An immersed boundary method for complex terrain flow analysis

Jaewook Nam,Changhoon Lee 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.4

We present modified immersed boundary method (IBM) for complex terrain flow analysis which is done on coarse grid and based on large-eddy simulation (LES). The main idea is that IBM force to make fluid velocity perpendicular to terrain surface zero and to revive tangential fluid velocity near the terrain surface is applied at Lagrangian point on terrain surface. For smoothing out the effect of IBM force on coarse grid, IBM force at Lagrangian point is distributed on collocated grid and gathered at the position of fluid velocity on staggered grid. For validation of our method, we conduct complex terrain flow analysis for mountainous terrain which is mock-up model of coastal region in Gyeongju and compare our simulation results with wind-tunnel experiment results and other simulation using ANSYS. Our simulation results show better agreement with wind-tunnel experiment results than ANSYS simulation results and properly capture various flow characteristics occuring in complex terrain.

Wind Speed Prediction in Complex Terrain Using a Commercial CFD Code

우재균,김현기,백인수,유능수,남윤수 한국태양에너지학회 2011 한국태양에너지학회 논문집 Vol.31 No.6

Investigations on modeling methods of a CFD wind resource prediction program, WindSim for accurate predictions of wind speeds were performed with the field measurements. Meteorological Masts having heights of 40m and 50m were installed at two different sites in complex terrain. The wind speeds and direction were monitored from sensors installed on the masts and recorded for one year. Modeling parameters of WindSim input variables for accurate predictions of wind speeds were investigated by performing cross predictions of wind speeds at the masts using the measured data. Four parameters that most affect the wind speed prediction in WindSim including the size of a topographical map, cell sizes in x and y direction, height distribution factors, and the roughness lengths were studied to find out more suitable input parameters for better wind speed predictions. The parameters were then applied to WindSim to predict the wind speed of another location in complex terrain in Korea for validation. The predicted annual wind speeds were compared with the averaged measured data for one year from meteorological masts installed for this study, and the errors were within 6.9%. The results of the proposed practical study are believed to be very useful to give guidelines to wind engineers for more accurate prediction results and time-saving in predicting wind speed of complex terrain that will be used to predict annual energy production of a virtual wind farm in complex terrain.

Sensitivity of WindSIM in Complex Terrain

신종원(Shin, Chongwon),한경섭(Han, Kyungseop) 한국신재생에너지학회 2010 한국신재생에너지학회 학술대회논문집 Vol.2010 No.11

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.

Non-Gaussian wind features over complex terrain under atmospheric turbulent boundary layers: A case study

Hongtao Shen,Weicheng Hu,Qing-shan Yang,Fucheng Yang,Kunpeng Guo,Tong Zhou,Guowei Qian,Qinggen Xu,Ziting Yuan 한국풍공학회 2022 Wind and Structures, An International Journal (WAS Vol.35 No.6

In wind-resistant designs, wind velocity is assumed to be a Gaussian process; however, local complex topography may result in strong non-Gaussian wind features. This study investigates the non-Gaussian wind features over complex terrain under atmospheric turbulent boundary layers by the large eddy simulation (LES) model, and the turbulent inlet of LES is generated by the consistent discretizing random flow generation (CDRFG) method. The performance of LES is validated by two different complex terrains in Changsha and Mianyang, China, and the results are compared with wind tunnel tests and onsite measurements, respectively. Furthermore, the non-Gaussian parameters, such as skewness, kurtosis, probability curves, and gust factors, are analyzed in-depth. The results show that the LES method is in good agreement with both mean and turbulent wind fields from wind tunnel tests and onsite measurements. Wind fields in complex terrain mostly exhibit a left-skewed Gaussian process, and it changes from a softening Gaussian process to a hardening Gaussian process as the height increases. A reduction in the gust factors of about 2.0%-15.0% can be found by taking into account the non-Gaussian features, except for a 4.4% increase near the ground in steep terrain. This study can provide a reference for the assessment of extreme wind loads on structures in complex terrain.

