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Member
hkdavid
Posts: 3
Registered: ‎02-20-2012
Message 1 of 14 (741 Views)
Accepted Solution

Edit built in formula (pipe friction factor) manually

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:

http://wikihelp.autodesk.com/Revit/enu/2012/Help/Revit_User%27s_Guide/3156-Referenc3156/3173-Pipe_Si...

 

which is 

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

 

thanks!

*Expert Elite*
CADastrophe
Posts: 3,117
Registered: ‎08-28-2009
Message 2 of 14 (719 Views)

Re: Edit built in formula (pipe friction factor) manually

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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Employee
martin.schmid
Posts: 1,297
Registered: ‎11-16-2005
Message 3 of 14 (716 Views)

Re: Edit built in formula (pipe friction factor) manually

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?

 

 



Martin Schmid, P.E.
Product Manager - Revit MEP
Architecture, Engineering, and Construction
Autodesk, Inc.

Member
hkdavid
Posts: 3
Registered: ‎02-20-2012
Message 4 of 14 (704 Views)

Re: Edit built in formula (pipe friction factor) manually

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.

Employee
martin.schmid
Posts: 1,297
Registered: ‎11-16-2005
Message 5 of 14 (688 Views)

Re: Edit built in formula (pipe friction factor) manually

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.pdf be an acceptable method to solve?



Martin Schmid, P.E.
Product Manager - Revit MEP
Architecture, Engineering, and Construction
Autodesk, Inc.

Member
hkdavid
Posts: 3
Registered: ‎02-20-2012
Message 6 of 14 (686 Views)

Re: Edit built in formula (pipe friction factor) manually

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.

Member
bas2107
Posts: 5
Registered: ‎02-20-2013
Message 7 of 14 (499 Views)

Re: Edit built in formula (pipe friction factor) manually

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

Employee
martin.schmid
Posts: 1,297
Registered: ‎11-16-2005
Message 8 of 14 (433 Views)

Re: Edit built in formula (pipe friction factor) manually

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.

 



Martin Schmid, P.E.
Product Manager - Revit MEP
Architecture, Engineering, and Construction
Autodesk, Inc.

Member
bas2107
Posts: 5
Registered: ‎02-20-2013
Message 9 of 14 (349 Views)

Re: Edit built in formula (pipe friction factor) manually

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.

 

Member
bas2107
Posts: 5
Registered: ‎02-20-2013
Message 10 of 14 (257 Views)

REVIT 2014 - change pipe calculation method

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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