• Wind and Structures
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• 제23권6호
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• pp.505-521
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• 2016

The objective of this study is to investigate numerically the effect of building roof shaps on wind flow and pollutant dispersion in a street canyon with one row of trees of pore volume, $P_{vol}=96%$. A three-dimensional computational fluid dynamics (CFD) model is used to evaluate air flow and pollutant dispersion within an urban street canyon using Reynolds-averaged Navier-Stokes (RANS) equations and the Explicit Algebraic Reynolds Stress Models (EARSM) based on k-${\varepsilon}$ turbulence model to close the equation system. The numerical model is performed with ANSYS-CFX code. Vehicle emissions were simulated as double line sources along the street. The numerical model was validated by the wind tunnel experiment results. Having established this, the wind flow and pollutant dispersion in urban street canyons (with six roof shapes buildings) are simulated. The numerical simulation results agree reasonably with the wind tunnel data. The results obtained in this work, indicate that the flow in 3D domain is more complicated; this complexity is increased with the presence of trees and variability of the roof shapes. The results also indicated that the largest pollutant concentration level for two walls (leeward and windward wall) is observed with the upwind wedge-shaped roof. But the smallest pollutant concentration level is observed with the dome roof-shaped.

• 한국산학기술학회논문지
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• 제18권2호
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• pp.672-680
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• 2017

태양광 발전 시스템은 태양광 패널이 부착되어 있는 구조물, 이를 지지하는 부분과 발전된 전력을 계통 또는 부하측에 공급하는 장치로 구성된다. 태양광 패널의 발전효율은 태양빛의 입사량에 영향을 받기 때문에 패널이 태양빛을 가장 많이 받을 수 있는 방향으로 패널 구조물을 설치한다. 그러나 태양은 계속 이동하기 때문에 고정식 보다는 태양을 향하여 패널이 회전하는 방식이 더욱 효율이 좋다. 태양광 패널 구조물은 야외에 설치되므로 풍하중, 적설하중 지진하중 등이 작용한다. 본 논문에서는 태양광 패널 구조물에 가장 영향이 큰 풍하중을 유한요소법을 사용하여 구하고 이를 적용하여 태양 추적식 발전 장치의 구조물을 설계하였다. 특히 패널간의 간격에 따른 풍하중을 구하고, 패널 구조물이 지면과 이루는 각도에 따른 풍하중의 변화도 구하였다. 패널간의 간격은 간격이 없을 경우, 간격이 40 mm, 80 mm일 경우 등 3가지 경우에 대하여 해석을 하였으며, 지면과의 각도는 30도, 45도, 60도 등에 대하여 해석을 하였다. 해석결과 풍하중은 패널간의 간격이 없을 경우가 가장 적게 나타났고, 지면과의 경사각이 클수록 커지는 것을 알 수 있었다.

• 대한기계학회논문집B
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• 제33권12호
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• pp.1007-1013
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• 2009

The purposes of this study are to evaluate the power performance through CFD analysis and structural integrity through uni-directional FSI analysis in aerodynamic design and structure design of wind turbine blade. The blade was designed to generate the power of 2MW under the rated wind speed of 11 m/s, consisting of NACA 6 series, DU series and FFA series airfoil. The inside section of the blade was designed into D-spar structure and circular stiffener was placed to reinforce the structural strength in the part of hub. CFD analysis with the application of transitional turbulence model was performed to evaluate the power performance of blade according to the change of TSR and 2.024MW resulted under the condition of rated wind speed. TSR of 9 produced the maximum power coefficient and in this case, Cp was 0.494. This study applied uni-directional FSI analysis for more precise evaluation of structural integrity of blade, and the results of fiber failure, inter fiber failure and eigenvalue buckling analysis were evaluated, respectively. For the evaluation, Puck's failure criteria was applied and the result showed that fiber failure and inter fiber failure did not occur under every possible condition of the analysis. As a result, power performance and structural integrity of 2 MW blade designed in this study turned out to satisfy the initial design goals.

• Wind and Structures
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• 제22권2호
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• pp.253-272
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• 2016

The paper concerns with the method and results of wind tunnel investigations of the Strouhal number (St) of a stationary iced cable model of cable-supported bridges with respect to different angles of wind attack. The investigations were conducted in the Climatic Wind Tunnel Laboratory of the Czech Academy of Sciences in $Tel{\check{c}}$. The methodology leading to the experimental icing of the inclined cable model was prepared in a climatic section of the laboratory. The shape of the ice on the cable was registered by a photogrammetry method. A section of an iced cable model with a smaller scale was reproduced with a 3D printing procedure for subsequent aerodynamic investigations. The St values were determined within the range of the Reynolds number (Re) between $2.4{\cdot}10^4$ and $16.5{\cdot}10^4$, based on the dominant vortex shedding frequencies measured in the wake of the model. The model was oriented at three principal angles of wind attack for each of selected Re values. The flow regimes were distinguished for each model configuration. In order to recognize the tunnel blockage effect the St of a circular smooth cylinder was also tested. Good agreement with the reported values in the subcritical Re range of a circular cylinder was obtained. The knowledge of the flow regimes of the airflow around an iced cable and the associated St values could constitute a basis to formulate a mathematical description of the vortex-induced force acting on the iced cable of a cable-supported bridge and could allow predicting the cable response due to the vortex excitation phenomenon.

