[TowerTalk] MODEL FOR TOWER

[Jim Brown]

There is also at least one equation I found on the web that computes the 
effective diameter of a triangular tower based on it's cross-section. It 
might be possible to get a reasonable approximation of the tower by 
breaking the tower down into multiple sections.

The equation I found is tricky to express via email.  The equivalent 
diameter is the cube root of (D x Fsquared /2), where D is the diameter 
of a leg and F is the face width.

There may be a comparable equation for a tower with a square cross section.

Elaborating on Jim's method, EZNEC has a command that allows wires to be 
duplicated rotated about some center point. That would allow one of the 
vertical members to be modeled, then duplicated in 90 or 120 degree 
increments. Cross-members could then be added between the intersections 
of the "wires."

In my professional life, I generated models of large and small 
performance spaces to aid in the design sound systems by studying their 
coverage of the audience and their interaction with the acoustic 
environment. The largest and most complex space I "built" was the Staple 
Center in Los Angeles. Those models use the same x, y, z coordinate 
system, and the surfaces are all planes with their acoustic 
characteristics defined. In building those models, I made a table of x, 
y, and z coordinates of the points defining the surfaces before trying 
to build the model.  A similar approach would be applicable here.

73, Jim K9YC

On 4/23/2019 11:11 AM, jimlux wrote:
> On 4/22/19 8:53 PM, Greg Best via TowerTalk wrote:
>> I have an 80 ft Rohn windmill tower that is equivalent or stronger 
>> than the same height SSV. The base dimension is 7’ 7” and the tower 
>> tapers to 24 “ at the top . I am wondering if anyone has a NEC model 
>> for this tower (or a very similar one)?  I have a 20 m 4 el yagi I am 
>> considering installing at abt 60 ft and I am concerned about the 
>> tower impact on the pattern. The yagi at 60 ft would be in a stack 
>> with another yagi at 95 ft that is mounted on a mast.
>>
>>
>
> This is one of those things that might be easiest to generate with a 
> short program in the language of your choice to generate the lattice 
> of vertical, horizontal, and diagonal members.   I've done that to 
> generate a model for a truss - it was easier to do that than to try 
> and figure out the coordinates by hand.
>
> There *might* be a cad program in which you could quickly draw the 
> tower, and export the segment endpoints.
>
> Because it's tapered, it doesn't lend itself to using a GM card to 
> replicate segments.
>
> You'd model it as a wire for each structural member, and pick the 
> diameter of the wire to have the same circumference as the perimeter 
> of the structural member (or, heck, just make em all 2" diameter wires).
>
>
> for each section do:
>     calculate the coordinates of the 8 corners
>         (or 6 corners if it's three sided)
>     generate a wire for the 4 verticals corners
>     generate wires for each of the horizontals
>     generate wires for the diagonal braces
>
>
>
>
>
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