/[MITgcm]/manual/s_algorithm/text/time_stepping.tex
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revision 1.1.1.1 by adcroft, Wed Aug 8 16:15:16 2001 UTC revision 1.2 by jmc, Thu Aug 9 16:22:09 2001 UTC
# Line 76  The equation for $\eta$ is obtained by i Line 76  The equation for $\eta$ is obtained by i
76  continuity equation over the entire depth of the fluid,  continuity equation over the entire depth of the fluid,
77  from $R_{min}(x,y)$ up to $R_o(x,y)$  from $R_{min}(x,y)$ up to $R_o(x,y)$
78  (Linear free surface):  (Linear free surface):
79  \begin{displaymath}  \begin{eqnarray}
80  \epsilon_{fs} \partial_t \eta =  \epsilon_{fs} \partial_t \eta =
81  \left. \dot{r} \right|_{r=r_{surf}} + \epsilon_{fw} (P-E) =  \left. \dot{r} \right|_{r=r_{surf}} + \epsilon_{fw} (P-E) =
82  - {\bf \nabla}_r \cdot \int_{R_{min}}^{R_o} \vec{\bf v} dr  - {\bf \nabla}_r \cdot \int_{R_{min}}^{R_o} \vec{\bf v} dr
83  + \epsilon_{fw} (P-E)  + \epsilon_{fw} (P-E)
84  \end{displaymath}  \label{eq-cont-2D}
85    \end{eqnarray}
86    
87  Where $\epsilon_{fs}$,$\epsilon_{fw}$ are two flags to  Where $\epsilon_{fs}$,$\epsilon_{fw}$ are two flags to
88  distinguish between a free-surface equation ($\epsilon_{fs}=1$)  distinguish between a free-surface equation ($\epsilon_{fs}=1$)
# Line 325  with Line 326  with
326    
327  Substituting \ref{eq-rtd-hmom} into \ref{eq-rtd-cont}, assuming  Substituting \ref{eq-rtd-hmom} into \ref{eq-rtd-cont}, assuming
328  $\epsilon_{nh} = 0$ yields a Helmholtz equation for ${\eta}^{n+1}$:  $\epsilon_{nh} = 0$ yields a Helmholtz equation for ${\eta}^{n+1}$:
329  $$  \begin{eqnarray}
330  \epsilon_{fs} {\eta}^{n+1} -  \epsilon_{fs} {\eta}^{n+1} -
331  {\bf \nabla}_r \cdot \Delta t^2 (R_o-R_{min})  {\bf \nabla}_r \cdot \Delta t^2 (R_o-R_{min})
332  {\bf \nabla}_r B_o {\eta}^{n+1}  {\bf \nabla}_r B_o {\eta}^{n+1}
333  = {\eta}^*  = {\eta}^*
334  \label{solve_2d}  \label{solve_2d}
335  $$  \end{eqnarray}
336  where  where
337  $$  \begin{eqnarray}
338  {\eta}^* = \epsilon_{fs} \: {\eta}^{n} -  {\eta}^* = \epsilon_{fs} \: {\eta}^{n} -
339  \Delta t {\bf \nabla}_r \cdot \int_{R_{min}}^{R_o} \vec{\bf v}^* dr  \Delta t {\bf \nabla}_r \cdot \int_{R_{min}}^{R_o} \vec{\bf v}^* dr
340  \: + \: \epsilon_{fw} \Delta_t (P-E)^{n}  \: + \: \epsilon_{fw} \Delta_t (P-E)^{n}
341  $$  \label{solve_2d_rhs}
342    \end{eqnarray}
343    
344  Once ${\eta}^{n+1}$ has been found substituting into \ref{eq-rtd-hmom}  Once ${\eta}^{n+1}$ has been found substituting into \ref{eq-rtd-hmom}
345  would yield $\vec{\bf v}^{n+1}$ if the model is hydrostatic  would yield $\vec{\bf v}^{n+1}$ if the model is hydrostatic

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