• 한국항해항만학회지
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• 제28권5호
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• pp.353-358
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• 2004

ISSC 스팩트럼을 기초로 종래의 불규칙파가 아닌 새로울 과도 불규칙파를 설계하였다. 이 설계불규칙파를 장수조에서 조파기를 사용하여 발생시키고, 파고계와 6자유도계를 설치하여서 모형선의 횡동요 운동을 계측하였다. 모형선의 최대 횡동요각의 실험값과 이론값을 비교하여 단기 해상에서 발생 가능한 횡동요 피크치를 추정하는 방법에 관하여 검토하였다.

• 대한조선학회논문집
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• 제38권3호
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• pp.47-53
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• 2001

선박이 파랑중에 충격력을 받거나 불규칙한 외력을 받았을 경우에 시간영역에서의 운동방정식을 해석하는 것이 편리하다. 본 연구에서는 주파수영역에서 3차원 Green함수를 이용한 패널방법을 사용하여 부가질량, 파랑감쇠계수, 1차항 파강제력과 시간평균된 표류력을 계산하였고, 기억효과를 포함한 시간영역의 운동방정식에서 Newmark-$\beta$방법을 사용하여 수치적분하였다. 계산 예로 계열 60 선박($C_B=0.7$)을 선정하여 불규파중에서 전진할 때의 6자유도 운동, 선수미에서의 가속도, 갑판침수 횟수 및 선저 노출 횟수 등을 계산하였다. 또한 2차항 파강제력을 운동방정식에서 고려하여 파도중에서 추력증가에 대해서 검토하였다.

• 대한조선학회논문집
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• 제47권3호
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• pp.291-305
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• 2010

A three-dimensional time-domain calculation method is of crucial importance in prediction of the motions and wave loads of a ship advancing in a severe irregular sea. The exact solution of the free surface wave-ship interaction problem is very complicated because of the essentially nonlinear boundary conditions. In this paper, an approximate body nonlinear approach based on the three-dimensional time-domain forward-speed free-surface Green function has been presented. The Froude-Krylov force and the hydrostatic restoring force are calculated over the instantaneous wetted surface of the ship while the forces due to the radiation and scattering potentials over the mean wetted surface. The time-domain radiation and scattering potentials have been obtained from a time invariant kernel of integral equations for the potentials which are discretized according to the second-order boundary element method (Hong and Hong 2008). The diffraction impulse-response functions of the Wigley seakeeping model advancing in transient head waves at various Froude numbers have been presented. A simulation of coupled heave-pitch motion of a long rectangular barge advancing in regular head waves of large amplitude has been carried out. Comparisons between the linear and the approximate body nonlinear numerical results of motions and wave loads of the barge at a nonzero Froude number have been made.

• 한국해안·해양공학회논문집
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• 제20권6호
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• pp.583-588
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• 2008

2008년 2월에 동해안에서 발생하였던 너울 관측 자료에 대하여 웨이블릿 방법을 사용하여 분석하였다. 시간에 따른 파군, 첨두 주파수 및 스펙트럼의 변화를 볼 수 있었으며 그 결과를 시간에 따라 평균하여 푸리에 스펙트럼과 비교한 결과 시간에 따른 형태나 첨두 주기의 변화는 유사하게 나왔으나 첨두 주파수 에너지와 유의 파고에 있어서는 차이를 나타냈다. 웨이블릿 분석 방법은 주파수 뿐 만 아니라 시간에 따른 스펙트럼의 변화를 볼 수 있어서 이상 파랑이나 갑작스러운 너울과 같은 일시적이고 불규칙적인 현상 연구에 효과적 것인으로 보이며 향후 우리나라 파랑 자료에 대한 많은 적용과 분석 연구가 필요하다.

• The Korean Journal of Physiology and Pharmacology
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• 제3권2호
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• pp.119-125
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• 1999

Mammalian gastric smooth muscles generate spontaneous rhythmic contractions which are associated with slow oscillatory potentials (slow waves) and spike potentials. Spike potentials are blocked by organic $Ca^{2+}-antagonists,$ indicating that these result from the activation of L-type $Ca^{2+}-channel.$ However, the cellular mechanisms underlying the generation of slow wave remain unclear. Slow waves are insensitive to $Ca^{2+}-antagonists$ but are blocked by metabolic inhibitors or low temperature. Recently it has been suggested that Interstitial Cells of Cajal (ICC) serve as pacemaker cells and a slow wave reflects the coordinated behavior of both ICC and smooth muscle cells. Small segments of circular smooth muscle isolated from antrum of the guinea-pig stomach generated two types of electrical events; irregular small amplitude (1 to 7 mV) of transient depolarization and larger amplitude (20 to 30 mV) of slow depolarization (regenerative potential). Transient depolarization occurred irregularly and membrane depolarization increased their frequency. Regenerative potentials were generated rhythmically and appeared to result from summed transient depolarizations. Spike potentials, sensitive to nifedipine, were generated on the peaks of regenerative potentials. Depolarization of the membrane evoked regenerative potentials with long latencies (1 to 2 s). These potentials had long partial refractory periods (15 to 20 s). They were inhibited by low concentrations of caffeine, perhaps reflecting either depletion of $Ca^{2+}$ from SR or inhibition of InsP3 receptors, by buffering $Ca^{2+}$ to low levels with BAPTA or by depleting $Ca^{2+}$ from SR with CPA. They persisted in the presence of $Ca^{2+}-sensitive$ $Cl^--channel$ blockers, niflumic acid and DIDS or $Co^{2+},$ a non selective $Ca^{2+}-channel$ blocker. These results suggest that spontaneous activity of gastric smooth muscle results from $Ca^{2+}$ release from SR, followed by activation of $Ca^{2+}-dependent$ ion channels other than $Cl^-$ channels, with the release of $Ca^{2+}$ from SR being triggered by membrane depolarization.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.214-214
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• 2003

