# rblock clump command

Syntax

rblock clump keyword <range>

Primary keywords:

Create a single clump from the rblocks within range or add an rblock to an existing clump. The rblocks are transformed to clump pebbles and are removed from the container of rblocks.

Add rblocks within range to an existing clump. The id keyword must be given to specify to which clump the rblock is to be added.

create [modblock]

Create a clump from the rblocks within range.

rblock clump Keyword Block

The following keywords may be used to modify the base value supplied. add-pebble and create.

calculate keyword ...

Compute the clump position, volume, and inertia tensor. There are two modes, either from summing contributions directly from the rigid blocks (using the from-rblocks keyword) or from a voxelization approach (the default). The voxelization approach accounts for arbitrary rigid block overlaps, whereas the from-rblocks approach assumes minimal overlap between rigid blocks. The default voxelization approach can be rather computationally expensive.

If the from-rblocks is not given, the space containing the clump is recursively subdivided into boxes that are {squares in 2D; cubes in 3D}. These boxes are termed voxels. The {areas in 2D; volumes in 3D} and inertia tensors of all voxels that fall completely within any pebbles are accumulated. In this way rigid blocks can overlap arbitrarily and the overlapping sections will not be counted multiple times. The parallel axis theorem is used to accumulate the inertia tensors. For each iteration the “final” volume is extrapolated, and the iterations cease when either 1) the total number of cells to be subdivided reaches 1e6 or 2) the extrapolated and estimated volumes are within the desired tolerance. The clump centroid is assigned from the volume weighted average position of the voxels falling completely inside any pebbles.

density f

Clump density with default value 1.0.

group s <slot slot > <pebble> ...

The group name at slot slot is set to s for the newly created clump. The optional pebble keyword specifies that the group is assigned to the pebbles and not to the clump. If slot is not specified, then the group name at slot Default is set to s.

id i

Clump ID. If not specified, then the next available ID is used.

inertia fe11 fe22 fe33 fe12 fe13 fe23 (only 1 component in 2D)

Set the inertia “tensor” of the clump in its current configuration. This value of the inertia tensor, {a float in 2D corresponding to the polar moment of inertia; a 2nd order tensor in 3D}. In 3D, 6 parameters must be specified in the order e11,e22,e33,e12,e13,e23 using the row/column convention. One must also specify the volume, and this keyword cannot be specified with the calculate keyword.

position v

Clump position that is the origin by default. This is the position of the clump centroid. This keyword cannot be given with the calculate keyword.

position-x f

The $$x$$-component of the clump centroid position that is 0 by default. This keyword cannot be given with the calculate keyword.

position-y f

The $$y$$-component of the clump centroid position that is 0 by default. This keyword cannot be given with the calculate keyword.

position-z f (3D ONLY)

The $$z$$-component of the clump centroid position that is 0 by default. This keyword cannot be given with the calculate keyword.

volume f

Set the {volume per unit thickness in 2D; volume in 3D} to f. One must also specify the inertia tensor, and this keyword cannot be given with the calculate keyword. Please be aware that this parameter doesn’t affect the geometry of the clump; as a result, the apparent geometric volume of the clump remains unchanged. This is the volume (from which the mass is computed) that is used to solve the law of motion for the clump.