• Journal of the Society of Naval Architects of Korea
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• v.57 no.4
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• pp.213-220
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• 2020

In the present paper, implosion responses of two adjacent cylindrical tubes under external hydrostatic pressure were experimentally investigated. The cylinder models were fabricated of aluminium alloy 6061-T6 commercial tubes. In the experiment, a pair of two-cylinders were placed inside of a support frame in a medium-size pressure chamber, whose design pressure was 6.0MPa. The distance between the two-cylinders was 30 millimeter measured from outer shell at the mid-length. The implosion tests were performed with water and compressed nitrogen gas as the pressurizing media. The ambient static pressure of the chamber and local dynamic pressure near the two-imploded models were measured simultaneously. It was found that the energy released during an implosion from the first, weaker cylinder triggered the instability of the second, stronger cylinders. In other words, the resulting shock wave of the first implosive impact from the weaker cylinder could cause the premature failure of the neighboring stronger cylinders. The non-contact implosion phenomena from the two-cylindrical tube were clearly observed.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.4
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• pp.198-206
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• 2020

In this study, the dynamic structural behavior of pressure vessels due to pressure pulse initiated by implosion of neighbouring airbacked equipments including Unmanned Underwater Vehicles (UUV), sensor system, and so on were dealt with for the structural design and safety assessment of pressure hulls of submarine. The dynamic buckling and collapse responses of pressure vessel in deep sea were investigated considering the effects of initial hydrostatic pressure and fluid-structure interactions. The governing equations for circular cylindrical shells were formulated theoretically assuming a relatively simple displacement fields and the derived nonlinear simultaneous ordinary differential equations were analysed by developed numerical solution algorithm. Finally, the introduced safety assessment procedures for the dynamic buckling behaviors of pressure hulls due to implosion pressure pulse were validated by comparing the theoretical analysis results with those of experiments for examples of simple cylinders.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.1
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• pp.8-14
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• 2020

The implosion phenomena of pressure vessels operating in deep water under extremely high external pressure have been well known. The drastic energy release to ambient field in the form of pressure pulse is accompanied with catastrophic collapse of shell structure. Such a proximity shock wave could be a serious threat to the structural integrity of adjacent submerged body and several suspected accidents have been reported. In this study, basic research for the occurrence and development of shock wave due to implosion was carried out. The mechanism of pressure pulse generation and energy dissipation were investigated, and a simplified kinematic model to approximate the collapse modes of circular tubes which can be generated by external pressure and implosion was examined. Using the simplified kinematic model, the process of energy dissipation was formulated, and the magnitude of released pressure shock wave was estimated quantitatively. To investigate the validity of developed kinematic model and shock wave estimation process, the results from a nonlinear FE analysis code and collapse test carried out using pressure chamber were compared with the results from the developed kinematic model.

• Journal of KIISE:Information Networking
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• v.27 no.1
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• pp.58-67
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• 2000

The paper presents a representative-based feedback mechanism and rate adaptation policy for congestion control in multicast traffic for multimedia applications. In multicast congestion control, feedback implosion occurs as many receivers send feedback to a sender. We propose to use representatives to avoid the feedback implosion. In our scheme, receivers feedback packet loss information periodically and a sender adapts the sending rate based on the information collected through a hierarchy of representatives. A representative is selected in each region and roles as a filter to decrease the number of feedbacks. The simulation results show that the proposed scheme solves the feedback implosion problem and well adapts in a congested situation.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.11b
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• pp.1659-1662
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• 2002

SRM[1][2]은 ALF(application level framing)과 LWS(light-weight session)을 위한 신뢰성 있는 멀티캐스트 구조로써 송신자가 아닌 수신자들이 오류가 발생하였는지를 검사하고, 오류가 발생했을 때, NACK 메시지를 전송하여 패킷 손실 복구를 요청한다. 그러나 다수의 수신자들이 송신자에게 패킷의 손실 복구를 요청하게 되면 NACK 폭주(NACK implosion)가 발생한다. 이 논문에서는 NACK 과부하 문제는 해결하기 위해서 수신자가 송신자에서 자신까지의 거리와 request 타이머 인자 값에 의해서 정해지는 구간에서 선택된 임의의 시간동안 기다리는 request 타이머를 개선하여 노드마다 카운터를 주어 안정적인 네트워크에서의 흐름일 경우는 그 구간을 짧게 하고, 반대로 불안정적인 네트워크 일 경우에는 구간을 길게 하여 가변적인 네트워크에 효율적으로 NACK를 억제하는 방법을 제시한다.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.1
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• pp.58-71
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• 2009

The blast wave released during the initiation of energetic materials gives rise to pulse energy generation, characterized by a sudden increase of potential energy. A highly efficient energy source, sought from pulse-type lasers, may be utilized in various space propulsion and power applications. This paper introduces a scheme of utilizing the laser energy in 1) attitude control of a satellite requiring of a low thrust, 2) innovative laser-induced drug delivery, 3) implosion-based micro piston development, 4) deflecting and zapping of space debris for laser kill purpose, and 5) finally lunar detection using laser induced breakdown spectroscopy.

