Vibro-Acoustic Analysis And Optimum Design Of Composite Structures With Viscoelastic Core

Composite plate and shell structures(with ribs)have excellent mechanical properties and are important bearing structures in civil and military fields such as modern aircraft,ships and submarines.With the rapid development of sonar detection technology,the requirement for the acoustic behavior of composite structures is getting higher and higher.Co-curing damping treatment is the most effective method to reduce vibration and noise of composite structures.However,the research on vibro-acoustic analysis and optimization design work are not comprehensive and in-depth,and finite element methods existed are not accurate and efficient enough to analyze highly anisotropic structures with significant shear effect.For this purpose,a finite element model with relatively few degrees of freedom and high accuracy is established in this paper.And a parametric study on the vibro-acoustic characteristics of composite(stiffened)structures with viscoelastic core was conducted,and a fast and efficient layout scheme of partial constrained layer damping is proposed.The main contents are as follows:(1)A hybrid finite element model is established with eight-noded continuum shell elements based on layerwise theory and eight-noded solid elements.Further,the infinite element method is used.Several numerical examples are solved to validate the approach.This method present is more accurate than the method based on equivalent single layer theory,and requires less computation than the models with three-dimensional solid elements discretized entirely.(2)The free vibration and damping analysis of composite stiffened sandwich plates is conducted,and the relationship between stiffeners parameters(types,dimensions and arragements)with model loss factors is established.Then,a design idea of sandwich composite stiffened plates with multi-index requirements(weight,natural frequency and loss factor)considering actual constraints is given.(3)The parametric effects on acoustic radiation of laminated laminates are comprehensively considered,such as orthogonal layers,angle layers,symmetry and the number of lamina layer.The results show that symmetry has a greater impact on the orthogonal layers than the angle layers.On this basis,the effects of the thickness of the facesheet,the thickness and position of the core and the ply angle adjacent to the damping layer are considered.The results show that excessive increase in the thickness of the damping layer is not conducive to the vibration and noise reduction,and it is more advantageous when the damping layer is far away from the middle plane of the plate.(4)Taking the typical panel of the command room envelope as an example,the relation among modal shapes,shear strain and denoising index is established.The results show that the maximum index occurs at the nodal line and borders.Then six schemes of partial constrained damping layer are presented according to the modal shapes.The results validate that the constrained damping layer layout schemes with high noise reduction efficiency can be designed rapidly according to the modal shapes.Finally,considering the simply supported boundary condition and clamped boundary condition,the quantitative relationship between different coverage and the vibro-acoustic evaluation values is established separately,which can be used as a guideline to design practical engineering structures.