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Mar 10, 2022
09:49 AM

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Mar 10, 2022
09:49 AM

Piping System Flow Problem Using Solve Block

Hello,

Please see the attached problem for a piping system. Essentially I have the flow rates in and the pipe length and diameters and I am trying to solve for the flow rate in each leg of the piping system. This is example two in the attached Mathcad sheet. I will attach the tutorial below (from older Mathcad version).

The problem I am having is that the results produced by Mathcad from the solve block is not satisfying the equations for flow rate (see the last page on my attached worksheet). I am fairly sure the equation have been set up correctly so I don't see why Mathcad is accepting the answers I get as a solution when they are so far off from the constraints.

I have tried the following so far:

1. When using the find solver I get the error message that TOL/CTOL cannot converge. After playing with the tolerance I can get a solution using this method if CTOL 10^-2. I was thinking this may be why the constraint criteria is not met.

2. I have also tried to solve using the minerr function and the results are much the same.

Any help would be appreciated and thanks in advance for the help.

Many thanks,

Callum

Solved! Go to Solution.

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Mar 10, 2022
10:49 AM

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Mar 10, 2022
10:49 AM

You typed the wrong variables at the highlighted position (you repeated the previous summand with index BD instead of using the variables with index DC):

So the results sure are better that way

Now you may also user "find" instead of "minerr" (as shown in the screenshot of real Mathcad you provided).

With the typo you made Mathcad tried to do its best to minimize the errors and so far did a good job anyway but the system had no perfect solution that way 😉

2 REPLIES 2

Mar 10, 2022
10:49 AM

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Mar 10, 2022
10:49 AM

You typed the wrong variables at the highlighted position (you repeated the previous summand with index BD instead of using the variables with index DC):

So the results sure are better that way

Now you may also user "find" instead of "minerr" (as shown in the screenshot of real Mathcad you provided).

With the typo you made Mathcad tried to do its best to minimize the errors and so far did a good job anyway but the system had no perfect solution that way 😉

Mar 10, 2022
10:54 AM

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Mar 10, 2022
10:54 AM

Ah thanks Werner_E, I thought it must have been something silly like that!

That seems to be it working now.

Best Regards,

Callum