• 전자공학회논문지
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• 제49권11호
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• pp.103-109
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• 2012

논문에서는 천해역에서 운용가능한 소형의 자율무인잠수정 "BOTO"의 개발과 실해역 자율주행 성능시험에 관한 내용을 다룬다. BOTO의 개발을 위해 6자유도 운동방정식을 이용하여 시뮬레이션을 수행하였으며, 시뮬레이션 결과를 바탕으로 소형 자율무인잠수정을 개발하였다. 시뮬레이션에 사용되는 운동모델의 계수와 주행성능을 확인하기 위해 회류수조에서 저항계수 측정 시험도 수행하였다. 운동모델을 기반으로 무인잠수정의 선회반경 시뮬레이션과 수평면에서의 경로추종을 위한 알고리즘을 적용하여 시뮬레이션을 수행하였고, 설계된 제어기를 이용하여 실해역 자율주행시험을 수행하였다. 실해역 자율주행시험은 선회반경 측정시험과 경로점 추종시험을 실시하였으며, 실해역에서 목표 경로점을 잘 추종하는 것을 확인하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.117-120
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• 2008

Numerical simulations and experiment of a hydrodynamic and thermally developed turbulent flow through square ducts (3.0 ${\times}$ 3.0 cm) with twisted tape inserts and with twisted tape inserts plus interrupted ribs are conducted to investigate regionally averaged heat transfer and friction factors. Turbulent swirl flows having Reynolds numbers ranging from 8,900 to 29,000, a rib height-to-channel hydraulic diameter(e/D$_h$) of 0.067, and a length-to-hydraulic diameter(L/D$_h$) of 30, are considered. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. The twisted tape has 0.1 mm thick carbon steel sheet with diameter of 2.8 cm, length of 90 cm, and 2.5 turns. Each wall is composed of isolated aluminum sections, and two cases of surface heating are set. The results show that uneven surface heating enhances the heat transfer coefficient over uniform heating conditions, and square ducts with twisted tape inserts plus interrupted ribs produces the best overall transfer performance.

• 대한기계학회논문집A
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• 제32권1호
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• pp.7-12
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• 2008

The vacuum interrupter (VI) is used for medium-voltage switching circuits due to its abilities and advantages as a compacted environmental friendly circuit breaker. In general, the application of a sufficiently strong axial magnetic field (AMF) permits the arc to be maintained in a diffused mode to a high-current vacuum arc. A full understanding of the vacuum arc physics is very important since it can aid to improve the performance of vacuum interrupter. In order to closely examine the vacuum arc phenomena, it is necessary to predict the magnetohydrodynamic (MHD) characteristics by the multidisciplinary numerical modeling, which is coupled with the electromagnetic and hydrodynamic fields, simultaneously. In this study, we have investigated the effect of changing geometrical parameters for electromagnetic behaviors of high-current vacuum arcs with two different types of AMP contacts, which are coil-type and cup-type, using a commercial finite element analysis (FEA) package, ANSYS. The present results are compared with those of MAXWELL 3D, a reliable electromagnetic analysis software, for verification.

• Fisheries and Aquatic Sciences
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• 제13권2호
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• pp.182-189
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• 2010

An active stimulating device (ASD) using a rope apparatus may operated by the flow of turbulence inside a cod end, generating variable stimuli in addition to flow-related effects to minimize the by-catch of juvenile fishes. Preliminary testing involved a hydrodynamic effect inside the cod end with a rotating rope kite or conical rope array to generate variable stimuli (visual stimuli, water flow, or physical contact with fish) to change fish position. The experimental rope kite offered more choice in rotating period and range of sweeping action; adjusting the towing line or flow velocity helped to drive fish toward the net panel and encouraged escape. The conical shape of the rope array in the cod end helped to clear a path for fish by disturbing the rigging and providing more contrast between objects, preventing an optomotor response. This enabled more black porgy to be herded toward the net at an early stage of towing. Therefore, either a conical rope array or a rotating rope kite can be used as an effective ASD to prevent juvenile by-catch.

• Journal of Power Electronics
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• 제11권4호
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• pp.591-598
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• 2011

This paper investigates a power supply of medium voltage with enhanced ignition characteristics for plasma torches. A series resonant half-bridge topology is presented as a suitable ignition circuitry. The ignition circuitry is integrated into the main power conversion system of a multi-phase staggered three-level dc-dc converter with a diode front-end rectifier. A plasma torch rated at 3MW, 2kA and having a physical size of 1m is selected to be the high enthalpy source for a waste disposal system. The steady-state and transient operations of a plasma torch are simulated. The parameters of a Cassie-Mary arc model are calculated based on 3D magneto-hydrodynamic simulations. The circuit simulation waveform shows that the ripple of the arc current can be maintained within ${\pm}10%$ of its rated value under the presence of a load disturbance. This power conversion configuration provides a high enough ignition voltage, around 5KA, during the ignition phase and high arc stability under the existence of arc disturbance noise resulting in a high-performance plasma torch system.

