Page 214 - Theory and Design of Air Cushion Craft

Water surface deformation in SES air cushion 197

Fig. 5.8 Wave amplitude due to an ACV on shallow water in/off air cushion.

5.3 Water surface deformation in/beyond SES air cushion
on calm water

The wave-making of an SES moving on water is different from that of an ACV, result-
ing from immersion of the two sidehulls in the water. Thus in addition to wave-making
induced by the air cushion, the interference of wavemaking between two sidewalls and
sidewalls with the air cushion has to be considered.
Based on Standing's formula [54], senior research engineer H. Z. Rong of MARIC
developed the wave profile calculation of an ACV into that for an SES [32]. He
assumed that the flow around the craft was uniformly distributed, incompressible,
non-viscous, with no vortex flow and that the wave height was small with respect to
the wave length.
On this basis he established a mathematical model for an SES running at constant
speed over water with infinite depth, namely distributed Kelvin sources on the surface
of calm water (i.e. the pressure surface at z = 0) and on the centre longitudinal plane
of both sidewalls (i.e. r = b) and also distributed a Kelvin doublet (source/sink) on the
surface extending as far as infinity. The coordinate system is as shown in Fig. 5.9.
Using linear water wave theory [56], the equation which defines the disturbing
velocity potential and its boundary condition can be obtained and the <f> broken down
into
A = / + / + / + f (5.7)