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 for TIME INTEGRATOR=HHT-TF or HHT-MD. Allowable values are 0 (no damping) to –0.5. The value of –0.333 provides maximum damping. The default for TIME INTEGRATOR=HHT-TF is ALPHA=–0.05, which provides slight numerical damping.

Use this parameter to choose a time integration method. Other parameter values are determined by the time integration method selected. You can override the defaults by specifying these parameter values directly.

Set APPLICATION=TRANSIENT FIDELITY (default for problems without contact in the model) to choose a method for an accurate solution with slight numerical damping. The TIME INTEGRATOR=HHT-TF, IMPACT=AVERAGE TIME, and INCREMENTATION=CONSERVATIVE are set.

Set APPLICATION=MODERATE DISSIPATION (default for problems with contact in the model) to choose a method with larger than default numerical damping and a more aggressive time incrementation scheme at the expense of some solution accuracy. The TIME INTEGRATOR=HHT-MD, IMPACT=NO, and INCREMENTATION=AGGRESSIVE are set.

Set APPLICATION=QUASI-STATIC to choose a method with very significant numerical damping that is primarily intended to obtain quasi-static solutions. The TIME INTEGRATOR=BWE, IMPACT=NO, and INCREMENTATION=AGGRESSIVE values are set. In addition, the default step amplitude is set to RAMP instead of STEP.

Set this parameter equal to a nondefault value, , in the implicit operator for TIME INTEGRATOR=HHT-TF or HHT-MD. Allowable values are positive.

Include this parameter to choose direct user control of the incrementation through the step. If this parameter is included and no contact impacts or releases occur, constant increments of the size defined on the data line are used. If this parameter is omitted, Abaqus/Standard uses the automatic time incrementation scheme after trying the user's initial time increment for the first attempt at the first increment. The DIRECT parameter and the HAFTOL and HALFINC SCALE FACTOR 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 a nondefault value, , in the implicit operator for TIME INTEGRATOR=HHT-TF or HHT-MD. Allowable values are greater or equal to 0.5.

Set this parameter equal to the half-increment residual tolerance to be used with the automatic time incrementation scheme. For automatic time incrementation this value controls the accuracy of the solution if HALFINC SCALE FACTOR is not specified. It is recommended that the HALFINC SCALE FACTOR parameter be used instead of the HAFTOL parameter. If both are included, the HAFTOL parameter is ignored. 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.

Set this parameter equal to a scale factor applied to Abaqus/Standard calculated time average force and moment values to be used as the half-increment residual tolerance with the automatic time incrementation solution accuracy checking scheme. The DIRECT and HALFINC SCALE FACTOR parameters are mutually exclusive. The HALFINC SCALE FACTOR is ignored when NOHAF parameter is set.

The HALFINC SCALE FACTOR parameter is unitless. As a guideline, with smaller HALFINC SCALE FACTOR values, more accurate solutions should be obtained at the expense of using finer time increments. By default for APPLICATION=TRANSIENT FIDELITY, it is set to 10000 if contact is present in the model and to 1000 otherwise. These defaults differ from the suggested HAFTOL ratios primarily because the HALFINC SCALE FACTOR is applied to known force averages; hence, they need not be as conservative.

Use this parameter to choose a time incrementation type when contact impacts or releases occur during analysis.

Set IMPACT=AVERAGE TIME to choose a time incrementation scheme that employs average time of impact/release cut backs to enforce energy balance and maintains velocities and accelerations compatible on the active contact interface. The IMPACT=AVERAGE TIME and TIME INTEGRATOR=BWE settings are mutually exclusive.

Set IMPACT=CURRENT TIME to choose a “marching through” scheme without impact/release cut backs. The velocities and accelerations are compatible on the active contact interface.

Set IMPACT=NO to choose a “marching through” scheme without impact/release cut backs and without velocity/acceleration compatibility computations.

Use this parameter to choose a general time incrementation type.

Set INCREMENTATION=CONSERVATIVE to choose a time incrementation scheme that maximizes solution accuracy.

Set INCREMENTATION=AGGRESSIVE to choose a time incrementation scheme based only on convergence history, similar to a scheme typically used in static problems without rate or history dependence. Setting INCREMENTATION=AGGRESSIVE also sets the value of the NOHAF parameter.

By default, Abaqus/Standard will calculate or recalculate accelerations at the beginning of the step if an IMPACT value other than NO is used. Set INITIAL=NO to bypass the calculation of initial accelerations at the beginning of the step.

If INITIAL=NO, Abaqus/Standard assumes 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 causes 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-increment residuals and thus skip some accuracy checking for the automatic time incrementation scheme. For fixed time incrementation with the DIRECT parameter included, Abaqus/Standard calculates the half-increment residuals by default; the NOHAF parameter switches off this calculation, saving some of the solution cost.

Use this parameter to control velocity and acceleration adjustments if a singular global mass matrix is detected during initialization or during contact impact/release computations.

Set SINGULAR MASS=ERROR (default) to issue an error message and stop execution if a singular global mass matrix is detected when calculating the velocity and acceleration adjustments.

Set SINGULAR MASS=WARNING to issue a warning message and avoid these velocity and acceleration adjustments (i.e., continue time integration using the current velocities and accelerations) if a singular global mass matrix is detected.

Set SINGULAR MASS=MAKE ADJUSTMENTS to adjust velocities and accelerations even if a singular mass matrix is detected. This setting can result in large, non-physical velocity and/or acceleration adjustments, which can, in turn, cause poor time integration solutions and artificial convergence difficulties. 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.

Use this parameter to choose the time integration method.

Set TIME INTEGRATOR=BWE to choose the backward Euler time integrator.

Set TIME INTEGRATOR=HHT-TF to choose the Hilber-Hughes-Taylor time integrator with default parameter settings which provide slight numerical damping. This is the default for APPLICATION=TRANSIENT FIDELITY.

Set TIME INTEGRATOR=HHT-MD to choose the Hilber-Hughes-Taylor time integrator with default parameter settings that provide moderate numerical damping. This is the default for APPLICATION=MODERATE DISSIPATION.

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.