Propagation of a Hovercraft Air Cavity Under a Floating Ice Sheet

Abstract

An ACIB is an air cushion device being developed in Canada for icebreaking purposes. When mated with the bow of a tugboat, the ACIB currently operational can break ice sheets about 1 m thick. During ACIB operations, the water surface directly beneath the craft is sometimes depressed below the lower edge of the ice sheet, and an air cavity is formed under the sheet. This air cavity is known to have a significant effect on the icebreaking capability of the ACIB. In a study for Transport Canada, DeHavilland Aircraft of Canada used underwater explosion theory to model its propagation. This paper shows that the explosion theory is incorrect. A more realistic theory backed up with experimental data is presented herein. The new theory is based on a theory for gravity currents developed by Benjamin.

Numerical Simulation of the Ice Breaking Process for Hovercraft

“…Therefore, when d is less than 0.9 hi, the air cavity cannot be formed under the ice sheet. In Hinchey's [3] experiment, he observed that the air cavity radiates out in a semicircular shape under the ice sheet. Without considering the air leakage, the relationship between the radius and height of the air cavity is written as:…”

“…Hinchey et al [1] conducted a model test of hovercraft breaking ice at low speed and analyzed corresponding ice resistance. Hinchey [3] carried out model tests and believed that the theory of gravity currents was more consistent with reality. Lu et al [4,5] analyzed the ice-breaking mechanism of hovercraft at high speed and came up with the critical speed.…”