Analysis Of Ultimate Strength Of FPSO Hull Girder With Composite Repairing

As a marine engineering equipment,FPSO usually works in the sea for a long time.It will cause crack damage under the action of various alternating loads on the bad sea condition.At the beginning of the crack damage,it is necessary to reinforce and repair the hull structure at the crack area.Welding repair is the most commonly used structural damage repair technology.But there are some limitations.CFRP has the advantages of high elastic modulus,high strength,good fatigue resistance and corrosion resistance.The technology of CFRP repair of damaged steel structure has broad application in the repair of naval architecture and ocean engineering.In this paper,the nonlinear finite element method is used to analyze the ultimate strength of cracked stiffened panel repaired by CFRP subjected to axial compression.The effect of CFRP paste length,paste width,paste layers,ply angle and other parameters is investigated on the ultimate strength after repaired.Meanwhile,the ultimate strength of cracked stiffened panel repaired by CFRP,cracked stiffened panel repaired by stop hole and CFRP,cracked stiffened panel repaired by center hole and CFRP is compared and analyzed.On this basis,the ultimate strength of cracked FPSO repaired by CFRP is analyzed.The specific research contents are as following:(1)The linear eigenvalue buckling analysis of stiffened panel is carried out.The first buckling mode is introduced as the geometric initial defect to the ultimate strength calculation.The result shows that the ultimate strength of stiffened panel is significantly decreased by introduced the geometric initial defect.The nonlinear finite element method is used to calculate the ultimate strength of cracked stiffened panel repaired by CFRP.The ultimate strength of cracked stiffened panel is obviously improved repaired by CFRP.It is close to the ultimate strength of intact stiffened panel with geometric initial defect.At the same time,the adhesive stress and adhesive damage process were analyzed.The adhesive layer degumming was caused by the shear stress of the adhesive layer.The maximum shear stress of the adhesive layer was located at the edge of the crack and the end of CFRP.The adhesive layer degumming occurred in the falling section of the load-displacement curve.(2)For the stiffened panel with the same length crack,the influence of different CFRP paste length,paste width,paste layer and ply angle is analyzed on the ultimate strength after repair.The result shows that the ultimate strength of stiffened panel increases with the increase of CFRP size.As it approaches the ultimate strength of intact stiffened panel with geometric initial defects,there is no obvious increase of the ultimate strength by increasing the CFRP size.For the stiffened panel with different length crack,the reasonable CFRP repair parameters are selected for ultimate strength analysis.The result shows that the CFRP size will also increase correspondingly with the increase of crack length.(3)In order to improve the ultimate strength of stiffened panel and prevent the crack propagation,the ultimate strength of cracked stiffened panel repaired by CFRP only or stop hole and CFRP are compared.The existence of the stop hole reduces the ultimate strength of stiffened panel compared with the crackd stiffened panel.The ultimate strength of the two repair ways are almost the same.Meanwhile,a new method for repairing small crack is proposed,that is to use center hole and CFRP to repair the cracked stiffened panel.Compared with stop hole,the existence of center hole improves the ultimate strength of stiffened panel,but it requires a larger CFRP size to repair.(4)A FPSO cabin model is estimated including the intact,cracked and cracked one with CFRP repairing.The stress distribution and ultimate bending moment of the above models were studied by nonlinear finite element method in sagging or hogging.Compared with the ultimate bending moment of intact structure,the existence of the crack reduces the ultimate bending moment of FPSO.The cracked FPSO repaired by CFRP can improve the ultimate bending moment.