Customizing general solution controls

Abaqus/CAE displays the General Solution Controls Manager showing the steps defined in the model and the general solution controls associated with each step.

The General Solution Controls Editor appears.

• Choose Propagate from previous step if you want the solution controls settings from the previous step to remain active in the current step.

• Choose Reset all parameters to their system-defined defaults if you want all of the parameters on all of the tabbed pages in the editor to revert to their default values.

• Choose Specify if you want to enter new values for particular parameters for this step.

1. If you want to select a particular type of equation for which the solution control parameters are being defined, choose Specify individual fields. Otherwise, choose Apply to all applicable fields to apply the values that you enter to all fields.
2. Enter new values for one or more of the following parameters:

   • $R_n^{\alpha }$, convergence criterion for the ratio of the largest residual to the corresponding average flux norm for convergence. Default $R_n^{\alpha }=5\times {10}^{-3}$.

   • $C_n^{\alpha }$, convergence criterion for the ratio of the largest solution correction to the largest corresponding incremental solution value. Default $C_n^{\alpha }={10}^{-2}$.

   • ${\tilde{q}}_0^{\alpha }$, initial value of the time average flux for this step. The default is the time average flux from previous steps or ${10}^{-2}$ if this is Step 1.

   • ${\tilde{q}}_u^{\alpha }$, user-defined average flux. When this value is defined, ${\tilde{q}}^{\alpha }\left(t\right)={\tilde{q}}_u^{\alpha }$ for all t.

   The remaining items rarely need to be reset from their default values:

   • $R_P^{\alpha }$, alternative residual convergence criterion to be used after $I_P^{\alpha }$ iterations. Default $R_P^{\alpha }=2\times {10}^{-2}$.

   • ${ϵ}^{\alpha }$, criterion for zero flux compared to ${\tilde{q}}^{\alpha }$. Default ${ϵ}^{\alpha }={10}^{-5}$.

   • $C_{ϵ}^{\alpha }$, convergence criterion for the ratio of the largest solution correction to the largest corresponding incremental solution value when there is zero flux in the model. Default $C_{ϵ}^{\alpha }={10}^{-3}$.

   • $R_l^{\alpha }$, convergence criterion for the ratio of the largest residual to the corresponding average flux norm for convergence to be accepted in one iteration (that is, for a linear case). Default $R_l^{\alpha }={10}^{-8}$.

   • $C_f$, field conversion ratio used in scaling the relationship between two active fields when one is of negligible magnitude. Default $C_f=1.0$.

   • ${ϵ}_l^{\alpha }$, criterion for zero flux compared to the time averaged value of the largest flux ${\tilde{q}}_{\max }^{\alpha }$ in the model during the current step. Default ${ϵ}_l^{\alpha }={10}^{-5}$.

   • ${ϵ}_d^{\alpha }$, criterion for zero displacement increment (and/or zero penetration if the Convert severe discontinuity iterations setting for the step is On) compared to the characteristic element length in the model. This item is used only for the displacement field and warping degree of freedom equilibrium equations. Default ${ϵ}_d^{\alpha }={10}^{-8}$.

At any time you can click System-defined Defaults for this Page to return all parameters on this tabbed page to their system-defined default values. For more information, see Defining Tolerances for Field Equations.

1. Toggle on Discontinuous analysis to set $I_0=8$ and $I_R=10$. These settings can help avoid premature cutbacks of the time increment.
2. Enter new values for one or more of the following parameters:

   • $I_0$, number of equilibrium iterations (without severe discontinuities) after which the check is made whether the residuals are increasing in two consecutive iterations. Minimum value is $I_0=3$. Default $I_0=4$. If you toggled on Discontinuous analysis, $I_0=8$ and cannot be changed.

   • $I_R$, number of consecutive equilibrium iterations (without severe discontinuities) at which logarithmic rate of convergence check begins. Default $I_R=8$. If you toggled on Discontinuous analysis, $I_R=10$ and cannot be changed. The logarithmic rate of convergence is not checked if fixed time incrementation is used.

   The remaining items rarely need to be reset from their default values:

   • $I_P$, number of consecutive equilibrium iterations (without severe discontinuities) after which the residual tolerance $R_p$ is used instead of $R_n$. Default $I_P=9$.

   • $I_C$, upper limit on the number of consecutive equilibrium iterations (without severe discontinuities), based on prediction of the logarithmic rate of convergence. Default $I_C=16$.

   • $I_L$, number of consecutive equilibrium iterations (without severe discontinuities) above which the size of the next increment will be reduced. Default $I_L=10$.

