Study On Vibration Characteristics Of Laminated Composite Double-layer Plate And Shell Coupling Structures

The quantitative acoustic design level of underwater vehicle is very important to enhance survival ability and combat ability,and accurate dynamic characteristic analysis provides essential theoretical basis and key technical support for the quantitative acoustic design of underwater vehicle structures.The existing numerical simulation technology and ship experiment have many difficulties in the dynamic analysis of complex ship models,including low calculation efficiency,difficult in medium and high frequency prediction,high cost and so on.Research on rapid modeling method and strategy remains a challenging in dynamic performance evaluation of ship structures.Using composite materials has become a trend embodying progressiveness of an underwater vehicle.Therefore,establishing a reliable and high-efficient model of laminated double-layer plate and shell coupling structure has an important theoretical significance and practice value for improving the level of ship quantitative acoustic design,which can provide a reference for the design of the laminated double-layer shell underwater vehicles.In our research,the laminated double-layer underwater vehicle is selected as the research object,the structural dynamics modeling of the deck with raft and vibration isolator,double shell structure of bow,midship and stern of the hull,typical cabin structure involving the deck,complete hull complex shell and plate coupling structure is established to carry out the dynamic characteristics research.Specifically,the main research contents are as following:(1)The displacement functions are established based on the spectro-geometric method(SGM)to study the internal mechanism between the selection of auxiliary functions and the adaptability of boundary conditions.Then,according to the SGM,an analytical model of a laminated double-layer plate including a raft and isolator system is established.At the same time,the three-dimensional damping vibration isolator and elastic raft frame structure considering the damping effect are used to equivalently simulate the floating raft vibration reduction system.Finally,the equations of vibration characteristics of laminated double-layer plate systems are obtained by the Rayleigh-Ritz method.Through the free and steady-state response analysis of the double-layer plate structure and comparing it with the results from finite element calculation,the convergence speed and calculation accuracy of the proposed method and the established model are verified.On this basis,parametric researches are further carried out to discuss the effects of coupling relationship,material parameters and geometric parameters on the dynamic characteristics of the double-layer plate structure.(2)According to the structure of the bow,middle and stern of the underwater vehicle,a unified mathematical model by using the SGM is established for the dynamic characteristics analysis of laminated double-layer cylindrical/conical/spherical shell coupling structure.The inner and outer shells are joined by numerous annular plates,which are distributed nonuniformly.Considering the symmetry of the rotating structure of the cylinder,cone,spherical shell and annular plate,the hybrid expansion form of spectral geometric series and trigonometric series are adopted to uniformly set the displacement allowable function of the structure.Then,linear springs and rotary springs are introduced at the coupling positions according to the coordination conditions of forces and displacements between the substructures.Based on both the dynamic model of laminated double-layer cylindrical/conical/spherical shell structure and laminated double-layer plate including elastic floating raft damping system,the theoretical dynamic analysis model of a laminated double-layer cylindrical shells and double rectangular plates coupling structure is established according to the typical midship cabin of the double-layer hull.By comparing with both the existing literature and finite element results,the correctness and reliability of the established model are verified.Subsequently,the effect of various parameters on the vibration characteristics of the laminated double shell coupling structure is discussed in detail and a new opinion for the design of laminated ship cabins is provided.(3)Taking the complete double shell hull structure as the research object,the dynamic analysis model for the complex rotating shell and plate coupling structure is established,which includes double conical shells,double cylindrical shells,double spherical shells,annular plates and a rectangular deck.Furthermore,the displacement components of each substructure are constructed in a unified and efficient way using bidirectional two-dimensional spectral geometric series.Meanwhile,two types of springs are introduced at the coupling positions among the substructures to ensure the displacement continuity conditions and combination constraint relations of each substructure.Benefiting from the convenience of the SGM in establishing displacement function and handling coupling boundary,this proposed model fully reflects the advantages of dealing with complex coupling models.Finally,the performance in terms of both convergence and accuracy of the proposed model is verified through numerical examples.Besides,the influence of substructure coupling parameters,geometric parameters and material parameters on the vibration characteristics of the complex coupling structure for the laminated rotating shell structure is discussed and a theoretical basis for the rapid evaluation of the dynamic performance of underwater vehicles is provided.(4)Experimental research is carried out to verify the proposed models established in our research.For the main purpose to verify the mechanism of the proposed theoretical model,the isotropic rectangular plate structure,double-layer cylinder/cone/spherical shell,cylindrical shell and rectangular plate coupling structure and double-layer conical-cylindrical-spherical shell complex coupling structure,respectively,are taken as experimental objects by the multipoint excitation single point/multi-point response method to carry out structural free vibration and response vibration experiments.The proposed theoretical model and theory are demonstrated through the experiments and show good agreement within the allowable error.