먼저 제작한 다음 금형에 삽입한 후 진공상태에서 수지를 주입하여 경화시키는 RTM공법을 이용하였다. 본 연구의 목적은 브레이드 패턴 및 방압개소 설계 등의 기초적인 자료조사 및 실험을 통하여 폴리머 피뢰기의 폭발 비산을 방지할 수 있는 압력해소 성능을 위한 기초 자료를 확보하고자 하는 것이다. 브레이드 복합재료의 기본적인 경화거동을 등온 및 동적 DSC를 이용하여 고찰하였고, 기본적인 전기적 특성을 평가하였으며, 방압개소를 가진 폴리머 피뢰기 모듈의 고장전류시험시 예상되는 열 충격에 대한 성능을 검증하기 위하여 열팽창계수를 측정하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.1
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• pp.129-135
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• 2003

Optical fiber has many advantages, such as high reliability, long lifetime, immunity to the electromagnetic interference, high speed response and low cost. In this study, we proposed and developed an optical fiber impact and pressure sensor for prevention of accident which occurs in the automatic system or auto door. The principle of the sensor is to detect different optical intensity caused by variation of a speckle pattern due to the external perturbation. Speckle pattern appears at the end of a multimode fiber in which coherent beam propagates. The fabricated sensor in this study was tested. As a result of experiments, amplitude of the output signal isn't linear, but it has sufficient sensitivity for a sensor. Moreover, we can control sensitivity of the sensor by an amplifier at receiver. It has several advantages which are ability of detection at all point on the multimode fiber, large sensitive area, and many application areas for a sensing impact and pressure.

• Journal of Ocean Engineering and Technology
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• v.24 no.6
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• pp.30-33
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• 2010

This study presents the effect of filling ratio on sloshing impact pressure. The experiment was done with three filling ratios of 20%, 70%, and 95% of the tank height. The input of the motion was regular excitation. The total number of sensors in use were 53. They were installed on tank top and tank wall. The maximum pressures and the average of one third highest impact pressures for the whole pressure sensors were investigated. The result shows clearly the location of sensors which are exposed to the high impact pressures for different filling ratios. The characteristics of the impact patterns for three filling ratios were also examined.

• Proceedings of the KSEE Conference
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• 2008.10a
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• pp.17-28
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• 2008

국책사업이나 SOC의 확충을 위한 도로 및 철도의 건설에서 적용되는 터널의 단면크기를 보면, $50m^2$에서부터 $100m^2$이상의 중 대단면 터널이 주를 이루고 있으나, 전력구, 통신구, 소규모로 운영되는 광산의 채광용 터널, 용수를 위한 도수로터널 등 특수한 용도로 설계, 시공되고 있는 터널에서는 $20m^2$이하의 단면크기를 갖는 경우가 있다. 이러한 소단면 터널의 경우에는 협소한 작업공간으로 인하여 적용공법 뿐만 아니라 장비의 사용 또한 제약을 받게 되어 작업효율이 저하되고 공사기간이 늘어나게 되는 등 여러 가지 문제점을 안고 있다. 특히, 에멀젼 폭약을 사용하는 발파에서 먼저 기폭된 발파공의 충격압력에 의해 인접공의 폭약이 예비압축(Precompression)되어 사압현상을 일으키고 잔류약을 발생시키는 사례가 종종 발생하고 있다. 사압현상은 당해 발파의 실패와 함께 2차적인 사고의 위험요인이 될 수 있으므로 이를 방지하기 위한 대책을 수립하여야 한다. 이를 위해 기존 문헌을 통하여 사압현상의 원인과 발생 가능성을 검토하였고, 국내에서 주로 사용되는 에멀전폭약의 수중 내충격성시험과 충격압력 전달시험을 실시하여 사압현상의 발생정도를 측정하였으며, 사압현상이 발생한 소단면 터널현장을 대상으로 대책을 수립하여 적용하였다. 심발방법을 변경하여 전단의 충격압력을 견딜 수 있는 공간격을 확보하고 뇌관의 초시간격을 적절하게 배치한 발파패턴을 적용한결과, 사압현상을 억제하고 잔류약의 발생을 감소시켜 계획 굴진장을 확보하고 파쇄석의 크기를 감소시키는 등 양호한 결과를 얻을 수 있었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.7
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• pp.26-31
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• 2003

