tDisable tangential interaction when rotation is disabled - Granular.jl - Julia package for granular dynamics simulation
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---
(DIR) commit e930b68a2463f6b6e9c335d95278ed172ee93737
(DIR) parent 5cdd91e9b941cf754b528c62fe0fbe24516930d3
(HTM) Author: Anders Damsgaard <anders@adamsgaard.dk>
Date: Wed, 6 Jun 2018 08:45:15 -0400
Disable tangential interaction when rotation is disabled
Diffstat:
M src/interaction.jl | 185 +++++++++++++++++++------------
1 file changed, 111 insertions(+), 74 deletions(-)
---
(DIR) diff --git a/src/interaction.jl b/src/interaction.jl
t@@ -143,18 +143,27 @@ function interactGrains!(simulation::Simulation, i::Int, j::Int, ic::Int)
# Contact kinematics
vel_lin = simulation.grains[i].lin_vel - simulation.grains[j].lin_vel
vel_n = dot(vel_lin, n)
- vel_t = dot(vel_lin, t) -
- harmonicMean(r_i, r_j)*(simulation.grains[i].ang_vel +
- simulation.grains[j].ang_vel)
- # Correct old tangential displacement for contact rotation and add new
- δ_t0 = simulation.grains[i].contact_parallel_displacement[ic]
- δ_t = dot(t, δ_t0 - (n*dot(n, δ_t0))) + vel_t*simulation.time_step
-
- # Determine the contact rotation
- θ_t = simulation.grains[i].contact_rotation[ic] +
- (simulation.grains[j].ang_vel - simulation.grains[i].ang_vel) *
- simulation.time_step
+ if !simulation.grains[i].rotating && !simulation.grains[j].rotating
+ rotation = false
+ else
+ rotation = true
+ end
+
+ if rotation
+ vel_t = dot(vel_lin, t) -
+ harmonicMean(r_i, r_j)*(simulation.grains[i].ang_vel +
+ simulation.grains[j].ang_vel)
+
+ # Correct old tangential displacement for contact rotation and add new
+ δ_t0 = simulation.grains[i].contact_parallel_displacement[ic]
+ δ_t = dot(t, δ_t0 - (n*dot(n, δ_t0))) + vel_t*simulation.time_step
+
+ # Determine the contact rotation
+ θ_t = simulation.grains[i].contact_rotation[ic] +
+ (simulation.grains[j].ang_vel - simulation.grains[i].ang_vel) *
+ simulation.time_step
+ end
# Effective radius
R_ij = harmonicMean(r_i, r_j)
t@@ -175,24 +184,30 @@ function interactGrains!(simulation::Simulation, i::Int, j::Int, ic::Int)
# Effective normal and tangential stiffness
k_n = E * A_ij/R_ij
#k_t = k_n*ν # Kneib et al 2016
- k_t = k_n * 2. * (1. - ν^2.) / ((2. - ν) * (1. + ν)) # Obermayr 2011
+ if rotation
+ k_t = k_n * 2. * (1. - ν^2.) / ((2. - ν) * (1. + ν)) # Obermayr 2011
+ end
else # Micromechanical parameterization: k_n and k_t set explicitly
k_n = harmonicMean(simulation.grains[i].contact_stiffness_normal,
simulation.grains[j].contact_stiffness_normal)
- k_t = harmonicMean(simulation.grains[i].contact_stiffness_tangential,
- simulation.grains[j].contact_stiffness_tangential)
+ if rotation
+ k_t = harmonicMean(simulation.grains[i].contact_stiffness_tangential,
+ simulation.grains[j].contact_stiffness_tangential)
+ end
end
γ_n = harmonicMean(simulation.grains[i].contact_viscosity_normal,
simulation.grains[j].contact_viscosity_normal)
- γ_t = harmonicMean(simulation.grains[i].contact_viscosity_tangential,
- simulation.grains[j].contact_viscosity_tangential)
