** FLOW-3D** v11.1, which has just been released, users now have the option of having boundary water elevations dynamically adapt to the conditions inside the domain. This can be achieved through the use of rating curves provided by the user, or in the absence of rating curves; the solver can dynamically adjust the elevation to vary smoothly with the conditions inside the fluid domain. These variations may be further constrained to certain Froude regimes or absolute elevation bounds.

** FLOW-3D** model setup interface. At a given cross-section, for a certain specific energy, there can be two possible depths. This arises from the quadratic relationship between specific energy and the depth (see the equation below). The two mathematical depths manifest into supercritical and subcritical depths in reality. In the case of a perfect unique solution to the quadratic equation, the flow is critical.

A rating curve can only be defined for volume flow rate and pressure boundary conditions in ** FLOW-3D** v11.1. For volume flow rate type boundary conditions, instantaneous elevations are calculated using the rating curve to find the elevation corresponding to the flow rate. For a pressure type boundary condition, the volume flow rate is calculated by the solver and elevation is calculated using the rating curve. Rating curves can be applied at both upstream and downstream boundaries. It is important to note that an incorrect rating curve can result in nonphysical flow fluctuations.

Natural boundary conditions can only be defined at the inlet. Flow categories can be defined from one of the following:

- Supercritical flow (y<yc)
- Subcritical flow (y>yc)
- Critical flow (y=yc)
- Automatic flow regime (calculated by the solver)

The user can define maximum and minimum limits of elevation for any of these flows. If the depth for a particular flow regime violates the maximum and minimum limits of elevation, the latter will take precedence.

** FLOW-3D **v11.1 allows for more natural variations of the water level for environmental applications.

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