Structural Strength And Fatigue Property Analysis Of Grab Dredger

Now with the development of border trade and regional economic growth, the inland waterway transport of Heilongjiang river has been received far more attention, so to ensure the channel keep unobstructed and safe is becoming more and more important. The dredger is needed to solve the problem such as sediment deposition, shallow draft existing in some channel segment in the upstream of Heilongjiang river and to clean up the waterway so to ensure navigation.Grab dredger is a kind of dredger with simple structure and highly efficiency. It uses grab assembling at the end of the deck to insert the bottom to dig sediment and it can be used in different channel conditions to perform channel dredging mission . When at work, grab claw executes repeated actions dropping,dredging,lifting,rotating and unloading,producing the periodic,cyclic stress response in the structure. After a long time of operation,some parts of the dredger likely produce fatigue crack fracture and lead to structure failure.So we have to cal-culate the fatigue life of the grab dredger and forecast its safety service life.This paper is based on a four cubic meters grab dredger project.First of all,we determine the working condition of the grab dredger and choose an operating period as the research tar-get and then decide calculating cases according to the working condition. Then we use soft-ware MSC. Patran/Nastran to build finite element model of the dredger,set the boundary con-ditions and constraints and calculate the stress values in each condition then compare them with the allowable stress values in the specification,find that all the structural strength meet the requirements. We find that stress concentration exist in some parts of the structure by ana-lysing the calculation results which are also parts that were easy be damaged by fatigue so we select the appropriate nodes in this area as check points to calculate fatigue life. Then we conduct transient response calculation to the digging case and unloading case of the grab dredger and we get stress response results of the two processes. Combine that with the result of static calculation so we get the stress load spectrum of the checking point .In the last part,we use computer program of the rain flow count method to count the stress load spectrum of the checking points and get the amplitude, mean and frequency of stress. Then we combine those information with the revised S-N curve of materials and the Miner linear theory to cal-culate fatigue injury tolerance and fatigue life of the checking points. The calculation results confirme that the fatigue life of dredger meet the requirements.