Research On The Design Of The Test-bed For Ship Axle Diameter Optimization And The Assistant Judging Method

As an important part of ship power plant,the reliability of ship shafting is closely related to the safety of ship navigation.With the development of materials science and manufacturing technology,the fatigue strength and stiffness of ship shafting materials have been significantly improved,which makes it possible to optimize the shaft diameter of ships.To optimize the shaft diameter of a ship,the fatigue test should be carried out on the relevant test bench.At present,there are some research reports on shafting test-bed for different purposes,but there is no report on shafting test-bed for optimal verification.In this paper,the design and verification of the test-bed,the on-line crack monitoring method of fatigue test and so on are studied.Firstly,the calculation methods of alignment,strength and vibration of ship shafting are described.Then,the shaft system of the test rig is composed of three shaft sections: Propeller Shaft,Stern Shaft and intermediate shaft.Referring to the calculation method of ship shaft system,the design scheme of the test rig is calculated and analyzed,and the initial load and initial torque of the platform are determined.In order to solve the problem that the counter force of some bearings is negative in the calculation results,the design scheme is optimized by replacing several bearings of the bearing system platform with roller bearings.For the convenience of monitoring and construction of the shafting test-bed,the shaft with only one shaft diameter is set up,and the effect of the initial scheme is achieved by changing the load.In order to solve the problem of lack of on-line crack condition monitoring method and judgement knowledge in fatigue test,the on-line monitoring of the platform crack on the bench is realized by monitoring the vibration feedback of the shaft before and after the crack is prodced through comprehensive analysis of the existing crack detection method and combining with the demand of the fatigue resistance test of the shafting bench.In order to verify the feasibility of the method,the numerical simulation analysis of the shafting on a small test bench in the laboratory shows that the difference of vibration displacement of the shafting before and after a certain crack is obvious,which can be used as a basis for crack detection.Then,on the test-bed,the results of vibration displacement monitoring before and after the crack of shafting are found to be consistent with the simulation results,which verifies the feasibility of the method.Based on the idea of digital twin,the dangerous section of shafting is determined by the numerical simulation calculation of the test-bed of shaft diameter optimization.When the cracks of different sizes are produced at the dangerous section,the displacement in the specific parts of the shafting,the natural frequency changes of the shafting,and the response changes of the shafting under different external excitation signals are analyzed.The results show that the radial vibration displacement and the natural frequency of the shafting do not change obviously before and after the shafting crack,so it is not convenient to carry out on-line monitoring.When the crack shaft and the intact shaft are subjected to the external excitation load,the difference of the feedback force and the feedback displacement is obvious,and the optimum position of the external excitation is determined to be far from the testing point,and the feedback difference between the different state shafts increases when the external excitation load increases appropriately.These conclusions provide the corresponding decision knowledge for the fatigue crack state identification of the real axle diameter optimization test-bed,and provide the reference for the condition judgment of the test-bed program.