In RF‑/DYNAM Pro, I get the error message No. 10040: "It was impossible to calculate all eigenvalues with required accuracy. [...]." How can I fix this error?

In a dynamic analysis, you can only calculate as many mode shapes as the structural system has degrees of freedom. The degrees of freedom mean the number of mass points multiplied by the number of the directions in which the masses act.

Example

A cantilever that is not split by the FE mesh has a mass point at the end. The action direction of the masses in RF‑/DYNAM Pro is limited to the X and Y direction. Thus, the system has 2 degrees of freedom, thus 2 mode shapes can only be calculated.

Please note: In this case, the selection of the method for solving eigenvalue problem is very important. In contrast to the "Root of the characteristic polynomial" method, the Lanczos method cannot calculate all eigenvalues of the system, but only n -1, which means only 1 eigenvalue in this example.

Reference

 [1] Manual RF-DYNAM Pro. (2018). Tiefenbach: Dlubal Software.