Modal Analysis And Study On Marine Diesel Crankshaft Crack

Crankshaft is an important component in Marine Diesel Engine. It endures various wallops, torques, wear, stress in the process of work which come into being structure change and damage. Moreover, its work environment is enclose relatively and is difficult to arrive. Therefore, it is need urgently to finding damage in time and carrying through maintenance. Early, people detect damage by Ultrasonic, X-ray, Magnetic particle inspection and so on. Because these methods need to know the approximate location in advance,the location is accessible to arrive ,these methods belong to static detecting and these methods are need to stop Marine Diesel Engine, thus these methods are limited on board. It is need to search an effective and reasonable detecting method to ensure the safe operation of Marine Diesel Engine and to prevent disaster such as crankshaft rupture.The paper collects and absorbs a large number of data from home and aboard, then put forward the study ideas of damage identification on the change of modal. The premise of identification method is that the location and depth of damage can are identified according to the change of modal parameters before and after the structure is damaged. The main researching fields are following:1 The theory and the research situation of modal parameters of engineering structures, the feasibility and advantages of damage identification from the change in natural frequencies are expatiated through listing the advantages and disadvantages of these methods.2 The paper has a recommendation on The Finite Element Theory and The Modal Analysis Theory. According to different method gained of modal parameters, it explains respectively calculated modal analysis and experimental modal analysis. The paper also proves the right of theory and formula on modal identification of frequency. Finally, prove that the"frequency change ratio"is only function of damage location and damage identification can be achieved by between"frequency change ratio"and"frequency rate of change".3 The paper introduces simply the software of ANSYS. Thirty damages of five locations and six depths on smooth-shaft and crankshaft are simulated and worked out their corresponding natural frequency by ANSYS, and then find out the way to identify injury by analysis and summarize of frequency change. Finally according to the analytical results of smooth-shaft and crankshaft we can know that damage identification method of smooth-shaft is possible to instead of this method of crankshaft. Consequently, it is capable of modeling time and improving work efficiency.4 Tests of smooth-shafts prove that the ways of"frequency change ratio"and"frequency rate of change"can identify damage by right of test equipment and conditions and verify this method in the validity of the actual project.5 this paper on the study work carried out summary of the study subject and the further research direction in this field are given.