基于尾流模型的风场偏航控制优化研究

在风机大尺度化与风场大型化的趋势下,如何通过合适的控制策略以降低尾流损失成为关键问题。以包括30台NREL-5MW风机并采用5行6列平行四边形布置方式的小型风场为研究对象,基于显示尾流模型,以各风机偏航角度为优化参数,风场总功率为目标函数,使用粒子群优化算法对比分析了偏航控制对不同风速、风向、湍流强度下的风场性能提升效果。结果表明,偏航控制优化可在风向与风机行或列方向平行时发挥明显效果,当风机行列间距为4倍风轮直径且湍流强度为5%时,在不同风速下偏航控制可分别将风场总体发电量提升15%~20%,但对于布置间距大于7倍风轮直径或湍流强度高于15%时的风场,其作用十分有限,总体发电量提升在5%以内。     

基于致动线模型的错列式两风机尾流场数值模拟

风电场中风机之间存在十分复杂尾流相互干扰现象,尾流相互干扰效应对风机的功率输出、叶片载荷等产生十分显著的影响。采用致动线模型以及计算流体力学方法,研究两风机之间的复杂尾流干扰效应。在保持两风机纵向间距一样的情况下,考虑两风机在不同横向间距下,数值模拟两风机的部分尾流相互干扰现象,分析两风机的气动功率输出特性、尾流速度变化特性、风轮平面附近轴向诱导因子分布特性,尾涡结构以及尾流干扰效应。数值模拟结果表明:在上下游风机在沿着流向方向距离保持不变的情况下,随着横向间距的变化,上下游风机的尾流存在十分复杂的尾流相互干扰效应,对下游风机的气动功率输出以及两风机风电场的整体流场产生了显著的影响。     

一次典型层积云的飞机观测结果及与卫星资料的对比分析

飞机探测可直接获取云的微观结构特征量,但只是一些线段;卫星遥感资料可大范围监测云环境,但不是直接获得云参量,需要反演。因而开展云的飞机观测结果与卫星资料的对比分析是必要的。对1999月6月4日华北平原上一次层积云过程两个架次的飞机微物理探测资料进行了详细分析,并将飞机盘旋上升和下降取得的5次云参数垂直探测结果作为辐射传输模式SBDART2.4的输入,采取正演的方式与GMS5/VISSR、NOAA15/AVHRR反射通道的资料进行了对比分析。飞机探测显示层积云云厚约1000 m,云粒子浓度最大值425 cm-3,含水量最大值0.2 g/m3。第1架次云粒子浓度、含水量、有效半径的平均值为225±75 cm-3、0.08±0.03 g/m3、7.2±1.6μm,第2架次云粒子浓度、含水量、有效半径的平均值为196±73 cm-3、0.04±0.02 g/m3、4.9±1.4μm。按500 m垂直分层后,云粒子有效半径平均值为6.1±1.7μm,主体云层(1000—1500 m)柱含水量平均值为29.5±17.5 g/m2。敏感性试验表明当有云存在时,云的光学厚度是影响可见光通道反照率的主要因子,利用飞机探测云参数...     

A Case Study of Rayleigh-Bénard Convection with Clouds

A turbulence data set collected by the research aircraft Hercules and Falcon in the planetary boundary layer (PBL) over the North Sea during Rayleigh-Bénard convection (RBC) is analysed. Altogether nearly three hundred cell passages at different levels and in two different flight directions were sampled.The convective boundary-layer height (H) was about 1 km, and the RBC cells had a diameter D of roughly 2–3 km, resulting in an aspect ratio A = D/H 2–3. This value is also found in the case of RBC in laboratory-scale flows, whereas most of the recent PBL experimental work reports convection PBL rolls with A 3 and mesoscale cellular convection (MCC) with A 10–40 over the oceans.The large number of RBC cell passages made it possible to composite their average structure. Due to the more complex three-dimensional structure and the importance of thermals to the RBC dynamics, spectral, temporal and spatial decompositions and model calculations were necessary to illuminate structure, dynamics, energetics and organisation. The final impression is that the structure of RBC in the PBL is given by a honeycomb-like arrangement of short-lived mixed-layer thermals with more passive downward motions in between. The regularity of the Cu-cloud cover results partly from the more stationary flow in the cloud-free cell centres. On the other hand it is shown that active as well as inactive clouds contribute to the cloud cover. Thus, the PBL flow and the cloud cover are decoupled, at least temporarily and locally.Due to sparse observational and measured information about RBC occurrence and structure in the PBL, additional material was gathered, resulting in the impression that RBC is one additional realised mode of organised convection in the PBL, as has already been clarified for PBL rolls and MCC by recent investigations.     

