• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1997년도 가을 학술발표회 논문집
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• pp.134-141
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• 1997

A geometrically non-linear finite element formulation of spatial cable networks is presented using three cable elements. Firstly, derivation procedures of tangent stiffness and mass matrices for the space truss element and the elastic catenary cable element, and the isoparametric cable element are summarized. The load incremental method based on Newton-Raphson iteration method and the dynamic relaxation method are presented in order to determine the initial static state of cable nets subjected to self-weights and support motions. Furthermore, static non-linear analysis of cable structures under additional live loads are performed based on the initial configuration. Challenging example problems are presented and discussed in order to demonstrate the feasibility of the present finite element method and investigate static non-linear behaviors of cable nets.

• 천문학회보
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• 제36권1호
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• pp.54.1-54.1
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• 2011

Formation of self-gravitating gas clouds and hence stars in galaxies is a consequence of both thermal and dynamical evolution of a gaseous medium. Using hydrodynamics simulations including cooling and heating explicitly, we follow simultaneously thermal and dynamical evolution of galactic gas disks to study dynamics and structures of galactic spiral shocks with thermal instability and regulation of the star formation rates (SFRs). We first perform one-dimensional simulations in direction perpendicular to spiral arms. The multiphase gas flows across the arm soon achieve a quasi-steady state characterized by transitions from warm to cold phases at the shock and from cold to warm phases in the postshock expansion zone, producing a substantial fraction of intermediate-temperature gas. Next, we allow a vertical degree of freedom to model vertically stratified disks. The shock front experiences unsteady flapping motions, driving a significant amount of random gas motions, and self-gravity promotes formation of bound clouds inside spiral arms. Finally, we include the star formation feedback in both mechanical (due to supernova explosion) and radiative (due to FUV heating by young stars) forms in the absence of spiral arms. At saturation, gravitationally bound clouds form via thermal and gravitational instabilities, which are compensated by disruption via supernova explosions. We find that the FUV heating regulates the SFRs when gas surface density is low, confirming the prediction of the thermal and dynamical equilibrium model of Ostriker et al. (2010) for star formation regulation.

• 광물과 암석
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• 제35권3호
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• pp.173-182
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• 2022

제주도 중산간 지역인 해발고도 약 700 m에 위치하고 있는 동수악 분화구에서 분출한 알칼리현무암은 새롭게 발견된 스피넬 페리도타이트라는 맨틀암석을 포획하고 있다. 맨틀 내에서 평형 상태에 있었던 동수악 스피넬 페리도타이트는 잔쇄반상조직을 보이며, 감람석, 사방휘석, 단사휘석, 스피넬로 구성되어 있다. 동수악 스피넬 페리도타이트 구성광물의 주성분원소 및 미량원소 분석 결과는 동수악 스피넬 페리도타이트는 지하 약 66~88 km 깊이에서, 약 960℃~1068℃의 평형온도 하에 있었음을 지시해준다. 분별용융 모델로 계산된 동수악 스피넬 페리도타이트의 부분용융 정도는 약 1~3%이며, 새로운 광물을 포함하고 있지 않고 LREE가 부화된 패턴을 보이는 동수악 스피넬 페리도타이트는 규산염 용융체에 의해 은폐교대작용을 받아 부화 되었다.

• 대한전기학회논문지:시스템및제어부문D
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• 제51권9호
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• pp.413-422
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• 2002

In a power plant, disturbance detection and diagnosis are massive and complex problems. Once a disturbance occurs, it can be either persistent, self cleared, cleared by the automatic controllers or propagated into another disturbance until it subsides in a new equilibrium or a stable state. In addition to the Physical complexity of the power plant structure itself, these dynamic behaviors of the disturbances further complicate the fault monitoring and diagnosis tasks. A data structure called a disturbance interrelation analysis graph(DIAG) is proposed in this paper, trying to capture, organize and better utilize the vast and interrelated knowledge required for power plant disturbance detection and diagnosis. The DIAG is a multi-layer directed AND/OR graph composed of 4 layers. Each layer includes vertices that represent components, disturbances, conditions and sensors respectively With the implementation of the DIAG, disturbances and their relationships can be conveniently represented and traced with modularized operations. All the cascaded disturbances following an initial triggering disturbance can be diagnosed in the context of that initial disturbance instead of diagnosing each of them as an individual disturbance. DIAG is applied to a typical cooling water system of a thermal power plant and its effectiveness is also demonstrated.

• 한국해안해양공학회지
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• 제11권4호
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• pp.173-188
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• 1999

김등(1999)은 등매개 케이블요소(isoparametric cable element)의 접선강성행렬과 질량행렬을 유도하고, 하중증분법을 이용하여 지점 변위를 일으키고 자중, 부력 및 조류력을 받는 해양케이블의 초기평형 상태를 결정하였다. 또한 초기의 정적평형상태를 기준으로 자유진동해석법을 제시하였다. 본 연구에서는 이전의 연구를 확장시켜서 파랑하중을 받는 해양 케이블의 비선형 동적 해석을 수행한다. 규칙파 및 불규칙파에 의한 파력을 받는 수중케이블에 대하여 비선형해석을 수행하고, 해석결과의 결과분석을 통하여 해양케이블의 동적특성을 파악한다.

