水面衝撃水圧に関する一考察

抄録

Water impact of wedges and cones is a very essential phenomenon to wave impact loads on ships. For many years, invesigations on water impact pressure on wedges and other models such as ships have been carried out extensively, and today some methods are proposed to predict wave impact loads on ships, whose application might be limited.
But, we still have problems about water impact pressure, one of which is scaling law of water impact pressure. It has been pointed out that there might be discrepancy between test data and the scaling law.
The author carried out water impact test of a wedge to study scaling law of water impact pressure. The test result implies (1) Water impact pressure may obey Wagner's water impact theory of wedges, (2) The test data might be modulated by pressure gages.
Accoding to the assumption that impact pressure obeys Wagner's theory, response of pressure gage was analyzed. The response of pressure gage showed very good agreement with the test data. This means the assumption is true, but to assure it, it must be recognized for, other test data.
The purpose of this paper is to show that the same assumption can be applied successfully to other test results.
S. L. Chuang performed investigations on water impact of wedges and cones. He compared the test data with theories on the basis of the velocity at the moment when the model touched the water surface.
In order to compare the test data with theories rigorously, the velocity at the moment when the pressure gage comes across the water surface must be used.
Therfore, in this paper, equation of motion of falling body must be solved with reaction forces given by the impact theory to get actual impact velocity which is the velocity at the moment when the pressure gage comes across the water surface.
Water impact theories are given by H. Wagner for wedges, and also given by S. L. Chuang for cones.
Characteristics of pressure gages are very simple in this case. The natural frequency is more than 200 kHz, and the diaphragm is thought rigid. The output of the gage can be assumed to be proportional to the forces acting on the diaphragm.
At first, impact peak pressures are given by the theory using actual impact velocity, then they are modified by characteristics of the pressure gage. The results correspond to the measured data in water impact tests.
The comparison between the test data and the calculated data under the assumption showed very good agreement for all impact angles and impact velocities but very small impact angles.
Now, we may be able to conclude that the water impact pressure on wedges and cones obeys the theory by Wagner or Chuang.