Model Tension Cable in SW Simulation 1

[SATLITEENGR]

I am trying to analyze a tripod whose legs are connected by tension cables. I already know the pretension and stiffness values. I'm wondering what mechanism in Simulation to use to model them. I've tried using the spring connection and spring fixtures but both so far are looking for parallel faces for the end fixtures which I don't have. Does anyone know a better way or a way around this parallel faces issue? I've attached a picture so you can see the situation. The picture doesn't show too much detail for security reasons, sorry.

 

[GregLocock]

Some multibody simulation programs eg Working model have a 'rope' constraint that would do what you need. The maths is easy so if your software can't handle it you may be able to write an extension.

Basically

if distance from point 1 to point 2 is less than length then

tension=0

else distance = original length of rope

endif

you could put this in series with a simple spring if you need elasticity.

Alternatively create a series of rods and join them appropriately, eg with UJs. That technique works better if you are worried about the dynamics of the rope itslef, rather than just the length constraint.




Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[SATLITEENGR]

Thank you Greg for your help unfortunatley the assembly is far more complicated than that and analyzing it by hand would be a nightmare and as things go mgmt wants answers now. I need to model the tension cable in Solid Works so I can use Solid Works Simulation to tell me what kind of stresses and deformations I will see once I apply a torgue about the azimuth and elevation axis of the satellite antenna that will be attached to the tripod. All this makes the loading conditions somewhat complex. I have analyzed certain individual components but I need an overall picture as well. What you saw in the picture is a very dumbed down version of the assembly for security reasons. What I'm looking for here in this forum is to see if anyone knows a way to model the tension cables in solid works simulation for FEA purposes.

Thanks again for your help,

 

[kellnerp]

Use Cosmos/M. It has a tension only element.

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[SATLITEENGR]

Kellnerp - Thank you for your post, that was an interesting idea but it doesn't lend me the data I'm looking for, stresses and deflections. It does show me what happens but I need numbers to go along with the analysis. Again thanks for your help, watching the animation play was fun.

-Cynthia

 

[kellnerp]

Use a Spar/Truss element with a non-linear elastic material curve. Define the curve so that the Truss can only take tension and give it a tiny compressive modulus just to keep things from blowing up.

Analyze this in Cosmos/M, not Simulation (motion simulation). Build a model with beam and truss elements. See Kinematics and stress in one FEA run. That model has a moving 4 bar linkage, a beam in which stress is recovered, and an over center spring. It is a simple model to build and quite appropriate for your tripod. Because this model used beam, truss and spring elements it runs super fast so you can do all kinds of load cases.

TOP
CSWP
BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."