Origami-adapted clam design for wave energy conversion

Abstract

The Clam wave energy converter (WEC) is a floating device composed of two side plates connected by a hinge that closes and opens under interaction with wave crests and troughs. A linear power take-off (PTO) may be installed between the two side plates to convert the mechanical motions to electricity, or the volume change may be used to pump air between chambers and across an air turbine PTO. The basic concept has been discussed since 1978 and featured as part of the UK Wave Energy research programme [1]. Some simplified clam models have been built since then and preliminary investigations were conducted by Phillips [2] to understand the wave-structure interactions at the COAST laboratory, University of Plymouth. However, the simplified models were not enclosed and hence seawater can be trapped in the device. To further the investigation, we will design the outer shell of the clam model that is enclosed and thus suitable for use in the (adverse) marine environment.   Since no enclosed flexible polyhedral structure can change its volume without bending or stretching of facets according to the bellows conjecture, the clam model must be strained when it is in motion. A portion of the wave energy will be consumed to deform the outer shell of the clam model and the rest can be captured by the PTO. Therefore, the design of the clam model will aim at minimising the strain on its facets while achieving the largest volumetric change of the device to maximise the power extraction by the PTO. Inspired by origami, we will construct the enclosed clam-type offshore device by connecting rigid panels and elastic membranes with rotational hinges. We model the rigid panels to rotate about the hinges without facet deformation and allow stretching on elastic membranes. The strain on the elastic material shall be minimised for better structural integrity and minimal energy loss. Satisfying all the design requirements, the best geometric design is obtained through an optimisation process. Based on the optimised geometry, a downscaled prototype will be built using rigid plywood and rubber membranes and tested under dynamic wave-induced loads to prove that the strain incurred is negligible in response to forces.   References: [1] Peatfield, A. M., Duckers, L. J., Lockftt, F. P., Loughridge, B. W., West, M. J., & White, P. R. S. (1984). The SEA-Clam wave energy converter. In Energy Developments: New Forms, Renewables, Conservation (pp. 137-142). Pergamon. [2] Phillips, J. W. (2017). Mathematical and Physical Modelling of a Floating Clam-type Wave Energy Converter (Doctoral dissertation, University of Plymouth).