Fatigue Reliability Analysis Of Ship Hull Girder Structure

Fatigue and fracture are the most significant factors to be considered in the safety assessment of ship and offshore structures.It is necessary to analyze fatigue and fracture based on reliability theory because they are influenced by many uncertain factors.At present,the calculation of fatigue and fracture reliability are mainly aimed at a specific crack of local structure,which is a local failure and could hardly be related to the hull girder collapse.However,the increasing number of fatigue cracks and their growth in size will decrease the load carrying capacity of the ship hull structure.The failure probability of the structure is increased due to the load capacity of the structure is lower than the environmental load.So it is very necessary to study and analyze the fatigue damage of ship hull as a failure mode.The stiffened panels are the foundation of the reliability analysis of the hull girder as the important integral part of hull.In this paper,the crack propagation of stiffened panels with combined cracks are calculated based on the fracture mechanics and reliability theories,the fatigue reliability of the ship is also calculated.At first,The 3D models of stiffened panels with combined cracks on the midship are established.And the crack tip geometry correction coefficients of the stiffened panels under tensile and bending load are calculated.In order to calculate the crack growth of stiffened panels under combined loads.The stress intensity factor in Paris formula is considered as the superposition of stress intensity factor under the tension and bending load.The load distributions of stiffened panels are calculated based on three dimensional potential flow theory.The fatigue crack growth of stiffened panel is predicted by the Monte Carlo method,and the crack growth probability model is obtained by means of least square method.The critical crack sizes of stiffened panels are obtained based on the second level fatigue assessment diagram,and the fatigue reliability of stiffened panels are calculated by first order two moment method.Finally,the fatigue reliability of the ship hull girder under different phase parameters is calculated based on the crack propagation results of the stiffened panels,and the fatigue reliability of ship hull girder is analyzed accounting for inspection and repair.