Assessment of the Dynamic Responses and Allowable Sea States for a Novel Offshore Wind Turbine Tower and Rotor Nacelle Assembly Installation Concept Based on the Inverted Pendulum Principle

Abstract

This paper presents a numerical study for preliminary assessment of the dynamic responses and allowable sea states for the installation of an offshore wind turbine (OWT) tower and rotor nacelle assembly (RNA) based on a novel method. This method is based on the inverted pendulum principle and consists of various sequential activities for which the allowable limits of sea states need to be established. For critical installation activities, numerical analyses methodologies have been applied to model the actual operations. For the parameters limiting the execution of the operations, response statistics are provided. It is found that at least 45 seeds are required to achieve convergence of snap force statistics during the OWT lift-off. The response statistics are used to calculate a characteristic value corresponding to a target probability of non-exceedance. For the lift-off and mating operations, these characteristic values are compared with the allowable limits of the response parameters to establish the allowable limits of sea states. In addition, sensitivity study on key modeling parameters are conducted. Spring coefficients of contact elements and hinged connections, winch speed, and hoist wire stiffness are shown to be important modeling parameters. The results provided in this paper are important for future finite element modeling (FEM) and cost-effective design of the structural components.