Vibro-acoustic Characteristics Of Stiffened Laminated Plates And Shells Baesed On Different Theoretical Model

Composite laminated plate and shell have been recognized as the structure with attractive multifunctional properties,such as lightweight,high specific stiffness and excellent energy absorption capability,etc.They have been widely used in aerospace,shipbuilding and marine engineering and other applications.But little attention have been paid to theoretical research on the vibration and sound radiation of the periodically stiffened composite laminated plate and shell structures.The engineering background of the present research came from the moving submarine.Theoretical methods used to predict vibration and sound radiation of three kinds of typical submarine structures in uniform flow are given,such as single and double laminated plate with periodic stiffeners,and periodically stiffened laminated shell.Numerical simulation and model tests are used to verify the accuracy and applicability of the present theoretical model.The purpose of this paper is to provide certain theoretical support for acoustic design of typical submarine structures.The main content of present work is arranged as following.In the first part,the related research about structural and acoustic characteristics of periodically stiffened plates and shells was summarized in three main aspects,i.e.,fluid state,plate and shell theories and structural style.Based on the review,the weaknesses in the recent theoretical prediction on underwater vibration and sound radiation of submarine structures in moving state are presented,and the outline of further research is also determined.Taking an infinite plate in uniform flow as the research object,and based on the convected wave equation and boundary conditions,the basic procedure is carried out to solve vibration and acoustic responses of the infinite forced plate in wavenumber domain,by using the Fourier transform method and the stationary phase method.The impulse function(?)and Poisson summation formula are applied to deal with the discrete distribution of line force and line moment,which are the reactive force and moment exerted by the stiffeners on the plate and obtained by fully analyzing the forced bending and torsion movement of the stiffeners.Using the same methodology as the infinite forced plate,the vibro-acoustic coupling model of the infinite parallel stiffened plate in uniform flow is established,then a solving expression,which can be numerically solved by truncating it to finite insofar as the solution converges,having a form of matrix,is gained.The validation of the present theoretical model is performed by comparing the present model calculating results with numerical simulation results,and then with the existing theoretical model predictions.The influence of different system parameters on vibration and sound radiation characteristics is studied by employing far field sound pressure and the transverse displacement spectra.The case that the plate is isotropic or orthotropic materials and the stiffeners are orthogonal distribution with equal distance,a general form vibro-acoustic coupling model of infinite orthogonally stiffened plate in unilform flow is established,by introducing the concepts of generalized dynamic stiffness and dynamic flexibility.For an isotropic skin plate,firstly,the numerical truncation method is used to calculate far field sound pressure of infinite orthogonally stiffened plate;secondly,the underwater sound pressure of finite orthogonally stiffened plate are measured by model tests;at last by comparing the present model predictions with model test results,and then with previously published data,it can be seen that results from the present model and the model tests has a corresponding trend,and the former one agrees well with the existing theoretical model.Through the above comparision,the present theoretical model is verified.Far field sound pressure and the transverse displacement spectra clearly show the vibro-acoustic coupling characteristics of the infinite orthogonally stiffened plate.Based on the first-order shear deformation theory(FSDT)and applying the generalized dynamic stiffness and dynamic flexibility to deal with composite laminated plate,a general form of vibrao-acoustic governing equations of orthogonally stiffened composite laminated plate is derived.Then taking the same procedure as previous chapter to establish theoretical model,a general form of vibro-acoustic coupling model of orthogonally stiffened composite laminated plate is established.Consequently,the analytical expression of the vibration response and radiated sound pressure is found.For an isotropic skin plate,sound pressure calculated by the three different plate theories(FSDT,the classical laminated plate theory(CLPT)and the classical thin plate theory(CTPT))is compared.The differences of sound pressure between the former and the latter two theories are shown in high frequency range.The influence of the different system parameters on the vibrao-acoustic characteristics of the structure is studied by carrying on the numerical analysis.For theoretical modeling of vibro-acoustic response of a double plate structure with outside laminated plate and parallel periodic placed studs,the approximation"mass-spring-mass" system is used to simulate the effects of reactive force and moment generated by studs on inside and outside plates.Firstly,a simple smeared theoretical model is established,by assuming that the equivalent translational force,torsion moment and lumped mass are distributed uniformly on inside and outside plates.Secondly,the equivalent translational force,torsion moment and lumped mass are distributed discretely on inside and outside plates with equal distance,a more accurate theoretical model called periodic model is formed,considering the periodic nature of the present double plate structure,and applying the Poisson summation formula.The solution of the above two models to the laminated plate is the same as last chapter,so they are both general forms of theoretical models.On the basis of these,the influence of different system parameters is studied through numerical analysis.For the orthogonally stiffened double plate structure with composite laminated inside and outside plates,the effect of the orthogonal studs is approximately replaced by discretely distributed translational spring,rotational spring and lumped mass.Based on the work in last chapter,a general form of vibro-acoustic coupling model of orthogonally stiffened double plate structure is established.By comparing the sound radiation results of all metal orthogonally stiffened sandwich structure calculated by the present model with that of an existing theoretical model,the rationality of the way that deals with the effect of orthogonal studs is checked.Then the influence of different system parameters on vibration and sound radiation characteristics is investigated systematically.Based on the first-order shear deformation theory,and applying the convected wave equation and boundary conditions in the cylindrical coordinate system,a theoretical model of sound radiation from composite laminated cylindrical shell with periodic ring ribs in uniform flow is developed.The periodic ring ribs are coupled with the cylindrical shell though normal forces and moments.The solution expression is given in a matrix by using Fourier transform method.The analytical formulation of the far field radiation sound pressure is found by employing the stationary phase method in wavenumber domain.The present theoretical model is validated by comparision of the sound pressure calculated by different shell theories and the contrastion of different ways to deal with ring ribs.Some suggestions used to reduce noise of ribbed cylinder shell are obtained though parameter study.Finally,the vibration and sound radiation of periodically stiffened plates and shells are summarized,and the key points of the future research are pointed out.