Lagrangian Physical Properties#

In this subsection, gravitational acceleration, and the physical properties of the particles and walls are defined. These properties include number of particle types, and for each type, particle diameter, particle density, Young's modulus of particle and wall, Poisson ratio of particle and wall, restitution coefficient of particle and wall, friction coefficient of particle and wall and rolling friction coefficient of particle and wall.

subsection lagrangian physical properties
  # Gravitational acceleration vector
  set g                       = 0.0, 0.0, 0.0

  # Number of particle types
  set number of particle types = 1

  # Entering particle type 0
  subsection particle type 0

    # Choices are uniform, normal or custom
    set size distribution type            = uniform

    # If distribution type = uniform or normal
    set diameter                          = 0.001

    # If distribution type = custom
    set custom diameters                  = 0.001 , 0.0005
    set custom volume fractions           = 0.6   , 0.4

    # If distribution type = normal
    set standard deviation                = 0.0
    # If distribution type = normal or custom
    set distribution prn seed          = 1

    # For every distribution types
    set number of particles               = 0
    set density particles                 = 1000
    set young modulus particles           = 1000000
    set poisson ratio particles           = 0.3
    set restitution coefficient particles = 0.1
    set friction coefficient particles    = 0.1
    set rolling friction particles        = 0.1
    set rolling viscous damping particles = 0.1
    set surface energy particles          = 0.0
    set Hamaker constant particles        = 4.e-19
    set thermal conductivity particles    = 1
    set specific heat particles           = 1000
    set microhardness particles           = 1.e9
    set surface slope particles           = 0.1
    set surface roughness particles       = 1.e-9
    set thermal accommodation particles   = 0.7
    set real young modulus wall           = 0.

  end

  # Wall properties
  set young modulus wall           = 1000000
  set poisson ratio wall           = 0.3
  set restitution coefficient wall = 0.1
  set friction coefficient wall    = 0.1
  set rolling friction wall        = 0.1
  set rolling viscous damping wall = 0.1
  set surface energy wall          = 0.0
  set Hamaker constant wall        = 4.e-19
  set thermal conductivity wall    = 100
  set microhardness wall           = 1.e9
  set surface slope wall           = 0.1
  set surface roughness wall       = 1.e-10
  set thermal accommodation wall   = 0.7
  set real young modulus wall      = 0.

  # Interstitial gas properties
  set thermal conductivity gas     = 0.01
  set specific heat gas            = 1000
  set dynamic viscosity gas        = 1.e-5
  set specific heats ratio gas     = 1
  set molecular mean free path gas = 68.e-9
end

The g parameter defines the gravitational acceleration in x, y, and z directions. The deprecated version of this parameter is the 3 parameters gx, gy, and gz.
The number of particle types parameter specifies the number of particle types in a simulation. Particles with different sizes, size distributions, and physical properties have to be defined as separate particle types.
For each particle type, we have to define a separate subsection (for instance, subsection particle type 0) to specify its physical properties.

Note

If the particles in a simulation are monodispersed and have the same physical properties, the number of particle types should be equal to zero. For polydispersed systems, the number of particle types is selected equal to the number of particles types in the simulation. For each particle type, a separate subsection particle type n should be defined (n starts from zero to number of particle types - 1) which contains all the physical properties related to that particle type.

The size distribution type parameter specifies the size distribution for each particle type. For each particle type, three size distribution type can be defined: uniform, normal and custom.
- For the uniform size distribution, the diameter of the particles is constant.
- For the normal size distribution, the particle diameters are sampled from a normal distribution with an average diameter and a standard deviation.
- For the custom size distribution, particle diameters are sampled from a list of diameters with a corresponding list of probabilities.

Note

In the custom size distribution, the probability values are based on the volume fraction taken by all the particles of the associated diameter, not to the total number of particles. For example, if a probability is equal to 0.5 , this means that half of the total volume of inserted particles will be occupied by particle with the associated diameter value.

