SIMULATION OF AN ARRAY OF FENCES IN SAEMANGEUM RECLAIMED LAND USING CFD TECHNOLOGY

( J. P. Bitog ),이인복 ( I. -b. Lee ),홍세운 ( S. -w. Hong ),황현섭 ( H. -s. Hwang ),서일환 ( I. -h. Seo ),유재인 ( J. -i. Yoo ),권경석 ( K. -s. Kwon ),최지선 ( J. -s. Choi ) 한국농공학회 2009 한국농공학회 학술대회초록집 Vol.2009 No.-

This paper discusses about the quantitative effect of windbreak fences on wind velocity in the reclaimed land at Saemangeum semi-arid desert in South Korea. Windbreak fences were constructed in the reclaimed land purposely to prevent the generation and diffusion of dust. Using CFD simulations, the effects of fence porosity, fence height, and the distance between the adjacent fences were investigated. A wind tunnel experiment was initially conducted and data gathered were used to develop the CFD models. From the experiments and CFD simulations, the overall percentage difference of the measured velocities was 7.81% which is generally acceptable to establishing the reliability of the CFD models. The reduction effect on wind velocity was measured in between the adjacent fences up to a height of 0.6 m from the ground surface. In terms of porosity (ε= 0, 0.2, 0.4, 0.6), 0.2 was found to be the optimum value. Conversely, the effect of fence height (0.6, 0.8 and 1.0 m) showed no significant difference; therefore, 0.6 m height is recommended. In addition, the effect of distance between the adjacent fences (2, 4 and 6 m) having a 0.2 porosity has decreased to about 75% regardless of the distance. In the case of the reclaimed land in Saemangeum, a decrease of 75% can prevent the generation and diffusion of dusts. However, the source of dusts is very large. Therefore, constructing an array of windbreak with 6 m distance between them is deemed necessary.

Optimised hydrodynamic parameters for the design of photobioreactors using computational fluid dynamics and experimental validation

Bitog, J.P.P.,Lee, I.B.,Oh, H.M.,Hong, S.W.,Seo, I.H.,Kwon, K.S. Academic Press 2014 BIOSYSTEMS ENGINEERING Vol.122 No.-

A numerical simulation using computational fluid dynamics (CFD) was utilised to investigate the flow hydrodynamics of cylindrical bubble column type photobioreactors (PBRs) with a 30l culture medium. To establish the reliability of the simulation study, the CFD model was validated using particle image velocimetry (PIV) computed data under various air flow rates. There were 32 simulation cases for the study comprising two PBR designs, four air flow rates and four nozzle size diameters. Hydrodynamic analyses such as % volume of dead zones, average circulation time and turbulence intensity inside the simulated PBRs were evaluated. Results have shown that the most appropriate PBR for microalgae cultivation was a design with internal baffle and an extended cone-shaped bottom section. In addition, the recommended nozzle diameter was found to be 10 mm and a minimum air flow rate of 0.10 vvm. To eliminate dead zones inside the PBR, the flow rate can be slightly increased but should not exceed 0.15 vvm. Practical evaluation through laboratory experiments has further confirmed the results of the study where the biomass concentration of Chlorella vulgaris from the proposed PBR was significantly higher compared to the standard PBR design. Based on the numerical investigation and practical evaluation, the improved PBR can be seen to be more effective in culturing microalgae particularly for larger scale mass production.

