--- manual/s_algorithm/text/tracer.tex 2001/11/13 18:15:26 1.10 +++ manual/s_algorithm/text/tracer.tex 2004/10/14 19:53:04 1.17 @@ -1,8 +1,8 @@ -% $Header: /home/ubuntu/mnt/e9_copy/manual/s_algorithm/text/tracer.tex,v 1.10 2001/11/13 18:15:26 adcroft Exp $ +% $Header: /home/ubuntu/mnt/e9_copy/manual/s_algorithm/text/tracer.tex,v 1.17 2004/10/14 19:53:04 jmc Exp $ % $Name: $ \section{Tracer equations} -\label{sec:tracer_equations} +\label{sect:tracer_equations} The basic discretization used for the tracer equations is the second order piece-wise constant finite volume form of the forced @@ -15,7 +15,7 @@ described here. \subsection{Time-stepping of tracers: ABII} -\label{sec:tracer_equations_abII} +\label{sect:tracer_equations_abII} The default advection scheme is the centered second order method which requires a second order or quasi-second order time-stepping scheme to @@ -123,6 +123,10 @@ \section{Linear advection schemes} +\label{sect:tracer-advection} +\begin{rawhtml} + +\end{rawhtml} \begin{figure} \resizebox{5.5in}{!}{\includegraphics{part2/advect-1d-lo.eps}} @@ -349,6 +353,9 @@ \section{Non-linear advection schemes} +\begin{rawhtml} + +\end{rawhtml} Non-linear advection schemes invoke non-linear interpolation and are widely used in computational fluid dynamics (non-linear does not refer @@ -387,7 +394,7 @@ r = \frac{ \tau_{i+1} - \tau_{i} }{ \tau_{i} - \tau_{i-1} } & \forall & u < 0 \end{eqnarray} as it's argument. There are many choices of limiter function but we -only provide the Superbee limiter \cite{Roe85}: +only provide the Superbee limiter \cite{roe:85}: \begin{equation} \psi(r) = \max[0,\min[1,2r],\min[2,r]] \end{equation} @@ -449,7 +456,7 @@ The DST3 method described above must be used in a forward-in-time manner and is stable for $0 \le |c| \le 1$. Although the scheme -appears to be forward-in-time, it is in fact second order in time and +appears to be forward-in-time, it is in fact third order in time and the accuracy increases with the Courant number! For low Courant number, DST3 produces very similar results (indistinguishable in Fig.~\ref{fig:advect-1d-lo}) to the linear third order method but for @@ -654,6 +661,39 @@ \section{Comparison of advection schemes} +\begin{table}[htb] +\centering + \begin{tabular}[htb]{|l|c|c|c|c|l|} + \hline + Advection Scheme & code & use & use Multi- & Stencil & comments \\ + & & A.B. & dimension & (1 dim) & \\ + \hline \hline + centered $2^{nd}$order & 2 & Yes & No & 3 pts & linear \\ + \hline + $3^{rd}$order upwind & 3 & Yes & No & 5 pts & linear/tracer\\ + \hline + centered $4^{th}$order & 4 & Yes & No & 5 pts & linear \\ + \hline \hline +% Lax-Wendroff & 10 & No & Yes & 3 pts & linear/tracer, non-linear/flow\\ +% \hline + $3^{rd}$order DST & 30 & No & Yes & 5 pts & linear/tracer, non-linear/flow\\ + \hline \hline + $2^{nd}$order Flux Limiters & 77 & No & Yes & 5 pts & non-linear \\ + \hline + $3^{nd}$order DST Flux limiter & 33 & No & Yes & 5 pts & non-linear \\ + \hline + \end{tabular} + \caption{Summary of the different advection schemes available in MITgcm. + ``A.B.'' stands for Adams-Bashforth and ``DST'' for direct space time. + The code corresponds to the number used to select the corresponding + advection scheme in the parameter file (e.g., {\em tempAdvScheme=3} in + file {\em data} selects the $3^{rd}$ order upwind advection scheme + for temperature). + } + \label{tab:advectionShemes_summary} +\end{table} + + Figs.~\ref{fig:advect-2d-lo-diag}, \ref{fig:advect-2d-mid-diag} and \ref{fig:advect-2d-hi-diag} show solutions to a simple diagonal advection problem using a selection of schemes for low, moderate and