• 제어로봇시스템학회논문지
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• 제3권2호
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• pp.162-168
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• 1997

Digital variable structure controller(DVSC) is implemented to control the temperature for the hot water heating circulating pump control system. For the DVSC, a control algorithm is suggested, which using a nonlinear sliding surface and a PID sliding surface outside and inside of steady state error boundary layer, respectively. Smith predictor algorithm is used for the compensation of long dead time. The DVSC of the suggested algorithm yields improved control performance compared with the one of existing algorithm. The system responses with the suggested DVSC shows good responses without overshoot and steady state error inspite of heating load change. By decreasing sampling time, dead time and rise time are increasing, and system output noise by flow dynamics is amplified.

• Nuclear Engineering and Technology
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• 제41권9호
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• pp.1205-1214
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• 2009

The critical heat flux (CHF) levels that occurred due to exponential heat inputs for varying periods to a 1.0-mm diameter horizontal cylinder immersed in various liquids were measured to develop an extended database on the effect of high subcoolings for quasi-steady-state and transient maximum heat fluxes. Two main mechanisms of CHF were found. One mechanism is due to the time lag of the hydrodynamic instability (HI) which starts at steady-state CHF upon fully developed nucleate boiling, and the other mechanism is due to the explosive process of heterogeneous spontaneous nucleation (HSN) which occurs at a certain HSN superheat in originally flooded cavities on the cylinder surface. Steady-state CHFs were divided into three regions for lower, intermediate and higher subcooling at pressures resulting from HI, transition and HSN, respectively. HSN consistently occurred in the transient boiling CHF conditions that correspond to a short period. It was also found that the transient boiling CHFs gradually increased, then rapidly decreased and finally increased again as the period became shorter.

• 대한기계학회논문집B
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• 제26권12호
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• pp.1729-1737
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• 2002

A mathematical model for the prediction of carbon-dioxide absorption rate during the transient state of rotary type absorber is developed. The rotary type absorber operates using a fast rotating porous structure and clean water. The model for the transient state rotary type absorbers is based on the steady state model of packed tower absorber. The paper manipulates the operating data of an arbitrary quasi-steady state condition of rotary type absorber for the determination of the coefficients involved in the model developed. The prediction accuracy is evaluated from the measured data of rotary type absorber operated under fast transient state. The measured data include the mole fraction of carbon dioxide in mixed gas and the pressure of absorber. The relative error in carbon dioxide prediction is estimated to be 20% at maximum. The model is successfully applied for the prediction of the behavior of a closed cycle diesel engine.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2006년도 총회 및 춘계학술발표회
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• pp.293-297
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• 2006

Submarine groundwater discharge (SGD) and the interface between seawater and freshwater in an unconfined coastal aquifer was evaluated by numerical modeling. A two-dimensional vertical cross section of the aquifer was constructed. Coupled flow and salinity transport modeling were peformed by using a numerical code FEFLOW In this study, we investigated the changes in groundwater flow and salinity transport in coastal aquifer with hydraulic condition such as the magnitude of recharge flux, hydraulic conductivity. Especially, transient simulation considering tidal effect and seasonal change of recharge rate was simulated to compare the difference between quasi-steady state and transient state. Results show that SGD flux is in proportion to the recharge rate and hydraulic conductivity, and the interface between the seawater and the freshwater shows somewhat retreat toward the seaside as recharge flux increases. Considered tidal effect, SGD flux and flow directions are affected by continuous change of the sea level and the interface shows more dispersed pattern affected by velocity variation. The cases which represent variable daily recharge rate instead of annual average value also shows remarkably different result from the quasi-steady case, implying the importance of transient state simulation.

