NLPARM

Bulk Data Entry Defines parameters for Nonlinear Static Analysis, Nonlinear Transient Analysis, and Nonlinear Heat Transfer Analysis solution control.

Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
NLPARM ID NINC DT     MAXITER CONV    
  EPSU EPSP EPSW     MAXLS   LSTOL  
    TTERM MAXAUG            

Example

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
NLPARM 99 5              

Definitions

Field Contents SI Unit Example
ID Each NLPARM Bulk Data card must have a unique ID.

No default (Integer > 0)

  
NINC Number of implicit load sub-increments. 2

Default = 1 (one increment) for Nonlinear Static, Nonlinear Transient, and Nonlinear Heat Transfer Analysis.

(Integer > 0)

  
DT Initial load increment. 4

Default = Blank (Real ≥ 0.0)

  
MAXITER Limit on number of implicit iterations for each load increment (for Nonlinear Static, Nonlinear Transient, and Nonlinear Heat Transfer Analysis). 6, 12

Default = 25 (Integer > 0)

  
CONV Implicit convergence criteria flags. 3

Default = UPW for Nonlinear Static and Nonlinear Transient Analysis

(Any combination of U, P and W)

  
EPSU Error tolerance for displacement (U) criterion. 3

Default = 1.0E-3 (Real > 0.0)

  
EPSP Error tolerance for load (P) criterion. 3

Default = 1.0E-3 (Real > 0.0)

  
EPSW Error tolerance for work (W) criterion. 3

Default = 1.0E-7 (Real > 0.0)

  
MAXLS Setting MAXLS to a positive integer value activates line search method. MAXLS identifies the maximum number of line searches allowed for each iteration in Small Displacement Nonlinear Static Analysis (NLSTAT). 7

Default = 0 (Integer > 0)

  
LSTOL Line search tolerance.

Default = 1.0E-3 (Real > 0.0)

  
TTERM Termination time. 4 5

Default = 1.0 (Real > 0.0)

  
MAXAUG Number of allowed augmentations within each time increment when the augmented Lagrange multiplier method for nonlinear contact is activated. 12

Default = 50 (Integer > 0)

  

Comments

  1. The NLPARM Bulk Data Entry is selected by the Subcase Information command NLPARM=option. Each subcase for which Nonlinear Static Analysis is desired requires either an NLPARM or NLCTRL command. Nonlinear Transient Analysis requires one of the following three entries: NLPARM, NLCTRL, or TSTEPNL, and for the first two entries, the TSTEP entry is required in addition.
  2. The solution method for Nonlinear Static Analysis (ANALYSIS = NLSTAT) is full Newton. The stiffness matrix is updated at each iteration. NINC > 0 represents the number of equal subdivisions that the total load in a given subcase will be divided into. If NINC is blank, the entire load for a given subcase is applied at once. The Newton method will be applied to consecutive load levels until the final load is reached.
  3. For increased accuracy, all three convergence criteria are set together at their default values. If one or more convergence criteria are excluded, the result accuracy may vary. For more information regarding convergence criteria, refer to Nonlinear Convergence Criteria in the User Guide.
  4. If DT is specified, NINC field is not required and thus is ignored. If DT is not specified, the default initial load increment is equal to TTERM/NINC. The DLOAD Subcase Information Entry can be used in a NLSTAT subcase to reference the TLOAD1 Bulk Data Entry. This allows for the specification of a user-defined loading curve via the TID field on the TLOAD1 entry. The TID field references the Time (X) versus Load Scale Factors (Y) that scales the loading specified on the EXCITEID field. If DT, TTERM, and NINC are not specified, the default initial load increment is equal to 1.0 (TTERM/NINC with their default values 1.0/1.0).
  5. TTERM on NLPARM is to be input as subcase time (not total time). For instance, in a multiple subcase setup, if subcase 3 starts at 2.0 and ends at 3.0, then TTERM for subcase 3 should be set to 1.0, since it is based on subcase time.
  6. MAXITER is supported for:
    1. Large Displacement Nonlinear Analysis (both NLSTAT and Nonlinear Transient Analysis)
    2. Small Displacement Nonlinear Analysis (both NLSTAT and Nonlinear Transient Analysis) with PARAM,EXPERTNL,NO
    3. Nonlinear Heat Transfer Analysis (NLHEAT, both steady-state and transient)
      Note:
      • When the number of iterations reaches MAXITER, the run will be terminated for (b) and (c) above, but not for (a). For (a), MAXITER is respected, and the number of iterations is limited at MAXITER for a particular load increment.
      • When the augmented Lagrange multiplier method for nonlinear contact is activated, MAXITER is respected within each augmentation of a time increment.
      • For Small Displacement Nonlinear Analysis (NLSTAT, DTRAN nonlinear) with PARAM,EXPERTNL,AUTO/YES, the EXPERTNL solution may continue even after MAXITER is reached.
  7. When MAXLS=0, Line Search may still be activated by the “expert system” for small displacement Nonlinear Static analysis (NLSTAT). For more details, refer to PARAM, LSNLEXP.
  8. For details on how PARAM,EXPERTNL,AUTO/YES interacts with other nonlinear controls, refer to Nonlinear Static Analysis in the User Guide.
  9. Additional convergence criteria may be defined via NLADAPT Bulk Entry. Such convergence criteria, for instance, NLADAPT,ERRINF,MAX should be satisfied in addition to the UPW criteria from NLPARM Bulk Data.
  10. The NLCTRL Bulk Data and Subcase Information Entries can be used instead of NLPARM Bulk Data and Subcase Information Entries as an alternate way to control nonlinear implicit convergence criteria. Both NLPARM and NLCTRL cannot be specified together in the same nonlinear implicit subcase.
  11. Detailed convergence check information for implicit nonlinear subcases, increments, and Newton-Raphson iterations are printed in the _nl.out file. Additional options for checking Nonlinear Analysis run information and monitoring progress of Nonlinear Implicit Analysis jobs are listed in Runtime Monitoring in the User Guide.
  12. For more information on the augmented Lagrange multiplier method, refer to Augmented Lagrange Multiplier (ALM) Method (Nonlinear Analysis) in the User Guide.
  13. This card is represented as a load collector in HyperMesh.