compute pair/gran/local command
compute wall/gran/local command
compute pair/gran/local/bond command
compute wall/gran/local/bond command
Warning
These commands are deprecated, please use calculate particle_contact_network, calculate wall_contact_network, calculate particle_bond_network or calculate wall_bond_network instead
Syntax
compute ID group-ID pair/gran/local(/bond) general_keywords general_values interaction_with_group interaction_group_id keywords ...
compute ID group-ID wall/gran/local(/bond) general_keywords general_values interaction_with_mesh mesh_id keywords ...
ID, group-ID are documented in compute command
pair/gran/local or wall/gran/local = style name of this compute command
general_keywords general_values are documented in compute
interaction_with_group optional keyword for pair/gran/local
interaction_group_id value associated with previous keyword, sets the group with which interactions are to be calculated
interaction_with_mesh optional keyword for wall/gran/local
mesh_id value associated with previous keyword, sets the mesh with which interactions are to be calculated
zero or more keywords may be appended
keyword = pos or vel or ids or force or force_normal or force_tangential or torque or torque_normal or torque_tangential or history or contactArea or delta or contactPoint or ms_id or shearrate or heatFlux or heatConductionArea or verbose pos = positions of particles in contact or particle position and mesh contact point (6 values) vel = velocities of particles in contact or particle velocity and mesh velocity at contact point (6 values) ids = IDs of particles in contact and a periodicity flag (3 values) or IDs of the mesh, the triangle and the particle (3 values) force = contact force (3 values) force_normal = normal component of contact force (3 values) force_tangential = tangential component of contact force (3 values) torque = contact torque (3 values) torque_normal = normal component of torque (3 values) torque_tangential = tangential component of torque (3 values) history = contact history (# depends on pair style, e.g. 3 shear history values) contactArea = area of the contact (1 value) delta = overlap of the contact (1 value) contactPoint = contact point (3 values) ms_id = multisphere IDs of clumps where of particles in contact belong to (in case of wall, second value will be -1) (2 values) shearrate = shear rate - relative tangential velocity divided by distance of center - between contact partners (1 value) heatFlux = conductive heat flux of the contact (1 value) heatConductionArea = contact area used for heat flux computation (1 value) electricConductance = conductance (inverse of electric resistance) (1 value) electricCurrent = current flowing across the contact (1 value) verbose = print additional detailed screen information
Examples
compute 1 all pair/gran/local
compute 1 all pair/gran/local pos force
compute 1 all pair/gran/local/bond ids pos
compute 1 all wall/gran/local
compute interaction_group_a_b group_a pair/gran/local interaction_with_group group_b
compute interaction_group_a_mesh_cad group_a wall/gran/local interaction_with_mesh cad
Description
Define a computation that calculates properties of individual pairwise or particle-wall interactions of a granular pair style. For styles pair/gran/local and wall/gran/local, the number of datums generated, aggregated across all processors, equals the number of pairwise interactions or particle-wall interactions in the system. For styles pair/gran/local/bond and wall/gran/local/bond, interaction data is only generated for particle-particle and particle-wall pairs between which a bond exists. Note that this style can only be used together with cohesion model bond.
The local data stored by this command is generated by looping over the pairwise neighbor list. Info about an individual pairwise interaction will only be included if both atoms in the pair are in the specified compute group, and if the current pairwise distance is less than the force cutoff distance for that interaction, as defined by the pair_style and pair_coeff commands.
If the keyword interaction_with_group with associated value interaction_group_id is set, then the pairwise interaction will only be included if one particle is in the general compute group and the other is in the group with id interaction_group_id. Not setting this keyword will result in a default value of interaction_group_id equal to the general compute group (i.e. the group set before the pair/gran/local style).
If the keyword interaction_with_mesh with associated value mesh_id is set, then the interaction will only be included if the particles is in the general compute group and the id of the mesh is equal to the value set as mesh_id. If this keyword is not set, then all meshes are considered when calculating the interactions. mesh_id must be an id of a mesh command.
