Spatial binning pro

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This modifier produces a 1-, 2-, or 3-dimensional grid covering the entire simulation domain with uniformly shaped bins. Thus, the simulation cell is subdivided into equally sized bins along one, two, or all three cell vectors. The bins are always aligned with the edges of the (possibly sheared) simulation cell.

You can use this modifier to calculate a coarse-grained field representation of either the discrete particles in a simulation or the discrete dislocation lines previously computed by the Dislocation analysis (DXA) modifier.

Particles

The modifier assigns each particle into one of the uniformly sized bins. It then performs a reduction operation within each bin for a selected particle property (can be a scalar or vector property). This modifier thus allows you to project the particle-based information to a structured grid and produce a coarse-grained, continuous field representation of some particle property. You can choose between different reduction operations, e.g. sum, average (mean), minimum or maximum, to be applied per grid cell.

Dislocations

The modifier can calculate the dislocation density and Nye tensor in each grid cell. The local dislocation density is expressed in units of 1/length². When projecting to a 1- or 2-dimensional binning grid, the dislocation density and Nye tensor are still calculated from the 3-dimensional cell volume and dislocation lines. Note, this mode is restricted to orthogonal and axis-aligned simulation cells.

The calculation follows the method described in section 2 of:

N. Bertin, Connecting discrete and continuum dislocation mechanics: A non-singular spectral framework

Int. J. Plast. 122, (2019) [doi:10.1016/j.ijplas.2018.12.006]

A preprint is available here.

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Added in version 3.11.0.

Data output options

When mapping values to a one-dimensional bin grid using this modifier, you can subsequently access the computed data table in the data inspector. From here you can export the bin values to a text file.

When mapping the values to a three-dimensional voxel grid using this modifier, you can subsequently employ the Create isosurface modifier to render isosurfaces of the computed field. Alternatively, Slice modifier can be used to visualize different slices through the voxel grid.

When creating two- or three-dimensional grids, you can also export the computed grid data to a text file using OVITO’s file export function. Select VTK Voxel Grid as output format.

Parameters

Operate on: Selects whether the modifier should use particles or dislocations lines as input.
Input property (only for particles): The source particle property the reduction operation should be applied to. Select <None> to take uniform 1 as input value for all particles, which can be useful for counting the number of particles in each bin (reduction operation: sum) or calculating the number of density of particles (reduction operation: sum divided by bin volume).
Use only selected elements (only for particles): Restricts the calculation to the subset of particles that are currently selected.
Binning direction(s): This option selects the axes of the simulation cell along which the bins are created. It determines the dimensionality of the generated grid.
Number of bins: Number of bins in each of the active binning directions.
Reduction operation (only for particles): The type of reduction operation to be carried out. Available are sum, mean, min, and max. There is an additional option sum divided by bin volume, which sums over all particles of a bin and then divides the result by the volume of the bin. This operation is useful for computing pressure (or stress) within bins from the per-atom virial.
Compute first derivative: Numerically calculates the first derivative of the binned data using a finite differences approximation. This works only for one-dimensional bin grids. (It is useful to e.g. compute the derivative of a flow velocity profile to obtain the local shear rate.)
Fix property axis range: If selected, the plotted property range (or color scale for 2D grids) will be set to the values given in the From and To fields. Otherwise, the minimum and maximum data values will be used to automatically adjust the plotting range.