• Journal of Advanced Marine Engineering and Technology
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• 제26권3호
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• pp.328-336
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• 2002

decrease in efficiency due to cavity fluid fluctuation. The purpose of this study is to examine erosion aspect on the SS400 specimen by cavitation and the effect of impact pressure generated from the demolition of the cavity of ultrasonic vibrator horn in the marine sludge oil environment. The erosion damage of specimen was investigated mainly on weight loss, weight loss rate and maximum erosion rate with variation of the vibration amplitude of $50{\mu}m, 24{\mu}m$ as well as the change of space between transducer horn and specimen. The experimental results showed that as the space between ultrasonic vibrator horn and specimen disk increased, the weight loss and weight loss rate decreased and the values were larger in SFO than in SLO. These findings would help interpret the aspect of cavitation erosion damage in metallic materials of different operating environment and material characteristics.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.21-24
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• 2007

This paper deals with introduction of testing equipments for the evaluation of dynamic tensile characteristics of auto-body steel sheets and the crashworthiness of auto-body members. The servo-hydraulic high speed material testing machine was developed for tensile tests at the intermediate strain rate to obtain the tensile material properties at the strain rate under 500/sec. The split Hopkinson bar apparatus using the elastic wave was developed for dynamic material characteristics at the high strain rate ranged from 1,000 to 10,000/sec. The servo-hydraulic high speed crash testing machine is the equipment for the evaluation of the collapse load and crashworthiness of auto-body members. High speed carrying truck crashes to specimen with the maximum velocity of 17 m/sec.

• Journal of Forest and Environmental Science
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• 제10권1호
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• pp.38-48
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• 1994

강원도산(江原道産) 참나무과(科) 4수종(樹種)의 건조특성(乾燥特性)을 파악코져 $100^{\circ}C$에서 급속건조(急速乾燥)를 실시하여 건조중(乾燥中) 함수율(含水率)과 건조경과(乾燥經過), 초기할렬(初期割裂)(목구할렬(목구할렬(木口割裂))과 표면할렬(表面割裂)), 찌그러짐, 내부할렬(內部割裂) 등의 건조결함(乾燥缺陷)을 조사(調査)하여 추정건조(推定乾燥)스케쥴을 작성(作成)한 결과(結果)는 다음과 같다. 건조시간별(乾燥時間別) 건조중(乾燥中) 함수율(含水率)은 초기함수율(初期含水率)이 높은 판재(板材)일수록 급속(急速)한 곡선적(曲線的) 감소(減少)를 나타내었고 건조소요시간(乾燥所要時間)이 길었으며 굴참나무가 건조중(乾燥中) 할렬(割裂)의 발생량(發生量)이 가장 크게 나타났으며 구해진 추정건조(推定乾燥)스케쥴은 $T_5-C_2$였다. 또한 모든 수종(樹種)의 목리방향별(木理方向別) 수축율(收縮率)은 접선방향(接線方向)(T) > 방사방향(放射方向)(R) > 섬유방향(纖維方向)(L)의 순위(順位)였으며 급속건조법(急速乾燥法)에 의한 수축율(收縮率)이 정상적인 수축율(收縮率)보다 크게 나타났다.

• 한국방재안전학회논문집
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• 제11권1호
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• pp.31-38
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• 2018

국내 중소규모 저수지의 99.1%는 흙댐으로, 건설비용이 저렴하여 용이한 시공성을 갖고 있다. 그러나 흙댐은 월류에 취약하기 때문에, 홍수 시 급격한 붕괴 가능성이 있다. 이러한 붕괴가 발생할 경우 급격한 홍수량 증가로 이어지기 때문에, 하류 치수 안전성이 위협 받을 가능성이 크다. 이에 본 연구에서는 흙댐 사면에 포설한 사석의 붕괴 지연효과를 실험을 통해 검토하였다. 실험은 사각단면의 직선형 개수로에서 수행하였으며, 보호공 사석의 크기를 3가지로 결정하였다. 선행 연구들과 차이점은 부정류로 실험을 수행한 것이며, 대상은 일반적인 형태의 가물막이로 결정하였다. 실험결과 차원해석 및 선행연구를 이용하여 서석보호공이 포설된 흙댐 붕괴 시간에 대한 새로운 공식을 제시하였다. 또한 사석 보호공이 설치된 경우 실험을 통해 붕괴 지연효과에 대해 검토한 결과 포설된 사석의 2배 이상의 효과가 있는 것으로 확인되었다. 본 연구 결과는 EAP (Emergency Aciton Plan) 수립 및 제방 설계와 같은 하천 계획에 도움이 될 것으로 판단된다.

