primitive_wall command

Purpose

Create walls from simple geometrical objects.

Note

This command is supported by Aspherix GPU.

Syntax

primitive_wall keyword value

General obligatory keywords:

Keywords	Description
id	obligatory string; name of the object
material	obligatory; a previously defined material material
type	obligatory; available options are `plane`, `cylinder` and `disk`; type-specific keywords are given below

Optional syntax

General optional keywords:

Keywords	Description
shear	either shear velocity vector or shear velocity dimension (`x`, `y` or `z`) and velocity value units: [velocity]
temperature	temperature of the wall for heat conduction units: [temperature]

Keywords for the definition of a plane:

Finite plane:

Keywords	Decription
origin	obligatory vector; coordinates of one corner of the plane
point_1	obligatory vector; coordinates of an additional corner of the plane
point_2	obligatory vector; coordinates of an third corner of the plane `origin`, `point_1` and `point_2` most form an orthogonal system

Infinite axis-aligned plane:

Keywords	Decription
normal_axis	obligatory; coordinate direction of plane (`x`, `y` or `z`)
offset	obligatory; offset from coordinate origin units: [length]

Keywords for the definition of a cylinder:

Finite cylinder:

Keywords	Decription
center_bottom	obligatory vector; position of center at bottom of cylinder
center_top	obligatory vector; position of center at top of cylinder
radius	obligatory; cylinder radius units: [length]

Infinite axis-algined cylinder:

Keywords	Decription
axis	obligatory; coordinate direction of cylinder axis (`x`, `y` or `z`)
center	obligatory vector; the cylinder’s center point
radius	obligatory; cylinder radius units: [length]

Keywords for the definition of a disk:

Keywords	Decription
center	obligatory vector; position of center of the disk
normal	obligatory vector; normal vector of the disk plane
radius	obligatory; radius of the disk units: [length]
inner_radius	radius of the hole (optional) units: [length]

Examples

primitive_wall id plane material steel type plane normal_axis z offset 0.
primitive_wall id finite_plane material steel type plane origin (0, 0, 0) point_1 (0, 0, 1) point_2 (0, 1, 0)
primitive_wall id plane material steel type plane normal_axis z offset 0.01 shear y 1.3

primitive_wall id cylinder material steel type cylinder axis z center (0., 0., 0.) radius 1.
primitive_wall id finite_cylinder material plastic type cylinder center_bottom (0, 1, 0) center_top (1, 2, 4) radius 0.3 shear (1, 1, 0)

primitive_wall id disk material steel type disk center (1, 0, 0) normal (0, 1, 1) radius 0.1
primitive_wall id disk_with_hole material steel type disk center (0.1, 0.1, 0) normal (1, 0, 1) radius 0.1 inner_radius 0.05

Description

Creates a primitive wall in the simulation domain. The difference to a meshed wall is that the wall is not made from triangles, but from an analytic description. There are six types of primitive walls implemented currently:

Infinite planes aligned to an axis
Finite planes with arbitrary orientation
Finite cylinders with arbitrary orientation
Infinitely long cylinders aligned to an axis
Disks with arbitrary orientation
Disks with arbitrary orientation and a hole in their middle

All particles in the group interact with the wall when they are close enough to touch it. The equation for the force between the wall and particles touching it is the same as the corresponding equation on the wall contact model doc page, in the limit of one of the two particles going to infinite radius and mass (flat wall).

The contact models used are need to be specified prior to using this command using the wall_contact_model command.

For type plane there are two options, a finite and an infinite plane. The former is defined by three points in space, origin, point_1 and point_2. Note, that these three points must form an orthonormal basis, i.e. the area spanned by these three points must be a rectangle. The infinite plane is defined by its normal vector (normal_axis) and its offset from the coordinate origin (offset).

Similarly for type cylinder a finite and an infinite option exists. The finite cylinder is defined by two points center_bottom and center_top which are the center points at the two ends of the cylinder. Note, the cylinder has no end caps, i.e. it is open. The radius parameter then defines the radius of the cylinder. The infinitely long cylinder is defined by the axis keyword determining the orientation of its axis, a base point (center), and its radius (radius).

The type disk creates a disk which is centered around the center point, it is orthogonal to the vector defined by normal, and it has a radius set by the radius keyword. Additionally, it is possible to add a hole at the center of the disk by setting inner_radius greater than zero.

Using the shear keyword a surface velocity can be imposed on the different primitive walls. For the plane and disk walls the velocity must be in the same plane as the wall. While for the plane wall the velocity will be constant across it, for the disk the velocity will be orthogonal to the radius vector of the contact point. Thus it will appear to the particle as if the disk was rotating. For the cylinder wall the component of the shear velocity parallel to the axis will be constant and the orthogonal component will also be treated as rotation, similar to the disk case.

As an example, if we assume a cylinder which is parallel to the x-axis and two disks at each end we can impose the shear velocity of (0, 1, 0) which will induce a surface velocity that simulates a rotating drum.

The description of the other additional keywords is available in enable_heat_transfer and wall_contact_model.

Restart, fix_modify, output, run start/stop

If applicable, contact history is written to binary restart files so simulations can continue properly. None of the modify_command options are relevant to this command. No global scalar or vector or are stored by this command. No parameter of this command can be used with the start/stop keywords of the run command.

Restrictions

none