[ppy1111]

I ran a 3d modal analysis, modelling it as a 3d solid using hexahedral mesh, in Ansys to obtain natural frequency of a pipe, and compare the values from my analytical solution.

When I compared it to my analytical solution my I have .5% error on 1st mode, 3.4%, 7.8%, 13.7% and 20% on mode 2, 3, 4 and 5 repectively. in this case the L/D ratio of the pipe is 18

So I decided to increase the L/D ratio of the pipe to see if natural frequency values would match at higher L/D ratio. So I increase to 50. My results show that in this case my percent errors are 2%, 3%, 3.6%, 4.3% and 5.3% on modes 1,2,3,4 and 5 which are much lower than my first case.

Does anyone know why at higher L/D ratios the percent error between analytical and numerical values are decreasing? Do you guys know any literature related to this?