mesh_module contactdeletion

Purpose

Command for deleting or deactivating slow particles in contact with the wall.

Syntax

mesh_module contactdeletion id module-ID keywords values

• id = obligatory keyword

• module-ID = user-defined name for the mesh module

• zero or more contact_keyword/value pairs may be appended

• keyword = v_threshold or time_threshold or contact_deletion_method

v_threshold value = vthresh
  vthresh = velocity threshold which particles must fall below to be eligible for deletion (velocity units)
time_threshold value = tthresh
  tthresh = minimum time below velocity threshold for particles to be eligible for deletion (time units)
contact_deletion_method value = remove or deactivate
  remove = completely remove particles from the simulation when criteria are fulfilled
  deactivate = exclude particle from integration and neighbor list build when criteria are fulfilled

Examples

mesh_module contactdeletion id my_contactdel v_threshold 0.005 time_threshold 0.001

Description

This mesh module evaluates particles which are: - in contact with the wall and - the relative velocity with the wall is below v_threshold for at least time_threshold

If the above criteria are fulfilled, particles are either flagged for deletion from the simulation (if contact_deletion_method = remove) or are deactivated (if contact_deletion_method = deactivate)

The removal itself is performed with the next neighbor list build. In case of deactivation, the user has to define two groups with names ‘is_active’ and ‘is_inactive’ which are then used by this command. Group ‘is_active’ has to be used for the integration commands. Error checks are in place to ensure there are no user error with this.

The following per-mesh element properties are registered by the mesh module:

mass_deleted_per_area (mass per area)
n_deleted_per_area (1 per area)
mass_deleted_per_area_step (mass per area)
n_deleted_per_area_step (1 per area)

The two former properties refer to all particles deleted from the simulation, and the two latter to particles flagged for deletion in the current time-step. Please note that the counters are increased when particles are flagged for deletion, not when actually deleted, so minimal time-lags may be possible (if contact_deletion_method = remove) .

All of these 4 properties can be can be dumped into VTK format using output_settings.

Additional information

This mesh module stores a global vector with two components for access by various output commands. The first component is equal to the total particle mass deleted by the mesh (or: stored on the mesh), the second component stores the total number of deleted particles (or: particles on the mesh). See mesh command. For easier use the property values can also be accessed via the property name: for example, id_myMesh.deleted_particle_mass will return the deleted particle mass. See the table below for a complete overview of the available properties and how to access them.

Mesh module property	property name (dot access)	probable array position
deleted particle mass	deleted_particle_mass	1
deleted number of particles	deleted_particle_count	2

Restrictions

None

Related commands

mesh_module, mesh

Default

v_threshold = 0.0, time_threshold = 0.0, contact_deletion_method = remove