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# AliDispersionControl: Difference between revisions

Ali's Dispersion Correction is a correction to the dispersive behavior of very long waves in a compressible ocean on an elastic Earth. It is intended to be used in lieu of the self-attraction and loading tide prescribed through the fort.24 file. It should be used with the sixth-digit of IM equal to 3 (fully implicit gravity wave term).

## Version

 ADCIRC version: ≥ 55 Tech Preview

This is considered a technical preview in version 55. Theoretical work is still ongoing.

## Controlling Dispersive Behavior

The feature is triggered by the presence of the &AliDispersionControl namelist at the bottom of the fort.15 file. Here is an example of how this line is used (the following floats are the default values):
&AliDispersionControl CAliDisp=T, Cs=1500.0, Ad = 0.0050189, Bd = 0.23394/

• CAliDisp logical flag to turn Ali's dispersion correction on (F=false by default).
• Cs is the speed of sound in water [m/s] for the Mach number based dispersive correction. Set Cs to a negative value to turn the Mach number based correction off.
• Ad the power law constant.
• Bd the power law exponent.

For the following equation: ${\displaystyle Correction=1-{\frac {Ma^{2}}{4}}-{A_{d}}H^{B_{d}}}$

where Ma is the Mach number (${\displaystyle Ma={\frac {\sqrt {gH}}{Cs}}}$) and H is the total water depth.