tUse frictional energy equation from Nguyen 2009 - Granular.jl - Julia package for granular dynamics simulation
  HTML git clone git://src.adamsgaard.dk/Granular.jl
   DIR Log
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       ---
   DIR commit ee17a2d649961009a9f878201878098572f64596
   DIR parent 6a2b205579d371f3ce2760cc445517592956600c
  HTML Author: Anders Damsgaard <andersd@riseup.net>
       Date:   Wed, 21 Feb 2018 15:42:30 -0500
       
       Use frictional energy equation from Nguyen 2009
       
       Diffstat:
         M src/interaction.jl                  |      14 ++++++++++++--
       
       1 file changed, 12 insertions(+), 2 deletions(-)
       ---
   DIR diff --git a/src/interaction.jl b/src/interaction.jl
       t@@ -261,7 +261,12 @@ function interactGrains!(simulation::Simulation, i::Int, j::Int, ic::Int)
                if force_t > μ_d_minimum*abs(force_n)
                    force_t = μ_d_minimum*abs(force_n)
                    simulation.grains[i].contact_age[ic] = 0.0
       -            E_shear = abs(force_t)*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
       t@@ -278,7 +283,12 @@ function interactGrains!(simulation::Simulation, i::Int, j::Int, ic::Int)
                    force_t = μ_d_minimum*abs(force_n)*force_t/abs(force_t)
                    δ_t = (-force_t - γ_t*vel_t)/k_t
                    simulation.grains[i].contact_age[ic] = 0.0
       -            E_shear = abs(force_t)*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