3D Open Channel Flow Overview
The 3D shallow water equations in AdH can be used to model open channel flow
environments such as rivers, estuaries, reservoirs, and coastal regions.
Regions of the domain can be 2D, and use the 2D shallow water equations, or 3D.
These equations have an assumed hydrostatic pressure distribution. This means
that vertical inertia is neglected. This assumption allows AdH (and other
shallow water models) to efficiently calculate water depth and velocity for
typical open channel conditions. The hydrostatic assumption would be violated
near abrupt geometric changes where one might find variations in vertical
inertia to be significant. Most open channel models make this assumption,
for example, RMA10, CH3D, EFDC.
The model equations can represent the effects of density driven flows such as
one would regularly find in estuaries or reservoirs. AdH also includes
sedimentation and bed change (morphology). Since AdH utilizes the SEDLIB
sediment library it represents noncohesive as well as cohesive sediment
processes. (Noncohesive are sands and gravels like one would find in rivers,
and cohesives are clays more like the type of problem found in estuaries.)
AdH is locally mass conservative and so can be regarded as either a finite
volume model or a conservative form finite element model.
Like all modules of AdH, it is portable (multiprocessor, single processor, PC,
Unix, Linux, Mac). The equations are represented by a tetrahedral element mesh.
From a plan view (from above) the mesh appears as triangles and the mesh in this
view is unstructured. In the vertical nodes must be aligned. So in elevation
view the mesh is more ordered. It can have different numbers of elements in
each column, however, the mesh must be arranged in columns. The most noteworthy
aspect of AdH is that the mesh can automatically refine or coarsen. For this
module the refinement will always create columns from surface to bed.
Since the mesh is unstructured in the horizontal plane, some very complicated
geometry may be represented. The arrangement in the vertical is represented
accurately as well. The bed is represented as linear between nodes, and the
number of nodes can change. This allows for complex behaviors in density
flow, such as a dense plume falling down a slope or salinity intrusion in a
navigation channel, can be accurately simulated.
The 3D Shallow Water Module of AdH is currently in the final development stages
and is undergoing testing and verification. The module is expected to be
released in the near future.
3D Shallow Water Applications:
Galveston Bay, TX
Mobile Bay, AL