A wind tunnel study on aerodynamic porosity and windbreak drag

J. P. Bitog,이인복,H.-S. Hwang,M.-H. Shin,홍세운,I.-H. Seo,E. Mostafa,Z. Pang 한국산림과학회 2011 Forest Science And Technology Vol.7 No.1

Natural windbreaks such as trees are very efficient barriers to high velocity winds. The windbreaks exert drag force causing a net loss of momentum and thus disturb the characteristics of flow. The main factors which can affect the efficiency of the windbreaks are tree height, width, tree arrangement, porosity, etc. However, tree porosity which is strongly related to the windbreak drag is very difficult to establish. In this study, the results of a wind tunnel test were introduced to find the aerodynamic porosity and resistance factor of a tree windbreak. Black pine tree (Pinus thunbergii), a typical tree windbreak in Korea was chosen as the experimental tree. With the main factors of wind velocity, static pressure and density of the tree, the aerodynamic porosity as well as the resistance factor of the tree was found. The average porosity at varied tree density were found to be 0.91, 0.69 and 0.42 for one, two and three trees, respectively. The resistance factors which can be equaled to the drag coefficient were 0.55, 0.82 and 1.08 for one, two and three trees, respectively. The determined aerodynamic porosity and windbreak drag will be used later as input data in computer simulation studies such as computational fluid dynamics (CFD). Moreover, the experimental procedure as well as the use of real trees in the wind tunnel experiment of finding the aerodynamic porosity and windbreak drag of various tree windbreaks was established through this study.

CFD 시뮬레이션을 활용한 미세조류 배양용 버블 칼럼 광생물반응기 설계

유재인 ( J. -i. Yoo ),이인복 ( I. -b. Lee ),황현섭 ( H. -s. Hwang ),서일환 ( I. -h. Seo ),홍세운 ( S. -w. Hong ),( J. Bitog ),권경석 ( K. -s. Kwon ),최지선 ( J. -s. Choi ) 한국농공학회 2009 한국농공학회 학술대회초록집 Vol.2009 No.-

Photobioreactors (PBRs) that houses and cultivates microalgae providing a suitable environment for its growth, such as light, nutrients, CO2,heat, etc. is now getting more popular in the last decade. Among the many types of PBRs, the bubble column type is very attractive because of its simple construction and easy operation. However, despite the availability of these PBRs, only a few of them can be practically used for mass production. Many limitations still holdback their use especially during their scale-up. To enlarge their culture volume and productivity by supplying optimum environmental conditions, various PBR structures and processes for controlling are needed to be compared. In this study, computational fluid dynamics (CFD) was used to design a bubble-column type PBR to economically take the place of field experiments. CFD is a promising technique which can simulate the growth and production of microalgae in the PBR. To study bubble column PBR with CFD, the most important factor is the possibility of realizing bubble. In this study, multi-phase models which are generally used were compared by theoretical approaches and 2D preliminary simulations. As a result, the VOF (Volume of Fluid)model was found to be the most effective to realize the bubble shape and flow inside PBR which is made by bubble injection. Considering the accuracy and economical efficiency, 0.005 sec of time step size was chosen for 2.5 mm mesh size. With these initial conditions, 3-D PBR trial simulation and PIV (Particle Image Velocimetry) validation test were conducted. The verified CFD simulation model will be used as criteria for PBR scale-up research.

나무의 공극률과 방풍 효과에 대한 풍동 실험

제시비톡 ( J. P. Bitog ),이인복 ( I. -b. Lee ),황현섭 ( H. -s. Hwang ),홍세운 ( S. -w. Hong ) 한국농공학회 2010 한국농공학회 학술대회초록집 Vol.2010 No.-

Natural windbreaks such as trees are very efficient barriers to high velocity winds. The windbreaks exert drag force causing a net loss of momentum and thus disturb the characteristics of flow. The main factors which can affect the efficiency of the windbreaks are tree height, width, tree arrangement, porosity, etc. However, tree porosity which is strongly related to the windbreak drag is very difficult to establish. Recently, computational fluid dynamics (CFD) have been actively used to investigate wind flow characteristics around artificial and natural windbreaks such as trees. As a first step in the simulation, the CFD model had to be designed as a porous media because of the complexity of the physical structure. In this study, the results of wind tunnel test were introduced to find the porosity and aerodynamic resistance of a tree windbreak. Black pine tree (Pinus thunbergii), a typical tree windbreak in Korea was chosen as the experimental tree. With the main factors of wind velocity, static pressure, and density of the tree, the aerodynamic porosity as well as the resistance factor of the tree was found. The average porosity at varied tree density were found to be 0.91, 0. 69 and 0.42 for one, two and three trees, respectively. The resistance factors which can be equaled to the drag coefficient were 0.55, 0.82 and 1.08 for one, two and three trees, respectively. The determined aerodynamic porosity and windbreak drag will be used later as input data of CFD models. Moreover, the experimental procedure as well as the use of real tree in the wind tunnel experiment of finding the aerodynamic porosity and windbreak drag of various tree windbreaks was established through this study.

