# 4.3. Mesh¶

The Mesh pane has two tabs:

## 4.3.1. Background Mesh¶

The Background tab is for specifying the mesh used by the Eulerian solver. A uniform mesh can be specified by entering the number of cells in the x, y, and z directions. The resulting Cell Size is computed from the geometry and the number of cells (Cell Size is not editable directly). The resulting mesh will be visible in the model setup view. The visibility of the mesh can be toggled with the (Visibility) button at the top of the model setup view.

Control points can be added by pressing the button. Once a control point has been added, the position, number of cells, stretch, first and last parameters can be changed. To split a control point, right-click on the control point and select split from the resulting menu. This operation will create a new control point at the midpoint between the previous control point and the selected control point, dividing the cells evenly between the two. Control points can be removed by pressing the button.

The stretch parameter is a value that will apply a non-uniform grid spacing to the cells. The value is defined as $${Last Width} \over {First Width}$$. A value larger than 1 stretches the grid as x increases, while a value smaller than one compresses the grid as x increases. A value of exactly 1 will keep the spacing uniform.

The first and last values allow the specification of the first and last widths. The other cell widths adjust accordingly. If a negative value is specified in the column “First”, the last width from the previous grid segment is copied. If a negative value is specified in the column “Last”, the first width from the next segment is copied.

## 4.3.2. Mesher¶

Meshing of complex geometry is performed dynamically by the solver at runtime. The Mesher tab exposes options to adjust the cut-cell mesher. These options include:

Option

Description

External flow

select internal or external flow. Note: this depends on which way the normals are pointing on the STL file. If they are pointing out of the geometry, then the text will be correct.

Small cell tolerance

tolerance to detect, and remove small cells

Small area tolerance

tolerance to detect, and remove cells with small faces

Merge tolerance

tolerance used to merge duplicate nodes

Snap tolerance

tolerance to move an intersection point to an existing cell corner

Allocation Factor

factor used in allocation of cut-cell arrays

Maximum iterations

maximum number of iterations used to find intersection points

Intersection tolerance

tolerance used to find intersection of background mesh and STL triangles

Facet angle tolerance

ignore STL facets that have an angle less than this tolerance

Dot product tolerance

tolerance used to determine if a point lies in a facet

Max facets per cell

maximum number of facets allowed in a cell