Response statistics of monopile OWT to fully nonstationary seismic motion. (15th June 2022)

• Record Type: Journal Article
• Authors: Cao, Qianying; Hu, Sau-Lon James; Li, Huajun
• Is Part Of: Ocean engineering. Volume 254(2022)
• Publication Date: 2022-06-15
• Subjects: Monopile offshore wind turbines -- Response statistics -- Nonstationary seismic motion -- Pole -- Residue; Ocean engineering -- Periodicals; Ocean engineering; Periodicals; 620.4162
• DOI: 10.1016/j.oceaneng.2022.111389
• Languages: English
• ISSNs: 0029-8018

Abstract

Abstract: At present, the vast majority of offshore wind turbines (OWTs) have been the monopile type. Although design standards recommend seismic assessments be included in their designs, there has been no guidance on how to conduct an analysis due in part to a lack of efficient methods, particularly related to the nonstationary nature of seismic motions. This article contributes to the development of an efficient pole-residue method operated in the Laplace domain to analytically compute response statistics, including the response evolutionary power spectrum (EPS) and time-varying mean square values. While the nonstationary seismic motions are treated as a uniformly modulated random process, both exponential and gamma models are considered for the modulating function. Furthermore, a fully nonstationary seismic motion with multiple independent modulated subprocesses is also studied. In the numerical studies, a 5 MW monopile OWT subjected to nonstationary stochastic seismic motion is studied; Monte Carlo simulations are employed to verify the correctness of the analytical solutions. Numerical studies confirm that the response EPS at the tower top is contributed mainly by the OWT's first bending mode. While applying the linear superposition principle, the proposed method can also be extended to the situation that an OWT is subjected to fully nonstationary earthquake and stationary wave loadings simultaneously. Highlights: Develop an efficient analytical method for OWTs to nonstationary seismic motion. Derive the response evolutionary power spectrum (EPS) in closed-form. Treat the seismic motion as a fully nonstationary random process. Verify the derived analytical solutions by Monte Carlo simulations.