새만금 간척 지역의 비산 및 부유 먼지 확산 모니터링 및 예측

황현섭 ( H. -s. Hwang ),이인복 ( I. -b. Lee ),서일환 ( I. -h. Seo ),홍세운 ( S. -w. Hong ),( J. Bitog ),유재인 ( J. -i. Yoo ),권경석 ( K. -s. Kwon ),최지선 ( J. -s. Choi ) 한국농공학회 2009 한국농공학회 학술대회초록집 Vol.2009 No.-

A study on fugitive dust dispersion was conducted in a 40,100ha reclaimed land located at the west coastal part of Korea. The dusts are composed mainly of minerals with high salinity that is very harmful to human’s health such as skin and eye irritations and If frequently inhaled, respiratory disease can occur. More so, the highly concentrated salty dusts can be very harmful to farms located nearby. A computational fluid dynamics (CFD) model was developed to predict the dispersion of fugitive dust from Saemangeum reclaimed land considering the topography of the area. Field experiment is the ideal method to understand real aerodynamic phenomenon. Nevertheless, it is very difficult to find a correlation between weather condition and dust dispersion because of limited measuring points, labor and time. Moreover, the weather condition is always unstable and unpredictable as well as cannot be artificially controlled. To overcome these limitations, CFD simulation was used to quantitatively and qualitatively analyze the dust dispersion phenomenon according to various weather conditions. Great effort has been needed to improve the CFD accuracy with topographical design, mesh structure, particle generation, and computational process by parallel processing technique. Results from this study in 2006, 2007 and 2008 showed that the changes in dust source are highly connected with the changes of dust concentration. The dust concentration shows a decreasing trend in 2008, and it is expected to decrease further as more dust source areas are being covered by plants. The samples analyzed through SEM showed that most dust particles are large in size with irregular dimension. Dust dispersion ranges of CFD result were compared with that of field experiment at the same measuring points for the CFD validity, and the results at stable weather condition were very acceptable with an average error of 6.8%. The vertically dust concentration of the CFD results also became very similar with the general log-profile of fugitive and suspended dust presented by Gillies et al. (2004). The results also showed that the dispersion of the fugitive dust was mainly affected by particle size, wind speed as well as wind direction. On the basis of 10 μm particle size, the diffused distance of fugitive dust resulted in 3,100m with the wind speed of 1.7m/s at 10 m height from the ground while 6,300m with 3.9m/s. Through this study, it was found that the CFD technology can be effectively used to complement the field experiment at studies and more accurate of reliable results can be obtained.

CFD를 활용한 복잡한 지형 내 축산 악취의 확산 예측

홍세운 ( S. -w. Hong ),이인복 ( I. -b. Lee ),황현섭 ( H. -s. Hwang ),서일환 ( I. -h. Seo ),유재인 ( J. -i. Yoo ),( J. P. Bitog ),권경석 ( K. -s. Kwon ),최지선 ( J. -s. Choi ) 한국농공학회 2009 한국농공학회 학술대회초록집 Vol.2009 No.-

