CNVTOL

CNVTOL, Lab, VALUE, TOLER, NORM, MINREF
Sets convergence values for nonlinear analyses.

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Lab

Valid convergence labels.

DisciplineDisplacement ConvergenceForce Convergence
LabelLabel DescriptionLabel Label Description
StructuralUDisplacementsFForces
 ROTRotationsMMoments
 HDSPHydrostatic PressureDVOLVolume
 JOINT [1]Joint Element Constraint Check  
 COMP [2]Volumetric Compatibility Check  
ThermalTEMPTemperatureHEATHeat Flow
FluidPRESPressuresFLOWFluid Flow
 VVelocityVFFluid Force
ElectricVOLTVoltageAMPS or CHRGCurrent Flow or Charge
 EMFElectromotive ForceCURTCurrent Flow
MagneticMAGScalar PotentialFLUXScalar Flux
 AVector PotentialCSGCurrent Segments
DiffusionCONCConcentrationRATEDiffusion Flow Rate
  1. 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. TOLER is the only other valid argument when Lab = JOINT.

  2. 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. TOLER is the only other valid argument when Lab = COMP

VALUE

Typical reference value for the specified convergence label (Lab).

VALUE defaults to the maximum of a program calculated reference or MINREF. For degrees of freedom, the reference is based upon the selected NORM and the current total DOF value. For forcing quantities, the reference is based upon the selected NORM and the applied loads.

If VALUE is 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).

TOLER

Tolerance; defaults to 0.005 (0.5%) for force and moment, 1.0E-4 (0.01%) for DVOL, 0.05 (5%) for displacement when rotational DOFs are not present, and 0.05 (5%) for HDSP.

If Lab = JOINT, TOLER must be a positive value; defaults to 1.0E-7. This value rarely needs to be changed. A loose tolerance value may lead to inaccurate or incorrect solutions. VALUE, NORM, and MINREF are ignored.

If Lab = COMP, TOLER must be greater than zero and less than one; defaults to 1.0E-3. VALUE, NORM, and MINREF are ignored.

NORM

Specifies norm selection:

2

 — 

L2 norm (check SRSS value). Default, except for Lab = U.

1

 — 

L1 norm (check absolute value sum).

0

 — 

Infinite norm (check each DOF separately). Default for Lab = U.

MINREF

The minimum value allowed for the program calculated reference value. If negative, no minimum is enforced. Used only if VALUE is blank. Defaults to 0.01 for force, moment, and volume convergence, 1.0E-6 for heat flow, 1.0E-12 for VLTG and CHRG, 1.0E-6 for HDSP, and 0.0 otherwise.

Command Default

For static or transient analysis, check the out-of-balance load for any active DOF 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.

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 (DOF) 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.

When the GUI is on, 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 ANSYS 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 ANSYS program's Graphical Solution Tracking (GST) feature. Use the /GST command to turn GST on or off. By default, GST is ON for interactive sessions and OFF for batch runs.

At the first iteration of a substep, the reference value uref (see Convergence in the Mechanical APDL Theory Reference) for the displacement convergence check is calculated from the total displacement at the current time step since the current incremental displacement is not yet available. At the second iteration and higher, uref is calculated from the current incremental displacement. Therefore, if your analysis only takes one iteration within a substep to converge, the displacement check may not be sufficiently stringent. In this case, you should tighten your displacement convergence tolerance.

This command is also valid in PREP7.

Menu Paths

Main Menu>Preprocessor>Loads>Analysis Type>Sol'n Controls>Nonlinear
Main Menu>Preprocessor>Loads>Load Step Opts>Nonlinear>Convergence Crit
Main Menu>Preprocessor>Loads>Load Step Opts>Nonlinear>Harmonic
Main Menu>Preprocessor>Loads>Load Step Opts>Nonlinear>Static
Main Menu>Preprocessor>Loads>Load Step Opts>Nonlinear>Transient
Main Menu>Solution>Analysis Type>Sol'n Controls>Nonlinear
Main Menu>Solution>Load Step Opts>Nonlinear>Convergence Crit
Main Menu>Solution>Load Step Opts>Nonlinear>Harmonic
Main Menu>Solution>Load Step Opts>Nonlinear>Static
Main Menu>Solution>Load Step Opts>Nonlinear>Transient

Release 18.2 - © ANSYS, Inc. All rights reserved.