Methodology for optimizing composite towers for use on floating wind turbines

Abstract

A methodology for the design and optimization of a composite wind turbine tower for use on a floating offshore platform is presented. A composite turbine tower on a floating offshore platform not only has the potential to reduce maintenance and upkeep costs associated with the use of steel offshore but also has potential to reduce the tower mass and subsequently the support platform mass. The optimization problem is formulated to obtain a turbine tower that meets all strength and serviceability criteria and minimizes the tower mass. The optimization and design process link a number of dynamic analyses and finite element routines using a genetic algorithm. This work documents the optimization and design software and illustrates its use in various case studies for a 6 MW floating wind turbine system. Case studies include the optimization of a steel tower as a comparison to a composite material tower and the use of a cored, sandwich panel composite tower versus a solid composite tower. The results demonstrate that significant reductions in the tower mass are likely when comparing a steel tower with a composite tower. Also demonstrated for the platform and turbine configuration considered in this work is that the minimum mass tower design is driven towards a solid shell composite configuration, rather than a sandwich panel tower shell, in the face of reasonable design constraints.

The Influence of Flexible Towers on the Dynamics of Offshore Wind Turbine Gravity Base Structures

“…It is possible that even with additional optimization composites may remain an unsuitable for the tower of a standardized "soft-stiff" OWT design due to secondary effects on the foundation. Composite tower concepts that mitigate the flexible behavior, such as the C-Tower's "soft-soft" design [3], concepts that use active-pitch control to minimize displacement via blade drag, or concepts that use the lower mass of a tower to reduce foundation size and cost such as VolturnUS [2] remain viable.…”

“…The increasing size of structures reduces the benefits of steel as selfweight becomes a design driver in the traditionally steel dominated offshore industry. Composite towers are being considered [2,3] as alternatives for offshore wind turbines (OWT). Composites consisting of glass fibers in an epoxy resin matrix may provide benefits such as better fatigue performance and corrosion resistance.…”

“…The focus of this study was the dynamic behaviour of the composite tower and how it influenced the overall structure's response to environmental loading. Previous work has discussed the ultimate strength of composite towers [2,3]. The combination of a more flexible wind turbine tower and a concrete gravity base foundation (GBF) was chosen for this study as it has been noted [2] that such flexible composite towers may weigh less than stiff steel towers.…”

“…Previous work has discussed the ultimate strength of composite towers [2,3]. The combination of a more flexible wind turbine tower and a concrete gravity base foundation (GBF) was chosen for this study as it has been noted [2] that such flexible composite towers may weigh less than stiff steel towers. If the tower had a lower mass the center of gravity of the superstructure would be lowered, which could be beneficial in reducing the over-turning moment of the structure and allowing the foundation size and mass to be reduced, saving on material and installation costs.…”

Parallel Analysis of Offshore Wind Turbine Structures under Ultimate Loads

“…The work of Zuo et al [16] used multiple tuned mass dampers to control vibrations from the fundamental and higher modes of an OWT tower, under combined wind, sea wave, and earthquake excitations. The work of Young et al [17] presented an optimal design for a floating wind turbine tower, while the steel tower was compared to the composite materials tower, and the results demonstrated that the composite can significantly reduce the tower mass. Abhinav and Saha [18] investigated the response of a jacket supporting an OWT with the Define SSI, where the effect of the SSI became predominant for an OWT in loose sands.…”