Thank you for your reply. I want to know that, are these lambda values which are given along with the frequency relation such as 4.73, 7.85, 10.99 etc. valid only for the isotropic beam or pipe? Since I am considering the composite pipe.
There some analytical solutions in literature, similar to MrPedrazzi's response. Keypoint is that which precision level and assumptions done especially for fluid and support conditions. Analytical solutions and fem solutions may varry to highly diff. Linear and non-lin. viewpoints may change to everything. it better to specify your solution tech, and assuptions.