Warning
For accessing particle-wall contact data, only mesh walls (see fix mesh/surface) can be used. For computing particle-wall (compute wall/gran/local), the code will automatically look for a fix wall/gran command that uses mesh walls. The order of the meshes in the fix wall/gran command is called the mesh id (starting with 0), and the triangle id reflects the order of the triangles in the STL/VTK file read via the dedicated fix mesh command. For how to output the triangle id, see dump mesh/vtk command.
The output pos (6 values in distance units) is the particle positions for pairwise interactions or particle position and the contact point in case of particle-wall interactions. Keyword vel will output the velocities for particle-particle interactions, or the particle velocity and mesh velocity at the contact point for particle-wall interactions. For computing pairwise data, the output ids will be the two particle IDs (using this option requires to use an atom map) and a flag that is 1 for interaction over a periodic boundary and 0 otherwise. For computing particle-wall data, the output ids will be the mesh id, the triangle id and the particle id. The output force, force_normal and force_tangential are the total contact force, the normal and tangential components of the contact force in force units. torque, torque_normal and torque_tangential are the contact torque and its normal and tangential components in torque units. Note that the normal and tangential components are not necessarily exactly equal to the forces added by the normal and tangential model used , but are geometrically composed, using the connection line between the particle centers as normal direction. Note also that the torque does NOT contain any rolling friction torque. The output history will depend on what this history represents, according to the granular pair style used. The output contactArea will output the contact area, in distance^2 units. Note that contactArea is based on an analytic geometric calculation of sphere-sphere or sphere-plane intersection rather than a calculation based on mechanics. This is to ensure that contactArea works with all types of contact models. The contactPoint output will store the point at which contact forces between two particles are computed.
The output delta will output the overlap (sum of radii - distance between
particle centers or radius - distance to mesh element respectively) in distance
units. The output heatFlux (available only if a fix
heat/gran/conduction [or another type of heat
conduction fix with the exception of heat/gran/radiation] is used to compute
heat fluxes) will output the per-contact conductive heat flux area, in
energy/time units. The heatConductionArea variable is also only
available for simulations with heat conduction and outputs the (modified)
contact area used for heat conduction calculations. electicConductance is the
conductance of a contact in units of 
, and electricCurrent
is the current flowing across the contact in Ampere. These two values are only
available if an enable_electrical_conductivity command is present in the simulation.
Warning
The data associated to the different keywords is output in the following order: pos, vel, ids, force, force_normal, force_tangential, torque, torque_normal, torque_tangential, history, contactArea, delta, contactPoint, ms_id, shearrate, heatFlux, heatConductionArea, electricConductance, electricCurrent. This is independent of the order in which the keywords are specified.
Note that as atoms migrate from processor to processor, there will be no consistent ordering of the entries within the local vector or array from one timestep to the next. The only consistency that is guaranteed is that the ordering on a particular timestep will be the same for local vectors or arrays generated by other compute commands. For example, pair output from the compute property/local command can be combined with data from this command and output by the dump local command in a consistent way.
Warning
This compute, will, when invoked, issue a call to the pair or wall contact models to calculate what would be the contact forces given the current positions, velocities etc
Since this compute is typically done when output is created (at the end of the time-step), this is not necessarily exactly equal to (with machine precision) the p-p or p-w forces which were calculated within one time-step.
Output info
This compute calculates a local vector or local array depending on the number of keywords. The length of the vector or number of rows in the array is the number of pairs. If a single keyword is specified, a local vector is produced. If two or more keywords are specified, a local array is produced where the number of columns = the number of keywords. The vector or array can be accessed by any command that uses local values from a compute as input. See this howto for an overview of Aspherix® output options.
For information on the units of the output, see above.
Restrictions
Can only be used together with a granular pair style. For accessing particle-wall contact data, only mesh walls can be used.
Default
By default, following output keywords are activated: positions, velocities, ids, forces, torques, history and contact area are output.