【作者】 王莺歌；

【导师】 李正农；

【作者基本信息】 湖南大学 ， 结构工程， 2011， 博士

【摘要】 定日镜是一种在钢结构支撑下,可以实时进行方位角和仰角的调整,跟踪太阳的反射镜系统。定日镜群是塔式太阳热能发电站的主要设备,也是电站的主要投资部分,其造价约占整个发电站总造价的一半以上。从塔式太阳能电站建立开始,定日镜抗风问题就一直是设计中的难题,一般定日镜设计要满足在6级风作用下正常工作,在8级风作用下不受破坏的要求。在使用过程中必须保证入射到平面镜上的太阳光经反射后能始终准确地投向目标点,定日镜与目标点的位置较远,绕转动轴的微小偏移就能带来巨大的误差,影响到聚光效果。在强风作用下,定日镜还容易受到破坏,历史上已经多次发生定日镜受到风荷载破坏的实例,我国已建成的定日镜也曾多次发生过风致倾覆和结构破坏事故。太阳能发电系统往往都位于空旷平整的场地,大气流动对于镜身所产生的风力作用较大,所以对于定日镜表面风荷载及其风致响应的研究非常必要。太阳热能发电技术发展得比较成熟的国家,如美国、西班牙等都形成了符合其气候、地貌环境的抗风标准与设计方法,但对于太阳能技术起步较晚的国家来说,如何解决反射装置在一定风速下正常工作,以及在大风情况下保证设备安全还是个亟需解决的问题,目前相关的研究比较少。本文通过理论分析、风洞试验、数值模拟等技术,针对定日镜结构进行表面风压分布、脉动特性、统计特性、流场面貌、风致响应、等效风荷载等方面的精细化研究,同时提出了具有通用性的新插值方法。主要研究成果有:(1)根据定日镜群辐射状布置,不同位置单体仰角、风向角各不相同的特点,进行多工况风洞试验,得到了定日镜结构在0°~90°仰角、0°~180°风向角范围内,共130种工况下的风压分布状况;总结了其风压分布随风向角及仰角的变化规律;计算出各工况下的阻力系数、升力系数、及风力坐标下三个方向的力矩系数;找出最不利工况,指明各工况局部风压极值及其所处位置。(2)使用数值模拟技术,建立了典型工况下的单个定日镜CFD模型;编制相应的UDF程序,模拟出与风洞试验一致的风场入口条件;选取标准k ?ε湍流模型进行计算,模拟得到的定日镜表面风压分布与风洞结果一致。另外弥补了风洞试验中不易获取流场分布的缺陷,更深层次地解释了定日镜风压分布的成因,找出其影响因素和变化规律。通过数值模拟技术研究定日镜群流场的干扰效应。针对不同工况、不同距离、不同布置形式进行模拟,计算相关干扰因子,结合流场分布状况,深入分析各因素对定日镜表面风压的影响。(3)对定日镜表面风压的脉动特性进行了深入研究,通过对比分析测点风压功率谱来解释其脉动特性。利用偏度、峰度等指标评价了各工况风压的统计特性,给出了不同峰值因子下的正态保证率,并对其进行了拟合优度检验,对风压的高斯特性进行判别。针对定日镜的局部非高斯特性,使用目标概率法确定其表面风压的计算峰值因子。修正了脉动风压系数估算公式,利用CFD模拟得到的镜面平均风压系数及镜面参考点风速、湍流动能等参数估算了镜面脉动风压系数,与风洞试验得到的结果进行对比。(4)提出新的插值方法,该方法基于POD技术并借鉴地理统计学中“网格化”思想,对具有“准静态”特征的空间本征向量进行处理。引入Kriging插值方法,编制与Surfer软件接口的Matlab程序,利用Surfer软件强大的空间插值功能,对结构表面各阶本征向量进行空间插值。该方法具有较强的通用性,可广泛应用于风洞试验和现场实测中,并有进一步拓展的前景。(5)进行了定日镜结构风振响应的时域与频域分析。实现定日镜多工况下的参数化建模,利用定日镜结构频率、振型、振型参与系数、质量参与系数等动力特性对其风振响应进行预判。通过有限元计算模型,进行动力时程分析,计算动态响应,得到不同工况下定日镜的风振系数。结合POD技术与CQC法,根据随机荷载的大部分能量集中在少数模态中,只取少数几阶模态就能够代表真实过程这一特点,在响应计算中使用占用多数能量的前若干阶时间主坐标与本征向量的组合代替原有时程数据,提高计算效率。研究时域、频域法计算得到的风振响应结果,发现定日镜风振共振响应以整体运动的前几阶模态为主,且具有良好的分离性的特征,由此论证了惯性力——LRC法对该种结构的适用性。根据分析结果研究寻找更为实用的设计方法,制定出详细的定日镜抗风设计相关参数。更多还原

