COSMOS: Simulating Cable on a tower - design exercise

Hello,

I am getting back into playing with COSMOS. For fun I thought I'd
model up a simple tower (2" sched 40 aluminum pipe ) 30 ft high with
guywires located 120 degrees apart.

Thought this would be a straight forward process (which it was) until
I came to simulating the guywires 1/8"cable.

My problem is with a side load (due to wind) the bending of the tower
will 'unload" the downwind cable(s) and "tension" the upwind one.
Depending on the orientation of the wind it would be possible to
unload one cable entirely (downwind) and have the two upwind cables
split the load.

I am at a loss as to how to simulate the force and boundary conditions
of the cable.

Any suggestions?

Len

 

I am not that familiar with Cosmos works. But, had some ideas about
simulating cable.

Essentially the idea is to make a series of links connected with pivot
joints. In your case, you may be able to get by with only 3 or 4
lengths along the length of the cable. It might be best to make the
joints between the segments not pivot joints, to reduce the amount of
freedom, just a plane pivot joint would work.

Joe Dunfee

 

I don't use Cosmos, but some codes have cable (tension only) elements.

Jerry

 

If you don't need to account for the weight of the cables, you could
replace them with extension only springs. Make your spring constant
equal to the stiffness of the cable. Actually, if you include a
preload you should be able to do a reasonable job of simulating the
weight of the cables as well.

 

Obviously the cables will be pretensioned and have a significant
weight. They will always be in tension. Cosmos/M can handle this with
truss elements which can only take an axial force. You might get a
beam element to almost behave that way by giving it a real small
moment of inertia. That coupled with a non-linear elastic material
definition would certainly come close. I don't know if you can get
there in CosmosWorks. I use NE Nastran and this kind of thing would be
a piece of cake.

One of the things that is important in tower design is the aero-
elastic behavior and none of the above will catch this easily without
coupling them with a CFD program.

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