The Method Of Rational Alignment And Load Measurement Technology Of Propulsion Shafting

The stress state of the propulsion shafting is very important to the safe operation of the ship,and the shafting alignment method is to calculate the elevation of each bearing so that the stress state of the shafting is in a reasonable range,at the same time,because the additional dynamic excitation during the operation of the shafting has a great influence on the bearing load,it is of great significance to study the static and dynamic alignment method of the shafting.When the shafting alignment is not good,it may lead to shafting vibration,excessive load and other problems.In order to test the quality of shafting alignment and realize the load monitoring and control during shafting operation,an efficient and accurate load measurement technology is needed to determine the bearing force and provide data reference for shafting alignment optimization.Based on the above two requirements,this paper studies the static and dynamic rational alignment method and bearing load measurement technology respectively.The main contents and conclusions are as follows:（1）The rational alignment analysis is carried out under the static condition of the shafting.Based on the finite element method,a rational alignment model is established for the shafting test bench.Through the static calculation,the influence law of the elevation of the fore and aft bearings of the stern tube on the bearing reaction force,the bending moment of the shaft section and the rotation angle is analyzed,which provides a reference for improving the alignment quality of the shaft system.Finally,the load influence coefficient matrix and bending moment influence coefficient matrix of each bearing are obtained.（2）The dynamic alignment modeling method of shafting with oil film stiffness is established.Based on the two-dimensional Reynolds equation,the oil film characteristics of the stern tube aft bearing of the test bench are calculated,the influence of different rotational speed and dynamic viscosity of oil film on the oil film stiffness of the bearing is analyzed,the composite form of oil film stiffness and bearing stiffness is given,and the dynamic alignment model of shafting considering the influence of oil film stiffness is established.Based on the model,and the influence laws of different bearing elevation,rotational speeds and propeller unbalance forces on the bearing dynamic reaction force are calculated through the modal truncation method.The results show that the stiffness of oil film decreases nonlinearly with the increase of rotational speed and dynamic viscosity.Both rotational speed and bearing displacement will greatly change the amplitude of dynamic support reaction force,and propeller unbalance force has little effect on support reaction force.（3）The calculation method of the bearing load backstepping is put forward and a set of load measurement system is designed.Based on the relationship between bearing elevation,bending moment of the shaft section and the reaction force of the bearing,this paper proposes the calculation method of the bearing load backstepping.This method reverses the reaction force of the bearing by measuring the strain of the shaft section.A set of load measurement system is designed,including the strain measurement system under the static condition of the shafting and the wireless telemetry system under the rotating condition.A force measuring plate is arranged between the aft bearing of the stern tube and the base to directly measure the reaction force,which is verified by comparison with the reaction force derived from strain inversion.（4）The static and dynamic tests of bearing load measurement are carried out for the shafting test bench.The shafting strain at different bearing elevation and different rotating speeds is measured,the bearing reaction force under this working condition is obtained based on the load backcalculation algorithm,and the bearing load also be measured by using the force measuring plate.The results show that the error between the bearing load measurement method proposed in this paper and direct measurement is about 5% when the shafting is static and about 15% when the shafting is running,which proves the accuracy of the measurement method.