Multiple Tuned Mass Damper Based Vibration Mitigation of Offshore Wind Turbine Considering Soil–Structure Interaction

The dynamics of jacket supported offshore wind turbine （OWT） in earthquake environment is one of the progressing focuses in the renewable energy field. Soil-structure interaction （SSI） is a fundamental principle to analyze stability and safety of the structure. This study focuses on the performance of the multiple tuned mass damper （MTMD） in minimizing the dynamic responses of the structures objected to seismic loads combined with static wind and wave loads. Response surface methodology （RSM） has been applied to design the MTMD parameters. The analyses have been performed under two different boundary conditions： fixed base （without SSI） and flexible base （with SSI）. Two vibration modes of the structure have been suppressed by multi-mode vibration control principle in both cases. The effectiveness of the MTMD in reducing the dynamic response of the structure is presented. The dynamic SSI plays an important role in the seismic behavior of the jacket supported OWT, especially resting on the soft soil deposit. Finally, it shows that excluding the SSI effect could be the reason of overestimating the MTMD performance.

Dynamic Analysis of Tension Leg Platform for Offshore Wind Turbine Support as Fluid-Structure Interaction

Tension leg platform （TLP） for offshore wind turbine support is a new type structure in wind energy utilization. The strong-interaction method is used in analyzing the coupled model, and the dynamic characteristics of the TLP for offshore wind turbine support are recognized. As shown by the calculated results： for the lower modes, the shapes are water＇s vibration, and the vibration of water induces the structure＇s swing; the mode shapes of the structure are complex, and can largely change among different members; the mode shapes of the platform are related to the tower＇s. The frequencies of the structure do not change much after adjusting the length of the tension cables and the depth of the platform; the TLP has good adaptability for the water depths and the environment loads. The change of the size and parameters of TLP can improve the dynamic characteristics, which can reduce the vibration of the TLP caused by the loads. Through the vibration analysis, the natural vibration frequencies of TLP can be distinguished from the frequencies of condition loads, and thus the resonance vibration can be avoided, therefore the offshore wind turbine can work normally in the complex conditions.

Dynamic Analysis of A 5-MW Tripod Offshore Wind Turbine by Considering Fluid–Structure Interaction

Fixed offshore wind turbines usually have large underwater supporting structures. The fluid influences the dynamic characteristics of the structure system. The dynamic model of a 5-MW tripod offshore wind turbine considering the pile-soil system and fluid structure interaction （FSI） is established, and the structural modes in air and in water are obtained by use of ANSYS. By comparing low-order natural frequencies and mode shapes, the influence of sea water on the free vibration characteristics of offshore wind turbine is analyzed. On basis of the above work, seismic responses under excitation by E1-Centro waves are calculated by the time-history analysis method. The results reveal that the dynamic responses such as the lateral displacement of the foundation and the section bending moment of the tubular piles increase substantially under the influence of the added-mass and hydrodynamic pressure of sea water. The method and conclusions presented in this paper can provide a theoretical reference for structure design and analysis of offshore wind turbines fixed in deep seawater.

Three-dimensional Analysis of Prestressed Concrete Offshore Wind Turbine Structure Under Environmental and 5-MW Turbine Loads

A concrete gravity base structure may not be suitable for offshore weak soil because of its heavy weight. Therefore, a conceptual model for a concrete offshore wind turbine structure suitable for weak soils is proposed. The proposed model is composed of a prestressed concrete(PSC) supported by a pile foundation. For a three-dimensional analysis of the large concrete structure, wave pressures based on the diffraction wave theory are developed using a three-dimensional solid finite element method. Static and dynamic analyses were performed to achieve the conceptual model of a PSC structure subjected to ocean environmental loads and a 5-MW turbine load on southwest coast in Korea. From the analysis, the maximum displacement and stresses of the proposed model did not exceed the allowable values from design standard, and the first mode of natural frequency of the structure was in a safe range to avoid resonance. The proposed model has enough structural stability to withstand external loads, and it is expected to be used in locations suitable for concrete gravity structures.

Multi-criteria assessment of offshore wind turbine support structures based on dynamic property optimization

Increasing size of wind turbine and deep water deployment have raised the issue of appropriate selection of the most suitable support structure to make offshore wind energy cost competitive.The paper presents an optimization methodology for decision making process of bottom mounted supports of offshore wind turbines （OWTs） through reasonable engineering attributes derivation.Mathematic models of support structures are reduced by the generalized single-degree-of-freedom theory with relatively fewer structural parameters.Soft-stiff design optimization based on dynamic properties of OWTs is performed for monopile and lattice supports with different wind turbines,water depth and hub height.Attributes of support structures,wind turbines and environment conditions are applied in the multi-criteria decision making method——TOPSIS for benchmarking of those options.The results illustrate the effectiveness of the proposed optimazation methodology combined with economical and environmental attributes together.

