• 한국항공우주학회지
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• 제45권1호
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• pp.1-9
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• 2017

본 논문은 초음속 공탄성(aeroelastics) 해석 시간 절약을 위한 준-정상 축약 모델을 제안하고 이를 검증하였다. 유동이 초음속이고 유동의 특성시간이 구조변형의 특성시간에 비해 작을 경우, 유동의 비정상성이 작아 비정상 유동해 대신 정상 유동해를 이용하여 공탄성 해석을 할 수 있다. 크리깅 기법을 적용하여 유동의 축약모델을 구축하였다. 매 시간 축약모델로부터 예측된 표면해가 구조해석의 경계조건으로 사용되었다. 크리킹 기법을 적용한 축약모델을 비정상해석 결과와 비교하여 검증하였다.

• 한국기계가공학회지
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• 제5권1호
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• pp.51-58
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• 2006

The objective of this research work is to investigate into heat transfer characteristics of the laser cutting of CSP 1N sheet using high power CW Nd:YAG laser. In order to investigate the heat transfer characteristics, three dimensional quasi stationary and steady-state heat transfer analysis has been carried out. The laser heat source is assumed as a volumetric heat source with a gaussian heat distribution in a plane. Through the comparison of the results of analyses with those of experiments, the proper finite element model has been obtained. In addition, characteristics of the three-dimensional heat transfer and temperature distribution have been estimated by the finite element model. Finally, the minimum temperature at the center for cutting of the material has been estimated.

• Wind and Structures
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• 제5권5호
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• pp.393-406
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• 2002

Aerodynamic pressures and forces were measured on a model of a solar panel containing six slender, parallel modules. Of particular importance to system design is the aerodynamically induced torque. The peak system torque was generally observed to occur at approach wind angles near the diagonals of the panel ($45^{\circ}$, $135^{\circ}$, $225^{\circ}$ and $315^{\circ}$) although large loads also occurred at $270^{\circ}$, where wind is in the plane of the panel, perpendicular to the individual modules. In this case, there was strong vortex shedding from the in-line modules, due to the observation that the module spacing was near the critical value for wake buffeting. The largest loads, however, occurred at a wind angle where there was limited vortex shedding ($330^{\circ}$). In this case, the bulk of the fluctuating torque came from turbulent velocity fluctuations, which acted in a quasi-steady sense, in the oncoming flow. A simple, quasi-steady, model for determining the peak system torque coefficient was developed.

• Wind and Structures
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• 제19권2호
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• pp.113-144
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• 2014

Separation bubble and conical vortices on a large-span flat roof were observed in this study through the use of flow visualization. The results indicated that separation bubble occurred when the flow was normal to the leading edge of the flat roof. Conical vortices that occur under the cornering flow were observed near the leading edge, and their appearance was influenced by the wind angle. When the wind changed from along the diagonal to deviating from the diagonal of the roof, the conical vortex close to the approaching flow changed from circular to be more oblong shaped. Based on the measured velocities in the conical vortices by flow visualization, a proposed two-dimensional vortex model was improved and validated by simplifying the velocity profile between the vortex and the potential flow region. Through measured velocities and parameters of vortices, the intensities of conical vortices and separation bubble on a large-span flat roof under different wind directions were provided. The quasi-steady theory was corrected by including the effect of vortices. With this improved two-dimensional vortex model and the corrected quasi-steady theory, the mean and peak suction beneath the cores of the conical vortices and separation bubble can be predicted, and these were verified by measured pressures on a larger-scale model of the flat roof.

• 천문학회지
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• 제29권spc1호
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• pp.1-5
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• 1996

Recent discussions of observational constraints on the standard hot big bang model are reviewed and it is argued that now there is room for considering alternative cosmologies. The quasi-steady state cosmology is briefly described. This model seems to explain most of the observed features of the universe, including the m-z relation, radio source count, the light nuclear abundances and the microwave background.

• Ecology and Resilient Infrastructure
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• 제2권4호
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• pp.317-323
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• 2015

본 연구는 장기하상변동 모의를 이용하여 댐 하류 하천에서의 하상변동이 어류 물리서식처에 미치는 영향에 대하여 연구하였다. 이를 위하여 흐름모형은 준정류 모형을 이용하였으며, 서식처 모형은 서식처 적합도 지수 (HSI) 모형을 이용하였다. 장기하상변동 모의를 위하여 Exner 방정식을 이용하였으며 하상재료 입도분포의 변화를 고려하였다. 내성천 영주댐 하류에서 모의결과 침식과 장갑화가 진행되었으며 이에 따라 피라미의 물리서식처가 변하게 되었다. 지형과 하상재료의 변화가 어류 물리서식처에 영향을 끼치는 것을 확인할 수 있다.

• 상하수도학회지
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• 제22권6호
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• pp.657-664
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• 2008

This research compared several unsteady friction models for transient analysis of pipeline system. Unsteady friction is an important factor for accurate simulation of hydraulic transient. Steady friction, quasi-steady friction, Zielke's model and two versions of Brunone model were compared with measurement data of identical pipeline conditions. This study showed that the existing simple steady friction model can be useful for the safer design of pipeline system due to its overestimation of waterhammer, but introduction of more elaborate models are required for advanced analysis such as inverse transient analysis of friction or leakage and the preliminary analysis of water quality prediction of water distribution system.

• Structural Engineering and Mechanics
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• 제12권3호
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• pp.267-281
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• 2001

Transient and quasi-steady-state vertical vibrations of a multi-span beam steel bridge located on a single-track railway line are considered, induced by a superfast passenger train, moving at speed 120-360 km/h. Matrix dynamic equations of motion of a simplified model of the system are formulated partly in the implicit form. A recurrent-iterative algorithm for solving these equations is presented. Excessive vibrations of the system in the resonant zones are reduced effectively with passive dynamic absorbers, tuned to the first mode of a single bridge span. The dynamic analysis has been performed for a series of types of bridges with span lengths of 10 to 30 m, and with parameters closed to multi-span beam railway bridges erected in the second half of the $20^{th}$ century.

• 설비공학논문집
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• 제14권1호
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• pp.10-20
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• 2002

A dynamic model of a water heater system heated by a heat pump was developed. The water heater system was composed of heat pump and hot water reservoirs. Finite volume method (FVM) was applied to describe the heat exchangers. A new constraint on electronic expansion valve (EEV) or thermostatic expansion valve (TXV) that can control superheat after the evaporator was developed. Dynamic performances were evaluated for various sizes of the reservoir. In order to compare those performances, time scale was normalized by time constant representing the characteristics of reservoir size. Time constant was determined from quasi steady-state simulation of the system. From the simulation, the size of the water heater reservoir was found to have a large influence on the transient performance of the sys- tem. Therefore, the optimization of the reservoir size is needed in a design process.

• 한국추진공학회지
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• 제14권6호
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• pp.45-52
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• 2010

본 논문에는 분리장치 종류 중 하나인 가스푸셔와 가스발생기의 수학적-물리적 모델이 기술되어있다. 준정상상태 모델이 가스푸셔와 가스발생기로 구성된 PAD의 성능해석을 위해 도입되었다. 실험적 상수인 열손실계수와 마찰계수는 시험에 의해 결정되었다. 그레인 형상설계에 기초한 가스발생기와 가스푸셔 내부의 연소과정, 유동과 피스톤 거동이 수치해석적 방법으로 시뮬레이션 되었다. 개발된 예측기법은 향후 유사한 분리메카니즘 시스템 설계시에 유용하게 사용될 수 있을 것이다.