Forced vibration analysis of a simply supported beam with axial tension

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  • Last Post 31 August 2019
rajeshsimhadri posted this 19 August 2019

Hello everyone,

I want to simulate a pre-tensioned overhead electric conductor subjected to wind induced vibrations. As a initial validation part I'm validating previous work done in this domain. The reference work is attached with this post. In the reference work a conductor in axial tension is modeled as pin supported beam. Then it subjected  to a time varying sinusoidal lift force due to wind in vertical direction. They have carried a transient structural analysis to see the displacements with respect  to time.  I have modeled it as a beam in ansys workbench as a line body with circular cross-section pinned at the one end and roller support at the other end . I have performed a transient analysis with two time steps . The total time of simulation is 21 sec (reference simulation was 20 sec). The loading for the two steps are:

1. axial tension(constant)(1 sec) at roller end.

2. axial tension(constant) at roller end and wind load(line pressure- sinusoidal) acting on the conductor in vertical direction for next 20 sec.

My results are not matching  the reference work results. Is it due to wrong BC applied? . Please help me , how to consider Pre-tension in a beam?

Thanks

 

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BenjaminStarling posted this 20 August 2019

My initial observation is that they are doing a 2D analysis with two pinned supports. The fact that you mentioned a roller support leads me to believe you require this to apply your pretension. There are other ways to acheive this with two pinned supports. See the D command with the %_fix% label. https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v194/ans_cmd/Hlp_C_D.html

This analysis seems suited for workbench also, using a pre-stressed modal to then perform an MSUP harmonic, or a direct transient, this is the beauty of workbench, running and organising multiple analysis in the one window.

I will have a closer look at that document you attached and get back to you with some more details.

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rajeshsimhadri posted this 28 August 2019

Dear Benjamin,

Thanks for the suggestions. i am a new user of ansys and i dont know how to use commands. How to apply pretension in the cable before giving the pinned supports at the ends. Can we do it using a multi step analysis ( tension applied in first step and then applying simply supported BC in the next step)?

Thanks again

peteroznewman posted this 28 August 2019

Dear Rajesh,

The thesis has two fixed ends. That is a very different BC than having one end with a roller and force.  Read the following links to figure out how to apply tension to a cable using the INISTATE command in a Command object.

Discussion 1

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peteroznewman posted this 28 August 2019

On page 67 of the thesis where the ANSYS model is described, I read the following:

"The tension is considered to be zero so that the effect of the damper properties on the natural frequency can be isolated"

If you are trying to reproduce those results, then you don't need any tension.

I don't think a zero tension model could be validated against experimental data, because gravity acting on the cable and damper will tension the cable.

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rajeshsimhadri posted this 31 August 2019

Dear Sir,

Thanks for your quick response and help. I tried the command described in the post you have mentioned and it worked. 

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