Manning's Equation Question

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As far as the exam is concerned, I only ever used DW for closed pipe, and HW for open channel flow...might be oversimplifying it, but that's what comes to mind at the moment.

Edit: also mechanicals rarely use HW, at least in my experience. Also, DW is good for gases and other stuff besides water. HW is water only, I believe.

 
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For pipe flow, you can use either. It would just be about what you're given in a problem. 

For example:

f = 0.015 - definitely Darcy-Weisbach

C = 120 - definitely Hazen-Williams

 
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Will.I.Am PE said:
For pipe flow, you can use either. It would just be about what you're given in a problem. 

For example:

f = 0.0015 - definitely Darcy-Weisbach

C = 120 - definitely Hazen-Williams
Click to expand...
Neat! Elegant way of putting this. You're the hero EB needs, not the one it deserves. :rotflmao:

 
civilrobot said:
How do you know when to use Hazen - Williams vs the Darcy-Weisbach equation? 
Click to expand...
Also, another "trick" I learned was that even if not given, you can kinda-sorta-maybe get away with just assuming f=0.02 if it's water problem and proceed with solving DW. Be super careful about using this assumption, but if you're lucky, it might save you a few steps and a nice trick to keep in your back pocket. I used it once or twice, caveat emptor.

 
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squaretaper LIT AF PE said:
Also, another "trick" I learned was that even if not given, you can kinda-sorta-maybe get away with just assuming f=0.02 if it's water problem and proceed with solving DW. Be super careful about using this assumption, but if you're lucky, it might save you a few steps and a nice trick to keep in your back pocket. I used it once or twice, caveat emptor.
Click to expand...
yeah I have this written into my notes. 

if i'm given both f and C, I will use both to solve for the answer and review the options to select the available answer. that's the conclusion I needed to get to. I thought I was missing some other small elemental detail but @Will.I.Am PE confirmed that it's an either/or scenario.

 
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civilrobot said:
another PE?
Click to expand...
Electrical - Power. I explained it in the Power thread (no expectation for you to read all that), but basically I R super, super bad at strategy and I don't qualify for the license at this time. Buuuuut, I *DO* qualify for the electrical if I pass the stupid exam so...I'm still going to be around (and I'm basically doing it to make more money, stupid CA real estate pricing cleaned me out). Aaaanyway, you have another study buddy. You can do it! Go! Go! @civilrobot

 
squaretaper LIT AF PE said:
Electrical - Power. I explained it in the Power thread (no expectation for you to read all that), but basically I R super, super bad at strategy and I don't qualify for the license at this time. Buuuuut, I *DO* qualify for the electrical if I pass the stupid exam so...I'm still going to be around (and I'm basically doing it to make more money, stupid CA real estate pricing cleaned me out). Aaaanyway, you have another study buddy. You can do it! Go! Go! @civilrobot
Click to expand...
this is amazing!! i'll head over to power to read about it.

 

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