Nonlinear - Advanced Options

The Advanced tab in the Nonlinear dialog box sets options for controlling the solution method. This tab appears only after clicking the Advanced Options button on the Solution tab. The following are the options to set on this tab (click any of them to get more information).

Method

Sets the control technique and the iterative method to be used.

Control Choose a control technique . Only Force control is available for dynamic studies.

Force

Use force control.

Displacement

Use Displacement control.

Arc length

Use Arc-length control.

Surface to surface formulation is used for no-penetration contacts when you select the Arc length Control method.
Iterative Sets the numerical technique to be used for iterations.

Newton-Raphson (NR)

Use the Newton-Raphson (NR) iterations.

Modified Newton-Raphson (MNR)

Use the Modified Newton-Raphson (MNR) iteration scheme.

Integration Sets the integration method.

Displacement control options

Select a vertex or reference point to control the analysis Select a vertex or a reference point to drive the solution. If you select a reference point, the program uses the closest node to the specified point.
Displacement component for the selected location Displacement component. Sets the displacement component to be used in the displacement control method. The valid components are:
UX: X Translation displacement in the Global X-direction
UY: Y Translation displacement in the Global Y-direction
UZ: Z Translation displacement in the Global Z-direction
RX: X Rotation rotation about the Global X-direction for shell studies only
RY: Y Rotation rotation about the Global Y-direction for shell studies only
RZ: Z Rotation rotation about the Global Z-direction for shell studies only
Displacement variation with time Click Edit to define a time variation of the displacement using the Time Curve dialog box. After defining the time variation of the selected displacement component, click Graph to view the displacement as a function of time.

Arc-Length completion options

Maximum load pattern multiplier The maximum load-pattern multiplier at which the solution is to be terminated (approximate value). Default is 1.0E8.
Maximum displacement (for translational DOF) The analysis terminates if any displacement DOF exceeds this value.
Maximum number of arc steps The analysis terminates if the number of arc length steps reaches this limit. Default is 50.
Initial arc length multiplier  

Step/Tolerance options

Sets convergence and equilibrium parameters.

Do equilibrium iteration every Sets the frequency of performing equilibrium in number of solution steps.
Maximum equilibrium iterations Sets the maximum number of equilibrium iterations for any solution step.
Convergence tolerance Relative displacement tolerance used for equilibrium convergence.
Maximum increment strain Sets tolerance for strain increment for models with creep or plasticity.
Singularity elimination factor (0-1) Sets stiffness singularity elimination factor (normal solution if set to 1; if less than 1.0, the program modifies stiffness terms causing singularity to help convergence). If normal solution fails, trying a different value, for example 0, may help convergence.
The table lists the features supported by the Direct Sparse and Intel Direct Sparse solvers for each Control method.
  Force Prescribed Displacement No Penetration Contact Force + Prescribed Displacement Prescribed Displacement + No penetration Contact Force + No penetration Contact Force + Prescribed Displacement+No penetration Contact
Force Control Yes Yes Yes Yes Yes Yes Yes
Displacement Control Yes No No No No No No
Arc Length Control Yes No Yes No No Yes No
Neither the Arc Length nor the Displacement Control method can resolve rigid body motions that can occur during a nonlinear solution. If you encounter a rigid body motion during a nonlinear analysis, use the Force Control method with a Prescribed displacement to improve chances of reaching convergence.