+ if rotation
+ γ_t = harmonicMean(simulation.grains[i].contact_viscosity_tangential,
+ simulation.grains[j].contact_viscosity_tangential)
- μ_d_minimum = min(simulation.grains[i].contact_dynamic_friction,
- simulation.grains[j].contact_dynamic_friction)
+ μ_d_minimum = min(simulation.grains[i].contact_dynamic_friction,
+ simulation.grains[j].contact_dynamic_friction)
+ end
# Determine contact forces
if k_n ≈ 0. && γ_n ≈ 0. # No interaction
t@@ -223,8 +238,10 @@ function interactGrains!(simulation::Simulation, i::Int, j::Int, ic::Int)
end
# Grain-pair moment of inertia [m^4]
- I_ij = 2.0/3.0*R_ij^3*min(simulation.grains[i].thickness,
- simulation.grains[j].thickness)
+ if rotation
+ I_ij = 2.0/3.0*R_ij^3*min(simulation.grains[i].thickness,
+ simulation.grains[j].thickness)
+ end
# Contact tensile strength increases linearly with contact age until
t@@ -232,24 +249,36 @@ function interactGrains!(simulation::Simulation, i::Int, j::Int, ic::Int)
tensile_strength = min(simulation.grains[i].contact_age[ic]*
simulation.grains[i].strength_heal_rate,
simulation.grains[i].tensile_strength)
- shear_strength = min(simulation.grains[i].contact_age[ic]*
- simulation.grains[i].strength_heal_rate,
- simulation.grains[i].shear_strength)
- M_t = 0.0
- if tensile_strength > 0.0
- # Determine bending momentum on contact [N*m],
- # (converting k_n to E to bar(k_n))
- M_t = (k_n*R_ij/(A_ij*(simulation.grains[i].contact_radius +
+ if rotation
+ shear_strength = min(simulation.grains[i].contact_age[ic]*
+ simulation.grains[i].strength_heal_rate,
+ simulation.grains[i].shear_strength)
+ M_t = 0.0
+ if tensile_strength > 0.0
+ # Determine bending momentum on contact [N*m],
+ # (converting k_n to E to bar(k_n))
+ M_t = (k_n*R_ij/(A_ij*(simulation.grains[i].contact_radius +
simulation.grains[j].contact_radius)))*I_ij*θ_t
+ end
end
# Reset contact age (breaking bond) if bond strength is exceeded
- if δ_n >= 0.0 && abs(force_n)/A_ij + abs(M_t)*R_ij/I_ij > tensile_strength
- force_n = 0.
- force_t = 0.
- simulation.grains[i].contacts[ic] = 0 # remove contact
- simulation.grains[i].n_contacts -= 1
- simulation.grains[j].n_contacts -= 1
+ if rotation
+ if δ_n >= 0.0 && abs(force_n)/A_ij + abs(M_t)*R_ij/I_ij > tensile_strength
+ force_n = 0.
+ force_t = 0.
+ simulation.grains[i].contacts[ic] = 0 # remove contact
+ simulation.grains[i].n_contacts -= 1
+ simulation.grains[j].n_contacts -= 1
+ end
+ else
+ if δ_n >= 0.0 && abs(force_n)/A_ij > tensile_strength
+ force_n = 0.
+ force_t = 0.
+ simulation.grains[i].contacts[ic] = 0 # remove contact
+ simulation.grains[i].n_contacts -= 1
+ simulation.grains[j].n_contacts -= 1
+ end
end
# Limit compressive stress if the prefactor is set to a positive value
t@@ -268,53 +297,55 @@ function interactGrains!(simulation::Simulation, i::Int, j::Int, ic::Int)
simulation.grains[idx_weakest].thickness += 1.0/(π*Δr)
end
- if k_t ≈ 0. && γ_t ≈ 0.
- # do nothing
+ if rotation
+ if k_t ≈ 0. && γ_t ≈ 0.
+ # do nothing
- elseif k_t ≈ 0. && γ_t > 0.
- force_t = abs(γ_t * vel_t)
+ elseif k_t ≈ 0. && γ_t > 0.
