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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