Dear Forum,

I am new to SimScale and are currently evaluating SimScale for the company I work in. I am experienced in CFD having used various codes in engineering and research for about 10 years (including OpenFOAM). I am however, a novice in FEA. Firstly, I wanted to do a simple frequency analysis of a pipe (2ββ, Schedule 10S, 2000mm, titanium grade 2) and compare it with hand calculations. However, I am getting some strange results. I started by doing a mesh convergence test and got results as expected, mesh convergence was achieved with a reasonable mesh. The results for the first mode compares well with the hand calcluations, but the second mode is way off. The hand calculations yields a first mode eigenfrequency of 86.7, while the FEM-results yields a value of 85.91 (less than 1 % off). The second mode from the hand calculations is 239, and the thrid mode is 469. Results from FEA is listed below.

Eigenmode Eigenfrequency

1.0 85.91846

2.0 85.94912

3.0 233.0151

4.0 233.1042

5.0 447.498

6.0 447.6537

7.0 721.7241

8.0 721.9563

9.0 724.851

My hand calculations can off course be wrong, or my interpreteation of the results, but I find it very strange that the FEA results seems to yield results for mode 1 and 2 which are very similar. Furthermore, the same thing can be observed for mode 3 and 4, 5, and 6, and 7 and 8.

Have anyone any input to this?

Stig