Reliability-based design optimization of a spar-type floating offshore wind turbine support structure

Mareike Leimeister,Athanasios Kolios

doi:10.1016/j.ress.2021.107666

Abstract

The application of reliability-based design optimization (RBDO) methods to offshore wind turbine systems is highly relevant regarding economic efficiency and for considering prevailing uncertainties within the design process. Furthermore, RBDO is a very promising approach in optimizing systems when classification and standardization are not fully available. The level of difficulty of design optimization already increases when including the reliability aspect, but becomes even more challenging when dealing with the highly complex system of floating wind turbines (FWTs), which has not yet been applied. Thus, this paper presents for the first time an integrated framework for RBDO of FWTs, combining concepts of optimization with reliability-based design and advanced modeling, requiring reasonable computational effort and time expenditure. In preprocessing, environmental conditions, limit states, and uncertainties are specified, an appropriate reliability assessment approach is elaborated, and response surfaces for various system geometries in the optimization design space are generated ahead of the RBDO execution. These are finally used by means of an interpolation approach for the reliability calculation integrated in the iterative design optimization. On the example of a spar-buoy FWT system, the application of the presented methodology and the feasibility of coupling FWT design optimization with reliability assessment are shown.

Highlights

With the end of 2018, the first renewable energy directive from 2009 [1], which set the target of a minimum share of 20% of renewable energy in the European energy demand by 2020, was revised and replaced
To continue the highly time-consuming iterative reliability-based design optimization (RBDO) instead of restarting the optimization algorithm, the last fully simulated generation is used as start population of the run, utilizing the operator
It is interesting to see that, for the spar base height and ballast density, the individuals in the end tend to cluster around the original value of the reference floating wind turbine (FWT) system, while the spar base diameter approaches a much lower value compared to the original one

Summary

Introduction

With the end of 2018, the first renewable energy directive from 2009 [1], which set the target of a minimum share of 20% of renewable energy in the European energy demand by 2020, was revised and replaced. The majority of the world oceans exhibits great water depths [4,5,6] To exploit these sites for energy generation from offshore wind turbines, floating systems need to be utilized. More flexible design provisions would enable more innovation and allow for accelerating the market uptake of floating offshore wind To this end, structures could adhere to a goal-setting design approach, where reliability is the key driving criterion, and concepts of structural reliability can be adopted in order to systematically account for uncertainties and different design criteria. These uncertainties may significantly affect the dynamic system response, but are not accounted for in deterministic design optimization (DDO) methods which are commonly used for offshore structures [9,11,13]

Results

Discussion

Conclusion