• Wind and Structures
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• 제36권4호
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• pp.221-236
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• 2023

The lateral component of turbulence and the vortices shed in the wake of a structure result in introducing dynamic wind load in the acrosswind direction and the resulting level of motion is typically larger than the corresponding alongwind motion for a dynamically sensitive structure. The underlying source mechanisms of the acrosswind load may be classified into motion-induced, buffeting, and Strouhal components. This study proposes a frequency domain framework to decompose the overall load into these components based on output-only measurements from wind tunnel experiments or full-scale measurements. First, the total acrosswind load is identified based on measured acceleration response by solving the inverse problem using the Kalman filter technique. The decomposition of the combined load is then performed by modeling each load component in terms of a Bayesian filtering scheme. More specifically, the decomposition and the estimation of the model parameters are accomplished using the unscented Kalman filter in the frequency domain. An aeroelastic wind tunnel experiment involving a tall circular cylinder was carried out for the validation of the proposed framework. The contribution of each load component to the acrosswind response is assessed by re-analyzing the system with the decomposed components. Through comparison of the measured and the re-analyzed response, it is demonstrated that the proposed framework effectively decomposes the total acrosswind load into components and sheds light on the overall underlying mechanism of the acrosswind load and attendant structural response. The delineation of these load components and their subsequent modeling and control may become increasingly important as tall slender buildings of the prismatic cross-section that are highly sensitive to the acrosswind load effects are increasingly being built in major metropolises.

• 한국컴퓨터정보학회논문지
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• 제28권9호
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• pp.55-62
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• 2023

본 논문에서는 기하학 기반의 사운드 생성 기법을 활용하여 1)다중 음원, 2)바람의 이류와 3)온도에 따른 상호작용을 효율적으로 처리할 수 있는 방법을 제시한다. 최근에 절감된 광선추적법(Reduced raytracing) 기반으로 사운드(Sound) 위치를 업데이트하고 많은 레이(Ray)의 재귀적인 반사/굴절 없이 사운드 전파와 회절을 효율적으로 계산하는 방법이 제안되었지만, 이 접근법은 사운드의 전파 특징만을 고려했지 다중 음원, 바람의 이류와 온도에 따른 상호작용은 고려하지 못했다. 이러한 한계는 정적인 사운드만 생성하기 때문에, 다양한 가상환경에서 사운드를 통한 장면 제작을 어렵게 만든다. 본 논문에서는 여러 개의 사운드가 배치된 상황에서 사운드 맵을 효율적으로 구성할 수 있는 방법과 이것을 통해 효율적으로 에이전트의 움직임을 제어할 수 있는 방법을 제시한다. 뿐만 아니라 바람의 이류와 온도를 고려하여 사운드 전파를 제어를 할 수 있는 방법을 제안한다. 본 논문에서 제안하는 방법은 사운드를 기반으로 콘테츠 몰입을 개선시킬 수 있는 게임뿐만 아니라 메타버스 환경 디자인, 군중 시뮬레이션 등 다양한 분야에서 활용이 가능하다.

• Wind and Structures
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• 제11권4호
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• pp.275-289
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• 2008

