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pwilmink1-Visitor
1-Visitor
July 22, 2014
Solved

sum several sin

  • July 22, 2014
  • 2 replies
  • 4583 views

Hi All,

I have a problem. Here I discribe the case.

A triplex plunger pump will produce water hammer. This will create a sinus wave, by opening the inletvalve and closing the inletvalve. I have 3 plunjers so 6 vibration sinus.

I like to sum these sinus. See my enclosed worksheet.

by calculating with my hand calculator I get an answer. In mathcad I get only 'zero' (0). What do I wrong.

Best answer by Fred_Kohlhepp

Your sheet is correct. Mathcad has tolerances for numbers close to zero being displayed as zero. If you change these values (format/results/tolerances, you get very small numbers. If you calculate y for various values of alpha, you can see that the summation is always very small.

2 replies

R
RichardJ19-Tanzanite
19-Tanzanite
July 22, 2014

Terms 1, 2, and 3 sum to zero. So do terms 4, 5, and 6. This is true for all values of alpha, alpha2, and beta.

sumtozero.png

F
Fred_Kohlhepp23-Emerald IAnswer
23-Emerald I
July 22, 2014

Your sheet is correct. Mathcad has tolerances for numbers close to zero being displayed as zero. If you change these values (format/results/tolerances, you get very small numbers. If you calculate y for various values of alpha, you can see that the summation is always very small.

W
Werner_E25-Diamond I
25-Diamond I
July 22, 2014

Fred Kohlhepp wrote:

Your sheet is correct. Mathcad has tolerances for numbers close to zero being displayed as zero. If you change these values (format/results/tolerances, you get very small numbers. If you calculate y for various values of alpha, you can see that the summation is always very small.

Yes, but these are roundoff errors. As Richard had shown the sum should always total to a perfect zero as in every of the two sets of three sines they are phase shifted by exactly 1/3 od their period!

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