SMS:WAM Grid Options

The Grid Options dialog is accessed by clicking on Model Control command in the WAM menu. The Grid Options dialog contains three tabs which are as follows:

General Tab

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WAM Grid Options dialog showing the General

Model options

• Water depth model – Choosing a shallow depth model specifies the use of the full dispersion equation. Dispersion equation is $w^{2}=gk\tanh(kh)$ where $w$ is radial frequency, $g$ is acceleration due to gravity, $k$ is the wave number, and $h$ is the water depth. Computes all phase and group celerity where there is depth dependence.
• Refraction model – If running in deep water, specify "Not used." It is not recommend to use if grid resolution is greater than 3-min (0.05 deg) on a spherical grid.
• Breaking – It is recommended that breaking be used when the water depth model is "Shallow." This will implement limited breaking within the WAM model.

Model time steps

• Propagation time step – The propagation time step is controlled by the CFL condition. The CFL condition requires that the numerical solution cannot move faster than the group speed of the waves. It is recommended that the other model time steps and output time steps be multiples of the propagation time step.
• The CFL criteria must be less than 1.0 for WAM to run successfully. The estimated CFL value is shown below the time step. The value shows in green if the settings meet the criteria or red if not. The CFL computation is dependent upon whether deep or shallow water depth model is being used as well as the refraction model. Currently the CFL estimation in SMS does not account for currents but this is used within WAM. Therefore, the CFL estimate may look okay in SMS but fail when running WAM. If this occurs further reduce the propogation time step or change some of the other options.
• Source time step – This is the time step for the source term integration time step. Increasing this value can greatly decrease run times. However, it should be used with caution. It is recommended that the source term time step be no greater than 10 times the propagation time step.

Output time steps

• Spatial datasets – This is the frequency of output that will be generated that can be loaded into SMS as datasets. The WAM file it creates is the "integrated parameter map file."
• Spectra – This is the frequency of output for spectra data at defined observation cells.
• Close/Reopen – When writing files on a computer, often data being written is stored temporarily in RAM before being written to disk. If a file is in this state and WAM crashes, the final data may not be complete. Closing and reopening the output files forces the file system to complete writing the data to file.

Output Tab

The Output tab consists of different Model options.

• Sea waves: waves generated by the wind blowing at the time, and in the recent past, in the area of observation.
• Swell waves: waves which have travelled into the area of observation after having been generated by previous winds in other areas. These waves may travel thousands of kilometres from their origin before dying away. There may be swell present even if the wind is calm and there are no 'sea' waves.

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WAM Grid Options dialog showing the Output tab

Spatial Inputs Tab

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WAM Grid Options dialog showing the Spatial Inputs tab

WAM uses spatial input for ice cover, currents, and wind. The Spatial Inputs section of the WAM Model Control is used to manage these datasets.

Ice Cover

Dataset

The ice cover dataset is an editable scalar dataset. After creating the dataset using the Editable Datasets dialog accessed from the Model Control, the dataset will be displayed in the project explorer in a folder named Editable Datasets. Only one ice cover dataset may exist at a time.

File

Rather than using a dataset, a user can specify the file name for ice.

Currents

Dataset

The currents dataset is specified to be any vector dataset on the current grid. The dataset and time step must both be selected. The selection may be removed by clicking on the Clear button. This deselects the dataset as the specified currents dataset, but it does not remove the dataset from the SMS project.

File

Rather than using a dataset, a user can specify the file name for currents.

Wind

Dataset

The winds dataset can be set to any vector dataset that belongs to the current grid or another grid whose angle is zero and whose extents cover the current grid. Nested grids may use the wind dataset of the parent grid. The time steps in the dataset used must match those used with the WAM simulation.

File

PBL can be used to create an input wind file for WAM by selecting "WAM input" in the PBL Model Control. The fort.12 file created by PBL may be selected as the wind data. Note: This option is only useful if there is access to the "Planetary Boundary Layer" model which isn't available through SMS.

Related Topics

• WAM