• 설비공학논문집
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• 제13권5호
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• pp.388-397
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• 2001

This paper addresses characteristics of compressible flow dynamics inside a pipe with an accumulator and an inlet orifice. It also presents a simple but stable numerical method associated with the accumulator-orifice calculation. In particular, a focus is given to developing a method of finding an optimum design of the accumulator-orifice system (i.e., the accumulator size and the throttle resistance) that gives the most effective dissipation of the water-hammering problem. It is found that there exists indeed an optimum set of parameter values for the most effective dissipation of the wave energy.

• 대한전자공학회논문지SP
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• 제46권3호
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• pp.125-137
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• 2009

음향방출 기법은 작동중인 상태에서 기계 설비를 비파괴 검사할 수 있는 기법이며, 균열성장 같은 장애의 신뢰성 있는 감시를 위해서 순간적인 균열신호뿐만 아니라 동특성을 이용하는 것이 중요하다. 균열성장을 검출하기 위해 널리 사용되는 물리적 파괴 3단계는 음향방출 현상이 시간에 따라 서로 겹치는 문제점이 있어 정확한 균열성장 시간을 추정하기 어렵다. 제안한 패턴인식 기법은 오경보와 미탐지를 최소화하기 위해서 음향방출 동특성을 입력으로 사용하고, 균열성장 시간을 정확히 추정하기 위해 시간에 따른 클러스터링 기법을 사용한다. 실험결과는 제안한 패턴인식 기법이 압력의 변화에 의한 음향방출의 변화의 강인함 때문에 실용화에 효율적임을 보여준다.

• 한국전산구조공학회논문집
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• 제27권3호
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• pp.173-182
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• 2014

동역학의 새로운 변분이론인 혼합 합성 변분이론은 수학물리학을 비롯한 공학에 있어 초기치-경계치 문제해석에 광범위하게 적용될 수 있는 기반을 제공하는 것으로, 본 논문은 이 이론을 토대로 시간에 대한 이차의 형상함수가 적용된 시간 유한요소해석법을 개발하고 그 해석법의 수치특성 확인을 통해 향후 다양한 동적시스템 해석의 적용에 대한 가능성을 살펴보았다. 이를 위해 가장 기본적인 선형탄성의 단자유도계가 고려되었다. 에너지 보존시스템의 경우(비감쇠 시스템에 외력이 작용치 않는 경우), 제안된 알고리즘 모두는 time-step에 관계없이 안정적이며 수치감쇠가 없이 에너지와 모멘텀이 보존되는 symplecticity property를 가지고 있음을 확인할 수 있었고, 감쇠시스템인 경우, time-step이 점점 작아질수록 정확한 해에 빠르게 수렴하는 것을 확인하였다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2015년도 학술발표회
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• pp.229-229
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• 2015

Downscaling is a fundamental procedure in the assessment of the future climate change impact at regional and watershed scales. Hence, it is important to investigate the spatial variability of the climate conditions that are constructed by various downscaling methods in order to assess whether each method can model the climate conditions at various spatial scales properly. This study introduces a fundamental research from Jang and Kavvas(2015) that precipitation variability from a popular statistical downscaling method (BCSD) and a dynamical downscaling method (MM5) that is based on the NCAR/NCEP reanalysis data for a historical period and on the CCSM3 GCM A1B emission scenario simulations for a projection period, is investigated by means of some spatial characteristics: a) the normalized standard deviation (NSD), and b) the precipitation change over Northern California region. From the results of this study it is found that the BCSD method has limitations in projecting future precipitation values since the BCSD-projected precipitation, being based on the interpolated change factors from GCM projected precipitation, does not consider the interactions between GCM outputs and local geomorphological characteristics such as orographic effects and land use/cover patterns. As such, it is not clear whether the popular BCSD method is suitable for the assessment of the impact of future climate change at regional, watershed and local scales as the future climate will evolve in time and space as a nonlinear system with land-atmosphere feedbacks. However, it is noted that in this study only the BCSD procedure for the statistical downscaling method has been investigated, and the results by other statistical downscaling methods might be different.

