CNVTOL
CNVTOL, Lab, VALUE, TOLER, NORM, MINREF
Sets convergence values for nonlinear analyses.
LabValid convergence labels.
Discipline Displacement Convergence Force Convergence Label Label Description Label Label Description Structural U Displacements F Forces ROT Rotations M Moments HDSP Hydrostatic Pressure DVOL Volume JOINT[a] Joint Element Constraint Check COMP[b] Volumetric Compatibility Check ENGY System Energy Error Norm ENGY Energy Error[c] Nonlocal field GFV Gradient Field Degree of Freedom GFRS Gradient Field Residual Thermal TEMP Temperature HEAT Heat Flow Fluid PRES Pressures FLOW Fluid Flow V Velocity VF Fluid Force Electric VOLT Voltage AMPS or CHRG Current Flow or Charge EMF Electromotive Force CURT Current Flow Magnetic MAG Scalar Potential FLUX Scalar Flux A Vector Potential CSG Current Segments Diffusion CONC Concentration RATE Diffusion Flow Rate [a] JOINT specifies a tolerance for the joint element constraint check and is applicable to MPC184 joint elements. It is a nonlinear element convergence status value, not a displacement convergence value.
TOLERis the only other valid argument whenLab= JOINT.[b] COMP specifies a tolerance for the volumetric compatibility check in current-technology plane and solid elements (18x elements). It is a nonlinear element convergence status value, not a displacement convergence value.
TOLERis the only other valid argument whenLab= COMP.[c] ENGY specifies the convergence criterion for structural analysis based on the system of total energy accuracy. It is a combination of force and displacement criterion. The default energy error criterion is generally more relaxed than the default force criterion. Use ENGY to achieve a moderately accurate solution with a smaller number of iterations compared to the force convergence criterion.
VALUETypical reference value for the specified convergence label (
Lab).VALUEdefaults to the maximum of a program calculated reference orMINREF. For degrees of freedom, the reference is based upon the selectedNORMand the current total degree-of-freedom value. For forcing quantities, the reference is based upon the selectedNORMand the applied loads.If
VALUEis negative, the convergence criterion based on the specified label is removed, including the default convergence criterion value. The convergence criterion for all other labels remain as they were (either a default value or a previously specified value).TOLERTolerance value used for the specified
Labconvergence label. Default values are described below.If CNVTOL is issued with a
Labvalue specified but noTOLERvalue, the default tolerance values are:0.05 (5%) for displacement (U).
1.0E-7 for the joint element constraint check (JOINT). This value rarely needs to be changed. A loose tolerance value may lead to inaccurate or incorrect solutions. When
Lab= JOINT,VALUE,NORM, andMINREFare ignored.1.0E-3 for the volumetric compatibility check (COMP). When
Lab= COMP,VALUE,NORM, andMINREFare ignored.0.05 for energy error (ENGY).
For all other
Lablabels, the default tolerance value is 0.005 (0.5%).
If CNVTOL is not issued, the
TOLERdefaults are as follows:0.005 (0.5%) for force (F) and moment (M)
1.0E-4 (0.01%) for volume (DVOL)
0.05 (5%) for displacement (U)
0.05 (5%) for hydrostatic pressure (HDSP)
1.0 for temperature (TEMP) when the iterative QUASI solver is used (THOPT,QUASI,,,,,,1)
1.0E-3 (0.1%) for acoustics pressure (PRES) and 1.E-3 (0.1%) for acoustic velocity potential using the degree of freedom PRES.
If you choose to specify a
TOLERvalue, it must be greater than zero and less than 1. This is true for allLablabels.The program may adjust the force convergence tolerance if you do not explicitly set a value via CNVTOL. See Notes for details.
NORMSpecifies norm selection:
0
—
Infinite norm (check each degree of freedom separately) (default for
Lab= U and forLab= TEMP when the iterative QUASI solver is used (THOPT,QUASI,,,,,,,1).The infinite norm is also used for the energy error criterion (ENGY) and is the only option available for ENGY.
1
—
L1 norm (check absolute value sum).
2
—
L2 norm (check SRSS value) (default, except for
Lab= U).3
—
Infinite norm (check each degree of freedom separately). The reference is calculated using the infinite norm of the displacement increment of the substep. Valid only for
Lab= U.MINREFThe minimum value allowed for the program-calculated reference value. If negative, no minimum is enforced. Used only if
VALUEis blank. Default values are as follows:maximum of 0.01 or internally calculated minimum reference value for force (F), moment (M)
a small factor times the average element length of the model for displacement (U) convergence
0.01 for volume (DVOL) convergence
1.0E-4 for gradient field residual (GFRS)
1.0E-6 for heat flow (HEAT)
1.0E-6 for diffusion flow (RATE)
1.0E-12 for charge (CHRG)
1.0E-6 for hydrostatic pressure (HDSP)
1.0 for temperature (TEMP) when the iterative QUASI solver is used (THOPT,QUASI,,,,,,,1)
1.0 for energy error convergence (ENGY)
1.0E-5 for acoustics pressure (PRES)
0.0 otherwise
Command Default
For static or transient analysis, check the out-of-balance load
for any active degree of freedom using the default VALUE,
TOLER, NORM, and
MINREF. Also check the translational displacement convergence in
most cases. For harmonic magnetic analysis, check the out-of-balance of the degrees of
freedom. The energy criterion convergence check is off by default.
Notes
This command is usually not needed because the default convergence criteria are sufficient for most nonlinear analyses. In rare cases, you may need to use this command to diagnose convergence difficulties.
Values may be set for the degrees of freedom and/or the out-of-balance load for the corresponding forcing quantities.
Issuing CNVTOL to set
a convergence criterion for a specific convergence label (Lab) does not affect the convergence criterion for
any other label. All other convergence criteria will remain at their
default setting or at the value set by a previous CNVTOL command.
If CNVTOL is not issued for any force convergence
label (F, M, DVOL, and so on as listed under the Lab argument), the
default convergence tolerance for a particular force label is increased dynamically during the
Newton-Raphson iterations in the range of 1 to 1.66 times the default value. For example, the
F label default tolerance is 0.005. Therefore, the maximum convergence tolerance with the
adjustment is 0.0083. This adjustment is not activated until the 8th or higher Newton-Raphson
iteration. If you do not want the program to adjust the tolerance, issue
CNVTOL to specify the convergence tolerance for the appropriate force
label.
When using the Mechanical APDL graphical user interface (GUI), if a "Delete" operation in a
Nonlinear Convergence Criteria dialog box writes this command to a
log file (Jobname.log or Jobname.lgw), you will
observe that Lab is blank, VALUE = -1,
and TOLER is an integer number. In this case, the GUI has assigned
a value of TOLER that corresponds to the location of a chosen
convergence label in the dialog box's list. It is not
intended that you type in such a location value for TOLER in an
interactive session. However, a file that contains a GUI-generated CNVTOL
command of this form can be used for batch input or with the /INPUT
command.
Convergence norms specified with CNVTOL may be graphically tracked while the solution is in process using the Graphical Solution Tracking (GST) feature. Issue /GST to enable or disable GST. By default, GST is ON for interactive sessions and OFF for batch runs.
The energy convergence check (ENGY) is not available when the arc-length method (ARCLEN,ON) is used.
For more information on convergence calculations in a nonlinear analysis, see Convergence in the Theory Reference.
This command is also valid in PREP7.