7.2.1 Convergence and time integration criteria: overview

Numerous control parameters are associated with the convergence and integration accuracy algorithms in ABAQUS/Standard. These parameters are assigned default values that are chosen to optimize the accuracy and efficiency of the solution for a wide spectrum of nonlinear problems. You can change the solution control parameters, as described in the following sections:

A brief synopsis of the more important solution control parameters, together with a description of the circumstances in which they can be used effectively, is provided in “Commonly used control parameters,” Section 7.2.2. This section is likely to be the most useful for the general user and should be read first.

ABAQUS/Standard incorporates an empirical algorithm designed to solve the equilibrium equations of nonlinear systems accurately and economically. The criteria used to establish convergence of nonlinear increments and the automatic adjustment of increment size based on the convergence rate are described in “Convergence criteria for nonlinear problems,” Section 7.2.3.

ABAQUS/Standard allows you to choose “time integration accuracy parameters” in problems that have a physical time scale. The algorithms that use these parameters for automatically controlling time increment sizes are described in “Time integration accuracy in transient problems,” Section 7.2.4.

Modifying the default solution controls

The default values for the solution control parameters need not be adjusted for most cases. You can reset them, however, within a step definition.

Values given for the solution control parameters remain in effect for the remainder of the analysis or until they are reset.

**Input File Usage: ** | *CONTROLS |

| The *CONTROLS option can be repeated, if necessary, with different parameters. |

**ABAQUS/CAE Usage: ** | Step module: : toggle on **Specify** |

#### Resetting all default solution controls

You can restore all solution control parameters to their default values.

**ABAQUS/CAE Usage: ** | Step module: : toggle on **Reset all parameters to their system-defined defaults** |