 ## Ansys Free Student Software

• Venkata Subramanian M
Subscriber

For the modal analysis of the structure the eigenvalues and eigenvectors are extracted from the different methods (Supernode method, block lanczos, etc., using characteristic equations. Is that correct?

Another question is if I have assigned the number of modes required as 10 or 200 based on the requirement . How the mass matrix and stiffness matrix are taken for mode 10 and mode 200 for calculating the natural frequency .Is that if i assigned 10 or 200 the mass and stiffness matrix are changed according to the mode number?. Sir/madam Kindly explain that it would be helpful for my research.

• Ashish Khemka
Ansys Employee

Hi Venkata,

Yes, the methods you indicated are different ways of mode extraction. But please use the Program Controlled settings. If you are looking for comparison of mode-extraction methods then please refer to following links:

3.8. Comparing Mode-Extraction Methods (ansys.com)

For number of modes to be used, please refer to the following Ansys Innovation Course:

Mode Participation Factor and Effective Mass | Ansys Courses

Regards,

Ashish Khemka

• Venkata Subramanian M
Subscriber

Thanks for your reply. I understood that the mode participation factor is the method used to define the Number of modes required in the analysis.

I have the doubt regarding if i assigned Number of modes required as 10 or in the same analysis with Number of modes required as 200. How it would affect the mathematical calculation for finding the mode shape (Eigenvector) and natural frequency (Eigenvalue) in different methods of Eigenvector and Eigenvalue extraction. Would that change the structural stiffness matrix or mass stiffness matrix accordingly to find the natural frequency and mode shape ? for assiging number of modes as 10 or 200. 