NOVELTY - The turbine (88) has entry and exit sets positioned on opposite ends of vertically-aligned sides of a central opening (70) for directing bidirectional fluid flow through the opening and inducing a vortex swirl in the bidirectional fluid flow. A hub is provided on a propeller type shaft mount, and self-pivoting blades are spaced around a circumference of the hub. The blades are coupled to a pivot mechanism to provide self-pivoting movement in response to axial flow forces of water acting on the blades to adjust blade angle such that the shaft turns in a rotational direction of axial water flow.    USE - Bidirectional axial flow zero-head tidal, water or air turbine for use in a central opening of submerged horizontally-aligned structure i.e. submerged breakwater, forming a wave energy conversion device in standing wave applications e.g. basins or harbors, to dampen oscillations and generate wave energy for warning boat or ship.    ADVANTAGE - The self-pivoting blades can be constructed to twist along the length of the blade in respective twist configurations corresponding to changes in flow direction so as to provide improved efficiency for the turbine. The turbine improves the efficiency with which energy is captured by altering the angle of attack to the turbine-blades. The turbine has simple structure, which directly applies wave- induced water-particle motion to the turbine without compressible air column or mechanical motion conversion components as a medium or intermediary. The turbine focuses wave-induced flow through the center opening of the structure in a cost-effective manner, by allowing the turbine to be smaller in size, and simplifies the mechanical design. The turbine has a robust design that can withstand a severe wave environment while being submerged beneath the waves. The turbine has less corrosion when the turbine is manufacture using steel, and requires less maintenance as the device is not situated at or above an air/water boundary. The turning operates over a wide range of wavelengths, and wave heights. The turbine can operate in a multidirectional wave field, and is submerged below the water surface. The turbine can easily be maintained as the turbine uses well-established hydro-technology. The turbine operates efficiently to convert water-particle movement directly into water turbine generated electric energy, and can control the height of the sides or submergence depth of the structure. The turbine has reduced wave height in the down wave direction, and creates a calmer region so as to reduce coastal erosion, provide a quieter zone, and provide a protected area for ships. The self-pivoting blades are constructed with variable end-stops and twisted compliant surface, so that turbine is very amenable to changing wave environment to maximize power output.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a wave energy conversion device employing one-way check valves that convert bidirectional wave-induced flow into unidirectional flow through the turbine.    Central opening (70)    Progressive wave (81)    Top surface (82)    Holes (83)    One-way valve (84)    Bidirectional axial flow turbine (88)