Numerical and experimental investigation of wave energy devices with inflated bags

Our study is concerned with a class of wave energydevices with air-filled compressible volumes. As the volumeexpands and contracts under wave action, air is pumped intoa separate volume via a self-rectifying turbine. Here we considerdevices where the compressible volume is in the form of aninflated bag, which may be surface-piercing or completely submerged. The bag is essentially a lobed balloon inflated to a certain pressure, where loads are carried in the meridional direction by a number of uniformly spaced tendons. The paper looks mainly into the behaviour of a device with a surface-piercing bag instill water, where it is found by numerical calculations as well as physical model tests that depending on the amount of air inside the bag, two different equilibrium bag shapes are possible for the same internal pressure, thus offering a way of tuning the device to a range of wave periods. Physical model tests and preliminary numerical modelling of the device in the dynamic case are also described, where, firstly, the device is forced to oscillate in water by pumping air into and out of the bag and, secondly, the device is taking off power under incident wave excitations.