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741 Views, 13 Replies

02-20-2012 12:14 AM

I would like to edit Revit default formula for pipe friction factor,

where can I edit it?

The following link shows Revit's formula:

which is

friction factor (f) = (1 / (2 * log10 (3.7*e))) ^ 2

thanks!

Solved! Go to Solution.

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02-21-2012 07:28 AM in reply to:
hkdavid

I don't think that you can edit Revit's calculation formulas, they are hard-coded. Submit your issue with Autodesk Feedback/Support and provide reasons why you wish to edit this formula.

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02-21-2012 07:52 AM in reply to:
hkdavid

The current formula is a simplified, factorable version of the Colebrook equation. It is presently not possible to edit this formula. What would you expect the formula to be?

Product Manager - Revit MEP

Architecture, Engineering, and Construction

Autodesk, Inc.

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02-21-2012 08:05 AM in reply to:
martin.schmid

Martin:

Thanks for your reply.

Your are right, according to Colebrook equation

1/√f = -2log(2.51/Re/√f+ε/3.7D)

In Revit, it simplifies to

1/√f = 2log(3.7*D/ε)

My formula expressd Colebrook in a expanded form

1/√f =1.74-2log(18.7/Re√f+2ε/D)

which has a more accurate result

So I would like to edit Revit's forumla which leads a more accurate result.

Thanks anyway.

Hope Revit can allow edit built in equations in the future.

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02-22-2012 12:34 AM in reply to:
hkdavid

One challenge with the stnadard Colebrook formula is that it is inherently recursive, which computing may be detrimenal to performance. Would the solution to this as presented in: http://math.unice.fr/~didierc/DidPublis/ICR_2009.p

Product Manager - Revit MEP

Architecture, Engineering, and Construction

Autodesk, Inc.

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02-22-2012 01:23 AM in reply to:
martin.schmid

Thanks Martin. It really helps to get a closer answer.

Hope Revit can intergrate a better customize computation method to suit engineers.

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02-20-2013 10:55 AM in reply to:
martin.schmid

Dear,

I've made a lot of pipedrop calculations with REVIT but the answers seems to be incorrect for turbulent flow. I think the friction factor calculation is much to far simplified. The answer seems to be a factor 3 incorrect with other computer calculations or manufacture tables.

I've made two caculations for REVIT and 1 calculation for a alternative friction factor formulas (see the pdf attached). This formula is commonly used in piping software. I really hope that I do something incorrect.

I'll hope you can help me.

Greatings,

Bastiaan

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02-26-2013 06:42 AM in reply to:
bas2107

Hello Bastiaan-

I want to make sure I understand the full extent of your scenario.

I'm trying to replicate your case, and am not quite sure how you got the Reynolds value of 6391.

From the document, I am getting:

R = pVL / u

p = exactly 983 kg/m^3

v= exactly 0.215 m/s

L = exactly 0.012 m

u = exactly 4.0e-4 Pa*s

R = 6340

If I use the un-rounded value for v from Revit (0.215142), I get :

R = 6345

How did you arrive at

R=6391

Thanks for any clarification you can provide.

Product Manager - Revit MEP

Architecture, Engineering, and Construction

Autodesk, Inc.

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03-07-2013 06:59 AM in reply to:
hkdavid

I think the difference is the use of Pi.

I rounded this number on 3.14.

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04-18-2013 12:29 PM in reply to:
hkdavid

Can you please help me to change the calculation method of the pipe settings calculation??

In the new version (revit 2014) the method of the "duct" calculation is correct but for "pipe" is still the wrong simplified Colebrook equation used.

How can I change this pipe calculation methode to be the same as the "duct"?

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