• 한국수자원학회:학술대회논문집
• /
• 한국수자원학회 2018년도 학술발표회
• /
• pp.317-317
• /
• 2018

Baseflow which is one of the unmeasurable components of streamflow and slowly flows through underground is important for water resource management. Despite various separation methods from researches preceded, it is difficult to find a significant separation method for baseflow separation. This study applied the MRC method and developed the improved approach to separate baseflow from total streamflow hydrograph. Previous researchers utilized the whole streamflow data of study period at once to derive synthetic MRCs causing unreliable results. This study has been proceeded with total nine areas with gauging stations. Each three areas are selected from 3 domestic major watersheds. Tool for drawing MRC had been used to draw MRCs of each area. First, synthetic MRC for whole period and two other MRCs were drawn following two different criteria. Two criteria were set by different conditions, one is flow condition and the other is seasonality. The whole streamflow was classified according to seasonality and flow conditions, and MRCs had been drawn with a specialized program. The MRCs for flow conditions had low R2 and similar trend to recession segments. On the other hand, the seasonal MRCs were eligible for the baseflow separation that properly reflects the seasonal variability of baseflow. Comparing two methods of assuming MRC for baseflow separation, seasonal MRC was more effective for relieving overestimating tendency of synthetic MRC. Flow condition MRCs had large distribution of the flow and this means accurate MRC could not be found. Baseflow separation using seasonal MRC is showing more reliability than the other one however, if certain technique added up to the flow condition MRC method to stabilize distribution of the streamflow, the flow conditions method could secure reliability as much as seasonal MRC method.

• 한국가스학회지
• /
• 제15권3호
• /
• pp.53-57
• /
• 2011

본 연구는 배열회수보일러(HRSG)에서의 유동특성을 유동수치해석을 통하여 분석하였다. HRSG 입구영역은 가스터빈 후류의 출구에 해당하고 가스터빈 후류는 강한 선회 및 난류 유동이다. 따라서 HRSG 입구 유동은 가스 터빈 출구 유동 특성이 고려되어야 한다. 본 연구에서는 HRSG 입구 유동 경계조건을 가스터빈 출구 유동 해석을 통하여 도출된 결과를 이용하였다. 가스터빈 출구 유동해석 결과를 보면 축방향 속도가 가장 크게 나타나는 곳이 원형 덕트의 벽면 측이고 난류운동에너지와 소산율이 크게 나타나는 곳이 속도 구배가 급격한 곳으로 축방향 속도가 최대가 되는 곳과 차이가 있다. 본 연구에서는 HRSG 입구영역에서의 난류 성분을 가스터빈 출구 유동을 계산 한 결과를 이용한 경우와 난류강도를 속도의 10%를 이용하고 원형 덕트의 직경을 특성 길이로 사용한 두 가지 경우에 대하여 유동해석을 통하여 유동 특성을 비교하였다. 본 연구를 통하여 HRSG 입구 유동 경계조건은 반드시 난류성분이 올바르게 적용되어야 HRSG 유동 특성 해석의 정확성을 기할 수 있음을 알았다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.3021-3026
• /
• 2007

In this paper, experimental data on flow pattern transition of inclination angles from 0-90 are presented. A test section is constructed 2 mm long and I.D 1inch using transparent material. The test section is supported by aluminum frame that can be placed with any arbitrary inclined angles. The air-water two-phase flow is observed at room temperature and atmospheric condition using both high speed camera and void impedance meter. The signal is sampled with sampling rate 1kHz and is analyzed under fully-developed condition. Based on experimental data, flow pattern maps are made for various inclination angles. As increasing the inclination angels from 0 to 90, the flow pattern transitions on the plane jg-jf are changed, such as stratified flow to plug flow or slug flow or plug flow to bubbly flow. The transition lines between pattern regimes are moved or sometimes disappeared due to its inclined angle.

• 한국전산유체공학회지
• /
• 제13권1호
• /
• pp.14-20
• /
• 2008

The flow characteristics around a rudder in open water condition is analyzed by the computational method. Reynolds averaged Navier-Stoke's equation is utilized for the computation. The computational hydrodynamic force coefficients are verified through comparing with the experimental results. The information of these flow characteristics is necessary to predict cavitation and maneuvering performances, to estimate steering gear capacitance, and to get the bending moment which is useful for the structural analysis. The pressure distribution, the three-dimensional flow separation, and the tip vortices are investigated. The pattern of the three-dimensional flow separation is analyzed utilizing a topological rule. The tip vortices are also investigated through a visualization technique.

• 한국산학기술학회논문지
• /
• 제3권4호
• /
• pp.285-289
• /
• 2002

본 논문에서는 아이스크림용 아이스 콘에서 콘 부분을 만들기 위한 금형의 제작시 필요한 구조적 안정성을 평가 할 수 있는 유동해석을 수행하였다. 유동해석을 수행하기 위하여 상용 유한요소해석 코드인 ANSYS를 활용하였으며 내압조건, 경계조건, 구속조건 등을 고려하여 아이스 콘 금형 내부의 유동 흐름을 압력조건의 변화에 따라 구하였다.

