Reply To: Modal analysis and density

[Sai Deogekar]

Yes, change in density will affect the natural frequencies of a structure and hence affect the results of a modal analysis.

In FEM, natural freequencies are calculated by solving the equation: det [K - omega^2 * M] = 0 (det - determinant, K - stiffness matrix, omega - natural frequency, M - mass matrix). Changing density will change the mass matrix, M, and hence affect the natural frequencies, omega, even if all other material properties are unchanged.

You can find more explanation about the above equation in lesson 3 of this course: Modal Analysis | Ansys Innovation Courses

You can also learn more about Modal Analysis in Ansys Mechanical here: Modal Analysis in Ansys Mechanical | Ansys Courses

Hope this helps.