# NLADAPT

Bulk Data Entry Defines parameters for time-stepping and convergence criteria in Nonlinear Analysis.

## Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
NLADAPT ID PARAM1 VALUE PARAM2 VALUE PARAM3 VALUE
PARAM4 VALUE PARAM5 VALUE PARAM6 VALUE

## Example

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
NLADAPT 23 NCUTS 5 DTMAX 4.0 DTMIN 1.0
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
NLADAPT 23 ERRF MAX TOLF 0.001

## Definitions

Field Contents SI Unit Example
ID Each NLADAPT Bulk Data Entry should have a unique ID.

No default (Integer > 0)

NCUTS Number of cutbacks allowed to reduce the time increment.

Default = 5 (Integer > 0)

DTMAX Maximum time increment allowed.

No default (Real > 0.0)

DTMIN Minimum time increment allowed.

If DTMIN is not specified, a default value of 1e-5*TTERM is applied internally for each subcase, where TTERM is the termination time (or subcase time) defined on the NLPARM Bulk Data card. User specified DTMIN will overwrite the default value.

(Real > 0.0)

NOPCL Number of grids allowed to have open-close contact status change. 2

(Integer ≥ 0)

NSTSL Number of grids allowed to have stick-slip contact status change when the current time step converged.

No default (Integer ≥ 0)

EXTRA
LINEAR
Activates linear extrapolation in the Newton-Raphson method. The displacement value from the previous load increment is used as the initial guess for the current load increment.
NO (Default)
Extrapolation is turned off.

DIRECT
NO (Default)
Adopt adaptive time increment scheme. Cutback is triggered if the time increment does not converge and none of the stopping criteria are satisfied.
YES
Adopt fixed time increment. In case of divergence, the run will stop immediately.

STABILIZ Scale factor value to control the stabilization energy limit. 3
YES or 1.0 (Default)
Limits the stabilization energy to 1.0e-4 times the strain energy. Since the strain energy can vary during the solution, the corresponding maximum stabilization energy for the YES option also varies accordingly.
Real > 0.0
The stabilization energy is limited to Scale Factor * 1.0e-4 *strain energy. For example, if STABILIZ is set to 2.0, the stabilization energy is limited to 2.0*1.0e-4*strain energy. Since the strain energy can vary during the solution, the corresponding maximum stabilization energy for the Real > 0.0 option also varies accordingly.
Real < 0.0
The negative sign for scale factor simply indicates that the stabilization energy will remain constant throughout the solution. It is calculated using the strain energy at the beginning of the solution. The stabilization energy is equal to Abs(Scale Factor) * 1.0e-4 * (Initial strain energy) for the entire solution, where Abs (Scale Factor) indicates the absolute value of the scale factor, and Initial Strain Energy indicates that the initial value of the strain energy is used for the calculation of stabilization energy for the entire solution. For example, if STABILIZ is set to -3.0, the stabilization energy is set equal to (+3.0)*1.0e-4*(initial strain energy), and this value is used for the entire solution.
Note: For a “buckling” type of phenomenon, which is an unstable problem, in large displacement analysis, a fixed stabilization energy is more stable than a varying one.

ERRF Controls the activation of maximum residual grid point force-based convergence criteria in the translational direction.

Nonlinear convergence criteria via ERRF, if active, should be satisfied, in addition to any criteria from NLPARM Bulk Data.

MAX
Activates translational grid point force-based convergence criteria.
If MAX is set, the maximum translational residual grid point force of any grid should be lower than TOLF*Maximum translational grid point force. 5
This parameter can also have a separate TOLF parameter which allows changing the default tolerance is 0.005.
No default

TOLF Specifies the tolerance factor.

Default = 0.005 (Real)

ERRM Controls the activation of maximum residual grid point moment-based convergence criteria.
Nonlinear convergence criteria via ERRM, if active, should be satisfied in addition to any criteria from NLPARM Bulk Data.
MAX
Activates grid point moment-based convergence criteria.
If MAX is set, the maximum residual grid point moment of any grid should be lower than TOLM*Maximum grid point moment.
This parameter can also have a separate TOLM parameter which allows changing the default tolerance of 0.005.
No default

TOLM Specifies the tolerance factor for ERRM if activated.

Default = 0.005 (Real)

## Comments

1. The NLADAPT Bulk Data Entry is selected by the Subcase Information Entry NLADAPT=ID. The NLADAPT Subcase Entry can be specified in any Nonlinear Subcase.
2. The following table summarizes the support of different fields in NLADAPT for different analysis types.
NLADAPT Field Small Displacement Nonlinear Analysis (SMDISP) Large Displacement Nonlinear Analysis (LGDISP)
Static Transient Static Transient
NCUTS Not Supported Not Supported Supported Supported
DTMAX Supported Supported Supported Supported
DTMIN Supported Supported Supported Supported
NOPCL Supported Supported Supported Supported
NSTSL Supported Supported Supported Supported
EXTRA Not Supported Not Supported Supported Not Supported
DIRECT Supported Supported Supported Supported
STABILIZ Not Supported Not Supported Supported Supported
ERRF Supported Supported Supported Supported
ERRM Supported Supported Supported Supported
3. This is a static stabilization based on viscous damping, where the viscous forces are added to the equilibrium equations. The viscous damping force (${F}_{v}$ ) is:(1)
${F}_{v}=c*v$
Where,
$c$
f (scale factor from STABILIZ, compliance/strain energy)
$v$
Velocity of the nodes ( $\frac{du}{dt}$ ) calculated from the time increment ( $dt$ ).
4. For details on how PARAM,EXPERTNL,AUTO/YES interacts with other nonlinear controls, refer to Nonlinear Static Analysis in the User Guide.
5. For ERRF/ERRM, the reference maximum grid point force/moment is defined as:
• For Force-loaded models (which also may contain enforced SPC/SPCD load):
• Small Displacement (SMDISP): The reference force/moment is the external force/moment at each grid.
• Large Displacement (LGDISP): The reference force/moment is either the external force/moment or the reaction force/moment at each grid. The one which has the maximum absolute value in a single dof is chosen as reference.
• For enforced displacement loading models (which only contain enforced SPC/SPCD load):
• Small Displacement (SMDISP): Not available.
• Large Displacement (LGDISP): The reference force/moment is the reaction force/moment at each grid. The one which has the maximum absolute value in a single dof is chosen as reference.