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1 afe 1.4 % $Header: /u/gcmpack/manual/part3/case_studies/rotating_tank/tank.tex,v 1.3 2004/07/26 16:21:15 afe Exp $
2 afe 1.1 % $Name: $
3    
4     \bodytext{bgcolor="#FFFFFFFF"}
5    
6     %\begin{center}
7 afe 1.3 %{\Large \bf Using MITgcm to Simulate a Rotating Tank in Cylindrical
8     %Coordinates}
9 afe 1.1 %
10     %\vspace*{4mm}
11     %
12     %\vspace*{3mm}
13 afe 1.3 %{\large May 2001}
14 afe 1.1 %\end{center}
15    
16 afe 1.3 \section{A Rotating Tank in Cylindrical Coordinates}
17     \label{sect:eg-tank}
18 afe 1.2 \label{www:tutorials}
19    
20 afe 1.4 This section illustrates an example of MITgcm simulating a laboratory
21     experiment on much smaller scales than those common to geophysical
22     fluid dynamics.
23    
24     \subsection{Overview}
25     \label{www:tutorials}
26    
27    
28     This example experiment demonstrates using the MITgcm to simulate
29     a laboratory experiment with a rotating tank of water with an ice
30     bucket in the center. The simulation is configured for a laboratory
31     scale on a
32     $3^{\circ}$ $\times$ 20cm
33     cyclindrical grid with twenty-nine vertical
34     levels.
35     \\
36    
37    
38 afe 1.2
39     This example experiment demonstrates using the MITgcm to simulate
40 afe 1.3 a Barotropic, wind-forced, ocean gyre circulation. The experiment
41     is a numerical rendition of the gyre circulation problem similar
42     to the problems described analytically by Stommel in 1966
43     \cite{Stommel66} and numerically in Holland et. al \cite{Holland75}.
44    
45     In this experiment the model
46     is configured to represent a rectangular enclosed box of fluid,
47     $1200 \times 1200 $~km in lateral extent. The fluid is $5$~km deep and is forced
48     by a constant in time zonal wind stress, $\tau_x$, that varies sinusoidally
49     in the ``north-south'' direction. Topologically the grid is Cartesian and
50     the coriolis parameter $f$ is defined according to a mid-latitude beta-plane
51     equation
52    
53     \begin{equation}
54     \label{EQ:eg-baro-fcori}
55     f(y) = f_{0}+\beta y
56     \end{equation}
57    
58     \noindent where $y$ is the distance along the ``north-south'' axis of the
59     simulated domain. For this experiment $f_{0}$ is set to $10^{-4}s^{-1}$ in
60     (\ref{EQ:eg-baro-fcori}) and $\beta = 10^{-11}s^{-1}m^{-1}$.
61     \\
62     \\
63     The sinusoidal wind-stress variations are defined according to
64    
65     \begin{equation}
66     \label{EQ:eg-baro-taux}
67     \tau_x(y) = \tau_{0}\sin(\pi \frac{y}{L_y})
68     \end{equation}
69    
70     \noindent where $L_{y}$ is the lateral domain extent ($1200$~km) and
71     $\tau_0$ is set to $0.1N m^{-2}$.
72     \\
73     \\
74     Figure \ref{FIG:eg-baro-simulation_config}
75     summarizes the configuration simulated.
76    
77     %% === eh3 ===
78     \begin{figure}
79     %% \begin{center}
80     %% \resizebox{7.5in}{5.5in}{
81     %% \includegraphics*[0.2in,0.7in][10.5in,10.5in]
82     %% {part3/case_studies/barotropic_gyre/simulation_config.eps} }
83     %% \end{center}
84     \centerline{
85     \scalefig{.95}
86     \epsfbox{part3/case_studies/barotropic_gyre/simulation_config.eps}
87     }
88     \caption{Schematic of simulation domain and wind-stress forcing function
89     for barotropic gyre numerical experiment. The domain is enclosed bu solid
90     walls at $x=$~0,1200km and at $y=$~0,1200km.}
91     \label{FIG:eg-baro-simulation_config}
92     \end{figure}
93    
94     \subsection{Equations Solved}
95     \label{www:tutorials}
96     The model is configured in hydrostatic form. The implicit free surface form of the
97     pressure equation described in Marshall et. al \cite{marshall:97a} is
98     employed.
