Discretization Parameters in ParaDiS - Revision history

Caiwei: /* Input Checks */

2007-12-20T19:26:52Z

Input Checks

← Older revision		Revision as of 19:26, 20 December 2007
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	maxSeg > rTol * 32 / sqrt(3)		maxSeg > rTol * 32 / sqrt(3)
	minSeg <= 0.5 * maxSeg		minSeg <= 0.5 * maxSeg
	maxSeg <= minCellSize 0.49		maxSeg <= minCellSize * 0.49

	Here are more conditions that will lead to Warning messages if violated.		Here are more conditions that will lead to Warning messages if violated.

Caiwei: /* Default values */

2007-12-20T19:26:18Z

Default values

← Older revision		Revision as of 19:26, 20 December 2007
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	If you do not specifiy <tt>minSeg</tt>, it will be assigned a default value based on <tt>maxSeg</tt> and <tt>rTol</tt>. You can overwrite the value of <tt>rTol</tt> in the input file. But you cannot change <tt>rann</tt>.		If you do not specifiy <tt>minSeg</tt>, it will be assigned a default value based on <tt>maxSeg</tt> and <tt>rTol</tt>. You can overwrite the value of <tt>rTol</tt> in the input file. But you cannot change <tt>rann</tt>.

	<tt>rTol</tt> is the error tolerance in the time integrator (trapezoid method). The time step will be automatically reduced if we are making an error larger than <tt>rTol</tt>. A larger value of <tt>rTol</tt> will lead to a larger time step, but may make the simulation unstable.		<tt>rTol</tt> is the error tolerance in the time integrator (trapezoid method). The time step will be automatically reduced if we are making an error larger than <tt>rTol</tt>. A larger value of <tt>rTol</tt> will lead to a larger time step, but may make the simulation unstable. The default value for <tt>rTol</tt> (above) is reasonable but you may need to reduce it even further.

	The acceptable value of <tt>rTol</tt> (the largest value that does not lead to instability) may depend on your choice of <tt>minSeg</tt> and <tt>maxSeg</tt>. Smaller discretization lengths will usually require a smaller <tt>rTol</tt> which will lead to a smaller time step.		The acceptable value of <tt>rTol</tt> (the largest value that does not lead to instability) may depend on your choice of <tt>minSeg</tt> and <tt>maxSeg</tt>. Smaller discretization lengths will usually require a smaller <tt>rTol</tt> which will lead to a smaller time step. You are advised to conduct a convergence study of both <tt>rTol</tt> and <tt>minSeg</tt> before you trust your simulation results.

	==Input Checks==		==Input Checks==

Caiwei: /* Default values */

2007-12-20T19:23:56Z

Default values

← Older revision		Revision as of 19:23, 20 December 2007
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	If you do not specifiy <tt>minSeg</tt>, it will be assigned a default value based on <tt>maxSeg</tt> and <tt>rTol</tt>. You can overwrite the value of <tt>rTol</tt> in the input file. But you cannot change <tt>rann</tt>.		If you do not specifiy <tt>minSeg</tt>, it will be assigned a default value based on <tt>maxSeg</tt> and <tt>rTol</tt>. You can overwrite the value of <tt>rTol</tt> in the input file. But you cannot change <tt>rann</tt>.

			<tt>rTol</tt> is the error tolerance in the time integrator (trapezoid method). The time step will be automatically reduced if we are making an error larger than <tt>rTol</tt>. A larger value of <tt>rTol</tt> will lead to a larger time step, but may make the simulation unstable.

			The acceptable value of <tt>rTol</tt> (the largest value that does not lead to instability) may depend on your choice of <tt>minSeg</tt> and <tt>maxSeg</tt>. Smaller discretization lengths will usually require a smaller <tt>rTol</tt> which will lead to a smaller time step.