• Journal of Magnetics
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• 제15권3호
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• pp.116-122
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• 2010

An accurate analytical equation for the total energy in the framework of the single domain model is used to study the thermal stability of nanostructured synthetic ferrimagnets. Elliptical cells are considered that have lateral dimensions of 160 nm (long axis)$\times$80 nm (short axis) and varying values of thickness asymmetry for the two magnetic layers. The direction of the applied magnetic field, which points to the $45^{\circ}$ direction, is in the opposite direction to the thicker layer magnetization. A significant difference is observed in the applied magnetic field dependencies of the equilibrium magnetic configuration and the magnetic energy barrier when using the simplifying assumption that the self-demagnetizing field is identical in magnitude to the dipole field. At a small thickness asymmetry of 0.2 nm, for example, the magnetic energy barrier is reduced from 68 kT (T=300 K) to 6 kT at the remanent state and a progressive switching behavior changes into a critical behavior, as the simplifying assumption is used. The present results clearly demonstrate the need for an accurate analytical equation for the total energy in predicting the thermal stability of nanostructured synthetic ferrimagnets.

• 한국소음진동공학회논문집
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• 제13권12호
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• pp.903-910
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• 2003

A two-degree-of-freedom model is suggested to describe basic dynamical behaviors of the interaction between the pad and the disc of a disc brake system. Although a pad (and a disc) has many modes of vibration in practice, only one mode of each component Is considered. In this paper, a linear analysis is performed by means of the stability analysis to show various conditions for the system to become unstable, and is based on the assumption that the existence of limit cycle (this corresponds to an unstable equilibrium point inside the limit cycle) represents the squeal state of the disc brake system. The results of the stability analysis show that the damping of the disc is as much Important as that of the pad, whereas the damping of the pad only is considered In most practical situations.

• Journal of Mechanical Science and Technology
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• 제20권8호
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• pp.1292-1301
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• 2006

This article investigates numerically the carrier-phonon interactions in thin gallium arsenide (GaAs) film structures irradiated by subpicosecond laser pulses to figure out the role of several recombination processes on the energy transport during laser pulses and to examine the effects of laser fluences and pulses on non-equilibrium energy transfer characteristics in thin film structures. The self-consistent hydrodynamic equations derived from the Boltzmann transport equations are established for carriers and two different types of phonons, i.e., acoustic phonons and longitudinal optical (LO) phonons. From the results, it is found that the two-peak structure of carrier temperatures depends mainly on the pulse durations, laser fluences, and nonradiative recombination processes, two different phonons are in nonequilibrium state within such lagging times, and this lagging effect can be neglected for longer pulses. Finally, at the initial stage of laser irradiation, SRH recombination rates increases sufficiently because the abrupt increase in carrier number density no longer permits Auger recombination to be activated. For thin GaAs film structures, it is thus seen that Auger recombination is negligible even at high temperature during laser irradiation.

• 한국공간구조학회논문집
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• 제21권4호
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• pp.49-56
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• 2021

This study aims to develop a form-finding algorithm for a single-layered pneumatic membrane. The initial shape of this pneumatic membrane, which is an air-supported type pneumatic membrane, is to find a state in which a given initial tension and internal pneumatic pressure are in equilibrium. The algorithm developed to satisfy these conditions is that a nonlinear optimization problem based on the force method considering the deformed shape is formulated, and, it's able to find the shape by iteratively repeating the process of obtaining a solution of the governing equations. An computational technique based on the Gauss-Newton method was used as a method for obtaining solutions of nonlinear equations. In order to verify the validity of the proposed form-finding algorithm, a single-curvature pneumatic membrane example and a double-curvature air pneumatic membrane example were adopted, respectively. In the results of these examples, it was possible to well observe the step-by-step convergence process of the shape of the pneumatic membrane, and it was also possible to confirm the change in shape according to the air pressure. In addition, the calculation results of the shape and internal force after deformation due to initial tension, air pressure, and self-weight were obtained.

• 천문학회보
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• 제46권1호
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• pp.51.2-51.2
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• 2021

Nuclear rings are sites of intense star formation at the center of barred spiral galaxies. A straightforward but unanswered question is what controls star formation rate (SFR) in nuclear rings. To understand how the ring SFR is related to mass inflow rate, gas content, and background gravitational field, we run a series of semi-global hydrodynamic simulations of nuclear rings, adopting the TIGRESS framework to handle radiative heating and cooling as well as star formation and supernova feedback. We find: 1) when the mass inflow rate is constant, star formation proceeds in a remarkably steady fashion, without showing any burst-quench behavior suggested in the literature; 2) the steady state SFR has a simple linear relationship with the inflow rate rather than the ring gas mass; 3) the midplane pressure balances the weight of the overlying gas and the SFR surface density is linearly correlated with the midplane pressure, consistent with the self-regulated star formation theory. We suggest that the ring SFR is controlled by the mass inflow rate in the first place, while the gas mass adjusts to the resulting feedback in the course of achieving the vertical dynamical equilibrium.