[walteppich]

Hey everybody,

I have two materials (composite and a thermoplast) and wanted to evaluate the effectiveness of damping when I put on the thermoplast. I have the experimental frequencies and damping for each mode. By curvefitting I found that the best approximation of the real damping is with alpha = 450 and beta = 0 without thermoplast and alpha = 450 and beta = 3*10^(-6) with the thermoplast. Putting these inputs in the harmonic analysis settings for the whole system gives good correlation with the experimental data.

In help viewer under "4.25.1. Material Damping Matrix" it is stated, that the damping is just a summation of alpha_i * M_i (and beta_i * K_i) over i.

So to test it, I assigned an alpha damping of 450 to the composite material (no beta, no thermoplast) in the engineering data and no alpha/beta damping in the harmonic response analysis settings. But the alpha damping gets totally ignored by ansys mechanical when I solve for the harmonic response and I get huge outputs as I would have with no damping. If I set damping = on in the modalanalysis the frequencies shrink, so it seems to work there. But if I want to do a harmonic response with damping = on in the modalanalyses I get an error because of the damping in the modalanalysis.

If on the other hand I assign a constant damping to the material in the engineering data it works fine.... So why doesn't alpha/beta damping work?

I would really appreciate some input.

[walteppich]

SOLVED! The solution was to use the full method in the harmonic analysis by uncoupling modal and harmonic analysis