The Wave Resistance of an Air-Cushion Vehicle in Accelerated Motion

Abstract

This report is concerned with the theoretical wave resistance of an air-cushion vehicle (ACV) traveling over water of uniform finite or infinite depth, in steady or unsteady motion Referring first to steady motion, it is shown that the unrealistic oscillations in the wave resistance curve at low Froude numbers found by previous workers can be eliminated by using a smoothed out pressure distribution rather than one with sharp edges studied exclusively in the past.The main result of unsteady motion calculations is that the peak wave resistance in shallow water, ever in moderately accelerated motion, is appreciably less than the corresponding steadystate value. In fact, cases have been found where an ACV starting from rest under the action of a constant thrust would seem to be unable to cross the critical depth Froude number on the basis of quasi-steady estimates of wave resistance, while the more elaborate unsteady calculations show that it has sufficient power to reach its final supercritical cruising speed. An interesting feature of unsteady motion is that besides wave resistance there is another mechanism transferring energy to the free surface which is here called the dynamic sustention power. Contrary to intuition, the wave resistance in unsteady motion over finite depth sometimes becomes negative at supercritical Froude numbers before finally approaching zero at infinite speed.ii ACKNOWLEDGMENTS

Effect of broken ice on the wave resistance of an amphibian air-cushion vehicle in nonstationary motion

“…For a zero fotation parameter (e = 0), the wave-resistance curve calculated by formulas (2.7) and (2.8) agrees with tile results of [6], which are plotted as diagrams, for all the depth, elongation, and acceleration parameters, which were considered in [6], namely, for 3` = 0.25 and ? = oc and co = 2; k~ = 0.05 and k~ = 0.1, and the stationary motion.…”

“…If a rectangular or elliptic, in plan, system of constant pressures q(x, y) -= qo -const is taken as a system of moving pressures q(x, y), the theoretically obtained curve of wave resistance [1,2,5,6] has an infinite number of vibrations in the region of small velocities. This result is not supported by experimental data.…”

“…This result is not supported by experimental data. This drawback of the theory can be overcome by introducing a system of pressures q(x,y) that is described by means of the function of hyperbolic tangent [6]:…”

“…As c~l, (~2 --' co, we have q equivalent to q0 uniformly distributed over the rectangle. For better agreement between the theoretical and experimental results, Doctors and Sharma [6] proposed to use alL = a2L = 10.…”

Free-surface pressure distributions with minimum wave resistance

“…This formula and computations from it agree with Newman and Poole [9] and Doctors and Sharma [3]. More generally 2κbC D can be identified with the series on the right of (7) providing the pressures p j have been normalised by dividing by their mean p 0 , which we assume to be the case.…”