SMAC Primer
(Overview Menu)

 

 

By George M. Bonnett JD

 

 

 

Welcome to SMAC-RT and this Primer on SMAC in general.  This new version focuses on SMAC-RT and uses screen captures from SMAC-RT. 

 

SMAC-RT is the property of REC-TEC LLC and is free to all REC-TEC users with a current Platinum option.  We will continue to upgrade this basic version of SMAC.  The SMAC engine we are using is a modification of the 1997 version that Calspan obtained from UMTRI.  In its original form as downloaded from Calspan, it was unusable.  It has been modified slightly to make it functional and to produce the required/desired output files.

 

There are some idiosyncrasies associated with this particular version:

 

  1. Print Output timing is not totally controlled by the Print output time entered in Card 1.  The timing sequence shifts during the collision phase, and returning after collision.

 

  1. Rear wheel steering is not controlled by Cards 4 and 5, but by Cards 10 and 11.  The forces in Cards 10 and 11 can be toggled On/Off using the green/gray Vertical bars (even in the Evaluation copy) creating an entirely different scenario.

 

  1. Wheel (Torque) Forces may be entered by the traditional method of using a percentage of the weight on each wheel multiplied by the friction factor.  Alternatively, the program interface will compute the information if a number between –1 and + 1 is used for braking/acceleration.

 

  1. Wheel Forces and Steer Angles can be entered by either a fixed time interval, or by using a variable time interval (number of entries). With the Variable Time Interval a Checkbox is Enabled permitting the use of the Collision Detect feature for that wheel.  Collision Detect holds a change spanning the time before and after the collision from ramping up from Collision to the Time frame immediately after Collision detection.  

 

  1. Files are “Saved” and “Opened” using the .Si5 format.  The file created by the interface to run SMAC-RT is “Input.DAT.”  This file is formatted to work in the SMACRT.EXE engine doing the majority of the number crunching necessary for the Graphics and Animation output.

 

 

Check the next page to take a tour and see what SMAC-RT will do.

 

We are actively working on Additional features that will be added over time, and some of these may come from third parties. 

 

Please remember that SMAC could be a very dangerous tool in the hands of the un-educated or un-scrupulous reconstructionist.  It is NEVER the first tool used in a reconstruction.  It is the last.  It helps refine computations and calculations based on physical evidence. 

 

Hopefully by making the program free, it will encourage more facilities to provide instruction on SMAC and therefore encourage users to purchase SMAC programs that go far beyond the basic features offered by this variant.

 

Here are some tips to help get you started (you may want to print this page so you can follow the steps):

 

  1. When selected, the SMAC-RT module should automatically load the file Sample3.Si5.  The Inputs  (left most column) should be headed by a block that is labeled “Default.”  In the lower right screen quadrant, you should see a block labeled “smacRT Simulation.” 

 

  1. You might want to go “Full Screen” with the program in order to see all of the features.  Now look on the Right side of the screen and find the Wheel Forces section.  Click on the two vertical Green/Gray bars turning them Gray thus disabling the braking on the vehicles letting them reach their target blocks.  You may want to play with the Braking and Steering later on, turning them on/off for the different vehicles. This, and the instructions following, are applicable to both the licensed and Evaluation copies of the program.

 

  1. Click on the "smacRT Simulation" button.  A message will appear allowing several options for the LAMBDA value (Card 13-3).  For this run, select “No.”  This will run the SMACRT.exe engine and then bring up a panel showing the output file that may be used for data or high-resolution animations, or by REC-TEC to display both Graphics and Animations.

 

  1. Click on the Animation button at the bottom of this panel.  This will start an animation that should show a 4-second animation.  The program automatically goes to Zoom Extents for the problem.

 

  1. In the bottom-center of the screen, there are eight buttons and a checkbox (toggles rest positions on/off).  The fourth button will be selected.  Place you cursor on the different buttons and you will see that they describe different modifications to the animation.  Select the seventh button.  You should see two vehicles on the screen.  They are not moving.  Click again on Zoom Extents.  The two vehicles now fill the screen.  Press the “+” key (Shift + if you don’t have a number pad) and you will see the vehicles advance towards each other in the selected print output interval.

