distorted catenary by one point-mass (specific load)

hi all,

i´m trying to achieve a simply distorted catenary, adding mass to a specific point of the

catenary. The problem is that when the catenary stabilizes it doesn´t get any distortion,

is like the "mass-point" has the same mass as the rest of points (have been playing with

stiffness , damping, gravity, and mass for a while but it always stabilize as an ordinary

catenary)....

i let you the supposed distorsion and the file..

thanks a lot!!

Attachments:

distortcatenary.jpg, 68 KB
distorted catenary.ghx, 249 KB

Replies to This Discussion

Permalink Reply by Daniel Piker on February 11, 2011 at 6:14am

Was this file created with an old version of Kangaroo ? Version 0.044 is now available and offers significant improvements:
https://groups.google.com/group/kangaroophysics/web/download

Regarding adding mass to a catenary, the thing to remember is that mass and weight (the force due to gravity) are two separate properties. Larger masses take more force to accelerate, but they do not automatically have more weight unless you assign it. Of course in everyday life here on the surface of the earth mass and weight always go together, but for form-finding purposes it is often quite useful to be able to treat them separately.
That said, we do intend to add a global gravity option to the kangaroo settings which would apply a force to all particles in the simulation in the -Z direction, proportional to their mass.

Permalink Reply by j.j. sendra on February 13, 2011 at 2:24pm

mmmm.. understood.... if there is no way to assign weight, i´ll have to cretae some atractor, trying to simulate the distortion, any idea for the starting up¿?

thanks a lot for the didactic answer!

(´ll try in the new version)

Permalink Reply by Daniel Piker on February 13, 2011 at 2:47pm

You can assign weight - just add a unary force to the particles in the negative z direction.

There are some examples of this with the download of the new version.

If for example you are trying to add an extra load to one point of a catenary chain, you could create one unary force component with the start point input being a list of all the vertices of the chain, and another unary force component with just the particular point you want to apply the extra load to as the start point input.

Permalink Reply by j.j. sendra on February 16, 2011 at 7:31am

OK! i was able to distort a 2d catenary, with extra load in 1 point.. now i´m trying in a 3d catenary, with the same logic, but :

"the index was out of the interval. it has to be not negative and inferior to the size of the collection. Name of the parameter: index"

i´m doing something wrong¿? (surely yes)

thanks a LOT for the answers!

Attachments: