Effects of Wind Fences on the Wind Environment around Jang Bogo Antarctic Research Station

This study investigated the flow characteristics altered by Jang Bogo Antarctic Research Station using computational fluid dynamics(CFD) modeling. The topography and buildings around Jang Bogo Station were constructed with computeraided-design data in the CFD model domain. We simulated 16 cases with different inflow directions, and compared the flow characteristics with and without Jang Bogo Station for each inflow direction. The wind data recorded by the site's automatic weather station(AWS) were used for comparison. Wind rose analysis showed that the wind speed and direction after the construction of Jang Bogo Station were quite different from those before construction. We also investigated how virtual wind fences would modify the flow patterns, changing the distance of the fence from the station as well as the porosity of the fence. For westerly inflows, when the AWS was downwind of Jang Bogo Station, the decrease in wind speed was maximized(-81% for west-northwesterly). The wind speed reduction was also greater as the distance of the fence was closer to Jang Bogo Station. With the same distance, the fence with medium porosity(25%–33%) maximized the wind speed reduction.These results suggest that the location and material of the wind fence should be selected carefully, or AWS data should be interpreted cautiously, for particular prevailing wind directions.     

平台障碍物对海气通量观测影响的数值分析

基于计算流体动力学模型（CFD）模拟了背景风风速为2 m·s-1、4 m·s-1、6 m·s-1下通量观测平台周围的风场分布,确定了不同风速下平台障碍物对观测影响最小的风向范围。发现风速不同,平台对背景风的影响范围不同,风速越大,平台对背景风的影响越大。运用涡动相关法计算不同风向条件下的湍流通量,定量分析由于平台干扰对海气通量计算的影响,发现选取迎风条件下的数据计算得到的海气通量会比实际偏低。     

水平轴潮流能水轮机数值模拟方法对比分析

叶素动量理论和CFD方法是水平轴潮流能水轮机性能分析中运用较为广泛的数值模拟方法,文中结合小尺寸水轮机模型试验,对比分析了叶素动量理论和CFD方法在水轮机性能分析中的准确性和适用性.验证结果表明:叶素动量理论和CFD方法均能对水轮机的性能进行预报,且CFD精度高于动量叶素理论;大尖速比时,动量叶素理论偏离较高,不再适合性能预报;在小尖速比下,建议采用RNGk-ε模型的CFD方法进行分析计算;动量叶素理论适合设计初期设计方案的对比分析,而CFD方法适合对设计结果的验证校核和详细分析.     

Optimization of Blade Motion of Vertical Axis Turbine

In this paper, a method is proposed to improve the energy efficiency of the vertical axis turbine. First of all, a single disk multiple stream-tube model is used to calculate individual fitness. Genetic algorithm is adopted to optimize blade pitch motion of vertical axis turbine with the maximum energy efficiency being selected as the optimization objective. Then, a particular data processing method is proposed, fitting the result data into a cosine-like curve. After that, a general formula calculating the blade motion is developed. Finally, CFD simulation is used to validate the blade pitch motion formula. The results show that the turbine’s energy efficiency becomes higher after the optimization of blade pitch motion; compared with the fixed pitch turbine, the efficiency of variable-pitch turbine is significantly improved by the active blade pitch control; the energy efficiency declines gradually with the growth of speed ratio; besides, compactness has lager effect on the blade motion while the number of blades has little effect on it.     

Numerical and Experimental Studies on the Propulsion Performance of A Wave Glide Propulsor

This paper introduces a newly developed Unmanned Wave Glide Vehicle (UWGV), which is driven only by extracting energy from gravity waves, and presents a comprehensive study on the propulsion performance of the UWGV’s propulsor―Wave Glide Propulsor (WGP) in a regular wave. By simplifying the WGP as six 2D tandem asynchronous flapping foils (TAFFs), a CFD method based on Navier?Stokes equations was first used to analyze the hydrodynamic performance of TAFFs with different parameters of non-dimensional wave length m and non-dimensional wave height n. Then, a series of hydrodynamic experiments were performed. The computational results agree well with the experimental results when n≤0.07 and both of them show the thrust force and input power of the WGP are larger at smaller m or larger n. By analyzing the flow field of TAFFs, we can see that a larger m is beneficial to the forming, merging and shredding of the TAFFs’ vortices; as TAFFs are arranged in tandem and have the same motions, the leading edge vortex and wake vortex of the TAFFs are meaningful for improving the thrust force of their adjacent ones.     

Numerical simulations of wave–current flow in an ocean basin

Wave–current flow is a phenomenon that is present in many practical engineering situations. Over the past several decades, this type of flow has been increasingly investigated under controlled laboratory conditions. This paper presents a numerical study of wave–current flow in the ocean basin of the LabOceano (COPPE/UFRJ). A homogeneous multiphase model based on the RANS equations and the k–ɛ turbulence model implemented in ANSYS-CFX code were used. A cross section of the ocean basin was represented. A regular wave with a height of 0.08 m and a period of 1.80 s (i.e., a wave steepness of H/L = 0.016), propagating on favourable currents, was simulated. The behaviour of the free surface elevation over time and the streamlines along the basin for wave and wave–current flows were presented. The numerical results were compared to the non-viscous theory given by the Rayleigh equation applied to the problem of wave–current interaction. Good agreement was found between the wave length estimated by the numerical results and the analytical solutions, with a deviation of less than 2%.     