풍수 형기론(形氣論)으로 본 대순진리회 금강산토성수련도장

신영대 대진대학교 대순사상학술원 2020 대순사상논총 Vol.36 No.-

본 논문은 대순진리회 금강산토성도장을 풍수학의 형기학적인 관점에서 전반적인 풍수의 국세와 특징들을 밝히고자 하였다. 겉으로 드러난 산의 형세를 보고, 그 안에 흐르는 기의 세력을 살펴 산천에서 발생하는 기운의 강약과 후박 등을 통해 생기의 흐름을 파악하고 그에 따른 길흉을 살펴보았다. 이곳은 특히 “일만 이천의 도통군자로 창성하리라”라는 상제님의 말씀이 서려있는 곳이며, 미륵불과 도전님의 능소가 있다는 점에서 수도를 하는 사람들에게 매우 의미 있는 도장으로 알려져 있다. 이와 관련하여 풍수론에 부합한 금강산토성수련도장의 풍수적 상징성과 생왕지지에 대해 탐색하고, 그에 따른 지세와 형국, 동해의 맑은 수기가 어울린 용맥과 지맥, 금강산의 산세, 대순진리회 금강산토성수련도장의 풍수적 입지와 지세, 지맥 등을 탐색하고자 하였다. 백두대간은 금강산을 거쳐 신선봉으로 이어지고 그 중 한 줄기는 금강산토성수련도장으로 이어졌고, 다른 한 줄기는 상봉을 거쳐 미시령과 설악산으로 이어져 내려간다. 따라서 대순진리회의 여러 도장들 가운데 금강산토성수련도장을 형기풍수론을 토대로 살펴봄으로써, 대순진리회가 종교 건축물의 입지조건으로서 주위 환경과의 관계를 강력히 고려하고 있다는 사실을 풍수지리 제반 이론들을 토대로 학술적 접근을 통해 그 본의를 논증하고자 하였다. 동시에 금강산토성수련도장이 자리하고 있는 현장을 중심으로 산과 물의 흐름을 파악하고 주변의 지세가 어떤 형태로 풍수의 이치에 부합하고 있는지 전반적으로 살펴보았다. 제반 풍수이론에 근거하여 볼 때 금강산토성수련도장은 신선봉을 필두로 하여 주맥이 행도 과정에서 산줄기가 흘러내리면 물이 따라 흐르고, 물이 휘돌아 흐르는 곳에 산이 따라 이어지는 수많은 지리적 음양변화를 거치며 금강산토성수련도장으로 이어져 내렸다. 자연의 이치라 할 수 있는 산과 물의 유기적인 관계로 볼 때 때 금강산토성수련도장의 가장 두드러진 풍수적 특징은 음양합덕에 부합한 빼어난 수세와 청룡과 백호가 조화를 이룬 국세를 형성하고 있다는 점에서 전통적인 풍수이론에 부합하고 있음을 알 수 있다. This study aims to reveal the overall Fengshui figuration and geomantic features of Daesoon Jinrihoe’s Geumgangsan (Mt. Geumgang) Toseong Training Temple Complex from the Hyeonggi (Energy of Form) Theory in Fengshui. This study first looked at the mountain landscape viewable from the surface, examined the influence of Qi (Energy) flowing inside it, comprehended the flow of its vitality in terms of its strengths and weaknesses, and gauged the depth of the energy produced from mountain streams to determine fortune and misfortune. There is a special significance to this site due to Sangje’s teaching that “…it will be prosperous with 12,000 Dotonggunja (Dao-empowered Sages),” and it is also known as a efficacious grounds for cultivation among ascetics due to it housing the royal mausoleum of Dojeon (interpreted by some as Maitreya). Concerning this, this study explores the geomantic symbolism and growth-supporting land of Geumgangsan Toseong Training Temple Complex as it corresponds to Fengshui theory, and in keeping with this, the topography and conditions are likewise examined. The mountain range and its energy pathways (veins) harmonize with the pure water energy coming from the East Sea. The mountain terrain of Mount Geumgang, and the geomantic location, topography, and energy pathways that influence Daesoon Jinrihoe Geumgangsan Toseong Training Temple Complex are all explored. The Baekdudaegan Mountain Range extends through Mount Geumgang to Sinseonbong Peak, and one range extends to Geumgangsan Toseong Training Temple Complex whereas the other range extends through Sangbong Peak down to Misiryeong Valley and Mount Seorak. Thus, this study demonstrates that Daesoon Jinrihoe has always strongly considered the relationship between its temple complexes and their surrounding environment. The order has always selected locations that exhibit optimal conditions which suit the construction of sacred spaces. The determinations in this paper were made through an academic approach that drew upon various theories of Fengshui while examining Daesoon Jinrihoe’s Geumgangsan Toseong Training Temple Complex. The in-depth analysis was specifically based on Hyeonggi Fengshui. At the same time, this study also looked into the surroundings of Geumgangsan Toseong Training Temple Complex. In particular, the mountains and flow of nearby bodies of water were comprehensively examined to show how the surrounding topography corresponds to the principles of Fengshui. An integral approach combining all major theories of Fengshui revealed that Geumgangsan Toseong Training Temple Complex starts from Sinseonbong Peak, and its energy flows through the main mountain range, going through numerous geographical changes of yin and yang. When the range flows down, the water flows accordingly, and where the water whirls, the mountains are shaped accordingly. Eventually, this energy reaches Geumgangsan Toseong Training Temple Complex. From the organic relationship between mountains and bodies of water, which can be said to be the essence of the order of nature, it can be judged that the most prominent geomantic feature of Geumgangsan Toseong Training Temple Complex corresponds to traditional theories of Fengshui in that it forms a configuration wherein optimal water energy supports the Virtuous Concordance of Yin Yang and harmonizes the Blue Dragon with the White Tiger.

