Study on optimal structure used for offshore wind turbine facilities

为了将西北欧周边出现的海上风电场扩展到日本，我们必须应对我国特有的自然环境条件，如强台风、地震、柔软的海底和陡峭的水深。风力涡轮机的下部结构应具有适当的刚度和强度，其配置可以抵御风荷载。由于波动的风、波浪和各种机械振动作用于其上，因此需要共振规避、减少这些激励和疲劳损伤。因此，我们提出了一种钢管桁架替代传统的钢圆柱塔用于固定底部或浮动设施。为了验证该方法的适用性，我们在5MW风力发电机上进行了两个子结构的设计，并进行了风洞模型试验和数值研究，考虑了桩土相互作用。最后，我们得出如下结论：1)由小直径构件组成的桁架塔构成的子结构优于圆柱塔和单桩。虽然钢材料的重量大了约1.7倍，但抗弯刚度适当为1.5倍。这意味着从疲劳的角度来看，所提出的子结构具有优势。2)由特征值分析得到的第一个自然周期为2.5s，可以比旋转叶片与塔相交的1.0 ~ 2.0s周期长，比旋转叶片与塔相交的3.0 ~ 6.0s周期短。这些与塔影效应有关的时期由于尾流带来不同的成员力。因此，可以进行避免设备自然周期共振的优化设计。3)实测桁架塔的面外加速度和振荡载荷均小于圆柱塔。桁架塔产生的电能略大。4)带套基础的桁架塔具有足够的延性，通过推覆分析，与屈服变形相比，其倒塌变形可达4 ~ 5倍。少

So as to expand offshore wind farms emerging around North-West Europe into Japan, we have to cope with natural environmental conditions such as severe typhoons, earthquakes, the soft seabed and steep bathymetry peculiar to our country. Substructures of a wind turbine should have due rigidity and strength with the configuration as to ward off wind loads. Since fluctuating winds, waves and various mechanical vibrations are acting on them, resonance evasion, reduction of those excitation and fatigue damage are required. So we have proposed a steel tube truss alternative to a conventional steel cylindrical tower for fixed bottom or floating facilities. To confirm the applicability, we carried out design of both substructures onto a 5MW wind generator, a wind tunnel model experiment and numerical study taken the pile and soil interaction into consideration. Finally, we concluded as follows ;1)The substructures made of a truss tower composed of small number of members having small diameter a … More nd jacket is better than a cylindrical tower and monopile. Although the weight of steel materials is larger about 1.7 times, the flexural rigidity is appropriately 1.5 times. This implies that proposed substructure takes advantage from the fatigue perspective.2)The first natural period of 2.5s obtained by the eigenvalue analyses can be longer than the period of 1.0-2.0s that a rotating blade intersects the tower, and shorter than rotating period of 3.0-6.0s. These periods pertaining to tower shadow effects due to wake bring varying member forces. Thereby, the optimal design avoiding the resonance from the natural period of the facility may be done.3)The measured out-of-plane accelerations and oscillation loads in the truss tower were smaller than those of the cylinder tower. The electricity generated by the truss tower is slightly larger.4)The truss tower with jacket foundation has enough ductility, such that it can deform four or five times during collapse compared with the deformation at yielding by a pushover analysis. Less