Model Coupling: Difference between revisions

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       <math> \eta(x,y,t+\Delta t) = \eta(x,y,t) </math>   
       <math> \eta(x,y,t+\Delta t) = \eta(x,y,t) </math>   
where <math>\eta</math> is the water surface elevation.


However, in many coastal engineering projects it is desirable and common to use relatively large steering intervals of 2-3 hours and 3 hours is especially common since many wave buoy data products are at 3 hour intervals. In cases where the relative surface gradients at any time are much smaller than the mean tidal elevation, a better approximation of water level may be expressed as
However, in many coastal engineering projects it is desirable and common to use relatively large steering intervals of 2-3 hours and 3 hours is especially common since many wave buoy data products are at 3 hour intervals. In cases where the relative surface gradients at any time are much smaller than the mean tidal elevation, a better approximation of water level may be expressed as


       <math> \eta(x,y,t+\Delta t) = \bar{\eta}(x,y,t+\Delta t) + \eta(x,y,t) - \bar{\eta}(x,y,t) </math>
       <math> \eta(x,y,t+\Delta t) = \bar{\eta}(x,y,t+\Delta t) + \eta^\prime(x,y,t) </math> 
 
where  <math> \bar{\eta} </math> is the component due to astronomical tides, and <math> \eta^\prime(x,y,t) </math> 
is the component due to tidal, wave, and wind generated surface gradients and can be approximated as <math>\eta(x,y,t) - \bar{\eta}(x,y,t)</math>.




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|  <math>\eta</math>  || Water surface elevation || m
|  <math>\eta</math>  || Water surface elevation || m
|}
|}
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[[CMS#Documentation_Portal | Documentation Portal]]
[[CMS#Documentation_Portal | Documentation Portal]]

Revision as of 21:45, 13 May 2010

Introduction

CMS-Flow and CMS-Wave can be run separately or coupled together using a process called steering. The variables passed from CMS-Wave to CMS-Flow are the significant wave height, peak wave period, wave direction, wave breaking dissipation, and radiation stress gradients. CMS-Wave uses the update bathymetry, water levels, and currents from CMS-Flow. The time interval (constant) at which CMS-Wave is run is called the steering interval. The steering process is as follows:

1. CMS-Wave model is run for the first two time steps (time = t and time = t+Δtw) and the wave information is passed to CMS-Flow.
2. CMS-Flow runs from time = t until time = t+Δtw+Δt and interpolates the wave variables from during the simulation
3. CMS-Wave is run again for time = t+2Δtw and
4. The process is repeated over until the end of the steering simulation.

Prediction of Water Levels and Currents

Because CMS-Wave requieres the water surface elevation at times that are ahead of the hydrodynamics, the water surface elevation and currents. If the steering is relatively small (~<30 min), than the values from the previous time step may be used without significant error. This may be expressed in the following form 

     η(x,y,t+Δt)=η(x,y,t)

where η is the water surface elevation.

However, in many coastal engineering projects it is desirable and common to use relatively large steering intervals of 2-3 hours and 3 hours is especially common since many wave buoy data products are at 3 hour intervals. In cases where the relative surface gradients at any time are much smaller than the mean tidal elevation, a better approximation of water level may be expressed as 

     η(x,y,t+Δt)=η¯(x,y,t+Δt)+η′(x,y,t)

where η¯ is the component due to astronomical tides, and η′(x,y,t) is the component due to tidal, wave, and wind generated surface gradients and can be approximated as η(x,y,t)−η¯(x,y,t).


Symbol Description Units
η Water surface elevation m


Documentation Portal

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