【Abstract】 Heliostat is a kind of reflector tracking the sun on support of steel structure by regulating its azimuth and elevation in real time. A heliostat group is the major part of solartower power station, also the power station’s principal investment part since its construction cost accounts for approximately 50% of the total. Starts from the tower system solar energy power plant establishment, problem of heliostat’s wind resistance has been a hard one in design from establishment of tower-typed solar power station. Generally the design of heliostat need to satisfy normal work under strong breeze, and undestroyed under fresh gale. When heliostat works, the sunlight reaching the lens must be guaranteed to always reflect to the target accurately. Since distance between heliostat and target point is comparatively far, a minute deflection on axis of rotation brings huge error, influencing effect of light collecting. Heliostat is also easy to be destroyed subjected to action of strong wind. Such cases are not few in history. And in China heliostat’s accidents due to wind destruction happen now and then. Usually solar power system locates at spacious & smooth ground where atmosphere flow affects greatly on the body for its great strength, so it’s necessary to study heliostat’s surface wind load and its wind effects. In countries whose industry of electricity generation by solar energy is mature, such as the US, Spain, etc., there have been proper wind resistant standard and design methods tuned with the specific climate and landform environment. But in countries that start later on solar energy technology, it’s still an urgent problem to assure the reflex attachment’s normal work under wind of certain velocity and the equipment’s safety. And the present related researches are comparatively few.This dissertation develops fine investigation on heliostat’s aspects of surface wind pressure distribution, fluctuating property, statistical property, flow field appearance, wind vibration response, equivalent wind load and so on through technologies of theoretical analysis, wind tunnel test, numerical simulation, etc. Simultaneously, a new versatile interpolation method is proposed. The main research products include:(1) A wind tunnel test on numerous operating conditions got carried on with heliostat group’s radiating arrangement and features of different elevation angles & wind directions on various positions accorded. The heliostat’s wind pressure distribution under 130 operating conditions in range of 0°~90°elevation angle and 0°~180°wind direction was obtained. The wind pressure distribution’s variation rules at different wind directions & elevation angles got summarized. The drag coefficients, the lift coefficients, and the three-dimensional moment coefficients in wind power coordinate under all operating conditions were computed with the least advantageous operating condition got discovered and the local wind pressure’s extreme value and position indicated.(2) The CFD model of single heliostat under typical operating situation was founded with technology of numerical simulation used. The corresponding UDF program was framed and used to simulate the wind field entry conditions coincident with the wind tunnel test. The standard k ?εonflow model was selected to compute, and the obtained simulated heliostat’s surface wind pressure distribution is consistent with the result of wind tunnel. Moreover, the flow field distribution uneasy to acquire in wind tunnel test was compensated to further explain origin of heliostat’s wind pressure distribution, and the influencing factors and the variation rules were discovered. The interference effect of heliostat group’s wind field was investigated through numerical simulation. Simulations on different operating situations, different distances and different arrangements were executed to compute correlated interference factors. The flow field distribution was referred to further analyze each factor’s influence on heliostat’s surface wind pressure.(3) The fluctuating wind pressure’s property of heliostat’s surface wind pressure was deep researched by contrastive analyzing the measuring points’wind pressure power spectrum. Indexes like skewness, kurtosis and so on were used to appraise wind pressure’s statistical property under each operating situation; the normal guarantee rates under different peak value factors were given; the goodness of fit was examined; the wind pressure’s Gaussian features were discriminated. For heliostat’s non-Gaussian features in local parts, the method of target probability was used to determine its surface wind pressure’s calculated peak value factors. The fluctuating wind pressure estimation formula got revised; the mean wind pressure coefficients on mirror surface obtained through CFD simulation, the wind speeds of reference points at mirror surface and the onflow kinetic parameters are used to estimate the fluctuating wind pressure coefficient on mirror surface, which was contrasted with the result obtained in wind tunnel test.(4) A new interpolation method basing on POD technology and referring‘grid’thought in geographical statistics was proposed to deal with spatial latent vectors which are‘quasistatic’. The Kriging interpolation method was introduces to frame Matlab program interfacing with Surfer software whose powerful space interpolation capacity got played to carries on the spatial interpolation to the structure’s surface latent vectors of each phases. This method is strongly universal, could be widely applied in wind tunnel tests & field surveying, and is prospective to be further expanded. (5) The time domain analysis and the frequency domain analysis on heliostat’s wind vibration response were made. In order to realize heliostat’s parameterized modeling under varied operating situations, the dynamic properties including the heliostat structure frequency, the mode of vibration, the mode’s participating coefficient of vibration, mass participating coefficients and so on were used to predict its wind vibration response. The finite element computation model was established to make kinetic time interval analysis, compute dynamic response, and obtain its wind vibration coefficients under different operating situations. In response computation, with the POD method and the CQC method combined, according to the feature that random load’s major energy concentrates in several few modalities while only several modalities could represent the real process, combination of the first certain steps of time main coordinates accounting for most energies and the latent vectors were used to replace the original time interval data to enhance calculating efficiency. Study on the result of wind vibration response obtained through methods of time domain and frequency domain discovers that the wind vibration’s resonating response weighs much on its modalities of the first several steps, and is good to separate. Thus the method of IWL - LRC’s applicability to this kind of structure got proved. The analysis results were based to search more practical design method and formulate heliostat’s detailed parameters of wind resistance design.更多还原