The Analysis Of Loads And Structural Strength For The Shaft Bracket

At home and abroad in recent years, the study of shaft bracket mainly focused on processing and installation technology and vibration characteristics, which can effectively avoid the resonance problem of the shaft bracket system. However, the study of yield strength of shaft bracket has been still stayed in the 90s. The study of fatigue strength of the shaft bracket has been still in the blank. Based on a large ship as an example, the load and the structure strength of the shaft bracket was studied. The main contents included the following aspects:1) According to the structure of the shaft bracket and working environment, analyzed and summarized the load of the shaft bracket. Outside load of the shaft bracket that lead to yield failure is the unbalanced force (centrifugal force and eccentric thrust), which is caused by the destruction of the propeller by accident, or the force that made the stern shaft broken. The force that results in fatigue damage of the shaft bracket contains four: screw rotation causes the propeller exciting force; the wave loads when the ship sails in waves indirectly affect the shaft bracket; the inertia force of the propeller, shaft, and shaft bracket caused by accelerating motion; the shaft bracket's own movements lead to the change of the local hydrodynamic.2) Summarized the traditional statics method of the yield stress calculation of the shaft bracket, and pointed out the faults of the standard method, analyzed the causes of computing misalignment, compared and demonstrated the calculation results with the finite element method and the specification method.3) Various Technical problem of the calculation of stern shaft bracket fatigue damage is studied and solved in this paper. Loads are divided into high frequency and low frequency according to their characteristics. High frequency loads are propeller exciting force, while low frequency loads are wave loads and local fatigue hydrodynamic. Firstly, the stern shaft bracket damage under the action of both high and low frequency loads are studied separately.The empirical formula is rationally used in the calculation of propeller exciting force. In order to calculate the exciting force of the stern shaft bracket fatigue damage, Patran software is used in dynamic analysis to obtain the stress calendar. Time domain fatigue damage calculation method of shaft bracket under low frequency loads is studied. The stern shaft bracket stress time history method and steps under the combined action of irregular wave loads and local fatigue hydrodynamic are detailed described. And the fatigue damage was calculated by rain flow counting and linear cumulative damage theory. Finally, a set of effective calculation method of the fatigue of stern shaft bracket is accordingly developed.