| With the rapid development of China’s industry,the contradiction between the ever-increasing demand for oil and gas resources and the ever-decreasing onshore oil and gas resources reserves have become increasingly significant.It is imperative that oil and gas exploration and development enter the deep sea.Crown-Mounted Compensator is a deepwater oil and gas exploration and development equipment which is widely used in the world.It adopts rocker mechanism to realize the function of tensioning steel wire rope,reducing the number of wire rope winding and improving the service life of wire rope.Due to the cyclical changes in the contact stress between the steel wire rope and the pulley and the tension of the steel wire rope,the pulley will have contact fatigue,which will lead to fatigue wear.This will cause grooves on the surface of the pulley rope groove and eventually expand into indentations,which will affect the service life of the pulley and wire rope.At present,the research on heave compensation system is mainly focused on the improvement of its control strategy.Research on the structural safety of critical parts of the heave compensation system is very rare.It is very important for the service life of the heave compensation device and even the maintenance and inspection of the deepwater oil and gas exploration and development platform.Therefore,this dissertation carries out the research on the damage mechanism of the rocker mechanism pulley mechanism of the Crown-Mounted Compensator.The main contents and conclusions are as follows:(1)A kinematic analysis of the rocker mechanism and the stress analysis of the steel wire rope were carried out.According to the movement law of the drilling platform,the change model of the wrap angle of the rocker mechanism steel wire rope and the pulley and the mathematical model of the rocker mechanism movement were established.The change curve of the wrap angle and the curve of the speed and angular velocity of the pulley were established.The force model of the wire rope-pulley was established,and the tension curve of the wire rope is obtained.The results show that the change angle of the wrap angle between the steel wire rope and the pulley Ⅱ(the rocker and the connecting rod hinged part)is the largest,and it is more prone to fatigue.When the crown moves to the highest point,the rocker link has a larger inertia force and the wire rope tension reaches the maximum at this time,which will aggravate the wire rope’s wear and tear.(2)The analysis of the contact stress between the steel wire rope and the pulley was conducted.A microelement mechanics model of the steel wire rope was established,and the relationship between the wire rope tension and the wrap angle of the pulley was obtained;then the contact model of the wire rope and the pulley,the side strand of the wire rope and the outer wire of the side strand and the pulley was established in turn,and the pulleys with different contact models were obtained.The contact stress of the pulley under different contact models was obtained,and the distribution of the contact stress at the contact surface between pulley Ⅱ and the steel wire at the maximum ballast point was plotted.The contact stress of the sheave groove calculated by the three contact models is compared and analyzed,and the calculation accuracy is taken into consideration.To calculate the cost,the contact model of the side strands and pulleys of the wire rope was finally selected as an applicable model for actual calculation.(3)The simulation analysis of rocker mechanism of Crane-Mounted Compensator was carried out.A kinematics simulation model of the Crane-Mounted Compensator was established to calculate the motion of the rocker mechanism under the action of the heave of the ocean wave.The change law of angular velocity and angular acceleration of the rocker and connecting rod was obtained;the steel rope was formed as a whole And contact simulation models of the side strands of the steel wire ropes and the pulley rope groove,the contact stress of the pulley was calculated and solved.The variation law of the contact stress on the rope groove of the pulley with time and the stress distribution at the contact point were obtained.The results show that when the car is at the highest point on the day,the angular accelerations of the rocker and connecting rod are the largest,and the contact stress reaches the maximum at this time.It is also found that the results of the finite element simulation are in good agreement with the analytical calculation results,which is the next pulley.The calculation of the number of fatigue cycles provides the basis.(4)The damage mechanism and fatigue life of the rocker mechanism pulley were studied.According to fatigue wear theory,the cause of the indentation on the surface of the pulley rope groove is analyzed.The fatigue wear caused by the micro-cutting of the pulley rope groove by the steel wire rope leads to the damage of the pulley.The fatigue life prediction model of the pulley is established and the fatigue of the pulley is estimated.The life span is 184 days,and several measures to reduce the fatigue of the pulley are proposed according to the damage mechanism of the pulley. |
