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# Mathcad help finding variable value

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## Mathcad help finding variable value

(OP)
I have a set of results from a simulation, in the form of a velocity along with the corresponding distance from the pipe centre. There are about 20 points.

I also have an equation that tries to model this, so i can enter in the same distances from the pipe centre and i want the output to be as close as possible to the simulation velocities.

To do this i have added some variables (at the moment 1 ("b") but i may progress to have 2 variables) to my formula which i wish mathcad to define for me...

How do i go about this, i have tried but, very, unsuccessful

### RE: Mathcad help finding variable value

MathCad does units REALLY well.  Not using them is totally irresponsible.  In your sheet you define R:0.1524.  Well if you'll let it, MathCad will call "R" "temperature in degrees Rankine".

If I can puzzle out where you started, it looks like
"d" is density and if I assume water, then it is in kg/m^3
"v" is viscosity (I'll assume 20C) in N*s/m^2
"R" is radius and I'll guess it is in m
"Vm" by process of eliminiation it must be mean velocity in m/s

Those assumptions get to the Reynolds Number you calculated.

Given that, I couldn't get the solve block to converge.  Why are you trying to use "find" instead of "genfit"?  I don't think that MathCad will do a "find" with an imbeded array.

David

### RE: Mathcad help finding variable value

IRstuff,
That answer gives you a different "b" for every "r".  He's looking for a single "b" that generates a data set that matches "v".

David

### RE: Mathcad help finding variable value

Then he should be doing a curve fit

### RE: Mathcad help finding variable value

Dang, that is what I told him 2 days ago.

David

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