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lvanlieren1-Visitor
1-Visitor
July 4, 2016
Solved

Programming Mathcad prime- time steps, numerical evaluation

  • July 4, 2016
  • 11 replies
  • 5571 views

Hey guys,

I'm Laura and im currently working on a worksheet in mathcad Prime 3. The first time programming and having a hard time trying to compute a rather simple loop for an explicit time-stepping (numerical evaluation) problem. For those who are familiar, it's the book of Chopra-Dynamics of structures ->chapter 5, p. 207,  Central Difference Method

Central difference-time steps.png

If someone could help me out, tips making the program work, that would be greatly appreciated!

Laura

    Best answer by -MFra-

    Hi Laura, now it seems that everything is fine.

    Greetings

    FM

    forLaura 2.jpg

    11 replies

    W
    Werner_E25-Diamond I
    25-Diamond I
    July 4, 2016

    Your file is in Prime 3.1 format which I (as may others here who also did not bother upgrading) unfortunately can't read. PTC provides no way to convert so all you could do is to additionally provide a screenshot or a pdf-Print of your file.

    Regards

    WE

    V
    VladimirN24-Ruby IV
    24-Ruby IV
    July 5, 2016

    Werner,

    PDF copy of this Prime worksheet can be found in attachment.

    L
    lvanlieren1-VisitorAuthor
    1-Visitor
    July 5, 2016

    I'd like to thank you VladimirN for uploading the pdf. Much appreciated.

    A
    AndyWesterman12-Amethyst
    12-Amethyst
    July 4, 2016

    Hi Laura,

    there are a couple of issues with the worksheet,

    The first, in the program is that you try to reference u[-1; the origin is either 0 or 1 - so this variable does not exist.

    Too fix this I have added 1 to all the references - it seems to work but will need to be checked & tidied up

    Capture.PNG

    The second issue is with the plot.

    the index variable needs to be written as a subscript & the function needs all the parameters.

    Attached is Prime 2 version.

    Hope this helps

    Andy

    L
    LucMeekes23-Emerald IV
    23-Emerald IV
    July 4, 2016

    "the origin is either 0 or 1". No, it is whatever you define it, by default it's 0, but if you like you can set it to -1. See:

    Luc

    -
    -MFra-21-Topaz II
    21-Topaz II
    July 4, 2016

    Hello Laura, since there are enough other files offered by the community, I'll show only a photo of your problem solved by me, from which you can take whatever you need.

    Cheers

    FM

    forLaura.jpg

    L
    lvanlieren1-VisitorAuthor
    1-Visitor
    July 5, 2016

    Dear FM,

    It is very kind of you responding that fast. Thanks a lot. However, unfortunately, when I compare the results of the example presented in the book of Chopra and those that are derived from the program I don't get the same answers. I highlighted the differences in green. I hope you are willing to take a look at it.

    Book vs. mathcad.jpg

    A
    AndyWesterman12-Amethyst
    12-Amethyst
    July 6, 2016

    Hi Laura,

    I haven't managed to reproduce the results here (yet), but I think that you need to compare the program against the book you are following.

    So far I have noted that:

    the x (p) input appears to have an additional 0 at the start.

    c is defined as 0 in the program but 0.1592 in the book example.

    the definition for a in the program is

    Capture.PNG

    but the book says

    Capture.PNG

    None of the above significantly affect the calculation, but it does suggest that  there are further corrections to be made.

    regards

    Andy

    -
    -MFra-21-Topaz IIAnswer
    21-Topaz II
    July 7, 2016

    Hi Laura, now it seems that everything is fine.

    Greetings

    FM

    forLaura 2.jpg

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