# Solids model

## Solids settings

Enabling the SOLIDS solver and specifying options common to both DEM and PIC models. The following inputs must be preceded by the “solids.” root

| Description | Type | Default
--- | --- | --- | ---
types | Specified name(s) of the SOLIDS types or None to disable the SOLIDS solver. The user defined names are used to specify DEM and/or PIC model inputs. | String | None
molecular_weight | Value of constant solid molecular weight | Real | 0
specific_heat | Specify which specific heat model to use for solid. Available options include: ‘constant’ for constant specific heat model | String | None
specific_heat.constant | Value of species molecular weight. [required if fluid.specific_heat = ‘constant’]. | Real | 0
reference_temperature | Value of the reference temperature used for specific enthalpy | Real | 0
species | Specify which species can constitute the fluid phase [defined species must be a subset of the species.solve arguments]. | String | None
newton_solver.absolute_tol | Define absolute tolerance for Damped-Newton solver | Real | 1.e-6
newton_solver.relative_tol | Define relative tolerance for Damped-Newton solver | Real | 1.e-6
newton_solver.max_iterations | Define max number of iterations for Damped-Newton solver | int | 100

Below is an example for specifying the solids solver model options.

    solids.types = my_solid0  my_solid1

    solids.reference_temperature = 298.15

    solids.specific_heat = mixture

    solids.species = Fe2O3  FeO

## DEM model settings

Enabling the DEM solver and specifying model options.

| Description | Type | Default
--- | --- | --- | ---
dem.solve | Specified name(s) of the DEM types or None to disable the DEM solver. The user defined names are used to specify DEM model inputs. | String | None
dem.friction_coeff.pp | Friction coefficient :: particle to particle collisions [required] | Real | 0
dem.friction_coeff.pw | Friction coefficient :: particle to wall collisions [required] | Real | 0
dem.spring_const.pp | Normal spring constant :: particle to particle collisions [required] | Real | 0
dem.spring_const.pw | Normal spring constant :: particle to wall collisions [required] | Real | 0
dem.spring_tang_fac.pp | Tangential-to-normal spring constant factor :: particle to particle collisions | Real | 0.2857
dem.spring_tang_fac.pw | Tangential-to-normal spring constant factor :: particle to wall collisions | Real | 0.2857
dem.damping_tang_fac.pp | Factor relating the tangential damping coefficient to the normal damping coefficient :: particle to particle collisions | Real | 0.5
dem.damping_tang_fac.pw | Factor relating the tangential damping coefficient to the normal damping coefficient :: particle to wall collisions | Real | 0.5

The following inputs use the DEM type names specified using the dem.solve input to define restitution coefficients and are proceeded with dem.restitution_coeff. These must be defined for all solid-solid and solid-wall combinations.

| Description | Type | Default
--- | --- | --- | ---
[solid0].[solid1] | Specifies the restitution coefficient between solid0 and solid1. Here the order is not important and could be defined as [solid1].[solid0] | Real | 0
[solid0].wall | Specifies the restitution coefficient between solid0 and the wall. Order is not important and this could be defined as wall.[solid0] | Real | 0

Below is an example for specifying the inputs for two DEM solids.

    dem.solve = sand  char

    dem.friction_coeff.pp     =     0.25
    dem.friction_coeff.pw     =     0.15

    dem.spring_const.pp       =   100.0
    dem.spring_const.pw       =   100.0

    dem.spring_tang_fac.pp    =     0.2857
    dem.spring_tang_fac.pw    =     0.2857

    dem.damping_tang_fac.pp   =     0.5
    dem.damping_tang_fac.pw   =     0.5

    dem.restitution_coeff.sand.sand =  0.85
    dem.restitution_coeff.sand.char =  0.88
    dem.restitution_coeff.char.char =  0.90

    dem.restitution_coeff.sand.wall =  0.85
    dem.restitution_coeff.char.wall =  0.89

## PIC model settings