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*GRDAMEM
Data format:
A single line with up to 7 values
IGR ITAB IOP TCAL IOA AMP
Status :
Optional (dynamics)
Purpose :
To define a specific damping per frequency on a group of elements in time domain
Restrictions :
All elements of the group must be beam elements
Details :
| Parameter | Description |
|---|---|
| IGR | Group ID number |
| ITAB | Table ID number defined by *TABLEMCOL |
| IOP | = 0 : Triangle function (Recommended) = 1 : Step function |
| TCAL | Time to compute retardation function. If TCAL=0, a table is defined with a single line and three columns then Rayleigh damping is used based on \(\frac{\epsilon}{𝜋𝑓}\) where \(f\) and \(\epsilon\) are the frequency and damping ratio in the table |
| IOA | = 0 Amplitude given by the formula below (note 2) - Damping on velocity = 1 Amplitude is directly \(𝐵_{max}\) - Damping on velocity = 2 Amplitude given by the formula below (note 2) - Damping on velocity gradient = 3 Amplitude is directly \(𝐵_{max}\) - Damping on velocity gradient |
| AMP | If ITAB=0, AMP is used directly without memory effect |
| IDOF | Six digit integer to apply damping on specific dofs in local frame (For instance 111000 for translations). If not provided or 0, all dofs are damped |
1- The table must have three columns :
if TCAL non zero: Frequency (Hz), Frequency increment (Hz) [considered symmetric], Damping (\(\beta\))
Otherwise : Frequency (Hz), 0, Damping ratio (\(\epsilon\))
2- The damping is applied as $𝐵_{max}=\beta K $ where \(K\) is the complete stiffness matrix of the element. The retardation function is then computed as \(\frac{2}{\pi}\int_{0}^{\infty} {𝐵_{max} B(\omega) \cos{(\omega t})d\omega}\)
