VARIABLEDT - Revision history

Guillaume at 19:28, 15 February 2012

2012-02-15T19:28:51Z

2012-02-15T19:28:14Z

2012-02-15T19:27:55Z

2012-02-15T19:27:02Z

2012-02-15T19:26:22Z

2012-02-15T19:25:53Z

2012-02-15T19:25:22Z

2012-02-15T19:23:54Z

2012-02-15T19:23:18Z

2012-02-15T19:22:37Z

@@ Line 42: / Line 42: @@
 <math> \Delta t = \min_{p\;ijk} \left( \frac{ m }{ \Phi } \right) \quad\;\;\;\; \text{if}\quad\;\;\Phi \gt 0</math>.
-where <math>m</math> and <math>\Phi</math> are, respectively, the mass (<math>kg\,m^{-3}</math>) and the massic flow (<math>kg\,m^{-3}\,s^{-1}</math>) of the property <math>p</math> at the cell indexed by <math>i,\,j,\,k</math>.
+where <math>m</math> and <math>\Phi</math> are, respectively, the mass (<math>kg\,m^{-3}</math>) and the net massic flow (<math>kg\,m^{-3}\,s^{-1}</math>) of the property <math>p</math> at the cell indexed by <math>i,\,j,\,k</math>.
 This takes into account only advective and diffusive fluxes but disregards sources and sink terms. For momentum, it also disregards the time-step constraints imposed by the gravity surface wave mode or any other physical process occuring at scales below ten times the computed <math> \Delta t </math>.

@@ Line 42: / Line 42: @@
 <math> \Delta t = \min_{p\;ijk} \left( \frac{ m }{ \Phi } \right) \quad\;\;\;\; \text{if}\quad\;\;\Phi \gt 0</math>.
-where <math>m</math> and <math>\Phi</math> are, respectively, the mass (<math>kg\,m^{-3}</math>) and massic flow (<math>kg\,m^{-3}\,s^{-1}</math>) of the property <math>p</math> at the cell indexed by <math>i,\,j,\,k</math>.
+where <math>m</math> and <math>\Phi</math> are, respectively, the mass (<math>kg\,m^{-3}</math>) and the massic flow (<math>kg\,m^{-3}\,s^{-1}</math>) of the property <math>p</math> at the cell indexed by <math>i,\,j,\,k</math>.
 This takes into account only advective and diffusive fluxes but disregards sources and sink terms. For momentum, it also disregards the time-step constraints imposed by the gravity surface wave mode or any other physical process occuring at scales below ten times the computed <math> \Delta t </math>.

@@ Line 42: / Line 42: @@
 <math> \Delta t = \min_{p\;ijk} \left( \frac{ m }{ \Phi } \right) \quad\;\;\;\; \text{if}\quad\;\;\Phi \gt 0</math>.
-where <math>m</math> and <math>\Phi</math> are the mass (<math>kg\,m^{-3}</math>) and massic flow (<math>kg\,m^{-3}\,s^{-1}</math>) of the property <math>p</math> at the cell indexed by <math>i,\,j,\,k</math>.
+where <math>m</math> and <math>\Phi</math> are, respectively, the mass (<math>kg\,m^{-3}</math>) and massic flow (<math>kg\,m^{-3}\,s^{-1}</math>) of the property <math>p</math> at the cell indexed by <math>i,\,j,\,k</math>.
 This takes into account only advective and diffusive fluxes but disregards sources and sink terms. For momentum, it also disregards the time-step constraints imposed by the gravity surface wave mode or any other physical process occuring at scales below ten times the computed <math> \Delta t </math>.

@@ Line 38: / Line 38: @@
 ==Physical rationale==
-The main idea to compute an ideal time-step is to choose the largest time-step above which the numerical model iteration would overshoot. This is equivalent to make sure that no cell in any property can deplete more than its property mass in one time-step, given that it has a net flux with positive divergence. Mathematically speaking this would be equivalent to:
+The main idea to compute an ideal time-step is to choose the largest time-step above which the numerical model iteration would overshoot. This is equivalent to making sure that no cell in any property can deplete more than its property mass in one time-step, given that it has a net flux with positive divergence. Mathematically speaking this would be equivalent to:
 <math> \Delta t = \min_{p\;ijk} \left( \frac{ m }{ \Phi } \right) \quad\;\;\;\; \text{if}\quad\;\;\Phi \gt 0</math>.

@@ Line 38: / Line 38: @@
 ==Physical rationale==
-The main to compute an ideal time-step is to choose the largest time-step above which the numerical model iteration would overshoot. This is equivalent to make sure that no cell in any property can deplete more than its property mass in one time-step, given that it has a net flux with positive divergence. Mathematically speaking this would be equivalent to:
+The main idea to compute an ideal time-step is to choose the largest time-step above which the numerical model iteration would overshoot. This is equivalent to make sure that no cell in any property can deplete more than its property mass in one time-step, given that it has a net flux with positive divergence. Mathematically speaking this would be equivalent to:
 <math> \Delta t = \min_{p\;ijk} \left( \frac{ m }{ \Phi } \right) \quad\;\;\;\; \text{if}\quad\;\;\Phi \gt 0</math>.

@@ Line 7: / Line 7: @@
 A log file DTLog.txt is stored in the results folder ''/res'' of the main domain if the option DT_LOG is set in the nomfich.dat file in ''/exe'' folder of the main domain. Such a log file is useful to trace which cell of which property
-is the weakest link prone to unstabilize.
+is the weakest link that could generate an instability.
   DT_LOG                    : ..\res\DT_Log_2.log

@@ Line 2: / Line 2: @@
 To activate a variable time step bounded between a minimum and maximum DT, in configuration file Model_x.dat
-  VARIABLEDT : 1
+  VARIABLEDT  : 1
-  DT : 10.
+  DT          : 10.
-  MAXDT : 100.
+  MAXDT       : 100.
 A log file DTLog.txt is stored in the results folder ''/res'' of the main domain if the option DT_LOG is set in the nomfich.dat file in ''/exe'' folder of the main domain.
@@ Line 46: / Line 46: @@
 ==See also==
-*[[ModuleTime]]
+*[[Module Time]]
 [[Category:MOHID]]

← Older revision		Revision as of 19:22, 15 February 2012
Line 42:		Line 42:

	where <math>m</math> and <math>\Phi</math> are the mass (<math>kg\,m^{-3}</math>) and massic flow (<math>kg\,m^{-3}\,s^{-1}</math>) of the property <math>p</math> at the cell indexed by <math>i,\,j,\,k</math>.		where <math>m</math> and <math>\Phi</math> are the mass (<math>kg\,m^{-3}</math>) and massic flow (<math>kg\,m^{-3}\,s^{-1}</math>) of the property <math>p</math> at the cell indexed by <math>i,\,j,\,k</math>.
		+
		+	This takes into account only advective and diffusive fluxes but disregards sources and sink terms. For momentum, it also disregards the time-step constraints imposed by the gravity surface wave mode or any other physical process occuring at scales below the computed <math> \Delta t </math>

	==See also==		==See also==