Reliability-based design optimization of offshore wind turbine support structures using analytical sensitivities and factorized uncertainty modeling

Abstract

Abstract. The need for cost effective support structure designs for offshore wind turbines has led to continued interest in the development of design optimization methods. So far, almost no studies have considered the effect of uncertainty, and hence probabilistic constraints, on the support structure design optimization problem. In this work, we present a general methodology that implements recent developments in gradient-based design optimization, in particular the use of analytical gradients, within the context of reliability-based design optimization methods. By an assumed factorization of the uncertain response into a design-independent, probabilistic part and a design-dependent, but completely deterministic part, it is possible to computationally decouple the reliability analysis from the design optimization. Furthermore, this decoupling makes no further assumption about the functional nature of the stochastic response, meaning that high fidelity surrogate modeling through Gaussian process regression of the probabilistic part can be performed while using analytical gradient-based methods for the design optimization. We apply this methodology to several different cases based around a uniform cantilever beam and the OC3 Monopile and different loading and constraints scenarios. The results demonstrate the viability of the approach in terms of obtaining reliable, optimal support structure designs and furthermore show that in practice only a limited amount of additional computational effort is required compared to deterministic design optimization. While there are some limitations in the applied cases, and some further refinement might be necessary for applications to high fidelity design scenarios, the demonstrated capabilities of the proposed methodology show that efficient reliability-based optimization for offshore wind turbine support structures is feasible.

Impact of climate-change scenarios on offshore wind turbine structural performance

“…In other words, surrogate models mimic the behaviour of the simulation model as closely as possible while remaining computationally cheaper to evaluate. Various surrogate modelling approaches have been recently proposed in the literature for OWTs on monopile foundations, including Gaussian Process (GP) regression (8)(9)(10)(11) and for onshore wind turbines using Polynomial Chaos Expansion (12,13). These models significantly improve the computational efficiency of FLS assessment, and therefore also enable structural reliability assessment and the development of probabilistic risk models for OWTs to predict the potential financial impact of OWT failures.…”

Uncertainty modeling in reliability analysis of floating wind turbine support structures

“…To facilitate quick assessment of computationally-expensive-to-evaluate structural responses, surrogate models have gained popularity. Authors such as [7][8][9] to mention a few, have carried out reliability-based analysis of wind turbines by employing surrogate models. Morató et al [7] carried out reliability analysis of a monopile supported wind turbine using Kriging surrogate models.…”

“…[8], only environmental uncertainties and the associated metamodel uncertainty was covered. Surrogate modeling in form of Gaussian process regression was also employed by Stieng and Muskulus [9] in the reliability-based design optimization of an offshore wind turbine (OWT) support structure. Yang et al [10] demonstrated the use Kriging model for reliability-based optimization of a tripod sub-structure.…”

“…Modeling uncertainties were neglected in their study as well. A substantial amount of the literature on OWT reliability-based analysis have focused on fixed foundation concepts [7][8][9][10][11]. The structural dynamics of FWTs are different from fixed concepts as floating systems are more compliant to environmental loads implying greater variability in structural loading.…”

Dynamic Response Optimization of Steel Jackets for Offshore Wind Turbines With Fatigue and Time-Dependent Constraints

“…The optimization is rarely approached using a coupled model and the definition of the optimization problem along with the optimization algorithm used is very different from research to research. Significant contributions can be found in [4]- [8]. Most works share the use of analytical sensitivities, but the treatment of the dynamic problem differs.…”