6.9 Boundary Conditions
6.9.1 Command Status
Optional - 3D features can be optionally applied to the boundary implementations specifed during 2D HD model construction.
6.9.2 Description
This section describes boundary condition construction specific to the 3D hydrodynamic simulation class. The steps of implementation are not re-described here but the layout broadly parallels that of Section 5.16.
6.9.2.1 Boundary Model Implementations
Table 6.10 summarises the available implementations and provides example applications. The links in the Model Implementation column direct the reader to dedicated sections describing configuration options and TUFLOW FV syntax examples. This table is not the full list of boundary condition implementations available in TUFLOW FV. It is a sub-set relevant to the 3D HD simulation class. This is the parallel of Step 1 from Section 5.16.2.1.
| Model Implementation | Description |
|---|---|
| Inflow/Outflow | Inflow or outflow boundary conditions. Used to include river and catchment inflows, outfalls or flow extractions. |
| Force | Force vector boundary conditions. For example to include the influence of a jet, propeller wash or used in combination with an inflow/outflow boundary to assign flow momentum. |
6.9.2.2 Boundary Location Definition
Boundary locations are defined as per Step 2 in Section 5.16.2.2 and remain unchanged for the 3D HD Simulation Class other than for type GRID, which is described in Section 6.9.2.2.1.
6.9.2.2.1 Grid
Grid definition blocks define the location of gridded boundary condition types. These definitions establish an interpolation mapping from the grid to the computational mesh. Only coordinate definition using the
The available grid definition commands for the 3D HD simulation class are the same as those presented in Table 5.34. Additional z coordinate attributes are required for use in the 3D Simulation Class.
6.9.2.3 Boundary Condition Block
Boundary locations are linked with associated data via boundary condition blocks, as described in Section 5.16.2.3. The commands available within each block are described in Table 5.35, with additional 3D specific commands provided in Table 6.11.
| Command | Description |
|---|---|
| Vertical Distribution FIle | Optional - BC block command that sets the vertical distribution of the application of a 3D boundary condition. |
| Vertical Coordinate Type | Optional - Sets the vertical coordinate system for entries in the Vertical Distribution File. Defaults to Depth. |
| Sub-Type | Optional - BC block command that modifies the manner in which boundary conditons are applied in 3D. Defaults to 1. |
6.9.3 Inflow/Outflow
These boundaries are typically applied to represent water exchange. The behaviours of these boundaries in 3D can be specified as follows.
- Setting a vertical distribution across a column of cells (Section 6.9.3.1)
- Setting the manner of interaction with boundary faces (Section 6.9.3.2)
- Assigning fully three dimensional fields (Section 6.9.3.3)
6.9.3.1 Vertical Distribution
The specification of QC, QC_POLY, QCM and QG boundaries can include two additional paired commands to set the vertical distribution of the specified inflow. These commands are
The syntax block below demonstrates these commands using a QC boundary example. Example vertical distribution files are also provided for each vertical coordinate type. The same syntax applies to QC_POLY, QCM and QG.
The vertical distribution file contains two columns of data as follows.
- Vertical coordinate, as per the specified type. Header: Height/Depth/Elevation/Sigma
- Flow weighting at each vertical coordinate, as a number between 0 and 1. Weights are normalised and do not need to sum to a particular total value, Header: Weight
An example of a Height specification that delivers flow to the bottom two metres (to the nearest centimetre) of the water column follows.
HEIGHT,WEIGHT
0.00,1.0
2.00,1.0
2.01,0.0
2.10,0.0
99.0,0.0An example of a Depth specification that delivers flow to the water column between 1 and 3 metres below the water surface (to the nearest centimetre) follows.
DEPTH,WEIGHT
0.00,0.0
0.99,0.0
1.00,1.0
3.00,1.0
3.01,0.0
99.0,0.0An example of an Elevation specification that delivers flow to the water column between 10.5 and 11.5 metres absolute elevation (to the nearest centimetre) follows.
ELEVATION,WEIGHT
-99.0,0.0
10.49,0.0
10.50,1.0
11.50,1.0
11.51,0.0
99.00,0.0An example of a Sigma specification that delivers flow to the middle 50 percent of the water column (to the nearest percent) follows.
SIGMA,WEIGHT
0.00,0.0
0.24,0.0
0.25,1.0
0.75,1.0
0.76,0.0
1.00,0.06.9.3.2 Boundary Face Interaction
The specification of a Q boundary can include an additional command to set the manner in which the flow interacts with the boundary faces. This is a sub-type command as follows.
Sub-Type == 2 . Assigns a uniform flow distribution to the inflow and prevents 3D recirculation on the boundary. Momentum is not added directly to the computational domainSub-Type == 4 . Assigns a depth1.5 flow distribution to the inflow and prevents 3D recirculation on the boundary. Momentum is not added directly to the computational domain
6.9.3.3 3D Flow Field
This is applied as per Section 5.16.4.4, but with the additional spatial coordinate (z).
6.9.4 Force
These boundaries apply an x and y component force vector to the model as introduced in Section 5.16.8. In 3D the boundary behaviour can also be configured with a vertical distribution (Section 6.9.4.1).
6.9.4.1 Vertical Distribution
The specification of FORCE and FORCE_POLY boundaries can include two additional paired commands to set the vertical distribution of the specified force. These commands are