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GKatEng1-Visitor
1-Visitor
March 29, 2018
Solved

Simple Static Force Equilibrium Analysis

  • March 29, 2018
  • 4 replies
  • 6593 views

I am new to MathCAD and am doing a simple static force equilibrium analysis. My goal is to understand the best way to do this type of analysis so that I can then scale it to more complex problems. MathCAD document is attached (prepared in MathCAD Prime 3.0) and a scan of the sample problem that I’m working on is shown on the second page of the document.

 

I was able to get the correct result using Method-1 and Method-3 but I’m not able to get Method-2 to work. In Method-2 I’m attempting to make the resultant loads Bx and By (the variables I’m solving for) variables within a function called B. I’m then trying to call function B in the moment equilibrium equation to simplify the form of the equation. If I could get this approach (or something similar) to work it would be great because for more complex problems it would be very convenient to write equilibrium equations as a function of reaction load [B] where [B] represents Bxi + Byj + Bzk.

 

Also, as mentioned, Method-3 works but I don’t really understand the utility of this method if I need to manually enter the numeric coefficients into [M] and [v]. Is it possible to automatically populate the coefficients in [M] and [v] from the equilibrium equation shown in Method-1 and -2?

 

Another question is I’m interested in any recommendations to simplify my solution approach and / or apply best practices that others are using. For example – is it possible to do this evaluation without needing to explicitly define the unit vectors i, j, and k? Any other tips / suggestions?

Best answer by Werner_E

The reason your second method did not work is because of an infamous Prime feature called auto labeling.

The Bx and By in front (B(Bx,By)) are labeled "variable", but the Bx and By after the solve command are labeled "automatic" (-). For the symbolics these are not the same variables and so it fails. If you label all the same (either variable or auto)y your 2nd methods works OK.

B1.png

 

Here are some other ways to achieve the same result. As you don't really need a symbolic result, a numeric solve block could be an option and is more reliable (also wrt labeling).

B2.png

4 replies

G
GKatEng1-VisitorAuthor
1-Visitor
March 29, 2018

MathCAD file is attached. 

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-MFra-21-Topaz II
21-Topaz II
March 31, 2018

Hi,

solution with Mathcad15. Unit vectors are in black bold while vectors are in blue bold and as such are defined.

Static Force Analysis Example.jpg

W
Werner_E25-Diamond IAnswer
25-Diamond I
April 1, 2018

The reason your second method did not work is because of an infamous Prime feature called auto labeling.

The Bx and By in front (B(Bx,By)) are labeled "variable", but the Bx and By after the solve command are labeled "automatic" (-). For the symbolics these are not the same variables and so it fails. If you label all the same (either variable or auto)y your 2nd methods works OK.

B1.png

 

Here are some other ways to achieve the same result. As you don't really need a symbolic result, a numeric solve block could be an option and is more reliable (also wrt labeling).

B2.png

    L
    LucMeekes23-Emerald IV
    23-Emerald IV
    April 1, 2018

    How is this question related to this one: https://community.ptc.com/t5/PTC-Mathcad-Questions/Simple-Static-Loads-Analysis/td-p/542736

    ?

     

    Luc

    W
    Werner_E25-Diamond I
    25-Diamond I
    April 1, 2018
    @LucMeekes wrote:

    How is this question related to this one: https://community.ptc.com/t5/PTC-Mathcad-Questions/Simple-Static-Loads-Analysis/td-p/542736

    ?

     

    Luc

    Ahhh! I knew that I had already seen that question but wasn't sure if I just intended to answer or if I really did.

    Unnecessary waste of time and ressources 😞

    G
    GKatEng1-VisitorAuthor
    1-Visitor
    April 2, 2018

    Thanks very much for the help!

     

    Very sorry about the double post. After I first posted this it did not appear on the list of new questions for over a hour and I assumed I must have done something wrong. I then reposted the same question under a different heading and the new post immediately appeared on the list of new questions. I was unaware that this original post eventually made its way onto the new questions list until I was notified of the responses.

     

    Thanks again for the help!

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