The main grid editor sets the base cell size and extents of the simulation space and provides the default values for any part with PrOGrid grid regions enabled. Users can specify fixed points and grid regions, as well as view information about the grid. For reference, the gridding algorithm page explains how the main grid fits into the overall gridding framework.
Users can access the Editing Grid editor by either double-clicking on the Grid node in the FDTD branch of the Project Tree, or using the drop-down arrow in the upper-left corner of the Geometry window to select Grid Tools, and then clicking the Edit Grid button.
The gridding specifications influence the simulation's memory requirement, so an estimate is always visible on the right side of the editor. The Current bar displays the amount of memory required to run a simulation in the project's current state. The New bar displays the amount of memory required to run a simulation based on unsaved changes in the editor's six tabs.
Four buttons appear in the upper-right corner:
- Revert: discards changes and restores the editor's settings to the previous saved version.
- Done: closes the editor and saves the entered specifications, which are visible when the editor is re-opened.
- Cancel: closes the editor but does not save the entered specifications.
- Apply: leaves the editor open and saves the entered specifications, which are visible when the editor is re-opened.
When changes are made in the grid editor, the mesh view controls open across the bottom of the geometry window allowing users to visualize the grid.
Cell Size Tab
The Cell Size tab sets the base cell size for the main grid and allows users to configure the default geometric feature size settings for parts with PrOGrid enabled.
Enable PrOGrid Project Optimized Gridding is the only single point of access for enabling or disabling PrOGrid project-wide. Unchecking the option disables the left side of the editor and ignores all previously specified PrOGrid settings on the main grid, part gridding properties, and discrete sources. By default, this checked option activates PrOGrid for the current project and allows users to define its parameters. Enabling this setting does not necessarily apply all PrOGrid features to the project or indicate that PrOGrid is enabled for each part. Users can enable or disable PrOGrid behavior independently for individual parts and discrete sources.
The Min Cells Per Wavelength, in conjunction with the free space wavelength of the project's upper frequency of interest value, sets the base cell size of the grid. This setting also serves as the default value for any part with PrOGrid grid regions enabled. Increasing this value reduces cell edge lengths, therefore increasing accuracy and run time.
Parts are classified as either good or poor conductors based on their material properties. Transmission lines and substrates are resolved differently, so they are specified separately in main grid editor.
Three settings define the parameters for both good and poor conductors and serve as the default values for parts using PrOGrid grid regions:
- Min Feature Size: the length of the smallest geometric feature that is relevant to resolve. Users can enter this value as either an absolute distance or a ratio.
- Ratio: checking this option calculates the minimum feature size as a ratio of the Target Cell Size to the Min Feature Size. When unchecked, the Min Feature Size is entered as a fixed distance.
- Cells Across: each feature meeting the Min Feature Size requirement is resolved by at least this number of cells.
The right side of the editor pertains to the base cell size of the main grid. By default, the checked Use PrOGrid Base Cell Sizes option determines the base cell size from the project's frequency range of interest and the Min Cells Per Wavelength.
Unchecking this option allows users to manually define base cell sizes in each of the X, Y, and Z directions.
Three settings are available when manually defining base cell sizes:
- Target: the largest desirable cell size of the main grid.
- Minimum: the smallest desirable cell size of the main grid. This is the simulation space's smallest cell unless defined elsewhere in a grid region. Users can enter this value as either an absolute length or a fraction.
- Ratio: checking this option calculates the minimum base cell size as a ratio to the Target value. When unchecked, the Min Feature Size is entered as a fixed length.
The Extents tab determines the spatial bounds of the simulation space, or the distance between the outer boundary and the bounding box enclosing all geometry and discrete sources. The parameters that define the grid's extents are dependent upon which of the two available modes is selected.
The default Specify Padding mode defines the simulation space using the bounding box containing the project's geometry, circuit components, and waveguides with additional padding applied to each side. Its associated Free Space Padding (base cells) settings allow users to create padding by manually entering the number of base cells on each side of the grid with a Lower and Upper value for each of the X, Y, and Z directions.
The PrOGrid Padding On Absorbing Boundaries option determines the padding based on the free space wavelength in the project's frequency range of interest. This value is represented by the Automatic entry in the disabled Free Space Padding (base cells) fields. Unchecking this default selection allows users to specify a value for each field.
The Advanced Options drop-down arrow provides accesss to additional size and padding options.
The Size Options section contains three settings that determine the un-padded bounds of the project on which the padding is based:
- Include Unmeshed Objects: when checked, the bounding box of the geometry includes unmeshed parts unaccounted for in the simulation.
- Include Circuit Components: when checked, the bounding box includes all enabled circuit components.
- Include Waveguides: when checked, the bounding box includes all enabled waveguides.
