Experimental investigation on the air-cushion effect during free fall of a trimaran section using an air escape control method

Abstract

Slamming is common when a trimaran sails in rough seas. Owing to the semiclosed structural shape of a trimaran, an air cushion can easily form, reducing the slamming pressure. Therefore, the air-cushion effect during water entry of a trimaran section is investigated in this work. To study the air-cushion effect quantitively, an experimental procedure together with a novel model design is presented. Partly opened acrylic plates are pasted to a trimaran section model and the opening size is changed to control the efficiency of air escape from the front and rear of the model. The formation of the air cushion and the transformation of the water surface are captured by a high-speed camera. The influences of the opening size and the initial release height of the model on the slamming pressure are analyzed to investigate the air-cushion effect. The most novel idea of the present paper is the design of the asymmetrical openings on the front and rear acrylic plates pasted to the symmetrical model. Through this design, the significant difference produced by the air-cushion effect can be clearly distinguished by comparing the left and right halves of the model. Results show that the air cushion can postpone the emergence time of the pressure peak, decrease the magnitude of the pressure peak, and magnify the pressure fluctuation phenomenon.