• Journal of Advanced Research in Ocean Engineering
• /
• 제3권2호
• /
• pp.59-65
• /
• 2017

When an anchor is dropped into the sea, there exists a danger of collision on the pipeline and subsea cables in the seabed. This collision could cause huge environmental disasters and serious economic losses. In order to secure the safety of subsea structures such as pipelines and subsea cables from the external impact, it is necessary to estimate the exact external force through the anchor's terminal velocity on the water. FLUENT, a computational fluid dynamic program, was used to acquire the terminal velocity and drag coefficient computation. A half-symmetry condition was used in order to reduce the computational time and a moving deforming mesh technique also adapted to present hydrostatic pressure. The results were examined with the equation based on Newton's Second Law to check the error rate. In this study, three example cases were calculated by stockless anchors of 5.25 ton, 10.5 ton, and 15.4 ton, and for the onshore experiment dropped height was back calculated with the anchor's terminal velocity in the water.

• 대한기계학회논문집B
• /
• 제23권11호
• /
• pp.1410-1417
• /
• 1999

A thorough understanding of the transient behavior during start-up is essential in the design and operation of the heat recovery steam generator(HRSG). During this period of time, material that is exposed to high temperature and experiences a large temperature variation is subject to high thermal stress. In this work, a transient formulation of the HRSG is constructed including the estimation of the thermal stress and fatigue of the drum wall. Start-up behavior of a single-pressure HRSG is analyzed and the effect of bypassing part of the gas turbine exhaust flow on the thermal stress evolution is examined. It is found that the modulation of the gas flow rate using a bypass damper is very useful in view of reducing the thermal stress of the drum and ensuring the fatigue lifetime.

• 한국소음진동공학회논문집
• /
• 제12권4호
• /
• pp.261-271
• /
• 2002

The fluid-elastic instability analysis of the U-tube bundle inside the steam generator is very important not only for detailed design stage of the SG but also for the change of operating condition of the nuclear powerplant. However the calculation procedure for the fluid-elastic instability was so complicated that the consolidated computer program has not been developed until now. In this study, the numerical calculation procedure and the computer program to obtain the stability ratio were developed. The thermal-hydraulic data in the region of secondary side of steam generator was obtained from executing the ATHOS3 code. The distribution of the fluid density can be calculated by using the void fraction, enthalpy, and operating pressure. The effective mass distribution along the U-tube was required to calculate natural frequency and dynamic mode shape using the ANSYS ver. 5.6 code. Finally, stability ratios for selected tubes of the CE type steam generator were computed. We considered the YGN 3.4 nuclear powerplant as the model plant, and stability ratios were investigated at the flow exit region of the U-tube. From our results, stability ratios at the central and the outside region of the tube bundle are much higher than those of other region.

• 소음진동
• /
• 제8권2호
• /
• pp.331-335
• /
• 1998

회전 상태에 있는 증기 터빈 버킷의 진동 시험 및 해석 결과를 본 논문에 기술하였다. 중고압용 터빈 로터에서 9단 휠 도브테일의 치수 변경으로 인해 9단 버킷의 치수 수정이 불가피하였고, 진동 시험과 해석은 수정된 9단 버킷의 고유 진동수가 노즐 통과 주파수로부터 공진을 피할 수 있는 주파수 분리 여유를 갖는지를 검정하기 위하여 이루어졌다. 해석은 상용 유한 요소 해석 프로그램을 이용하였고 실험 전 설계 변경의 성공 가능성 파악 및 후속 시험에 도움을 주기 위해 행하였다 진동 시험은 기존 밸런싱 설비를 이용해 진공 상태에서 회전하고 있는 버킷에 공기 분사 가진및 무선진동신호 측정 시스템을 이용해 행하였다. 시험 결과를 경험식의 결과와 비교하였고, 수정된 버킷이 제시된 주파수 분리 여유를 만족함을 보였다.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2007년도 춘계학술대회논문집
• /
• pp.833-836
• /
• 2007

Load/Unload technology has more benefits than the conventional CSS technology. However, it remains unsolved technical problem on the unloading process. While the slider climbs up the ramp at the outer edge of the disk, the possibility of the slider-disk contact by lift-off force and rebound of the slider increases. This paper focuses on no slider-disk contact. To prevent the slider-disk contact, we apply the disk bump on disk outer edge proceeding unload. Firstly, in the simulation, the bump dimension is determined by changing bump design parameters. Secondly, dynamic stability of slider have to be checked on disk bump before unload analysis, and unload analysis is performed by applying stable bump shapes to unload simulation. Thirdly, we select optimal bump shape to improve unload performance by unload analysis. Finally, in the experiment, the disk bump is mechanically manufactured by pressing disk surface using diamond tip. That is variously processed by changing pressing pressure. After confirming bump shape by nano-scanner, proper bump shape is applied to real experimental unload process. Through this investigation, we propose the optimal bump design to prevent the slider-disk contact, and then we can realize improved unloading performance.