 

  1. On both the right and left upper corners of the screen, you will see four blocks labeled “aV” (acceleration vector), “vV” (velocity vector), “CG” (center of gravity trace), and “TT” (Tire Trace) for Vehicles 1 (Left) and 2 (Right).  Try turning on all of the Vectors.

 

  1. Use the Plus key to advance the vehicles into the collision.  You may also use the minus (-) key to back up the vehicle to the pre-collision positions.  If you have repeat turned on for your keyboard, you may simply hold the key down to step the animation.

 

  1. Right clicking on the mouse will start the animation.  Let it run until it stops (off of the screen).   Click on Zoom Extents again and then right click the mouse.  The animation will start again.  It may be paused (and re-started) by using the right mouse key or the spacebar.

 

  1. The blocks at the top of the screen will let you move the display right, left, up, and down.  It will also let you zoom in or out on the display.  One button will reset the animation parameters, and others will let you alter the speed of the animation.  There are buttons to shift the orientation clockwise and counter-clockwise and even a button allowing the animation to repeat.  Clicking “R” (Repeat) or “Dsp” (Display All modes) to see various options randomly selected.

 

  1. If you select the 8th Animation button (bottom center) and then select either the 6th or 7th button, the program will not clear the screen between runs UNLESS you use the Plus or Minus keys to Step the animation for one time increment or more.

 

  1. When you have finished exploring the animation variants, press Escape on your keyboard.  Now Click on Graphics.  There are all sorts of displays and curves for acceleration to velocities.  Check them out on your own, noticing that you can select either vehicle for the displays and that the curves can be “timed” − Enjoy!

 

New Procedures and Protocols in SMAC-RT:

 

REC-TEC is capable of transferring information from 360 Linear Momentum to SMAC.  Without vehicle information, only very basic information can be transferred.  REC-TEC Platinum and Pro versions can compute the Centroid of Damage for the vehicles if CRUSHV information (.crs file) is introduced into the 360LM module (see Animation interface).  The program also computes the Kv values for both of the vehicles.  The help file for 360 LM contains additional information on this topic.

 

In REC-TEC Platinum, SMAC-RT incorporates a Collision Interface Protocol (CIP) that will reposition the point of collision interface on the display with or without a bitmap file in place. 

 

Open the SMAC-RT module in REC-TEC and “Open” the “LMTransfer.si5” file.  “Run” the SMAC simulation.  Click on the “Animation” button bringing up the following display.

 

Figure 1

 

 

The program drew the animation positioning it in the center of the screen as it automatically engaged the “Zoom Extents” feature prior to setting the configuration for displaying the animation on the screen.

 

Notice that in the upper right corner of the display is a small round white (radio) button.  This button is used to engage or “trigger” the Collision Interface Protocol.

 

The CIP consists of two steps:

  1. Left Click on the current Collision Interface.
  2. Left Click on the desired Collision Interface position on the screen.

 

If an LMTransfer file is loaded, the Collision Interface is located at the 0,0 position.  This allows skipping the first step in the procedure as the program will use the 0,0 point as the Collision Interface.

 

If a non-LMTransfer file is loaded, the Collision Interface is located at an unknown position.  This requires that the Collision Interface position be marked on the screen so the program can compute the Collision Interface.

For non-LMTransfer files, once the Collision Interface Protocol button is clicked, the following messages will appear.

 

Figure 2

 

Figure 3

 

Once the above steps have been completed for non-LMTransfer files, or if the file is an LMTransfer file, the following message will appear.

 

Figure 4

 

Place the Cursor on the desired location for the Collision Interface and Left Click on the Mouse.  The Animation is automatically redrawn running over your cursor at collision.

 

You may still draw on the screen using the mouse.  Zooming in and out on the animation or using the “C” or “CC” buttons to alter the animation has no effect on CIP operations.

 

The Repeat and Display options function differently if a Bitmap is in the scene background.  With the bitmap loaded into the module, the program is not allowed to change the position, rotate the diagram (the bitmap cannot be rotated), or independently alter the position of the Collision Interface as it is allowed to do if no bitmap is loaded.

 

Utilizing the 360LM Transfer with the vehicles from CRUSH in conjunction with the Collision Interface Protocol in SMAC makes the tedious job of positioning vehicles correctly in SMAC and then on a bitmap with the Animation run as an overlay, just a few mouse clicks away.  The picture on the next page shows a collision positioned on a Google Earth bitmap with the collision quickly moved to show the Collision Interface at the correct location on the bitmap.

