• Wind and Structures
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• v.28 no.4
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• pp.239-253
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• 2019

Accurate numericalsimulation of wind field over complex terrain is an important prerequisite for wind resource assessment. In this study, numerical simulation of wind field over complex terrain was further carried out by taking the complex terrain around Siu Ho Wan station in Hong Kong as an example. By artificially expanding the original digital model data, Gambit and ICEM CFD software were used to create high-precision complex terrain model with high-quality meshing. The equilibrium atmospheric boundary layer simulation based on RANS turbulence model was carried out in a flat terrain domain, and the approximate inflow boundary conditions for the wind field simulation over complex terrain were established. Based on this, numerical simulations of wind field over complex terrain under different inflow wind directions were carried out. The numerical results were compared with the wind tunnel test and field measurement data for land and sea fetches. The results show that the numerical results are in good agreement with the wind tunnel data and the field measurement data which can verify the accuracy and reliability of the numerical simulation. The near ground wind field over complex terrain is complex and affected obviously by the terrain, and the wind field characteristics should be fully understood by numerical simulation when carrying out engineering application on it.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.180.2-180.2
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• 2010

The purpose of this research is to analyze the sensitivity of WindSIM in complex terrain. As the flat areas for wind turbine installation become scarce globally, it becomes inevitable to install wind turbines in complex terrain. In order to predict annual energy production (AEP) in a more precise manner in complex terrain, it is of great importance to conduct such research. Three parameters: reference velocity, roughness and resolution have been chosen to see to which parameter WindSIM was the most sensitive in terms of annual energy production in complex terrain. By fixing two parameters and setting one parameter as a variable, it could be easily found that how annual energy production was effected by the change in each parameter.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.493-495
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• 2010

A three-dimensional flow simulation is performed to investigate the flow field in the ski resort on complex terrain. The present paper aims to study the wind effects of mountainous terrain on the gondola safety. Strong wind happens in the ski resort on the mountain by complex terrain and it causes the dangerous accident of gondola. A digital map around the ski resort area is used to model the actual complex terrain for a 3-D analysis domain. Wind direction and speed to be used as a boundary condition are taken from local meteorological reports. The numerical results show details of the velocity distribution around a ski resort. From the results, we can suggest the modification of the installation of gondola for the safety due to strong wind.

• Journal of Korean Society for Atmospheric Environment
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• v.14 no.2
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• pp.81-94
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• 1998

Six complex terrain dispersion models recommended by the U. S. Environmental Protection Agency were investigated using a hypothetical case in which a plume approaches complex terrain. The six models considered were Valley, CTSCREEN, COMPLEX 1, SHORTZ, RTDM, and CTDMPLUS, the latter four being closely studied. Highest concentrations were predicted for 48 receptors and plume behaviors were compared for stable and unstable meteorological conditions. Under stable conditions, ground-level concentrations were determined by the height of the plume centerline above the terrain. The concentrations estimated by SHORTZ and COMPLEX I were higher than those estimated by CTSCREEN, with CTDMPLUS predicting the lowest concentrations. In particular, the height of the lift midpoint, as well as the co.nterline of the plume, are important in the model calculation of CTDMPLUS. Under unstable conditions, the vertical dispersion plays a key role in determining ground -level concentrations. For this case, concentrations predicted by CTDMPLUS were the 'highest, whereas those predicted by SHORTZ were the lowest. Concentration distributions predicted by CTDMPLUS are quite similar to typical Gaussian distributions even on complex terrain, except for a slight shift of the plume centerline due to the of(tract of the geostrophic wind. In addition,24-hour average concentrations were estimated for comparison with results from the Valley model. Among the four models studied closely, CTDMPLUS predicted the lowest 24-hour average concentrations, but the concentrations estimated by Valley were lower than those estimated by CTDMPLUS.

• Structural Engineering and Mechanics
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• v.45 no.1
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• pp.1-18
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• 2013

The typhoon wind characteristics designing for buildings or bridges located in complex terrain and typhoon prone region normally cannot be achieved by the very often few field measurement data, or by physical simulation in wind tunnel. This study proposes a numerical simulation procedure for predicting directional typhoon design wind speeds and profiles for sites over complex terrain by integrating typhoon wind field model, Monte Carlo simulation technique, CFD simulation and artificial neural networks (ANN). The site of Stonecutters Bridge in Hong Kong is chosen as a case study to examine the feasibility of the proposed numerical simulation procedure. Directional typhoon wind fields on the upstream of complex terrain are first generated by using typhoon wind field model together with Monte Carlo simulation method. Then, ANN for predicting directional typhoon wind field at the site are trained using representative directional typhoon wind fields for upstream and these at the site obtained from CFD simulation. Finally, based on the trained ANN model, thousands of directional typhoon wind fields for the site can be generated, and the directional design wind speeds by using extreme wind speed analysis and the directional averaged mean wind profiles can be produced for the site. The case study demonstrated that the proposed procedure is feasible and applicable, and that the effects of complex terrain on design typhoon wind speeds and wind profiles are significant.

