하천 유량,수질변화 특성을 고려한 수질오염총량관리 기준유량 조건에 관한 연구

박준대 ( Jun Dae Park ),오승영 ( Seung Young Oh ),최윤호 ( Yun Ho Choi ) 한국물환경학회 ( 구 한국수질보전학회 ) 2012 한국물환경학회지 Vol.28 No.3

The variation of stream flow is the one of the most important factors which influence on that of water quality in the unit watershed. The target water quality goal is established and permissible load is allotted in the base of the standard flow condition along with its water quality for the management of Total Maximum Daily Loads (TMDLs). A standard flow selected could cause problems in the load allotment if it was not properly arranged. This study reviewed the acquisition of water quality data, the self-variation and the retainability in water quality on the specific flow conditions. This study also proposed the median and the adjusted average flow condition out of general flow conditions as alternative standard flow conditions. It is considered that the alternatives can make the water quality data easily acquired and the water quality representativeness more enhanced on the standard flow conditions.

Stability of Ricci flows based on Killing conditions

Peibiao Zhao,Qihui Cai 대한수학회 2009 대한수학회지 Vol.46 No.6

C. Guenther studied the stability of DeTurck flows by using maximal regularity theory and center manifolds, but these arguments can not solve the stability of Ricci flows because the Ricci flow equation is not strictly parabolic. Recognizing this deficiency, the present paper considers and obtains the stability of Ricci flows, and of quasi-Ricci flows in view of some Killing conditions. C. Guenther studied the stability of DeTurck flows by using maximal regularity theory and center manifolds, but these arguments can not solve the stability of Ricci flows because the Ricci flow equation is not strictly parabolic. Recognizing this deficiency, the present paper considers and obtains the stability of Ricci flows, and of quasi-Ricci flows in view of some Killing conditions.

Transient Aspects of Rayleigh Flow at Transonic Speeds

Rajarshi Das,Heuy-Dong Kim 한국추진공학회 2015 한국추진공학회 학술대회논문집 Vol.2015 No.11

Development of high speed combustors requires extensive investigation into transonic and supersonic flow under conditions of heat addition. Conventional Rayleigh theory covers this phenomenon but is limited to steady state conditions. In addition, Rayleigh theory falls short of explaining the effects of heat addition at sonic conditions. In this work, effects of heat addition at choking conditions for Rayleigh flow is investigated treating the flow as unsteady and modifying the governing equations suitably. During the study it was observed that, at sonic conditions, the mass flow unexpectedly changes thereby necessitating an overall change in the flow parameters. Taking this anomaly into account, an analytical solution is proposed in the paper for investigating such flows. The primary observations of this analysis are the unsteady fluctuation of the flow properties at sonic conditions.

Steady and Unsteady Rayleigh Flow with Heat Addition at High Subsonic Mach Numbers

Rajarshi Das,Huey Dong Kim 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.12

The heat addition process in compressible flows essentially accompanies unsteadiness, but such a time-dependent behavior of the compressible Rayleigh flow has seldom been known to date. In the present study, an analytical study has been performed to investigate the effect of different types of heat transfer to compressible flows at high subsonic Mach numbers. Changes in basic flow properties due to both steady and unsteady heat transfer into a constant area, frictionless duct over different periods of time were solved numerically. Flow Mach number and velocity were observed to increase rapidly as the flow approached sonic conditions. Change in flow enthalpy and temperature were however different showing an increase initially and then reducing in the vicinity of sonic conditions. Once sonic conditions were attained, the trend in change of flow properties changed substantially with decrease in Mach number under further heat transfer. Attainment of sonic state was observed to depend largely on the amount of heat transfer and the initial conditions.

Investigation of pressure pulsations in a reactor coolant pump with mixed-flow vaned diffuser and spherical casing

Xide Lai,Daoxing Ye,Bo Yu,Xiaoming Chen,Yaguang Heng 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.1

