Model Coupling: Difference between revisions

From CIRPwiki
Jump to navigation Jump to search
No edit summary
No edit summary
Line 11: Line 11:
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
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


       <math> \eta^{n+1} = \eta^{n} </math>   
       <math> \eta(x,y)^{n+1} = \eta(x,y)^{n} </math>   


where <math>\eta</math> is the water surface elevation and <math> n </math> indicates the CMS-Wave time step.
where <math>\eta(x,y)</math> is the water surface elevation and <math> n </math> indicates the CMS-Wave time step.


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 obtained by decomposing the water level into
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 obtained by decomposing the water level into


       <math> \eta<sup>n+1</sup> = \bar{\eta}<sup>n+1</sup> + \nabla \eta<sup>n+1</sup> </math>   
       <math> \eta(x,y)^{n+1} = \bar{\eta}^{n+1+ \nabla \eta(x,y)^{n+1} </math>   


where <math> \bar{\eta} </math> is the mean water level, and <math> \nabla \eta </math> is the component due to tidal, wave, and wind generated surface gradients. <math> \bar{\eta} </math> can be estimated from water level boundary conditions and is generally much larger than <math> \nabla \eta </math> so the later may be neglected. For some cases in which the surface gradients do not vary significantly over time (open coast beach), the second term may be approximated as
where <math> \bar{\eta} </math> is the mean water level, and <math> \nabla \eta </math> is the component due to tidal, wave, and wind generated surface gradients. <math> \bar{\eta} </math> can be estimated from water level boundary conditions and is generally much larger than <math> \nabla \eta </math> so the later may be neglected. For some cases in which the surface gradients do not vary significantly over time (open coast beach), the second term may be approximated as


     <math>\nabla \eta<sup>n+1</sup> = \nabla \eta<sup>n</sup> = \bar{\eta}<sup>n</sup> - \eta<sup>n</sup> </math>.
     <math>\nabla \eta^{n+1} = \nabla \eta^{n} = \bar{\eta}^{n} - \eta^{n} </math>.





Revision as of 22:08, 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 = and time = ) and the wave information is passed to CMS-Flow.
2. CMS-Flow runs from time = until time = and interpolates the wave variables from during the simulation
3. CMS-Wave is run again for time = 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

       

where is the water surface elevation and indicates the CMS-Wave time step.

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 obtained by decomposing the water level into

       

where is the mean water level, and is the component due to tidal, wave, and wind generated surface gradients. can be estimated from water level boundary conditions and is generally much larger than so the later may be neglected. For some cases in which the surface gradients do not vary significantly over time (open coast beach), the second term may be approximated as

    .


Symbol Description Units
Water surface elevation m



Documentation Portal