99     A horizontal Laplacian operator $\nabla_{h}^2$ provides viscous
100     dissipation. The wind-stress momentum input is added to the momentum equation
101     for the ``zonal flow'', $u$. Other terms in the model
102     are explicitly switched off for this experiment configuration (see section
103     \ref{SEC:code_config} ), yielding an active set of equations solved in this
104     configuration as follows
105 afe 1.1
106 afe 1.2 \begin{eqnarray}
107 afe 1.3 \label{EQ:eg-baro-model_equations}
108     \frac{Du}{Dt} - fv +
109     g\frac{\partial \eta}{\partial x} -
110     A_{h}\nabla_{h}^2u
111     & = &
112     \frac{\tau_{x}}{\rho_{0}\Delta z}
113 afe 1.2 \\
114 afe 1.3 \frac{Dv}{Dt} + fu + g\frac{\partial \eta}{\partial y} -
115     A_{h}\nabla_{h}^2v
116 afe 1.2 & = &
117 afe 1.3 0
118 afe 1.2 \\
119     \frac{\partial \eta}{\partial t} + \nabla_{h}\cdot \vec{u}
120     &=&
121     0
122     \end{eqnarray}
123    
124 afe 1.3 \noindent where $u$ and $v$ and the $x$ and $y$ components of the
125     flow vector $\vec{u}$.
126 afe 1.2 \\
127 afe 1.1
128 afe 1.3
129     \subsection{Discrete Numerical Configuration}
130     \label{www:tutorials}
131    
132     The domain is discretised with
133     a uniform grid spacing in the horizontal set to
134     $\Delta x=\Delta y=20$~km, so
135     that there are sixty grid cells in the $x$ and $y$ directions. Vertically the
136     model is configured with a single layer with depth, $\Delta z$, of $5000$~m.
137    
138 afe 1.1 \subsubsection{Numerical Stability Criteria}
139     \label{www:tutorials}
140    
141 afe 1.3 The Laplacian dissipation coefficient, $A_{h}$, is set to $400 m s^{-1}$.
142 afe 1.2 This value is chosen to yield a Munk layer width \cite{adcroft:95},
143 afe 1.3
144 afe 1.2 \begin{eqnarray}
145 afe 1.3 \label{EQ:eg-baro-munk_layer}
146 afe 1.2 M_{w} = \pi ( \frac { A_{h} }{ \beta } )^{\frac{1}{3}}
147     \end{eqnarray}
148    
149 afe 1.3 \noindent of $\approx 100$km. This is greater than the model
150     resolution $\Delta x$, ensuring that the frictional boundary
151     layer is well resolved.
152 afe 1.2 \\
153    
154     \noindent The model is stepped forward with a
155 afe 1.3 time step $\delta t=1200$secs. With this time step the stability
156 afe 1.2 parameter to the horizontal Laplacian friction \cite{adcroft:95}
157    
158    
159 afe 1.3
160 afe 1.2 \begin{eqnarray}
161 afe 1.3 \label{EQ:eg-baro-laplacian_stability}
162     S_{l} = 4 \frac{A_{h} \delta t}{{\Delta x}^2}
163 afe 1.2 \end{eqnarray}
164    
165 afe 1.3 \noindent evaluates to 0.012, which is well below the 0.3 upper limit
166     for stability.
167 afe 1.2 \\
168    
169 afe 1.3 \noindent The numerical stability for inertial oscillations
170 afe 1.2 \cite{adcroft:95}
171    
172     \begin{eqnarray}
173 afe 1.3 \label{EQ:eg-baro-inertial_stability}
174     S_{i} = f^{2} {\delta t}^2
175 afe 1.2 \end{eqnarray}
176    
177 afe 1.3 \noindent evaluates to $0.0144$, which is well below the $0.5$ upper
178     limit for stability.
179 afe 1.2 \\
180    
181 afe 1.3 \noindent The advective CFL \cite{adcroft:95} for an extreme maximum
182     horizontal flow speed of $ | \vec{u} | = 2 ms^{-1}$
183 afe 1.2
184     \begin{eqnarray}
185 afe 1.3 \label{EQ:eg-baro-cfl_stability}
186     S_{a} = \frac{| \vec{u} | \delta t}{ \Delta x}
187 afe 1.2 \end{eqnarray}
188    
189 afe 1.3 \noindent evaluates to 0.12. This is approaching the stability limit
190     of 0.5 and limits $\delta t$ to $1200s$.
