Learning Forum

[Rifaat93]

hello People

"Material Constant Damping Ratio defined in Engineering Data is not contributing to modal damping calculations"
What does this mean ? and how can i avoid/stop it ?

[peteroznewman]

The default for a Modal analysis is the Undamped natural frequencies and mode shapes. If this is what you want, you can ignore this message.

What do you plan to do with the Modal results?  If you are using them to perform a Modal Superposition Transient Structural analysis, you apply the damping in the Transient Structural model.

Did you specifically want the Damped natural frequencies? Is so, this is warning you that the Material Constant Damping Ratio defined in Engineering Data is not contributing to modal damping calculations.  This means that if in Engineering Data you added Constant Damping Coefficient, it will not be used in the Damped Modal calculation. 

If you want the Damped Natural Frequencies, you have to use the Damping Controls in the Modal Analysis Settings.

These controls accept the Rayleigh Damping coefficients to form the Damping Matrix as shown below.

Do you need more information on Rayleigh damping coefficients?

[Rifaat93]

I am trying to calculate the dissipated energy of a body that is dynamically compressed 

When a body ( in my Project its a Concrete cylinder) is dynamically compressed  then there will be internal friction  and probably through this Friction  , Energy will be dissipated
thats what i am trying to simulate 

Can you help me with this? 

[peteroznewman]

What do you know about the dissipation? What data do you have?

I needed to know the damping ratio of a large steel structure. I put an accelerometer on the structure and shook it with my hand. Analysis of the decay of the oscillations after I stopped shaking provided the damping ratio.