NOVELTY - The flexible diaphragm or membrane (14) is located between two fluids. The flexible diaphragm or membrane moves in response to variations in the fluids to permit energy transfer between the fluids. The diaphragm or membrane is made of a fabric or woven material. The diaphragm is shaped so as to have a non-planar cross section in a neutral, rest or unpressurised state. A portion of the diaphragm extends outwardly relative to another portion of the diaphragm in neutral, rest, or unpressurised state.    USE - Flexible diaphragm or membrane for use in a diaphragm assembly of a cassette or a module of a wave energy conversion device of a natural or man-made structure (all claimed).    ADVANTAGE - The flexible diaphragm or membrane moves in response to variations in the fluids to permit energy transfer between the fluids which ensures that the diaphragm, frame and limit apparatus are provided in a releasably attachable module or cassette which readily enables interchange of the diaphragm during repair or maintenance operation. The elastic straining of the diaphragm is minimized as the diaphragm is having a low elasticity relative to rubber membranes. The fabric of diaphragm is having good power capture capability and low stiffness response. The operational load is efficiently reduced on the diaphragm which improves the diaphragm life and a sufficiently large diaphragm is enabled to be produced and shaped by appropriately shaping and bonding the panels.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following    (1) a diaphragm assembly comprises a retainer at the periphery of the diaphragm;    (2) an energy conversion device comprises a common support structure;    (3) a method for fabricating a diaphragm for an energy conversion device; and    (4) a method for converting energy.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional perspective view of a wave energy conversion device.    Flexible diaphragm or membrane (14)    Internal chamber (16)    Limit apparatus (20)    Single apex (24)    Frame (36)