Study On The Influence Of The Clearance Between Rudder Shaft And Adapter Shaft On The Modal Characteristics Of Rudder Surface

In this paper,based on the finite element contact algorithm and prestressed modal method,the modal characteristics of the rudder surface with clearance are studied.The simulation results are in good agreement with the experimental results,which makes the modal simulation of the rudder surface with clearance no longer depend on the experimental results.In addition,the modal characteristics of the rudder surface with clearance in thermal environment are simulated based on the proposed method.Firstly,a test piece was designed to simulate the boundary conditions of the clearance fit between the rudder shaft and the transfer shaft.Modal tests were carried out on the rudder surfaces in different states by hammering method,and the variation rules of modal parameters were obtained.Secondly,the spacing between the rudder shaft and the simulated adapter shaft under the action of preloading force was measured and the contact state between the two interfaces was analyzed: the rudder surface rotates counterclockwise under the action of preloading force,and contacts and extrudes with the simulated adapter shaft to form a face to face contact.With the decrease of assembly clearance and the increase of preload,the contact area between them presents an upward trend.Then,based on the measured contact state between the rudder shaft and the simulated transfer shaft,the model of the clearance contact was built based on the finite element contact algorithm,and the modal parameters of the rudder surface with clearance under the preload force were simulated by combining the prestressed modal method.The simulation results are in good agreement with the test results.Based on the variation rule of contact area between rudder shaft and simulated adapter shaft,it can be concluded that the natural frequency of the rudder surface with clearance is closely related to the contact area between the rudder surface and simulated adapter shaft.When the preload increases or the assembly clearance decreases,the contact area between the rudder shaft and the simulated converter shaft increases,and the supporting stiffness of the rudder shaft increases,eventually leading to the rise of the natural frequencies of the rudder surface.Finally,based on the above methods,the modal characteristics of the rudder surface with clearance under thermal conditions were studied,especially the influence of clearance changes caused by thermal expansion of the rudder shaft on the modal parameters of the rudder surface.The results show that: for the rudder surface with clearance,if only the thermal expansion of the rudder shaft is considered,with the increase of temperature,the clearance between the rudder shaft and the simulated adapter shaft gradually decreases,and the contact area between the two gradually increases,and the support stiffness of the simulated adapter shaft to the rudder surface increases,finally resulting in the rise of natural frequencies of all orders of the rudder surface with clearance.However,the change of material properties caused by temperature increase will greatly reduce the natural frequencies of rudder surfaces.By comparing the effects of the two on the frequency of the rudder surface with clearance,it can be found that for the Q235 low carbon steel rudder surface whose elastic modulus is more sensitive to temperature,the influence of material properties on the frequency of the rudder surface under thermal environment is far greater than that caused by the thermal expansion of the rudder shaft.