How to Idealize Guy wires working under tension only that support silencer chimneys

Question

Hello PTC community,I am using Creo Simulate (version 7) to perform the following FEA study. I need to idealize four Guy wires within the genset exhaust and silencer assembly that will help stabilize the chimney when high wind loads might be experienced. The four Guy wires are meant to be attached to the frame which is supposed to be mounted onto the flange of the top most part of the chimney as shown in the pictures attached.I have tried single and multiple beam elements till now but both of them behave unnaturally. I have used a rigid connection at the top for connecting frame and the beam elements and have used fixed translation free rotation for all at the bottom point (ground) of the beam. Please see attached some of the pictures that will help communicate better.For the single beam element, when wind loading is experienced, two ropes must be in tension like state while the opposite two must behave different to these. However, all four more or less seem to behave the same? Also the behavior of these ropes at a scaling factor 1 (actual deformation) does not seem to be natural as the ropes could be seen sagging towards the ground. Would that be because of the own weight of the ropes? Because the solver has been specified with own load of the assembly to be taken into consideration as well along with the wind loads. Please guide.

SweetPeasHub · Accepted Answer

The step @YT_4948 is missing is using prestress analysis. The standard linear analysis uses superposition so the sag of the guys due to gravity does not account for pretension - it is done independently. I have attached a complete example for a tower with guy wires modelled as beam elements that includes the incorrect and the correct prestress techniques for the static and the modal cases. Also an example for the buckling case is included but you would need to suppress the beams for that example. This is Creo 10 so hopefully you can upgrade to see it.

FYI this is a similar technique as that used for stringed musical instruments.

Wind and Gravity + Pretension = WRONG ANSWER

Run pretension first, and then Prestress static and you get correct results.

First/LH case below has the check box to include the results from the pretension run.

The increase and decrease in tension in the wires due to the wind load are also correct and there is no exaggerated sag due to gravity.

I believe if solid elements were used, a non-linear analysis would provide correct final results without the need for a pretension analysis step. Also, with non-linear analysis you can time-stagger the loads, accomplishing the pretension in another way.

tbraxton · Answer

Beam elements are not the solution as you have found. Take a look at this old thread dealing with the same issue. How to simulate and analyze a steel rope (steel ca... - PTC Community

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