## Questions on the CCI Option

General questions on the SMAC, msmac3D and other Collision Simulation programs
MSI
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Joined: Thu Jun 18, 2009 12:37 pm

### Questions on the CCI Option

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Question #1? I am reviewing a SMAC analysis which was run in McHenry and was wondering what the CCIX and CCIY variables represent? I am assuming it has something to do with the CG location but am not sure. If it does have to do with the CG I am not positive as to which direction from the default CG position positive and negative are. Any help on this matter is greatly appreciated.
• Answer #1 CCI is the Center of Collision Interface Option. In original SMAC and all other vehicles of SMAC beside mSMAC, the collision interface is locked to the CG of the vehicle. Sometimes when a collision is offset from the CG and/or runs very near the CG the collision interface may have problems. The CCIX & CCIY options are for changing the Center of Collision Interface. The option is explained in more detail in our paper "SMAC-97" SMAC-97 SAE paper 97-0947
Question #2 The paper helped but I have two more questions:
1. Does the impact force in a situation where the center of collision is moved, still act about the original CG of the vehicle.
2. Also, does the iteritive force calculation still take into account that the force being solved for is being calculated for an impact that is not directly centered over the true CG of the vehicle?
1) yes
2) yes.
The CCI is for reference purposes only. The CG was used for the CCI in original SMAC for convenience and/or memory limitations. It created problems if the 'reference vectors' got near 90 degrees. Therefore we added the ability to move the CCI. For each 'reference vector' which interacts with a 'reference vector' on the other vehicle, an equilibrium force is determined based upon the distance of the equilibrium point from the undeformed periphery of each of the vehicles. Once a balance is found at the equilibrium point, the forces and moments are calculated relative to the CG.
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MSI
Posts: 1815
Joined: Thu Jun 18, 2009 12:37 pm

### Re: Questions on the CCI Option

Another question on the CCI came up. Please read our SAE paper Below are figures and excerpts from the SAE paper which discuss and demonstrate the CCI and how in some impact configurations it MUST be moved for accuracy.
• NOTE: msmac3D/2D is the ONLY version of SMAC which allows movement of the CCI.
So ask yourself if you or others are using these other versions of SMAC:
• How do these other versions of SMAC (EDSMAC, WinSMAC, etc.) handle this situation to provide accurate collision force simulations? They don't!
CCI desc.png (34.72 KiB) Viewed 1184 times
CCI fig1.png (46.96 KiB) Viewed 1184 times
CCI disc2.png (18.69 KiB) Viewed 1184 times
CCI1.png (111.15 KiB) Viewed 1184 times
CCI2.png (90.47 KiB) Viewed 1184 times
CCI3.png (112.51 KiB) Viewed 1184 times
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MSI
Posts: 1815
Joined: Thu Jun 18, 2009 12:37 pm

### Re: Questions on the CCI Option

A couple of clues which will help the SMAC user to determine if a CCI is required.
First you may get this error message:
CCI related error message.jpg (27.1 KiB) Viewed 865 times
• This indicates that there was a force balance issue in a SMAC simulation.
• another indication is if you run a simulation in 2D and then 3D and get dramatic different results.
The video below is a demonstration of a T-Bone type collision where the damage in one of the vehicles is near or exceeds the midpoint of the vehicle.
If the SMAC Collision interface reference vectors (CCI) start at the CG this can cause a problem with ANY VERSION OF SMAC.
McHenry SMAC is the ONLY version of SMAC which allows you to move the CCI from the CG to enable simulation of these types of collisions.
• Important note: the vectors are NOT force vectors they are merely used to find common points on the two vehicles, the forces and moments are calculated relative to the actual damage interface)
The following is a simple example of a t-bone wherein the 3D simulation and 2D simulation differ dramatically.
• All 3D and 2D simulations can be run with the 2D animation:
• simply press the C button
or
• select the 'Colldisp:off button on popup dialog which comes up when you press the right mouse button
collision display.jpg (51.84 KiB) Viewed 861 times
• and the vectors will display.
In the following video we show the difference between 3D and 2D in the 3D Graphics.
• We then run the simulation in the 2D animation and show the reference vectors.
• Then we move the CCI and rerun 2D animation.
• Then a comparison of 2D to 3D simulations in 3D Graphics
• Lastly we include an overhead and angled view to show the roll/pitch response in a typical severe side impact which explains why the results of a 3D may be different than a 2D simulation.
• NOTE: Minor variations may occur between 3D and 2D simulations due to the added degrees of freedom of 3D over 2D (the vehicle can roll and pitch towards and/or away from the collision interface.
• NOTE: Be sure to set the height of collision interaction which is generally around the bumper height 14" to 20"
• NOTE: You can vary the height of collision interaction if too much, or too little, roll occurs. the characteristics of the damage in your crash will provide a good indication of the amount of roll.