Development and application of dynamic increasing wave analysis (DIWA) methodology for wave-induced response assessment of offshore wind turbines

This paper aims to introduce an extension of the dynamic increasing amplitude and period (DIAP) technique, termed as the dynamic increasing wave analysis (DIWA) method, which is set to be further developed for dynamic analysis of offshore wind turbines under combined environmental actions. The DIWA is an effective dynamic analysis methodology that simulates both the frequency and intensity dependencies of the dynamic wave loadings and load effects during the passage of a storm in a single progressive dynamic analysis. In the present work, the basic concept and generation procedure of this analysis approach based on two wave models, linear and nonlinear models taking into account the bottom effects, are described, exemplified, and examined using a fully coupled time-domain hydro-servo-elastic multi-rigid-flexible-body (HSE-MRFB) model of a jacket-supported reference OWT. The performance and applicability of this method are then comparatively demonstrated using short-term extreme statistical measures of dynamic loadings and structural responses predicted by the common practice individually performed dynamic time-history analysis (ITHA) approach and the DIWA method. The results show that the DIWA method is not only a reliable analysis approach for design loads and damage assessment of jacket-supported OWT foundations under evolutionary wave actions of a storm event but also leads to consistent trend yet relatively conservative characteristic values with an overestimation up to 14%–31% in 10–100-year mean return period (MRP), respectively, which can be overcome to some extent by further future developments. The findings also indicate that the nonlinearity of the waves increases the structural dynamic responses, up to ~13% in the vicinity of the mean sea level (MSL), while bottom effects reduce the conservatism in design, more than ~25%, stipulating the importance of nonlinear waves incorporating bottom effects over common practice for OWTs in transient waters.