The Study On Buckling Behaviour And Optimization Design Of Cantilever Beam On Jack-up Platform

Cantilever beam is the main load-bearing equipment for self-elevating drilling platform equipment.The main components of the cantilever beam are stiffened plates with a high ratio of height to thickness.The buckling performance is an important index to measure the bearing capacity of the stiffened plates,which having great significance to analyze the buckling characteristics of the cantilever beam and optimize the design of the structure.In this paper,the mechanical model of cantilever girder is established first,and its critical buckling load formula is deduced by theoretical analysis.The weight ratio of each influencing factor to the buckling load of the main beam was analyzed based on the investigation of the scale parameters of the cantilever beam.The effect of the reinforcement arrangement on the buckling performance of the cantilever beam was studied from the perspective of the lateral bending stiffness ratio after establishing finite element model of the overall structure of the cantilever beam.The load-displacement curve of the nonlinear buckling of the cantilever was obtained by the arc length method.The linear buckling load and the nonlinear buckling load were compared quantitatively and the buckling safety coefficient was different from the classification societies rules.The mechanical properties of the box-type cantilever and gantry cantilever were compared by theories,and the results were verified using the finite element method.At the same time,taking into account the manufacturing and installation accuracy,the cantilever beam will have an overall lateral tilt under drilling conditions.The angle of inclination was analyzed from the point of view of strength and stability,and the empirical formula of the ultimate bearing capacity of the cantilever beam varying with this angle of inclination was fitted.The wind load on the drilling platform derrick was calculated according to the classification society rules.The buckling load of the cantilever beam under 24 wind direction angles was quantitatively studied by eigenvalue buckling analysis on multiple working conditions.The most unfavorable wind direction of the cantilever beam and influence of wind loads angular on its carrying capacity was obtained.The topology optimization of cantilever main beam and cross beam was carried out respectively in order to optimize the minimum structural flexibility.The comparison of the calculated Mises stress results shows that the strength performance of the structure is better after the topology optimization.On the basis of topology optimization,with the maximum buckling load capacity as the optimization goal,the layout optimization design of the main beam and the cross beam is carried out respectively.The accuracy of the layout optimization of stiffeners was verified by comparing the buckling loads before and after the optimization of the cantilever beams under various working conditions,which can provide certain theoretical basis for the optimization design of cantilever beam.