• 한국해안해양공학회지
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• 제5권2호
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• pp.107-120
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• 1993

본 논문은 유사변환기법을 이용한 새로운 3차원 연직 모우드 전개 모델의 개발에 대하여 기술한다. 기본방정식을 External 모우드와 Internal 모우드로 분리시킨 다음 Internal 모우드식에 Galerkin 방법을 적용하고 구성되는 행열방정식에 유사변환기법을 적용, 기저함수의 계수 값을 구하였다. 최종 얻어지는 기저함수의 계수 값은 마찰장을 제외하고는 비연계되어 시간 간격의 제약을 거의 받지않고 연직 구조를 구할 수 있기 때문에 경제성면에서 탁월하다. 수립된 모델은 어떤 기저함수라도 적용 가능하나 현 단계에서는 Chebyshev 다항식함수가 사용되었으며, 바람응력은 일정한 것으로 가정하였다. 모델 테스트로서 정상상태의 균일한 바람응력이 가해지는 장방형 Basin에 적용하여 모델의 적용 가능성을 검증하였다.

• 한국자동차공학회논문집
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• 제3권6호
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• pp.55-68
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• 1995

Approximately 30 to 70 % of the mechanical losses in a reciprocating engine are contributed by the friction at the piston ring-cylinder interface. The friction characteristics of the piston ring during engine operation is known to as mixed lubrication experimentally. The mixed lubrication models based on the Average Reynolds Equation have been used by this time in order to study the tribological performance of the ring. However, the Average Reynolds Equation contains the expected value term(${\bar{h}}_r$) of local film thickness as well as nominal film thickness(h), so that the work of numerically solving ${\bar{h}}_r$ must be included to obtain the pressure in the oil film. The process of solving ${\bar{h}}_T$ causes a greater multiplying in the numerical solution. In this paper the mixed lubrication analysis using the Simplified Average Reynolds Equation in the piston ring is presented. This equation has only h as oil film thickness term. Therefore the tedious numerical procedure required to obtain ${\bar{h}}_T$ is not needed, and also, computation time can be reduced.

• 전산구조공학
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• 제9권3호
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• pp.125-134
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• 1996

건물기초를 지진절연하면 건물뿐만 아니라 그 내부구조물의 지진응답도 크게 감소한다는 사실이 많은 연구를 통해 확인되어 왔다. 그런데 이러한 내부구조물이 유체내에 잠기고 부가질량효과가 크게 작용되는 조건에 놓이는 경우 오히려 지진응답이 증가할 수 있다. 본 논문은 건물 내 수중구조물의 지진해석을 통해 그러한 예를 제시하고자 한다. 해석결과 지진절연된 건물의 경우 이러한 내부 수중구조물의 지진응답이 상당히 증가할 수 있기 때문에 이에 대한 조치가 필요함을 보였고, 적절한 설계에 의하여 부가질량효과를 조절함으로써 어느정도 응답을 줄일 수 있다는 사실을 알 수 있었다.

• 해양환경안전학회지
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• 제20권4호
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• pp.426-434
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• 2014

본 연구에서는 서해안의 해양레저 대중화를 위해 누구나 세일링을 즐길 수 있고, 두 개의 킬로 선체를 지지하여 육상 및 갯벌에서도 선체가 기울지 않고 설 수 있는 트윈킬 요트를 개발하고자 한다. 기존 세일링 요트중 성능이 좋은 편인 블루워터21의 선형을 활용하고 트윈킬 요트의 경우 모노킬 요트보다는 저항성능이 불리할 것으로 예상되므로, 블루워터21의 모노킬 면적 및 무게중심 등을 고려한 트윈킬을 개발하여 모형시험을 수행하였다. 그 결과, 모노킬과 트윈킬의 저항성능에 대한 차이가 약 4 %정도로 예상보다 크지 않음을 확인하였다.

• 설비공학논문집
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• 제11권2호
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• pp.224-235
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• 1999

The present study investigated the effects of the experimental parameters on the cooling characteristics of the multichip module cooled by the indirect liquid cooling method using water, PF-5060, and paraffin slurry. The experimental parameters were coolants including Paraffin slurry with mass fraction of 2.5~7.5%, heat flux of 10~40W/$\textrm{cm}^2$ for the simulated VLSI chips and Reynolds numbers of 3,000~20,000. The size of paraffin slurry was constant as 10~40${\mu}{\textrm}{m}$ before and after the experiment. The chip surface temperatures for paraffin slurry were lower than those for water and PF-5060. The local heat transfer coefficients for the paraffin slurry were larger than those for water and the local heat transfer coefficients reached a row-number-independent and thermally-fully-developed value approximately after the third row. The local Nusselt numbers for paraffin slurry with a mass fraction of 7.5% were larger by 20~38% than those for water. The paraffin slurry with a mass fraction of 5% shelved the best thermal and hydrodynamic characteristics when local heat transfer and pressure drop were considered simultaneously.