 

 

 

Just because it is easy and quick, it does not relieve the investigator from gathering the information, analyzing it in light of all the facts of the case, and doing a proper reconstruction.  These tools in REC-TEC are designed to provide for rapid checking of the hypothesis drawn from the reconstruction.  They are not a substitute for the hard work required as an integral part of a good reconstruction.

 

Figure 5

 

The image above used a Google Earth captured image that was placed into Microsoft Paint and exported as a JPEG (.JPG) file imported as a bitmap type (.bmp, .gif, .jpg) file.  The animation was reduced in size to match the image and positioned using the procedure outlined above.  The entire process took less than 10 minutes.

 

Bitmaps cannot be manipulated in REC-TEC.  They must be set up in other programs (CAD or Paint) and turned into a .gif, .jpg, or .bmp file, which can be imported into REC-TEC.

 

The animation can be manipulated.  It can be rotated by 90 degrees at a time. I can be zoomed in or out so that it matches the scale of the bitmap. 

 

Photomaps (Google Earth or Microsoft Virtual Earth) can be rotated and cropped to produce a bitmap that can serve as a background for the animation with or without a CAD overlay for a hybrid-view bitmap.  Using the Zoom (+/-) feature, the user can manually attempt to scale the animation to the bitmap.

 

A more accurate method is to “measure” some features, which then can be used to scale the animation to the bitmap. This feature is only available when a bitmap is loaded.  The control for scaling is the radio button located in the upper center of the picture.

 

 

 

Figure 6

 

Clicking on the center radio button brings up the above message box.  Select two points where the distance between them is known (measured).  For this exercise we will use the lane width (distance between lane stripes) with a known distance of 8 feet (96 inches).

 

Figure 7

 

After clicking on the second point, an input box appears on the screen asking for the distance between points in inches or millimeters depending on the configuration.  After entering the distance, click on OK.  This causes a redraw of the animation, which is now scaled to the bitmap.

 

Figure 8

The rescaled animation now must be placed at the correct location over the photograph using the Collision Interface Protocols as outlined above.

 

Figure 9

 

Figure 10 shows the animation scaled to a bitmap, cropped using Paint, and positioned in the correct location using the Collision Interface Protocol.  The CTRL button has been used to clear the screen controls.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 10

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Congratulations!  You finally made the big move to a SMAC program.  Now the fun (and the learning) begins.  Just make sure that your computer meets the specifications required by the program and that you have enough room on your hard drive to install all of the features you require.

 

The REC-TEC program contains a SMAC program called SMAC-RT.  The SMAC-RT program works as an evaluation program unless your license permits you to use the full program.  The Sentinel.exe file is the licensing file for both the REC-TEC Program and the SMAC-RT program.  In order to use the SMAC-RT program your Sentinel file must include a current Plus Option.  SMAC-RT requires the Plus option.  This will allow all of the installations permitted under your license to run the licensed SMAC-RT software. 

 

The SMAC-RT program in REC-TEC is our model.  Clicking on REC-TEC on the upper navigation bor  on the main screen causes the dropdown menu to appear.  At the bottom, we see the SMAC selection.

 

Figure 508

 

Clicking on SMAC brings up the SMAC-RT module screen (Figure 509).

 

Figure 509  

 

This may seem confusing, even mind-boggling! Be patient, the program is actually rather simple. It is just setting up two cars to crash into each other. We all know cars, right? You just have to learn the way the inputs for each car are arranged and a little about the inputs.

 

Several steps are key to understanding how to setup and run this program. With any new toy, or tool the first steps always seem the hardest.  The program has sample case studies that can be loaded and run showing the data and graphics produced by SMAC.  Click on the Open .Si5 File button. 

 

A dialog box (Figure 510) appears showing the standard windows file selection dialog box. Each of these files is a sample smac input file. As you new files are created, this dialog will display filenames. Select  the filename Sample3.Si5.

 

Figure 510

 

Opening the Sample3.si5 file in SMAC-RT (Figure 511) replaces all of the numbers in the opening data screen.  There are quite a few zeros on the screen, and it has at least one blank box.  For those users new to SMAC, it can be a confusing bunch of numbers and blocks. That is OK.  Soon it will all make sense! 