	==Input Checks==		==Input Checks==

Caiwei: /* Input Checks */

2007-12-20T19:18:33Z

Input Checks

← Older revision		Revision as of 19:18, 20 December 2007
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	If <tt>rc < 0.1</tt>, then you must specify the core energy <tt>Ecore</tt>. Otherwise, the default value for <tt>Ecore</tt> will be negative and a warning message will be printed.		If <tt>rc < 0.1</tt>, then you must specify the core energy <tt>Ecore</tt>. Otherwise, the default value for <tt>Ecore</tt> will be negative and a warning message will be printed.

	<tt>rann <= 0.5 * rc</tt> is a reasonable condition, although it is not absolutely necessary. Both <tt>rann</tt> and <tt>rc</tt> represent the "thickness" of the dislocation line. If the distance between two dislocations ~~are~~ smaller than <tt>rann</tt>, they will be merged into one dislocation. If the distance between two dislocations is smaller than <tt>rc</tt>, their interactions will be significantly different from what is predited by singular linear elasticity theory.		<tt>rann <= 0.5 * rc</tt> is a reasonable condition, although it is not absolutely necessary. Both <tt>rann</tt> and <tt>rc</tt> represent the "thickness" of the dislocation line. If the distance between two dislocations is smaller than <tt>rann</tt>, they will be merged into one dislocation. If the distance between two dislocations is smaller than <tt>rc</tt>, their interactions will be significantly different from what is predited by singular linear elasticity theory.

			The condition <tt>rann <= 0.5 * rc</tt> can be violated (if you know what you are doing), but it will be very strange if your <tt>rann</tt> value is too big. Then all your dislocations will be merged together into a single node.

			A reasonable choice of <tt>rc</tt> is between <tt>0.1 b</tt> and <tt>1 b</tt>. If you set the length unit <tt>burgMag</tt> to be the same as <tt>b</tt>, then your value of <tt>rc</tt> is usually between <tt>0.1</tt> and <tt>1</tt>.

	The condition <tt>rann <= 2.0 * rTol</tt> is useless because rann is set to 2 * rTol, see above.		The condition <tt>rann <= 2.0 * rTol</tt> is useless because rann is set to 2 * rTol, see above.

Caiwei at 19:13, 20 December 2007

2007-12-20T19:13:52Z

@@ Line 8: / Line 8: @@
  rc = -1.0
  maxSeg = -1.0
@@ Line 18: / Line 17: @@
  rann = 2 * rTol
-You can overwrite the value of <tt>rTol</tt> in the input file.  But you cannot change <tt>rann</tt>.
+If you do not specifiy <tt>minSeg</tt>, it will be assigned a default value based on <tt>maxSeg</tt> and <tt>rTol</tt>.  You can overwrite the value of <tt>rTol</tt> in the input file.  But you cannot change <tt>rann</tt>.

Caiwei at 18:47, 20 December 2007

2007-12-20T18:47:29Z

← Older revision		Revision as of 18:47, 20 December 2007
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	In ParaDiS, the following length parameters are important to control the discretization and tolerance of the DD simulation:		In ParaDiS, the following length parameters are important to control the discretization and tolerance of the DD simulation:

	~~lmin~~, ~~lmax~~, ~~a, rann~~, rTol, rmax		minSeg, maxSeg, rc, rTol, rmax, rann

			The <tt>rann</tt> parameter can be set as an input in DDLab, but not in ParaDiS.

			==Default values==

			rc = -1.0
			minSeg = -1.0
			maxSeg = -1.0

			These are not valid values and force you to choose your own numbers for these three parameters.

			After you set acceptable values for <tt>rc</tt>, the default values for <tt>rTol</tt> and <tt>rann</tt> are set as follows.

			rTol = 0.25 * rc
			rann = 2 * rTol

			You can overwrite the value of <tt>rTol</tt> in the input file. But you cannot change <tt>rann</tt>.

Caiwei: added content

2007-12-20T18:38:20Z

added content

New page

In ParaDiS, the following length parameters are important to control the discretization and tolerance of the DD simulation:

lmin, lmax, a, rann, rTol, rmax