• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.291-295
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• 2005

This paper presents the modeling of grounding system on Korean electric railway system. The system model is composed of the catenary system, the grounding-system, the sub-sectioning post, the fault point, the sectioning post, the autotransformer in the substation, and the electric vehicle. The increment of rail-ground voltage may be thought as an amplifier of danger on human body of equipment insulation. The rail-ground voltage on steady state and on fault condition should be under standard limit voltage. To analyze grounding system for steady state and fault condition on Korean railway, modeling for each railway system is performed by 10-port network model. Modeling and analysis of present grounding-system are important to protect human and electronic equipments. The examinations for systematic grounding-system are investigated.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.790-795
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• 2004

The characteristics of refrigerator noise recorded in anechoic chamber was investigated in condition of a the real living room and a kitchen. To predict the noise propagation in an apartment unit, room acoustic simulation software was used. It was found that the noise level in the real living room was $4\sim8dB$ higher than in the anechoic chamber. When a noise barrier and absorption materials were used on the rear wall and floor, the noise level reduced up to $3\sim4dB$. In addition, when the subjective evaluation of auralized refrigerator noise was undertaken using headphone, it was revealed that 21dB (A) is the allowable sound pressure level of 95% satisfaction.

• 터널과지하공간
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• 제13권5호
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• pp.389-396
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• 2003

본 연구는 정상류 Navier-Stokes 방정식에 섭동(perturbation) 이론을 적용하여 주기함수 간극에 대한 삼승법칙의 수정에 대해 논하였다. 이를 위해, 주기함수를 진폭과 파장에 대한 무차원 함수로 전환한 뒤 미소 계수에 대한 무차원 유동함수와 연속 방정식을 적용하였다. 이러한 과정을 통해 정상류 Navier-Stokes 방정식의 섭동 근사해를 구하였으며 이를 유한 차분법에 적용하였다. 단일 절리 모델에 대한유한 차분 수치해석을 통해, 수정된 삼승 법칙이 주기함수 간극의 유체 유동에 대한 정상류 Navier-Stokes 방정식의 섭동 근사해와 잘 일치하는 것으로 나타났다. 이를 통해 본 연구에서 제시된 삼승 법칙이 간극 분포에 따른 유체 유동의 평가에 있어 유용하게 적용될 수 있는 것으로 나타났다.

• Journal of applied mathematics & informatics
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• 제29권3_4호
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• pp.901-908
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• 2011

In this paper, we establish a sharp condition of global existence for the solution of the Gross-Pitaevskii equation with an angular momentum rotational term. This condition is related to the ground state solution of some steady-state nonlinear Schrodinger equation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2769-2774
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• 2007

In vacuum ejector-diffuser systems where a finite volume secondary chamber is used, the secondary jet exhibits transient characteristics during start-up. A steady state is achieved after some time in which mass entrainment prevails indefinitely inside the ejector, though there is no flow from the secondary chamber. An attempt is made in this work to study the infinite entrainment of secondary jet into the primary jet from a finite secondary chamber, with the help of a computational fluid dynamics method. The present study is also intended to identify the operating range of vacuum ejector-diffuser systems where the steady flow assumption can be applied without uncertainty. The results obtained show that the only condition in which an infinite mass entrainment is possible is the generation of a re-circulation zone near the primary nozzle exit. The flow in the secondary chamber attains a state of dynamic equilibrium at this point. Steady flow assumption is valid only after this point.

• 상하수도학회지
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• 제11권3호
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• pp.67-78
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• 1997

The objective of study was to examine to transient response of hydraulic shock loading in activated sludge process for treatment of municipal sewage. The general experiment approach was to operate the system under steady-state(pre-shock), then to apply step changes during 24hours in fourfold hydraulic shock loading at the same organic loading. Performance was assessed in both the transient state and the new steady-state(post-shock). Three bench scale activated sludge reactors were operated to investigate the effect of fourfold hydraulic shock loading on TSS and COD removal efficiency. In activated sludge reactors operated with 13hours and 7hours of HRT, effluent quality of all reactors was not changed for few effects, and also showed no foaming and no sludge bulking. Those results are the same as sludge withdrawn reactors. The effect of fourfold hydraulic shock loading on the activated sludge reactors operated with 3hours of HRT was most severe. The effluent quality was deteriorated significantly and generate foaming in reactors. Less than 24hours after the fourfold shock loading applied, the activated sludge system seemed to attain a new steady-state condition as show by effluent.

