AFLR3 SURFACE FACE RECONNECTION FLAG

In AFLR3 the reconnection flag for each boundary surface tria face controls reconnection of the surface triangulation during boundary recovery. If the flag is zero then the face can be reconnected with any of its three neighbors. This allows reconnection of the face during boundary recovery. If the flag is positive then the face can not be reconnected with one or more "restricted neighbors" in specified directions. The "restricted neighbors" are specified as follows.

If faces itria and itria3 should not be reconnected with each other than the appropriate flag for boundary face itria would have a value of four. The flag for boundary face itria4 does not have to be set. AFLR3 will reset the reconnection flag for neighbor faces so each has compatible flags. Priority is always given to restricting reconnection whenever the reconnection flag is reset.

For boundary surface quad faces the reconnection flag is set by AFLR3. The value obtained from the input file is ignored. Within AFLR3 all quads are converted to trias and the reconnection flag is set such that the quad edges are preserved.

In general, reconnection of the surface grid should be allowed wherever possible. AFLR3 will reconnect only if necessary for boundary recovery and if the resulting quality is within specified limits or better then that of the existing grid. The resulting volume grids are usually of optimal quality if surface reconnection is allowed. If part of a surface grid must be connected to another grid with a prescribed triangulation then limit reconnection only on those faces that must match up. The default value for the reconnection flag is zero.

AFLR3 INITIAL NORMAL SPACING

In AFLR3 the initial normal spacing for boundary-layer elements can be specified as part of an input surface grid. If it is specified then a value must be given for every surface node. Only those values for nodes on a boundary face with a negative grid boundary condition flag will actually be used. The initial normal spacing is only used if the boundary-layer option is selected. The default value for the initial normal spacing is zero.

VOLUME GRID FIVE NODE PENT ELEMENT CONNECTIVITY

The node connectivity for five node pent elements is ordered as shown below.

where

 inode1 = Vol_Pent5_Connectivity[ipent5][0];
 inode2 = Vol_Pent5_Connectivity[ipent5][1];
 inode3 = Vol_Pent5_Connectivity[ipent5][2];
 inode4 = Vol_Pent5_Connectivity[ipent5][3];
 inode5 = Vol_Pent5_Connectivity[ipent5][4];

SPLIT FACE HEX ELEMENT CONNECTIVITY

The ICE option (-ice or m_ice=1) of AFLR3 generates a grid with a Cartesian core of hex elements that vary in size based on the background mesh and surface mesh. Size variations between neighboring hex elements is limited to a factor of two. Neighboring hex elements of varying size produce split faces. Split quad faces match only at the outermost corner points and have hanging internal edges and nodes. Additional information is required in order to create a map of element neighbors. AFLR outputs this information in the form of a SPLIT type data file for applications that require an element neighbor map. The SPLIT file contains a list of hex elements that have split faces. The data for each hex element with a split face includes the hex element index, the split face index (face), the four non-matching edge-mid-points (inode1, inode2, inode3, inode4), and the one non-matching face-mid-points (inode5). See the SPLIT file type description for more information.

The face index varies from 1 to 6 and its ordering is shown below (face1 is 1, face2 is 2, etc.) The node indicies shown are defined by the hex element connectivity. Each face consist of four nodes. For example, face 2 is made up of node indicies inode3, inode2, inode6, and inode7.

The hanging or non-matching points are numbered relative to a given face of the hex element. The ordering of the four edge-mid-points and one face-mid-point along with the four corner points is shown below. A node index for each of these points is given in the SPLIT file. If any of them do not

Each split face matches up to either four quad faces of four neighboring hex elements or three to six tria faces of three to six tet elements. No other configurations are possible. If all five mid-points exist then the split face matches four quad faces as shown below.

If four mid-points exist then the split face matches to six tria faces as shown below. Note that the solid line and the dashed line represent the two possible triangulations of the face.

If three mid-points exist then the split face matches to five tria faces as shown below. Note that the solid line and the dashed line represent the two possible triangulations of the face. Also, this configuration can be rotated for four similar configurations.

If two mid-points exist then the split face matches to four tria faces in one of the two configurations shown below. The first configuration can be rotated for four similar configurations and the second one shown can be rotated for two similar configurations. Note that the solid line and the dashed line represent the two possible triangulations of the face.

The final possible configuration is for a single mid-point and it matches to three tria faces as shown below. This configuration can also be rotated for four similar configurations.

Note that if the hex element is not split, it still may have a hanging edge. Each non-split face matches up to either one quad face of the one neighboring hex element or two tria faces of the two neighboring tet elements. This non-split situation with neighboring tet elements is shown below. Note that the solid line and the dashed line represent the two possible triangulations of the face.