Offshore wind turbine (OWT) structures are highly sensitive to complex ambient excitations, especially extreme winds. To mitigate the vibrations of OWT structures under windstorm or typhoon conditions, a new eddy current with tuned mass damper (EC-TMD) system that combines the advantages of the eddy current damper and the tuned mass damper is proposed to install at the top of them. In the present study, the electromagnetic theory is applied to estimate the damping feature of the eddy current within the EC-TMD system. Then, the effectiveness of the EC-TMD system for vibration mitigation is demonstrated by small-scale tests. Furthermore, the EC-TMD system is used to alleviate structural vibrations of the OWT supported by composite bucket foundations (CBF) under extreme winds at the Xiangshui Wind Farm of China. It is found that the damping of the EC-TMD system can be ideally treated as having linear viscous damping characteristics, which are influenced by the gaps between the permanent magnets and the conductive materials as well as the permanent magnet layouts. Meanwhile, the RMS values of displacements of the OWT structure can be mitigated by 16% to 28%, and the acceleration can also be reduced significantly. Therefore, the excellent vibration-reducing performance of the EC-TMD system is confirmed, which provides meaningful guidance for application in the practical engineering of OWTs.
The offshore wind turbine (OWT) supported by bucket foundations can be installed in the integrated transportation process by a dedicated vessel. During the integrated transportation process, the wind turbine is considered as a coupling system with the transport ship, which is easily influenced by waves and storms. In view of the motion response and influential factors, the heave and rock stiffness of the entire floating system was proposed, and then the analytical dynamic motion model of the coupling system was established based on the movement mechanism of the traditional floating body in the wave in this paper. Subsequently, the rationality of the proposed motion model was verified based on the field observation data, with the maximum deviation of the motion responses less than 14%. Further, the influence on the heave and pitch motion of the coupling system considering different factors (vessel speed, wave height, wind speed and wave angle) and the factor sensitivity were discussed by the novel analytical model. It is explained that the heave and pitch motion responses rise with the increase of the wave height and wave angle. Simultaneously, the responses decrease as the vessel speed increases considering sailing along the waves. On the contrary, the responses show an obvious increasing trend with the increase of vessel speed in the case of the top wave sailing. In addition, it is also illustrated that the wave height has the greatest influence on the heave and pitch motion responses, followed by the vessel speed. The wave angle has the lowest sensitivity when the heave and pitch motion are far away from its harmonic resonance region.
Zhang and co-workers have recently advanced the carbon [5 + 2] cycloaddition of vinylcyclopropane and alkyne (VCP-alkyne) to the hetero-[5 + 2] cycloaddition of vinyloxirane with alkyne (VOR-alkyne). Herein, we present a systematic computational study to gain insights into the detailed reaction mechanisms and origins of mechanistic differences of the two types of cycloadditions (all-carbon [5 + 2] cycloaddition vs. hetero-[5 + 2] cycloaddition). Instead of the general mechanism of rhodium-catalyzed VCP-alkyne cycloaddition that involves cyclopropane cleavage, alkyne insertion and reductive elimination, the rhodium-catalyzed VOR-alkyne cycloaddition occurs via oxidative alkyne-alkene cyclization, oxirane cleavage and reductive elimination. The cycloaddition of VOR-alkyne represents the first example of preferring the oxidative alkyne-alkene cyclization mechanism within rhodium-catalyzed [5 + 2] cycloadditions. The origins of the mechanistic difference are derived from the stabilizing effects due to the favorable ligand-substrate C-H/π dispersion interaction and the substrate-substrate C-HO hydrogen-bond interaction in the oxidative alkyne-alkene cyclization step of the hetero-[5 + 2] cycloaddition. The VOR-alkyne cycloaddition gives a bicyclo[5.3.0] product featuring a 2,5-dihydrooxepin moiety, which can further undergo a [3,3]-sigmatropic rearrangement giving the final bicyclo[3.1.0] product, because a carbonyl structure is more favorable than an enolate structure.
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