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Edit built in formula (pipe friction factor) manually

13 REPLIES 13
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Message 1 of 14
hkdavid
1576 Views, 13 Replies

Edit built in formula (pipe friction factor) manually

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!

13 REPLIES 13
Message 2 of 14
CoreyDaun
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.

Corey D.                                                                                                                  ADSK_Logo_EE_2013.png    AutoCAD 2014 User  Revit 2014 User
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⁞|⁞ Please use Mark Solutions!.Accept as Solution and Give Kudos!Give Kudos as appropriate to further enhance these forums. Thank you!
Message 3 of 14
Martin__Schmid
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
Product Line Manager
Mechanical Detailing and Electrical Design
Architecture, Engineering, and Construction
Autodesk, Inc.

Message 4 of 14
hkdavid
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.

Message 5 of 14
Martin__Schmid
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
Product Line Manager
Mechanical Detailing and Electrical Design
Architecture, Engineering, and Construction
Autodesk, Inc.

Message 6 of 14
hkdavid
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.

Message 7 of 14
bas2107
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

Message 8 of 14
Martin__Schmid
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
Product Line Manager
Mechanical Detailing and Electrical Design
Architecture, Engineering, and Construction
Autodesk, Inc.

Message 9 of 14
bas2107
in reply to: hkdavid

I think the difference is the use of Pi. 

 

I rounded this number on 3.14.

 

Message 10 of 14
bas2107
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"?

Message 11 of 14
Martin__Schmid
in reply to: bas2107

in your pdf previously, you showed using the Swamee-Jian equation
Currently, Revit computes the Duct friction factor using the Altshul-Tsal method.

 

Would you prefer Swamee-Jian for both, or Altshul-Tsal?

 



Martin Schmid
Product Line Manager
Mechanical Detailing and Electrical Design
Architecture, Engineering, and Construction
Autodesk, Inc.

Message 12 of 14
bas2107
in reply to: Martin__Schmid

Both the formula's have almost the same answer for my working field. It's also okay to use the Altshul-Tsal formula. Is it easy to use this one for "pipe" also?

Message 13 of 14
bas2107
in reply to: Martin__Schmid

Dear Martin,

 

It's really disappointing that I get nog response from Autodesk. My subscription helpdesk tels me that I'll have to wait for your solution but I don't get any response on this forum.

 

I really got a big problem because my model is worthless because the friction factor formula for pipe is incorrect. Can you please give me the option to use the "duct calculation" methode als for the "pipe calculation" in Revit 2014. The solution seams very nearby and this makes it even more frustrating.

 

Or can you tell me how to adjust the formula?

 

Waiting for your response.

 

Greatings,

Bastiaan

 

Message 14 of 14
baltt
in reply to: hkdavid

Hi David

 

A workaround would be to apply your own "Constant Factor" to your results.

 

Do a few calculations and notice a pattern. Use your engineering skills to figure out what that constant is and apply

it to your results. In other words develope your own formula.

 

Cool stuff uh?

 

 

 

 

 

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