MITgcm/doc/OpenBound.txt

Open Boundaries Implementation in MITgcmUV

These are some quick explanatory notes regards implementation of open
boundaries (OB) and the example configuration found in
.../verification/exp4/


Input and control of OBs

   * The open boundaries code is used only if the LOGICAL parameter
     openBondaries is .TRUE.
   * Four 1-dimensional INTEGER arrays indicate the position of an OB:
     OB_Jnorth, OB_Jsouth, OB_Ieast and OB_Iwest.

The values of OB_* indicate the absolute computational coordinate of an open
boundary. eg. OB_Jsouth(3)=4
means that in the column I=3 there is a "southern" OB at tracer point J=4.
Similarly OB_Iwest(2)=1 means that
the tracer point (2,1) is an OB point. This structure for specifying OBs
assumes that there will be only one northern and southern OB per column and
similar in the other direction. An entry of 0 (zero) means there is now OB
in that column/row.

The reference to "tracer points" above introduces an important distinction
between particular boundaries due to the C-grid staggering of variables. At
a northern OB tracer point (i,j) the OB v-velocity point is at (i,j)  while
at a southern OB tracer point (i,j) the OB v-velocity point is at (i,j+1).
This is all taken care of in the code but when specifying OB values it is
important to remember the physical coordinates of T,S,U and V are not the
same for a given computational index.


Changing the type of open boundary

The supplied code simply specifies model variables at the appropriate
points. The value to be specified can (and should) be determine using a
radiative condition. A skeleton code is supplied set_obcs.F to illustrate
how
this might be done. This is the only routine that needs to be edited. Edit
others at your own peril!


The examples

There are three examples in .../verification/exp4/

  1. A zonal channel (solid side walls) with open boundaries at either end:
     data.channel
  2. A zonal channel with a Gaussian bump and open boundaries at either end:
     data.bumpchannel
  3. An open domain (OBs on four sides) with a Gaussian bump: data.bump

Each data file has a corresponding topog.* file which is specified through
the variable bathyFile in data.*
The physical problem has a flow of U=25 cm/s specified at all open
boundaries. The details of the experiment can be found in Adcroft's thesis
(Imperial College) and in Adcroft, Hill and Marshall, MWR 1997.

The differences between the supplied data.* files also show how to turn
particular OBs on and off.

Compiling and running the examples

The examples supplied are the barotropic zonal flow over a Gaussian bump in
a channel.

   * Header files: Copy or link SIZE.h, CPP_OPTIONS.h and CP_EEOPTIONS.h
     from .../verification/exp4/code/ to .../model/inc/, .../model/inc/ and
     .../eesupp.inc/ respectively
   * Modified source: Copy set_obcs.F to .../model/src/

Now compile the code as usual:

   * cd bin
   * ../tools/genmake -makefile
   * make depend
   * make

To run the code you must first choose a data file to use:

   * cd ../verification/exp4/input
   * cp data.bump data
   * ../../exe/mitgcmuv

Happy Open Boundarying!
1	Open Boundaries Implementation in MITgcmUV
2
3	These are some quick explanatory notes regards implementation of open
4	boundaries (OB) and the example configuration found in
5	.../verification/exp4/
6
7
8	Input and control of OBs
9
10	* The open boundaries code is used only if the LOGICAL parameter
11	openBondaries is .TRUE.
12	* Four 1-dimensional INTEGER arrays indicate the position of an OB:
13	OB_Jnorth, OB_Jsouth, OB_Ieast and OB_Iwest.
14
15	The values of OB_* indicate the absolute computational coordinate of an open
16	boundary. eg. OB_Jsouth(3)=4
17	means that in the column I=3 there is a "southern" OB at tracer point J=4.
18	Similarly OB_Iwest(2)=1 means that
19	the tracer point (2,1) is an OB point. This structure for specifying OBs
20	assumes that there will be only one northern and southern OB per column and
21	similar in the other direction. An entry of 0 (zero) means there is now OB
22	in that column/row.
23
24	The reference to "tracer points" above introduces an important distinction
25	between particular boundaries due to the C-grid staggering of variables. At
26	a northern OB tracer point (i,j) the OB v-velocity point is at (i,j) while
27	at a southern OB tracer point (i,j) the OB v-velocity point is at (i,j+1).
28	This is all taken care of in the code but when specifying OB values it is
29	important to remember the physical coordinates of T,S,U and V are not the
30	same for a given computational index.
31
32
33	Changing the type of open boundary
34
35	The supplied code simply specifies model variables at the appropriate
36	points. The value to be specified can (and should) be determine using a
37	radiative condition. A skeleton code is supplied set_obcs.F to illustrate
38	how
39	this might be done. This is the only routine that needs to be edited. Edit
40	others at your own peril!
41
42
43	The examples
44
45	There are three examples in .../verification/exp4/
46
47	1. A zonal channel (solid side walls) with open boundaries at either end:
48	data.channel
49	2. A zonal channel with a Gaussian bump and open boundaries at either end:
50	data.bumpchannel
51	3. An open domain (OBs on four sides) with a Gaussian bump: data.bump
52
53	Each data file has a corresponding topog.* file which is specified through
54	the variable bathyFile in data.*
55	The physical problem has a flow of U=25 cm/s specified at all open
56	boundaries. The details of the experiment can be found in Adcroft's thesis
57	(Imperial College) and in Adcroft, Hill and Marshall, MWR 1997.
58
59	The differences between the supplied data.* files also show how to turn
60	particular OBs on and off.
61
62	Compiling and running the examples
63
64	The examples supplied are the barotropic zonal flow over a Gaussian bump in
65	a channel.
66
67	* Header files: Copy or link SIZE.h, CPP_OPTIONS.h and CP_EEOPTIONS.h
68	from .../verification/exp4/code/ to .../model/inc/, .../model/inc/ and
69	.../eesupp.inc/ respectively
70	* Modified source: Copy set_obcs.F to .../model/src/
71
72	Now compile the code as usual:
73
74	* cd bin
75	* ../tools/genmake -makefile
76	* make depend
77	* make
78
79	To run the code you must first choose a data file to use:
80
81	* cd ../verification/exp4/input
82	* cp data.bump data
83	* ../../exe/mitgcmuv
84
85	Happy Open Boundarying!