How valid is SMAC (or crash) for sideswipes?

General Questions related to the CRASH Program and clones
Damage Analysis & Momentum Based Analysis programs
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MSI
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How valid is SMAC (or crash) for sideswipes?

Post by MSI »

[*] From March 21, 2014 email sent to us:
  • Q: How valid is m-smac (or crash) for simulating sideswipes? Currently, I have investigated the work of We are looking for a software solution, but currently use hand calculations and FBD’s.
    We currently utilize the work Watts and use energy methods to determine closing velocity from crush. He does cover sideswipes, but is brief about it.
    The SAE papers go into more detail, but 2004-01-1185 utilizes in house code and presents the general methodology. They compare to EDSMAC and that codes predictions to experiments is not great as illustrated in one of their bar graphs.
    The other paper, 1999-01-0094, provides more details about slip regions and a working example. However, the later paper, 2004-01-1185, makes critiques that may or may not be valid.
    Ideally, we would like to model sideswipes with a degree of confidence that is verifiable to publications that provide experimental data.
[*] From March 21, 2014 our email response:
  • A: 1st I hope you’re aware of the misleading statements about SMAC included in that book by Watts. CRASH should NOT be used in side-swipe collisions. From the CRASH3 manual: (page 1.7 , underline added):
      • crash sideswipes.png
        crash sideswipes.png (25.84 KiB) Viewed 671 times
    SMAC can be used for sideswipe collision but there are limitations, particularly for original SMAC and/or EDSMAC or other original SMAC clones.
    If the sideswipe is a glancing collision with mainly compressive forces then SMAC should be fine.
    • The only possible issue might be if the sideswipe covers the entire side of the vehicle.
      • There may be issues with original SMAC due to the CCI (Center of Collision Interface) issue.
        See our paper SMAC-97 with discussion about the collision interface.
        • See section DEFINITION OF THE COLLISION INTERFACE in paper SMAC-97, page 3
        In a sideswipe collision if it scrapes all along the side the reference vectors may become near perpendicular near the ends due to the limitation of original SMAC (EDSMAC or other original SMAC clones) to allow the collision interface origin reference ONLY at the CG.
        msmac/msmac3D allows moving the CCI from the CG to other locations (like to the other side of the vehicle) to avoid the issue (if that is the issue/reason for a problem)
    • Secondly of the sideswipe includes interaction where part of the vehicles interlock (a SNAG)
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MSI
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Posts: 1408
Joined: Thu Jun 18, 2009 12:37 pm

Re: How valid is SMAC (or crash) for sideswipes?

Post by MSI »

From March 21, 2014 email:
Q: I did read that statement in the 4th edition. I agree, that statement is misleading as I am looking at your SMAC product. However, I have read his book several times over and it does have some usefulness to it. I was able to get comparable numbers to another AR’s Wincrash report for a impact into a rigid movable barrier example.
In the meantime, I will review your publications that you have graciously linked on your website.
As for the papers, the 2004-01-1185 is from BRC and they have a direct link:
The other paper, By Toor et. al, we had to purchase from the SAE store.
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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