NLPARM

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

Format

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

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 (no increments) for ANALYSIS = NLSTAT and NLHEAT

(Integer > 0)

  
DT Initial load increment. 4

No default (Real ≥ 0.0)

  
KSTEP Number of iterations before stiffness update.

(Integer > 0)

  
MAXITER Limit on number of implicit iterations for each load increment. (ANALYSIS = NLSTAT and NLHEAT). 6

Default = 25 (Integer > 0)

  
CONV Flags to select implicit convergence criteria. 3

Default = UPW for ANALYSIS = NLSTAT

(Any combination of U, P and W)

  
EPSU Error tolerance for displacement (U) criterion. 3

Default = 1.0E-3 for ANALYSIS = NLSTAT

(Real > 0.0)

  
EPSP Error tolerance for load (P) criterion. 3

Default = 1.0E-3 for ANALYSIS = NLSTAT and NLHEAT

(Real > 0.0)

  
EPSW Error tolerance for work (W) criterion. 3

Default = 1.0E-7 for ANALYSIS = NLSTAT, NLTRAN and NLHEAT

(Real > 0.0)

  
MAXLS Maximum number of line searches allowed for each iteration.

Default = 0 for ANALYSIS = NLSTAT

(Integer > 0)

  
LSTOL Line search tolerance.

Default = 1.0E-3 (Real > 0.0)

  
TTERM Termination time. 4 5

Default = 1.0 (Real ≥ 0.0)

  

Comments

  1. The NLPARM Bulk Data Entry is selected by the Subcase Information command NLPARM=option. Each subcase for which nonlinear analysis is desired requires an NLPARM command.
  2. The solution method for quasi-static nonlinear 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. U, P, and W are convergence criteria for nonlinear solutions. U is the Displacement-based convergence criterion, P is the Load-based convergence criterion, and W is the Work/Strain-based convergence criterion. For increased accuracy, all three convergence criteria are set together as the default for NLSTAT analysis. If one or more convergence criteria are excluded, the result accuracy may vary. For additional information regarding convergence criteria, see Nonlinear Convergence Criteria.
  4. The DT and TTERM fields allow for an alternate method (instead of NINC) to define the loading curve for Nonlinear Static Analysis. DT and TTERM, if specified together, override the value defined on the NINC field. 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) vs Load Scale Factors (Y) that scales the loading specified on the EXCITEID field. If DT is not specified, the default initial load increment is equal to TTERM/NINC. If DT, TTERM, and NINC are not specified, the default initial load increment is equal to 0.1 (that is, 1.0/10).
  5. TTERM on NLPARM is to be input based on subcase time (not total time). For instance, in a multiple subcase setup, if subcase 3 starts at 2.0 and you want it to end 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 (NLSTAT, DTRAN nonlinear)
    2. Small Displacement Nonlinear Analysis (NLSTAT, DTRAN nonlinear) with PARAM,EXPERTNL,NO
    3. Nonlinear Heat Transfer Analysis (NLHEAT, both steady-state and transient)

      When the number of iterations reaches MAXITER, then 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.

      For Small Displacement Nonlinear Analysis (NLSTAT, DTRAN nonlinear) with PARAM,EXPERTNL,AUTO/YES, the EXPERTNL solution may continue even after MAXITER is reached.

      PARAM,EXPERTNL has two functionalities embedded within it:
      • Automatic Time-stepping schema (YES/AUTO/NO). This is applicable only for Small Displacement Nonlinear Analysis.
      • Contact Stabilization (CNTSTB). This is applicable to both Small and Large Displacement Analysis.
  7. This card is represented as a load collector in HyperMesh.