   • $I_G$, maximum number of consecutive equilibrium iterations (without severe discontinuities) allowed in consecutive increments for the time increment to be increased. Default $I_G=4$.

   • $I_S$, maximum number of severe discontinuity iterations allowed in an increment if the Convert severe discontinuity iterations setting for the step is Off. Default $I_S=12$. This parameter is not used if the Convert severe discontinuity iterations setting for the step is On.

   • $I_A$, maximum number of cutbacks allowed for an increment. Default $I_A=5$.

   • $I_J$, maximum number of severe discontinuity iterations allowed in two consecutive increments for the time increment to be increased if the Convert severe discontinuity iterations setting for the step is Off. Default $I_J=5$. This parameter is not used if the Convert severe discontinuity iterations setting for the step is On.

   • $I_T$, minimum number of consecutive increments in which the time integration accuracy measure must be satisfied without any cutbacks to allow a time increment increase. Default $I_T=3$. Maximum allowed $I_T=10$.

   • $I_S^c$, maximum number of severe discontinuity iterations allowed in an increment if the Convert severe discontinuity iterations setting for the step is On. Default $I_S^c=50$. This parameter serves only as a protection against failure of the default convergence criteria and should rarely need to be changed. This parameter is not used if the Convert severe discontinuity iterations setting for the step is Off.

   • $D_f$, cutback factor used when the solution appears to be diverging. Default $D_f=0.25$.

   • $D_C$, cutback factor used when the logarithmic rate of convergence predicts that too many equilibrium iterations will be needed. Default $D_C=0.5$.

   • $D_B$, cutback factor for the next increment when too many equilibrium iterations ($I_L$) are used in the current increment. Default $D_B=0.75$.

   • $D_A$, cutback factor used when the time integration accuracy tolerance is exceeded. Default $D_A=0.85$.

   • $D_S$, cutback factor used when too many iterations ($I_S$) arise because of severe discontinuities. Default $D_S=0.25$.

   • $D_H$, cutback factor used when element calculations have problems such as excessive distortion in large-displacement problems. Default $D_H=0.25$.

   • $D_D$, increase factor when two consecutive increments converge in a small number of equilibrium iterations ($I_G$). Default $D_D=1.5$.

   • $W_G$, ratio of average time integration accuracy measure over $I_T$ increments to the corresponding tolerance for the next allowable time increment to be increased. Default $W_G=0.75$.

   • $D_G$, increase factor for the next time increment, as a ratio of the average integration accuracy measure over $I_T$ increments to the corresponding tolerance, when the time integration accuracy measure is less than $W_G$ of the tolerance during $I_T$ consecutive increments. Default $D_G=0.8$.

   • $D_M$, maximum time increment increase factor for all cases except dynamic stress analysis and diffusion-dominated processes. Default $D_M=1.5$.

   • $D_M$, dyn, maximum time increment increase factor for dynamic stress analysis. Default $D_M=1.25$.

   • $D_M$, diff, maximum time increment increase factor for diffusion-dominated processes (creep, transient heat transfer, soils consolidation, transient mass diffusion). Default $D_M=2.0$.

   • $D_L$, minimum ratio of proposed next time increment to $D_M$ times the current time increment for the proposed time increment to be used in a linear transient problem. This parameter is intended to avoid excessive decomposition of the system matrix and should be less than 1.0. Default $D_L=0.95$.

   • $D_E$, minimum ratio of proposed next time increment to the last successful time increment for extrapolation of the solution vector to take place. Default $D_E=0.1$.

   • $D_R$, maximum allowable ratio of time increment to stability limit for conditionally stable time integration procedures. Default is 1.0.

   • $D_F$, fraction of stability limit used as current time increment when the time increment exceeds the above factor times the stability limit. This value cannot exceed 1.0. Default 0.95.

   • $D_T$, increase factor for the time increment directly before a time point or end time of a step is reached. This parameter is used to avoid the small time increment that is sometimes necessary to hit a time point or to complete a step and must be greater than or equal to 1.0. If output or restart data are requested at exact times in a step, the default $D_T=1.25$; otherwise, the default $D_T=1.0$.

   At any time you can click System-defined Defaults for this Page to return all parameters on this tabbed page to their system-defined default values. For more information, see Controlling the Time Incrementation Scheme.

• $T^{vol}$, volumetric strain compatibility tolerance for hybrid solid elements. Default $T^{vol}={10}^{-5}$.

