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04-30-2013
08:53 PM

04-30-2013
08:53 PM

Mathcad Prime Solve Blocks Not Working!

I'm running into major problems with Mathcad Prime not wanting to solve my equations. They work in the old versions but not in this one. The find wasn't working and now it's saying my Velocities arn't defined. Any help would be greatly appreciated.

16 REPLIES 16

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04-30-2013
09:34 PM

04-30-2013
09:34 PM

Re: Mathcad Prime Solve Blocks Not Working!

The answers should be:

8.408

-4.345

12.753

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05-01-2013
04:23 AM

05-01-2013
04:23 AM

Re: Mathcad Prime Solve Blocks Not Working!

This is again a problem with mathcad prime solve block........

the labeling

in your solve block

for the definitions, all Vs are labeled as "variable"

then everywhere else they are labeled as "none"

try changing all Vs label, (definitions, equations , and fin() ) to "variable"

or change all of them to "none".

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05-01-2013
04:44 AM

05-01-2013
04:44 AM

Re: Mathcad Prime Solve Blocks Not Working!

Seth Erickson wrote:

The answers should be:

8.408

-4.345

12.753

If you substitute these 'solutions' into your equations you find that the RHS of the third equation does not match that of the LHS.

Alan

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05-01-2013
04:53 AM

05-01-2013
04:53 AM

Re: Mathcad Prime Solve Blocks Not Working!

Agree with Alan...I just spotted that too

and the RHS of the second and third equation are the same...so he has only 2 equation with 3 unknowns?

looks like the second two equation is energy balance (bernoulli equation) why there is a negative for the kinectic energy term on the LHS? I am confused. Do they come from the RHS originally? I do not understand the physics. Do you have a split? is your control volume enclosing the junction?

I think : Energy into junction = Energy out from split A + Energy out from split B

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05-01-2013
05:11 AM

05-01-2013
05:11 AM

Re: Mathcad Prime Solve Blocks Not Working!

Changing the labels did not work for me. But deleting the three guess values and retyping them will let the error vanish. Try it yourself - type V_3x= right after the definition of the guess und you get the error of the variable not known. This happens even if they are labeled the same.

But the solutions now are just the guess values, so obviously there is still something wrong.

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05-01-2013
05:14 AM

05-01-2013
05:14 AM

Re: Mathcad Prime Solve Blocks Not Working!

and the RHS of the second and third equation are the same...so he has only 2 equation with 3 unknowns?

Why? This would only be true if the third equation would consist of setting equal the two LHSs which is not the case.

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05-01-2013
05:28 AM

05-01-2013
05:28 AM

Re: Mathcad Prime Solve Blocks Not Working!

I think a got the main probem - it was not the labelling: It looks like the guess values and equations were typed outside the solve block and then dragged inside. So they look like they are in the solve block template but for Prime they aren't. Prime does not "see" these definitions. Thats the reason is seemed to work when I retyped the guess values.

Copy and paste should work (there was an error in the first release of Prime2 with copied expressions in a solve block) but moving it does not.

You may try it yourself: if you are able to drag/move a region outside of the solve block template, then there is something wrong.

Addiotionally the multiplication signs after pi were missing in the first equation.

In the attached all should be corrected, nevertheless Prime finds no solution which could be because, as Alan pointed out, there seems to be something wrong with the equations as the supposed solutions don't fit.

EDIT: If you change L_2h in the third equation to L_3, you get the expected results.

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05-01-2013
11:53 AM

05-01-2013
11:53 AM

Re: Mathcad Prime Solve Blocks Not Working!

You are right. what was I thinking...um...

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05-01-2013
12:13 PM

05-01-2013
12:13 PM

Re: Mathcad Prime Solve Blocks Not Working!

I see in your sheet pi(D)^2 (a function) but must be pi*D^2 (multiplication).

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