CMS-Flow Bottom Friction

Overview

In SMS versions 10.1 and earlier, the bottom roughness is specified using the Manning's n coefficient in the Cells tab of the CMS-Flow Model Control window (see Figure 1). In SMS 11.0, the option is provided to use a roughness height, or bottom friction coefficient in addition to the Manning's coefficient. In SMS 11.0 the bottom roughness is specified in the Bottom Friction Dataset section of within the Input tab of the CMS-Flow Model Control window (see Figure 2). The Bottom Friction Dataset is specified at every computational (ocean) cell and is required for each model simulation.

Figure 1. Specification of Manning's n coefficient in the Cells tab of the CMS-Flow Model Control window in SMS 10.1

Figure 2 Specification of the Bottom Friction Dataset the Input tab of the CMS-Flow Model Control window in SMS 11.0

Creating a Bottom Friction Dataset

Figure 2.3. Three SMS Project Explorer showing the Manning's n, Bottom Friction Coefficient and Roughness Height datasets.

In SMS 11.0 each time a new CMS-Flow simulation is created a bottom friction (roughness) dataset needs to be created using the Create Dataset button. 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.

Figure 2.4. Initialization ofthe Bottom Friction Dataset in SMS 11.0

Table 1. SMS Cards related to the bottom friction

Card	Arguments	Default	Range	Description	Versions
USE_WALL_FRICTION	CHARACTER	ON	ON | OFF	Turns on or off wall friction	>=3.5
MANNING_N_DATASET	CHARACTER CHARACTER	[<grid file>] [<grid name>//"Datasets/ManningsN"]	none	Grid file name and dataset path for the input Manning's n dataset	>=v3.5
BOTTOM_FRICTION_COEF_DATASET	CHARACTER CHARACTER	[<grid file>] [<grid name>//"Datasets/BottomFricCoef"]	none	Grid file name and dataset path for the input bottom friction coefficient dataset	>=v4.0
ROUGHNESS_HEIGHT_DATASET	CHARACTER CHARACTER	[<grid file>] [<grid name>//"Datasets/RoughnessHeight"]	none	Grid file name and dataset path for the input roughness height dataset	>=v4.0

Advanced Features

Table 2. Advanced Cards related to the bottom friction

Card	Arguments	Default	Range	Description	CMS Versions
BED_SLOPE_FRICTION_FACTOR	character	OFF	ON| OFF	Specifies whether to include the bed slope friction factor or not in the calculation of the bed friction	>=4.0
WAVE-CURRENT_MEAN_STRESS	character	W09	W09 | DATA2 | DATA13 | F85 | HT95	Defines the model used for calculating the mean bottom shear stress used in hydro	>=4.0
MANNING_N_CONSTANT	real number	none	>=0.0	Specifies a constant input Manning's n coefficient. Over-rides any previous bottom friction cards.	>=v4.0
BOTTOM_FRICTION_COEF_CONSTANT	real number	none	>=0.0	Specifies a constant input Bottom Friction Coefficient. Over-rides any previous bottom friction cards.	>=v4.0
ROUGHNESS_HEIGHT_CONSTANT	real number	none	>=0.0	Specifies a constant Roughness Height in m. Over-rides any previous bottom friction cards.	>=v4.0

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