dump custom fx fy fx

Submitted by xiaobaishu67 on Wed, 03/11/2015 - 15:40

Hi, liggghts users~~
I want to know what the specific forces included in the dump fx fy fz for per-atom? Because I calculate contact force and weight for per-atom. They cannot match the fx fy fz. Anybody knows?

Thanks!!
xiaobaishu

Forums:

JoshuaP | Wed, 03/11/2015 - 16:12

It is the sum of forces on the particle in each direction. These are forces that generates an acceleration. So particles in equilibrium have no force. If you want the real contact forces you need to use
compute 1 all pair/local force

regards

xiaobaishu67 | Wed, 03/11/2015 - 16:44

yes. I use compute 1 all pair/local force to get contact force. I insert one type particles with radius 0.0005 and let them settle down. In the end i compare the contact force and fx fy fz for a specific particle, they cannot match even though I add the weight of the particle. So i am wondering what other forces i didnt take into account?

JoshuaP | Thu, 03/12/2015 - 10:14

as I wrote before: if you calculate the contact force, it is the force between to particles. But if you look for fx fy fz, these are the forces acting on one particle. So if you have a particle with mass lying on another particle, the contact force would be the weight*gravity, but the force fz on the top particle is 0, because you have the force of the weight minus the contact force that acts against the weight.
That means each particle that is in equilibrium should have zero force fx fy fz, but still can have contact forces to other particles.

Regards

xiaobaishu67 | Thu, 03/12/2015 - 16:15

Dear Joshuap,

Thank you so much.^^ I got it!!

Best
xiaobaishu