• 한국수자원학회논문집
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• 제36권6호
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• pp.949-960
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• 2003

정상상태 가정을 완화시킨 습윤지수의 해상도 문제가 수치지형모형에서 다루어졌다. 반 동역학적 습은지수와 동력학적 습윤지수의 변화성을 수치고도모형의 격자 크기와 배수시간을 변화시키면서, 공간적 통계적으로 고찰하였다. 변화하는 배수시간과 격자크기에 따라 습윤지수의 구조화 양상이 관찰 되었다. 설마천 유역의 적용결과 비교적 짧은 배수시간에서는 습윤도의 천이성이 관찰되었고, 10,000 시간 이상의 배수 시간에서는 통계적 분석 결과가 정상상태의 특성으로 수렴함을 보여주고 있다. 반 동역학적 및 동역학적 습윤지수의 확률밀도 함수들은 계산결과의 안정성과 일관성에 관련이 있는 경계 격자 크기가 존재함을 보여주고 있다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.702-705
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• 2001

This paper deals with a method to predict the flying state of the head slider in a optical disk drive(ODD). The Dual Solver based on the Quasi-Newton method and the Newton method has been developed to simulate the steady-state flying conditions. The numerical results show the effectiveness and reliability of this new solver.

• 대한기계학회논문집
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• 제18권5호
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• pp.1087-1095
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• 1994

Chain drive power transmission system was developed for a low head hydro-turbine which generates power by energy transformation on the turbine blades attached to chains. Also, experimental and theoretical analysis for the sprocket wheel tooth load distribution were performed. The tooth load was measured by the specially designed load sensor. It was found that the tooth load distribution for the steady state operation was in good accordance with the quasi-static state results showing the peak load at the final meshing tooth. The trend of the experimental results agreed with the theoretical results based on the spring model analysis and difference in the magnitude of the maximum tooth load was considered to be the effect of the variable spring constant due to the moving contact point between the roller and sprocket wheel tooth.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 추계학술대회 논문집 학회본부
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• pp.381-384
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• 1988

This paper analysed basic operation in Zero-voltages-switching quasi-resonant buck converter and considered steady state characteristics. Especially, it is confirmed that converter operating at maximum 1MHz switching frequency in load characteristics. In this paper, a novel slope method is proposed and implemented in regulation characteristics analysis. It is proved that experimenental results coincide with theory results.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권5호
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• pp.456-465
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• 2016

In order to optimize the performance of a Wells turbine with fixed guide vanes, the designs of an end plate and a ring on the tip of the turbine rotor are proposed as penetrating blade tip treatments. In this study, numerical investigations are made using computational fluid dynamics (CFD)-based ANSYS Fluent software, and validated by corresponding experimental data. The flow fields are analyzed and non-dimensional coefficients $C_A$, $C_T$ and ${\eta}$ are calculated under steady-state conditions. Numerical results show that the stalling phenomenon on a ring-type Wells turbine occurs at a flow coefficient of ${\phi}=0.36$, and its peak efficiency can reach 0.54, which is 16% higher than that of an unmodified turbine and 9% higher than in the case of an endplate-type turbine. In addition, quasi-steady analysis is used to calculate the mean efficiency and output work of a wave cycle under sinusoidal flow conditions. As a result, it has been found that the ring-type turbine is superior to other types of Wells turbines.

• 한국지반공학회논문집
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• 제19권1호
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• pp.61-75
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• 2003

한계상태 토질역학을 사질토의 전단거동에 대한 적용을 용이하게 하기 위해서, 표준삼축 시험으로부터 사질토에서의 한계상태정수 결정에 관하여 종합적인 고찰을 실시하였다. 첫째로, 문헌에 있는 어휘론적인 차이점들을 명확히 함으로써, 한계상태는 대변형에서의 궁극적인 최종상태를 나타냄을 추론하였다. 둘째로, 한계상태정수의 특성들에 관하여 검토하였고, 초기상태, 구주 하중조건 및 배수조건에 따른 한계상태선의 유일성과 유사한계상태조건의 민감성을 검증하였다. 셋째로, 한계상태정수로부터 액상화후 전단강도 즉 액상화된 흙에서의 신뢰할 수 있는 궁극적인 전단강도를 산정하기 위하여 한계상태 토질역학을 예제로서 적용하였다.