• Nuclear Engineering and Technology
• /
• 제53권2호
• /
• pp.446-454
• /
• 2021

Critical heat flux (CHF) has traditionally been evaluated using look-up tables or empirical correlations for nuclear power plants. However, under complex moving condition, it is necessary to reconsider the CHF characteristics since the conventional CHF prediction methods would no longer be applicable. In this paper, the additional forces caused by motions have been added to the annular film dryout (AFD) mechanistic model to investigate the effect of moving condition on CHF. Moreover, a theoretical model of the natural circulation loop with additional forces is established to reflect the natural circulation characteristics of the loop system. By coupling the system loop with the AFD mechanistic model, a CHF prediction program called NACOM for natural circulation loop under moving condition is developed. The effects of three operating conditions, namely stationary, inclination and rolling, on the CHF of the loop are then analyzed. It can be clearly seen that the moving condition has an adverse effect on the CHF in the natural circulation system. For the calculation parameters in this paper, the CHF can be reduced by 25% compared with the static value, which indicates that it is important to consider the effects of moving condition to retain adequate safety margin in subsequent thermal-hydraulic designs.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 추계학술대회
• /
• pp.1383-1388
• /
• 2004

The flow characteristics in the blade passage of a low speed axial flow fan have been investigated by experimental analysis using a rotating hot-wire sensor for design and off-design operating conditions. The results show that the tip leakage vortex is moved upstream when flow rate is decreased, thus disturbing the formation of wake flow near the rotor tip. The tip leakage vortex interfaces with blade pressure surface, and results in high velocity fluctuation near the pressure surface. From the relative velocity distributions near the rotor tip, large axial velocity decay is observed at near stall condition, which results in large blockage compared to that at the design condition. Througout the flow measurements using a quasi-orthogonal measuring points to the tip leakage vortex, it is noted that the radial position of the tip leakage vortex is distributed between 94 and 96 percent span for all flow conditions. High spectrum density due to the large fluctuation of the tip leakage vortex is observed near the blade suction surface below the frequency of 1000 Hz at near stall condition.

• 한국소음진동공학회논문집
• /
• 제16권11호
• /
• pp.1115-1123
• /
• 2006

Nuclear fuel rods are exposed to axial flow in a reactor, and flow-induced-vibration due to the flow usually causes damage in the fuel rods. Thus a prior knowledge about dynamic behavior of a fuel rod exposed to the flow condition should be provided. This paper shows that dynamic characteristics of a nuclear fuel rod depend on axial flow velocity. Assuming small lateral displacement, the effects of uniform axial flow are investigated. The analytic results show that axial flow generally reduces fuel rod stiffness and raises its damping in normal condition. Also, the critical axial velocities which make the fuel rod behavior unstable were found. That is, solving generalized eigenvalue equation of the fuel rod dynamic system, the eigenvalues with positive real part are detected. Based on the simulation results, on the other hand, it turns out that the ordinary axial flow in nuclear reactors does not affect to stability of a nuclear fuel rod even in the conservative condition.

• 한국지반신소재학회논문집
• /
• 제6권3호
• /
• pp.9-16
• /
• 2007

토양증기추출공법(SVE)은 불포화 지반상태에서 휘발성 유기화합물(VOCs)과 유류오염 물질을 제거하는데 효과적이고 경제적인 공법중의 하나이다. 본 연구에서는 기존 연약지반의 지반개량시 사용된 연직배수재(PVDs)를 토양증기추출시스템에 적용하여 짧은 공기배출거리로 최대한 신속하게 오염물질을 제거할 수 있게 하여 투기계수가 낮은 지반에서 오염된 토양을 효과적으로 복원할 수 있는 토양증기추출공법을 적용하는데 목적이 있다. 연직배수재를 이용한 토양증기추출시스템 적용시 실제 현장에서 나타나는 무한 경계 조건을 만족하기 위해서 실내에서 파일럿 규모의 오염복원 모형실험을 결과로 유한경계조건 시스템에서 이미지웰 중첩이론을 이용하여 압력분포를 가정하였다. 즉, 압력강하가 없는 일정수두 경계조건 상태와 토조의 상 하부와 같이 흐름이 없는 불투수경계조건 상태를 유지하기 위해서 이미지웰 중첩이론을 도입하여 경계조건을 수립하였다. 결과, 공기흐름률이 증가할수록 흐름비율도 증가하였다. 따라서 높은 흐름률에 대한 흐름비율도 더 커지게 되는 것이고, 최적화과정동안 공기흐름률은 측정 압력수두와 이미지웰 중첩이론으로부터 구해진 이론 압력수두의 오차율에 미치는 가장 중요한 인자로 판단된다.

• Journal of Advanced Marine Engineering and Technology
• /
• 제38권10호
• /
• pp.1244-1250
• /
• 2014

The temperature of the main engine cabin of commercial vessel is very high. The material SS-316L undergoes creep damage at temperatures exceeding $450^{\circ}C$. It is essential to maintain the highly stressed engine cabin below the creep regime. Hence, seawater is employed in this kind of maritime vehicles as cooling liquid. It obtains the thermal energy at the cooling pipe line after passing through main engine cooling system. To harness the energy in the seawater, a turbine can be installed to absorb the energy in the seawater before being released into the sea. In this study, a cooling pipe line is selected to apply the tubular type hydro turbine for transferring the energy. Numerical analysis for investigating the performance and the internal flow characteristics of the tubular turbine is conducted. The results show that the maximum efficiency of 85.8% is achieved although the efficiency drops rapidly at partial flow rate condition. The efficiency descends slowly at the condition of excess flow rate. There is a relatively wide operating range of flow rate of this turbine to keep high efficiency at the excess flow rate condition. For the internal flow of the turbine, there is uniform streamline on the suction and pressure sides of the blade at the design point. However, the secondary flow appears at the suction and pressure sidesat the excess flow rate.In addition, it appears only at pressure side at the partial flow rate condition.