CMS-Flow:Features

Boundary Conditions

CMS-Flow Boundary Conditions window

CMS-Flow has five types of boundary conditions which are listed and discussed below. The figure below shows the CMS-Flow Boundary Conditions window in SMS. All CMS-Flow boundary conditions are forced at the edges of the domain by use of cellstrings defined with the Surfacewater Modeling System (SMS). Cellstrings can either be created manually or using the SMS tool called Generate Along Boundary which is found under the Cellstring menu.

Land

The land boundary conditions is equivalent to a zero flux boundary condition. The land boundary condition is the default boundary condition when a cell string is created. It is not necessary to define land boundaries in the interior of the CMS-Flor domain, since land boundarys will automatically be detected by CMS-Flow based on the local water depths and the presence of inactive land cells.

Flow Rate-Forcing

The flow rate boundary condition specifies a time series of water fluxes in units of m^3/s per cell.

NOTES:

• Total flow rate specified is divided between the total number of cells in the cellstring with each carrying a portion of the total.
• This boundary type may only be specified along cell strings which are straight.
• 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

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. Define curve (single time series curve for each cell string)

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. The time series curve may be specified by either importing an SMS *.xys file, copying tabular data into SMS, or manually entered the time series information in SMS.

2. Extract from data set (time series curve for each cell on cell string)

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.

Tidal Constituent Forcing

Tidal Constituent Forcing window in SMS

CMS-Flow as the option of forcing with a harmonic tidal water surface elevation. To assign a boundary as a tidal boundary:

1. Select a cellstring
2. Click under CMS-Flow | Assign BC...
3. In the CMS-Flow Boundary Conditions window, click on Tidal constituent-forcing, and click OK.
4. Open the CMS-Flow Model Control window and click on the tab labeled Tidal.
5. Enter the amplitudes and phases of the tidal constituents. Note that the same amplitude and phase are applied to entire cellstring and click OK

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).

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. The salinity concentrations must be provided in units of 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

Wind Curve

SMS 10.1

Temporally varying, spatially constant winds are input in CMS in the Wind Section of the CMS-Flow Model Control Window. To add wind forcing to a current CMS-Flow project click on CMS-Flow | Model Control and then on the Wind/Wave tab. Activate wind forcing by clicking on the Include Wind check box. Winds may be imported using an *.m2w file or by specifying a curve for wind speed and direction. To specify a curve for each click on the respective box which says Curve undefined which will open the XY Series Editor. The time series may be manually entered, copied or imported from an *.xys file in the XY Series Editor.

Spatially Variable Wind and Atmospheric Pressure CMS-Flow V4.0 and higher have the option to use spatially variable wind and atmospheric pressure forcing. Currently, this feature is specified in the advanced card section using the cards listed in the table below.

CMS-Flow cards related to wind

Card	Arguments	Type
WIND_OUT_TIMES_LIST	Id number of output times list	integer
WIND_DRAG_COEFFICIENT	kappa in Hsu (1988) (default 0.4)	real
WIND_INPUT_CURVE	Name of model parameter file followed wind curve path	character
ANEMOMETER_HEIGHT	Height of wind speeds	meter
OCEANWEATHER_WIND_FILE	Name of Oceanweather, Inc. wind file (*.win)	character
OCEANWEATHER_PRES_FILE	Name of Oceanweather, Inc. pressure file (*.pre)	character
OCEANWEATHER_XY_FILE	Name of Oceanweather, Inc. coordinate file (*.xy)	character

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

SMS 10.1

The sediment transport controls are located in the Transport section of the CMS-Flow Model Control window as shown in the figure below.

Transport model

1. Equilibrium Total load

In this model, both the bed load and suspended load are assumed to be in equilibrium. The bed change is solved using a simple mass balance equation known as the Exner equation. More information on the this model can be found here.

2. Equilibrium Bed load plust Advection-Diffusion Suspended Load

Calculations of suspended load and bed load are conducted separately. The bed load is assumed to be in equilibrium and is included in the bed change equation while the suspended load is solved through the solution of an advection-diffusion equation.

More information on the this model can be found here.

3. Non-equilibrium Total Load

The non-equilibrium sediment transport algorithm (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. NET 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).

Additional information on NET can be found here.

All of the previously mentioned models account for hard bottom and effect of the bed slope on bed load.

Transport Formula

The nearbed sediment concentation or concentration capacity are calculated with one of the following transport formula:

1. Lund-CIRP (2006)
2. Van Rijn (1998)
3. Watanabe (1987)
4. Soulsby-van Rijn (1997) (V4.0 and higher)

Scaling Factors

Transport Scaling Factors

The bed and suspended transport scaling factors multiply directly by the transport capacity or near -bed sediment concentration calculated from the transport formula. Due to the large uncertainty in the transport formula, it is generally acceptable to use scaling factors in the range of 0.5-1.5.

