Vibration Analysis Of Propulsion Shafting Based On Spectral Geometric Series Description Under Hull Structure Constraints

When the submarine is sailing underwater,the propeller rotation and flow field disturbance will cause the propulsion shafting to vibrate.After transmission,the vibration will have an impact on the safety and health of equipment and personnel.In addition,the vibration will also cause radiation noise,damage the stealth performance of submarines,and weaken the marine combat capability.In order to meet the objective requirements of vibration and noise reduction in practical engineering,it is necessary to explore a more accurate and efficient dynamic modeling and performance calculation method for propulsion shafting system,and conduct in-depth and mechanical analysis of its vibration performance.In this paper,the energy method will be used as the research means to carry out theoretical modeling research,and the vibration performance of the propulsion shafting system considering the influence of the hull structure will be calculated and analyzed.The main research contents include:Firstly,the principle of spectral geometry method is introduced,and the advantage of its series form as the displacement function of structural vibration is clarified.The advantages and disadvantages of two modeling methods based on differential control equation and energy variational principle are compared,and the research method of spectral geometry combined with energy principle is determined.An example is given to illustrate how to decompose a complex structure into several elastic supported / coupled substructures to establish a vibration calculation model,which shows the accuracy and universality of this method.Then,the propulsion shafting is regarded as a one-dimensional beam structure,and the influence of the simplified characteristics of the bearing system is mainly considered.The main structure of the hull is treated as a rigid foundation,and the vibration calculation model of the ship shafting is established by using the spectral geometric series and the energy method.Based on this model,combined with the liquid film pressure distribution of the stern bearing,the equivalent form of the stern bearing stiffness and the influence of the liquid film pressure distribution on the lateral vibration of the shafting are discussed,and the influence of the rotating speed on the response of the shafting under the lateral excitation of the propeller is analyzed.Furthermore,considering the bending deformation of shafting caused by gravity,a plane curved beam vibration calculation model considering the changes of curvature and other parameters is established.Then,in order to consider the influence of shafting support structure hull vibration characteristics,based on the unified modeling idea in this paper,the main structure of the hull is expanded from one-dimensional structure to three-dimensional structure,and the main structure of the hull is regarded as a plate shell coupling structure,and an accurate and efficient low-frequency vibration model of the complex plate shell coupling structure is obtained.The effects of bulkheads,decks and stiffeners on the vibration characteristics of the hull structure are studied by numerical examples.Finally,the shaft boat system under the slipway state is reasonably simplified,and the beam cylindrical shell / conical column composite shell structure is studied.Combined with the previous work,the vibration calculation model of the coupling system is established.The correctness of the calculation model is verified by comparing with the calculation results of the finite element software.Using this model,the vibration transmission law is analyzed,and the effects of the shell structure and the stiffness of the beam shell coupling spring set on the vibration characteristics of the coupling system are clarified.The results show that for the low-frequency vibration calculation model of the shaft boat coupling system in which the coupling relationship of the subsystem is established in the point-to-point correspondence mode and the coupling effect is expressed by the corresponding coupling spring,the vibration modes can be divided into the shaft boat decoupling mode and the shaft boat coupling mode according to whether the hull subsystem participates in the vibration or not.For the decoupled mode of shaft boat,the modal vibration mode is that the hull is a rigid foundation and the shafting is in the form of bending vibration.Combined with the previous contents,it can be seen that this kind of modal vibration characteristics are determined by the simplified characteristics of the coupling system(such as the location of the simplified coupling point of the bearing,the simplified dynamic parameters of the coupling system,etc.)and the structural characteristics of the propulsion shafting itself;At the same time,for the shaft boat coupling mode that focuses on the shaft boat coupling effect,the vibration characteristics of the coupling system are obviously affected by the structural dynamic characteristics of the hull subsystem.It is necessary to establish an accurate calculation model of the vibration performance of the hull structure first,and take the dynamic characteristics of the hull structure into consideration in the analysis of the vibration performance of the propulsion shafting.This paper presents the theoretical solution method of the propulsion shafting vibration problem under the constraints of the hull structure from simple to deep,from easy to difficult,establishes a unified,efficient and accurate calculation and analysis model of the propulsion shafting vibration performance that meets different constraints,and systematically carries out the vibration mechanism research of the shafting hull coupling system,enriches the theoretical system in this field,and lays a foundation for achieving the goal of vibration reduction and noise reduction.