Patent ID: 6324480
Filing Date: 2001-11-27
Classification: B63B,G01N,Y02T

Abstract:
A method for analyzing effects of generating bubble jets in a flow field near a ship surface on reducing skin-friction in a cruising ship comprising the steps of:obtaining a shear stress decrement .tau..sub.t, produced by having a bubble in said flow field in terms of a resistive force .DELTA.R.sub.v acting on said bubble, derived from movements of said bubble, in a fluid flow direction, x-direction, along said cruising ship as well as in a direction at right angles to a ship wall surface, y-direction, in accordance with a definition of a high frequency band region in which a product of a bubble time-constant T and a turbulence frequency .omega..sub.L in said flow field is greater than 1;obtaining an operative wall constant .kappa..sub.1 in the wall law when there is a bubble having a parametric bubble diameter d.sub.b, by assuming that said shear stress decrement is generated by a decrease in a mixing length; andobtaining a solution for skin-friction ratio, C.sub.f /C.sub.f0 in said high frequency band region, according to an expression relating said operative wall constant .kappa..sub.1 to a local friction factor C.sub.f for bubbly flow, and an expression relating a normal wall constant .kappa. in the wall law in non-bubbly flow to a local friction factor C.sub.f0 in non-bubbly flow.