Unitless Calculations?

[ibartonico]

i'm doing a calculation where the units cancel out in an exponential equation.  However, MathCad will not evaluate the equation because the value is unitless.  Is there a way to turn off units in a calculation? If not, is there a way to get around this error?  Thanks

[RichardJ]

That should work. Could you post a worksheet showing the problem (to post a worksheet, in the edit dialog click on "Use advanced editor" at the top right).

[ibartonico]

I hope i posted it correctly as an attachment.  Thanks for your reply and let me know if anything else is needed. 

[AndyWesterman]

Hi,

the value of L.z shows as 344.177 ft^1.2, so the error message that Mathcad is giving is correct.

The units don't cancel out properly.

If this is an empirical equation then it might be that you have to apply a correction factor,

Otherwise you will need to look at the definition of L.z again

regards

Andy

[ibartonico]

The bases of these equations are from ASCE...

So the only way to do unitless equations is to apply correction factors?

[AndyWesterman]

if the equation is correct and you have data that you can use to verify the program , then it is possible to multiply by say "ft^0.2" to reduce the result to a unit-less quantity  (as attached).

It is necessary to check, the result would be the same, but different if you multiplied by "m^0.2".

Mathcad would give an answer but there could/would be a scaling error (NASA syndrome).

Which one is correct ... ???

Regards

Andy

[RichardJ]

If you have an empirical equation it usually has specified units for the input quantities and the output quantity, but you can't use quantities with units attached because the units in the equation don't balance. In Mathcad you can modify the empirical equation by dividing all input quantities by the specified units, and multiplying the entire equation by the specified output units. Then it will work with input quantities with units attached.

[Fred_Kohlhepp]

You are dividing zbar by 33, but zbar is in feet.  If 33 is also feet, then your problem goes away.  (33 is close to the height of a column of water at 1 atmosphere, is that where it came from?