基于流固耦合的近海风电基础动力分析

发布时间：2018-04-16 09:18

本文选题：近海风电 + 流固耦合　；参考：《西北农林科技大学》2013年硕士论文

【摘要】：能源问题一直以来都是受人们所关注的焦点，风能作为一种可再生的清洁能源受到世界大多国家的亲睐，而近些年近海风能的开发利用又开创了风能利用的新阶段。未来海上风电工程有向更深的水域发展的趋势，随之风机基础的体积以及重量也不断加大。从而对于风机塔架基础结构也提出了更高的要求，故对于海上风电塔架支撑结构的研究很有必要。近海风电支撑结构体系位于沿海滩涂地带，其地基土由上覆淤泥层以及下面的砂层构成，而此类地基与上部整体结构于符合相应场地类别的地震动作用下的动力响应也是设计师所关注的问题。风力发电机为高耸结构，，且为保证风机的正常运行，对结构体系的水平变位有很高的要求，而风机结构在水平随机荷载作用下的振动特性与结构体系的水平变位有很大的关系，则研究水平随机荷载作用下的风机支撑结构体系的动力响应很有价值。本文以江苏响水海上风电场项目为依托，通过数值分析的方法，利用现行通用有限元软件ADINA对该项目海况条件下的单桩以及四脚桩建立三维模型，进行流固耦合条件下的动力特性分析,并于结构输入符合场地条件的地震动加速度时程，探讨水-结构动力相互作用即流固耦合条件下的动力响应（FSDI）。并结合结果分析的薄弱环节给出一些设计建议，初步取得以下一些成果。 1、建立实际资料单桩基础的海上风机整体结构无水层以及考虑水为势流体的两种工况之三维有限元模型，分别进行模态频率分析，得出水层存在对风电单桩基础以及四桩自振特性的影响规律为：水层的存在整体上将使结构体系的周期变长，自振频率减小，且水层存在对结构体系的高阶频率降低的幅度较大，低阶频率降低幅度不大。 2、论文将四桩与单桩基础自振频率做比较，得出桩型对风电单桩基础自振特性的影响规律为：无水情况，单桩与四桩之前两阶自振频率接近，三阶频率以后，单桩之各阶频率要高于四桩之频率；有水情况，四桩之前两阶频率要高于单桩，三阶频率以后，四桩各阶自振频率要要低于单桩。四桩基础的自振特性对水层存在的敏感性要低于单桩基础结构体系。 3、论文对近海滩涂地带无水风电单桩支撑体系进行地震响应分析，在多遇地震动输入作用下，得出结论为：结构淤泥层以上部分桩体以及塔筒的水平位移较大，且从下到上呈现递增的规律，水平位移极值发生在风机塔筒顶部机舱部位。建议设计时加强上部结构的整体刚度，以减小其在随机水平荷载作用下的水平变位。竖向沉降主要关注上覆淤泥层，得出沉降规律为：上覆淤泥层的竖向沉降主要集中在桩周淤泥部分。建议设计时对桩周部分一定范围内的淤泥层有一定的防止振动液化的处理措施。有效应力极值发生在风机塔筒上部外表面，设计时要特别关注塔筒上部材料强度问题。 4、论文对近海浅水风机支撑结构体系，基于流固耦合条件的多遇地震动输入下的地震响应分析认为：考虑水-土-结构动力相互作用（FSDI）是必要的，有水层风电支撑结构桩身以及风机塔筒竖向位移较小，满足使用要求。风机结构体系自淤泥层以上部位水平x向的位移自下到上逐渐增大，位移形态为弯曲形。自底向上，桩体插入地基最下面砂层部分位移较小，有反向的即沿x轴正向的鼓胀水平位移，插入淤泥层的桩体部分之水平位移为逐渐增加的。上覆淤泥层的沉降量主要发生在桩周淤泥部分。设计此类结构时，在桩周局部采取防止液化的地基处理措施是必要的。水层的波动较大，且在振动过程中，水层的竖向位移自外向内逐渐传递，地震动引起的波浪幅值从外围边界逐渐传递到内层桩周部分。而且位移到后期已经达到3.8m，此种地震动引起的水流波动效应对桩基结构的作用不可忽视。有效应力极值为306MPa，小于钢材之屈服强度345MPa，结构体系所用之钢材均未发生屈服。 5、与无水近海风电单桩基础之淤泥层与桩体的极值加速度时程做比较分析，得出考虑基于流固耦合的水层的存在对对上述两项加速度极值响应的影响规律，一般规律如下：水层的存在使得淤泥层的加速度峰值大幅减小，加速度峰值出现的时间提前，加速度幅值的卓越值分布时间大幅提前。水层的存在使得桩体部分极值加速度峰值的幅值减小、单桩桩身的加速度反应幅值的峰值出现的时间相对无水模型大幅提前、单桩体系桩体的加速度响应幅值的卓越值时段提前。
[Abstract]:The energy problem has always been the focus of the people ' s attention , and the wind energy as a renewable clean energy is favored by most countries in the world . In recent years , the development and utilization of offshore wind energy has opened up a new stage for the utilization of wind energy .

