• 상하수도학회지
• /
• 제22권1호
• /
• pp.49-63
• /
• 2008

The objectives of this research were to evaluate the pressurized/the main inlet water flowrate ratio which have been used as the most important parameter for operating the pump diffusion mixer until now, to suggest the alternative operating parameter and the relating criteria if the flowrate ratio was not inadequate. For the objectives of this research, computational fluid dynamics (CFD) simulation was conducted for 21 cases of flowrate ratio in full-scaled pump diffusion mixer. From the results of CFD simulation, the local velocity gradient values were calculated in each case in order to analyze the simulation results in more detail. For verifying CFD simulation, wet test was conducted. The wet test was to measure the factual coagulant dispersion distribution at a distance of 5.4m from deflector. From both results of CFD simulation and wet test, flowrate ratio was inadequate as operating parameter or criteria, on the other hand the pressurized/the main inlet velocity ratio(dimensionless) was useful in predicting the performance of pump diffusion mixer. Also, the injected coagulant could be dispersed evenly in overall cross section on the condition that pressurized/the main inlet velocity ratio(dimensionless) is over at least 20.

• 한국환경과학회지
• /
• 제8권3호
• /
• pp.355-361
• /
• 1999

The aim of this study is to develop the water quality simulation model (BAYQUAL) that deal with the physical, chemical and biological aspects of fate/behavior of pollutants in the bay. BAYQUAL is a two dimensional, time-variable finite element water quality model based on the flow simulation model in bay(BAYFLOW). The algorithm is composed of a hydrodynamic module which solves the equations of motion and continuity, a pollutnat dispersion module which solves the dispersion-advection equation. The applicability and feasibility of the model are discussed by applications of the model to the Kwangyang bay of south coastal waters of Korea. Based on the field data, the BAYQUAL model was calibrated and verified. The results were in good agreement with measured value within relative error of 14% for COD, T-N, T-P. Numerical simulations of velocity components and tide amplitude(M2) were agreed closely with the actual data.

• 설비공학논문집
• /
• 제17권11호
• /
• pp.1050-1059
• /
• 2005

Heat and $SF_6$ gas dispersions over a complex terrain were investigated using wind tunnel. The wind speed, temperature and concentration profiles were measured for the 1/1000 scale complicated terrain model in an Eiffel type boundary layer wind tunnel with test section of 2.5m in height and 4.5m in width. The scale model was mounted on the top of a plate which can rotate with respect to the approaching wind. Dispersion processes from a continuous emission source driven by various wind direction were investigated, including plume climbing over the steep up-slope of the mountain and down-spreading toward the lower level of the valley. Extensive dispersion experiment data (wind speeds and concentration profiles) were provided for verification and validation of dispersion models. Under the identical flow and emission conditions, the independently measured profiles of the temperature and $SF_6$ concentration showed an excellent agreement which ensured the credibility of the results.

• 한국전자통신학회논문지
• /
• 제8권8호
• /
• pp.1235-1240
• /
• 2013

본 논문에서는 색분산이 최적으로 보상된 광통신 시스템에서 자기위상변조와 색분산으로 인해 열화되는 신호의 아이페널티에 대해 근사적인 수학식을 유도하였다. 이러한 분석 연구를 통해 최적으로 색분산 보상된 광통신 시스템에서 신호의 왜곡에 대한 근사식을 얻을 수 있다. 우리는 이 근사식의 효용성을 보이기 위해서 이전 연구의 시뮬레이션 결과와 근사식의 결과를 비교하는 결과를 보인다. 본 논문의 결과를 이용하면 복잡한 비선형 시뮬레이션을 통해 얻을 수 있는 광신호의 왜곡에 대해 손쉽게 그 결과를 예측할 수 있으며, 각종 시스템 파라미터가 시스템에 미치는 영향도 쉽게 파악할 수 있다.

• 대한기계학회논문집B
• /
• 제26권4호
• /
• pp.570-577
• /
• 2002

Charged liquid particle's behavior in electric and flow field was simulated to define the effect of electric field on the contact area and its dispersion. For the simulation of flow and electric field finite volume method was applied. To find out the particle's moving path in that field lagrangian equation of motion was solved by Runge-Kutta methods. We assumed that the particle was charged 10% of Rayleigh limit while the particle passing through the electrode and the particle does not have an effect on the electric field. In case of 30[Kv] of voltage charging the particles injected from the central 60% of the nozzle injection area adhere to the grounded moving plate and no dispersion occurred. Increasing the charged voltage to 40[Kv], it brought about the same phenomena as that of 30[Kv] charging except the dispersion. Voltage increasing from 30[Kv] to 40 [Kv] caused higher Coulomb force acts on the particle and it made the particle dispersion.

• Membrane and Water Treatment
• /
• 제9권3호
• /
• pp.173-179
• /
• 2018

Microcystin-LR, one of algal toxins induced by the eutrophication of a reservoir, is known to be harmful to human by adversely affecting our liver and brain. Hypochlorous acid is very efficient to remove Microcystin-LR in a clear well. The previous researches showed that CT, pH and temperature affected removal rate in batch tests. It was noted that hydrodynamic properties of clear well could also influence its removal rate. A mathematical model was built using an axial dispersion reactor model and software was used to simulate the removal rate. The model consisted of the second order differential equations including dispersion, convection, Microcystin-LR reaction with chlorine. Kinetic constants were obtained through batch tests with chlorine. They were $0.430{\times}10^{-3}L/mg/sec$ and $0.143{\times}10^{-3}L/mg/sec$ for pH 7.0 and 8.1, respectively. The axial dispersion reactor model was shown to be useful for the numerical model through conservative tracer tests. The numerical model successfully estimated the removal rate of Microcyctin-LR in a clear well. Numerical simulations showed that a small dispersion number, low pH and long hydraulic retention time were critical for higher removal rate with same chlorine dosage. This model could be used to optimize the operation of a clear well during an eutrophication season.

