Center of Collision Interface Example
The original version of SMAC had the limitation that the center of collision interface (CCI, origin for the radial springs of the collision model) had to be coincident with the Center of Gravity of the vehicle. This limitation can occasionally produce problems in simulated impacts where the damage may get close to and/or exceed the Center of Gravity of the vehicle. To accommodate these situations and as a part of research towards a more general fix, McHenry Software has provided an option to specify a separate location for the center of collision interface.
A long term general fix for the occasional problems encountered with the center of collision interface will be an automatic generalized re-positioning based on impact configuration. In general, you should only reposition the CCI location for those instances where the predicted damage occurs either close to the Center of Gravity or when default location of the CCI at the CG results in "PRESJ or PREJ tends negative" error messages and/or a jagged damage interface.
The expected generalized logic for re-positioning the center of collision interface will be to move the Center of Collision interface away from the impact location toward the opposite side or end of the vehicle (i.e., for a 90 degree impact on the right side (+X) the Center of collision interface would be set to CCIY=-20”).
This option is provided for our more advanced users. Please exercise caution when using this option. In general, the user should only reposition the CG location for those instances where the predicted damage is close to the Center of Gravity, when the impact configuration produces a jagged prediction of damage and/or when many "JPRES or IPRES tends negative" error messages occur. The new inputs for the damage measurements will be used for determination of the optimal location of the center of collision interface.
To demonstrate the use of the CCI Option, please proceed as follows:
• Open the Project in the DEMOS directory
o Center_of_Collision_Interface_Example
• The project is a simple 90 degree lateral impact.
• The file which should open up is CCI_Off.si5
• If that file is not pen, select Project->CCI_Off.si5
• Click the Run button to run m-smac
• The program will run and smac Graphics (msmacgr) automatically run.
• Press <Enter> to review the two smac Graphics (msmacgr) output pages.
o The results indicate Delta-Vs of 18.25 MPH Vehicle#1, 17.94 MPH Vehicle#2.
o Note: we only ran a 0.5 second burst through the impact phase
o Press <Esc> to return to medit.
• Now run the smac Animation (mGraphics) program.
• Click Run Menu and Select smac Animation (mGraphics).
o After it loads, press the <space bar> to view the animation.
o Let it run through once and then press the 'c' button.
§ The 'c' button displays the collision vectors during the collision. You will notice that they have origin at the CG.
§ You also display the collision vectors
by right clicking the mouse, and on the popup dialog select the 
which will change to
CollDISP:ON.
§ Then select the GO button to run the animation.
• Press <Esc> to return to medit.
Now we will demonstrate how to move the origin of the collision interface on vehicle #2 away from the impact.
§ You will 1st need to insert card 96
§ To insert a new card, do one of the following:
§ Click on the 
or the 
button
o This is found in the area above the grid
§ This will bring up the Card Helper dialog. Move the slider bar until you see card 96
§ 
Double click on the card and it will automatically insert card 96
• Or simply insert
a 96 in the card field 
and
then click on 
• Card 96 contains the X & Y location of the collision interface for vehicle #1 and Vehicle #2. Field 4 is the Y location of the CCI of Vehicle#2.
o Enter -25 in field 4 of card 96. This locates the CCI -25 inches away from the contact location.
o Run m-smac simply by clicking RUN
o The program will run and smac Graphics (msmacgr) automatically run.
• Press <Enter> t
• review the two smac Graphics (msmacgr) output pages.
• The results indicate Delta-V 18.7 MPH Vehicle#1, 18.3 MPH Vehicle#2.
• (You will notice that there is a minor difference
• Press <Esc> to return to medit.
Now run the smac Animation (mGraphics) program.
• Click Run Menu and Select smac Animation (mGraphics).
• After it loads, press the <space bar> to view the animation.
• Let it run through once and then press the 'c' button. The 'c' button displays the collision vectors during the collision. You will notice that they have origin at -25 inches from the CG on the other side of the damage region.
• Press <Esc> to return to medit.
Now we will increase the severity of the collision to demonstrate the benefits of the ability to move the center of collision interface .
• Click on Graphics display button
o (or for advanced users, you can simply insert 60 mph in the grid for the speed of vehicle 1
• For Vehicle #1, change the initial velocity from 25 MPH to 60 MPH.
o Click OK to keep changes
o Click the Run button to run m-smac
• The program will run and smac Graphics (msmacgr) automatically run.
Press <Enter> to review the two smac Graphics (msmacgr) output pages.
• The results indicate Delta-V 34.2 MPH Vehicle#1, 34.7 MPH Vehicle#2.
• You will notice that the graphics includes some diagonal lines.
• This represents a graphics 'glitch' which is one of the many items in final refinement to be included in the 'Official Release'. Please also notice the results:
• Impact speed change for Vehicle #1: 34.2 MPH, impact speed change for vehicle #2: 34.7 MPH.
• Now run the smac Animation (mGraphics) program.
• Click Run Menu and Select smac Animation (mGraphics).
• After it loads, press the <space bar> to view the animation.
• Let it run through once and then press the 'c' button. The 'c' button displays the collision vectors during the collision. You will notice that they have origin at -25 inches from the CG on the other side of the damage region.
• Press <Esc> to return to medit.
Now we will disable the CCI to demonstrate problems which occur in Original SMAC/EDSMAC when the collision interface is near the origin.
• Click on Card 96.
• Select the Comment in/out button
o This comments out Card 96 so the CCI is turned off
o Click the Run button to run m-smac
o The program will run and smac Graphics (msmacgr) automatically run.
o Press <Enter> to review the two smac Graphics (msmacgr) output pages.
o The results indicate Delta-V 41.7 MPH Vehicle#1, 42.1 MPH Vehicle#2.
o Obviously these are not the correct impact speed changes for the lateral collision. This demonstrates the inability of the Original SMAC/EDSMAC program to handle collision interfaces near the center of gravity.
o Now run the smac Animation (mGraphics) program.
§ Click Run Menu and Select smac Animation (mGraphics).
§ After it loads, press the <space bar> to view the animation. Let it run through once and then press the 'c' button. The 'c' button displays the collision vectors during the collision.
§ Press <Esc> to return to medit.
This Example should not be interpreted as an indication that valid results can be obtained at very high severity levels. Rather, the related modifications of SMAC are aimed at minimizing the effects of artifacts, in the computer implementation of the analytical relationships, on the predicted results. Evaluations of the ranges of validity of a mathematical technique should not, of course, be obscured by the presence of significant effects of artifacts.
Research is underway to establish a generalized fix to automatically locate the origin of the collision interface vectors on the basis of impact configuration, severity and/or measure damage locations. An automatic adjustment of the origin is considered to be highly desirable from the viewpoint of eliminating any possibility of related deviations from uniform interpretations of evidence. In the existing revised version of the SMAC program an option is presently included to permit the user to move the origin, where appropriate.
Please exercise caution when using the CCI option
Snag
Option