Simplified CFD modeling for bilge keel force and hull pressure distribution on a rotating cylinder

A horizontal, circular cylinder fitted with one bilge keel is forced to rotate harmonically around its axis. The bilge keel load and hull pressure distribution are investigated. A fully submerged condition (infinite fluid), and three partly-submerged conditions are considered. A two-dimensional numerical study is performed, and the results are validated against recently published experimental data by van’t Veer et al. [30]. In addition, comparisons for mass and drag coefficients are also made with experimental data for plate in infinite fluid (Keulegan and Carpenter [8]), and wall-mounted plate (Sarpkaya and O’Keefe [9]) in oscillatory flow.A Navier–Stokes solver based on the Finite Volume Method is adopted for solving laminar flow of incompressible water. The free-surface condition is linearized by neglecting the nonlinear free-surface terms and the influence of viscous stresses in the free surface zone, while the body-boundary condition is exact. This simplified modeling of the problem required the mesh to be fine only around the bilge keels, leading to a total number of cells around N ≃ 1 ×10⁴, which reduced computational cost significantly.The influence of draft and amplitude of oscillations on the bilge keel force and hull pressure distribution are considered. The bilge keel force is presented in terms of non-dimensional drag and mass coefficients including higher harmonic components. The numerical results are also compared with the industry standard empirical method for calculation of roll damping proposed by Ikeda et al. [4]. In general, a good agreement between the results of the present numerical method and the experimental data is obtained and the differences with those predicted by the empirical method are addressed.     

风电场流场特性及风机布局数值模拟研究

针对风电场流场特性研究对风力机工作性能提高的重要意义,采用计算流体力学（CFD）方法在单机风力机模拟验证的基础上,对某风电场单风力机和三种布局条件下的风电场流场特性进行了数值模拟研究。考察了不同布局条件下风电场速度、叶轮表面压力以及湍流涡的分布特性。结果表明：叶轮后方尾流效应明显,速度损失随着相对距离的增加而逐渐减小,风力机处中心尾流速度比率最低降为0.4;当相对距离超过4 d后,风速可恢复为初始速度的90%以上;尾流速度与涡流粘性呈负相关性;三风力机平行布置时,各风力机尾流速度比率基本一致;三风机组在错落布置时,尾流效应对下游风力机工作性能影响较小,错落角度越大,尾流损失越小。     

组合动力锚水动力特性数值模拟研究

作为海上浮式结构物的一种新型锚固基础,动力锚具有自安装、不受水深影响、适用范围广的特点。在动力锚的基础上研发的组合动力锚结合了动力锚自安装和板锚法向受荷的特点,具有安装快速、适用多种类型海床、承载效率高等性质。组合动力锚在水中自由下落时的水动力学特性（下落速度、方向稳定性等）会受到锚链、尾翼宽度和助推器质量等因素影响。若下落速度过小或方向稳定性过差,则会影响锚的安装成功率。采用计算流体动力学方法模拟流体对锚的冲击和锚在水中自由下落过程,以优化组合动力锚的尾翼尺寸;其次研究锚链作用力和助推器质量对组合动力锚下落速度和偏角的影响规律。计算结果表明：组合动力锚的拖曳阻力系数为0.45左右,尾翼宽度最优尺寸为翼板宽度的1.25倍。连接在锚眼处的锚链会减小组合动力锚的下落速度并加剧锚的偏转,需综合锚的下落速度和偏角来确定锚在水中下落高度。     

Experimental investigation of hydrodynamic force coefficients over AUV hull form

Extensive use of autonomous underwater vehicles (AUVs) in oceanographic applications necessitates investigation into the hydrodynamic forces acting over an AUV hull form operating under deeply submerged condition. This paper presents a towing tank-based experimental study on forces and moment on AUV hull form in the vertical plane. The AUV hull form considered in the present program is a 1:2 model of the standard hull form Afterbody1. The present measurements were carried out at typical speeds of autonomous underwater vehicles (0.4-1.4 m/s) by varying pitch angles (0-15°). The hydrodynamic forces and moment are measured by an internally mounted multi-component strain gauge type balance. The measurements were used to study variation of axial, normal, drag, lift and pitching moment coefficients with Reynolds number (Re) and angle of attack. The measurements have also been used to validate results obtained from a CFD code that uses Reynolds Average Navier-Stokes equations (ANSYS™ Fluent). The axial and normal force coefficients are increased by 18% and 195%; drag, lift and pitching moment coefficients are increased by 90%, 182% and 297% on AUV hull form at α=15° and Re_v=3.65×10⁵. These results can give better idea for the efficient design of guidance and control systems for AUV.