• 한국해안해양공학회지
• /
• 제11권3호
• /
• pp.141-148
• /
• 1999

圓形 파일에 작용하는 卷波性 碎波力은 쇄파제원과 동일한 正弦波를를 대상으로 한 모리슨식의 계산치보다 그 크기는 월등 크나 보통 백분의 수초 이내의 매우 짧은 시간 동안 작용한다. 따라서, 碎波力을 받는 파일의 설계에서 파일의 變位를 정확히 결정하기 위해서는 쇄파력 작용에 의한 動的擧動을 해석하여야 한다. 이를 위해서는 파일 延長上 쇄파력의 시게열에 대한 事前정보가 필요하며, 이는 파일 주변의 碎波壓 시계열로부터 간접적으로 추정할 수 있다. 본 연구에서는 卷波性 碎波의 작용에 따른 쇄파압의 특성을 정량적으로 고찰하기 위하여 實海域에 설치되어 잇는 원형파일에 波壓計를 부착하여 쇄파압을 관측하고 그 결과를 제시하였다.

• 한국대기환경학회지
• /
• 제12권2호
• /
• pp.189-198
• /
• 1996

Mercury (Hg) is ubiquitous throughout the earth's atmosphere. The uniqueness of its atmospheric geochemistry is well-known with the high environmental mobility and relatively long atmospheric residence time (c.a., 1 year) associated with its high chemical stability. Despite a growing recognition of the environmental significance of its global cycling, the prexisting Korean database for atmospheric Hg is extremely rare and confined to a number of concentration measurements conducted under relatively polluted urban atmospheric environments. To help activate the research on this suvject, an in-depth analysis on the current development in the measurements of atmospheric mercury and the associated fluxes has been made using the most using the most updated data ests reported worldwide. As a first step toward this purpose, the most reliable techniques commonly employed in the measurements of its concentration in the background atmosphere are introduced in combination with the flux measurement techniques over soil surface such as: dynamic enclosure (or field flux chamber) method and field micrometeorological method. Then the results derived using these measurement techniques are discussed and interpreted with an emphasis on its mobilization across the terrestrial biosphere and atmosphere interface. A unmber of factors including air/soil temperature, soil chemical composition, soil water content, and barometric pressure are found out to be influential to the rate and amount of such exchange processes. Although absolute magnitude of such exchange processes is insignificant relative to that of the major component like the oceanic environment, this exchange process is thought to be the the predominant natural pathway for both the mobilization and redistribution of atmospheric Hg on a local or regional scale.

• 한국자동차공학회논문집
• /
• 제6권1호
• /
• pp.43-51
• /
• 1998

Most of fuel-injection system operated with mechanical methods are difficult to control the injection quantity and injection timing as well as injection rate exactly. Moreover high pressure injection scheme is never be realized with conventional one. On the other hand, serious air pollution can be lessened with injection system equipped with those functions. Therefore, electronically controlled Unit Injuctor(UI) appeared to satify above mentioned desires. However, it is still difficult that the most important part, especially solenoid valve, is analyzed precisely, because of the existence of complex combination of electromagnetics, electrics and dynamic problems. In this study, experimental and theoretical analysis are accomplished for understanding of solenoid valve characteristics and further its design. As the result, the follows are obtained 1) As the increase of wire diameter, the response time became shorter and optimal inductance existed in relative with the response time and wire diameter. 2) According to increasing input voltage, the traction force increased, otherwise the response time was shortened. 3) As the increase of armature stroke, the traction force decreased and the response time became longer.

• International Journal of Aeronautical and Space Sciences
• /
• 제3권2호
• /
• pp.59-66
• /
• 2002

A vertical test stand based on launcher propulsion system was constructed and several tests for the determination of cyclogram were carried out. To make an accurate estimation, static and dynamic pressures were measured and analyzed. Especially, static pressure measurements using fast response sensors without extension tubes were used to determine operation sequence more evidently. The standard operation times of final valves were determined in cold flow tests with an engine head, and fire formation time in combustion chamber was checked in an ignition test with an ignitor only. On the basis of these tests, ignition sequence was established and combustion test cyclogram was finally determined. According to combustion test, test results were well matched with the determined cyclogram within 0.05 sec.

• 공업화학
• /
• 제16권1호
• /
• pp.131-138
• /
• 2005

활성탄과 제올라이트 13X에 대한 벤젠의 정적흡착실험으로부터 Freundlich isotherm과 Toth isotherm을 구하였으며 똑같은 흡착제로 충진된 흡착탑을 이용하여 벤젠의 파과곡선을 측정하였다. 파과시간과 벤젠 분압의 관계를 해석하여 Freundlich isotherm의 파라미터를 결정하였다. 파과실험 결과의 해석으로부터 예측되는 벤젠의 흡착량이 정적 실험 결과로부터 예측되는 것과 비교적 잘 일치하였다. 활성탄에 대한 동적 실험 결과에서 좀 더 대칭형태에 가까운 파과곡선이 얻어져서 제올라이트 13X에 비해 더 적은 오차가 나타났다.