# Calculating wind turbine tower loads - Page 4

Posted by Curbie on February 25, 2009, 2:14 pm

Jim,

Sounds like you're where I want to be, metaphorically, spend a little
time on Euler, spend a little time on logs. Bliss.

I found the kind of site I like (almost) yesterday, its has an example
with not only the explanations to the math, but answers to check the
equations.
https://ecourses.ou.edu/cgi-bin/ebook.cgi?doc=&topic=me&chap_sec    .1&page=case_sol

I felt the whole thing was making perfect mathematical sense until the
last equation (the "almost" above),  I was getting 7,955 for Pcr and
the example said I should get 1,593. I tore my spreadsheet expression
apart   Pcr =PI() ^ 2 * E * I / L ^ 2   but couldn't find my problem.

Cylinder Outside Diameter (do)    1.5    Inches
Cylinder Inside Diameter (di)    1.4375    Inches
Cylinder Wall Thickness (Tc)    0.0625    Inches
Cylinder Outside Radius (ro)    0.75    Inches
Cylinder Inside Radius (ri)    0.6875    Inches
Moment of Inertia (I)        0.073043851
Length of Mast (Lm)        4    Feet
Length of Member in Feet (Lf)    4.272    Feet
Length of Member in Inches (L)    51.26402247    Inches
Young's modulus (E)        29,000,000    PSI
Factor of Safety (Fs)        2.00
Critical Buckling Load (Pcr)    7955    Lbs.

Will hit it again today.
notes, haven't quite figured out where it fit in, but I'm sure to run
into "it's place" in the scheme of things.

Curbie
On Wed, 25 Feb 2009 04:41:48 -0800 (PST), Jim Wilkins

Posted by Jim Wilkins on February 25, 2009, 6:20 pm

Posted by Curbie on February 25, 2009, 9:56 pm
Jim,

Well, Cylinder Outside Diameter (do) & Cylinder Wall Thickness (Tc)
are just input to feed  radius calculations, which in turn feed the
Moment of Inertia (I) calculation   =PI() / 4  * ((ro ^ 4) - (ri ^ 4))

Since the results from the Moment of Inertia (I) calculation matches
the results given in the example I presume that's not my problem. The
only calculation which is not producing the same results as the
examples is for Critical Buckling Load Pcr=PI() ^ 2 * E * I / L ^ 2

I don't expect you find my problem, thanks for trying though, I
thought something might jump out at you (mathematically or
syntactically) from the Critical Buckling Load (Pcr) expression.

I'll just keep hammering away at it, it's what I do, learn the
properties of thing long enough to define them in computer equation
then move on and let the programs do their work.

Curbie
On Wed, 25 Feb 2009 10:20:40 -0800 (PST), Jim Wilkins

Posted by Jim Wilkins on February 25, 2009, 10:41 pm

If the wall thickness is 0.062, the radii are 0.750 and 0.6875. 1/2 of
1.437 is 0.71875.

Posted by daestrom on February 25, 2009, 9:45 pm

https://ecourses.ou.edu/cgi-bin/ebook.cgi?doc=&topic=me&chap_sec    .1&page=case_sol

Wouldn't that be .03125??  (1.5-1.4375)/2  There are two walls

I run into this a lot with heat exchanger fluid calcs.  I get the ID and the
wall thickness and have to calculate the OD to figure out the volume of
water displaced in the shell side.

daestrom