Large-eddy simulation and wind tunnel study of flow over an up-hill slope in a complex terrain

Tsang, C.F.,Kwok, Kenny C.S.,Hitchcock, Peter A.,Hui, Desmond K.K. Techno-Press 2009 Wind and Structures, An International Journal (WAS Vol.12 No.3

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.

Large-eddy simulation and wind tunnel study of flow over an up-hill slope in a complex terrain

C. F. Tsang,Kenny C. S. Kwok,Peter A. Hitchcock,Desmond K. K. Hui 한국풍공학회 2009 Wind and Structures, An International Journal (WAS Vol.12 No.3

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.

지형에 따른 육상풍력발전단지 난류강도 및 피로 하중 비교 분석

김영휘,김민지,백인수 한국풍력에너지학회 2023 풍력에너지저널 Vol.14 No.4

This study aimed to investigate differences in turbulence intensity and turbine loads among onshore wind farms located in various types of terrain. To achieve this, simulations were conducted for two onshore wind farms with identical wind turbines and capacity but situated on complex and flat terrains. The simulations used meteorological data gathered over a 10-year period from automatic weather stations nearest to the wind farms. WindSim and WindPRO software tools were employed for wind field and load analysis, respectively. The simulation results revealed that wind farm A, situated on complex terrain, exhibited significantly higher effective turbulence intensity than wind farm B on flat terrain, as expected. Consequently, the load indices of several wind turbines exceeded 100 % in wind farm A, indicating that the turbines could not reach their design lifespan. From the simulation study, aimed at reducing both the effective turbulence intensity and turbine loads, it became evident that while increasing turbine spacing could decrease effective turbulence intensity to some extent, it couldn't completely resolve the issue due to the inherently high ambient turbulence intensity on complex terrain. The problem with wind turbine loads could only be completely resolved by using wind turbines with a turbine class of A+, corresponding to a reference turbulence intensity of 0.18.

Characteristics of Canopy Turbulence over a Deciduous Forest on Complex Terrain

이인혜,이영희,홍진규 한국기상학회 2011 Asia-Pacific Journal of Atmospheric Sciences Vol.47 No.3

Canopy turbulence plays an important role in mass and energy exchanges at the canopy-atmosphere interface. Despite extensive studies on canopy turbulence over a flat terrain, less attention has been given to canopy turbulence in a complex terrain. The purpose of this study is to scrutinize characteristics of canopy turbulence in roughness sublayer over a hilly forest terrain. We investigated basic turbulence statistics, conditionally sampled statistics, and turbulence spectrum in terms of different atmospheric stabilities, wind direction and vertical structures of momentum fluxes. Similarly to canopy turbulence over a homogeneous terrain, turbulence statistics showed coherent structure. Both quadrant and spectrum analysis corroborated the role of intermittent and energetic eddies with length scale of the order of canopy height, regardless of wind direction except for shift of peak in vertical wind spectrum to relatively high frequency in the down-valley wind. However, the magnitude of the momentum correlation coefficient in a neutral condition was smaller than typical value over a flat terrain. Further scrutiny manifested that, in the up-valley flow, temperature skewness was larger and the contribution of ejection to both momentum and heat fluxes was larger compared to the downvalley flow, indicating that thermal instability and weaker wind shear in up-valley flow asymmetrically affect turbulent transport within the canopy.

A hybrid numerical simulation method for typhoon wind field over complex terrain

Wenfeng Huang,Huanlin Zhou 한국풍공학회 2014 Wind and Structures, An International Journal (WAS Vol.18 No.5

In spite of progress in the numerical simulation of typhoon wind field in atmospheric boundary layer (ABL), using typhoon wind field model in conjunction with Monte Carlo simulation method can only accurately evaluate typhoon wind field over a general terrain. This method is not enough for a reliable evaluation of typhoon wind field over the actual complex terrain with surface roughness and topography variations. To predict typhoon wind field over the actual complex terrain in ABL, a hybrid numerical simulation method combined typhoon simulation used the typhoon wind field model proposed by Meng et al. (1995) and CFD simulation in which the Reynolds averaged Navier-Stokes (RANS) equations and k-e turbulence model are used. Typhoon wind filed during typhoon Dujuan and Imbudo are simulated using the hybrid numerical simulation method, and compared with the results predicted by the typhoon wind field model and the wind field measurement data collected by Fugro Geotechnical Services (FGS) in Hong Kong at the bridge site from the field monitoring system of wind turbulence parameters (FMS-WTP) to validate the feasibility and accuracy of the hybrid numerical simulation method. The comparison demonstrates that the hybrid numerical simulation method gives more accurate prediction to typhoon wind speed and direction, because the effect of topography is taken into account in the hybrid numerical simulation method.