Pressure pulsations are an important factors that cause unstable phenomena such as vibration and noise in the reactor coolant pump (RCP), which is much more complex than inside a general mixed-flow pump due to its structure and actual operating conditions. It is necessary to figure out its characteristics at different operating conditions in order to meet the high requirements of reliability and safety in both design and operation phases. Pressure pulsations inside the impeller and diffuser vanes was carefully investigated by using 3D unsteady flow simulations of the completed pump at 5 operating conditions. To seek the relationship between the pressure pulsations characteristics and operating conditions, the timedomain and frequency-domain characteristics of pressure pulsations at different locations inside the RCP were analyzed. It has been shown that the dominant frequency of pressure pulsations is mainly governed by the blade-passing frequency due to rotor-stator interaction (RSI) between the impeller and diffuser vanes at all operating conditions, and the amplitude of pressure pulsations mainly depends on the operating discharges. The influence on the peak amplitude of its higher harmonics can be neglected when operating at the design discharge, but cannot be negligible for operating at the smaller discharge. The behavior of pressure pulsations at the inlet of the impeller in circumferential direction is not the same and more intensive on the suction side than the pressure side of a blade at different operating conditions, but it is almost the same at the outlet of the impeller as the interaction between the impeller and diffuser vanes. The maximum amplitude of pressure pulsations mainly depends on the operating discharge and reaches the smallest level at the design operating condition. Due to geometric features of the spherical casing, the vortex flow inside the spherical casing leads to the highly irregular and unsteady pressure pulsations inside flow channel of the impeller and diffuser under the smaller discharge operating conditions, and the amplitude of pressure pulsations in higher frequencies increases with the decreasing of the operating discharge. The amplitude of pressure pulsations inside the whole flow channel distinctly increases when the RCP is operating at the extreme small operating discharge. The spherical casing does have influence on the pressure pulsations inside the impeller and diffuser vanes, the effect is stronger under smaller discharge operating conditions than at larger ones.

A Model of Coupled Flow in Impeller and Volute of a Single Stage Centrifugal Pump with Interaction of Impeller-Tongue Gap Flow

Runmei Ma,Tianxin Ma 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.4

The impeller-volute interaction flow in centrifugal pump is influenced by the flow in impeller-tongue gap. In order to completely understand the mechanism of interaction between impeller-volute flow and impeller-tongue gap flow, a transient three-dimensional numerical simulation of the flow in a single stage centrifugal pump was carried out by applying sliding mesh approach and the standard k-ε turbulence model in CFD, and the derived transient flow data were time-averaged over a period of one blade passing the tongue. The analysis of the flow in the pump revealed that under off-design conditions, a reversed flow with lower pressure at small flowrates below the dutypoint or a stagnation region with higher pressure at high flowrates above the dutypoint appeared in the near tongue region in volute, which enhanced the asymmetric flow in impeller channels. It was consequently considered that the flow in impeller-tongue gap was a superposition of a drag flow by impeller and a pressure leakage flow driven by pressure difference between two sides of the tongue, and the pressure difference was zero at design condition, but increased with the deviation degree of the flow in impeller from the dutypoint. Under smaller flowrates, the gap leakage flow has direction opposite to that at higher flowrates, and affects much the volute flow. In the end, based on the analytical results, a semi-empirical model for the volute flow was deduced by one-dimensional flow continuity, and it may supply a reference for optimizing the flow in volute.

가솔린 직분사 엔진에서 운전 조건에 따른 공기 유동 특성에 의한 분무 거동 및 점화 채널에 관한 연구

이호승,박성욱 한국분무공학회 2023 한국액체미립화학회지 Vol.28 No.4

In this study, visualization of in-cylinder spray behavior and spark channel stretching by air flow characteristics depending on engine operating conditions were investigated. For in-cylinder spray behavior, increase in engine rpm did not alter the counter-clockwise air flow direction and location of in-cylinder dominant air flow but increased average air flow velocity, which hindered spray propagation parallel to the piston surface. When injection timing was retarded, direction of in-cylinder dominant air flow was changed, and average air flow velocity was reduced resulting in an increase in spray penetration length and change in direction. For spark channel stretching, increase in air flow speed did not affect spark channel stretch direction but affected length due to increase in spark channel resistance and limitation of energy ignition coil can handle. Change in air flow direction affected spark channel stretch direction where the air flow was obstructed by ground electrode which caused spark channel direction to occur in the opposing direction of air flow. It also affected spark channel stretch length due to change in air flow speed around the spark plug electrode from the interaction between the air flow and ground electrode.

