Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Experimental procedure to characterise the random acceleration of the free surface within the air cushion box of a surface effect ship

A source of hydrodynamic noise in a trimaran SES is due to the free surface random flow generated inside the air cushion box. Since the direct measurements of the acoustic pressure is not possible because of the noise due to the fan used to produce the overpressure an indirect measurents was performed.

The procedure implemented to obtain acoustic pressure inside the air cushion consists in the following steps:
- Measurements of the wave elevation due to a constant pressure generated by a fan inside a rectangular box;

- Derivation of the radiated acoustic pressure by analytical relations.

The rectangular box had the lateral sidewalls immersed to avoid air leak while the front and the rear side just above the free surface level. The wave pattern was measured with the fan on and with the fan off. This way, the disturbances produced by the sidewalls were subtracted in the post processing phase to the air cushion wave field. Front and back skirt was provided when necessary to limit air leak.

The results of the analyses done show that free surface excitation inside the air cushion box is of minor importance and thus its effect can be neglected in the evaluation of the total noise level on board.

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