Friction and Damping
Hello!
I would like to ask about my doubts concerning friction and damping.
sim.createInter
FrictionPrms(
name="friction",
youngsModulus=
poissonsRatio=0.25,
dynamicMu=0.4,
staticMu=0.6
)
)
sim.createInter
LinDampingPrms(
name="damping1",
viscosity=0.002,
maxIterations=50
)
)
sim.createInter
RotDampingPrms(
name="damping2",
viscosity=0.002,
maxIterations=50
)
)
According to the tutotial: "for elastodynamic problems, a small value is sufficient (viscosity < 0:05) whereas for quasi-static problems a value as large as viscosity ~ 0:5 might be appropriate." and "the staticMu coefficient of friction is applied when two particles are in static frictional contact, i.e., prior to the fi
rst time the frictional sliding criterion is met. Thereafter the dynamicMu coefficient of friction is applied. By setting dynamicMu < staticMu, one can simulate the physical observation that the frictional force required to maintain sliding is less than the force necessary to initiate sliding."
However, do these parameters (viscosity, dynamicMu, staticMu) depend on any parameters of the model?
Thank you and best regards!
Question information
- Language:
- English Edit question
- Status:
- Solved
- Assignee:
- No assignee Edit question
- Solved by:
- Dion Weatherley
- Solved:
- 2019-03-06
- Last query:
- 2019-03-06
- Last reply:
- 2019-03-05
|
#1 |
Hi Glaubiger,
There three are all model parameters that the user must specify.
The friction coefficients (dynamicMu and staticMu) are dimensionless and for real materials, are typically in the range 0.2-0.8. dynamicMu should be less than or equal to staticMu. Friction coefficients are technically the tangent of a friction angle. I typically use dynamicMu=
The viscosity parameter is generally a bit more difficult to specify. It has units of 1/Time so it's value depends on the system of units you choose to use for defining other model parameters such as particle density, Young's moduli, particle radii etc. Generally in simulations involving Lin/RotDamping, you will need to run a few simulations with different values of the viscosity parameter and observe whether the simulation is sufficiently damped. Plotting the total kinetic energy versus time is a good way to see if the viscosity is sufficient.
An alternative choice for damping is the LocalDampingPrms (and RotLocalDamping
Another interaction group you may find useful is the recently added SpringDashpotFr
sim.createInter
SpringDashpo
name = "pp_repel",
youngsModulus = 1.0e5,
poissonsRatio = 0.25,
restitution = 0.8,
dynamicMu = 0.6
)
)
The "restitution" parameter is a Coefficient of Restitution which is dimensionless and <=1.0. Rocks generally have a coefficient of restitution around 0.8.
Cheers,
Dion
Piotr Klejment (glaubiger) said : | #2 |
Thank you Dion for your help!
Piotr Klejment (glaubiger) said : | #3 |
Thanks Dion Weatherley, that solved my question.