Complex Modal Analysis And Harmonic Analysis Of Viscoelastic Damped Structures

Viscoelastic damping material is a generally used method in the sound and noise vibration reduction field.It can be applied in the engineering fields such as aerospace,shipbuilding and vehicles,and provided a valid method of vibration reduction.This paper mainly researched on the modal analysis and harmonic analysis of viscoelastic structures.This thesis introduced the element building method based on Mindlin plate theory.This paper used MATLAB software to program to solve the laminate element problem,and the results are compared to that calculated by Ansys and proved its validity in calculating laminated structures.This thesis also demonstrated the basic concepts and mechanical characteristics of viscoelastic damping material.This paper provided several iteration methods to solve the eigenvalue problem.This paper applied iteration method into the FEM software Ansys,proved the validity of the method by numerical simulation.This thesis summed-up the characteristic of and difference between real modes and complex modes,and introduced the concepts of modal complexity to demonstrate the complexity of modes,and calculated the characteristics of practical structures.According to the theories above,this paper analyzed the damping structures.This paper demonstrated that when viscoelastic frequency-dependent damping is applied,the natural frequency and damping ratio are both higher than that of Rayleigh damping,and modal complexity can be calculated.In the harmonic analysis,the amplitude of reference point is smaller than that of Rayleigh damping,which shows that the vibration reduction effect of complex mode is better than Rayleigh real mode.By analyzing the underwater cylinder,free damping yields higher natural frequency,and the mean damping ratio of free and constrained damping are similar.With force exerted on the cylinder,the amplitude of free damping tend to be smoother.These calculations shows the validity of the combination of finite element method and iteration method,analyzed the influence of damping types to the dynamic characteristics,and the influence of viscoelastic damping types to the vibration reduction influence.The researches provided reference to the numerical computation of viscoelastic structures.