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How does SMAC determine the DeltaV and PDOF?

Posted: Sat Jun 20, 2009 2:47 pm
by MSI
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:

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:
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  • 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:
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  • 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:
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    • leg1.jpg
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    • leg2.jpg
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Re: How does SMAC determine the DeltaV and PDOF?

Posted: Mon May 11, 2020 11:35 am
by MSI
After responding to a recent question on determining DeltaV from acceleration I realized this thread should also include some fundamentals on integration to determine velocity and displacement.
I did a quick search of the internet and here is an example of some related notes: There are also many others are available on the web.