Kangaroo First trial

Hi Daniel,

I am working on the form-finding of a flexible foil.

Assuming the profile is constant, the lift force should be constant along the span

So I used this a a first exercice with Kangaroo, but I have the feeling that only the initial force vectors are applied on the nodes, and are not re-calculated as the geometry changes (which is not physically accurate).

How should I change my definition ?

Should I use HoopSnake in combination with Kangaroo ?

Is that even possible, or will it blow my computer up ?

Thanks, and also : wow ! This looks very promissing.

Cheers,

Olivier

Replies to This Discussion

Permalink Reply by Daniel Piker on August 24, 2011 at 10:55am

Hi Olivier,

Yes - in your definition only the initial force vectors are being applied to the nodes.

What is it you want these forces to be dependent on ?

Permalink Reply by Olivier Suire on August 24, 2011 at 12:43pm

Hi Daniel, thanks for coming back to me.

I am trying to mimic a uniform pressure load on a flexible foil.

Since the shape is prismatic, I wanted to solve the problem in 2D.

So I applied a nodal force on each segment end which is oriented in the bissector line of the two adjacent segments, like the pressure would act, normal to the surface.

The whole point in doing this simulation is to find an equilibrium state with different positions for the anchor points, but the force vectors must be re-calculated to account for the new shape : your typical non-linear problem.

Can't the "unary forces" be put in the loop to account for the evolution of the geometry ?

Should I use a mesh instead, and use the "Pressure" load ? Will the load evolve with the shape then ?

Thanks !

Olivier

Permalink Reply by Daniel Piker on August 25, 2011 at 2:14am

Using a mesh with a Pressure force is the way to go, as this applies a force normal to the surface, which follows it and stays normal to it as it moves.

There is nothing quite like this just for lines - the closest is the "rocket" force, which acts along the vector between 2 points, and moves with them. You could set up some springs to hold a rocket perpendicular to each line - but really a 3d mesh with pressure is probably simpler.

As for combining HoopSnake and Kangaroo for looping the output back into the simulation setup - I have seen it done, and think it could open up some really interesting possibilities, though I haven't experimented much with this myself.

If you are doing this it probably makes sense to use a fairly high value for SubIterations, and make the input to ResetSimulation a list of 2 booleans "true,false" - so that it resets and solves for a large number of physics steps in a single grasshopper solve. This way there is no need to have any timer object connected to Kangaroo.

Permalink Reply by Olivier Suire on August 25, 2011 at 2:25am

Thank you Daniel,

If I didn't have two kids to feed, I'd quit my job, sell my car, move to a country where living is cheap, and spend most of my time kite-surfing and doing research with kangaroo !

Olivier

Permalink Reply by Hrvoje Petrovic on August 25, 2011 at 5:31am