Include this parameter to choose the subspace projection method (explicit integration of the model projected onto the eigenvectors obtained in the last *FREQUENCY step preceding this step).

If this parameter is omitted, implicit time integration of the dynamic equations for all global level degrees of freedom is used.

Include this parameter if an adiabatic stress analysis is to be performed. This parameter is relevant only for isotropic metal plasticity materials with a Mises yield surface and when the *INELASTIC HEAT FRACTION option has been specified.

Set this parameter equal to a nondefault value of the numerical (artificial) damping control parameter, , in the implicit operator. Allowable values are (no damping) to –.333 (maximum damping). The default is ALPHA=–0.05, which provides slight numerical damping.

Include this parameter to choose direct user control of the incrementation through the step. If this parameter is used, constant increments of the size defined on the data line are used. If it is omitted and the HAFTOL parameter is specified, ABAQUS/Standard will choose the increments (after trying the user's initial time increment for the first attempt at the first increment). The DIRECT and HAFTOL parameters are mutually exclusive.

The DIRECT parameter may have the value NO STOP. If this value is included, the solution to an increment is accepted after the maximum number of iterations allowed (as defined in the *CONTROLS option) have been done, even if the equilibrium tolerances are not satisfied. Small increments and a minimum of two iterations are usually necessary if this value is used. This approach is not generally recommended; it should be used only in special cases when the analyst has a thorough understanding of how to interpret results obtained in this way.

Set this parameter equal to the half-step residual tolerance to be used with the automatic time incrementation scheme. For automatic time incrementation this value controls the accuracy of the solution. If this parameter is omitted, ABAQUS/Standard will use a fixed time increment. The DIRECT and HAFTOL parameters are mutually exclusive.

The HAFTOL parameter has dimensions of force and is usually chosen by comparison with typical actual force values, such as applied forces or expected reaction forces. The following guidelines may be helpful. For problems where considerable plasticity or other dissipation is expected to damp out the high frequency response, choose HAFTOL as 10 to 100 times typical actual force values for moderate accuracy and low cost; choose HAFTOL as 1 to 10 times typical actual force values for higher accuracy. In such cases smaller values of HAFTOL are usually not needed.

For elastic cases with little damping the high frequency modes usually remain important throughout the problem; therefore, HAFTOL values should be smaller than recommended above. Choose HAFTOL as 1 to 10 times typical actual force values for moderate accuracy; choose HAFTOL as 0.1 to 1 times actual force values for higher accuracy.

By default, ABAQUS/Standard will calculate or recalculate accelerations at the beginning of the step. Set INITIAL=NO to bypass the calculation of initial accelerations at the beginning of the step.

If INITIAL=NO, ABAQUS/Standard will assume that the initial accelerations for the current step are zero if the current step is the first *DYNAMIC step. If the immediately preceding step was also a *DYNAMIC step, using INITIAL=NO will cause ABAQUS/Standard to use the accelerations from the end of the previous step to continue the new step. This is appropriate only if the loading does not change suddenly at the start of the new step.

Include this parameter to suppress calculation of the half-step residual. This is possible only if fixed time incrementation is used. Normally ABAQUS/Standard calculates the half-step residuals even if fixed time incrementation is used. The NOHAF parameter switches off this calculation and, thus, saves some of the solution cost.

Include this parameter to specify that this step should use a fixed time increment that is specified by the user.

Include this parameter to indicate that variable, automatic time incrementation using the element-by-element stable time increment estimates should be used. This method will generally require more increments and more computational time than the global time estimator.

Include this parameter to specify that this step should use a fixed time increment that will be determined by ABAQUS/Explicit at the beginning of the step using the element-by-element time estimator.