Research On Dynamic Stress Analysis Of Marine Diesel Engine Frame

Block is the basis and skeleton of the diesel engine, it bears complex loads, the magnitude and direction of which changing with the working condition and the crank angle, even some points of the forces are also changing all the time. The reliability of the block has important effect on the performance of the whole diesel engine, it basically determines the service life of the diesel engine.Simple static stress analysis has been unable to meet the needs of the design of a diesel engine today, dynamic stress analysis becomes more and more important.This paper presents a research on dynamic stress analysis of marine diesel engine frame, respectively, from both of theoretical calculation and experimental test of two ways. Major work and conclusions are as follows:1) Under the premise of the accuracy and calculation speed, physical model of 6L16/24 engine block is reasonable simplified, and a finite element model for dynamic stress calculation is established as well.2) Use multi-body dynamic analysis software ADAMS to compute the piston side thrust, vertical and horizontal component of the loads on main bearing,as the dynamic loads that loaded on the engine block.3) Load dynamic loads on the finite element model of 6L16/24engine block, define boundary conditions, calculate dynamic stress of a running cycle under the condition of speed at 1000rpm, single cylinder power at 90kW.4) Analyse the dynamic stress results, main conclusions are as follow:from the cloud of the dynamic stress, high stress regions mainly locate at the upper and lower contact surfaces between the cylinder liner and the block,as well as the region that around the main bearing, they are mainly influenced by the dynamic loads; Near the ignition point of each cylinder, the stress of the upper and lower contact surfaces,the cylinder wall and the associated two main bearings reach the maximum stress; The structure of corner is the region which is prone to stress concentration; Stress around engine flywheel is more stable, fluctuating around a fixed value; Stress of frontbox is lower, only the region near the junction presents relatively clear stress. 5) Considering the case of bolt preload, apply preload on the block using temperature method and direct method respectively, the results of two methods are basically consistent. Around the region of contact surface between nut and block, the stress is obvious. The stress of the middle main bearing is higher and the stress of the both sides is lower.6) Comparison of experimental tests and results Testing on dynamic strain and the cylinder pressure of 6L16/24 engine block, compare the results of tests and the dynamic stress analysis, to validate the correctness of the dynamic stress analisis method. Innovations are as follow:1) For the piston side thrust load, considering its location on the contact surfaces between cylinder liner and block,establish rigid regions and load the piston side thrust on the nodes which is the centre of the region.2) For the effect of air force on the engine block, this paper considers the condition that when the cylinder head locates on the block, the reaction of bolt causes a force on the contact surfaces between cylinder liner and block.3) Combination of a variety of analysis softwares:use powerful preprocessing software HyperMesh to facilitate accurate and analysis of dynamic stress; using the multi-body dynamic analysis software ADAMS to calculate the dynamic loads, it's more accurate than the classical method; using RADIOS S solver for dynamic analysis of the diesel engine block.