CMS-Flow:Features

Boundary Conditions

CMS-Flow has multiple types of boundary conditions which are listed and discussed below. All CMS-Flow boundary conditions are forced at the edges of the domain by use of cellstrings defined with the Surfacewater Modeling System.

Water Surface Elevation Forcing

Two types of Water Surface Elevation Forcing exist for CMS-Flow. Once a water surface elevation curve (or series of curves) is applied, the user is able to display the curve information graphically.

1. Single value for all cells on a cellstring
2. Multiple values on a cellstring (one for each cell)

Single Value

User creates a cellstring for the given boundary and defines a time-series curve. The value for each time on this curve is applied to all cells along the designated cellstring.

Multiple Values

User creates a cellstring for the given boundary and extracts multiple time-series curves from a dataset or database. Each cell along the cellstring is given its own time-series curve information. Examples are:

• Extraction of water surface elevation values from a larger domain solution (ie. Larger CMS-Flow or ADCIRC grid)
• Extraction of tidal constituent information from a tidal database, from which a water surface elevation curve can be generated.

Water Surface Elevation and Velocity Forcing

Users are able to extract both water surface elevations and velocity components from a larger domain solution (ie. Larger CMS-Flow or ADCIRC grid).

River Flow Forcing

User creates a cellstring for the given boundary, chooses a River Flow type for the cellstring, then creates a time-series curve of flow rates. NOTES:

• Total flow rate specified is divided between the total number of cells in the cellstring with each carrying a portion of the total.
• The sign of the flow rate curve is dependent on the direction of flow with respect to the origin (always lower-left hand corner of the grid). This guide should assist in proper assignment.
  • Flow rate from the East - Negative value
  • Flow rate from the West - Positive value
  • Flow rate from the North - Negative value
  • Flow rate from the South - Positive value

Salinity Concentration Forcing

If salinity transport is active for the simulation, the user has the ability to use existing hydrodynamic cellstrings in the interface in order to provide a time-series curve of salinity concentrations.

Introduction

In many estuaries, the density gradients caused by spatial variations in salinity can be an important driving force in the circulation. Salinity is also a key water quality variable in estuaries, since it affects the chemical and biological processes. Salinity is simulated in the Coastal Modeling System (CMS) in a depth-averaged sense. This means that the estuary or body of water is assumed to be well mixed vertically and the salinity is constant over the water column.

Governing Equation

The depth-averaged 2-D salinity transport equation is given by

        ${\frac {\partial (hC_{sa})}{\partial t}}+{\frac {\partial (U_{j}hC_{sa})}{\partial x_{j}}}={\frac {\partial }{\partial x_{j}}}{\biggl [}K_{sa}h{\frac {\partial C_{sa}}{\partial x_{j}}}{\biggr ]}$

where $t$ is time, $U_{j}$ is the current velocity in the jth direction, $h$ is the total water depth, $C_{sa}$ is the salinity concentration, and $K_{sa}$ is the salinity mixing coefficient.

Initial and Boundary Conditions

The initial salinity is specified as a constant in the whole domain. The value of the constant is specified in the SMS 10.1 interface. Inflow salinity concentrations are applied at specified salinity boundary cell strings. Salinity cell strings are specified in the same manner as the hydrodynamic boundary cells strings.

Numerical Methods

The salinity transport equation is solved with an explicit, finite volume method. The advection term is discretized with upwind scheme, and the diffusion term is discretized with the standard central difference scheme.

Units for Boundary Conditions

• Water Surface Elevation - meters ($m$)
• Current Velocity - meters per second ($m/sec$)
• Flow Rate - cubic meters per second ($m^{3}/sec$)
• Salinity Concentration - parts per thousand ($PPT$)

Global Forcing

There are two main types of global forcing available in CMS-Flow, wind and wave. Global forcing means that the forcing is applied on a cell-by-cell nature, rather than forcing along a boundary.

Wind Forcing

Temporally varying, spatially constant (ie. one value of wind applied for a given time to every computational cell in the domain.

• In the near future a variable wind will be allowed and an interface within the SMS will be provided.

Wave Forcing

Temporally and spatially varying.

• Wave forcing is generally provided by the user selecting to use the Steering Module within SMS. The mapping of wave data from wave grid to flow grid is automated during the course of the steering process.
• If a choice is made not to use the steering process, the user must provide several datasets of information which has been mapped to the flow grid geometery.
  • Radiation stress gradient
  • Wave height
  • Wave period
  • Wave direction
  • Wave dissipation

Transport Options

Sediment Transport

Non-equilibrium Sediment Transport (NET)

The NET simulates non-cohesive, single size sediment transport and bed change using a Finite Volume method and includes advection, diffusion, hiding and exposure, and avalanching.

Non-cohesive sediment transport is calculated with a non-equilibrium bed-material (total load) formulation. In this approach, the suspended- and bed-load transport equations are combined into a single equation and thus there is one less empirical parameter to estimate (adaptation length).

The governing equations are discretized using the Finite Volume Method on a staggered, non-uniform Cartesian grid. Time integration is calculated with a simple explicit forward Euler scheme. Diffusion terms are discretized with the standard central difference scheme. Advection terms are discretized with either the first order upwind scheme or the second order Hybrid Linear/Parabolic Approximation (HLPA) scheme of Zhu (1991).

Additional information on NET can be found here.

Powerpoint presentation on NET

Salinity Transport

In many estuaries, the density gradients caused by spatial variations in salinity can be an important driving force in the circulation. Salinity is also a key water quality variable in estuaries, since it affects the chemical and biological processes. Salinity is simulated in the Coastal Modeling System (CMS) in a depth-averaged sense. This means that the estuary or body of water is assumed to be well mixed vertically and the salinity is constant over the water column.

The salinity transport equation is solved with an explicit, finite volume method. The advection term is discretized with upwind scheme, and the diffusion term is discretized with the standard central difference scheme.

Additional information on Salinity Transport in CMS-Flow can be found here.

Other Features

Parallelization with OpenMP

Both Intel and AMD processors now are shipping chips with multiple cores/processors (henceforth referred to as "processors") available. CMS-Flow is now configured to make use of these extra processes that are available on newer machines.

Additional information on using Multiple Processors with CMS-Flow can be found here.

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