A Practical Decision Making on Design of Fixed Offshore Wind Turbine Support Structure Considering Socio-economic Impact

Wind energy is considered one of the most promising alternative energy sources against the conventional fossil fuels.However,the deployment of these structures in deep-water for better power production is considered as a complex task.This also has raised the issue regarding selection of appropriate support structures for various sea conditions by considering environmental impact and carbon footprint.This paper considers a jacket like support structure as a case study for an intermediate water depth(50m).The jacket is considered to be located in North of Dutch Sea,and 100-extreme wave is applied as load condition.Here,the presented methodology provides an insight towards environmental/social impact made by the optimized designs in comparison with reference design.

Preliminary Design of a Submerged Support Structure for Floating Wind Turbines

Cost-effective floating wind turbines with efficient installations are highly desired in deep waters(>50 m).This paper presents a submerged floating offshore wind turbines(SFOWT)concept for intermediate water depths(50-200 m).The performance of SFOWTs can be improved through a judicious choice of configuration,pretension,and mooring line layout.Four SFOWTs with different configurations and a similar mass,named Cyl-4,Cub-4,Cyl-3,and Hex-3,were designed and analyzed.The responses of the four SFOWTs were predicted under operational condition and extreme condition.The results show that the four SFOWTs exhibited good performance under both conditions.The effect of platform configurations on power output was negligible under the operational condition.Under the extreme condition,among the four SFOWTs,the mean bending moments at the tower base were very close,while the maximum values differed by up to 21.5%,due to the configurations.The effect of wind-wave misalignment under the extreme condition was further analyzed.In general,the motion performances of the four-pontoon SFOWTs,Cyl-4 and Cub-4,were superior to those of the three-pontoon SFOWTs,Cyl-3 and Hex-3.Optimization studies of the mooring system were carried out on Cub-4 with different mooring line pretensions and four mooring layouts.The optimized Cub-4 could reduce the maximum motion responses in the surge,heave,and yaw by 97.7%,91.5%,and 98.7%,respectively.

Prediction of Short-Term Distributions of Load Extremes of Offshore Wind Turbines

This paper proposes a new methodology to select an optimal threshold level to be used in the peak over threshold （POT） method for the prediction of short-term distributions of load extremes of offshore wind turbines. Such an optimal threshold level is found based on the estimation of the variance-to-mean ratio for the occurrence of peak values, which characterizes the Poisson assumption. A generalized Pareto distribution is then fitted to the extracted peaks over the optimal threshold level and the distribution parameters are estimated by the method of the maximum spacing estimation. This methodology is applied to estimate the short-term distributions of load extremes of the blade bending moment and the tower base bending moment at the mudline of a monopile-supported 5MW offshore wind turbine as an example. The accuracy of the POT method using the optimal threshold level is shown to be better, in terms of the distribution fitting, than that of the POT methods using empirical threshold levels. The comparisons among the short-term extreme response values predicted by using the POT method with the optimal threshold levels and with the empirical threshold levels and by using direct simulation results further substantiate the validity of the proposed new methodology.

CFD-Based Load Calculation Method for Monopile Support Configuration of Offshore Wind Turbine

An unsteady load calculation method for the support configuration of a monopile-supported offshore wind turbine is developed based on the Fluent software platform.Firstly,the water wave is generated by imposing the inlet boundary conditions according to the exact potential flow solution.Then the wave evolution is simulated by solving the unsteady incompressible Navier-Stokes(N-S)equations coupled with the volume of fluid method.For the small amplitude wave with reasonable wave parameters,the numerical wave result agrees well with that of the given wave model.Finally,a monopile support configuration is introduced and a CFD-based load calculation method is established to accurately calculate the unsteady load under the combined action of wave and wind.The computed unsteady wave load on a small-size monopile support located in the small amplitude wave flow coincides with that of the Morison formula.The load calculations are also performed on a large-size monopile support and a monopile-supported offshore wind turbine under the combined action of small amplitude wave and wind.