191 afe 1.2
192 afe 1.3 \subsection{Code Configuration}
193 afe 1.1 \label{www:tutorials}
194 afe 1.3 \label{SEC:eg-baro-code_config}
195 afe 1.1
196     The model configuration for this experiment resides under the
197 afe 1.3 directory {\it verification/exp0/}. The experiment files
198 afe 1.1 \begin{itemize}
199     \item {\it input/data}
200     \item {\it input/data.pkg}
201     \item {\it input/eedata},
202 afe 1.3 \item {\it input/windx.sin\_y},
203     \item {\it input/topog.box},
204 afe 1.1 \item {\it code/CPP\_EEOPTIONS.h}
205     \item {\it code/CPP\_OPTIONS.h},
206     \item {\it code/SIZE.h}.
207     \end{itemize}
208 afe 1.3 contain the code customizations and parameter settings for this
209 afe 1.1 experiments. Below we describe the customizations
210     to these files associated with this experiment.
211    
212     \subsubsection{File {\it input/data}}
213     \label{www:tutorials}
214    
215     This file, reproduced completely below, specifies the main parameters
216     for the experiment. The parameters that are significant for this configuration
217     are
218    
219     \begin{itemize}
220    
221 afe 1.3 \item Line 7, \begin{verbatim} viscAh=4.E2, \end{verbatim} this line sets
222     the Laplacian friction coefficient to $400 m^2s^{-1}$
223     \item Line 10, \begin{verbatim} beta=1.E-11, \end{verbatim} this line sets
224     $\beta$ (the gradient of the coriolis parameter, $f$) to $10^{-11} s^{-1}m^{-1}$
225    
226     \item Lines 15 and 16
227     \begin{verbatim}
228     rigidLid=.FALSE.,
229     implicitFreeSurface=.TRUE.,
230     \end{verbatim}
231     these lines suppress the rigid lid formulation of the surface
232     pressure inverter and activate the implicit free surface form
233     of the pressure inverter.
234 afe 1.1
235     \item Line 27,
236     \begin{verbatim}
237 afe 1.3 startTime=0,
238 afe 1.1 \end{verbatim}
239 afe 1.3 this line indicates that the experiment should start from $t=0$
240     and implicitly suppresses searching for checkpoint files associated
241     with restarting an numerical integration from a previously saved state.
242 afe 1.2
243 afe 1.3 \item Line 29,
244 afe 1.1 \begin{verbatim}
245 afe 1.3 endTime=12000,
246 afe 1.1 \end{verbatim}
247 afe 1.3 this line indicates that the experiment should start finish at $t=12000s$.
248     A restart file will be written at this time that will enable the
249     simulation to be continued from this point.
250 afe 1.1
251     \item Line 30,
252     \begin{verbatim}
253 afe 1.3 deltaTmom=1200,
254 afe 1.1 \end{verbatim}
255 afe 1.3 This line sets the momentum equation timestep to $1200s$.
256 afe 1.1
257 afe 1.3 \item Line 39,
258 afe 1.1 \begin{verbatim}
259 afe 1.3 usingCartesianGrid=.TRUE.,
260 afe 1.1 \end{verbatim}
261 afe 1.3 This line requests that the simulation be performed in a
262     Cartesian coordinate system.
263 afe 1.1
264 afe 1.3 \item Line 41,
265 afe 1.1 \begin{verbatim}
266 afe 1.3 delX=60*20E3,
267 afe 1.1 \end{verbatim}
268 afe 1.3 This line sets the horizontal grid spacing between each x-coordinate line
269     in the discrete grid. The syntax indicates that the discrete grid
270     should be comprise of $60$ grid lines each separated by $20 \times 10^{3}m$
271     ($20$~km).
272 afe 1.1
273     \item Line 42,
274     \begin{verbatim}
275 afe 1.3 delY=60*20E3,
276 afe 1.1 \end{verbatim}
277 afe 1.3 This line sets the horizontal grid spacing between each y-coordinate line
278     in the discrete grid to $20 \times 10^{3}m$ ($20$~km).
279 afe 1.1
280     \item Line 43,
281     \begin{verbatim}
282 afe 1.3 delZ=5000,
283 afe 1.2 \end{verbatim}
284 afe 1.3 This line sets the vertical grid spacing between each z-coordinate line
285     in the discrete grid to $5000m$ ($5$~km).
