Question #698572 on Yade changed:
https://answers.launchpad.net/yade/+question/698572
Status: Answered => Open
Rohit John is still having a problem:
Dear Jan,
I tried the same test, explain in the previous comment, on a clump which
is force to rotate about the origin using a penalty force model. The
change in angular momentum is still present, however, the magnitude is
much less. I suppose this could be because of an error in the
integration of the angular momentum.
Kind regards,
Rohit K. John
#
--------------------------------------------------------------------------------------------------------------------------------------------------------------------
Python
from math import *
from yade import *
from yade import utils, geom, plot
#
----------------------------------------------------------------------------------
bodies
sph1 = sphere((0, -2, 2), .5)
sph2 = sphere(center=(0, 0, 0), radius=.5, fixed=True)
sph3 = sphere((0, 0, 2), .5)
sph1_id = O.bodies.append(sph1)
sph2_id = O.bodies.append(sph2)
sph3_id = O.bodies.append(sph3)
O.bodies[sph3_id].state.vel = [0,-1,0]
g = Vector3([0,0,0])
stiffnes = 1e7
# ---------------------------------------------------------------- clump
clump_id = O.bodies.clump([sph1_id, sph2_id])
#
----------------------------------------------------------------------------------
engines
O.engines = [
ForceResetter(),
InsertionSortCollider([Bo1_Sphere_Aabb()]),
InteractionLoop(
[Ig2_Sphere_Sphere_ScGeom()], # collision geometry
[Ip2_FrictMat_FrictMat_FrictPhys()], # collision "physics"
[Law2_ScGeom_FrictPhys_CundallStrack()] # contact law -- apply
forces
),
PyRunner(command = "eccentricAxisEngine()", iterPeriod = 1),
NewtonIntegrator(gravity=g, damping=0.0),
PyRunner(command = "plotter()", iterPeriod = 100)
]
#
----------------------------------------------------------------------------------
additional engines
def eccentricAxisEngine():
pos_0 = O.bodies[sph2_id].state.pos
force = -stiffnes*pos_0
O.forces.addF(id = sph2_id, f = force)
plot.plots = {'t':('ax', 'ay', 'az')}
def plotter():
body_ids = [clump_id, sph3_id]
totalangVel = Vector3([0,0,0])
for i in body_ids:
totalangVel = totalangVel + getAngVelAboutOrigin(i)
plot.addData(t = O.time, ax = totalangVel[0],
ay = totalangVel[1], az = totalangVel[2]
)
plot.plot()
def getAngVelAboutOrigin(id):
state = O.bodies[id].state
pos = state.pos
vel = state.vel
angMom = state.angMom
mass = state.mass
total_ang_mom = angMom + mass*pos.cross(vel)
return total_ang_mom
#
----------------------------------------------------------------------------------
sim setup
O.dt = .5e-2 * PWaveTimeStep()
O.saveTmp()
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