Investigation of Maxima Assumptions in Modelling Tropical Cyclone- Induced Hazards in the South China Sea

The present study aims to examine the suitability of two commonly used assumptions that simplify modelling metoceanconditions for designing offshore wind turbines in the South China Sea (SCS). The first assumption assumes thatjoint N-year extreme wind and wave events can be independently estimated and subsequently combined. The secondone assumes peak wind and waves can be modelled as occurring simultaneously during a tropical cyclone (TC) event.To better understand the potential TC activity, a set of 10000 years synthetic TC events are generated. The wind fieldmodel and the Mike 21 spectral wave model are employed to model the TC-induced hazards. Subsequently, theeffect of the assumptions is evaluated by analyzing the peak structural response of both monopile and semisubmersibleoffshore wind turbines during TC events. The results demonstrate that the examined assumptions are generally accurate.By assessing the implications of these assumptions, valuable insights are obtained, which can inform andimprove the modelling of TC-induced hazards in the SCS region.

基于局域共振型声子晶体塔筒结构海上风机减振特性研究

针对海上风机的振动控制问题,提出一种局域共振型声子晶体塔筒结构,基于周期结构的Bloch定理,采用有限元法计算该结构的能带结构、特征模态所对应的位移场以及相应有限周期声子晶体塔筒结构的振动传输曲线,对其展现出的带隙特性进行分析。基于局域共振带隙的形成,研究声子晶体塔筒结构的振动控制问题,可将其应用于不同海洋环境中海上风机特定频率的减振。得出声子晶体塔筒结构在xy平面内与z方向上受激励时的振动传输曲线,选取两者在特定频率下的结构位移图分别进行分析,计算出非理想化声子晶体塔筒结构在xy平面内与z方向上受激励时的振动传输曲线并加以对比。研究各参数对声子晶体塔筒结构带隙衰减频段的影响规律,通过合理调整设计参数,可以实现结构特定范围内的低频隔振,证明其在复杂海洋环境中海上风机减振方面具有很好的应用前景。

考虑桩-土相互作用的超大型单桩式海上风机结构地震响应

为了解决桩-土相互作用对超大型单桩式海上风机结构地震响应影响的问题,基于IEA 15 MW的固定式单桩海上风机原型,使用Abaqus建立考虑桩-土相互作用与泥面固定2种风机结构模型,桩-土相互作用通过一组非线性弹簧模拟。考虑风-波浪与地震联合作用,分析桩-土相互作用对超大型固定式单桩海上风机结构动力响应的影响。结果表明:针对超大型海上风机,桩-土相互作用效应使风机支撑结构的特征频率降低3%~6%;考虑桩-土相互作用的大兆瓦风机动力响应远大于泥面固定风机模型的动力响应;海上风机尺寸越大,桩-土相互作用引起的海上风机结构动力响应偏差越显著。

浮式风机平台设计研究综述

大力发展风力发电技术是国家推动能源低碳转型、实现“双碳”目标的核心路径。随着陆上风电和近海风电资源开发逐渐饱和,风电开发从近岸走向深远海成为风电行业发展必然的趋势,而浮式风机平台的研发与优化是推进海上风电向深远海区域发展的关键。基于对国内外浮式风机平台发展现状的研究,进一步分析浮式风机平台设计中气动载荷、水动力载荷、系泊系统、耦合分析方法以及常用数值模拟工具的研究现状,重点梳理以提升结构稳性和降低成本为驱动的浮式风机平台的关键技术思路及构型特点,总结浮式风机平台优化的研究现状,以及其设计中存在的问题与挑战,以期为相关领域研究人员提供技术参考。

海上风机支撑结构承载性能试验研究

基于波流水槽开展的模型试验,设计了风机支撑结构受到水流、循环荷载、无水和静水环境条件等工况,获得了单向流作用、循环荷载作用以及单向流与循环荷载共同作用等不同荷载组合下风机支撑结构的承载性能.结果表明:循环荷载作用下风机支撑结构在无水条件下的产生的累积位移是静水条件下的46.12%,单向流和循环荷载共同作用时,支撑结构累积位移较单独荷载作用效果叠加时增加了60.84%.在有水的环境和多种荷载共同作用下,风机支撑结构承载性能有明显降低,因此,在海上风机结构设计和安全评估时应考虑多种荷载共同作用的影响.

