ABSTRACT 



The dynamic pressure on the sea bottom due to a constant, rectangular 

 pressure distribution moving at a steady speed over the calm-water surface 

 is determined. The problem is formulated and solved within the framework 

 of potential-flow, linear-wave theory. Numerical results are presented for 

 one beam-to-length ratio, for various water depths, and for both subcritical 

 and supercritical speeds. 



ADMINISTRATIVE INFORMATION 



This study was supported under Naval Ship Systems Command Subproject S-F011 02 32, 

 Task 2382. 



INTRODUCTION 



A pressure distribution moving over the calm-water surface will generate both a local 

 disturbance around the distribution itself and a wave system which propagates behind it 

 similar to those caused by a moving ship. Such a surface disturbance will obviously affect 

 the pressure on the sea bottom to an extent depending on the shape and magnitude of the 

 surface disturbance, its velocity, and the depth of water. 



The velocity potential associated with a pressure distribution of arbitrary shape moving 

 on the surface of a fluid of finite depth is given by Wehausen and Laitone 1 and, by using 

 Bernoulli's equation, the pressure can be found anywhere in the fluid. If, in particular, the 

 surface distribution is restricted to a rectangular area of constant pressure and if the potential 

 is evaluated on the sea bottom, the analysis is somewhat simplified. Nonetheless, the pres- 

 sures on the bottom are given in the form of integrals which must be numerically approximated. 

 The necessary numerical analysis and computer programming have been carried out, and the 

 results are presented herein. 



Insofar as a moving rectangle of constant pressure is a reasonably good approximation 

 to a ground-effect machine, the bottom pressures presented herein may be interpreted as those 

 due to the passage of such a vehicle. A knowledge of these pressure variations is of inter- 

 est in the study of pressure-activated mines. Such interest provided the motivation for this 

 investigation. 



MATHEMATICAL FORMULATION OF THE PROBLEM 



Assume that a constant pressure p = p is distributed over a rectangle of length L and 

 width B and that this pressure distribution is moving over the free surface of a fluid of depth 



References are listed on page 16. 



