NUMERICAL-SIMULATION OF LONGITUDINAL TACKLE OSCILLATIONS WHEN SALVAGING SUNKEN VESSELS FROM DEEP-WATER

A mathematical model is proposed for longitudinal oscillations of a ta ckle used for salvaging sunken vessels to the sea surface. The numeric al approximation of the obtained model along the tackle rope length is accomplished by means of the finite-difference method. To implement t his method, the transformation of independent coordinates is introduce d into the constant step mesh. The integration with respect to time is carried out by the theta-Wilson method. To solve the nonlinear system s of algebraic equations, iteration methods are used. There are exampl es of calculations for the vessel separation from the seabed and salva ge from 1655 m depth when using various methods of controlling the win ch shaft moment. The area of winch moment and heaving motion amplitude values that provide vessel emergency-free separation from seabed are calculated. It is shown that, with accuracy sufficient for practical u se, the rope system of the tackle can be replaced in some cases by a s ingle equivalent rope. Moreover, the rope mass can be neglected if it is considerably less than the mass of the vessel being salvaged. It is emphasized that the selection of the control of the velocity of salva ge depends to a large extent on winch operation peculiarities. (C) 199 7 Elsevier Science Ltd.