In this paper , based on the wind farm project in Jiangsu Province , a three - dimensional model of single pile and four - pin pile under the condition of current - solid coupling is established by using the current general finite element software ADINA , and the dynamic response ( FSDI ) of water - structure dynamic interaction , i.e . , the fluid - solid coupling condition , is discussed .

1 . A three - dimensional finite element model of the whole structure of offshore wind turbine with single pile foundation and two working conditions taking account of water as potential fluid is established , and the modal frequency analysis is carried out to obtain the influence of the existence of the water layer on the pile foundation and the self - vibration characteristics of four piles .

2 . The influence of pile type on the self - vibration characteristics of single pile foundation is obtained by comparing four piles with the frequency of single pile foundation . The frequency of single pile is higher than that of four piles before the third order frequency .
In the case of water , the frequency of the fourth pile before the fourth pile is higher than that of the single pile and the third order frequency . The self - vibration frequency of the four piles is lower than that of the single pile . The sensitivity of the self - vibration characteristic of the four pile foundation to the water layer is lower than that of the single pile foundation structure .

3 . In this paper , the seismic response analysis is carried out on the support system of the water - free wind power single pile in the beach area of the coastal area . The conclusion is that the horizontal displacement of the pile body and the tower barrel above the structural mud layer is large , and the horizontal displacement extreme value takes place at the top cabin part of the fan tower . The vertical settlement is mainly focused on the silt part of the pile . It is suggested that the settlement rule is that the vertical settlement of the overlying sludge layer is mainly concentrated in the soil part of the pile periphery . The effective stress extreme value occurs on the outer surface of the upper part of the tower cylinder of the fan . In the design , the strength of the upper material of the tower can be particularly concerned .

4 . In this paper , the structure system of shallow water fan in recent sea is analyzed . The seismic response analysis under the input of multi - condition ground motion based on the flow - solid coupling condition is that the vertical displacement of the pile body and the fan tower is small , and the displacement form is curved . In the course of vibration , the vertical displacement of the water layer is gradually increased from the outer boundary to the inner pile peripheral part .

5 . Compared with the time history of the extreme acceleration of the pile foundation of the non - water offshore wind power single pile foundation , the influence law of the existence of the water layer based on the flow - solid coupling is taken into consideration . The general rule is as follows : the existence of the water layer causes the acceleration peak of the sludge layer to be greatly reduced , the time of the acceleration peak appears , and the value distribution time of the acceleration amplitude value is greatly advanced . The existence of the water layer causes the amplitude of the peak value of the extreme acceleration of the pile body to be reduced , and the time of the peak of the acceleration response amplitude of the single pile body is greatly advanced relative to the anhydrous model , and the value of the acceleration response amplitude of the single pile system pile body is advanced .

【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU476.1

【参考文献】