Simulation Analysis: Effects of Input Variations

Question on 3D Simulation/msmac3D/HVOSM and other 3D Simulation models
MSI
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Simulation Analysis: Effects of Input Variations

Post by MSI »

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This is response to the question posted on INCR about Momentum which morphed into a question on simulation:
  • "I wonder how many of the simulation program users have played with some of the unmeasurable factors that go into the analysis, such as tire cornering stiffness, suspension parameters, inter-vehicle friction, etc. to see what the actual effects are? There is a tendency to blindly use default values without ever really knowing what the effects of these parameters are"
OUR RESPONSE:
  • Main points:
    • What was mentioned as 'unmeasureable" are measureable
      And then to point out the need to differentiate between simulation programs:

SMAC Type Simulation programs
  • First i'd mention that what you mention as 'unmeasureable" are measureable.
    • Cornering stiffness and suspension parameters are by default approximated however they can easily be changed via inputs based on measured values or to test sensitivities. In general typical approximated values for these variables correlate well in validation tests.
    • The inter-vehicle friction coefficient is a variable to represent and reflect how "sticky" the vehicle interactions are (how sticky is their interaction?) and the default approximation of 0.55 SHOULD be tested for sensitivities if an impact configuration and interaction seems to indicate more or less than 'typical' type interaction
      • msmac3D is also the only version of SMAC which includes the ability to model a SNAG option which can be used to model tensile forces in the event the collision interaction goes beyond simple collision forces and coulomb friction (say for example if a component like a tire gets ripped out during the collision interaction?
    .
Instantaneous Exchange Momentum Simulation Programs
  • When you get into Momentum simulation programs like PC-CRASH, Virtual Crash, Planar Impact Models, and others the inputs for suspension and tire properties are measurable, however...
    • Some inputs are NOT measurable, are subjective and arbitrary with no objective input instructions:
      For example, HOW to set the LOCATION, the ANGLE and the LOCATION for the INSTANT of the momentum to be "instantaneously exchanged"
      How do you best approximate the 50 to 150 or more instants during a collision interaction as a SINGLE INSTANT?
      • We paid to watch 401 Staged Collisions: Validation 401 a pc-crash instruction video. We were hoping to find objective guidance on the inputs for the momentum exchange approximation. There was nothing about how to objectively set the instantaneous exchange. They merely adjusted it to produce their desired/known result in the video.
        • Simplified momentum equations and programs require the user to pick a point and angle/direction to instantaneously exchange the momentum of a vehicular crash.
          Any vehicular crash takes 50-150 milliseconds (or more) for the collision interaction which these programs/equations consider a SINGLE 'instant'.
          When applying a momentum solution it is subjective and random HOW a user sets the LOCATION and the ANGLE/DIRECTION for the INSTANT of the momentum to be "instantaneously exchanged"

          Please see
        Until then BE SURE to test moving and changing your assumed point and angle or however characterized for the INSTANTANEOUS MOMENTUM EXCHANGE to see how much it changes your results. Sometimes minor changes can make dramatic differences.
        • In our experience in evaluating applications of momentum based programs which formed a basis for "expert" opinions we have been generally able to make minor changes/adjustments in the subjective inputs and "prove" an alternative opinion.
Main point is when talking about vehicle crash simulation programs be sure to differentiate between There IS a MAJOR difference!

When Raymond R McHenry invented SMAC (and the other programs he invented) he brilliantly found the right combination of scientific sophistication and modeling simplicity for the time and budget constraints. And the continued prevelance of so many of his ideas and programs is a great demonstration of his brilliance.His analytical modeling and inputs were and are based on his extensive experience in vehicle suspension design.

Please give our mSMAC3D program a try, 2020 year end specials in effect.

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