Study On Structural Strength And Time-Variant Reliability On Grab Dredger

This paper analyze structural strength of a grab dredger by MSC software and research its time-variant reliability considering effects of fatigue and corrosion.Considering both navigation and operation of the dredger and different positioning methods,calculation is divided into three parts.In each part,influences of wave directions,movement of grab and the angle between X axis and grab on structural strength are discussed.Results show that structures tend to be more dangerous in mooring positioning status than steel pile positioning status when other factors are the same.Results also show that structures tend to more dangerous when grab is at out-water period.It is also found that structures tend to be more dangerous when the angle between grab and X axis is 0° than that is 90°,which suggests that make grab work beside the dredger.This paper also gives the limit state function according to the structural failure of ship hull girder and analyzes its time-variant reliability.Cracks and corroded plates on the ship get inspected and repaired at certain intervals during service life.The influences on mid-ship section modulus of such inspection are quantified as well as the section modulus degradation due to fatigue and corrosion.The program was in Matlab.Results show that fatigue cracks and corrosion reduce reliability as time goes by,in which the effect of corrosion is the main factor and that inspection can increase reliability to some extent which is affected by the accuracy of crack inspection and the minimum allowed reduction ratio of corroded plates.It is suggested that inspection should be taken into consideration in further researches on time-variant reliability.