Dynamic response and mooring optimization of spar-type substructure under combined action of wind, wave, and current

Abstract

Floating wind turbines (FWTs) have become the preferred structures to exploit offshore winds since a large part of the offshore wind resource is located in deep water zones. In the harsh marine environment, a spar-type substructure is the most promising substructure for FWTs with good structure stability and economic advantages. In this study, the surge, heave, and pitch motions of the spar-type substructure under combined action of wind, wave, and current are analyzed by using the AQWA module of ANSYS. Besides, the effects of different parameters, namely, the mooring line distribution form, fairlead position, and line number of mooring systems, on the spar-type substructure motion response are also investigated. Based on the calculation results, a new spar-type substructure with an optimized mooring system is put forward and analyzed. It can be found that both the dynamic response and the mooring tension of the new spar-type substructure are significantly improved relative to the non-optimized structure. The results of this paper could offer reference for further development of spar-type FWTs in real marine environments.

A fully integrated optimization framework for designing a complex geometry offshore wind turbine spar-type floating support structure

“…8) innovative floater designs may not be technically feasible from a structural integrity and manufacturability point of view, adopting the standard manufacturing solutions. But they would be feasible if considering different structural realization approaches, such as braces and truss structures or tendons, as already used in the oil and gas industry (Chen et al, 2017;Perry et al, 2007;Bangs et al, 2002) or utilized in innovative floater concepts (Fig. 6) (Richard, 2019;Stiesdal, 2019).…”

“…This, however, leaves open the possibility of subsequent fine tuning of the conceptual design solution obtained through optimization based on hydrodynamic and system-level analyses. By addressing the mooring system in the subsequent detailed design optimization or even in a successive but separate optimization algorithm, the dynamic response of the FOWT system, as well as the mooring line tension itself, can be significantly improved by considering an advanced and more complex optimization problem, in which -apart from various line diameters and lengths -different mooring line arrangements and distribution forms can be utilized, the optimum number of lines within the mooring system and best fairlead position can be elaborated, different mooring types can be used or even mixed within segmented lines, and also clump weights can be incorporated (Tafazzoli et al, 2020;Barbanti et al, 2019;Men et al, 2019;Chen et al, 2017).…”

“…These approaches can range from truss structures to tendons to realize large diameter changes as well as very thin "distance" elements without utilizing tapered sections or having issues with the structural integrity. Idea and impulse providers for such alternative structural realization approaches can be, for example, the oil and gas industry with truss spar platform design solutions (Chen et al, 2017;Perry et al, 2007;Bangs et al, 2002) or innovative floating platform concepts like the TetraSpar by Stiesdal Offshore Technologies A/S (Fig. 6a) (Borg et al, 2020;Stiesdal, 2019) or the pendulum-stabilized Hexafloat floater (Fig.…”

“…A similarly structured advanced spar, equipped with damping fins for stabilization in sway and heave direction, was initially used for a 5 MW wind turbine (Fukushima Hamakaze); however, after some investigations and studies by Matsuoka and Yoshimoto (2015), the middle column was removed to optimize the system's restoring, motion performance, and construction cost (Yoshimoto and Kamizawa, 2019;James and Ros, 2015;Maine International Consulting LLC, 2013). Other advancements are inspired by the oil and gas industry and deal with, for example, truss spar platforms, in which a truss section connects a bottom tank with the floating platform and heave plates can be included (Chen et al, 2017;Perry et al, 2007;Bangs et al, 2002), or added helical strakes for improving the dynamic response of the FOWT system (Ding et al, 2017b, a). The advanced spar-type floater by the Massachusetts Institute of Technology (Lee, 2005), on the other hand, has a relatively shallow draft and gets stability support from a two-layered taut-leg mooring system, which goes beyond the common delta or so-called crowfoot connection of the mooring lines to the spar-buoy structure (Butterfield et al, 2007).…”

Numerical Analysis of a Catenary Mooring System Attached by Clump Masses for Improving the Wave-Resistance Ability of a Spar Buoy-Type Floating Offshore Wind Turbine

“…They also found that the viscous damping contributed by the heave plate is a major component of the total damping. Meanwhile, Chen et al [30] presented a spar-type substructure integrated with the heave plates moored by the optimized mooring system. The dynamic response of the platform under different load conditions were performed using AQWA.…”