Investigation of Hydrodynamic Forces for Floating Offshore Wind Turbines on Spar Buoys and Tension Leg Platforms with the Mooring Systems in Waves

Abstract

This study aims to develop a modularized simulation system to estimate dynamic responses of floating Offshore Wind Turbines (OWTs) based on the concepts of spar buoy and Tension Leg Platform (TLP) corresponding with two typical mooring lines. The modular system consists of the hydrodynamic simulator based the Cummins time domain equation, the Boundary Element Method (BEM) solver based on the 3D source distribution method, and an open-source visualization software ParaView to analyze the interaction between floating OWTs and waves. In order to realize the effects of mooring loads on the floating OWTs, the stiffness and damping matrices are applied to the quasi-static mooring system. The Response Amplitude Operators (RAOs) are compared between our predicted results and other published data to verify the modularized simulation system and understand the influence of mooring load on the motion responses in regular or irregular waves. It is also demonstrated that the quasi-static mooring system is applicable to different types of mooring lines as well as determining real-time motion responses. Eventually, wave load components at the resonance frequencies of different motion modes for selected floating OWTs would be present in the time domain.

Frequency-Domain Identification of Radiation Forces for Floating Wind Turbines by Moment-Matching

“…Without any loss of generality, a single Degree of Freedom (DoF) support-platform is considered in this study. Recall that the motion of a 1-DoF support-platform can be expressed, in the timedomain, according to Newton's second law, obtaining the following linear hydrodynamic formulation [5]:…”

“…The linearised hydrostatic force is given by ℱ 𝒽𝒽 (𝑡𝑡) = −𝑠𝑠 ℎ 𝑥𝑥(𝑡𝑡), where 𝑠𝑠 ℎ denotes the hydrostatic stiffness. The mooring force is defined as ℱ 𝓂𝓂 (𝑡𝑡) = −𝑏𝑏 𝑚𝑚 𝑥𝑥(𝑡𝑡) − 𝑠𝑠 𝑚𝑚 𝑥𝑥(𝑡𝑡) [5], where 𝑏𝑏 𝑚𝑚 and 𝑠𝑠 𝑚𝑚 denote the damping and stiffness of the mooring system, respectively. From linear potential theory, ℱ 𝓇𝓇 (𝑡𝑡) can be modelled using Cummins' equation [6]…”

“…Nevertheless, to harness the available offshore wind potential, wind farms have to be located in deeper water. To this end, and to reduce the costs related with the structure, floating support-platforms will have to be deployed to hold the turbines, for which several platform configurations can be found in the literature [4,5].…”

Wind Turbines Offshore Foundations and Connections to Grid

“…The tension leg turbine platform is considered a method for accessing offshore wind resources in moderately deep water [107]. The structure as per Moon and Nordstrom (2010) consists of a minimum of three submerged arms.…”

Mooring System Design and Verification for a Floating Vertical Axis Wind Turbine

“…In addition to the mooring system requirements for FVAWT, a design and optimisation process must be taken into account for the specific requirements of the floating structure, in terms of station keeping and stability. For example, in a study performed by Lin et al [6], two spar types and two Tension Leg Platform (TLP) floaters in different water depths and with different mooring systems (catenary and taut-leg) are compared, in order to investigate the influence of the type of floating platform and the mooring lines layout on the hydrodynamics forces generated. As shown in [6], significant differences in terms of added mass, damping coefficients and the Response Amplitude Operators (RAOs) have been identified.…”