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. For nonlinear heat transfer analysis, this
represents the error tolerance for temperature. 3 Default = 1.0E-3 (Real > 0.0) |
|
EPSP | Error tolerance for load
(P) criterion in structural analysis. For nonlinear heat
transfer analysis, this represents the error tolerance for the load (which can be
considered similar to an energy term in structural analysis, represented by the
residual*temperature). 3 Default = 1.0E-3 (Real > 0.0) |
|
EPSW | Error tolerance for work
(W) criterion in structural analysis. For nonlinear heat
transfer analysis, this represents the error tolerance for work (which can be
considered similar to an energy term in structural analysis, represented by
residual*temperature increment). 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
- 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.
- 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.
- 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.
For nonlinear heat transfer analysis (both steady-state and transient), the convergence occurs when the temperature increment and residual values become zero (basically when the corresponding error terms EPSU, EPSP, and EPSW reach values below their tolerance values defined here). For EPSP and EPSW in nonlinear heat transfer analysis, multiplying the residual by the temperature (or temperature increment), represents a term which can be considered equivalent to energy in structural analysis. They correspond to a form of equivalent energy in the principle of virtual displacements when applied to the energy conservation equation for heat transfer analysis. If these terms become zero, equilibrium is reached.
- 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).
- 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.
- MAXITER is supported
for:
- Large Displacement Nonlinear Analysis (both NLSTAT and Nonlinear Transient Analysis)
- Small Displacement Nonlinear Analysis (both NLSTAT and Nonlinear Transient Analysis) with PARAM,EXPERTNL,NO
- 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.
- 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.
- For details on how PARAM,EXPERTNL,AUTO/YES interacts with other nonlinear controls, refer to Nonlinear Static Analysis in the User Guide.
- 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.
- 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.
- 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.
- For more information on the augmented Lagrange multiplier method, refer to Augmented Lagrange Multiplier (ALM) Method (Nonlinear Analysis) in the User Guide.
- This card is represented as a load collector in HyperMesh.