• E2M - 전기 전자와 첨단 소재
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• 제8권2호
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• pp.176-183
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• 1995

The present work is concerned with the switching conduction characteristics of PI LB films in metal insulator metal sandwiches. By applying various DC voltage bias to MIM junctions, conduction characteristics of junctions can be changed between the high-voltage low-current(off) condition, the low-voltage high-current (on) condition and the medium(mid) condition. Switching conduction characteristics can be also observed in MIM junctions employing some aromatic compounds as insulators. Switching conduction characteristics is assumed to be owing to the existence of aromatic rings, space charge in films, impurities on metal-insulator interface, and difference in work functions of base and top electrodes metal. To study the conduction process of on, off, and mid conductions, we measured I-V, d$^{2}$V/d I$^{2}$-V characteristics of junctions with several different top electrodes under various temperatures. Small conductance changes of junctions can be measured by observing the second derivative, d$^{2}$V/dI$^{2}$, of I-V curve. A dynamical technique is used to get the second derivatives. That is, a finite modulation of the current is applied to the junctions and the second harmonic of the voltage is detected.

• KIEE International Transactions on Power Engineering
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• 제4A권1호
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• pp.18-25
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• 2004

This paper proposes a totally new method in the chaos characteristics' analysis of power systems, the introduction of topological invariants. Using a return histogram, a bifurcation graph was drawn. As well, the periodic orbits and topological invariants - the local crossing number, relative rotation rates, and linking number during the process of period-doubling bifurcation and chaos were extracted. This study also examined the effect on the topological invariants when the sensitive parameters were varied. In addition, the topological invariants of a three-dimensional embedding of a strange attractor were extracted and the result was compared with those obtained from differential equations. This could be a new approach to state detection and fault diagnosis in dynamical systems.

• 천문학회지
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• 제29권spc1호
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• pp.351-354
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• 1996

In this paper it is explained how most of asteroids can avoid very close approach to Jupiter, to the earth for earth orbit crossing asteroids, and to Neptune for Kuiper-belt asteroids by mechanisms which work also for Neptune-Pluto system. In fact the mutual distance of the planets cannot become very small as the critical argument librates around $180^{\circ}$ because of 2:3 mean motion resonance and the argument of perihelion of Pluto librates around $90^{\circ}$. And it is found that among nearly 40 Kuiper-belt asteroids discovered in recent years $40\%$ have orbits similar to Pluto. For main-belt asteroids the distribution with respect to the semi-major axes has peculiar characteristics and the author tries to explain how their peaks and gaps are created. It is also found that $30\%$ of 80 earth orbit crossing asteroids which have minimum perihelion distances less than 1.04AU have no chance to collide with the earth. Still $30\%$ of them have a few probability to collide with the earth as they have dynamical characteristics of short-periodic comets.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.607-610
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• 2002

As machines become smaller and faster multileaf foil bearings are used to overcome the problems with heat, friction and wear Systems with foil bearings do not need a separate system for lubrication. These bearings are self acting and are therefore green systems. Until now, there have been many studies on the structural and dynamical performances. Therefore the object of the present study is to predict the flow and structural characteristics by using the Fluid/structure interaction method. The increase in RPM led to the increase in pressure, temperature difference, maximum velocity, Mach number, shear stress and torque. In the case of 90,000 RPM effects such as choking led to a non-lineararity in the system. Also the effect of eccentricity ratio was observed and showed that eccentricity increased the maximum pressure and the density difference while decreasing the shear stress and torque.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.979-984
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• 2004

The ball bearing having faults generally shows, nonlinear vibration characteristics. For the effective method of fault diagnosis on bail bearing, non-linear diagnostic methods can be used. In this paper, the correlation dimension analysis based on nonlinear timeseries was applied to diagnose the faults of ball bearing. The correlation dimension analysis shows some Intrinsic information of underlying dynamical systems, and clear the classification of the fault of ball bearing.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.324-332
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• 1999

This paper presents the artificial life algorithm which is remarkable in the area of engineering for optimum design. As artificial life organisms have a sensing system, they can find the resource which they want to find and metabolize it. And the characteristics of artificial life are emergence and dynamical interacting with environment. In other words, the micro interaction with each other in the artificial life's group results in emergent colonization in the whole system. In this paper, therefore, artificial life algorithm by using above characteristics is employed into functions optimization. The effectiveness of this proposed algorithm is verified through the numerical test of single and multi objective functions. The numerical tests also show that the proposed algorithm is superior to genetic algorithm and immune algorithm for the Multi-peak function. And artificial life algorithm is also applied to optimum design of high-speed, short journal bearings and verified through the numerical test.