During a model test of Hutton TLP, a "ringing" response was first observed about 20 years ago. This phenomenon is a resonant build up over the time of wave period and this burst-like motion can cause the extreme load on the TLP tether. It is often detected in the large and steep irregular waves but the generation mechanism leading to the "ringing" is not yet well understood. According to the research since then, the higher order harmonic components may account for the "ringing" on the floating offshore structures. The main purpose of the present research is, thus, to measure the higher harmonic forces exerted on a vertical truncated circular column and to compare them with available data. A vertical truncated cylinder with a diameter of 3.5inch and a draft of 10.5inch is used as a test structure, which is a scaled model of ISSC TLP column. The cylinder is installed at a distance of 45ft from the wave maker in order to avoid parasitic waves created in the wave flap. Attached to the upper part of the cylinder are two force gages to measure the horizontal (surge) and vertical (heave) forces on the cylinder. The incoming waves are Stokes waves with a slope ranging from 0.06 to 0.24. The forces and waves are measured for 60 seconds with a sampling rate of 50 Hz. Among the recorded data, the first 10 waves are excluded because of transient behavior of the waves and the next The horizontal and vertical forces are analyzed up to 5th order harmonics. The horizontal forces are then compared to the values from the theoretical model called "FNV model". In addition, force transfer functions are also investigated. Major findings in this research are below. 1) The first order forces measured are slightly larger than the theoretical values of "FNV model" 2) The "FNV model" considerably overpredicts the second order forces. 3) The larger the amplitude and more extreme the wave slope, the smaller the predictions are compared to the experimental. 4) The higher harmonic forces are significantly smaller than the first harmonic force for all wave parameters. 5) The normalized forces vs. waves slopes are almost constant in the lower harmonics but vary a lot in the higher harmonics. 6) The trend of forces is more nonlinear in the horizontal forces than in the vertical forces as the wave slope increases. 7) The part of the results above is also observed by other researchers and confirmed again through the present work.

• Ocean Systems Engineering
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• 제7권3호
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• pp.179-193
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• 2017

Dynamic response analysis of offshore triceratops with stiffened buoyant legs under impact and non-impact waves is presented. Triceratops is relatively new-generation complaint platform being explored in the recent past for its suitability in ultra-deep waters. Buoyant legs support the deck through ball joints, which partially isolate the deck by not transferring rotation from legs to the deck. Buoyant legs are interconnected using equally spaced stiffeners, inducing more integral action in dispersing the encountered wave loads. Two typical nonlinear waves under very high sea state are used to simulate impact and non-impact waves. Parameters of JONSWAP spectrum are chosen to produce waves with high vertical and horizontal asymmetries. Impact waves are simulated by steep, front asymmetric waves while non-impact waves are simulated using Stokes nonlinear irregular waves. Based on the numerical analyses presented, it is seen that the platform experiences both steady state (springing) and transient response (ringing) of high amplitudes. Response of the deck shows significant reduction in rotational degrees-of-freedom due to isolation offered by ball joints. Weak-asymmetric waves, resulting in non-impact waves cause steady state response. Beat phenomenon is noticed in almost all degrees-of-freedom but values in sway, roll and yaw are considerably low as angle of incidence is zero degrees. Impact waves cause response in higher frequencies; bursting nature of pitch response is a clear manifestation of the effect of impact waves on buoyant legs. Non-impact waves cause response similar to that of a beating phenomenon in all active degrees-of-freedom, which otherwise would not be present under normal loading. Power spectral density plots show energy content of response for a wide bandwidth of frequencies, indicating an alarming behaviour apart from being highly nonlinear. Heave, being one of the stiff degrees-of-freedom is triggered under non-impact waves, which resulted in tether tension variation under non-impact waves as well. Reduced deck response aids functional requirements of triceratops even under impact and non-impact waves. Stiffened group of buoyant legs enable a monolithic behaviour, enhancing stiffness in vertical plane.

• 한국정보전자통신기술학회논문지
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• 제13권2호
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• pp.169-175
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• 2020

본 논문은 SET에 노출된 전자기기는 불규칙한 작동 및 출력 오류를 나타낼 수 있으므로 집적회로에서 SET 상황에 대해서 연구하였다. 폴디드 캐스코드 비교기에서 지수정류파(iexp)을 이용하여 SET 환경을 설정하였다. 비교기가 SET에 의해 어떤 영향이 있는지에 대해 실험하였다. SET현상을 발생시키지 않은 폴디드 비교기에서는 전파 지연은 0.26㎲, 이득은 0.649으로 측정되었다. SET현상을 발생시킨 폴디드 비교기에서 출력단과 가까운 MOSFET는 민감하게 측정되었으며 전파 지연은 0.36~0.37㎲,이득은 0.649로 계산되었다. 중간에 위치한 MOSFET는 0.28~0.30㎲, 이득은 0.649로 계산되었다. 폴디드 비교기에서 출력단과 가장 멀리 떨어져 있는 MOSFET는 전파지연이 0.25~0.26㎲, 이득은 0.649로 계산되었다. SET 환경에서, 폴디드 비교기에서 출력부분에 가까이 있는 MOSFET는 민감하였다. 그리고 출력부분과 멀리 떨어져 있는 MOSFET에서는 SET를 입력하지 않은 정상적인 폴디드 비교기와 같은 결과를 얻었다.