• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.197-205
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• 2015

Offshore structures for the gas production are exposed to the risk of gas leaks, and gas explosions can result in fatal damages to the primary structures as well as secondary structures. To minimize the damage from the critical accidents, the study of the dynamic response of structural members subjected to blast loads must be conducted. Furthermore, structural dynamic analysis has to be performed considering relationships between the natural frequency of structural members and time duration of the explosion loading because the explosion pressure tends to increase and dissipate within an extremely short time. In this paper, the numerical model based on time history data were proposed considering the negative phase pressure in which considerable negative phase pressures were observed in CFD analyses of gas explosions. The undamped single degree of freedom(SDOF) model was used to characterize the dynamic response under the blast loading. A blast wall of FPSO topside was considered as an essential structure in which the wall prevents explosion pressures from the process area to utility and working areas. From linear/nonlinear transient analyses using LS-DYNA, it was observed that dynamic responses of structures were influenced by significantly the negative time duration.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.4
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• pp.87-94
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• 1999

Empirical design is still used to avoid a structural damage because impact phenomenon and structural behaviour due to wave impact load can not examined accurately. The damage due to wave impact load is largely affected by impact pressure impulse and impact load area. The objective of this study is, as the second step, to develop an efficient scantling program of bow flare structure, and to predict its impact load area by comparing maximum dented deformations at center of idealized panel structure model of bow flare structure of 300k DWT VLCC using LS/DYNA3D code, which will be used for its verification of dynamic structural analysis, as the next step. Through this study, the impact load area was estimated as $1.5s{\times}1.5s$ stiffener space(s) in the case of panel with stiffeners and as $2.5s{\times}2.5s$, with stringers, under impact pressure curve with peak height 6.5MPa, tail height 1.0MPa, and duration time 5.0msec.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.50.2-50.2
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• 2011

자동차용 CNG 연료탱크의 복합재료 중앙부 표면에 150 kHz 공진형 음향방출센서를 부착하고, 물을 매질로 하여 용기의 내압을 단계적으로 상승시켜 가면서 각 단계에서 일정시간 압력을 유지시키고 그 때 발생하는 음향방출신호를 획득하였다. 이 때 획득한 음향방출신호의 amplitude, count, duration 및 risetime 등과 같은 음향방출 변수들의 분포를 살펴본 결과 복합재료 압력용기의 손상메커니즘을 추정하고 손상정도를 평가하는데 유용하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.10a
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• pp.9-9
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• 1999

액체로켓 엔진의 분사기와 연소실 설계에 사용될 재생냉각형 칼로리미터의 냉각유로를 설계하였다. 사용할 펌프의 수두는 5기압이며 이로써 끓는점 아래에서 작동할 수 있고 동시에 넓은 냉각 면적을 가지는 유로의 형상을 결정하였다. 유로에서의 압력강하와 온도분포는 전산유동해석에 의하여 구하였고 열부하는 기존의 연소 해석과 1차원해석에 의한 결과를 적용하였다. 해석결과로서 유로의 폭이 4mm에서 2.5mm까지 2단계로 줄었다가 다시 2단계로 늘어나는 냉각유로를 설계하였으며 이 때 높이는 2mm로 일정하게 유지하였다. 유량 변화에 의한 레이놀즈 수는 1.9$\times$$10^4$, 2.4$\times$$10^4$, 2.9$\times$$10^4$이며 세 경우 모두 주어진 펌프수두 이내의 압력강하를 보였으나 온도상승과 성능상의 여유를 고려하여 레이놀즈 수 2.4$\times$$10^4$인 경우를 최종 설계안으로 결정하였다.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.4
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• pp.77-86
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• 1999

