Advanced mass scaling (AMS) and added mass issue

[hadibijari23]

Hello everyone,

I am trying to run a model with AMS control. As mentioned here, https://help.altair.com/hwsolvers/rad/topics/solvers/rad/recommended_checklist_ams_r.htm, one of the checklist should be the comparison of the added mass in the traditional mass scaling method,DT/NODA/CST, and the AMS method. The problem is that in the AMS method, the added mass is zero. I have attached the snip of the engine files for simulation with AMS option (first picture) and NODA option (second picture)

I am wondering what could be the reason for that and would be thankful if someone could help me with it.

Thanks in advance for your time and help!
Regards,
Hadi

[MarianBulla]

Hello @hadibijari23,
Thanks for using OpenRadioss.
This is exactly, what is expected. With AMS, you usually will not get any added mass.
The approach is more complex and different to the traditional mass scaling.
It will add you sufficient amount of mass on the diagonal part of the mass matrix and subtract it on the horzontal lines.
For more details, please review the paper from Lars OLOVSSON and Kjell Simonsson: "Iterative solution technique in selective mass scaling"
So, your added mass will be, at the end, = zero.

Hope it helps you ?

Thanks and best regards,
Marian

[hadibijari23]

Hello Marian and thank you so much for the clarification.
I was confused because I had followed this example , https://help.altair.com/hwsolvers/rad/topics/solvers/rad/out_file_examples_ams_r.htm, where it shows mass being added when AMS is used and I thought maybe in my simulation is wrong.
So in this case, when using AMS, the mass added must always stay zero?
Thanks for your time.
Regards,
Hadi

[MarianBulla]

Hello @hadibijari23,
yes this can be the case, if you select the entire model to be used with AMS.
If you just have selected single parts, then the rest of the model can still use the classical mass scalling approach and you will get added mass on your model.
So, it depends (as always) :-)

Thanks and best regards,
Marian