• $T^{axial}$, axial strain compatibility tolerance for hybrid beam elements. Default $T^{axial}={10}^{-5}$.

• $T^{tshear}$, transverse shear strain compatibility tolerance for hybrid beam elements. Default $T^{tshear}={10}^{-5}$.

• $T^{cont}$, contact and slip compatibility tolerance. If the Convert severe discontinuity iterations setting for the step is On, the ratio of the maximum error in the contact or slip constraints to the maximum displacement increment must be less than this tolerance.

  If the Convert severe discontinuity iterations setting for the step is Off, this item is used only with softened contact specified in the contact interaction property. The ratio of the error in the soft contact constraint clearance to the user-specified clearance at which the contact pressure is zero must lie below this tolerance for $p>p^0$, where $p^0$ is the pressure value at zero clearance. Default $T^{cont}=5\times {10}^{-3}$.

• $T^{soft}$, soft contact compatibility tolerance for low pressure. This tolerance, which is used only if the Convert severe discontinuity iterations setting for the step is Off, is similar to $T^{cont}$ for softened contact, except that it represents the tolerance when $p=0.0$. The actual tolerance will be interpolated linearly between $T^{cont}$ and $T^{soft}$ for $0\le p\le p^0$. Default $T^{soft}=0.1$.

• $T^{disp}$, displacement compatibility tolerance for distributing coupling elements. The ratio of the error in the distributing coupling displacement compatibility to a measure of the characteristic length of the coupling arrangement must lie below this tolerance. This characteristic length is twice the average of the coupling node arrangement principal radii of gyration. Default $T^{disp}={10}^{-5}$.

• $T^{rot}$, rotation compatibility tolerance for distributing coupling elements. Default $T^{rot}={10}^{-5}$.

At any time you can click System-defined Defaults for this Page to return all parameters on this tabbed page to their system-defined default values. For more information, see Defining Tolerances for Constraint Equations.

• $N^{ls}$, maximum number of line search iterations. Default $N^{ls}=0$ for steps that use the Newton method and $N^{ls}=5$ for steps that use the quasi-Newton method. A suggested value for activation of the line search algorithm is $N^{ls}=5$. Specify $N^{ls}=0$ to forcibly deactivate the method.

• $s_{max}^{ls}$, maximum correction scale factor. Default $s_{max}^{ls}=1.0$.

• $s_{min}^{ls}$, minimum correction scale factor. Default $s_{min}^{ls}=0.0001$.

• $f_s^{ls}$, residual reduction factor at which line searching terminates. Default $f_s^{ls}=0.25$.

• ${\eta }^{ls}$, ratio of new to old correction scale factors below which line searching terminates. Default ${\eta }^{ls}=0.10$.

At any time you can click System-defined Defaults for this Page to return all parameters on this tabbed page to their system-defined default values. For more information, see Activating the “Line Search” Algorithm.

For most crack propagation simulations using VCCT or the enhanced VCCT criterion, the deformation can be nearly linear up to the point of the onset of crack growth; past this point the analysis becomes very nonlinear. In this case linear scaling can be used to reduce the solution time effectively to reach the onset of crack growth. For more information, see Linear Scaling to Accelerate Convergence for VCCT in Abaqus/Standard.

• $I_{PI}$, iteration number at which the periodicity condition is first imposed. Default $I_{PI}=1$.

• $C{R}_n^{\alpha }$, stabilized state detection criterion for the ratio of the largest residual coefficient on any terms in the Fourier series to the corresponding average flux norm. Default $C{R}_n^{\alpha }=5\times {10}^{-3}$.

• $C{U}_n^{\alpha }$, stabilized state detection criterion for the ratio of the largest correction to the displacement coefficient on any terms in the Fourier series to the largest displacement coefficient. Default $C{U}_n^{\alpha }=5\times {10}^{-3}$.

• $C{R}_0^{\alpha }$ , plastic ratcheting detection criterion for the ratio of the largest residual coefficient on the constant term in the Fourier series to the corresponding average flux norm. Default $C{R}_0^{\alpha }=5\times {10}^{-3}$ .

• $C{U}_0^{\alpha }$ , plastic ratcheting detection criterion for the ratio of the largest correction to the displacement coefficient on the constant term in the Fourier series to the largest displacement coefficient. Default $C{U}_0^{\alpha }=5\times {10}^{-3}$ .

At any time you can click System-defined Defaults for this Page to return all parameters on this tabbed page to their system-defined default values. For more information, see Controlling the Solution Accuracy in Direct Cyclic Analysis.