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SM_646517810-Marble
10-Marble
Jun 29, 2023 10:06 PM UTC
Solved

Beam bending using finite differences

Hi All, 

 

We have been using this worksheet for a while which in theory allow us to look at different restrain configurations. Its always been a bit flakey, but converting to Prime seems to have finally killed it. 

 

I just wonder if anyone has some advice on how to get it to work?

 

 

 

 

 

Werner_E
Werner_EAnswer
25-Diamond I
Jun 29, 2023 10:31 PM UTC

I stopped at the first error thrown

The error about unit mismatch is thrown because you can't add a dimensionless quantity (C) and a quantity with unit N*m/s^2 (P).

Werner_E_1-1688077620736.png

Prime isn't using SUC (static unit check) anymore and so its necessary to apply a unit even if the value is zero!

But even if we fix this, we get a similar error, This time because Load is a vector in N, but add(P) results in a vector in N*m/s^2.

Werner_E_2-1688077831097.png

Haven't look further as this sure has to be fixed first.

It may have worked in Mathcad because all involved values seem to be zero anyway. But you sure can't and shouldn't add quantities of different dimensions!

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6 replies

Werner_E
Werner_E25-Diamond IAnswer
25-Diamond I
Jun 29, 2023 10:31 PM UTC

I stopped at the first error thrown

The error about unit mismatch is thrown because you can't add a dimensionless quantity (C) and a quantity with unit N*m/s^2 (P).

Werner_E_1-1688077620736.png

Prime isn't using SUC (static unit check) anymore and so its necessary to apply a unit even if the value is zero!

But even if we fix this, we get a similar error, This time because Load is a vector in N, but add(P) results in a vector in N*m/s^2.

Werner_E_2-1688077831097.png

Haven't look further as this sure has to be fixed first.

It may have worked in Mathcad because all involved values seem to be zero anyway. But you sure can't and shouldn't add quantities of different dimensions!

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    terryhendicott
    terryhendicott21-Topaz II
    21-Topaz II
    Jun 30, 2023 12:12 AM UTC

    Hi,

    Here is a fully working sheet with all errors gone.

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      SM_646517810-MarbleAuthor
      10-Marble
      Jun 30, 2023 12:15 AM UTC

      Thank you guys. It was doing my head in that it was working in MathCAD 15 last week, but now I want to use it in Prime it wasn't,

       

      What a fantastic community this is!

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        BillWadsworth10-Marble
        10-Marble
        Jul 12, 2023 11:15 AM UTC

        From the snippet of code I recognised this as mine.  (I'm sorry it has proved to be 'flaky', it works OK for me in 'proper' mathcad.)

        Of course the Load vector add(P) vector need to be in the same units, which are kN. 

        Thought you might like the latest version, I discovered that it only took some small additions

        to allow the distributed loads and suppots to be trapezoidal, not just uniformly distributed.  

         

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