Numerical analysis and optimization of wrinkling in flexible floating structures

Very Large Flexible Floating Structures (VLFFSs) for offshore solar photovoltaic (OPV) energy generation are recently seen as one of the offshore renewable energy resources. The primary objective of these structures is to support solar panels near the sea surface, which typically have small weight hence the payload on these structures is low. On the other hand, to maximize the energy output, these structures can span large areas on the sea surface, with in-plane dimensions up to hundreds of meters. Concepts for VLFFSs for OPV can either be based on linked rigid modules that are globally following the wave elevation, or they can be based on the idea of a (continuous) thin sheet with integrated solar panels. The former concept closely links to floating multi-body problems known in offshore engineering, whereas the latter concept requires a new paradigm in ship and offshore structures: the interplay between a thin, (possibly non-metallic) flexible structure and the air-water interface. In addition, due to the low payload on the structure and the large in-plane dimensions, the thin floating sheet is susceptible to the wrinkling instability, which is omnipresent for membranes with a very small thickness compared to its in-plane dimensions.

In the FlexFloat project, we aim to provide insights and tools for the design and analysis of VLFFSs for OPV applications. That is, the physics and modeling of wrinkling of thin floating membranes under different loading conditions and in waves will be investigated. In Hugo’s project in particular, the focus will be on the wrinkling mechanics of such structures, from the development of analysis methods, to the application of these methods for more applied cases, e.g. wrinkling in combination with stiff zones or optimization of geometries with holes.

The numerical methods for the analysis of wrinkling in thin membranes will strongly rely on isogeometric analysis (IGA) and arc-length methods (ALMs). Isogeometric analysis was first presented in 2005 and integrates Computer-Aided Design (CAD) with Finite Element Methods (FEM) employing the smoothness of the underlying splines in CAD as the basis for FEM. Compared to conventional FEM, IGA has shown benefits not only from the seamless integration of CAD and FEM, but also in terms of smoothness and geometric exactness. The latter is very important for geometric optimization problems where the solutions are highly depending on the geometry, e.g. wrinkling of membranes. Arc-length methods are well-known structural analysis methods for the modeling of structural instabilities; hence of interest for the modeling of wrinkles of thin membranes.

Concretely, Hugo’s project will unify IGA and ALMs for an efficient framework for the analysis of wrinkling in thin membranes. On the one hand, simplified load cases are investigated for the sake of method development and physical understanding of the wrinkling phenomena under different conditions. On the other hand, complex load cases with holes, rigid zones, etc., will be investigated as benchmark for the development of simplified engineering models for wrinkling, as well as for the optimization of geometries. The methods will be developed within the Geometry+Simulation Modules (https://www.github.com/gismo/) and will be made publicly available throughout the project.

This work resulted in a doctoral thesis which Dr. Hugo Verhelst successfully defended on 18 January 2024. That thesis can be found here.