Analysis Of Testing Method For Dynamic Loads Of The Propulsion Shafting System

The propulsion shafting system of warships bears complicated load and stress while sailing.Well load distribution is of great importance to ship's long-term and safe voyage.In this paper,a wireless telemetry system based on strain gages was designed to measure the dynamic loads of the propulsion shafting system in different shaft alignment states.On the basis of the strain in different sections measured and one-support calculation model,the real loads of different bearings can be calculated.When the shaft runs,bearing reaction suffers effect from horizontal exciting force,hull deformation,shaft vibration.In the data processing that follows,dynamic effect will be removed.Thus static bearing reaction derived from gravity of shaft and bearing elevation will be calculated.This paper first analyzes method and principle of the static and dynamic bearing load.The strain guage method first collects strain signal of the shaft section,then solves bearing load based on the signal separation technology and load calculation model.For jacking method,first we need to draw the jacking curve.Jacking coefficent will be calculated by the Three-Equation method.Results of the jacking test will verify veracity of the strain guage method.Taking a certain warship shaft as a model,an experiment table with three bearings was designed and processed.Two bearings can be elevated.To simulate bending horizontal exciting force of the propeller,a heavy stuff was planted on the propeller.Three testing system was planted on the shaft: modal test system gets shaft bending mode shape and frequency;wireless telemetry system with strain gages collects dynamic strain of the shaft section;vortex flow transducer monitors vibration signal of the testing point;Jacing system tests static bearing load.Modal test was carried out on the experiment table and mode frequency,shape and parameters was got.Then finite element model was used to anlyze bearing load,shaft moment in different shaft alignment states.Results showed that increment of one certain bearing reaction satisfies linear superposition of the effect of all bearing elevation.Under effect of the unbalanced weight,bearing load,deflection of the testing point,shaft moment was calculated.The results would be used in the test that followed.When the shaft was static,rotated and rotated with the unbalanced weight,bearing elevation and rotating speed was adjusted,then test of bearing load was carried out.Testing results of the vortex flow transducer was similar with the simulation results,thus veracity of the simulation model was verified.Dynamic strain deriving from the shaft vibration and unbalanced weight was separated for the strain signal and bearing load was calculated with the calculation model.When the shaft speed was 60/min,error between the jacking method and the strain guage method was 14%,thus reliability and veracity of the testing method was verified.At last,static feature and dynamic feature under different shaft alignment states was analyzed.The results served as theoretical basis for the test in the warship.Also,it was of great importance to optmize shaft alignment states.