Fatigue Characteristics Analysis And Structure Optimization Design Of Marine Diesel Engine Crankshaft

Crankshaft is one of the most important parts in diesel engine.It has complex structure,expensive cost and bad working environment.Crankshaft bears the bending and torsion of the alternating load and vibration in the process of working,with the increase of the diesel engine power,the requirements for crankshaft is more demanding,The life and reliability of diesel engine depend on the fatigue strength and life of crankshaft to some extent.Therefore,the fatigue strength analysis of crankshaft is particularly important.This paper uses different methods to study the fatigue strength of crankshaft.In this paper,we take the crankshaft of a marine high power medium speed diesel engine as the research object.Firstly,the traditional method recommended by Classification Society and GJB based on the simply supported beam method is used to calculate the crankshaft strength,and the safety factors of the main journal fillet and the crank pin fillet are obtained.And the program design of crankshaft strength calculation method of classification society is carried out.Then the static stress measurement test of unit crankshaft is carried out to study the distribution and transformation law of the crankshaft stress by changing the loading force.We use ANSYS,a finite element software,to simulate the static stress measurement test of unit crankshaft,and the stress result of finite element is compared with the test data,so as to verify the rationality and accuracy of the finite element simulation method.The transient dynamics simulation analysis of the crankshaft and connecting rod mechanism is carried out by ANSYS to study the distribution and variation trend of the crankshaft stress under dynamic working conditions.The safety factor of crankshaft calculated by different methods is 1.648 and 1.628,which is greater than the allowable safety factor of crankshaft,so the fatigue strength of crankshaft is qualified.The multi-body dynamics analysis software EXCITE was used to analyze the crankshaft system,and the operation stability of the crankshaft in a complete working cycle was studied.The stress data and load history of each web and fillet were obtained by unit load method,so as to calculate the safety factor of each fillet and study the stress distribution of the crankshaft.The calculated safety factor of crankshaft is 1.59,which meets the requirement of fatigue strength.Finally,the static finite element analysis of the unit crank is carried out in ANSYS to study the stress distribution of the crankshaft under different loads.Then,taking the maximum equivalent stress and the mass of the unit crankshaft as the objective function,the response surface multi-objective optimization analysis of the crankshaft structure is carried out to study the influence of the size parameters of the crankshaft on the objective function,and the optimal solution is found in the Pareto front and verified,which makes the crankshaft lightweight,reduces the stress and improves the safety and reliability of the crankshaft.