Dispersion equation of double shell-fluid coupled system

The dispersion behaviour of the double shell-fluid system,which consists of two thin concentric cylindrical elastic shells (hereafter referred to as a double shell simply) coupled by the entrained annular fluid,is a fundamental for investigation of it's vibroacoustical characteristics.Based on Flügge's infinite shell equation,the sound wave equation for the fluid field,and boundary conditions at the fluid-structure interfaces,the dispersion equation for the system is deduced and a corresponding numerical example is given in the paper