Model Coupling: Difference between revisions

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'''Introduction'''
'''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. First, the CMS-Wave model is run for the first two time steps (time = <math> t </math> and time = <math> t + \Delta t_w </math>) and the wave information is passed to CMS-Flow. CMS-Flow then interpolates the wave variables from during the first run until it reaches <math> t + \Delta t_f + \Delta t</math>
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 = <math> t </math> and time = <math> t + \Delta t_w </math>) and the wave information is passed to CMS-Flow.
:2. CMS-Flow runs from time = <math> t </math> until time = <math> t + \Delta t_w + \Delta t </math> and  interpolates the wave variables from during the simulation
:3. CMS-Wave is run again for time = <math> t + 2\Delta t_w </math> 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
      <math> \eta(x,y,t+\Delta t) = \eta(x,y,t) </math> 
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+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) </math> 


where
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! Symbol!! Description !! Units
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Revision as of 21:36, 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

       

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

       


Symbol Description Units
Water surface elevation m

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