Modelling surface contact in simscape multibody for non-spheri​cal/non-re​ctangular objects

I'm working on a model of a rocket being launched using simscape multibody and when trying to include the rocket falling and hitting the ground I noticed there doesn't seem to be a way to model the contact forces between the body and the ground. I have looked through Steve Miller's contact force library which is very useful but focuses mainly on spheres and does not go as far as to provide a force between a cylinder and a plane for example. In this case a cylinder represents the rocket body but there is no way to prevent this object from 'falling through the ground' as far as I can tell. The best I can achieve so far is to create a force between the centre point of the bottom surface of the cylinder and the ground which simply results in the rest of the body swinging around and hanging under the ground.

Any suggestions on how one might achieve contact forces between surfaces (particularly circular) rather than between points or any possible work-arounds would be much appreciated. I acknowledge that creating many reference points on the surface of the cylinder would be a possible answer but this seems like a lot of work to achieve an imperfect solution.

Answer 1

[Steve Miller]

Could you put a sphere at either end of the cylinder, where that sphere has the same radius as the cylinder? That would prevent the rocket from hanging at the surface when it returns to the ground.

Seems to me that once the rocket hits the ground, you probably aren't interested in the results after that point. If you are trying to model a reusable rocket, then you probably only care if the base lands on the ground, so if nose-to-ground contact is detected, you can probably stop the simulation.

Both of these solutions could be implemented with the Simscape Multibody Contact Force Library .

A solution that handles generic geometrical shapes will require a lot more computation and slow down your simulation significantly. There are problems that can only be solved this way, but if you can simplify your problem to simple geometric shapes it will be much more efficient.

Hope that helps, --Steve

[Gavin Cowie]

Thanks very much, this is useful to know although this is not the only situation I am looking to model contact forces between surfaces for.

Slowing down the simulation is an acceptable factor for me if it makes the model more accurate, so it would be great to get some more information (if you have it/know where I could access it) on how I could handle arbitrary shapes so that I could look to apply this in a more detailed model where there are multiple surface contact forces acting on different geometries. Unfortunately my model needs an extremly high level of accuracy so simplifying the geometry is not a permanent solution.

Cheers

[Jun Li]

Dear Gavin,

Have you solved the problem that modeling contact forces between generic surfaces in Simscape Multibody? Any advice would be greatly appreciated!

Thanks