 

Figure 511

 

This is the basic control point for setting the parameters for running a SMAC problem.  Instead of explaining all of the blocks at this point, see what it can do.  In the lower right section of the screen are the main control buttons for the program.  The Open.Si5 File button got us to this point.  Press the red Run button and jump right into the thick of things.  After a slight pause a new screen will appear (Figure 512).

 

Figure 512

 

As reported in Figure 512, the suggested maximum value for Lambda is 8.5 and the suggested minimum value is 4.4.  The value entered is 12 as shown in the (dark red) input textbox, and triggering this message.

 

The McHenry smac programs automatically lower a value over the Maximum (8.4 for this problem) to the Minimum (4.4 for this problem) for the computations, placing a note in the output files stating the value has been lowered.  REC-TEC (SMAC-RT) displays the above message, giving the user control (and knowledge) of the input used in the computation.  This value can have a dramatic effect on the outcome.

 

For the purpose of this exercise, select the “No” response.  This block (Figure 512) will not appear if the values are between the minimum and maximum.

Figure 513

 

 

Figure 513 is not exactly the rush that was anticipated.

 

Just as we are taking baby steps right now, so is the program.  Only the program did more than you realize.  It was also generating pages and pages of data and over a dozen files that it placed in the directory.  These files are the result of running the Simulation (number crunching) side of the program and are the documentation that you will need to effectively use the program in any litigation – civil or criminal.

 

The Datasets are now shown on the screen.  This will let us view what the program was doing when we pressed the Run button.  Several different files were created during the “Run” phase that may now be reviewed.  In addition to echoing the input data, these files will show all of the computations that the program has made showing the instantaneous speeds, distances, forces, accelerations (linear and angular), changes in velocity (delta V), damage, steer and tractive forces for the vehicles as well as other data that may be useful in your case.  All of these files are available and may be added to the report.

 

A note of Caution:  The files produced are for the particular problem being run.  The program writes over these files as new problems are run.  If you need to go back and retrieve a file that has been overwritten and not saved in a report, it will be necessary to re-run the original problem.  The main .Si5 file is not overwritten unless you purposefully overwrite it using the Save button.

 

 

 

 

 

 

 

 

 

 

 

 

 

The Graphics button will bring up Figures 514 and 515 (if the SMAC radio button is selected).

 

Figure 514  

 

Figure 515

 

These screens show both vehicles, including the damage pattern predicted by the program.  This is not the damage pattern input into the program using the Options button.  In fact, this has nothing to do with the damage pattern input into the program as “target damage.”  This is program predicted damage.  (The Options button and the “target damage” will be discussed later.)

 

In addition to the vehicles there are Graphics screens showing various information about this particular simulation.  There is a wealth of information available using this section.  It is a distillation of what occurred during the simulation.

 

Figure 516

 

Figure 517

 

Pressing the Escape key (or the center wheel on the mouse depending upon the mouse setup the user is returned to the screen shown in Figure 518. 

 

Figure 518

 

 

This is still not the kind of thing that will get the average cynic to hyper-ventilate, but there is still one more button to go – Animation (Figures 519, 520, and 521).

 

Figure 519

 

Figures 520 and 521 display the modified run produced by changing the Output Print Interval C1) and the clicking on the green Wheel Forces buttons C(8/9) in Figure 518. This effectively slows the animation and disables the input Wheel Forces.

Figure 520

 

Figure 521

 

I can hear the purists screaming from here.  Animation?  SMAC is a simulation program.  How can you talk animation when we are dealing with a simulation program?  The truth of the matter is that both terms are correct.  SMAC as a totality is a simulation program.  In fact, the term “SMAC” refers to Simulation Model of Automobile Collisions, and was created by Raymond McHenry and his crew of merry men in response to a 1970 National Highway Traffic Safety Administration (NHTSA) sponsored research project. 

 

The Run Button initiates the simulation.   The actual program run at that time is SMACRT.exe and it does the simulation, which produces the data files that have been previously discussed.  The Graphics Button reads some of these files to produce the graphics.  The Animation Button reads the files and produces the animation from the points specified in the files.  So, while SMAC is a simulation, clicking on the Animation button produces an animation, not a simulation.  Press Animation and…(Figure 522)

 

This is only the beginning.

