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Posted by Curbie on July 2, 2009, 9:35 pm
 

I went back after the math behind calculating loads exerted on wind
turbine tower masts and I'm still having trouble converting the
formulas to a spread-sheet so the results match the examples given.

The formula I'm having trouble converting is:
(34,000/1.9)[1 - (1/2)(101.8/132)^2] = 10,994

My question is how do I convert the contents of the left square
bracket "[" and right square bracket "]" to spread-sheet expression?
Or maybe just what is the purpose of the brackets.

Thanks for any help.

Curbie


Posted by vaughn on July 2, 2009, 10:08 pm
 


Just change those square brackets to round ones.  They were probably only
made square to help us humans keep track of things.  Computers (even cheap
scientific calculators) can handle multiple nested round brackets just fine.

Vaughn




Posted by Curbie on July 2, 2009, 11:34 pm
 Vaughn,


That worked for me in the past but using this spread-sheet expression:
(34000 / 1.9) * (1 - (1 / 2) * (101.8 / 132)^2) = 12,573

where their example is:
(34,000/1.9)[1 - (1/2)(101.8/132)^2] = 10,994

Different results, and since these formulas where taken from some
college physics department, I have to be interpreting that formula
incorrectly.

http://physics.uwstout.edu/StatStr/Statics/Columns/colse62c.htm

I always look for examples with results so I can check my math for
just this sort of mis-interpretation.

Curbie


Posted by Neon John on July 3, 2009, 12:39 am
 I worked this out by hand on a calculator to make sure I got my
operator precedence correct and got your answer of 12,573.  I can't
get 10,994 using any combination of the numbers, even abusing
precedence rules.  

I ran the formula using square root instead of square, figuring that
the guy might have hit the wrong key on his calculator.  That produces
10,037.  Closer but no cigar.  I think that he made a math error.  Why
not drop him a note and ask?

John

wrote:



Posted by Curbie on July 3, 2009, 1:16 am
 I'm sorry John, I didn't mean for anyone to run the calculations, just
explain the use of the "[ ]".

Do you think those "[ ]" could be replaced with "( )", it seems there
has to be more than that and that one of the students would have run
the math and gleefully pointed out the error (seems that would to be
worth some extra credit)?


I'll try, I've never had any luck doing that, their pretty busy.

Thanks,

Curbie


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