ACCEPTED SOLUTION
Accepted Solutions
Andy Stevenson wrote:
I don't think it's that simple but I've been wrong before. As the numerical integration moves forward in time, the input torque is a function of one of the computed states. So to use interpolation, I'd have to integrate for a few milliseconds, interpolate a new torque value based on shaft speed at the end of the integration, restart the integration with the new torque value and so on.
It depends upon what you're doing and how you're trying to do, but, yes, you're right. However, this isn't really a problem as far as Mathcad is concerned if you include the interpolation function in your DE, as in the example below. If you have a reasonably good fit to your data from one of the fitting functions then you could improve the efficiency by explicitly writing the parameters into the generic fitted function (eg, write a polynomial function using the regress parameters in the case below); this should improve performance if this turns out to be an issue.
Stuart
Andy Stevenson wrote:
I don't think it's that simple but I've been wrong before. As the numerical integration moves forward in time, the input torque is a function of one of the computed states. So to use interpolation, I'd have to integrate for a few milliseconds, interpolate a new torque value based on shaft speed at the end of the integration, restart the integration with the new torque value and so on.
It depends upon what you're doing and how you're trying to do, but, yes, you're right. However, this isn't really a problem as far as Mathcad is concerned if you include the interpolation function in your DE, as in the example below. If you have a reasonably good fit to your data from one of the fitting functions then you could improve the efficiency by explicitly writing the parameters into the generic fitted function (eg, write a polynomial function using the regress parameters in the case below); this should improve performance if this turns out to be an issue.
Stuart
Andy Stevenson wrote:
Do you have any suggestions for modeling stiction? Seems life a similar approach would work but modeling the stiction as a piece wise linear function of shaft speed and direction with speeds around zero causing coefficient of friction to increase and then converting to sliding friction outside the "zero" speed window.
That should work. I don't know anything about friction (having forgotten most of my O-Level physics!), but something like this?
Stuart
Andy Stevenson wrote:
You rock dude!
True. 
But you try telling that to the young folk of today, and they don't believe you!
