Numerical modelling of rope elasticity for heave compensation lifting in offshore crane operations

Every Often time, maritime jobs are put off unduly while waiting for the weather to serene down. An attempt to prolong and continue window operation during harsh weather condition can incur severe damages in the life of the workers; equipment and machine thereby inflect the cost of production. To overcome this, a hydro-mechanical approach encompassing the core constituents of the floating winch and lifting rig pitcher were modeled. This study deals with the numerical modelling of rope elasticity for heave compensation system in offshore floating crane for use in enhancing operation at Qua Iboe field. Real time data were collected using classy equipment / sensors. First, a mathematical model for wire rope extension was developed using Newton / Euler’s approach when heave compensation system (HCS) was turned off (WOC) and validated using associated wire rope physical properties. Second, the performance of wire rope based on rope stiffness was evaluated when HCS was turned off (WOC) and on (WC). The reciprocal of the slopes of the plots of extension against total tensile force on the wire rope regraded as stiffness were compared. Thirdly, heave compensation system performance based on heave, roll and pitch motion characteristics during WOC and WC was compared within ۵۰ seconds of resonating time under varying loads and subsequent computation of their % reduction in disturbance. The results showed that the developed mathematical model for the wire rope extension (e) derived from second order differential equation found directly proportional to the load applied but inversely proportional to the wire rope stiffness (β)  during WOC and WC were ۲.۵۰ × ۱۰۷ N.m-۱ and ۳.۳۳ × ۱۰۷ N.m-۱, respectively. The heave, roll and pitch motions were observed to be a regular wave pattern. The comparison of the variations of heave, roll and pitch (including their rates and accelerations) within resonating time (۵۰ seconds) during WOC with WC revealed that the heave compensation system could reduce heave, roll and pitch motion.

کلیدواژه ها:

Numerical modeling ، Lifting ، Compensation ، Rope elasticity ، Heave motion