I want to impact a board with a sphere in peri style, and the sphere has an initial velocity but without any external force on it, which means when it interacts with the board, the board will make it slow down. As I know, the fix indent command could make the sphere move with a constant speed, but that is not what exactly I want. Is there any solutions?
Fix indent is not suitable for that kind of model, since it doesn’t model dynamics.
If you want to have real dynamics, you have to model both objects with real particles.
Just create them apart from each other and equilibrate them.
To study the dynamics you need to turn off any thermostats and do time integration with fix nve.
And to have the impact you have to add an impact velocity to your sphere object with the velocity command — LAMMPS documentation
Typically, you want to use the keywords “set” and “sum yes” and possibly “units box”.
Thank you very much for your reply. But I’m still confused that in Peridynamics, the family of a particle is defined at the very beginning and it won’t change during the dynamic process. So how can I simulate the impact process if I create real particles for the sphere which may have no interactions with the particles of the board and cannot change its family during the process.
By the way, is there a way to learn which commands are suitable for dynamics or quasi-static problems? That will help me a lot.
How about you look up in the published literature what people wrote they did to do something similar? For example there is this example on the LAMMPS homepage, which has been around for quite a while. I am certain there are other, suitable examples, too.
That is what the documentation is for. It describes what something does. You already noticed that fix indent only allows to follow a prescribed trajectory.
Fix indent can do your job. You have initial velocity v_i and final velocity =0. You also have the total distance (indentation depth) and time (simulation time). So you can easily calculate the acceleration a=distance/time. Let z is the variable for indender position z=z_initial +v_i*t -at^2. Put v_z as the z position in your fix indent command, you can simulate an indentation with linear velocity.