Large eddy simulations have been performed within and over different types of urban building arrays. This paper adopted three dimensionless parameters, building frontal area density (${\lambda}_f$) the variation degree of building height (${\sigma}_h$), and the staggered degree of building range ($r_s$), to study the systematic influence of building spacing, height and layout on wind and turbulent characteristics. The following results have been achieved: (1) As ${\lambda}_f$ decrease from 0.25 to 0.18, the mean flow patterns transfer from "skimming" flow to "wake interference" flow, and as ${\lambda}_f$ decrease from 0.06 to 0.04, the mean flow patterns transfer from "wake interference" flow to "isolated roughness" flow. With increasing ${\lambda}_f$, wind velocity within arrays increases, and the vortexes in front of low buildings would break, even disappear, whereas the vortexes in front of tall buildings would strengthen and expand. Tall buildings have greater disturbance on wind than low buildings do. (2) All the wind velocity profiles and the upstream profile converge at the height of 2.5H approximately. The decay of wind velocity within the building canopy was in positive correlation with ${\lambda}_f$ and $r_s$. If the height of building arrays is variable, Macdonald's wind velocity model should be modified through introducing ${\sigma}_h$, because wind velocity decreases at the upper layers of the canopy and increases at the lower layers of the canopy. (3) The maximum of turbulence kinetic energy (TKE) always locates at 1.2 times as high as the buildings. TKE within the canopy decreases with increasing ${\lambda}_f$ and $r_s$ but the maximum of TKE are very close though ${\sigma}_h$ varies. (4) Wind velocity profile follows the logarithmic law approximately above the building canopy. The Zero-plane displacement $z_d$ heighten with increasing ${\lambda}_f$, whereas the maximum of and Roughness length $z_0$ occurs when ${\lambda}_f$ is about 0.14. $z_d$ and $z_0$ heighten linearly with ${\sigma}_h$ and $r_s$, If ${\sigma}_h$ is large enough, $z_d$ may become higher than the average height of buildings.

• 한국항공우주학회지
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• 제47권2호
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• pp.107-113
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• 2019

본 논문에서는 대기 속도 센서가 없는 항공기에서의 강인 필터 기반의 바람 추정 기법을 제안한다. 바람 속도(wind velocity)는 항공기의 유도 및 제어를 더욱 정밀하게 수행하기 위해 사용되는 정보이다. 일반적으로 바람 속도는, 대기 속도와 지면 속도의 차이를 계산하여 얻을 수 있다. 이때 대기 속도는 피토 튜브와 같은 항공기와 대기의 상대 속도를 측정하는 대기 속도 측정 센서에서 얻을 수 있고, 지면 속도는 항법 시스템으로부터 얻을 수 있다. 그러나 항공기의 구성을 간단하게하기 위하여 대기 속도 측정 센서를 장착하지 않는 경우, 바람 속도를 직접적으로 얻을 수 없기 때문에 필터를 이용한 바람 추정 기법이 필수이다. 이때 난류에 의해 항공기의 공력 계수가 변하게 되는데, 이는 바람 추정 필터의 시스템 모델의 불확실성을 유발하게 되고, 결국 바람 추정 성능이 저하된다. 따라서 본 연구에서는 공력계수 불확실성에 강인함을 확보하기 위해 $H{\infty}$ 필터를 적용한 바람 추정 기법을 제안하였다. 시뮬레이션을 통해 제안하는 기법이 공력계수의 불확실성이 있는 상황에서 성능을 개선하는 것을 확인하였다.

• Wind and Structures
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• 제30권5호
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• pp.485-497
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• 2020

A study, using potential water wave theory, is conducted on the oblique water wave motion over two fixed submerged rectangular blocks (breakwaters) placed over a finite step bottom. We have considered infinite and semi-infinite fluid domains. In both domains, the Fourier expansion method is employed to obtain the velocity potentials explicitly in terms of the infinite Fourier series. The unknown coefficients appearing in the velocity potentials are determined by the eigenfunction expansion matching method at the interfaces. The derived velocity potentials are used to compute the hydrodynamic horizontal and vertical forces acting on the submerged blocks for different values of block thickness, gap spacing between the two blocks, and submergence depth of the upper block from the mean free surface. In addition, the wave load on the vertical wall is computed in the case of the semi-infinite fluid domain for different values of blocks width and the incident wave angle. It is observed that the amplitudes of hydrodynamic forces are negligible for larger values of the wavenumber. Furthermore, the upper block experiences a higher hydrodynamic force than the lower block, regardless of the gap spacing, submergence depth, and block thickness.

• Wind and Structures
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• 제23권4호
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• pp.301-311
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• 2016

The numerous benefits of Savonius turbine such as simple in structure, has appropriate self-start ability, relatively low operating velocity, water acceptance from any direction and low environmental impact have generated interests among researchers. However, it suffers from a lower efficiency compared to other types of water turbine. To improve its performance, parameters such flow pattern, pressure and velocity in different conditions must be analyzed. For this purpose, a detailed description on the flow field of various types of Savonius rotors is required. This article presents a numerical study on a nonlinear two-dimensional flow over a classic Savonius type rotor and a Benesh type rotor. In this experiment, sliding mesh was used for solving the motion of the bucket. The unsteady Reynolds averaged Navier-Stokes equations were solved for velocity and pressure coupling by using the SIMPLE (Semi-Implicit Method for Pressure linked Equations) algorithm. Other than that, the turbulence model using $k-{\varepsilon}$ standard obtained good results. This simulation demonstrated the method of the flow field characteristics, the behavior of velocity vectors and pressure distribution contours in and around the areas of the bucket.