Study on TMD Control on Stability Improvement of Barge-Supported Floating Offshore Wind Turbine Based on the Multi-Island Genetic Algorithm

A floating offshore wind turbine (FOWT) has a great potential in producing renewable energy as offshore wind resource is rich in deep sea area (water deeper than 60 m) where fixed foundations are cost-effective or deployable. However, compared with a fixed-bottom installation, FOWT has to suffer more extreme loads due to its extra degrees of freedom. Therefore, the stability of an FOWT is a key challenge in exploiting offshore deep-water wind. Focusing on the stability of barge-type FOWT, this paper is to investigate the effect of passive structural control by equipping a tuned mass damper (TMD) on the nacelle. The turbulent wind with sharp fluctuations is established both in velocity and inflow direction based on standard Kaimal turbulence spectrum as suggested in the standard IEC61400-2. The irregular wave is generated according to the Pierson-Moskowitz spectrum. The dynamic structural characteristics of FOWT are calculated based on the fully coupled aero-hydro-servo-elastic solver FAST. Evidence has shown that the proposed method of the nacelle-based TMD is effective in controlling stability of an FOWT, as the sway and roll motions of barge and the side-side displacement of tower top decreased significantly. With the increase of mass, the side-side displacement of tower-top and the amplitude of roll motion of barge reveal a trend of increasing first and then decreasing. The stiffness and damping have little effect. Furthermore, the multi-island genetic optimization algorithm (MIGA) is employed to find globally optimum structural parameters (mass, stiffness and damping) of the TMD. The optimum structure parameters of TMD are achieved when the mass is 21393 kg, damping is 13635 N/(m/s) and stiffness is 6828 N/m. By adopting the optimized TMD, stability of roll motion of barge and side-side displacement of tower-top increase up to 53% and 50% respectively when compared with the normal TMD. The simulation results verify the validity and reliability of the proposed TMD control and the optimization methods.     

考虑二阶波浪荷载效应的海上TLP浮式风机分析

基于多数专业风机数值模拟软件只可进行一阶波浪荷载计算这一缺点,文中将以AQWA为基础,利用其可进行二次开发的技术优势,通过实时调用风机气动荷载,实现海上TLP浮式风机分析。分析中,浮式风机平台一阶、二阶波浪荷载由AQWA计算,实时调用的气动荷载由动态链接库提供。该动态链接库主要包含了根据叶素动量定理自行编译的气动荷载计算程序。经过与FAST比较,得知该方法能满足分析需求。垂荡、纵摇力的二阶效应尤为明显。仅计算浮式风机平台波浪荷载时,可以不考虑风荷载的影响,但必须考虑平台运动的影响,波浪荷载主要受纵荡、纵摇运动影响,几乎不受垂荡运动的影响;当研究浮式风机平台运动时,必须考虑风荷载和二阶波浪荷载的影响,二阶波浪荷载使得平台响应在整个频率范围内都明显增大。张力筋腱张力受二阶波浪荷载的作用更明显。     

海上浮式风机气动性能数值模拟

采用计算流体动力学(CFD)方法,基于RANS方程和SST k-ω湍流模型,对OC3-Hywind Spar浮式平台支撑的NREL5 MW风机进行气动性能模拟。对固定式风机的数值模型做网格无关性验证,同时考虑垂直风切变的影响,并将数值结果与NREL设计数据进行对比以验证模型的有效性。在FLUENT软件中,设定嵌入式滑移网格和用户定义程序(UDF)来模拟风机叶轮随平台的周期运动,分别研究浮式平台的纵荡、纵摇和首摇运动对风机气动荷载的影响。数值结果表明平台的纵荡和纵摇运动对输出功率影响较大,且平台运动幅值越大周期越低,其气动荷载变化越剧烈。合理控制平台的运动幅值对提高浮式风机的发电性能和疲劳强度有很大作用。