NLDIAG
NLDIAG, Label, Key
Sets nonlinear diagnostics functionality.
MP ME ST PR PRN DS DSS <> <> <> <> PP <> EME MFS
Label

Specifies a diagnostic function:

NRRE — 

Store the Newton-Raphson residuals information.

EFLG — 

Identify or display elements or nodes that violate the criteria.

MAXF — 

Set a maximum number of files (MaxFile) to create. Information is written to Jobname.ndxxx or Jobname.nrxxx, where xxx iterates from 001 through MaxFile. When the maximum number of files is reached, the counter resets to 001 and earlier files are overwritten.

CONT — 

Write contact information to a single Jobname.cnd text file during solution.

Key

Sets the characteristics of the diagnostic function:

OFF, or 0 — 

Suppresses writing of diagnostic information. This value is the default.

ON, or 1 — 

Writes diagnostic information to the Jobname.ndxxx, Jobname.nrxxx, or Jobname.cnd file. (If Label = CONT, this option is the same as the SUBS option described below.)

ITER  — 

Writes contact diagnostic information at each iteration. Valid only when Label = CONT.

SUBS  — 

Writes contact diagnostic information at each substep. Valid only when Label = CONT.

LSTP  — 

Writes contact diagnostic information at each load step. Valid only when Label = CONT.

STAT — 

Lists information about the diagnostic files in the current working directory.

DEL — 

Deletes all diagnostic files in the current working directory.

MaxFile — 

Sets the maximum number of files to create (Jobname.ndxxx or Jobname.nrxxx). Valid values are 1 through 999. The default is 4. (If you change the default MaxFile value, that value is retained until you change it again.) Valid only when Label = MAXF.

Command Default

No nonlinear diagnostic files are written.

Notes

The NLDIAG command is a nonlinear diagnostics tool valid for nonlinear structural analyses. It is a debugging tool for use when you must restart after an unconverged solution. The command creates Jobname.ndxxx, Jobname.nrxxx, or Jobname.cnd files in the working directory to store the information you specify.

Newton-Raphson residual. Issue the NLDIAG,NRRE,ON command to create Jobname.nrxxx files which store the relevant Newton-Raphson residual information for the last MaxFile equilibrium iterations. Issue a NLDPOST,NRRE,STAT command to list the load step, substep, time, and equilibrium iteration corresponding to each of the Jobname.nrxxx files in the working directory, then issue a PLNSOL,NRRES,,,,FileID command to point to the file from which you want to create a contour plot of your Newton-Raphson residuals.

For NLDIAG,NRRE,ON, any Jobname.nrxxx files in the current (working) directory are overwritten when you issue a new SOLVE command (or restart).

Element components that violate criteria. Issue a NLDIAG,EFLG,ON command to create Jobname.ndxxx files which store IDs for elements violating the following criteria:˙

  • Too large a distortion

  • Elements contain nodes that have near zero pivots for nonlinear analyses

  • Too large a plastic/creep strain increment (CUTCONTROL)

  • Elements for which mixed u-P constraints are not satisfied (mixed U-P option of 18x solid elements only)

For NLDIAG,EFLG,ON, all Jobname.ndxxx diagnostic files in the current (working) directory are deleted when you issue a new SOLVE command (or restart).

In the solution processor (/SOLU), use the STAT option to list the active status of this command. In the postprocessor (/POST1), issue a NLDPOST,EFLG,STAT command to list the load step, substep, time, and equilibrium iteration corresponding to each of the Jobname.ndxxx files in the working directory, then issue a NLDPOST,EFLG,CM,FileID command to create element components that violate the criteria.

Contact diagnostic. Issue the NLDIAG,CONT,ON command to create a Jobname.cnd file which stores contact information for all defined contact pairs at all substeps. Alternatively, you may issue one of the following commands to store contact information at a specific frequency:

  • NLDIAG,CONT,ITER to write at each iteration

  • NLDIAG,CONT,SUBS to write at each substep (default)

  • NLDIAG,CONT,LSTP to write at each load step

File Jobname.cnd is written during solution and lists, on a pair-base, the following contact information:

  • Number of contact elements in contact[1]

  • Number of contact elements in "sticking" contact status

  • Maximum chattering level

  • Maximum contact penetration/Minimum gap[2]

  • Maximum closed gap

  • Maximum normal contact stiffness

  • Minimum normal contact stiffness

  • Maximum resulting pinball

  • Maximum elastic slip distance

  • Maximum tangential contact stiffness

  • Minimum tangential contact stiffness

  • Maximum sliding distance

  • Maximum contact pressure

  • Maximum friction stress

  • Average contact depth

  • Maximum closed penetration

  • Number of contact points having too much penetration

  • Contacting area

  • Maximum contact damping pressure

  • Maximum tangential contact damping stress

  1. If >0, this quantity indicates the number of contact elements in contact. Other values are interpreted as follows:

    0 indicates that the contact pair is in near-field contact status.
    -1 indicates that the contact pair is in far-field contact status.
    -2 indicates that the contact pair is inactive (symmetric to asymmetric contact)
  2. A positive value indicates penetration and a negative value indicates a gap. If the contact pair has a far-field contact status, penetration and gap are not available and the value stored is the current pinball radius.

In the solution processor (/SOLU), use the NLDIAG,CONT,STAT command to list the active status of the contact information. If you subsequently issue a new SOLVE command (or restart), the Jobname.cnd file in the current (working) directory is not deleted; information is appended to it. Delete the existing file (NLDIAG,CONT,DEL command) if you do not want to retain diagnostic information from previous solutions.

For more information, see nonlinear diagnostics.

Menu Paths

Main Menu>Solution>Diagnostics>Nonlinear Diagnostics

Release 14.0 - © 2011 SAS IP, Inc. All rights reserved.