Morphologic Scaling Factors

The morphologic scaling factor is directly multiplied by the calculated bed change at every time step and is intended as a means of speeding up the computational time. It is only recommended for periodic boundary conditions or conditions that do not change rapidly over time.

Advanced Cards

CMS-Flow V3.75

Card	Arguments	Description
SEDIMENT_FALL_VELOCITY	REAL	Sets the sediment fall velocity to a constant in m/s
HIDING_EXPOSURE_COEFFICIENT	REAL	Hiding and exposure coefficient (0.6-1.0). Default is 0.7.
NET_LOADING_FACTOR	REAL	Used to specify under- or overloading at sediment inflow boundaries (0.5-1.5). Only for NET. Default is 1.0

CMS-Flow V4.0

Card	Arguments	Description
SEDIMENT_FALL_VELOCITY	REAL	Sets the sediment fall velocity to a constant in m/s
HIDING_EXPOSURE_COEFFICIENT	REAL	Hiding and exposure coefficient (0.6-1.0). Default is 0.7.
SEDIMENT_INFLOW_LOADING_FACTOR	REAL	Used to specify under- or overloading at sediment inflow boundaries (0.5-1.5). Default is 1.0
GLOBAL_SEDIMENT_BUDGET	ON | OFF	Calculates the global sediment budget for the entire domain
CALC_MORPH_DURING_RAMP	ON | OFF	Determines whether to calculate the morphology change during the ramp period (default is ON)

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 Processes

Bottom Friction

SMS Project Explorer showing CMS-Flow project.

The bottom friction parameter (related to Manning $n$) is spatially varying (cell-specific) over the grid domain. The default value upon grid creation is 0.025. At times a user may desire to represent locations where added friction is needed due to structures or increased turbulence due to sharp changes in current speed. More information on using this feature of CMS-Flow can be found here.

Card	Arguments	Description	Versions
MANNING_N_DATASET	Grid file name and dataset path	Specifies input Manning n dataset	>=v3.5
WAVE-CURRENT_MEAN_STRESS	W09 | DATA2 | DATA13 | F85 | HT95	Defines the model used for calculating the mean bottom shear stress used in hydro	>=4.0
USE_WALL_FRICTION	ON | OFF	Turns on or off wall friction	>=3.5

Hard Bottom

SMS Project Explorer showing Hard bottom dataset

Hard Bottom is a morphologic constraint that provides the capability to simulate mixed bottom types within a single simulation. This cell-specific feature limits the erodibility of the constrained cells down to a specified depth below the water surface. More information on the use of hard bottom within the SMS can be found here.

CMS-Flow Model Control window showing the location where the hard bottom dataset is specified.

Variable D50

When sediment transport and morphology change are activated, sometimes it may be desired to designate areas of the grid to have a certain grain size. This cell-specific parameter allows each cell to take on the characteristics of a certain sediment grain size. More information on the use of variable grain size (D50) can be found here.

Eddy Viscosity

Eddy Viscosity in CMS-Flow is not a user definable parameter. It is presently calculated with a subgrid turbulence model. More information 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.

Matrix solver

The four different solvers implemented in the implicit model are the Gauss-Seidel, Gauss-Seidel with Successive-Over-Relaxation, BICGSTAB, and GMRES. The same solver is applied to flow, sediment and salinity. The default solver is the GMRES. The solver may be changed using the advanced card in the table below.

Card	Arguments	Description	Default value
SOLVER_TYPE	GAUSS-SEIDEL | GAUSS-SEIDEL-SOR | BICGSTAB | GMRES	Determines the numerical solver used	GMRES
HYDRO_MAX_ITER	integer	Maximum number of iterations (outer loop) for the hydrodynamics	20
SEDIMENT_MAX_ITER	integer	Maximum number of iterations (outer loop) for the sediment transport	20
SALINITY_MAX_ITER	integer	Maximum number of iterations (outer loop) for the salinity transport	20

Advection scheme

As in the case of the solver, the same advection scheme is applied for the flow, sediment and salinity transport equations. There are three choices for advection schemes with upwinding in the implicit model: hybrid, exponential and HLPA. The hybrid scheme is fast but is the most diffusive. The exponential scheme is based on the 1D analytical solution to an advection-diffusion equation and produces very stable results. The HLPA is very stable and non-diffusive, but requires slightly more computational time. For most applications, the exponential scheme is recommended and is set as the default. The advection scheme may be change using the advanced card

Card	Arguments	Description	Default value
ADVECTION_SCHEME	HYBRID | EXPONENTIAL | HLPA	Determines the advection scheme	EXPONENTIAL

Units of Measurement

Variable	Units	Symbol
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	($ppt$)
Sediment Concentration	kilogram per meter cubed	($kg/m^{3}$)
Sediment Transport	meter squared per second	($m^{2}/sec$)

---

CMS-Flow