[MBDyn-users] Simulation of a nom compression element

Pierangelo Masarati pierangelo.masarati at polimi.it
Sat Jun 1 07:22:51 CEST 2013

On 06/01/2013 01:28 AM, Leonardo Roncetti wrote:
> How can I simulate an element the stands only tensile, like a cable?
> I want to simulate a cable hanging from the tip of the boom of the crane
> with a cargo at the tip of the cable.
> I tried to use a rod joint but many times in the simulation it supports
> compression, what is not true for real world.
> I also tried to split the cable in many rod joints. In the Easyanimm,
> the cable seems flexible but it still supports compression loads.
> Any idea to work it out?

Depending on how important it is for you to track the non-tensile 
behavior of the cable, you could use a non-linear constitutive law with 
tension-only (which might also introduce convergence issues); in this 
case try a piecewise linear constitutive law e.g. based on a piecewise 
linear scalar function with zero-slope for negative strain or even 
better using the cont-contact module and the corresponding contact model 
(i.e. the cable is essentially rigid in tension and yields zero force in 
compression; you may need to tweak coefficients a bit but you have the 
advantage of introducing a restitution coefficient that dissipates some 
energy under nearly impulsive tension).

If the dynamics of the cable is important, you need to use beams (3 node 
beams recommended) with very small bending stiffness and the appropriate 
axial and torsion stiffness, and you need to lump mass in nodes.  An 
appropriate number of beam elements is needed.

Cheers, p.

Pierangelo Masarati
Associate Professor
Dipartimento di Ingegneria Aerospaziale
Politecnico di Milano

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