 

Figure 522

 

 

 

The next few pages show screen captures all using the same basic setup in Sample3.Si5.  The difference between Figure 522 and Figure 520 is that the Steer angles for the right and left front wheels in Figure 518 C(10/11) were changed to 0 degrees in the animation for Figure 524 by clicking on the Green bars.

 

Notice that this minor change resulted in an entirely different post impact run out of the vehicles.  The secondary slap during the collision (Figure 523) does not occur in Figure 524.   The Target blocks are clearly visible in Figure 524 even though the final position for the four (4) second run in Figure 524 has the vehicles miss their mark.  Figures 525 and 526 show close-ups of the secondary slap with the Vector option turned on.

 

 

 

 

 

 

 

 

 

 

 

 

Figure 523

 

 

 

Figure 524

 

 

 

 

 

 

Figure 525

+

 

 

 

Figure 526

 

 

 

 

 

This is what SMAC does.  It takes the inputs entered and models the actions and reactions of the vehicles using the laws of physics.   By changing the inputs, the accident changes because the vehicles react differently to the forces acting upon them before, during and after the engagement phase of the incident being modeled.

 

Now that we have a basic feel for what SMAC is, and to some extent how it operates, we need to go back to the beginning and see what makes up the individual sections (cards) that make up the inputs screens and discuss how these inputs influence the final product.  Once the inputs are understood working different types of problems will be much easier.

 

In the final section, different types of problems will be presented and using a step-by-step approach the information will be entered into the input screens and tested.  The inputs will then be modified until the results displayed match the results of the incident we are trying to model as closely as possible.

 

With a thorough understanding of how the program works and the inputs that go into modeling the pre-collision, collision and post collision phases of the accident, SMAC will become a valuable tool in understand collisions.  SMAC cannot replace the meticulous investigation and evidence gathering at the scene of an accident.  It will not solve the accident for us by simply plugging in a few pieces of information gathered at the scene. 

 

What SMAC will do is test our theories of how a particular accident happened.  It will test and help us check and refine some of the data and preliminary conclusions arrived at using that data.

 

Now that we have seen what SMAC does, let us look at what goes into making it do it.  Figure 19 is the primary input screen with the Sample3.Si5 file loaded.  The frame at the upper left of the screen, labeled C(1) - Program Control Data allows setting up for one or two vehicles.  The C(1) refers to Card 1 of the cardset that makes up the input file. 

 

Figure 527

 

 

 

 

 

Figure 528 is a printout of the Sample3.Si5 file.  A close inspection of Figures 531 and 532 will show the relationship between the cardset (Figure 528) and the data in the individual card frames in Figure 527. 

 

In the early days when SMAC ran only on mainframes, punch cards were used to feed the data into the computers.  Using the card format not only simplifies the inputs for the program, it makes for compatibility among the various versions of SMAC.

 

Card 1 or C(1) sets the timing for the program and the parameters under which the program will end.  The data names for the individual inputs are shown by placing the cursor on the entry block for the information. 

 

Figure 528

 

The above input file is the cardset that comprises data making up the Sample3.Si5 scenario.  

 

Before moving on to setting up different scenarios, let’s take a look at some of the other features and widgets offered on the main SMAC-RT screen (Figure 527) that will play a part in producing the final output. 

 

 

 

 

 

 

 

More Buttons and gadgets

                                       

The only button not discussed is the Options button.  Clicking on the Options button modifies the screen to that seen in Figure 529.

 

Figure 529

 

 

 

 

Figure 530

Figure 531

 

Figure 532

 

 

Cards 80, 85 and 87 on this screen deal with targets.  They have nothing to do with the actual simulation or animation of the data within the datasets other than to act as targets.

 

Cards 80 and 85 are the targets for the damage to the respective vehicles.  Cards 86 and 87 are the targets for the Impact and Final position for the vehicles. 

 

What do we mean by targets?  A target is something we aim at in various sports.  In SMAC it is the result we are aiming for at the end of the run.  In the case of the damage, this is the location and extent of damage that we are trying to have the program produce.  In the case of the final rest positions, this is where the vehicles actually came to rest in the accident.  We are trying to see how close our SMAC model comes to the target damage and rest positions. 

