## Description

The Boundary Conditions tab allows you to specify how each bounding connector of a domain will be treated when using the T-Rex anisotropic meshing tool. The list operates nearly identically to the Set Boundary Conditions command for CAE use. It displays information on all the boundary conditions that have been set (including for blocks) regardless of your current domain selection.

This is the basic workflow:

1. Use the New command to create a new T-Rex boundary condition.
2. Select the connectors to be assigned to the new T-Rex boundary condition.
3. Check the appropriate Set checkbox to effectively assign the selected connectors to the T-Rex boundary condition.
Use the Boundary Conditions tab to specify how each bounding edge connector of a domain will be treated for T-Rex meshing.

When setting T-Rex boundary conditions, the currently selected connectors are highlighted in white (see figure below). Note that when there is either a connection between two domains or a baffle connector, arrows normal to the boundary are rendered to indicate which side of the connection or the baffle you are currently selecting.

Boundaries are selected in the List or Display window.

There are seven types of boundary conditions available for the T-Rex algorithm:

• Wall: Sets bounding connectors to have anisotropic cells (quads and/or triangles) grown off of them. The accompanying Δ defines the fixed initial height of those anisotropic cells.
• Angle: Sets bounding connectors to have anisotropic cells (quads and/or triangles) grown off of them. The accompanying Δ defines the 2D T-Rex turning angle (expressed in degrees) used to compute a variable initial height of those anisotropic cells along the bounding connectors.

This computation consists of walking along the bounding connectors assigned to this T-Rex boundary condition and sampling the underlying database surface in the transverse direction. For each grid point on the connectors (Point A), the algorithm will find the closest point on the underlying database surface (Point B) for which the angle between the normals to the underlying database surface at Point A and Point B is smaller than or equal to the specified turning angle. The distance between Point A and Point B is the calculated initial height at that particular grid point.

The final result is a smoothed distribution of T-Rex initial height values at each grid point along the connectors assigned to this T-Rex boundary condition. In the case when this T-Rex boundary condition is applied to both sides of a shared connector, the minimum spacing will be used in both domains.

Tip: The Angle T-Rex boundary condition calculates a distribution of T-Rex initial heights along the connectors bounding a given domain based on the curvature of the underlying database surface. This functionality therefore requires the domain in question to be constrained to such database surface.

• Aspect Ratio: Sets bounding connectors to have anisotropic cells (quads and/or triangles) grown off of them. The accompanying Δ defines the aspect ratio used to compute a variable initial height of those anisotropic cells along the bounding connectors.

This computation consists of walking along the bounding connectors assigned to this T-Rex boundary condition and calculating an initial height for each line segment in the connector (i.e. the segment between two consecutive grid points) based on the length of the line segment and the specified aspect ratio. The final result is a smoothed distribution of T-Rex initial height values at each grid point along the connectors assigned to this T-Rex boundary condition.

• Max Aspect Ratio: Sets bounding connectors to have anisotropic cells (quads and/or triangles) grown off of them. The accompanying Δ defines the aspect ratio used to compute the fixed initial height of those anisotropic cells based on the maximum edge length along the connectors (i.e. the maximum distance between two consecutive grid points). The resulting initial height is then smoothed to better match the surrounding mesh while not exceeding the user-specified aspect ratio.
• Match: Sets bounding connectors to have a grid point distribution that matches the growth of the interior anisotropic cells (quads and/or triangles). Note that for the connectors to be modified, you need to have the Push Attributes option checked on.
• Adjacent Grid: Sets bounding connectors to have anisotropic cells (quads and/or triangles) grown off of them while matching the initial cell hight to an adjacent domain.
• Off: Sets bounding connectors to not have anisotropic cells (quads and/or triangles) grown off of them. Note that these connectors will have isotropic triangles applied along with the remaining domain interior outside of the anisotropic layer.

Tip: When applying T-Rex boundary conditions, you can always leave connectors as Unspecified when you want to use type Off since Unspecified defaults to the Off boundary condition type.

The last column in the boundary condition table is the Adapt column. By default, this option will be set to Off. For the Unspecified boundary condition it cannot be changed from the default setting. You can change the value by double clicking in the field. When set to On, connectors assigned to the corresponding boundary condition will have their point clustering adapted, points added or removed, in order to meet the target cell sizes specified by any selected size field influencers on the Size Field tab.

Note: The Adapt option can be applied to any T-Rex condition that grows anisotropic cells (Wall Angle, Aspect Ratio, and Max. Aspect Ratio). In this case, the connectors will be adapted prior to marching T-Rex layers. This is the only way that the size field entities can influence T-Rex layers. Once the initial front is set, size field entities have no effect on the T-Rex layers.