• Journal of computational fluids engineering
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• v.14 no.3
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• pp.76-85
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• 2009

The shock wave is deformed and the vortex is elongated simultaneously during the shock-vortex interaction. More precisely, the shock wave is deformed to a S-shape, consisting of a leading shock and a lagging shock by which the corresponding local vortex flows are accelerated and decelerated, respectively: the vortex flow swept by the leading shock is locally expanded and the one behind the lagging shock is locally compressed. As the leading shock escapes the vortex in the order of microseconds, the expanded flow region is quickly changed to a compression region due to the implosion effect. An induced shock is developed here and propagated against the vortex flow. This happens for a strong vortex because the tangential flow velocity of the vortex core is high enough to make the induced-shock wave speed supersonic relative to the vortex flow. For a weak shock, the vortex is basically subsonic and the induced shock wave is absent. For a vortex of intermediate strength, an induced shock wave is developed in the supersonic region but dissipated prematurely in the subsonic region. We have expounded these three shock-vortex interaction patterns that depend on the vortex flow regime using a third-order ENO method and numerical shadowgraphs.

• Journal of KIISE:Information Networking
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• v.27 no.3
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• pp.360-369
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• 2000

통신의 규모가 사용자 수와 지리적 범위 두 가지 측면에서 커짐에 따라 신뢰적인 멀티캐스트 프로토콜의 implosion 및 exposure 문제는 더욱 심각해진다. 본 논문은 트리 기반 신뢰적 멀티캐스트를 위한 효율적이고 확장성 있는 손실 복구 기법을 제안한다. 먼저 에러 비트맵 정보를 통하여 멀티캐스트 라우팅 트리와 유시한 논리적 트리를 구성함으로써 멀티캐스트 라우팅 트리에서 상위에 위치하는 수신자들이 재전송을 요청한 수신자의 신뢰성을 책임지도록 하고 또한 효율적인 복구를 위해 구성된 트리 상에 독립된 멀티캐스트 주소를 가지는 지역 그룹을 형성한다. 논리적 트리는 세션 멤버쉽이나 멀티캐스트 경로의 변화에 따라 적응적으로 재구성되는데 이는 멀티캐스트 세션의 진행 동안 논리적 트리와 멀티캐스트 라우팅 트리 사이에 불일치를 최소화함으로써 멤버쉽과 경로가 변하는 상황에서도 implosion과 exposure를 감소시키는 강점을 지닌다. 제안한 기법과 정적 트리기반의 신뢰적 멀티캐스트 프로토콜과의 시뮬레이션을 통한 비교는 세션의 크기가 증가할수록 제안한 적응형 트리 기반의 복구방식이 더욱 효율적임을 보여준다.

• Explosives and Blasting
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• v.27 no.1
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• pp.62-78
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• 2009

Recently, construction techniques have been rapidly developed with reconstruction of old buildings, urban regeneration and efforts of restoring natural ecology, so demolition of deteriorated buildings has been rapidly increasing. Demolition work of building should be executed without damaging surrounding environments according to relevant regulations. There are various demolition methods and among them, explosives demolition is the most practical way for expenses and safety of work. As a part of Daejeon stream ecological restoration project, this thesis is a case of executing demolition of Chung-Ang Department Store which was built 35 years ago as covered structure on the upper part of Daejeon stream with explosives demolition. This structure is 8 stories high, total height of 41.6 m including basement floor, $1,650m^2$ for building area and $18,351m^2$ for total floor area. It is located in the center of Daejeon city where shopping centers and buildings are crowded and main facilities are Daejeon subway (18m), backside shopping center (20m), underground shopping center(15m), Mokchuk bridge, Eunjung bridge(0.25m) and fiber-optic cable(0.25m). In this project, implosion was selected for explosives demolition methods by considering this area being a busy urban area, and this project was executed after examining collapse movement of structure in advance using simulation program not to damage main facilities. Total 80kg of explosives and 1,000 detonators were being used. This project will be a good case of executing explosives demolition successfully by applying implosion on urban area in the country.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.9-11
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• 2006

Visualization has played an essential role in the development of our understanding of the complex unsteady flows associated with the initiation, propagation, and extinction of detonation waves. These methods and application to various aspects of detonation are illustrated by results obtained in my laboratory, particularly using combinations of the PLIF technique with other methods. Examples shown will include detonation initiation by projectiles, diffraction over ramps and steps, diffraction out of tubes, detonation implosion, and the cellular structure of detonation waves.