enable_buoyancy command

Purpose

Command for switching on buoyancy, default is in z-direction.

Note

This command is supported by Aspherix GPU.

Syntax

enable_buoyancy fluid_density rho fluid_level h keyword arg ...

  • fluid_density = keyword, mandatory for DEM only case, not allowed for coupled CFD-DEM case

  • rho = density of the fluid (mass/volume units)

  • fluid_level = optional keyword (default 1e14)

  • h = position where the fluid has its free surface (length units)

  • zero or more keyword/arg pairs may be appended

  • keyword = dimension or region or particle_group

fluid_density value = density-value
  density-value = fluid density in mass/length^3 units
dimension value = x or y or z
  x, y, z = define the water level as x=const, y=const, z=const plane
fluid_level value = level
  level = water level in length units, along the axis defined by dim
region value = region-ID
  region-ID = ID of region particles must be in to have added buoyancy force
particle_group = group-id
  group-id = group of particles that have added buoyancy force

Examples

enable_buoyancy fluid_level 0 fluid_density 1000
enable_buoyancy id buoyancy particle_group rubber_ducks fluid_level 0.06 dimension z fluid_density 2000

Description

Add a buoyancy force for each particle in the group. The water level is assumed to be a x=const, y=const or z=const plane, where the axis is defined via the dimension keyword and const is defined via the fluid_level keyword. E.g. dimension = x and fluid_level = 0.1 would define the water level as x = 0.1.

The buoyancy force is equivalent to the weight of the displaced fluid. Thus, if the particle is fully submerged, the buoyancy force is equal to particle volume * fluid density. If the particle is not submerged, the buoyancy force is 0. If the particle is partially submerged, the command will calculate the force based on the submerged particle volume. For multi-spheres a clump is considered either fully or not submerged. The fluid density is defined by keyword density.

As buoyancy is triggered by static pressure difference in a fluid usually caused by gravity, this command requires gravity enabled. The gravity vector has to be specified in the same axis as in this command (via the dimension keyword).

If the region keyword is used, the particle must also be in the specified geometric region in order to have buoyancy force added to it.

Additional information

No information about this command is written to binary restart files.

Restrictions

This command requires gravity to be enabled. The gravity vector has to be specified in the same axis as in this command (via the dimension keyword).

It is not allowed to use the enable_buoyancy command together with the enable_cfd_coupling command.

Warning

For multispheres the definition of fluid_level will be ignored, it is assumed that the clumps are always completely submerged in the fluid.

Default:

particle_group = all, dimension = z