 

Notice that there are Vehicle Damage Classification codes.   These are the codes produced by the program following the laws of physics for the information supplied.  They may or may not be the same as the user entered codes in Cards 80 and 85.  Likewise, we cannot specify where (position-wise) either of the vehicles is to finally come to a stop.  The user enters certain parameters in time, speed and rotation that will terminate the computations and animation, but not the actual positions.  The target positions are the positions where the vehicles in the incident came to rest. 

 

In the upper right of the screen, (Figure 527 – Card 1) two blocks control the Input and Output settings for the program.  The settings are Original, Default, and Metric.  The leftmost button controls the Input settings for the program.  Changing this setting will change how the data is shown on the screen. 

 

Caution should be used when changing to Metric as the inputs are truncated to the decimal setting selected for the program.  This change can have a small change in the files (Cards) that are used to create the Graphics and Animation for the program.

 

Above these two blocks are also two radio buttons that will configure the program for either one or two vehicles.  When the radio button is selected showing only one vehicle the second vehicle information is not only removed from view but is not sent to the datasets and therefore not be sent to the Graphics and Animation programs.

 

Figure 533 shows the Single Vehicle Interface. 

 

Figure 533

 

 

Selecting the 2 Vehicles radio button will restore the screen to the configuration in Figure 527. 

 

In the frame for Cards 4 and 5, the block labeled Inertia Moment (Yaw) is actually a button.  By clicking on this button a frame appears (Figure 534) that calculates the Yaw Moment of Inertia for the dimensions in the inputs for both vehicles.  These values can be transferred to the respective input blocks for the vehicles.

 

Figure 534

 

Down the center of the input blocks for Cards 4 and 5, two large buttons will allow the user to import the dimensions for different vehicles.  The buttons are labeled AS (AutoStats) and ASL (AutoStats Lite) Clicking on AS will bring up the frame shown in Figure 535.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 535

 

The new frame shows the Vehicle Exchange Files that can be set up in AutoStats.  Once a Vehicle’s data has been pulled up in the AutoStats program, it can be transferred to the Vehicle Exchange file by going to the last page of the data and pressing on selecting E for Exchange file (Figure 536).

 

Figure 536  

 

 

 

 

 

 

Figure 537

 

Once the vehicle is placed in the Vehicle Exchange Files, the REC-TEC program can call them up and then automatically transfer the data into the SMAC-RT section (or the Crush section).

 

Clicking on one of the vehicles displayed will transfer the data to REC-TEC and set up the frame for Cards 4 and 5 as shown in Figure 28.  Selecting V1 will then transfer the information to the input blocks for that vehicle as shown in Figure 35.  If the CNX button is selected, the data will not be transferred and the frame will return to its normal configuration (Figure 527).

 

Figure 538

 

 

Figure 539

 

Below the AS and ASL buttons are 2 buttons labeled V1 and V2 with a slider bar directly below them.  Clicking on these buttons will bring up a scale diagram of the vehicle based on the dimensions displayed in the input blocks.

 

Before displaying the Graphics for Vehicle 1, the setting for REC-TEC Graphics will be changed to a background color of Windows Default and for Wide Lines using the Graphics Icon directly below the main menu resulting in the display shown in Figure 540.

 

Figure 540

Selecting the ASL button brings up the AutoStats Lite page (Figure 541).  This selection does not require the user to own AutoStats as the Vehicle Exchange Option does.  If AutoStats is not installed on the computer then this is the only option for vehicle dimensions that will appear.  AutoStats Lite is built into the REC-TEC program and is available to all users.

 

Once the Make, Year and Model have been selected, the data for that vehicle will be displayed on the form.  In addition to the data, a block will appear that will return to SMAC-RT with the data (Figure 542).   Clicking on this block will cause the AutoStats Lite Page to disappear and bring up the SMAC-RT screen as displayed in Figure 543.

 

Figure 541

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 542

 

 

 

 

 

 

Figure 543

 

 

 

Figure 544

 

Clicking on the V2 Button will transfer the data to the input blocks on the SMAC-RT screen as shown in Figure 544.

 

Clicking on the 2 Button will bring up the REC-TEC graphics screen showing Vehicle 2 scaled to the dimensions shown in the input blocks (Figure 545).

 

Figure 545

 

Using the data transferred to the SMAC-RT screen using the AutoStats/AutoStats Lite files as the Run button is selected will change the outcome of the simulation as reflected in the Run animation and the Graphics and Animation as displayed in Figures 546 through 548.  Changing the dimensions of the vehicles, especially the masses of the vehicles even though the rest of the data remains the same has a dramatic effect on the simulation.

