Bungee Cord Modeling??

[Drkwing]

Cheers,

I want to model a bungee cord to apply force to a sledge like body. The problem with the bungee cords is a bungee cord cannot be compressed like a spring. It only exerts a pulling force when extended.

I would be very pleased if you can help me on how to model a bungee cord

 

[GregLocock]

Would a whole string of small mass elements connected by springs and spherical joints do:

http://support.mscsoftware.com/kb/results_kb.cfm?S_ID=1-KB8092&requestTimeout=2000

or a flex model, using beam elements?



Cheers

Greg Locock

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

 

[Drkwing]

I'd think of a special spring or sforce where the stiffness value is zero when the deformation is negative with the aid of a spline and akima function. But wouldnt think of the formulation of the sforce.

Regards

 

[GregLocock]

You could do it that way but it is not a very realistic dynamic simulation of a bungee. My way is likely to be pretty horrible computationally, but with some fine tuning it should behave like a real bungee.

Cheers

Greg Locock

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

 

[GregLocock]

Just for future reference I've been doing a lot of this stuff lately. A spring with a spline that looks like
X=-1,0,1,2,3,4,5,6,7,8 etc
Y=0,0,0,0,0,0,1,2,3,4,5


does work

Another option would be to use a sensor to measure between the two ends, and only activate the sforce statement when that distance exceeds the required length of the bungee.

The string of beads method I proposed above does work but is pretty ridiculous, particularly while you are tuning it.

The beam element method looks do-able, but I've never done it.

Cheers

Greg Locock

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