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I can't get Mathcad to symbolically solve this equation

BS_9878159
4-Participant

I can't get Mathcad to symbolically solve this equation

No matter how much I try, Mathcad can't add these expressions because it thinks they have different units (but they don't)... I need to simply and add the different stresses together but I can't. 

 

BS_9878159_0-1617706539974.png

As you can see in the picture, the stress at "A", is not simplified.  Because the stresses are not added together as the program thinks they have different unit.

9 REPLIES 9
-MFra-
21-Topaz II
(To:BS_9878159)

he is undefined!!!

BS_9878159
4-Participant
(To:-MFra-)

What are you talking about?  Only he is undefined, and even then, the program should be able to add the numerical values together and just leave he as it is.

-MFra-
21-Topaz II
(To:BS_9878159)

A is a constant or a function of h.e? since h.e is unknown,  A must be necessarily a function of h.e, otherwise, the given definition isn't correct.

BS_9878159
4-Participant
(To:BS_9878159)

it is the function of he

LucMeekes
23-Emerald III
(To:BS_9878159)

@-MFra-  is completely right.

he is undefined. Note (and look carefully) that you are using he (that is 'h sub e') in the definition of A, and in the definition of tau.dA. But in the definitions of J, tau.tAx and tau.tAy, you are using he (no 'sub'), and that is why Prime cannot combine what you think should be combined.

I would set it up like this:

LucMeekes_0-1617743037778.png

Success!

Luc

 

(Oh, in the above I assumed that your magic value 0.7071 should be sqrt(1/2)...)

I keep preaching but few listen.

 

Mathcad (and especially, now, Prime 7) is a very poor symbolic engine!

 

It's still a good numeric solver.  Attached is your file adjusted to be numeric.  Are you looking for stress VS. h_e?  

 

You might try playing to its strength

I'm trying to find the stress as a function of he. So the stress has to be some numerical value divided by he. in this case it will be       419.1/he

 

btw, I can't open it because I think the mathcad I have is the 2020 version. Can you just post a screenshot so I can see how you did it?

LucMeekes
23-Emerald III
(To:BS_9878159)

Here is Fred's file for Prime 6

 

Success!
Luc

LucMeekes
23-Emerald III
(To:BS_9878159)

LucMeekes_0-1617712559558.png

NOTE that the symbolic processor doesn't 'know' units. It usually treats them as undefined variables. You can set an option such that can better deal with units: Look under Calculation -> Calculation options.

Take heed of Fred's advice. And the following: If you want to work with symbolics, set up your equations and any solve(s) purely symbolic; best in the form of functions with parameters. That is: WITHOUT filling in any numbers.

Once you have the desired symbolic outcome (in the form of a function), you can fill in the (numerical values of) the parameters to obtain a numeric answer.

So instead of:

LucMeekes_2-1617713460856.png

 

you do:

LucMeekes_1-1617713389580.png

 

Success!
Luc

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