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Modelling Ropes and Pulleys

Modelling Ropes and Pulleys

Modelling Ropes and Pulleys

(OP)
I'm a novice at FEA and have been playing about with Cadre Pro and steadily getting the hang of it. I'm after some advice on modelling rope systems and particularly those involving pulleys if it is possible to do so.

My interest is to model rope systems to simulate real rope systems used in rescue, particularly to illustrate the second order effects to rescue students. For example, I have simple models showing load sharing anchor systems where one leg is a short loop and the other is a long single rope leg. When rigged unloaded, of course, the guys can understand how ropes share the load, but when it is loaded, differential stretch causes the short loop to be more highly loaded.

I have a double barrelled question:

1. If I add links between the wire elements (rope) and the anchor points in the above model to simulate karabiners, I get unstable model errors and I'm unable to see why that should be. Has anyone experienced anything similar or can offer some advice? (The anchor points are fixed in x,y and z but allow rotation about x, y and z).

2. I'd like to model some rope systems including pulleys. Has anyone done this before that can offer advice?

Thanks in advance!

Al.

RE: Modelling Ropes and Pulleys

The tension elements essentially have no bending stiffness and can easily lead to unstable model errors if there are any intermediate nodes.  This is especially true if the non-linear feature is used.  These elements are not designed to support the typical cable/rope types of mechanical systems.  Those systems are large displacement problems that are highly non linear and (if its a hanging cable type) need to be modeled with gravitational energy as well as strain energy.  Generally specialized applications are necessary for solving cable problems.  Few if any standard FEA software will handle them.  

Having said that, there are plenty of rope type problems (guyed towers, etc that can be solved to advantage as long as you are careful not to put intermediate nodes within the wire elements, and as long as the overall displacement is not too large.

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