• 한국가스학회지
• /
• 제8권2호
• /
• pp.8-14
• /
• 2004

본 연구는 염소가스의 소규모 연속누출에서 분산특성과 독성영향을 해석하였다. 염소 농도의 실험값과 이론값을 비교한 결과, Briggs의 분산계수와 유효누출높이를 사용한 가우시안 모델이 BM 모델보다 적용성이 우수하였다. 또한 가우시안 모델에 의해 염소농도를 산출하고 해석한 결과, 염소분산은 누출속도 보다 대기안정도와 바람속도에 크게 영향을 받으며, 독성영향은 염소분산에 미치는 매개변수의 영향과 유사한 경향을 나타내었다. 이때, 여러 독성기준에 의해 산출된 피해범위로부터 인명을 보호하기 위한 위험지역을 파악할 수 있었다.

• Nuclear Engineering and Technology
• /
• 제53권1호
• /
• pp.244-252
• /
• 2021

Wind plays an important role in cases of unexpected radioactive pollutant dispersion, deciding distribution and concentration of the leaked substance. The accurate prediction of wind has been challenging in numerical weather prediction models, especially near the surface because of the complex interaction between turbulent flow and topographic effect. In this study, we investigated the characteristics of atmospheric dispersion of radioactive material (i.e. ¹³⁷Cs) according to the simulated boundary layer around the HANARO research nuclear reactor in Korea using the Weather Research and Forecasting (WRF)-Mesoscale Model Interface (MMIF)-California Puff (CALPUFF) model system. We examined the impacts of orographic drag on wind field, stability calculation methods, and planetary boundary layer parameterizations on the dispersion of radioactive material under a radioactive leaking scenario. We found that inclusion of the orographic drag effect in the WRF model improved the wind prediction most significantly over the complex terrain area, leading the model system to estimate the radioactive concentration near the reactor more conservatively. We also emphasized the importance of the stability calculation method and employing the skillful boundary layer parameterization to ensure more accurate low atmospheric conditions, in order to simulate more feasible spatial distribution of the radioactive dispersion in leaking scenarios.

• 한국산업보건학회지
• /
• 제33권3호
• /
• pp.346-354
• /
• 2023

Objectives: Chemical accidents cause extensive human and environmental damage. Therefore, it is important to prepare measures to prevent their recurrence and minimize future damage through accident investigation. To this end, it is necessary to identify the accident occurrence process and analyze the extent of damage. In this study, the development process and damage range of actual chemical leakage accidents were analyzed using CFD. Methods: For application to actual chemical leakage accidents using FLACS codes specialized for chemical dispersion simulation among CFD codes, release rate calculation and 3D geometry were created, and scenarios for simulation were derived. Results: The development process of the accident and the dispersion behavior of materials were analyzed considering the influencing factors at the time of the accident. In addition, to confirm the validity of the results, we compared the results of the actual damage impact investigation and the simulation analysis results. As a result, both showed similar damage impact ranges. Conclusions: The FLACS code allows the detailed analysis of the simulated dispersion process and concentration of substances similar to real ones. Therefore, it is judged that the analysis method using CFD simulation can be usefully applied as a chemical accident investigation technique.

• 한국산학기술학회논문지
• /
• 제21권3호
• /
• pp.10-16
• /
• 2020

세탁시설에서 배출되는 탄화수소의 흡착제거 특성을 고찰하기 위하여 흡착 컬럼의 전산모사를 수행하였다. 흡착질은 세탁시설에서 배출되는 휘발성유기화합물 중 가장 대표적인 탄화수소를 선정하였으며 흡착제는 활성탄으로 전산모사를 수행하였다. 흡착컬럼의 수학적 방정식은 연속방정식과 Navier-Stokes 식을 적용하여 해석하였으며 Matlab 프로그램을 이용하여 미분방정식을 해석하였다. 흡착등온식은 선형흡착등온식, 프로인들리히 흡착등온식 그리고 랑뮈어 흡착등온식을 평가하였으며 흡착등온식의 흡착상수에 따른 흡착량을 비교하였다. 공극률은 0.79, 분산계수는 42.4 ㎠/min, 흡착제 밀도는 485 g/L, 흡착컬럼 직경은 2.0 cm, 흡착컬럼 길이는 2.5 cm라는 조건에서 전산모사를 수행하였다. 랑뮈어 흡착등온식에서 선속도, 분산계수, 공극률에 대한 흡착량의 영향을 비교하였다. 선속도는 50~200 cm/min, 분산계수는 100 ~400 ㎠/min, 공극률은 0.66~0.79로 변화시켜 수행하였다. 전산모사를 통한 결과는 활성탄-벤젠의 흡착에 대하여 랑뮈어 흡착등온식이 가장 잘 일치하였다. 동일한 조건에서 3가지의 흡착등온식을 비교한 후 전산모사를 통하여 탄화수소의 효율적인 흡착조건을 찾을 수 있으며 이를 고찰할 수 있다.