/[MITgcm]/manual/s_algorithm/text/time_stepping.tex
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revision 1.9 by cnh, Thu Oct 25 18:36:53 2001 UTC revision 1.12 by adcroft, Tue Nov 13 20:27:54 2001 UTC
# Line 80  FORWARD\_STEP \\ Line 80  FORWARD\_STEP \\
80  \>\> CALC\_GRAD\_PHI\_SURF \` $\nabla \eta^{n+1}$ \\  \>\> CALC\_GRAD\_PHI\_SURF \` $\nabla \eta^{n+1}$ \\
81  \>\> CORRECTION\_STEP \` $u^{n+1}$,$v^{n+1}$ (\ref{eq:un+1-rigid-lid},\ref{eq:vn+1-rigid-lid})  \>\> CORRECTION\_STEP \` $u^{n+1}$,$v^{n+1}$ (\ref{eq:un+1-rigid-lid},\ref{eq:vn+1-rigid-lid})
82  \end{tabbing} \end{minipage} } \end{center}  \end{tabbing} \end{minipage} } \end{center}
83  \caption{Calling tree for the pressure method algorihtm}  \caption{Calling tree for the pressure method algorihtm}
84  \label{fig:call-tree-pressure-method}  \label{fig:call-tree-pressure-method}
85  \end{figure}  \end{figure}
86    
# Line 554  is activated with the run-time flag {\bf Line 554  is activated with the run-time flag {\bf
554  {\em PARM01} of {\em data}.  {\em PARM01} of {\em data}.
555    
556  The only difficulty with this approach is apparent in equation  The only difficulty with this approach is apparent in equation
557  $\ref{eq:Gt-n-staggered}$ and illustrated by the dotted arrow  \ref{eq:Gt-n-staggered} and illustrated by the dotted arrow
558  connecting $u,v^n$ with $G_\theta^{n-1/2}$. The flow used to advect  connecting $u,v^n$ with $G_\theta^{n-1/2}$. The flow used to advect
559  tracers around is not naturally located in time. This could be avoided  tracers around is not naturally located in time. This could be avoided
560  by applying the Adams-Bashforth extrapolation to the tracer field  by applying the Adams-Bashforth extrapolation to the tracer field
# Line 611  $\eta^{n+1}$: {\bf etaN} (\em DYNVARS.h) Line 611  $\eta^{n+1}$: {\bf etaN} (\em DYNVARS.h)
611    
612    
613  Once ${\eta}^{n+1}$ has been found, substituting into  Once ${\eta}^{n+1}$ has been found, substituting into
614  \ref{eq-tDsC-Hmom} yields $\vec{\bf v}^{n+1}$ if the model is  \ref{eq:discrete-time-u,eq:discrete-time-v} yields $\vec{\bf v}^{n+1}$ if the model is
615  hydrostatic ($\epsilon_{nh}=0$):  hydrostatic ($\epsilon_{nh}=0$):
616  $$  $$
617  \vec{\bf v}^{n+1} = \vec{\bf v}^{*}  \vec{\bf v}^{n+1} = \vec{\bf v}^{*}
# Line 621  $$ Line 621  $$
621  This is known as the correction step. However, when the model is  This is known as the correction step. However, when the model is
622  non-hydrostatic ($\epsilon_{nh}=1$) we need an additional step and an  non-hydrostatic ($\epsilon_{nh}=1$) we need an additional step and an
623  additional equation for $\phi'_{nh}$. This is obtained by substituting  additional equation for $\phi'_{nh}$. This is obtained by substituting
624  \ref{eq-tDsC-Hmom} and \ref{eq-tDsC-Vmom} into  \ref{eq:discrete-time-u}, \ref{eq:discrete-time-v} and \ref{eq:discrete-time-w}
625  \ref{eq-tDsC-cont}:  into continuity:
626  \begin{equation}  \begin{equation}
627  \left[ {\bf \nabla}_h^2 + \partial_{rr} \right] {\phi'_{nh}}^{n+1}  \left[ {\bf \nabla}_h^2 + \partial_{rr} \right] {\phi'_{nh}}^{n+1}
628  = \frac{1}{\Delta t} \left(  = \frac{1}{\Delta t} \left(
# Line 702  In the code, $\beta,\gamma$ are defined Line 702  In the code, $\beta,\gamma$ are defined
702  {\it implicSurfPress}, {\it implicDiv2DFlow}. They are read from  {\it implicSurfPress}, {\it implicDiv2DFlow}. They are read from
703  the main data file "{\it data}" and are set by default to 1,1.  the main data file "{\it data}" and are set by default to 1,1.
704    
705  Equations \ref{eq-tDsC-Hmom} and \ref{eq-tDsC-eta} are modified as follows:  Equations \ref{eq:ustar-backward-free-surface} --
706    \ref{eq:vn+1-backward-free-surface} are modified as follows:
707  $$  $$
708  \frac{ \vec{\bf v}^{n+1} }{ \Delta t }  \frac{ \vec{\bf v}^{n+1} }{ \Delta t }
709  + {\bf \nabla}_h b_s [ \beta {\eta}^{n+1} + (1-\beta) {\eta}^{n} ]  + {\bf \nabla}_h b_s [ \beta {\eta}^{n+1} + (1-\beta) {\eta}^{n} ]

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