海上漂浮式风电机组塔筒优化方法研究

为适应复杂多变的海上环境,高效利用风资源、减少用钢成本,开展漂浮式风电机组塔筒的结构优化设计。以船载风电机组为研究对象,引入漂浮式基础的动态响应,作为影响塔筒弯曲变形的重要约束条件。在保证风电机组稳定功率输出的前提下,以质量最轻为优化目标,以塔筒构造要求和规范为基本约束条件,建立漂浮式基础风电机组塔筒的数值优化模型,并利用遗传算法完成了模型优化。结果显示,在保证风电机组稳定性和正常功率输出要求下,塔筒的质量降低了35%,刚度提高了25%。

蜂窝结构海上风力机防护装置性能研究

为便于风力机运输、安装及维护,海上风电场大多处于繁忙的航道,导致海上风力机受船舶碰撞概率大幅上升。为增强海上风力机抗撞能力,减轻碰撞区域受损程度,提高其抗风险性能,提出一种具有蜂窝结构特征的新型防护装置。采用显示动力分析软件LS-DYNA模拟5 000 t级船舶与4 MW海上风力机单立柱三桩基础碰撞过程,研究蜂窝结构新型防护装置与传统实心结构防护装置抗撞性能的差别。结果表明:具有蜂窝结构特征的新型防护装置可有效延长接触时间,降低接触力;较传统实心防护装置,新型装置内能转化能力提升15%以上,蜂窝结构起到提升内能转化能力的作用。蜂窝结构防护装置具备良好的吸能缓冲效果,可有效削减传递至风力机结构的内能及动能,降低基础损伤,起到提升单立柱三桩基础海上风力机安全性的功能。

不同风速对单桩式海上风电机组塔筒动态特性的影响

基于ANSYS有限元软件对NREL 5 MW单桩式海上风电机组塔筒系统进行三维实体建模,在考虑土构耦合与叶轮旋转作用下,模拟分析不同风速对塔筒结构动态响应特性的影响。选取机组切入风速3 m/s与切出风速25 m/s区间内6种平均风速及与之对应的叶轮转速作为模拟工况,分析结果表明:随着风速和叶轮转速的增加,塔筒结构的模态频率逐渐增大,前两阶模态频率变化最为明显;塔筒位移量峰值增大,但增幅减小,位移量呈非线性增长趋势;塔筒等效应力值随之增大,但变化趋势与位移量不同,大致为线性增长;塔筒疲劳寿命急剧下降,但都远超实际工作时长,疲劳损伤与安全系数危险值主要分布在塔筒底部与单桩处,与最大等效应力分布位置吻合。

软弱地基中海上风电大直径缩径单桩基础结构设计研究

基于真实设计参数和环境荷载,通过PLAXIS Monopile Designer和SACS软件实现某风场机位的缩径单桩优化设计,并进行结构极限强度、结构变形、自振频率和疲劳分析计算。相比于相同上部尺寸的常规单桩基础,缩径单桩具有较大的泥面转角和水平位移,较低的竖向位移和自振频率,计算结果验证了缩径单桩基础方案的可行性,并可实现节省10.9%的用钢量。

粉质黏土中缩径单桩静压沉桩阻力数值模拟研究

室内缩尺试验较难真实还原其沉桩特性,原型试验又较为耗时,基于耦合的欧拉-拉格朗日(CEL)数值分析方法可实现原比尺模型静压沉放过程模拟,且可直观获得桩-土相互作用过程。通过室内试验进行沉桩阻力的有限元方法验证,并将有限元法用于工程体型沉桩过程模拟与阻力计算;数值模拟结果表明,缩径段的体型设计使沉桩阻力增加,EVF云图可看出进入桩内土体的体积减少,使桩内出现泥面降低的情况;最后,研究不同缩径段尺寸对于沉桩阻力的影响。

多工况下弹性支撑海上风电机组传动链支撑参数优化

弹性支撑海上风电机组传动链在随机风浪耦合作用下,会受到因支撑平台大范围运动而产生的随机气动载荷与惯性载荷的综合影响,振动特性极为复杂。为了降低随机风浪对海上风电机组传动链振动响应的影响,文章以某6.2 MW海上风电机组传动链为研究对象,建立了弹性支撑海上风电机组传动链刚-柔耦合动力学模型,提出了基于代理模型的工况参数、支撑参数与海上风电机组传动链关键构件振动响应之间映射关系的重构方法,构建了多工况下海上风电机组传动链弹性支撑参数优化模型,对比了不同工况下海上风电机组传动链减振效果。研究结果表明:机舱运动与输入转矩增大会显著增加主轴轴承与发电机定子振动响应;优化弹性支撑参数可以有效降低机舱运动与输入转矩对主轴轴承与发电机定子振动响应的影响,其改善效果会随着平均风速的增加而愈加明显。此研究对提高海上风电机组传动链在随机风浪耦合作用下长期稳定运行的能力具有重要理论参考意义。