Analysis using ASDAbsorbingBoundary3D

[kolozvari]

Here is a follow up information on the previous post regarding application of Rayleigh damping via Regions command. I applied the same level of damping via Rayleigh command and results seem much more reasonable. I ran several cases (see below), and as you can see, every time I use Regions command to apply damping, results seem off.

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When defining Rayleigh damping via Regions command (previous post), I determined alphaM and BetaK based on Rayleigh command to correspond to 2.5% damping at T1 and 0.2T1 of the superstructure (common practice). I selected "Elements" and I elected "selection + include_auto_generated_elements" because I use shear hinge beams. All these make sense to me, but there must be something wrong the way I selecting these settings. I checked the Selection Set that I assigned to the Region command, and it is the entire structure including all geometry (see screenshot below).

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I would really appreciate if you can provide me with some insight about this. Thank you very much.

[STKO Team]

The damping applied via Rayleigh (global) or region (local to the region) should be equivalent.
The error comes from the fact you are using the wrong parameters in the region command.

In the Rayleigh command, we let the user define alphaM and Betak.
Now, betaK is used to the current stiffness (if Kcurr is selected), for the initial stiffness (if Kinit is selected) or for Kcomm (if Kcomm is selected).

Your Rayleigh parameters alphaM = 0.0682, BetaK = 0.00379, Kinit=True, translates to:
mass proportional factor = 0.0682
initial stiffness proportional factor = 0.00379

So your region command, to be equivalent, should be:
alphaM = 0.0682 -> mass proportional factor
betaK = 0 -> tangent stiffness proportional factor
betaKinit = 0.00379 -> initial stiffness proportional factor
betaKcomm = 0-> committed stiffness proportional factor

So the error comes from the fact that in the region you were using a huge damping for the inital stiffness term (i think you put 1 because you wanted to active it, but in this case is different)

[kolozvari]

Thank you, makes sense. I think my confusion came from the fact that in STKO the beta parameters are not spelled the same way, which made me think that betaKinit is just a flag, so I used 1.

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You should spell betaK, not Betak to avoid confusion. Thanks for your help.

[STKO Team]

Yes you're right. It is a bit confusing