• Journal of Mechanical Science and Technology
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• 제19권11호
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• pp.2077-2081
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• 2005

A symmetry breaking nonlinear fluid flow in a two-dimensional wall-driven square cavity taking symmetric boundary condition after some transients has been investigated numerically. It has been shown that the symmetry breaking critical Reynolds number is dependent on the time history of the boundary condition. The cavity has at least three stable steady state solutions for Re=300-375, and two stable solutions if Re>400. Also, it has also been showed that a particular solution among several possible solutions can be obtained by a controlled boundary condition.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 추계 학술대회논문집
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• pp.127-138
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• 1999

본 연구에서는 2 차원 캐비티 유동에서 경계조건 부여 방법의 차이에 따른 유체유동의 이력이 최종적인 정상상태에 미치는 효과를 수치실험을 통하여 관찰하였다. 그 결과 유동의 Reynolds 수가 작은 경우는 유동장이 가지는 이력이 시간의 경과와 함께 소멸하여 하나의 정상유동 상태를 가지는데 반하여, 큰 Reynolds 수에서는 유동장 이력이 소멸하지 않고 유지됨으로 인하여 다수의 정상유동 형태가 나타남이 확인이 되었다. 엄밀한 이론적 해석은 현재 이루워지지 않았으나 유체 운동량의 증가에 따라 Navier-Stokes 방정식의 비선형성이 영향을 미치고 있다고 여겨진다.

• 아시안잔디학회지
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• 제9권4호
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• pp.285-292
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• 1995

To elucidate the mineral cycles of potassium in a dynamic grassland ecosystem in a steady state condition, this investigation was cunducted along the northwest side on Mt. Kwanak. The exper-imental results may he summarized on communities of Z. japonica and M. sinensis as follows. As compared with some pronerties of the surface soils among two semi-natural grasslands, the levels of exchangeahle potassium were high in M. sinensis and low in Z. japonica. Contents of potassium for the litters of Z. japonica and M. sinensis were 1.69% and 2.51%, re-spectively. The annual production of potassium was 1.32 g /m$m^2$ in the Z. japonica grassland and 3. 08 g /m$m^2$in the M. sinensis grassland. For a case of steady production and release, the ratio of annual min- eral production to the amount accumulated on top of the mineral soil in a steady state provides estimates of the release constant k. The models of the release, accumulation and annual cycle of potassium in a grassland ecosystem are determined by the equation (1) to (3), respectively (Table 3). Since it requires a period of about each 0.693 /r, 3 /r and 5 /r years for the release and accumu-lation of 50, 95 and 99% of its steady-state level, the estimates for potassium in a dynamic grass-land ecosystem of Mt. Kwanak were 1.5, 6.6 and 11.0 years in the Z. japonica grassland, and were 2.7, 11.9 and 19.8 years in the M. sinensis grassland. The amounts of annual cycles for potassium in a grassland ecosystem under the steady-state conditions were 1.32 g /m$^2$ in the Z. japonica grassland and 3.08 g /$m^2$ in the M. sinensis grassland. Key words : ZQvsia japonica Ahscanthus sinensis, Mt. Kwanak, Potassium cycles.

• Nuclear Engineering and Technology
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• 제52권12호
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• pp.2789-2802
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• 2020

Small Modular Reactors (SMRs) are attracting wide attention due to their outstanding performance, extensive studies have been carried out for lead-based fast reactors (LFRs) that cooled with Lead or Lead-bismuth (LBE), and small modular natural circulation LFR is one of the promising candidates for SMRs and LFRs development. One of the challenges for the design small modular natural circulation LFR is to master the natural circulation thermal-hydraulic performance in the reactor primary circuit, while the natural circulation characteristics is a coupled thermal-hydraulic problem of the core thermal power, the primary loop layout and the operating state of secondary cooling system etc. Thus, accurate predicting the natural circulation LFRs thermal-hydraulic features are highly required for conducting reactor operating condition evaluate and Thermal hydraulic design optimization. In this study, a thermal-hydraulic analysis code is developed for small modular natural circulation LFRs, which is based on several mathematical models for natural circulation originally. A small modular natural circulation LBE cooled fast reactor named URANUS developed by Korea is chosen to assess the code's capability. Comparisons are performed to demonstrate the accuracy of the code by the calculation results of MARS, and the key thermal-hydraulic parameters agree fairly well with the MARS ones. As a typical application case, steady-state analyses were conducted to have an assessment of thermal-hydraulic behavior under nominal condition, and several parameters affecting natural circulation were evaluated. What's more, two characteristics parameters that used to analyze natural circulation LFRs natural circulation capacity were established. The analyses show that the core thermal power, thermal center difference and flow resistance is the main factors affecting the reactor natural circulation. Improving the core thermal power, increasing the thermal center difference and decreasing the flow resistance can significantly increase the reactor mass flow rate. Characteristics parameters can be used to quickly evaluate the natural circulation capacity of natural circulation LFR under normal operating conditions.