# doubt about fix addforce which is time-dependent

Hi all:
I am trying to simulate the fracture of cuboid rotating blade by peridynamics.I came up with two problems.
(1) I use "fix move rotate"command to rotate the blade around the x-axis. My doubt is whether it will produce centrifugal force automatically without imposinging any other force?
(2) I want to impose a tension force to the rotating blade to simulate the fracture.The blade rotates around the x-axis.The force is a constant along the longitudinal direction of the blade,and is vertical to x-axis always.So i use “fix addfore” command to define this time-dependent force without using the “minimize” command.
But i think this time-dependent force is not recognized likely, why? To impose this force, what commands shoud I use which are priority to the follow commands? I have written the input script as follows:

Hi all:
I am trying to simulate the fracture of cuboid rotating blade by
peridynamics.I came up with two problems.
(1) I use "fix move rotate"command to rotate the blade around the x-axis.
My doubt is whether it will produce centrifugal force automatically without
imposinging any other force?

think a little bit about where the centrifugal force is coming from.
best you consider a minimal system with just one fixed atom and a
second connected to it with a harmonic potential. you make the second
rotate around the first by giving it a push.

fix move will just move atoms on a prescribed trajectory without
paying *any* attention to forces. where would the centrifugal force
come from

(2) I want to impose a tension force to the rotating blade to simulate
the fracture.The blade rotates around the x-axis.The force is a constant
along the longitudinal direction of the blade,and is vertical to x-axis
always.So i use "fix addfore" command to define this time-dependent force
without using the "minimize" command.
But i think this time-dependent force is not recognized likely, why?

worse. your script is plain wrong. you use fix move to propagate
all(!) particles and then you add fix nve to do the same. haven't you
seen the warning that LAMMPS throws in this case?

you have two options:
- you impose the rotation like with a real blade at the axle only and
let the rest of the system follow. case closed. applying an external
force in addition would make no sense.
- you treat the centrifugal force as an external force (and make the
rotating blade your reference system). in that case you don't need the
rotation at all. apply the external force and integrate the equations
of motion. done.

these are all problems of rather elementary classical mechanics. it
may be helpful to dig around for some of your very old text books that
cover those topics and re-read them.

axel.