Description

The Voxel type is designed to encapsulate existing topology and extend it to a far boundary as part of a new field volume block. As such, the domains selected will be used as part of the bounding topology of this new block.

Voxel blocks are composed of hierarchical Cartesian cells which are clustered about and sized by the selected entities. Root voxel cell sizes are specified for the rectangular block and recursively subdivided based on the size field determined from the selected grid entities and any sources located inside a region computed as twice the size of the block's extent box. Subdivision stops when the voxel cell sizes match the local size field. Transitions between levels in the Cartesian mesh are made using tetrahedral cells and pyramids in order to maintain point-to-point cell face matching. Users can override the default minimum and maximum cell edge sizes and set a minimum number of cell transition layers using the tools in this panel.

A good example of use would be an external flow topology created, for instance, on a full aircraft, where the domains on the surface of the vehicle already exist. The Voxel command will use the surface domains to create a rectangular far boundary to produce a new block. Additionally, T-Rex tools are provided for easy setup up front of the T-Rex algorithm. Keep in mind that the resulting block will still need to be initialized (i.e. populated with volume cells). Please refer to the Grid, Solve section for further information regarding voxel blocks setup and initialization.

Finally, the domains selected for the creation of this block will automatically be used to define the block's interior face(s) and its size field (i.e. they will be added to the list of influencers).

Build Farfield Panel: Voxel
Use the Build Farfield command to create block topology quickly based on existing grid entities.

Block Type

The Block Type frame (shown above with the Voxel option circled in red) allows you to choose the type of block to be created: Unstructured or Voxel. When you enter the Build Farfield panel for the first time, the Block Type will be selected directly via the menu.

Shape

In the Shape frame (shown below), you can setup symmetry plane definition for the new block as well as its extents. By default for Symmetry Planes, the Automatic toggle is checked on. This means that the command will try to automatically determine up to two planes of symmetry from the selected topology. If for some reason, symmetry planes are not detected automatically, you can use the first and second pull-down lists to select them manually. Using one of the two pull-down lists will uncheck the Automatic toggle automatically. You can recheck this toggle to have the panel restore the automatically detected symmetry plane(s).

In order to form a symmetry plane, Pointwise will search for lamina connectors within the selected domains that form a closed loop and have all their grid points placed on one of the principal planes within a symmetry tolerance. The symmetry tolerance is computed as the smaller of the Connector tolerance and a small fractional percent of the maximum extent of the new block being defined by using the options in the Margins frame (explained below).

 

Tip: A group of lamina connectors could be identified by the Build Farfield command as not being on the symmetry plane (i.e. rendered in red color) by one of two reasons: they don't form a closed loop or their grid points do not fall on one of the principal planes within the symmetry tolerance. If the problem is the latter, we recommend to project those lamina connectors onto a database plane in the same location as the intended symmetry plane.

In the Margins frame, you will find entry fields to define the extents of the new block in the X, Y, and Z coordinates. The Uniform entry field allows you to enter a single number which will be used in all three coordinate directions. This value will automatically populate the individual coordinate direction fields just below (i.e. +X, -X, +Y, -Y, +Z, and -Z). The individual fields can also be used to enter unique numerical values for each coordinate minimum and maximum.

Use the Shape frame to specify the extents of the new block.
Use the Shape frame to specify the extents of the new block.

Voxel

The default Min. Edge and Max. Edge for voxel cells can be changed directly by unchecking Use Default and entering a new value in the corresponding text fields. These values are absolute limiters. Therefore if there is an influence domain selected for the construction of this block type, and that domain has cell edges smaller than the Min. Edge specified, the Min. Edge value is used.

The Transition Layers parameter is a target for the number of layers of equally-sized (i.e. isotropic) hexahedral cells placed between two consecutive transition layers in a voxel block. Note that the transition layers contain a combination of pyramid and tetrahedral volume cells. The default value for this parameter, when Use Default is checked on, is 3.

Use the Voxel frame to specify voxel edge and transition layer attributes for the new block.
Use the Voxel frame to specify voxel edge and transition layer attributes for the new block.

T-Rex

Using the options in the T-Rex frame, you can pre-populate attributes and boundary conditions for the T-Rex algorithm. This includes the number of Layers, Max. and Full, as well as the Growth Rate for advancing layers. At the bottom of this frame, you can select the Wall BC (i.e. T-Rex boundary condition of type Wall) to be used for the domains you selected initially to create the block. If there is not an existing Wall boundary condition, click New to create a new one.

Use the T-Rex frame to specify T-Rex attributes for the new block.
Use the T-Rex frame to specify T-Rex attributes for the new block.

Finally, you can click Update Grid Entities at the bottom of the panel to preview the bounding domains of the pending new block. If size field refinement or boundary adaption will be necessary, the Solve command for voxel blocks will need to be used. If desired, tools in the collapsed Selection frame will provide a selection mode to reselect the domains to be used by the new block. This would be equivalent to clicking Cancel to exit the command, changing your selection, and entering Build Blocks again.

Update and Selection commands
Use the Update Grid Entities command to preview the pending block boundaries. Additionally, use the commands in the Selection frame to update your initial entity selection.

When the new block is complete, click OK to save it and close the panel, click Cancel to discard it and close the panel, or click Apply to save it and continue on to creating another block.

Demonstration

Build Farfield Symmetry - Voxel Type