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DV_92255061-Visitor
1-Visitor
May 21, 2022
Solved

this is not a valid constraint. for example use the equal to operator

  • May 21, 2022
  • 2 replies
  • 2591 views

DV_9225506_0-1653148465126.png

Hi, i am doing some calculations on a project and am quite new to Mathcad. When using the solve block i keep on getting an error and i dont know how to solve this one. Any idea where i might be wrong?

 

    Best answer by LucMeekes

    Check your equations!

    You have 5 equations, and want to solve for only 3 variables. Normally you have 3 (independent) equations to solve for 3 variables.

    If I take just the first 3 equations, those in moments, and solve them I get:

    LucMeekes_0-1653251585998.png

    This is the symbolic solution, which can be found.

    Then I try to evaluate it numerically, I get:

    LucMeekes_1-1653251651018.png

    (Complaint that sol is undefined). On closer inspection the first 2 items have this is the numerator:

    LucMeekes_2-1653251702116.png

    Which, upon numeric evaluation yields:

    LucMeekes_3-1653251726605.png

    And that's exactly zero because:

    LucMeekes_4-1653252189177.png

    So you get a division by 0. Hence Prime judges sol to be undefined.

    And also Prime indicates the solve block cannot be solved.

    The two extra constraints in your solve block will not help to remedy this problem.

     

    However, if I remove the first two constraints, I get this result:

    LucMeekes_0-1653252660524.png

     

    Check your equations.

     

    Success!
    Luc

    2 replies

    F
    Fred_Kohlhepp23-Emerald I
    23-Emerald I
    May 21, 2022

    My first observation is that many of your constraints are not unit consistent; you mix terms of force (N} with moment (N m).  Fix that, see if it helps.

     

    Attaching the file would help too!

      D
      DV_92255061-VisitorAuthor
      1-Visitor
      May 22, 2022

      This is the part where i am stuck, unfortunately i cant upload the whole document

       

      L
      LucMeekes23-Emerald IVAnswer
      23-Emerald IV
      May 22, 2022

      Check your equations!

      You have 5 equations, and want to solve for only 3 variables. Normally you have 3 (independent) equations to solve for 3 variables.

      If I take just the first 3 equations, those in moments, and solve them I get:

      LucMeekes_0-1653251585998.png

      This is the symbolic solution, which can be found.

      Then I try to evaluate it numerically, I get:

      LucMeekes_1-1653251651018.png

      (Complaint that sol is undefined). On closer inspection the first 2 items have this is the numerator:

      LucMeekes_2-1653251702116.png

      Which, upon numeric evaluation yields:

      LucMeekes_3-1653251726605.png

      And that's exactly zero because:

      LucMeekes_4-1653252189177.png

      So you get a division by 0. Hence Prime judges sol to be undefined.

      And also Prime indicates the solve block cannot be solved.

      The two extra constraints in your solve block will not help to remedy this problem.

       

      However, if I remove the first two constraints, I get this result:

      LucMeekes_0-1653252660524.png

       

      Check your equations.

       

      Success!
      Luc

      T
      21-Topaz II
      terryhendicott21-Topaz II
      21-Topaz II
      May 21, 2022

      Hi,

      Can you please upload the worksheet?

      Cheers

      Terry

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