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egu1-Visitor
1-Visitor
April 6, 2016
Solved

Solving equations approximated simultaneously

  • April 6, 2016
  • 2 replies
  • 5073 views

Hi, I started using Mathcad a few days ago, and I´m trying to learn how to made some calculations for a paper. Right now, I´m having a problem to make an approximation with three different equations.

Before, I made this same calculation with excel, but I dont know how to make it now.

In this case, I have to calculate a velocity, and for that, I need a value, calculated by another depending of the velocity.

So, before, on excel, I started with an approximate number for the velocity, then Ifigured the constants, then with that, I obtained the velocity again, and so on until the value of the speed began to tend to a very similar number varying in a few thousandths of m/s.

Now, I´m not sure to do that step with mathcad. So I´m asking here for some help

Untitled-1.jpg

What I need to is the velocity "uf", and  with that velocity, the constant to calculate are Rep2 and Cd2, the others variables are defined.

I think twith an itteration I could resolve this, but I don´t know how to do it yet

I hope I was clear.

Thanks

Emiliano

Best answer by AlanStevens

Look up Solve block in Help.  Here's a solution.  I only have Prime 2, so I've shown an image as well (this should also work in Prime 3.1 or whatever version of Prime you have).

solveblock.PNG

Alan

2 replies

V
24-Ruby IV
ValeryOchkov24-Ruby IV
24-Ruby IV
April 7, 2016

1. Send please not only pictures but the sheet too!

2. It seems that I have solved this of same task.

See please pictures and sheets 17.11-17.14 here

Study 17. Cogeneration (CHP), trigeneration (CCHP) and quadrogeneration (CCHPI) or how much of mathematic is contain…

    A
    AlanStevens19-TanzaniteAnswer
    19-Tanzanite
    April 7, 2016

    Look up Solve block in Help.  Here's a solution.  I only have Prime 2, so I've shown an image as well (this should also work in Prime 3.1 or whatever version of Prime you have).

    solveblock.PNG

    Alan

      E
      egu1-VisitorAuthor
      1-Visitor
      April 7, 2016

      Thank you to both for your quick answer!

      Were very interesting the examples of Valery. And with Alan program I was able to continue correctly.

      May be It was very simple, but I don´t have too much experience with Mathcad.

      I take this opportunity to make you another questions.

      When Alan defined cd, what does it means NaN? and at the beginning when the values were define, there are any difference if they were another number different of one (except of zero)?

      Thanks!

      Emiliano

      W
      Werner_E25-Diamond I
      25-Diamond I
      April 7, 2016

      When Alan defined cd, what does it means NaN?

      NaN means "Not-a-Number" and is the "result" you get, if Rep2 > 200000.

      and at the beginning when the values were define, there are any difference if they were another number different of one (except of zero)?

      You mean the guess values? Give it a try.

      It depends upon the nature of the equations you solve.

      Sometimes a system is very stable and you come to the very same solutions no matter what the guess values are.

      Sometimes changing the guess values means you get a different (still valid) solution .

      And sometimes using a badly chosen guess makes the solve block fail finding no solution at all.

      WE

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