# Define tower properties

Hi everyone,
FAST uses two text files in order to acquire blade and tower properties. Both of them use fractional length as HtFract and BlFract which must be varied from 0 to 1.
My question is regarding how to specify these sections. Here, it is an example of how specifying a tower segments in two way which could result in a single input file.

Tower height - representative height
(0-4) - 0
(4-8) - 6
(8-12) - 10
(12-16) - 16

Tower height - representative height
(0-3) - 0
(3-9) - 6
(9-11) - 10
(11-16) - 16

I set the lower height in first section (0 in 0-4) as representative height and upper in last section (16 in 12-16). The other internal sections used an average value as representative height. But, you cannot recalculate the first column by just having the representative height column only. Then, how FAST deals with this representative height column?
Should it be any other relation between tower sections? Such as below

Tower height - representative height - section height
(0-2) - 0 - 2
(2-6) - 4 - 4
(6-10) - 8 - 4
(10-14) - 12 - 4
(14-16) - 16 - 2

Which means equal section height in internal sections and half of it in the first and last section.

Dear Feizbakhshi,

FAST (or the ElastoDyn module of FAST8) linear interpolates between the specified distributed properties to find properties at the analysis nodes.

When you describe your tower sections, I’m assuming you mean you want constant properties within each section. An appropriate way to specify the distributed properties would be to define two stations very close to each other at each step change. For example, for the following sections:

Tower height
(0-4)
(4-8)
(8-12)

You would specify:

HtFract
0.0000
0.3333
0.3334
0.6666
0.6667
1.0000

I hope that helps.

Best regards,