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Message #11205
[Bug 1360371] Re: Law2_ScGeom_ViscElPhys_Basic - Mass Always Equals 1
Thanks for pointing that out and for presenting the script!
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https://bugs.launchpad.net/bugs/1360371
Title:
Law2_ScGeom_ViscElPhys_Basic - Mass Always Equals 1
Status in Yet Another Dynamic Engine:
New
Bug description:
Hello everyone,
I have been testing the constitutive law Law2_ScGeom_ViscElPhys_Basic
(or rather Law2_Spheres_Viscoelastic_SimpleViscoelastic() in Version
1.07.0) by comparing the analytical [1] with the numerical solution.
The test scenario is a sphere that collides with a wall. I discovered
that the model (either the constitutive law or the integrator) did not
take into account the density of the sphere, even if its mass was
correct; maybe it's just a syntax error.
To illustrate the problem I created a minimal working example, in
which the sphere possesses a density of 1e6 kg/m³. Despite this high
density, the sphere's displacement is still that of a 1 kg sphere. In
this example, I plot the analytical and numerical solutions. For some
reason, the inertial force is not influence by a change in density
(rho).
[1]
http://en.wikipedia.org/wiki/Damping#Example:_mass.E2.80.93spring.E2.80.93damper
See either the following code or the attached file for the MWE.
Best regards and thank you in advance,
Dominik
============================================================================================
################################################################################
# CONSTITUTIVE LAW TESTING
from yade import plot,ymport
import math
################################################################################
# MATERIAL
rho = 1e6 # [kg/m^3] density
kn = 600 # [N/m] normal stiffness coefficient
ks = 0 # [N/m] tangential stiffness coefficient
cn = 40 # [-] normal damping coefficient
cs = 0 # [-] tangential damping coefficient
mu = 0.75 # [-] friction coefficient
frictionAngle = math.atan(mu)
m1 = O.materials.append(ViscElMat(kn=kn,ks=ks,cn=cn,cs=cs,
frictionAngle=frictionAngle))
m2 = O.materials.append(ViscElMat(kn=kn,ks=ks,cn=cn,cs=cs,
frictionAngle=frictionAngle,density=rho))
################################################################################
# GEOMETRY
r = 1 # [m] sphere radius
b1 = O.bodies.append(utils.wall((r,0,0),0,0,material=m1))
b2 = O.bodies.append(utils.sphere(center=(0,0,0),radius=r,material=m2))
################################################################################
# SIMULATION
O.dt = 1e-5 # [s] fixed time step
v = 1 # [m/s] velocity along x-axis
O.bodies[b2].state.vel[0] = v
O.engines=[
ForceResetter(),
InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Facet_Aabb(),Bo1_Wall_Aabb()]),
InteractionLoop(
[Ig2_Sphere_Sphere_ScGeom(),
Ig2_Facet_Sphere_ScGeom(),
Ig2_Wall_Sphere_ScGeom()],
[Ip2_ViscElMat_ViscElMat_ViscElPhys()],
[Law2_Spheres_Viscoelastic_SimpleViscoelastic()]
),
# new law name should be Law2_ScGeom_ViscElPhys_Basic
# (but not updated in Version 1.07.0)
NewtonIntegrator(damping=0),
PyRunner(command='addPlotData()',iterPeriod=1)
]
################################################################################
# INTERMEDIATE PARAMETERS OF THE ANALYTICAL MODEL
m = 1 #4/3 * math.pi * r**3 * rho (this should be the real mass)
omega0 = math.sqrt(kn/m)
zeta = cn / (2 * math.sqrt(kn * m))
omegad = omega0 * math.sqrt(1 - zeta**2)
################################################################################
# PLOT NUMERICAL AND ANALYTICAL SOLUTION
def addPlotData():
global v
global omega0
global zeta
global omegad
plot.addData(
t = O.time,
x1 = O.bodies[b2].state.pos[0],
x2 = v/omegad * math.exp(-zeta*omega0*O.time) * math.sin(omegad*O.time))
plot.plots={'t':('x1','x2')}
plot.plot()
################################################################################
# RUN
O.run(20000)
============================================================================================
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