MADYMO & Occupant Simulation Reconstruction IMPORTANT issues

Subjects related to the reconstruction and simulation of Occupants in vehicles and Pedestrians struck by vehicles, ATB & ATB clones #ATB #MADYMO #MultiBody
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MSI
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MADYMO & Occupant Simulation Reconstruction IMPORTANT issues

Post by MSI »

Q: Do you use or have you evaluated any MADYMO applications in litigation cases?

A: We do not use MADYMO but we have been hired to evaluate MADYMO applications used in litigation. In one case in particular, from a few years ago, we evaluated an expert report who used the MADYMO occupant simulation program to evaluate injury potential in a low speed collision.
This post is to demonstrate that ANY and ALL occupant simulation needs to be carefully evaluated.
EVERY HUMAN is different!
  • For any case specific application of ANY occupant simulation approach:
    • Use and/or evaluate with extreme caution!
Occupant simulation models come in several flavors, however ALL are based on or direct derivatives of the ATB program:
  • What is ATB?
    • Explanation of the origins of the ATB with links to papers on it including two papers we wrote in response to 'experts' using ATB to 'reconstruct occupant movements in a crash' and then trying to sell simple silly changes in the inputs as 'design changes' to prove that their proposed design changes produced 'mitigation' of the injuries. Total garbage. And to generalize our main quote
      • "Any results or conclusions drawn from arbitrary and speculative occupant simulations related to individual crashes which experts claim produce detailed occupant kinematics involve so many approximations, estimates, and assumptions that they must be recognized as not being compatible with sound engineering practices and principles and, therefore, not scientifically supportable.
  • MADYMO program:
    • Includes important research which has improved vehicle safety however not applicable to individual crash reconstructions
  • pc-crash Multi_body option
    • this is a version of the ATB hidden as the 'multi-body' option, the references they cite are NOT for occupant simulation programs
    multibody references all.png
    multibody references all.png (154.52 KiB) Viewed 333 times
    • These are advanced classroom textbooks which do not address the actual coding and implementation into a computer simulation program, as if, it might be easy work?!
      • See What is ATB where we present and discuss the brilliant pioneering work by Dr. John Fleck which included extremely efficient integration routines for economical execution of the program and the addition of many extensions and refinements to move the mathematical model from 2 dimensions to 3 dimensions
      • For some reason they pretend it is NOT ATB.
        IT IS ATB!
        • and therefore NOT applicable to individual crash reconstruction
  • pc-crash simplified MADYMO option
    • This is such a stripped down version of MADYMO it doesn't have ability to customize the interior to match and/or other severe limitations and of course NOT applicable to individual crash reconstruction
  • GATB
    • this is simply a version of the ATB that works in the HVE environment and NOT applicable to individual crash reconstruction
  • Virtual CRASH
    • They use a version of the ATB for their pedestrian and passenger simulations
      From the Virtul Crash Ver 3/4/5 User's Guide:
      • p 345: "Most biomechanics-type simulation tools, such as ATB, will treat the occupant model as essentially a flaccid body, with no active muscle control – Virtual CRASH is no different"
      • "Virtual CRASH includes the ability to simulate an “optimized” human model that will hold its pre-impact pose until it comes into contact with a surface within the environment, at which time the pose is “released” and the human model is treated as a flaccid body (the user can control joint rigidity)."
      • p621 "As in other biomechanics-type simulation programs, such as Articulated Total Body(27), the Virtual CRASH human model is a multi-ellipsoid system connected by joints."
      • reference 27: "See SAE 950131"
        • which is SAE Paper "Using ATB in collision reconstruction" by Wesley Grimes, author of GATB which is ATB working in the HVE environment. see GATB above
        NOTE: to simply Hold the pre-positioned ATB model until arbitrarily released by user choice is not a creation of a 'human model' and it does not improve or change the lack of fidelity of ATB for individual case reconstructions.
        It merely provides a way to try to hide the fact that ATB does NOT model active human muscles or responses it is as they say ATB is "essentially a flaccid body, with no active muscle control"
Here are the conclusions from the case where we evaluated a MADYMO application (Note NAMES AND DATES REDACTED):
  • Summary and Conclusions
    In summary, the authors of the EXPERT report did not properly perform a scientific investigation or reconstruction of the subject accident. They provided arbitrary and speculative opinions based on limited and incomplete information, they did not use or reference any current techniques to reconstruct a collision like the subject accident, they included arbitrary calculations of impact duration and range of speed with no scientific basis.
    The authors of the EXPERT report then used their opinions as the basis to perform a 3D occupant simulation of OCCUPANT in the subject collision.
    The authors of the EXPERT report utilized the MADYMO 3D simulation model with the following deficiencies:
    • They did not properly create an acceleration substantially similar to the acceleration in the subject accident.
    • They did not properly create and include any provisions for the interior of the Jeep with seat, floor, dash, center console, B pillar and side glass substantially similar to the vehicle at the time of the collision.
    • They did not properly create a 3-point restraint system substantially similar to the belt in the vehicle at the time of the accident.
    • They did not properly create inputs to model OCCUPANT and place her in a position and orientation for their MADYMO simulation that was substantially similar to the position and orientation of OCCUPANT at the time of the impact (i.e., turned to left in preparation for making a right turn).
    Any results or conclusions drawn from their arbitrary and speculative MADYMO 3D occupant simulation related to detailed occupant kinematics involve so many approximations, estimates, and assumptions that they must be recognized as not being compatible with sound engineering practices and principles and, therefore, not scientifically supportable.
Here's the original report (redacted):
For additional related information Please see:
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MSI
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Re: MADYMO & Occupant Simulation Reconstruction IMPORTANT issues

Post by MSI »

Just saw posted up to Linkedin by Explico Engineering Company the following:
  • "Explico's 3D visualization capabilities are rapidly expanding. Check out a recent visualization our team created, which can be interacted with through our custom, real-time, vehicle collision visualizer. The vehicle and occupant dynamics are input directly from Virtual CRASH and Simcenter MADYMO, respectively, and all rendering is real-time.
    #visualization #biomechanics #sideswipe #forensicengineering #siemensplm #MADYMO


Our response to the posting:
  • This is a similar situation to case discussed above. In this case...
    • A visualization was 'based' on
      • a Virtual Crash simulation (which includes the simplifying assumption of an instantaneous momentum exchange) to simulate a sideswipe interaction!
        • A sideswipe is
          • a much longer than instantaneous interaction,
          • much longer than a normal collision,
          • It is where forces acting along the vehicles interact as they pass each other for part or all of the side of the shorter vehicle
        • Then they fed something created from the "instantaneous exchange" reconstruction by Virtual Crash into the MADYMO simulation program to simulate the occupant movements.
          • No doubt the assumed some simple waveform approximation of the instantaneous momentum exchange to model the sideswipe
            What version of MADYMO? Did they measure the occupant space and make the MADYMO representation similar? since some have limits on the occupant space.
      Then these highly subjective 'reconstructions' (vehicles and occupants) were then fed to a visualizer by Explico Engineering Company to no doubt use in court to try to sway jurors to imply "scientific validity" when in fact it is simply a smoke screen without scientific foundation, validation or correlation with the actual reality of the 'sideslap' collision interaction and occupant response.


    Please read the summary of a similar fictionalization of occupant responses in another case documented above
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Re: MADYMO & Occupant Simulation Reconstruction IMPORTANT issues

Post by MSI »

added some references to some of the description in response to some questions on this post.
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Re: MADYMO & Occupant Simulation Reconstruction IMPORTANT issues

Post by MSI »

For additional information on the origins of MADYMO see:
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