• Journal of Korean Society for Atmospheric Environment
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• v.9 no.3
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• pp.242-246
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• 1993

Theoretically, spectral method has the highest accuracy among present numerical methods, but it is generally difficult to apply to complex terrains because of complex boundary conditions. Recently, spectral-element method, basically divide the domain into a set of rectangular subdomain and solve the equation at each subdomain, has been introduced. However, boundary conditions become more complex and requires more computing time, thus spectral-element method is not powerful for all complex terrain problems. In this paper, potential flow theory was intorduced to solve the air flows and diffusion phenomenon in the presence of terrain obstacles. Using the velocity potential-stream line orthogonal coordinate space, the diffusion problems of hilly terrain by pseudospectral method were solved and compared those with no terrain real scale solutions.

• Journal of Korean Society for Atmospheric Environment
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• v.16 no.4
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• pp.339-350
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• 2000

The three-dimensional new corrdinate system over a single hill double hills and complex terrain with a single hill and a rectangular obstacle was generated using a body-fitted coordinate system. Control of the coordinate line distribution in the field was executed by generalizing the elliptic generating system to Poisson equation. ▽2ξ=P. The new coordinate system was well fitted to the surface boundary of single hill and double hills. But in the case of complex terrain with hill and rectangular obstacle there was smoothing tendency around the rectangular obstacle. In order to show the validity of the body-fitted coordinate system the heat diffusion equation was transformed and the temperature distribution was calculated over the various terrain. The results showed the temperature distribution was very symmetrical and stable around hills and obstacle. As a result the couple of a body-fitted coordinate system and the heat diffusion equation were executed successfully. Wind field over complex terrain with hill and rectangular obstacle which represent urban area was simulated stably in body-fitted coordinate system. The qualitative result show the enhancement of wind speed at the upwind direction of a hill and a rectangular obstacle and the recirculation zone at the downwind direction.

• Wind and Structures
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• v.12 no.3
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• pp.219-237
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• 2009

This study examines the accuracy of large-eddy simulation (LES) to simulate the flow around a large irregular sloping complex terrain. Typically, real built up environments are surrounded by complex terrain geometries with many features. The complex terrain surrounding The Hong Kong University of Science and Technology campus was modelled and the flow over an uphill slope was simulated. The simulated results, including mean velocity profiles and turbulence intensities, were compared with the flow characteristics measured in a wind tunnel model test. Given the size of the domain and the corresponding constraints on the resolution of the simulation, the mean velocity components within the boundary layer flow, especially in the stream-wise direction were found to be reasonably well replicated by the LES. The turbulence intensity values were found to differ from the wind tunnel results in the building recirculation zones, mostly due to the constraints placed on spatial and temporal resolutions. Based on the validated mean velocity profile results, the flow-structure interactions around these buildings and the surrounding terrain were examined.

• Journal of Korean Society for Atmospheric Environment
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• v.13 no.6
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• pp.427-437
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• 1997

Complex terrain which is rather typical topographic character in Korea would greatly influence the dispersion of air pollutant. In this study, we investigated how the complex terrain in the vicinity of the coal-fired plant affects the air dispersion modeling results by using several US EPA models: SCREEN, CTSCREEN, ISCLT3, ISCST3, and RTDM. Screening analysis was followed by long-term analysis, and the plume movement over the terrain was precisely tracked for selected cases. Screening analysis revealed that the highest concentration of sulfur dioxide occurs at the downwind distance of 1.3 km under the unstable conditions with weak winds. However, this highest level of $SO_2$ could be raised by 4 times even in the presence of a hill of 170 m at a distance of 2 to 3 km. Seasonal and annual average concentrations predicted with the ISCLT3, ISCST3, and RTDM models showed a rapid incrase of $SO_2$ levels in front of the high mountains which are located more than 15 km away fromt the source. The highest concentrations predicted with ISCST3 were significantly higher than those with ISCLT3 and RTDM mainly because ISCST3 chooses simple-terrain model calculations for receptors between stack height and plume height. Although the highest levels under the stable conditions were usually found in the areas beyond 15 km or more, their absolute values were not so high due to enough dispersion effects between the source and the receptors.

• Wind and Structures
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• v.13 no.4
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• pp.375-383
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• 2010

A three-dimensional flow simulation was performed to investigate the wind flow around wind-power generation facilities on mountainous area of complex terrain. A digital map of eastern mountainous area of Korea including a wind farm was used to model actual complex terrain. Rotating wind turbines in the wind farm were also modeled in the computational domain with detailed geometry of blade by using the frozen rotor method. Wind direction and speed to be used as a boundary condition were taken from local meteorological reports. The numerical results showed not only details of flow distribution in the wind farm but also the variation in the performance of the wind turbines due to the installed location of the turbines on complex terrain. The wake effect of the upstream turbine on the performance of the downstream one was also examined. The methodology presented in this study may be used in selecting future wind farm site and wind turbine locations in the selected site for possible maximum power generation.