The diameter parameter defines the diameter of the particles in a uniform distribution. In the case of a normal distribution, this parameter indicates the average diameter.
For a normal distribution, the standard deviation parameter should be defined to indicate the standard deviation on the particle size distribution.
For a custom distribution, the custom diameters parameter defines the different diameter values used when generating particles. The custom volume fractions parameter defines the probabilities corresponding to each diameter value previously declared based on volume fraction. Both list must have the same length.
For a normal or a custom distribution, the distribution prn seed parameter defines the pseudo-random number (PRN) generator with which the diameters values are getting generated.
The number of particles parameter defines the number of particles for each type.
The density particles defines the density of particles for each type.
The young modulus particles defines the Young’s modulus for particles in each type.
The poisson ratio particles defines the Poisson’s ratio for particles in each type.
The restitution coefficient particles defines the restitution coefficient for particles in each type.
The friction coefficient particles defines the friction coefficient for particles in each type.
The rolling friction particles defines the rolling friction coefficient of particles for each type.
The rolling viscous damping particles` defines the rolling viscous damping coefficient of the particles for the elasto-plastic spring-dashpot rolling friction model.
The surface energy particles defines the surface energy of particles for each type. This parameter is used with the JKR and DMT force model.
The Hamaker constant particles defines the Hamaker constant of particles for each type. This parameter is used with the DMT force model.
The young modulus wall defines the Young’s modulus of the walls.
The poisson ratio wall defines the Poisson’s ratio of the walls.
The restitution coefficient wall defines the restitution coefficient of the walls.
The friction coefficient wall defines the friction coefficient of the walls.
The rolling friction wall defines the rolling friction coefficient of the walls.
The rolling viscous damping wall defines the rolling viscous damping coefficient of the walls for the elasto-plastic spring-dashpot rolling friction model.
The surface energy wall defines the surface energy of the walls. This parameter is used with the JKR and DMT force model.
The Hamaker constant wall defines the Hamaker constant of the walls. This parameter is used with the DMT force model.

Note

The following DEM parameters are used for multiphysic DEM simulations. All parameters should be specified in a consistent set of units (ideally SI).

The thermal conductivity particles defines the thermal conductivity of particles for each type.
The specific heat particles defines the specific heat of particles for each type.
The microhardness particles defines the microhardness of particles for each type.
The surface slope particles defines the surface slope of particles for each type. It is a non-dimensional parameter related to roughness and more precisely to the angle of the asperities on the surface. A higher surface slope entails a smaller microcontact resistance, as there are more microcontacts.
The surface roughness particles defines the surface roughness of particles for each type.
The thermal accommodation particles defines the thermal accommodation coefficient of particles for each type. The thermal accommodation coefficient characterizes the quality of thermal energy exchange between gas molecules and a solid surface.
The real young modulus particles defines the real Young’s modulus of particles for each type. It is used in multiphysic DEM to correct the thermal contact radius. This is useful when the Young’s modulus in the simulation is lowered to increase the time-step. An artificially low Young’s modulus would lead to an overestimated thermal contact radius. The real Young’s modulus can only be given a value that is higher than the Young’s modulus. Otherwise, the regular Young’s modulus will be used in the calculations.
The thermal conductivity gas defines the thermal conductivity of the interstitial gas.
The specific heat gas defines the specific heat capacity of the interstitial gas.
The dynamic viscosity gas defines the dynamic viscosity of the interstitial gas.
The specific heats ratio gas defines the specific heats ratio of the interstitial gas.
The molecular mean free path gas defines the molecular mean free path of the interstitial gas. It is the average distance a gas molecule will travel between collisions with other gas molecules.
The thermal conductivity wall defines the thermal conductivity of the wall.
The microhardness wall defines the microhardness of the wall.
The surface slope wall defines the surface slope of the wall.
The surface roughness wall defines the surface roughness of the wall.
The thermal accommodation wall defines the thermal accommodation coefficient of the wall.
The real young modulus wall defines the real Young’s modulus of the wall.