Child Geometry Output Data

Whether a child geometry produces output is determined by the family it belongs to and how it is used in the simulation. Some child geometries represent physical surfaces that are written to output, while others define internal regions used by the solver that do not generate output files.

Children in Static Body and Moving Body Families

When a child geometry belongs to a Static Body or Moving Body family, it represents a physical surface in the simulation. These surfaces act as boundary conditions for the fluid, particles, and scalar fields, and therefore carry real physical interactions.

Surface quantities can be evaluated directly on these surfaces to generate 3D visualization or reduced data across the surface to compute integrated or averaged quantities. These quantities are typically obtained by interpolating the underlying solution fields from the lattice onto the surface. The 3D data is written as binary visualization files, while the reduced quantities are written as ASCII text output.

3D Visualization Data

The child geometry is written to a binary .vtp file associated with that family for visualization and analysis within M-Star Post. Output is synchronized with both the Plane/Probe Write Interval and the Volume Write Interval, ensuring frame-consistent output for visualization and animation in both 2D and 3D renderings. As part of this child geometry output, surface variables may also be defined on these geometries. These include  Static Body Variables and Moving Body Variables, which are evaluated on the surface and written to the same output at each output interval.

The quality of the surface-resolved Static Body Output Data and Moving Body Output Data is directly related to the resolution and quality of the underlying computational mesh. Surface variables are evaluated from the fluid voxels adjacent to the geometry, so finer lattice spacings generally produce smoother and more accurate surface fields. For geometry that come into the model as a surface file type (e.g., IGES, STEP, Parasolid, etc.), the exported mesh resolution can be adjusted using the Edit Mesh command. See also this tutorial on Predicting Forces on Solid Bodies

Note

Mesh files are imported in their existing tessellated form and passed directly to the solver without modification. Edit mesh command is not available for these child geometry types.

Statistical Output

In addition to the 3D surface output data, the solver writes raw and reduced Output Statistics that capture time-resolved, surface-averaged statistical quantities for each moving and static body family. For the Moving Body Outputs, the statistics include quantities such as position, total stress, total force, and torque. For the Static Body Outputs, the statistics include total force, torque, and surface-integrated or surface-averaged species fluxes. These statistics are written to ASCII text files at the Statistics Output Write Interval.

Statistical data is computed at the family level. If a family contains multiple child geometries, the reported quantities represent the total or average across all child surfaces within that family. To obtain statistics for individual geometries, each must be assigned to its own family.

For example, if two impellers are grouped within a single moving body family, the reported torque corresponds to the combined torque on both impellers, not the torque on each impeller individually. To obtain per-impeller values, each impeller must be placed in a separate family so that it produces its own statistical output.

This decomposition affects only how results are aggregated and reported; it has no influence on the underlying fluid mechanics or solution.

Children in Other Families

Child geometries associated with other families are used internally by the solver and do not produce output files that can be visualized in M-Star Post. These include child geometries associated with massless tracers, inertial particles, liquid droplets, gas bubbles, and scalar fields. Within these families, the child geometry specifies where particles, species, or energy are introduced into the domain. It serves only as an internal region used for spatial mapping, and the geometry itself is not exported.

Similarly, child geometries attached to Global Variable families can define regions for localized reductions or evaluations. These geometries also serve only as internal spatial maps and are not exported. The same logic applies to Porous Media, where child geometries may define local porosity used within the solver. In these cases, the geometry again functions only as an internal mapping region and is not exported as an output file.

In all of these cases, the effects of the geometry appear through the physics of the simulation, but the geometry itself is not written to output. The geometry defines a region where solver operations occur rather than a surface that is exported.

Children in Scalar and Particle Injection Regions

The same rules apply to geometries used for scalar regions, particle regions, and heat-transfer initialization regions. These geometries specify the portion of the domain where quantities are initialized or introduced during the simulation. In these cases, the geometry functions purely as a spatial region definition used internally by the solver and does not generate output files.