FLOATING BREAKWATER WITH AIR CHAMBER AND DEVICES OF ENERGY DISSIPATION
Andrea Atzeni and Nicola Montaldo, Dip artimento di Ingegneria del Territorio, Universita di Cagliari, Piazza d'Armi, I - 09123 Cagliari, Italy
ABSTRACT
We present the results of experiments carried out on the model of a floating breakwater anchored to the sea-bed using a system of cables. Four types of breakwater with various mooring cable configurations are tested. With a combination of two of these one obtains a breakwater of changeable structural mode that reduces the transmitted wave component to a minimum, for a incident wave period range of 2.0 s to 5.0 s. The change in structural mode is obtained by adding or removing compressed air from the chamber which is in contact with the water. Two positions have been discovered which allow us to considerably reduce the transmitted wave. The first position is obtained by adding compressed air to the structure until the mooring cables are under tension. In this mode the breakwater can reduce the transmitted wave to values almost always less than 20% of the incident wave for periods of up to s3.8 s. Under these conditions the breakwater behaves mostly as a reflective structure . For periods greater than 3.8s the breakwater generates a lower transmitted wave when the chamber is without air. By adding an energy attenuator to the downstream face of the breakwater it is possible to obtain an average transmitted wave of around 20% of the incident wave for a period up to 5 s.
WAVE ENERGY DRIVEN RESONANT SEA WATER PUMP
Steven P.R. Czitrom, Instituto de Ciencias del Mary Limnologia, Circuito Exterior S/N, Ciudad Universitaria, UNAM, 04510 Mexico D.F., Mexico
ABSTRACT
A wave driven sea-water pump which operates by resonance is described. Oscillations in the resonant and exhaust ducts perform similar to two mass-spring systems coupled by a third spring acting for the compression chamber. Performance of the pump is optimized by means of a variable volume air compression chamber (patents pending) which tunes the system to the incoming wave frequency.
Wave tank experiments with an instrumented, 1:20 scale model of the pump are described. Performance was studied under various wave and tuning conditions and compared to a numerical model which was found to describe the system accurately. Successful sea trials at an energetic coastline provide evidence of the system s viability under demanding conditions.
