Vibrational And Acoustic Prediction Method Of Laminated Plates And Shells

Composite plates and shells have wide applications in aeronautic and astronautic,marine engineering. Study on the vibrational and acoustic characteristics is critical todesigning new ships and submarines. The present research contents are in the contextof the vibrational and acoustic behavior of submarine. Structural and acousticcharacteristics of five kinds of plates and shells are analyzed, such as laminatedcomposite plates with two sets of stiffeners, constrained layer damping cylindricalshells with ring stiffeners, laminated composite shells with multiple stiffeners,laminated conical shells and circular cylindrical shells with an axial rectangle plate.Laminated composite plate with stiffeners and laminated composite shells withmultiple stiffeners can be used to investigate acoustic radiation from underwatervehicles. Constrained layer damping cylindrical shell with ring stiffeners can beemployed to study acoustic radiation from submarine and torpedo hulls. Laminatedconical shell can be used to explore sound radiation from the stern of submarine.Circular cylindrical shells with an axial rectangle plate can be employed to examineacoustic radiation from submarine with the rib plate or complicated long base. Thepresent studies are given as follows:(1) Sound radiation from shear deformable stiffened laminated plates is studiedtheoretically. The equations of motion for the composite laminated plate are derivedon the basis of the first-order shear deformation plate theory. Two sets of parallelstiffeners interact with the laminated plate only through the normal line forces. Byusing the Fourier wavenumber transform and the stationary phase method, thefar-field sound pressure is described analytically. Sound pressure given by thefirst-order shear deformation plate theory and the classical thin plate theory iscompared, and the differences of sound pressure are shown in the high frequencyrange for an isotropic plate. Sound pressure and the transverse displacement spectraare presented to illustrate the effects of force location, stiffeners and angle-ply layers.Sound radiation from symmetric and antisymmetric composite plates with multiple loadings is investigated and the acoustic power of the stiffened laminated cylindricalshell is also presented.(2) Acoustic radiation from cylindrical shells stiffened by two sets of rings, withconstrained layer damping, is investigated theoretically. The governing equations ofmotion for the cylindrical shell with constrained layer damping are derived on thebasis of Sanders thin shell theory. Two sets of rings interact with the host cylindricalshell only through the normal line forces. The solutions are derived in thewavenumber domain and the stationary phase method is used to find an analyticalexpression of the far-field sound pressure. The effects of the viscoelastic material core,constrained layer and multiple loadings on sound pressure are demonstrated. Thehelical wave spectra of sound pressure and the radial displacement clearly show thevibration and acoustic characteristics of the stiffened cylindrical shell withconstrained layer damping. Constrained layer damping can effectively suppress theradial vibration and reduce acoustic radiation.(3) Acoustic radiation from shear deformable laminated cylindrical shells withmultiple periodic stiffeners is explored theoretically. Two sets of rings and one set ofcircumferential stringers are uniformly distributed along the inner surface of thelaminated cylindrical shell in the axial and circumferential directions. These structuresare widely used for the construction of the hulls for underwater vehicles. Two kindsof models are proposed to investigate acoustic radiation from stiffened laminatedcylindrical shells in the present work. One is a simplified method and only employedin the low frequency range in a condition of dense stringers. The other used in allfrequency range is a coupled model and needs to be solved numerically. It transpiresthat the axial wavenumber conversion is caused by the rings and the circumferentialwavenumber conversion is produced by the stringers, which is clearly identified bythe helical wave spectra of the radial displacement and sound pressure. Therefore, it isunderstandable that the axial waves and the circumferential waves would bemodulated, and the radial displacement and sound pressure would be suppressed oncethe cylindrical shell is reinforced by two sets of rings and circumferential stringers.The helical wave spectra of the radial displacement and the surface sound pressure for the antisymmetric laminated cylindrical shell just show these phenomena. Theproperly designed cylindrical shell with multiple periodic stiffeners will reduce thevibration and acoustic radiation. Above the ring frequency, the characteristic in thewavenumber domain of far-field acoustic radiation from a large cylindrical shell isconfined by an ellipse and only the waves inside the ellipse can radiate sound into thefar field. The circumferencial sringers can reduce the acoustic power and the inputpower of the laminated cylindrical shell, but the energy transformation efficiencyfrom the input power to the acoustic power is increased to great extent.(4) A model of acoustic radiation from conical shells is explored in detail and theequations of motion for the conical shell are described on the basis ofReissner-Naghdi thin shell theory. Fluid loadings acting on the conical shell aretackled by the approximation of dividing the laminated conical shell into smallcylindrical segments. The displacement field of conical shell is solved by using thewave propagation approach and Galerkin method. The far-field sound pressure isfound in the wavenumber domain by the superposition of acoustic radiation from eachcylinder with infinite circular cylindrical baffles at the two ends. Vibration andacoustic characteristics of laminated cone are studied.(5) A model of acoustic radiation from circular cylindrical shell with an axialrectangle plate is presented in the context of studying acoustic radiation fromsubmarine with a rib plate or long base panel. Transverse motion of the isotropicrectangle plate is described by using the classical thin plate theory and the equationsof in-plane motion for the plate are expressed on the basis of the two-dimensinalelastic theory. The reactive forces of the plate acting on the cylindrical shell aredetermined by using the displacements of the cylindrical shell. Due to the structuralnon-uniformity in the circumferential direction, the circumferential waves are coupled.The coupling systematic equations are solved in the wavenumber domain, and thenthe displacement field of the structure is obtained. The effects of the rectangle plate onthe vibrational and acoustic behavior of the cylindrical shell are studied under radialand axial loadings.In the end, the further studies of the structural acoustics for the plates and shellsare summarized and the future key points of the researches are pointed out.