Odor is one of the major nuisances in the environment. In most countries, odor annoyance from livestock production is an increasing problem in the community. In order to reduce the odor inconvenience and establish a good relation between livestock industries and the surrounding communities, many studies on the odor dispersion, such as diffusion simulations and field experiments have been investigated. Computational fluid dynamics (CFD) has been effectively and widely used to study this kind of research. CFD considers both various wind conditions as well as topographical conditions to study aerodynamic phenomenon. Therefore, the ultimate objective of the study was to develop an aerodynamic model to predict qualitatively and quantitatively odor diffusion from livestock. During the first year of this 3-year study, various phenomena and factors of odor diffusion from livestock houses were investigated from field experiments. In the second year, mesh models of the study area with a 1.8km radius were built with 5m resolution. Modules for the atmospheric phenomena were also made by user defined functions and linked into a main computing module. The dispersion of odor was predicted by the 3D CFD model and practically agreed to the field measured data. Later, this model will be used to arrange the odor-related conflicts as well as to predict the odor dispersion according to various meteorological conditions.

축산 악취의 확산 모델 개발을 위한 현장 실험

홍세운,이인복,황현섭,서일환,권혁진,유재인,권경석,하태환,김용희,Hong, S.W.,Lee, I.B.,Hwang, H.S.,Seo, I.H.,Kwon, H.J.,Bitog, J.P.,Yoo, J.I.,Kwon, K.S.,Ha, T.H.,Kim, Y.H. 한국농공학회 2008 한국농공학회논문집 Vol.50 No.4

Odor is one of the major nuisances in the environment. In most countries, odor annoyance from livestock production is an increasing problem in community. In order to reduce the odor inconvenience and establish a good relation between livestock industries and the surrounding communities, many studies, such as diffusion simulations and field experiments, on the odor dispersion and its reduction have been investigated. These studies need to accompany the aerodynamic approach, as a main mechanism of diffusion phenomenon, and computational fluid dynamics(CFD) can be effectively used to study this kind of research. CFD considers both various wind conditions as well as topographical conditions to study aerodynamic phenomenon. Therefore the ultimate objective of the study was to develop an aerodynamic model to predict qualitatively and quantitatively odor diffusion from livestock. In this study, as the first step of this study, various phenomena and factors of odor diffusion from livestock houses were investigated through field experiments in 2007. Later, those data will be also used to verify the CFD accuracy as well as to develop 3-dimensional CFD model.

The past, present and future of CFD for agro-environmental applications

Lee, I.B.,Bitog, J.P.P.,Hong, S.W.,Seo, I.H.,Kwon, K.S.,Bartzanas, T.,Kacira, M. Elsevier 2013 Computers and electronics in agriculture Vol.93 No.-

Computational fluid dynamics (CFD) is a proven simulation tool which caters to almost any field of study. The CFD technique is utilized to simulate, analyze, and optimize various engineering designs. In this review, the discussion is focused on the application of CFD in the external atmospheric processes as well as modeling in land and water management. With respect to its application in environmental investigations, numerous CFD studies have been done in the atmospheric processes where generally only the fluid flow characteristics are investigated. The application of CFD to soil and water management is still limited. However, with the present demand for conservation and sustainable management of our soil and water resources, CFD application in this field is fast emerging especially in structure designs of dams and reservoirs where CFD offers fast reliable results with less labor and cost. Every CFD model should be validated in order to be considered accurate and reliable. However, a benchmark or standard procedures in validating CFD models is not yet available. This probably answers why the success of the CFD models is still mostly attributed to the user's skills and experience. At present, the degree of application of CFD to the agro-environmental field is limited by the computing power and software used, however, the fast ever computing power of PCs continually expands the potential of CFD and can be generally more flexible at accounting for the unique aspects of every CFD project. This allows easy access to conduct simulation studies from simple to complex models. In this paper, after a state of art analysis of the past and present application of CFD in the agro-environmental applications, its future directions were discussed, in order to potentially serve as a guide for researchers and engineers on what project or investigations can be conducted.

축산악취의 확산 예측을 위한 전산유체역학 모델의 개발

이인복,홍세운,황현섭,서일환,J. Bitog,권경석 한국기상학회 2010 한국기상학회 학술대회 논문집 Vol.2010 No.4