船只衰落尾迹的小波多尺度广义分形特征分析

船只衰落尾迹遥感图像是弱反差纹理图像,检测强尾迹的方法不具有适用性。基于区域特征统计比较的思想,构建了一种会聚衰落尾迹异常的小波多尺度广义分形特征提取方法。该方法由小波多尺度分解、细节图像融合、多尺度基本特征计算、多尺度分形特征计算和广义分形特征计算等5步骤组成。仿真实验表明,该特征能完整表达尾迹并体现强弱差别,是一种有效的船只衰落尾迹检测技术,具有广泛的应用前景。     

在建导管架平台圆管风致涡激振动及减振研究

研究了大型导管架平台卧式建造时出现单边约束圆管的风致涡激振动问题。将建造过程中单边约束的导管架圆管简化成悬臂梁模型,采用van der Pol尾流振子模型模拟圆管受到的流体力,建立了圆管风致涡激振动动力学方程。使用伽辽金方法对建立的运动方程进行求解,数值分析了圆管在特定约化风速下的涡激振动特性。在圆管上附加非线性能量阱(NES)作为被动减振装置对圆管进行减振,并采用粒子群优化算法对NES的非线性刚度和阻尼参数进行了优化。结果表明,在约化速度为4.8时,得到的NES优化的非线性刚度和阻尼参数组合可以有效减小悬臂梁自由端风致涡激振动位移。本研究说明采用NES和粒子群优化算法可以有效减小圆管的风致涡激振动,为导管架安全建造提供一定的参考。     

Development of hybrid URANS-LES methods for flow simulation in the ship stern area

The paper presents the results of the application of a new hybrid URANS-LES method for the investigations of the ship wake behind the tanker KVLCC2. The switching between URANS and LES models is based on the ratio between the turbulence scale and the cell size of the mesh. Ship resistance, fields of the axial velocity and turbulent kinetic energy in the propeller plane are calculated and compared with measurements. Much attention is paid to the analysis of the unsteady velocities, their PDF distributions and spectra. Numerical analysis shows that the instantaneous velocities deviate substantially from their mean values which are usually used as the estimated velocities in modern engineering methodologies. The thrust variation in the unsteady wake is more than twice as large as that in the time averaged (frozen) wake. The results of the present study point out that the unsteadiness in the wake behind full ships can be very large and should be taken into account when propulsion and unsteady loadings are determined.     

华北积层混合云中冰晶形状、分布与增长过程的飞机探测研究

利用中国国家科技支撑计划重点项目环北京地区3架飞机联合云探测试验数据,分析了2009年4月18日和5月1日两次积层混合云中冰晶形状、分布与增长过程。结果表明：飞机在0—-16℃范围的云层内观测到的冰晶形状主要包括板状、针柱状、柱帽状、辐枝状和不规则状。云中低层的冰晶形状受云顶温度影响,云顶温度不同,冰晶形状不同,当云顶温度高于-8℃时,云中低层的冰晶以板状和针柱状为主;当云顶温度低于-13℃时,在云中低层可观测到辐枝状冰晶;当云顶温度低于-18℃时,在云中低层可观测到柱帽状冰晶。同时冰晶形态还受其所处云中位置的影响,在积层混合云中的嵌入对流区含有更多的凇附状冰晶;在融化层以上,冰晶的增长过程主要包括凝华、凇附和聚合过程,在垂直方向上,随着高度降低云中过冷水增多,冰晶的凇附增长也相应增强。积层混合云中的对流区和层云区粒子谱下落拓宽速率有明显差别,在4.8—4.2 km（-11.6—-8℃）高度层,对流区粒子谱拓宽速率为3 mm/km,而层云区为3.67 mm/km,层云中粒子拓宽增长的速率略高于对流区;而在4.2—3.6 km（-8—-5℃）高度层,对流区的粒子谱拓宽速率为6.67 mm/km,层云区为2.33 mm/km,对流区的粒子拓宽增长速率是层云区的近3倍,主要原因是对流区低层的过冷水含量较高。     

河北秋季层状云物理结构及适播性分析

利用2006-2010年河北省人工影响天气办公室对29块云体9架次飞机探测(或作业)资料,统计分析了河北地区秋季层状云气溶胶粒子、云凝结核CCN、小云粒子、大云粒子、降水粒子浓度和云粒子有效直径等物理特征。结果表明,河北地区适宜增雨作业的云系为中、低或高、中、低搭配的层状云,过冷层催化有利于云体发展,促使气流流入形成正反馈。适宜催化的作业层指标有:云层高度为4582 m,云内平均含水量≥0.1 g·m-3,所对应温度为-8.0℃,小云粒子浓度为236.5 cm-3。     

Modeling of tropical cyclone winds and waves for emergency management

This paper compares three commonly used parametric models of tropical cyclone winds and evaluates their application in the wave model WAM. The parametric models provide surface wind fields based on best tracks of tropical cyclones and WAM simulates wave growth based on the wind energy input. The model package is applied to hindcast the wind and wave conditions of Hurricane Iniki, which directly hit the Hawaiian Island of Kauai in 1992. The parametric wind fields are evaluated against buoy and aircraft measurements made during the storm. A sensitivity analysis determines the spatial and spectral resolution needed to model the wave field of Hurricane Iniki. Comparisons of the modeled waves with buoy measurements indicate good agreement within the core of the storm and demonstrate the capability of the model package as a forecasting tool for emergency management.