배열회수보일러(HRSG)의 입구유동 경계조건에 따른 유동특성 변화에 관한 연구

김태권(Tae Kwon Kim),이부윤(Boo Yoon Lee),하지수(Ji Soo Ha) 한국가스학회 2011 한국가스학회지 Vol.15 No.3

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 가스터빈 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. The present study has been carried out to analyze the flow characteristics of a heat recovery steam generator with the change of inlet flow conditions by using numerical flow analysis. The inlet of HRSG corresponds the outlet of gas turbine exit and the flow after gas turbine has strong swirl flow and turbulence. The inlet flow condition of HRSG should be included the exit flow characteristics of gas turbine. The present numerical analysis adopted the flow analysis result of gas turbine exit flow as a inlet flow condition of HRSG analysis. The computational flow analysis result of gas turbine exit shows that the maximum axial velocity appears near circular duct wall and the maximum turbulent kinetic energy and dissipation rate exist relatively higher gradient region of axial velocity. The comparison of flow analysis will be executed with change of inlet turbulent flow condition. The first case is using the inlet turbulent properties from the result of computational analysis of gas turbine exit flow, and the second case is using the assumed turbulent intensity with the magnitude proportional to the velocity magnitude and length scale. The computational results of flow characteristics for two cases show great difference especially in the velocity field and turbulent properties. The main conclusion of the present study is that the flow inlet condition of HRSG should be included the turbulent properties for the accurate computational result of flow analysis.

머신러닝 기법을 활용한 유황별 LOADEST 모형의 적정 회귀식 선정 연구: 낙동강 수계를 중심으로

김종건 ( Jonggun Kim ),박윤식 ( Youn Shik Park ),이서로 ( Seoro Lee ),신용철 ( Yongchul Shin ),임경재 ( Kyoung Jae Lim ),김기성 ( Ki-sung Kim ) 한국농공학회 2017 한국농공학회 학술대회초록집 Vol.2017 No.-

This study is to determine the coefficients of regression equations and to select the optimal regression equation in the LOADEST model after classifying the whole study period into 5 flow conditions for 16 watersheds located in the Nakdonggang waterbody. The optimized coefficients of regression equations were derived using the gradient descent method as a learning method in Tensorflow which is the engine of machine-learning method. In South Korea, the variability of streamflow is relatively high, and rainfall is concentrated in summer that can significantly affect the characteristic analysis of pollutant loads. Thus, unlike the previous application of the LOADEST model(adjusting whole study period), the study period was classified into 5 flow conditions to estimate the optimized coefficients and regression equations in the LOADEST model. As shown in the results, the equation #9 which has 7 coefficients related to flow and seasonal characteristics was selected for each flow condition in the study watersheds. When compared the simulated load(SS) to observed load, the simulation showed a similar pattern to the observation for the high flow condition due to the flow parameters related to precipitation directly. On the other hand, although the simulated load showed a similar pattern to observation in several watersheds, most of study watersheds showed large differences for the low flow conditions. This is because the pollutant load during low flow conditions might be significantly affected by baseflow or point-source pollutant load. Thus, based on the results of this study, it can be found that to estimate the continuous pollutant load properly the regression equations need to be determined with proper coefficients based on various flow conditions in watersheds. Furthermore, the machine-learning method can be useful to estimate the coefficients of regression equations in the LOADEST model.

머신러닝 기법을 활용한 유황별 LOADEST 모형의 적정 회귀식 선정 연구: 낙동강 수계를 중심으로

김종건,박윤식,이서로,신용철,임경재,김기성,Kim, Jonggun,Park, Youn Shik,Lee, Seoro,Shin, Yongchul,Lim, Kyoung Jae,Kim, Ki-sung 한국농공학회 2017 한국농공학회논문집 Vol.59 No.4

This study is to determine the coefficients of regression equations and to select the optimal regression equation in the LOADEST model after classifying the whole study period into 5 flow conditions for 16 watersheds located in the Nakdonggang waterbody. The optimized coefficients of regression equations were derived using the gradient descent method as a learning method in Tensorflow which is the engine of machine-learning method. In South Korea, the variability of streamflow is relatively high, and rainfall is concentrated in summer that can significantly affect the characteristic analysis of pollutant loads. Thus, unlike the previous application of the LOADEST model (adjusting whole study period), the study period was classified into 5 flow conditions to estimate the optimized coefficients and regression equations in the LOADEST model. As shown in the results, the equation #9 which has 7 coefficients related to flow and seasonal characteristics was selected for each flow condition in the study watersheds. When compared the simulated load (SS) to observed load, the simulation showed a similar pattern to the observation for the high flow condition due to the flow parameters related to precipitation directly. On the other hand, although the simulated load showed a similar pattern to observation in several watersheds, most of study watersheds showed large differences for the low flow conditions. This is because the pollutant load during low flow conditions might be significantly affected by baseflow or point-source pollutant load. Thus, based on the results of this study, it can be found that to estimate the continuous pollutant load properly the regression equations need to be determined with proper coefficients based on various flow conditions in watersheds. Furthermore, the machine-learning method can be useful to estimate the coefficients of regression equations in the LOADEST model.