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Feb 06, 2015
03:04 AM

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Feb 06, 2015
03:04 AM

how to handle unit less numerical factor in equation

Hello all

i am using mathcad 15

while defining a variable, mathcad shows an error for a unit less numerical factor

Error

"This value has units:Unitless,but must have units:Length."

in the same way i have used unit less numerical factor it doesn't shows any error

i am confused , anyone please help me out

regards

Balaji

Solved! Go to Solution.

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Feb 06, 2015
07:35 AM

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Feb 06, 2015
07:35 AM

Balaji k wrote:

Thanks for your reply'

i tried this option also

but this is the standard template sheet , in that i have to use the formula what it was given in code book(Design standard)....

is there any other option to solve this issue....(with out mentioning the unit inside the formula)

Regards

Balaji

With respect to your "code book":

This looks like pipe stress calculation, also known as hoop stress. For a given stress (f) you're solving for what pressure you may have.

Hoop stress is simple: stress = (pressure)*(radius)/thickness, and orthogonal to it (pressure)*(radius)/(2*thickness)

d is pipe diameter?

e_rt is wall thickness?

So your d-2 should be d/2 to get the radius.

8 REPLIES 8

Feb 06, 2015
03:09 AM

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Feb 06, 2015
03:09 AM

Hi,

It would be better if you attach Mathcad worksheet, not a picture.

Feb 06, 2015
03:34 AM

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Feb 06, 2015
04:01 AM

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Feb 06, 2015
04:01 AM

looks like d.o has units of mm so you need to tell mathcad what the offset units are: m, mm, ft, in ...

Feb 06, 2015
04:06 AM

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Feb 06, 2015
04:06 AM

Thanks for your reply'

i tried this option also

but this is the standard template sheet , in that i have to use the formula what it was given in code book(Design standard)....

is there any other option to solve this issue....(with out mentioning the unit inside the formula)

Regards

Balaji

Feb 06, 2015
05:11 AM

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Feb 06, 2015
05:11 AM

I think there isn't. Well, work without units altogether, but I consider that NO option.

If the "code book" is prescribing the formula as ".../[(do - 2) + ert]" it MUST (preferrably explicitly) define the unit of 2. If not, you can seriously question the "code book".

success!

Luc

Feb 06, 2015
05:15 AM

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Feb 06, 2015
05:15 AM

If you can't change the formula, that makes the problem very difficult.

The next option is to strip the units from everything.

Its not ideal, and does make you responsible for checking that every part of your calculation is correct.

With units, MathCad will at the very least give a little bit of a sanity check.

Unfortunately (as with the °C issue) MathCad has a simple interpreter to take the instructions on the sheet & determine the calculations to perform.

if you ask it to add 508mm and 2; what does that mean?

is it 2mm -> 510mm?

is it 2m -> 2508mm?

Even I (as a human) can't say if either of these answers is correct.

Feb 06, 2015
07:35 AM

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Feb 06, 2015
07:35 AM

Balaji k wrote:

Thanks for your reply'

i tried this option also

but this is the standard template sheet , in that i have to use the formula what it was given in code book(Design standard)....

is there any other option to solve this issue....(with out mentioning the unit inside the formula)

Regards

Balaji

With respect to your "code book":

This looks like pipe stress calculation, also known as hoop stress. For a given stress (f) you're solving for what pressure you may have.

Hoop stress is simple: stress = (pressure)*(radius)/thickness, and orthogonal to it (pressure)*(radius)/(2*thickness)

d is pipe diameter?

e_rt is wall thickness?

So your d-2 should be d/2 to get the radius.

Feb 06, 2015
08:25 AM

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Feb 06, 2015
08:25 AM

yes you are right,

i am calculating how much pressure a pipe can withstand at design condition...

yes i made a mistake while deriving the equation it is not " d - 2" it is "d - e"

thanks for your reply

i am in hurry to complete this task in a very tight schedule

but i am very new to mathcad ....started working in MATHCAD few day back

i need all of our PTC community members support

thankyou every one for spending your preciuos time and sharing your knowledge