In this paper, supersonic jets impinging on axisymmetric cone were investigated to obtain fundamental design data for jet deflector case of example being VTOL/STOL or rocket launch. It was of interest to study flow phenomena such as shock interactions and separation induced by shear layer. Experiments were conducted to obtain schlieren flow visualization and measurement of surface pressure. Numerical results are compared with the experimental result. The dominant feature of the flow is the shock pattern induced by the interaction between the cone shock and the barrel shock. This pattern can take a wide variety of forms depending on the structure of the free jet and strongly influences the form of the surface pressure distributions.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.1
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• pp.8-15
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• 2004

Supersonic jets impinging on $60^{\cire}$ wedge were investigated to obtain fundamental design data for jet deflector It was of interest to study flow phenomena such as shock interaction and separation induced by shear layer. Experiments using supersonic cold flow system were conducted for Schlieren flow visualization and measurement of surface pressure. Numerical results were compared with the experimental results. The major parameters are underexpansion ratio, distance from nozzle to apex and design Mach number. Flow conditions were obtained for the wedge shock to attach on or detach from the wedge. The dominant feature of flow-field is shock pattern induced by the Interaction between the wedge shock and the barrel shock.

• Korea Trade Review
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• v.48 no.3
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• pp.69-88
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• 2023

This study analyzes the dynamic characteristics of cargo volume (demand), ship fleet (supply), and freight rate (price) of container, dry bulk, and tanker shipping markets by using the VAR and VECM models. This analysis is expected to enhance the statistical understanding of market dynamics, which is perceived by the actual experiences of market participants. The common statistical patterns, which are all shown in the three shipping markets, are as follows: 1) The Granger-causality test reveals that the past increase of fleet variable induces the present decrease of freight rate variable. 2) The impulse-response analysis shows that cargo shock increases the freight rate but fleet shock decreases the freight rate. 3) Among the three cargo, fleet, and freight rate shocks, the freight rate shock is overwhelmingly largest. 4) The comparison of adjR² reveals that the fleet variable is most explained by the endogenous variables, i.e., cargo, fleet, and freight rate in each of shipping markets. 5) The estimation of co-integrating vectors shows that the increase of cargo increases the freight rate but the increase of fleet decreases the freight rate. 6) The estimation of adjustment speed demonstrates that the past-period positive deviation from the long-run equilibrium freight rate induces the decrease of present freight rate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.29-36
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• 2004

Supersonic inlet buzz can be defined as unstable subcritical operation associated with fluctuating internal pressures and a shock pattern oscillating about the inlet entrance. The flow pulsations could result in flameout in the combustor or even structural damage to the engine. An experimental study was conducted to investigate the phenomenon of supersonic inlet buzz on axisymmetric, external-compression inlet. An inlet model with a cowl lip diameter of 30mm was tested at a free stream Mach number of 2.0. Subcritical instability was investigated by considering the frequency of pressure pulsation and shock wave structure at the inlet entrance. The results obtained show that total pressure recovery ratios were varied from 0.42 to 0.78, and capture area ratio from 0.34 to 0.98. The frequency of the subcritical flow increased with decrease in capture area ratios. Frequency was measured at $224{\sim}240Hz$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.985-991
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• 2010

The objective of this work was to investigate the pintle-tip shape effect on nozzle flow and thrust by cold flow test. When nozzle throat area was decreased by pintle movement, chamber pressure was increased monotonously but thrust was increased differently according to every pintle-tip shape. At the same chamber pressure and nozzle throat area, thrust of convex pintle-tip shape was mostly larger than that of concave one. Nozzle wall pressure distribution and magnitude of pintle-tip load depended on the pintle-tip shape, pintle position and nozzle throat area.