How does SMAC determine the DeltaV and PDOF?

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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How does SMAC determine the DeltaV and PDOF?

Post by MSI » Sat Jun 20, 2009 2:47 pm

As part of our research for SAE paper 97-0961 we included documentation of the techniques for determination of the DeltaV and PDOF in SMAC and how that compares to the DeltaV and PDOF measured in full-scale testing.
Please see the paper for additional information. The following is posted for your convenience:

SMAC EQUIVALENT DELTA-V:
In the original form of the SMAC computer program, the speed-change for a given acceleration exposure was determined by the integration of the resultant acceleration. For each time increment, a resultant acceleration was determined by the vector sum of the x and y components of the vehicle accelerations:
Eq9.jpg
Eq9.jpg (4.76 KiB) Viewed 2718 times
  • Where:
    • ac = resultant acceleration, g-units
      ax = acceleration in the vehicle x direction, g-units
      ay = acceleration in the vehicle y direction, g-units
  • The resultant speed-change was determined by integration of the resultant acceleration from initial contact to separation.
  • The initial contact is defined as the first instance where the resultant acceleration goes above 1 g-unit.
  • The point of separation is defined as the first time that the acceleration again drops back below 1 g-unit.
  • It was assumed that in general handling maneuvers and vehicle spinouts that the resultant acceleration would normally be below 1 g-unit (given that the nominal friction coefficient of roadways is normally less than 1 g-unit).
  • The Direction of Principle Force (DOPF) was determined for a given acceleration exposure in the SMAC program as the direction of the acceleration at the instance of peak resultant acceleration by:
    • Eq10.jpg
      Eq10.jpg (6.04 KiB) Viewed 2718 times
TEST EQUIVALENT DELTA-V:
  • For the reported RICSAC full-scale tests the analysis of the accelerometer data to determine the vehicle speed-change consisted primarily of the integration of the vehicle ax & ay accelerometer traces to determine the time histories of velocities.
    The velocity time-history plots were then analyzed to determine the magnitude of the changes in the individual velocity components, ?Vx and ?Vy . The resultant speed change and speed-change angle were determined by the following:
    • EQ7.jpg
      EQ7.jpg (4.86 KiB) Viewed 2718 times
    Where:
    • leg1.jpg
      leg1.jpg (16.09 KiB) Viewed 2718 times
      Eq8.jpg
      Eq8.jpg (6.5 KiB) Viewed 2718 times
    Where:
    • leg2.jpg
      leg2.jpg (17.45 KiB) Viewed 2718 times
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MSI
Site Admin
Posts: 1300
Joined: Thu Jun 18, 2009 12:37 pm

Re: How does SMAC determine the DeltaV and PDOF?

Post by MSI » Thu Jun 14, 2012 4:27 pm

June 14, 2012: Q: (phone message) How is deltaV Calculated in SMAC?
A: in response to the phone message, we sent a link to this thread.
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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