• 지질공학
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• 제24권1호
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• pp.53-67
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• 2014

댐붕괴로 인하여 빚어지는 홍수위험지도 작성에서 물리적 현상을 재현해내기 위하여 수치모형이 사용되는 것이 일반적이다. 이때 모형의 정확도는 저수지의 수량과 댐붕괴 형성 및 진행을 포함한 모형의 물리적 구조, 입력인자 및 매개변수의 신뢰도에 의하여 결정되기 마련이다. 특히 입력인자 및 매개변수는 모형을 이용하기 이전에 미리 결정하여 입력하게 되며 사용자의 판단과 주관에 의지하므로 주의가 요구된다. 이 연구에서는 댐붕괴 모형을 FLO-2D와 연동하여 홍수 침수모의를 실시할 때에 댐붕괴 모형에서 세 개의 매개변수(붕괴각도 ${\theta}$, 저수지 형상계수 P, 붕괴율 k가 FLO-2D의 침수모의(침수범위, 침수깊이 등)에 어떻게 영향을 미치는 가를 살펴보았다. 붕괴각도 ${\theta}$는 FLO-2D의 침수모의에 있어 낮은 영향을 미치나 저수지 형상계수 P와 붕괴율 k는 중대한 영향을 미치는 것으로 나타났다. 이 연구는 향후 댐붕괴에 의한 홍수 위험의 피해를 저감하는데 기여할 것이다.

• Journal of Chest Surgery
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• 제9권2호
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• pp.133-138
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• 1976

The author reviewed 263 cases of pulmonary tuberculosis operated on at the Department of Thoracic Surgery, Seoul National University Hospital during the 19 year period, from January, 1957 to December 1975. Following observations were made: 1) The sex ratio was 2.8: 1 in male's favor, and 83.6% of the patients were between 20 and 49 years of age. 2) The trends in operative procedures revealed that surgical collapse as a definitive therapy of pulmonary tuberculosis has virtually disappeared and operations required for residuals of pleural diseases have increased. 3) The overall hospital mortality rate was 3-8%. The highest mortality rate was encountered in the cases of resection and decortication with 28.6%, 4) The rate of overall postoperative complications was 24.7%, the highest being encountered in decortication with 56.4%. 5) The most frequent cause of death was bleeding, while the dead space was the most frequent complication.

• 대한전기학회논문지:전력기술부문A
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• 제52권6호
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• pp.301-306
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• 2003

When a bulk power system experiences a serious disturbance or heavy load trip, the system frequency may drop and even collapse if the total generating power does not supply the system demand sufficiently. Since an isolated power system possesses a lower inertia and comes with limited reserves, the load shedding by under frequency relay becomes an important strategy to keep system natural frequency. This paper presents a scheme to determine the load shedding criteria by using the rate of change of frequency when the large disturbance happens.

• 천문학회지
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• 제15권1호
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• pp.19-36
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• 1982

For ${\sim}240$ nearby stars their age and mass were determined and kinematic parameters determined for 362 stars, applying Woolley's three-dimensional potential. Metallicity and kinematic parameters of these stars were correlated with their age, suggesting the slow collapse ($t{\gtrsim}a$ few billion years) of the Galaxy and the initial rapid enrichment in metal abundance (${\Delta}Z{\approx}1/3Z_1$(present) for ${\sim}4{\times}10^8$ yrs). The late slow enrichment rate is given by $d(Z/Z_{\odot})/dt=5.9{\sim}7.0{\pm}3.4$ per Gyr.

• 한국생산제조학회지
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• 제23권3호
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• pp.243-249
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• 2014

Currently, CFRP composites are rapidly replacing steel plates, as they are lighter, stronger, and more elastic; however, they are poorly suited to hygrothermal and impact-collapsed environments because moisture can alter their molecule arrangement and chemical properties. In this study, environments are experimentally simulated in order to investigate changes in the moisture absorption inside a CFRP composite and to determine its weakest point. Moreover, changes in the moisture absorption ratio at temperatures of $60^{\circ}C$ and $80^{\circ}C$ are studied and compared in order to understand how changes in temperature affect moisture absorption inside CFRP composites. Results show that moisture absorption leads to a strength reduction of around 50%. In addition, the moisture absorption rate inside CFRP composites is shown to change rapidly with increasing temperature. Accordingly, it showed that the change in matrix also has a weak point.

• 대한기계학회논문집B
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• 제28권4호
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• pp.395-405
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• 2004

The filling pattern and an adaptive grid refinement based on the finite element method and Eulerian mesh advancement approach have been developed to analyze incompressible transient viscous flow with free surfaces. The governing equation for flow analysis is Navier-Stokes equation including inertia and gravity effects. The mixed FE formulation and predictor-corrector method are used effectively for unsteady numerical simulation. The flow front surface and the volume inflow rate are calculated using the filling pattern technique to select an adequate pattern among four filling patterns at each triangular control volume. By adaptive grid refinement, the new flow field that renders better prediction in flow surface shape is generated and the velocity field at the flow front part is calculated more exactly. In this domain the elements in the surface region are made finer than those in the remaining regions for more efficient computation. Using the proposed numerical technique, the collapse of a water dam has been analyzed to predict flow phenomenon of fluid and the predicted front positions with respect to time have been compared with the reported experimental results.