Determining accelerations/DeltaV for locations other than the CG

Topics related to collision & Trajectory analysis formerly on our 'Registrants only' area however which we get asked about frequently so believe shoud be in the open forum too
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MSI
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Joined: Thu Jun 18, 2009 12:37 pm

Determining accelerations/DeltaV for locations other than the CG

Post by MSI » Wed Jul 29, 2015 11:19 am

Determining accelerations/DeltaV for locations other than the Center of Gravity (CG) When evaluating either measurements made with accelerometers not located at the CG or occupant exposure, we recommend using the msmac3D Tool smacthp to assist in your evaluation.
  • From Help->Getting Started
    • ->Demos and tutorials section
      ->Smacthp with ricsac2
      • Here’s a link to the help file msmac3D)
In the discussion you will see the important items you should consider when evaluating accelerometer or occupant information when not at the CG:
  • Be sure to rerun the msmac3D simulation during the collision with 0.001 output time increment and then you can run:
    • Tools->smacthp
      Select veh1 or veh2
      Indicate an X,Y location
      And start/end times (or use automatic)
    All items are discussed in the Smacthp with ricsac2 (use login: mchenry password: thankyou!) demo presentation
smacthp provides a direct way to compare the accelerations/deltaV’s for accelerometers at locations other than the CG
  • And FYI if you don’t know the exact location of either the accelerometer or the occupant you can try different locations and see how much it changes the max acceleration and the deltaV
smacthp is a great tool to demonstrate the differences in accelerations and deltaV’s due to location
  • It can help demonstrate why occupants (or accelerometers) see different DeltaVs for different locations (and therefore different possible injuries)
    • Different people experience different issues for the SAME accelerations
    • Due to positional differences, the accelerations may be different, so the differences in injuries might be more dramatic.
    • Of course there is a HUGE difference in accelerations/deltaVs in the event an occupant is in the crush zone, link a near side occupant in a side impact, where the deltaV for the occupant can be approaching the closing speed
And one aside about SMAC:
  • SMAC initially used the threshold of acceleration > 1 G to start DeltaV calculations and once it came back down below 1 G to end the DeltaV calculations.
  • In initial development logic had to be added to handle momentary blips in the acceleration! Etc.
  • Now that we’re working in 3D and we may have to rethink that logic
    • weight transfer after a collision may extend the acceleration > 1 G longer
    • What about the 1G threshold? Might we revisit that and make it lower? Or higher?
We are in the process of reconsideration of the default thresholds but in the meantime simply use the msmac3D Tool smacthp to consider different thresholds.
Question? Comment? Please email forum@mchenrysoftware.com. Also see the McHenry Forum Index
Visit McHenrySoftware.com for technical information & software.
(c) McHenry Software, Inc ALL Rights Reserved.

MSI
Site Admin
Posts: 1147
Joined: Thu Jun 18, 2009 12:37 pm

Re: Determining accelerations/DeltaV for locations other than the CG

Post by MSI » Wed Jul 29, 2015 12:08 pm

After reading the write-up, a user asked: What does smacthp stand for?

SMAC Time History Program.
Question? Comment? Please email forum@mchenrysoftware.com. Also see the McHenry Forum Index
Visit McHenrySoftware.com for technical information & software.
(c) McHenry Software, Inc ALL Rights Reserved.

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