The Modeling Method And Characteristic Analysis For Rotary Composite Laminated Plate And Acoustic Cavity Coupled System

Because of the high strength,fatigue resistance,corrosion preventive and designability,composite laminated structures have been widely used in defense and civil industries,such as aerospace and naval vessels.Due to the special working environment,composite laminated structures are often subjected to complex dynamic loads,which will cause mechanical vibration.The mechanical vibration will interact with the surrounding fluid and become the main noise source.Therefore,it is of great significance to study the vibro-acoustic characteristics of the coupled system consisted of the composite laminated plates and the surrounding acoustic field.However,there are few research results on the vibro-acoustic characteristics of the coupling system mentioned above,and the influence of elastic boundary or impedance boundary on vibro-acoustic characteristics is seldom involved.Based on this,a simplified plate theory and an improved Fourier-Ritz method are presented in this paper to study the structural domain,acoustical domain and structure-acoustic coupling system step by step.The main research work is as follows:Based on the simplified plate theory and an improved Fourier-Ritz method,a technical route for solving the vibro-acoustic characteristics of the composite laminated plate-cavity coupling system with complex elastic boundary conditions is established.Combined with classical plate theory and first-order shear deformation theory,the basic definition of the simplified plate theory is given to solve the vibration characteristics of the thin-to-moderately thick composite plates and shells.A 2D improved Fourier series method is presented to construct the displacement admissible function of the plates and shells under elastic boundary conditions,while a 3D improved Fourier series method is presented to construct the sound pressure admissible function of the enclosures under general impendence boundary conditions.Some numerical examples about the coupled system consisted of a composite laminated rectangular plate and a 3D acoustic cavity are carried out,which validates the practicability of the vibro-acoustic an alytical model established in this paper.According to the simplified plate theory and the 2D improved Fourier-Ritz method,a unified analytical model for vibration characteristics of the rotating composite laminated plates is established.On the basis of the correlation between geometric parameters and elastic mechanics of annular sector,circular sector,annular and circular plate structures,a unified expression of displacement function and energy equation is given.The elastic boundary potential energy and closed loop coupled boundary potential energy of rotating composite laminated plates are constructed by the artificial virtual spring technology,which will be replaced into the energy functional.By using Rayleigh-Ritz energy technique,the solving equations of vibration characteristics are obtained,and the natural characteristics of the composite laminated plates are achieved finally.Besides,the forced response of the composite laminated plates is further studied by applying a transverse harmonic point force on the plate's surface.Through a large number of numerical examples and data comparison,the fast convergence,feasibility and calculation accuracy of the simplified plate theory and the improved Fourier-Ritz method in analyzing the rotating composite laminated plates are verified.According to the fundamental of the acoustics and the 3D improved Fourier-Ritz method,a unified analytical model for sound field characteristics of the rotating conical,cylindrical and spherical enclosures is established.Based on the correlation between geometric parameters of conical,cylindrical and spherical acoustic cavities,a basic unit of the rotational hyperbolic enclosure is established,which could be used to describe the three kinds of enclosures at the same time.The 3D improved Fourier series method is used to construct the sound pressure admissible function of the enclosures.The 3D sound field problem is transformed into a solid mechanics problem,and the Lagrange energy equation of a rotating closed acoustic cavity is built.When the acoustic cavity has impendence walls,the impedance dissipation potential energy produced by these walls should be considered.When the rotation angle of the acoustic cavity is 2?,the left and right walls will be coupled together to form a closed loop cavity.In order to satisfy the continuity condition of sound pressure and particle vibration velocity,the coupling potential energy needs to be established and added to the energy functional of the acoustic cavity.Finally,the Rayleigh-Ritz energy technique is used to extremum the energy equation,and the solution equation of sound field characteristics could be easily obtained.By comparing the results obtained by the present method and those obtained by the finite element simulation software,the fast convergence and correctness of the 3D improved Fourier-Ritz method for the solution of the rotational closed acoustic cavity are verified.Based on the vibration characteristics analysis of the rotating composite laminated plates and the sound field characteristics analysis of the rotating enclosures,a unified analytical model for the vibro-acoustic study of their coupled system under complex boundary conditions is established.The structure-acoustic coupling potential energy generated by the interaction between the flexible laminated plate and the acoustic cavity at the interface is added into the energy functional of the structure domain and the acoustic domain,and the energy functional of the plate-cavity coupling system is obtained.Based on the energy variation principle,a set of nonlinear vibro-acoustic coupling equations is obtained and linearized to facilitate the final solution.Besides,by introducing external structural force and internal point sound source,the coupling mechanism between the flexible plate and the acoustic cavity is explained thoroughly from two aspects of "field-sound-field" and"sound-field-sound".In numerical examples,the effects of geometric parameters,material parameters,elastic boundary conditions,impendence boundary conditions and acoustic medium on the composite laminated plate-cavity coupled system are studied in detail.By comparing the results calculated by the classical plate theory,the simplified plate theory,the finite element method and the first-order shear deformation theory,the applicability and accuracy of the simplified plate theory in analyzing the composite laminated plate-cavity coupling system are verified.Finally,the experimental work will be carried out,which includes the vibration characteristics of rotating plates,sound pressure response prediction of cylindrical enclosed cavity and vibro-acoustic response prediction of the coupled system.The isotropic material is a special form of composite laminated material and is easier to obtain,so the filling materials of the plate structure used in the experiment are all isotropic materials to simply verify the correctness of the theoretical analysis model of the rotating plate structure and its plate-cavity coupling system.According to the contents of the experiment,the corresponding experimental principle is worked out and a feasible experimental platform is built.The experimental results are compared with the theoretical results to demonstrate the feasibility of the proposed analytical method and the established analytical model.