Rolling resistance of marine airbags at the longitudinal inclined slipway during ship launching

Abstract

There are three principal methods of launching a new ship including gravitational launching, floating-out launching and mechanical launching. A launching with marine airbags is a new kind of gravitational launching; it allows launching the ships which DWT is below 60,000 tonnes. In this paper the authors consider the ship launching by using marine airbags. The main principle of airbag ship launching is based on changing the force of sliding friction into rolling friction. One of the important characteristics of such devices is resistance force which occurs during airbag rolling under the compressive load. This force can be named rolling friction, however the authors show that the mechanism of the resistance force during airbag rolling, is fundamentally different from the well-known mechanism of rolling friction which occurs during rolling of the solid deformable body. The authors show that the rolling friction coefficient of airbags and ground depends on the ground situation and airbag bearing forces. The authors determine the marine airbag shape and three components of the force of rolling friction depending on geometric parameters and values of pulling and compressive forces. The authors show that the main component of this force is related to appearance of bending moments in the airbag shell during its rolling. The authors have shown that coefficient of rolling friction as a function of compressive force has a minimum after which it slightly depends on compressive force. The method of calculating the motion of a ship in case of ship launching from the longitudinal inclined slipway by using marine airbags is discussed.