How valid is SMAC & CRASH for sideswipes?
Posted: Thu Apr 02, 2015 10:46 am
- 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
- Watts (Accident Reconstruction Science 4th ed. Chapter 14)
- SAE paper: Analytical Model for Investigating Low-Speed Sideswipe Collisions 2004-01-1185,
- SAE paper: Practical Analysis Technique for Quantifying Sideswipe Collisions 1999-01-0094
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.
- Q: How valid is m-smac (or crash) for simulating sideswipes? Currently, I have investigated the work of
- 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.
- See section under 2003 in Explanation of erroneous statements on SMAC & CRASH
- Also can be found here:Explanation of erroneous statements on SMAC in Lawyers & Judges book
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
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)
- There may be issues with original SMAC due to the CCI (Center of Collision Interface) issue.
- Secondly of the sideswipe includes interaction where part of the vehicles interlock (a SNAG)
- Original SMAC (EDSMAC) can’t handle forces other than compressive collision forces whereas the SNAG option of msmac3D/msmac3D can handle that type of situation.
- The msmac/msmac3D with the SNAG option was invented/created to model collision interactions which are not all compressive forces.
- See the section in SMAC-97 paper on SUPPLEMENTARY IMPULSIVE CONSTRAINTS ON RELATIVE MOTION
- See the writeup DISCUSSION: SNAG option from the msmac/msmac3D manual
- See the forum topic What is the SNAG Option
- The msmac/msmac3D with the SNAG option was invented/created to model collision interactions which are not all compressive forces.
- Original SMAC (EDSMAC) can’t handle forces other than compressive collision forces whereas the SNAG option of msmac3D/msmac3D can handle that type of situation.
- See section under 2003 in Explanation of erroneous statements on SMAC & CRASH
- A: 1st I hope you’re aware of the misleading statements about SMAC included in that book by Watts.