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12-16-2013
10:06 AM

12-16-2013
10:06 AM

How to properly use constraints and rules followed by Mathcad's Solver

Below are some pictures of the inputs to Mathcad's solver using Prime 2.0. I am trying to design a bellville washer here that exerts F1=8,500lbs of force in one position y1, and than in a relaxed position (y1-alpha) provides a force F2>=8000

As can be seen above I have set up my constraints as well as possible yet at the end the F2 does not come out to something between 8000-8500, thus it does not meet the requirements of my constraint #3 above.

I am fine with Mathcad varying y1, t, and H as much as needed to obtain a solution, the question is 7021 the best that any combination of values can actually do? If so why doesn't Mathcad simply come back and say no solution since truly the F2=7021 does not meet the constraints?

One thing I should also mention that I find quite frustrating is when I go back to the top to my initial guess values and start varying the numbers up there, I often come up with closer and better answers at the bottom. Is there an order that Mathcad evaluates values inside of the solve function?

I can work out ideas for a for loop in my head as to how to evaluate this one but being so new to Mathcad and finding the syntaxt different from my prior LabVIEW and Matlab experience, I am still struggling to figure out how to program up the loops here, hence why I was hoping that the solver itself would be able to go back and ensure that any value found met all my criteria .

Thanks,

Adam

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4 REPLIES 4

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12-16-2013
11:14 AM

12-16-2013
11:14 AM

Re: How to properly use constraints and rules followed by Mathcad's Solver

In doing your check calculations you have changed the value of alpha!

Might be better done as in the attached.

However, as specified, there is no unique solution. For example, try initial guesses for t, H and y1 of 0.2, 0.25 and 0.22 respectively. The resulting solution is different from those arising from your initial guesses, but they still meet your criteria.

Alan

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12-16-2013
01:14 PM

12-16-2013
01:14 PM

Re: How to properly use constraints and rules followed by Mathcad's Solver

Hi Alan,

Thanks, I missed the alpha change that must have happend when I was playing around iwth it.

With that being said is there any way to get the solver to display multiple possible solutions if not all that it can find in a particular range?

Thanks,

Adam

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12-16-2013
03:49 PM

12-16-2013
03:49 PM

Re: How to properly use constraints and rules followed by Mathcad's Solver

adam miller wrote:

With that being said is there any way to get the solver to display multiple possible solutions if not all that it can find in a particular range?

Thanks,

Adam

There are an infinite number of solutions. If you look at the following picture you can see there are two solutions that satisfy the criteria (i.e. 2 values where the blue line hits 8500 and where the red line is between 8000 and 8500, and where t is between 0.05 and y1) . If you make minute changes to t and H you will get more. By making the changes as small as you like, you can see there are an infinite number. You would need to specify exact values for t and H (or y1) to get a finite number of solutions.

Alan

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12-16-2013
04:14 PM

12-16-2013
04:14 PM

Re: How to properly use constraints and rules followed by Mathcad's Solver

Here, for example, several results are determined for a range of values of t and H.

(Also, because there are sometimes multiple solutions for single values of t and H (as in the image in my previous post) the solution found by the solver may depend on the initial guess for y1.)

Alan

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