FURTHER EXPERIMENTS ON WAVE PRESSURES.

Abstract

Snopsis Experimental investigation of the pressures exerted by waves breaking against a vertical wall has provided further numerical information in support of the theory published in 1939 by Bagnold, who concluded that an air pocket between the wave and the wall played a dominant part in the generation of shock pressures. Although many precautions were taken to obtain exactly constant waves, which were then allowed to break in calm water, the pressure observations varied greatly; however, by taking a large number of waves it was possible to apply statistical methods of analysis which showed that the pressures were substantially proportional to wave-height. The greatest pressures were exerted on the upper part of the wall and extended chiefly over the upper four-tenths of the wave height. Their duration was very brief, of the order of 0.001 second for the more intense shocks, and, as found by Bagnold, the product of pressure and duration tended to be constant. The impulse contained in the shock was relatively small compared with the ordinary impulse of reflexion of the whole wave, and did not exceed 0.07 of the momentum of the wave; but the pressure-rise was very rapid, and the Paper includes an estimate of the greatest rate of rise of pressure to be expected from sea-waves. The probability of true scaling-up of the model results is also discussed.