Use the Release from Grid node to release particles from a grid of initial positions with user-defined coordinates.

Except for the Initial Position section described below, all settings are the same as for the Release node.

Select an option from the Grid type list: All combinations (the default), Specified combinations, Cylindrical (3D only), or Hexapolar (3D only).

For All combinations and Specified combinations enter Initial coordinates based on space dimension (qx,0, qy,0, and qz,0 for 3D components) for the particle positions or click the Range button () to select and define a range of specific coordinates.

If Specified combinations is selected, the number of initial coordinates entered for each space dimension must be equal, and the total number of particles released is equal to the length of one of the lists of initial coordinates. If All combinations is selected, the total number of particles released is equal to the product of the lengths of each list of initial coordinates.

For example, suppose a 2D model component includes a Release from Grid node with the following initial coordinates:

If All combinations is selected, a total of 16 particles will be released, including every possible combination of the initial x- and y-coordinates. If Specified combinations is selected, 4 particles will be released with initial positions (0,2), (1,4), (2,6), and (3,8).

The number of released particles may increase if the initial velocity or initial values of auxiliary dependent variables involve sampling from a distribution, in which case a large number of particles may be released at each initial position. The position for any particles with initial coordinates outside the geometry are set to not-a-number (NaN), so the particles do not appear when plotted during postprocessing.

For Cylindrical, enter coordinates for the Center location qc (SI unit: m). By default, the distribution is centered at the origin. Then enter the components of the Cylinder axis direction rc (dimensionless). The particles will be released at specified radial distances and angles in the plane containing the point qc and orthogonal to the direction rc.

Select an option from the Radial distribution list: Uniform radius intervals (the default), Uniform number density, or User defined.

For Uniform radius intervals or Uniform number density enter a value or expression for the Radius Rc (SI unit: m). The default is 1 m. Then enter a positive integer for the Number of radial positions Nc (dimensionless). The default is 5.

For User defined enter a list of Radial coordinates qr (SI unit: m) directly. An arbitrary number of radial coordinates can be entered in the list. The default is 1 m.

The effect of the Radial distribution setting on the resulting particle placement is illustrated in Figure 3-3. For Uniform radius intervals, the distances between the concentric rings of particles are all equal, but the number density of particles is greater at the center of the distribution than at the outer edge. The option Uniform number density corrects this imbalance by defining nonuniform increments in the radial position between the concentric rings.

Enter a positive integer for the Number of angles Nϕ (dimensionless). The default is 10.

The total number of particles released (before accounting for distributions of particle velocity or auxiliary dependent variables at each release point) is Nc × Nϕ + 1 because a single particle is also released at the center of the distribution.

For Hexapolar, enter coordinates for the Center location qc (SI unit: m). By default, the distribution is centered at the origin. Then enter the components of the Cylinder axis direction rc (dimensionless). The particles will be released at specified radial distances and angles in the plane containing the point qc and orthogonal to the direction rc.

Enter a value or expression for the Radius Rc (SI unit: m). The default is 1 m. Then enter a positive integer for the Number of radial positions Nc (dimensionless). The default is 5.

Unlike the Cylindrical grid types described in the previous section, each concentric ring of the Hexapolar grid contains a different number of particles, as shown in Figure 3-4. One particle is always released at the center. The first ring of particles surrounding the center has 6 particles arranged in a regular hexagon. Each ring of particles beyond the first has 6 more particles than the ring preceding it, with the particles arranged in a regular polygon. The radius increments between consecutive rings are uniform.

In the Initial Coordinates section, you can click the Preview Initial Coordinates  and Preview Initial Extents  buttons to visualize the initial particle positions. Clicking Preview Initial Coordinates will cause a point to appear in the Graphics window for every release position. Clicking Preview Initial Extents will cause a bounding box to appear, indicating the spatial extents of the released particles. Examples are shown in Figure 3-5 and Figure 3-6.