The bow flare structure of a ship is designed considering wave impact loads largely caused by relative motion of the ship and wave at rough sea. Empirical design is still used because impact phenomenon and structural behaviour due to wave impact load can not examined accurately. The objective of this study is, as the first step, to predict wave impact loads giving the structural damages to the bow flare structure from the damage data inversely, using dynamic nonlinear finite element code LS/DYNA3D, and to perform various parametric studies of wave impact pressure curve for its characteristics, such as peak height, duration time, tail height, rise time, etc.. The followings were obtained from this study: Dynamic structural responses against wave impact loads are largely affected by impact pressure impulse whose amount during duration time until peak deformation is very important.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5366-5370
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• 2013

For a easier bolt molding, an extrusion process, the 2nd step of the molding process, was moved to step 4, and the bolt head section was exclusively molded in steps 2 and 3. As a result, the molding process was made easier thanks to the minor modification, and the contact pressure decreased in step 1 and increased in step 2 over its earlier intensity. Also, the maximum effective stress, effective strain, and molding force were all increased in both steps 1 and 2.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.1
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• pp.99-110
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• 2000

The damages due to wave impact loads are largely affected by impact pressure impulse and impact load area. The objective of this study is, as the third step, to perform dynamic structural analysis of bow flare structure of 300,000 DWT VLCC using LS/DYNA3D code, and to verify its dynamic structural behaviors. The impact load areas of stiffener space $1.5s{\times}1.5s$ and $2.5s{\times}2.5s$ are applied to bow flare structure part with relatively flexible stiffeners, and with stiff members such as stringers, webs etc., respectively, under the wave impact load with peak height 6.5MPa, tail 1.0MPa, and duration time 5.0msec. Through the dynamic structural analysis in this study, it might be thought that the structural strength of bow flare structure is generally sufficient for these wave impact load and areas, except that large damages were found at bow flare structure area with flexible wide span stiffeners.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.187-195
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• 2015

The gas explosions in offshore installations are known to be very severe according to its geometry and environmental conditions such as leak locations and wind directions, and a dynamic response of structures due to blast loads depends on the load profile. Therefore, a parametric study has to be conducted to investigate the effects of the dynamic response of structural members subjected to various types of load shapes. To do so, a series of CFD analyses was performed using a full-scale FPSO topside model including detail parts of pipes and equipments, and the time history data of the blast loads at monitor points and panels were obtained by the analyses. In this paper, we focus on a structural dynamic response subjected to blast loads changing the magnitude of positive/negative phase pressure and time duration. From the results of linear/nonlinear transient analyses using single degree of freedom(SDOF) and multi-degree-of freedom(MDOF) systems, it was observed that dynamic responses of structures were significantly influenced by the magnitude of positive and negative phase pressures and negative time duration.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.1
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• pp.30-38
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• 1993

In this study, the combustion characteristics in a pre-combustion chamber diesel engine was investigated with experimental conditions of marine engine load. The heat release analysis used was a single-zone single-chamber thermodynamic analysis based on pre-combustion chamber pressure-time data. Based on the results of this investigation, the following conclusions were reached: 1) Increasing the load, peak pressure was increased and position of P sub(max) was retarded in crank angle degrees. 2) Ignition delay time was almost constant without relating to the load and the heat values to form a combusitible mixture were decreased apparently with increasing the load. 3) In premixed-combustion mode, the pattern of heat release rate was resembled without relating to the load and premixed-combustion time was shortened with increasing the load. 4) Increasing the load, mass of premixed-burned fuel was increased slightly, but was invariable beyond a certain fuel-air ratio. 5) Increasing the load, premixed-burned fraction was decreased.

• Clean Technology
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• v.15 no.2
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• pp.75-80
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• 2009

In order to separate oxygen from air, the effects of feed gas flow rate and rinse gas flow rate on the product purity and flow were examined using 2 bed PSA with 4 step cycle. The addition of product pressurization step increased the product purity and flow rate. The addition of pressure equalization increased the product flow rate. The test product was manufactured and the purity and flow rate of product oxygen was examined. The results were compared with the commercial medical oxygen generator of 5 ${\ell}/min$ and 90% oxygen purity.