Question:
When performing a dynamic calculation, I get the message: "The model has no free mass assigned. Therefore, dynamic calculation is not possible" or "Too many eigenvalues required". How can I calculate mode shapes?
Answer:
As many eigenvalues can be determined as there are degrees of freedom in the structure to which a mass is assigned. In order to determine the number of degrees of freedom, it is necessary to multiply the number of the nodal points of FE nodes by the active mass directions. The masses in fixed supports are not considered for this, as they cannot oscillate freely.
If "Divison for straight members" (RFEM) / "internal member division" (RSTAB) is not activated, it may happen, for example in the case of single-span beams, that the masses only exist in the supports and thus no eigenvalue can be determined. In such cases, activate the member division as shown in the images.
Since the Lanczos solver in RF‑DYNAM Pro cannot determine all existing eigenvalues, the "root of the characteristic polynomial" solving method can also provide a remedy.
More Videos:
► FAQ 000468 | When performing a dynamic calculation, I get the message: "The model has no free mass ...: https://www.youtube.com/watch?v=9jy0IZIymQw