 

Figure 546

 

 

Figure 547

 

Figure 548

 

REC-TEC LLC has made a commitment to continually improve and upgrade their products keeping their users supplied with the very finest accident reconstruction tools available.  Upgrades will refine and enhance the already extensive capabilities of the SMAC-RT program.

 

Wheel Forces and Steer Angles - Cards 8, 9, 10 & 11

 

Figure 549

 

 

Cards 8, 9, 10, and 11, as seen on Figure 549, need a bit of explaining beyond the scope of the Help files.  Some of the boxes and associated features may be confusing at first.

 

Cards 8 and 9 deal with the Wheel Forces for vehicles 1 and 2 respectively.  They are the tractive forces that control acceleration (positive values) or deceleration (negative values) acting on the vehicles.  Manipulating these values for specific periods controls the acceleration or deceleration of the vehicle. 

 

Wheel (Torque) Forces may be entered by the traditional method of using a percentage of the weight on each wheel multiplied by the friction factor.  Alternatively, the program interface will compute the information if a number between –1 and + 1 is used for braking/acceleration.

 

Wheel Forces and Steer Angles can only be entered by time interval, not by using number of entries.  Older .Si5 files if not in the time interval format must be converted.

 

Associated with the individual sections for both Wheel Forces and Steer Angles on each vehicle there are rectangular green bars.  These green bars indicate that the program is setup to utilize the values for these entries.  Clicking on these bars will change the color and detail of the bar to indicate that the values for the chosen vehicle will be disregarded when the program is run.  Figure 39 shows the Wheel Forces as disabled. This allows the user the flexibility of turning off these values and comparing the runs with and without the features engaged.

 

Now that we have a better understanding of the gadgets in the blocks controlling the Wheel Forces and Steer Angles, look at the actual numbers that are placed in the cards for the individual vehicles.  Figure 40 shows the single entry for Wheel Forces for Vehicle 1 and Figure 41 shows the Steer Angles over the time at the prescribed interval for Vehicle number 2.  This is where we insert or modify the actual values that go into the computations and animation/simulation. 

 

If the user enters values from –1 to +1, the interface will automatically compute the appropriate values to enter into” INPUT.DAT” for Maximum Braking or Maximum Acceleration for the entered surface friction.  It is up to the user to determine the correct values to enter depending on the situation being modeled. 

 

Figure 550

 

Figure 551

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The Fun Begins – Setting up out first problem.

 

So how do we start to set up a problem? 

 

Once the SMAC section is opened, loading a recently included file named Default.Si5 will give us a jump-start in setting up a problem.  If Default.Si5 does not appear on the file list, simply create one using the values shown in Figure 552 and save it to the folder.  This file will set up some common values that can always be modified as your particular problem dictates.

 

Figure 552

 

As can be seen some common values have now been set (or partially set) for Cards 1, 6, 7, 12, 13 and 14.  This will speed up the process for creating out first problem.  Notice that the screen is set to use Default as the Input and Output units involved in this problem.

 

With Card 1 preset, Cards 2 and 3 can now be used to set up the problem.  Setting up the Initial conditions for the vehicles can be the most difficult part of the process.    While the desire is to show as much as possible dealing with the pre-impact phase of the collision, if we start the vehicles too far from each other initially, they may not even collide.  One of the biggest tricks in setting up a SMAC run is to set up the vehicles so that they are fairly close to impact and do the post-impact phase first so that it closely resembles the data we have. Once that is set, work on the pre-impact phase of the collision becomes less of a nightmare and the vehicles can be backed away from impact. 

 

Our problem will have a 2003 Ford police unit traveling at 35 m/h from west to east (90 degrees) when it is struck by a 2002 Chevrolet Z06 Corvette traveling at 30 m/h from south to north (0 degrees).  Both vehicles will be positioned 50 feet from impact Autostats was used to get the data for the vehicles. The resulting configuration is shown in Figure 553.   The SMAC Animation is shown in Figure 554.

 

Figur                                                                                                                                                                                                                                                                                                                                                              e 553

 

Figure 554

 

Wow, with just those few entries we staged a collision in a successful SMAC run. 

