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May 02, 2012
06:46 PM

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May 02, 2012
06:46 PM

Create a lookup table from this graph?

Hello,

I have this graph attached below. I want to be able to just specify e/D and have mathcad spit out K. What is the easiest way to do this? Maybe some sort of lookup table? I'm not sure.

12 REPLIES 12

May 02, 2012
07:24 PM

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May 02, 2012
07:24 PM

Create a table with a few basic points and use an interpolation function.

For this curve, linterp (linear interpolation) should be adequate.

May 02, 2012
07:31 PM

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May 02, 2012
07:31 PM

I think I understand. So column 0 would be e/D and column 1 would be K. I would use:

**linterp(vx, vy, x)**

**where vx is column 0 and vy is column 1 and x is my e/D value?**

May 02, 2012
07:42 PM

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May 02, 2012
07:42 PM

Yes.

The "Help" files have many worked examples (called "Quick Sheets") for these kinds of things.

You should look at them whenever possible.

May 02, 2012
07:46 PM

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May 02, 2012
07:46 PM

Thanks for your help - I appreciate it.

What if it is a more complicated graph, like this:

May 02, 2012
08:42 PM

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May 02, 2012
08:42 PM

Assuming that you can't find an analytical curve fit in the literature,

You can create a general function, written as a program to interpolate D/w, Ftu/Eeu, Fty/Fut

Digitize each curve with as much accuracy as you want, as suggested above, for every curve.

Then with a program, interpolate along a curve for a given Ftu/Eeu.

If you fall between curves, then further interpolate between two curves.

If you fall between graphs, then further interpolate between graphs.

The program is pretty easy, digitzing the curves is a pain.

May 02, 2012
09:57 PM

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May 02, 2012
09:57 PM

To copy plots from print to mathcad.

A worksheet posted awhile back...

I hope it is helpful

Norm

May 04, 2012
02:03 AM

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May 04, 2012
02:03 AM

Norm,

This looks a superb feature but it doesn't seem to yield the correct results. Can you confirm that you are matching the graph values?

Mike

May 05, 2012
08:00 PM

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May 05, 2012
08:00 PM

Typing phi(X)= & phi(Y)= next to, or after the final graph should present your data. Table "R" is the original slected data without the "known values" (control click & shift click) to maintain the profile.

I do not use it, just have it in my tool box.

Norm

May 05, 2012
08:11 PM

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May 05, 2012
08:11 PM

My apologies, I meant theta(X)= and theta(Y)=. Essentually, just pull the "click" data from the two axis.

Norm

May 03, 2012
12:26 AM

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May 03, 2012
12:26 AM

I have converted some tables/plots into Mathcad WebSheets for Dow Chemical.

See the article:

http://twt.mpei.ac.ru/ochkov/Opt-Filtr/Ochkov-Rohm-Haas-Resin-Eng.pdf

Second example:

The Mathcad WebSheets - http://twt.mpei.ac.ru/MCS/Worksheets/Hydro/La-De-Re.xmcd

with this origin plot:

May 03, 2012
11:41 AM

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May 03, 2012
11:41 AM

You might be able to use "cubic spline interpolation" to create surfaces.

Look it up in the "Help" files. There is a quicksheet there on "2D Interpolation" that should be useful.

May 04, 2012
02:29 AM

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May 04, 2012
02:29 AM

This will take a bit of work, but it might be worthwhile if you use the graphs all the time.

I have discussed the Digitize function passed by Valery many times before, but as Norm indicated it requires a clean graph, which can be achieved using paint.

Mike