Extended Environmental Contour Methods for Long-Term Extreme Response Analysis of Offshore Wind Turbines1

Nianxin Ren,Qinyuan Li,Xiaolu Chen,Ye Li,Zhiyu Jiang

doi:10.1115/1.4046772

Abstract

AbstractEnvironmental contour method is an efficient method for predicting the long-term extreme response of offshore structures. The traditional environmental contour is obtained using the joint distribution of mean wind speed, significant wave height, and spectral peak period. To improve the accuracy of traditional environmental contour method, a modified method was proposed considering the non-monotonic aerodynamic behavior of offshore wind turbines. Still, the modified method assumes constant wind turbulence intensity. In this paper, we extend the existing environmental contour methods by considering the wind turbulence intensity as a stochastic variable. The 50-year extreme responses of a monopile-based offshore wind turbine are compared using the extended environmental contour methods and the full long-term method. It is found that both the environmental contour method and the modified environmental contour method, with the wind turbulence intensity included as an individual variable, give more accurate predictions compared with those without. Using the full long-term method as a benchmark, this extended approach could reduce the nonconservatism of the environmental contour method and conservatism of the modified environmental contour method. This approach is effective under wind-dominated or combined wind-wave loading conditions, but may not be as important for wave-dominated conditions.

Highlights

ASME Paper Title: Extended Environmental Contour Methods for Long-Term Extreme Response Analysis of Offshore Wind Turbines
(2) The T I was integrated into Environmental contour method (ECM) and modified ECM (MECM) as an extra environmental variable based on standard deviation σ, whose conditional probability density function (CPDF) was given as a three-parameter Weibull distribution
It proves that including T I as an extra environmental variable enabled ECM to predict responses induced by wind loads with the same satisfactory accuracy as responses induced by wave loads

Summary

Introduction

ASME Paper Title: Extended Environmental Contour Methods for Long-Term Extreme Response Analysis of Offshore Wind Turbines. Predicting the long-term extreme response of offshore struc- This approach is effective under wind-dominated or comtures. To improve the accuracy of traditional environmental contour method, a modified method was proposed considering the non-monotonic 1 Introduction aerodynamic behavior of offshore wind turbines. We extend the existing environmental con- In the design of any type of offshore structure, including offtour methods by considering the wind turbulence intensity shore wind turbines (OWTs) and wave energy converters, esas a stochastic variable. The 50-year extreme responses of timating the long-term extreme structure response or load efa monopile-based offshore wind turbine are compared us- fects for a given return period (50 yrs, for example) is an ing the extended environmental contour methods and the important step. The nonconservatism of the environmental contour method and Environmental contour method (ECM) proposed by [5] is a simplified Inverse First Order Reliability Method (IFORM)

Methods

Results

Conclusion