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Max Well · 07-13-2015, 03:43 PM

Thank you for your comments, exon.

All of your points are indeed very sound, and I suspect the folks who design professional vehicle modelling software implement coefficients and/or equations which can capture those concepts. As much as I would like to have the knowledge base (not only in Physics and Engineering but also computer programming) to incorporate such variables, as I mentioned in my introductory statements, 'this is an approximated simulation and cannot account for the infinite variables ...'. The model developed by Matthew Snare and Dr. Rakha, however, provides a reasonable and practical solution which fits quite nicely into the goal set forth initially - to be able to paint a broad picture of a vehicle's 'maximum acceleration rates' while (whilst) varying load, grade, altitude, and Cd. And I must admit I have been quite surprised to find it agreeing fairly closely with published times for 0-60 mph and 1/4 mile times as published by BMW and Automobile Catalog in Model (A) simulations.

As I was unable to find such information (how these variables affect our X3s) anywhere online, this at least provides us with a construct with some validity behind it to show how all these come together. And one point on the 'precision'. I always get confused over the terms 'precision' vs 'accuracy'. As this model makes calculations every 0.1 sec for 88 seconds, and the same construct of equations (and thereby methodology) is used for every simulation of the (A), (B), (C), and (G01) types, I think the precision should actually be quite good. What is clear, however, is that the 'accuracy' of the data points (in comparison to real-life measured data) is most certainly off to some extent. Matthew spend a lot of time proving this model provides a reasonable validation with actual field numbers in the 13 cars he and his team tested, so I am comfortable with using it for our purposes here.

And I'm not sure if you have had a chance to read Matthew's thesis yet, but he took it even one step beyond just the maximum vehicle acceleration model, by trying categorize 'acceleration behavior of drivers'. That is way beyond the scope of this thread, but clearly is also another important variable when it comes to merging in real life.

Thanks again for reading. Up next, the 20d and 20i models when I get some time.

07-13-2015, 03:43 PM	#7
Max Well Colonel 4789 Rep 2,546 Posts Drives: '22 BG X3MC, '20 BSM X3MC Join Date: Jun 2014 Location: Southeast USA iTrader: (0)	Thank you for your comments, exon. All of your points are indeed very sound, and I suspect the folks who design professional vehicle modelling software implement coefficients and/or equations which can capture those concepts. As much as I would like to have the knowledge base (not only in Physics and Engineering but also computer programming) to incorporate such variables, as I mentioned in my introductory statements, 'this is an approximated simulation and cannot account for the infinite variables ...'. The model developed by Matthew Snare and Dr. Rakha, however, provides a reasonable and practical solution which fits quite nicely into the goal set forth initially - to be able to paint a broad picture of a vehicle's 'maximum acceleration rates' while (whilst) varying load, grade, altitude, and Cd. And I must admit I have been quite surprised to find it agreeing fairly closely with published times for 0-60 mph and 1/4 mile times as published by BMW and Automobile Catalog in Model (A) simulations. As I was unable to find such information (how these variables affect our X3s) anywhere online, this at least provides us with a construct with some validity behind it to show how all these come together. And one point on the 'precision'. I always get confused over the terms 'precision' vs 'accuracy'. As this model makes calculations every 0.1 sec for 88 seconds, and the same construct of equations (and thereby methodology) is used for every simulation of the (A), (B), (C), and (G01) types, I think the precision should actually be quite good. What is clear, however, is that the 'accuracy' of the data points (in comparison to real-life measured data) is most certainly off to some extent. Matthew spend a lot of time proving this model provides a reasonable validation with actual field numbers in the 13 cars he and his team tested, so I am comfortable with using it for our purposes here. And I'm not sure if you have had a chance to read Matthew's thesis yet, but he took it even one step beyond just the maximum vehicle acceleration model, by trying categorize 'acceleration behavior of drivers'. That is way beyond the scope of this thread, but clearly is also another important variable when it comes to merging in real life. Thanks again for reading. Up next, the 20d and 20i models when I get some time.
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