The PrOGrid Padding Options section contains configuration settings that are enabled when PrOGrid Padding On Absorbing Boundaries is selected. The Number of Wavelengths value specifies the number of free space wavelengths of padding applied to each absorbing boundary.
The free space wavelength is evaluated at one of three options:
- Center Frequency: the center of the project's frequency range of interest.
- Lower Frequency: the low end of the project's frequency range of interest. This option is incompatible with a frequency range containing 0 Hz.
- Custom Frequency: a user-defined frequency value.
The Specify Bounds mode enables the Grid Bounding Box settings where users can manually set the extents of the simulation space. The entered Minimum and Maximum values for each of the X, Y, and Z directions are independent of any geometry within the space.
Fixed Points Tab
The Fixed Points tab defines the placement of manual fixed points in the geometry, forcing grid edges to locations in the space. The gridding algorithm is required to place a grid line at each fixed point without producing an error. Adding the first fixed point enables the tab settings.
Three buttons control the specified fixed points:
- Add: creates a fixed point.
- Delete: removes the selected fixed point.
- Delete All: removes all available fixed points.
The table displays each fixed point's X Location, Y Location, and Z Location, as specified in the adjacent Fixed Point Properties section. These editable settings determine which axis locations are fixed and define a fixed point's coordinates. The Type indicates whether the selected point is parameterized or fixed, and its X, Y, and Z fields are each enabled or disabled by selecting or deselecting its adjacent Fixed option, respectively.
Three buttons can be used to select a fixed point location based on geometry:
- : detach a fixed point from the geometry to which it is attached.
- : selects the fixed point location by clicking in the geometry window.
- : set advanced options for a referenced position.
Grid Regions Tab
The Grid Regions tab defines portions of the grid with a cell size that differs from the surrounding grid. This box-shaped region allows users to manually increase the grid resolution for a specific volume. Adding the first region enables the tab settings.
Three buttons control the specified regions:
- Add: creates a grid region.
- Delete: removes the selected grid region.
- Delete All: removes all available grid regions.
The Regions column lists each available grid region, as specified in the adjacent Region Bounds and Cell Sizes sections. Selecting or deselecting each X, Y, and Z option enables or disables its associated grid axis settings, respectively. The editable Lower and Upper values determine the bounding coordinates for each selected axis.
The right side of the editor provides cell size parameters that adjust the grid region resolution independently of the surrounding grid cells determined in the Cell Size tab.
Three settings define the cell size within a grid region:
- Target: the largest desirable cell size.
- Minimum: the smallest desirable cell size. Users can enter this value as either an absolute length or a fraction.
- Ratio: checking this option calculates the minimum base cell size by multiplying the Target value by the Minimum value. When unchecked, the Min Feature Size is entered as a fixed length.
The Advanced tab provides additional control over the gridding algorithm, as well as default PrOGrid settings for parts with PrOGrid enabled.
The Limits section defines criteria that the gridding algorithm must adhere to when generating the grid. The Maximum Cell Step Factor sets the allowable change in cell size ratio from one cell edge to the next along the same grid axis. This restricts the rate at which the gridding algorithm varies the cell sizes in order to place grid lines at certain locations, such as fixed points, grid regions, and conductor edges.
When checked, the Maximum Aspect Ratio sets the allowable ratio between the length and width of a Yee cell face. Reducing this ratio increases accuracy at the expense of run time. The Maximum Cells value sets the greatest allowable number of Yee cells in a simulation. When this option is checked, the grid must meet this criteria in order to be considered valid.
The PrOGrid Advanced Options section sets parameters that apply to parts using PrOGrid grid regions. The Poor Conductor Number of Padding Cells extends the grid region around parts with dielectric materials in order to reduce grid cell sizes for several cells beyond the part's bounding box. By default, PrOGrid does not apply this padding to good conducting parts.
Together, the boundary refinement controls reduce grid cell sizes near the boundaries of good conducting parts. This improves accuracy when simulating electrically large conductors with rapidly changing fields near the surface of the object, but do not penetrate deep within.The Good Conductor Boundary Refinement Ratio sets the size of refined cells by increasing the grid resolution near the boundaries of good conductor parts. By default, boundary refinement is disabled for poor conducting parts, and this setting does not affect voxel data or mesh objects. The Boundary Refinement Number of Cells determines how many cells are meshed at an increased resolution near the boundaries of good conductors, as defined by the refinement ratio.
The Info tab provides data about both the current and proposed grid. The Current data set pertains to the most recent saved grid settings, and the Proposed data set is based on changed settings that have not yet been applied to the project.
Each data set includes dimensions, upper and lower bounds, cell count, and minimum and maximum edge lengths. The two data sets display the same values once entered changes are applied.