 

Notice that while the X and Y values for the position of the cars is measured “globally” using the X and Y for the scene (world) that the U and V velocity components are local to the vehicle.  Understand this and half of the battle has been won in working up SMAC runs.

 

For our problem, the police unit (#1) is struck in the right front wheel with the damage centered on the wheel. Since we are sure of our impact speeds from our calculations, how do we get the vehicles to hit so that the position of the collision damage in SMAC matches the damage resulting from the real world collision

 

With the speed set, the only way is to change the distance from impact of the vehicles.  If the Vehicle 2 X-coordinate is changed to –10 and the Y-coordinate is changed to 17 feet the vehicles strike each other in the correct location as can be seen in Figures 555 and 556.

 

Figure 555

 

As will be seen in Figure 556 and 558 (Enlarged) something very interesting happens.  The vehicles now have a secondary slap involved in the collision.  The only thing changed was the distance from impact and as can be seen, the post-collision actions of both of the vehicles are drastically changed.  This is the power of SMAC.  It uses the laws of physics to compute the motion of the vehicles.

 

Please take note that by stepping through the Animation we discover that impact for this collision occurs at 0.213 seconds into the animation.  This time will become important when we start repositioning the vehicles before impact.

 

 

 

Figure 556

 

 

Figure 557

 

In order to be able to work on this particular scenario in the future, go back to the main SMAC screen and save the file.  Name the file Problem45.Si5 so that it can be called up later without having to type the information in all over again.

 

Figure 558

 

Set the braking due to damage on Vehicle 1 to reflect the locked brake on the front right wheel.  Impact starts at .213 seconds.  Getting the drag to come on between 0.213 and 0.215 seconds requires two entries for the braking.  The entries are at 0.213 seconds and 0.215 seconds.  This has the effect of ramping up the braking from zero to full braking in the 0.002-second period between 0.213 and 0.215 seconds. 

 

Figure 559

 

With these changes in place, (see Figure 559 – Vehicle 1 entries) the effects can be seen in Figure 560. Because we are dealing with braking or deceleration, the value has a negative sign.  Note that with the SMAC-RT, we can enter the torque value or the braking based on -1 being full lockup.

 

Figure 560

 

Assume that the steering of vehicle was also changed to positive 10 degrees during the impact.  This change is shown in the graphics displayed in Figure 561.  It also shows very dramatically, why linear momentum angles are not measured to point of rest.

 

Figure 561

If we need to show more pre-impact tracking of the vehicles some adjustments are needed.  Using a minimum distance before impact of 50 feet for (CG) Vehicle 1, what must be changed in the problem?

 

If Vehicle 1 is traveling at 35 miles per hour or 51.3333 f/s, what needs to be changed to have Vehicle 1 start at 50 ft before impact?

 

In order to visualize the linear relationships a little easier, it may help to have the collision occur at the intersection of the X and Y-axes.  Changing the Vehicle 1 X-coordinate to zero and the Y-coordinate to –17 and the Vehicle 2 X and Y-coordinates to –20 and zero respectively accomplish this in our problem.  These changes are reflected in Figure 562.

 

Figure 562

 

With these changes in place, the graphics diagram now has the X and Y-axes (Light Blue) as shown in Figure 563.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 563

 

With these changes in place, the position of Vehicle 1 at impact is –6.07 feet.  This can be read from the V1PVA.DAT file using 0.213 seconds as the time of Impact.  In order to increase this to 50 ft from impact requires a change of 50 feet to a position of –56.07 feet on the Y axis. 

 

 

It takes 0.974 seconds for Vehicle 1 to cover 50 ft. Vehicle 2 covers 42.857 ft. in 0.974 seconds.   Vehicle 2 at impact is at –10.63 feet from the Y-axis.  We must move Vehicle 2 to a position –53.487 feet from the Y-axis. These are the figures needed to alter the program to reflect the changes necessary.  Vehicle 1 is now 50 feet from impact and Vehicle 2 is 42.857 ft from impact.  These changes are shown in Figures 564 and 565.

 

It is imperative that the times for Card 8 and Card 10 be changed as seen in Figure 564.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 564

 

 

Figure 565

 

If enough data is available for both the reconstruction and the subsequent SMAC simulations, the results of the SMAC-RT run should match the scene evidence, including the tire traces and the damage to the vehicles resulting from the collision.