+ force_t = abs(γ_t * vel_t)
- # Coulomb slip
- if force_t > μ_d_minimum*abs(force_n)
- force_t = μ_d_minimum*abs(force_n)
+ # Coulomb slip
+ if force_t > μ_d_minimum*abs(force_n)
+ force_t = μ_d_minimum*abs(force_n)
- # Nguyen et al 2009 "Thermomechanical modelling of friction effects
- # in granular flows using the discrete element method"
- E_shear = abs(force_t)*abs(vel_t)*simulation.time_step
+ # Nguyen et al 2009 "Thermomechanical modelling of friction effects
+ # in granular flows using the discrete element method"
+ E_shear = abs(force_t)*abs(vel_t)*simulation.time_step
- # Assume equal thermal properties
- simulation.grains[i].thermal_energy += 0.5*E_shear
- simulation.grains[j].thermal_energy += 0.5*E_shear
- end
- if vel_t > 0.
- force_t = -force_t
- end
+ # Assume equal thermal properties
+ simulation.grains[i].thermal_energy += 0.5*E_shear
+ simulation.grains[j].thermal_energy += 0.5*E_shear
+ end
+ if vel_t > 0.
+ force_t = -force_t
+ end
- elseif k_t > 0.
+ elseif k_t > 0.
- force_t = -k_t*δ_t - γ_t*vel_t
+ force_t = -k_t*δ_t - γ_t*vel_t
- # Coulomb slip
- if abs(force_t) > μ_d_minimum*abs(force_n)
- force_t = μ_d_minimum*abs(force_n)*force_t/abs(force_t)
- δ_t = (-force_t - γ_t*vel_t)/k_t
+ # Coulomb slip
+ if abs(force_t) > μ_d_minimum*abs(force_n)
+ force_t = μ_d_minimum*abs(force_n)*force_t/abs(force_t)
+ δ_t = (-force_t - γ_t*vel_t)/k_t
- # Nguyen et al 2009 "Thermomechanical modelling of friction effects
- # in granular flows using the discrete element method"
- E_shear = abs(force_t)*abs(vel_t)*simulation.time_step
+ # Nguyen et al 2009 "Thermomechanical modelling of friction effects
+ # in granular flows using the discrete element method"
+ E_shear = abs(force_t)*abs(vel_t)*simulation.time_step
- # Assume equal thermal properties
- simulation.grains[i].thermal_energy += 0.5*E_shear
- simulation.grains[j].thermal_energy += 0.5*E_shear
- end
+ # Assume equal thermal properties
+ simulation.grains[i].thermal_energy += 0.5*E_shear
+ simulation.grains[j].thermal_energy += 0.5*E_shear
+ end
- else
- error("unknown contact_tangential_rheology (k_t = $k_t, γ_t = $γ_t")
+ else
+ error("unknown contact_tangential_rheology (k_t = $k_t, γ_t = $γ_t")
+ end
end
# Break bond under extension through bending failure
- if δ_n < 0.0 && tensile_strength > 0.0 && shear_strength > 0.0 &&
- abs(force_t)/A_ij > shear_strength
+ if δ_n < 0.0 && tensile_strength > 0.0 && rotation &&
+ shear_strength > 0.0 && abs(force_t)/A_ij > shear_strength
force_n = 0.
force_t = 0.
t@@ -323,15 +354,21 @@ function interactGrains!(simulation::Simulation, i::Int, j::Int, ic::Int)
simulation.grains[j].n_contacts -= 1
end
- simulation.grains[i].contact_parallel_displacement[ic] = δ_t*t
- simulation.grains[i].contact_rotation[ic] = θ_t
simulation.grains[i].contact_age[ic] += simulation.time_step
- simulation.grains[i].force += force_n*n + force_t*t;
- simulation.grains[j].force -= force_n*n + force_t*t;
+ if rotation
+ simulation.grains[i].contact_parallel_displacement[ic] = δ_t*t
+ simulation.grains[i].contact_rotation[ic] = θ_t
- simulation.grains[i].torque += -force_t*R_ij + M_t
- simulation.grains[j].torque += -force_t*R_ij - M_t
+ simulation.grains[i].force += force_n*n + force_t*t;
+ simulation.grains[j].force -= force_n*n + force_t*t;
+
+ simulation.grains[i].torque += -force_t*R_ij + M_t
+ simulation.grains[j].torque += -force_t*R_ij - M_t
+ else
+ simulation.grains[i].force += force_n*n;
+ simulation.grains[j].force -= force_n*n;
+ end
simulation.grains[i].pressure +=
force_n/simulation.grains[i].side_surface_area;