Fatigue Strength Analysis Of Large PCTC Based On Hinged Design Principle

Fatigue strength assessment is an important index to measure safety and reliability of ship.During long distance navigation,vessels are forced by alternate loading,which will lead to alternating stress,and the high cycles loading and unloading process will result in cracks and fatigue failure of structure finally.To satisfy the handling operation requirement,transverse bulkheads of Large PCTC are not installed in internal cargo and deck runs through the whole vessel,such large racking deformation will happen of heeling state,and high stress regions will occur at the connecting positions between vertical side frames and deck transverse girders and so on.For the PCTC based on flexible design principle,the racking deformation and the high stress are more serious than the PCTC based on rigid design principle,such it is more essential to take the fatigue performance assessment into consideration.Fatigue strength assessment results are related to constraints,balance adjustment and design load.Ship sailing in area is of a full free state,but the structure mechanical performance in base of specifications is always analyzed of the static state,with the design load according empirical formula from specifications and the additional load determined according the balance adjustment.Although balance adjustment can balance the constraint force,different balance adjustment methods and boundary conditions have different influence on stress and deformation of structure,and then affect the mechanical performance assessment of structure.In addition,during simplified fatigue calculation for Large PCTC,different GM values will affect the calculation of fatigue load,Weibull distribution parameters and the average zero crossing frequency.The main work of the thesis includes:(1)Different constraints types are analyzed including the constraint type in the DNV specifications for PCTC fatigue strength assessment and the single point constraint types,different balance adjustment methods are analyzed including vector force,inertia force and inertia relief adjustment;(2)The stress and displacement distribution of 7800 PCTC are compared with different boundary conditions and different balance adjustment methods,and the influence rule of constraint types and balance adjustment methods on structural response is studied;(3)The fatigue life of 7800 PCTC are compared with different boundary conditions and different balance adjustment methods,andthe influence rule of constraint types and balance adjustment methods on fatigue assessment is studied;(4)The fatigue life of 7800 PCTC are compared according different GM values,the influence rule of GM value on fatigue life is studied.In this paper,the study on the influence from different boundary conditions,different balance adjustment methods and GM value to fatigue assessment is of important significance,and there is a certain reference to develop the assessment methods of mechanical performance for other type ship.