When we look at the volume cells inside a block, we notice that, in general, not all cells are the same size. In parts of the block where more refinement is needed, the cells are smaller while in other parts of the block where a coarser grid is sufficient, the cells are larger.
The cell size distribution inside a block is driven by a size field (i.e. target spacing field) which is computed using three components: the background spacing, the calculation method, and the influencers. Note that the combination of the size field influencers along with the background spacing allows the control of grid spacing away from grid topology where spacing is defined explicitly.
Tip: You can visualize the size field for a block even before it is initialized using the Size Field diagnostic function.
The Size Field panel provides tools for controlling both global size field properties and individual influencers.
At the top of the Size Field panel, there is a Decay entry field where you can specify the decay factor to be applied to the bounding topology of the block(s) being solved. The Decay parameter varies from 0.0 to 1.0; a value of 0.0 indicates no influence beyond the boundary of the influence topology while a value of 1.0 indicates maximum influence.
The Background Spacing entry field allows you to specify a constant target spacing throughout the interior of a block. Keep in mind that if you are creating a T-Rex unstructured refinement block, the size field will only affect its isotropic portion. When left as its default value of 0.0, the Background Spacing is determined automatically in different ways depending on the type of refinement block being created:
Caution: The final size field can locally differ from the Background Spacing due to the influence of sources and grid entities marked as influencers (described below).
Once the source and/or grid influencers (described below) and the Background Spacing have been defined (or computed), the size field is calculated throughout the block(s) as an interpolation of radial basis functions (RBFs) represented at discrete points. This means that a source created as a cylinder shape, for example, will have a discrete representation used for size field calculations. Furthermore, this point cloud representation will increase its density as spacing values get smaller. This, in turn, increases the time necessary to initialize the interior of a block.
Note that the set of RBFs used by Fidelity Pointwise take into account the background edge target (i.e. Background Spacing), the source edge target (i.e. the sources), distance to source, and source decay, among other attributes. The Calculation pull-down list provides a set of choices for how the spacing target will be determined at any given location in the grid:
Tip: Sources can be used to control the grid density in blocks while remaining independent of the database geometry and the grid topology.
At the top of the Sources frame, you will find the Ignore All Sources checkbox. You can use this option to quickly deactivate the use of all sources, regardless of their status in the table below. For a selected source, or sources, the Reverse option will swap the Begin and End spacings and decay factors. Start Interactive Edit provides graphical objects in the Display window which you can click with the mouse and drag to change the spacing values in a visual style. Below these three commands, there is a Legend frame showing the symbols representing the beginning (Begin) and ending (End) of sources as rendered in the Display window.
The table of sources at the bottom of the Sources frame provides a Use checkbox to either enable (checked) or disable (unchecked) the use of individual sources. By default, any source(s) located inside a region computed as twice the size of the bounding box of the selected block(s) will be enabled for influence. Therefore uncheck any individual source you wish not to affect the cell size of the selected blocks.
In the second column of the table, the source Name is shown. These default names can be edited by double clicking the field and typing in a new name. In the third column, you can see the current source Spacing Type. Simply, double click the field to change type if desired. See the Grid, Sources command for further information. The final four columns show the spacing and decay at the beginning and end of the sources; you can be edit their values in the same way already described for the other columns.
Note: When the source Spacing Type is set to Constant, the Reverse command button will be unavailable.
At the top of the Grid frame, you will find the Sync with Selected Entities checkbox. You can use this option to quickly synchronize the list of influence grid entities with the list of grid entities selected before entering the Create, Build Refinement functionality (i.e. enclosed by the refinement block being created). Keep in mind that this selection can be updated while inside the functionality using the commands in the Selection frame located inside the Build tab.
The Ignore Selected Grid Entities checkbox allows you to quickly deactivate the use of all grid entities currently listed in the table at the bottom of this panel. Right after this option, you will find a Selection frame where Begin starts a selection mode for selecting grid entities to be used as influencers. The command button becomes an End command to be clicked once the desired grid entities have been selected. Selected entities will then show up in the table below with Name, entity Type, and minimum and maximum cell edge lengths (Min. Edge and Max. Edge respectively). All of these columns are for information purposes only and cannot be edited.