286 afe 1.1
287     \item Line 46,
288     \begin{verbatim}
289     bathyFile='topog.box'
290     \end{verbatim}
291     This line specifies the name of the file from which the domain
292     bathymetry is read. This file is a two-dimensional ($x,y$) map of
293     depths. This file is assumed to contain 64-bit binary numbers
294     giving the depth of the model at each grid cell, ordered with the x
295     coordinate varying fastest. The points are ordered from low coordinate
296     to high coordinate for both axes. The units and orientation of the
297     depths in this file are the same as used in the MITgcm code. In this
298     experiment, a depth of $0m$ indicates a solid wall and a depth
299 afe 1.3 of $-5000m$ indicates open ocean. The matlab program
300 afe 1.1 {\it input/gendata.m} shows an example of how to generate a
301     bathymetry file.
302    
303    
304 afe 1.3 \item Line 49,
305 afe 1.1 \begin{verbatim}
306     zonalWindFile='windx.sin_y'
307     \end{verbatim}
308     This line specifies the name of the file from which the x-direction
309     surface wind stress is read. This file is also a two-dimensional
310     ($x,y$) map and is enumerated and formatted in the same manner as the
311     bathymetry file. The matlab program {\it input/gendata.m} includes example
312 afe 1.3 code to generate a valid {\bf zonalWindFile} file.
313 afe 1.1
314     \end{itemize}
315    
316     \noindent other lines in the file {\it input/data} are standard values
317     that are described in the MITgcm Getting Started and MITgcm Parameters
318     notes.
319    
320 afe 1.2 \begin{small}
321 afe 1.3 \input{part3/case_studies/barotropic_gyre/input/data}
322 afe 1.2 \end{small}
323 afe 1.1
324     \subsubsection{File {\it input/data.pkg}}
325     \label{www:tutorials}
326    
327     This file uses standard default values and does not contain
328 afe 1.3 customizations for this experiment.
329 afe 1.1
330     \subsubsection{File {\it input/eedata}}
331     \label{www:tutorials}
332    
333     This file uses standard default values and does not contain
334 afe 1.3 customizations for this experiment.
335 afe 1.1
336     \subsubsection{File {\it input/windx.sin\_y}}
337     \label{www:tutorials}
338    
339     The {\it input/windx.sin\_y} file specifies a two-dimensional ($x,y$)
340     map of wind stress ,$\tau_{x}$, values. The units used are $Nm^{-2}$.
341     Although $\tau_{x}$ is only a function of $y$n in this experiment
342     this file must still define a complete two-dimensional map in order
343     to be compatible with the standard code for loading forcing fields
344     in MITgcm. The included matlab program {\it input/gendata.m} gives a complete
345     code for creating the {\it input/windx.sin\_y} file.
346    
347     \subsubsection{File {\it input/topog.box}}
348     \label{www:tutorials}
349    
350    
351     The {\it input/topog.box} file specifies a two-dimensional ($x,y$)
352     map of depth values. For this experiment values are either
353 afe 1.3 $0m$ or {\bf -delZ}m, corresponding respectively to a wall or to deep
354 afe 1.1 ocean. The file contains a raw binary stream of data that is enumerated
355     in the same way as standard MITgcm two-dimensional, horizontal arrays.
356     The included matlab program {\it input/gendata.m} gives a complete
357     code for creating the {\it input/topog.box} file.
358    
359     \subsubsection{File {\it code/SIZE.h}}
360     \label{www:tutorials}
361    
362     Two lines are customized in this file for the current experiment
363    
364     \begin{itemize}
365    
366     \item Line 39,
367     \begin{verbatim} sNx=60, \end{verbatim} this line sets
368     the lateral domain extent in grid points for the
369     axis aligned with the x-coordinate.
370    
371     \item Line 40,
372     \begin{verbatim} sNy=60, \end{verbatim} this line sets
373     the lateral domain extent in grid points for the
374     axis aligned with the y-coordinate.
375    
376     \end{itemize}
377    
378     \begin{small}
379 afe 1.3 \input{part3/case_studies/barotropic_gyre/code/SIZE.h}
380 afe 1.1 \end{small}
381    
382     \subsubsection{File {\it code/CPP\_OPTIONS.h}}
383     \label{www:tutorials}
384    
385     This file uses standard default values and does not contain
386 afe 1.3 customizations for this experiment.
387 afe 1.1
388    
389     \subsubsection{File {\it code/CPP\_EEOPTIONS.h}}
390     \label{www:tutorials}
391    
392     This file uses standard default values and does not contain
393 afe 1.3 customizations for this experiment.
394 afe 1.2

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