A multifield loads evaluation method for offshore wind turbines considering multivariate coherence effect

Abstract

The structural design and reliability assessment of offshore wind turbine systems for maximally exploring the renewable energy resources significantly rely on the actual marine environmental loads. The major challenges arising from the estimation of offshore wind turbine loads are the effects of rotating blades on wind velocity and the interactions among multiple components such as wind, waves and the structure. These factors make the environmental loads more complex and multivariately correlated. To address such issues, a multivariate coherence effect (MCE)-based evaluation method has been proposed to analyze the rotational effect on the wind velocity by discovering the perturbation mechanism of wind spectrum. Furthermore, analytical formulations in the form of the blade speed and wind spectrum have been developed to construct the MCE-based joint power spectrum matrix for the load redistribution via intercorrelations among multiple domains representing the ambient environment of offshore wind turbines. Results show that the MCE-based method has the ability to retain the characteristic multiple rotational frequencies of rotational blades and enables the simultaneous reconstructions of the stationary-state wind field, rotational wind field and wave height sequences for accurate load redistributions by decomposing the MCE-based joint power spectrum matrix. As compared with the traditional techniques, a more cost-effective approach can be further developed for the reliable estimation of the blade flapwise deflection using the proposed method. Summarily, the present work provides analytical formations for the accurate load configuration and dynamic analysis of offshore wind turbines subject to harsh marine environments.