Shape and cost analysis of pressurized fabric structures for subsea compressed air energy storage

Abstract

In this article, three different methods are presented for finding the deformed shape of pressurized fabric structures underwater. The methods are used here to analyse the shape and cost of ‘energy bags’, inflatable bags that can be anchored to the seabed and used for subsea compressed air energy storage. First, a system of coupled ordinary differential equations is derived which can be solved to find the shape of an inextensible axisymmetric membrane. Then finite-element analysis (FEA) of an axisymmetric natural shape bag is carried out using cable elements, giving the deformed shape of an extensible axisymmetric membrane. Finally, a full three-dimensional FEA is presented which includes cable and membrane elements. A simple optimization is also used to minimize the cost per unit of energy stored in an axisymmetric natural shape energy bag, and it is shown that if only materials costs are taken into account, the cost of surface is approximately equal to the cost of meridional reinforcement in the optimum-sized bag.