# Performing Nonlinear Analysis

## Notes on Defining Nonlinear Studies

- When defining a nonlinear study, you can choose a static or dynamic study. Nonlinear studies are solved in the time domain.
- Nonlinear analysis requires specifying a solution control method. The interface uses the Force control method by default as it is the proper choice in most cases. The Force control method allows you to control each load and restraint individually by a time curve. The Displacement and Arc-Length control methods calculate a multiplier for all loads at each solution step. In other words, all loads are changed proportionally at each solution step.
- To select the Displacement or the Arc-Length control method, click the Advanced Options button in the Solution tab.
- The Start time and End Time specified in the Solution tab, in seconds, are not used by the Arc-Length control method. Time values are pseudo values unless: 1) you are using material models with creep effects, 2) you are considering thermal effects from a transient thermal study.
- Time values are always real for nonlinear dynamic studies.
- The time increment in the Solution tab is interpreted based on the control method selected. For the Force and Displacement control methods, it is used to progressively increment time from Start time to End Time. For the Arc-Length control method, it is used internally to estimate an initial incremental value for the arc length. The solution stops based on parameters specified in the Advanced Options tab.
- The Restart option allows you to continue a solution from the last successful solution step. To make a study restartable, you must select the Save data for restarting the analysis before running the study. To restart a problem for which restart information is available, select the Restart check box in the properties of the study before running.

**Parent topic**Nonlinear Static Analysis

## Performing Nonlinear Analysis Using Force Control

To perform nonlinear analysis using Force control:

## Performing Nonlinear Static Analysis Using Displacement Control

To perform nonlinear static analysis using Displacement control:

- Create a nonlinear static study.
- Right-click the study's icon and select Properties.
- In the Solution tab, specify Start time, End time, Time increment parameters, and check the desired settings in the Geometry nonlinearity options and Solver boxes.
- Click the Advanced Options button to select the Displacement control method and set the Displacement control options where you specify the controlling degree of freedom as a function of time. This is the only time curve used by the Displacement control method. The time range should cover Start time and End time.
- To consider thermal or flow effects, click the Flow/Thermal Effects tab and set the desired options.
- Click OK.
- Define material properties, mesh, loads and restraints. No load or restraint is associated with a time curve.
- Right-click the Result Options folder in the tree to specify result saving options.
- Run the study and view the results as function of the load parameter.

## Performing Nonlinear Static Analysis Using Arc-Length Control

To perform nonlinear static analysis using Arc-Length control:

- Create a nonlinear static study
- Right-click the study's icon and select Properties.
- In the Solution tab, ignore Start time and End time. Specify Time increment parameters, and check the desired settings in the Geometry nonlinearity options and Solver boxes. The time increment is used internally by the program to calculate the initial arc-length for each step.
- Click the Advanced Options button to select the Arc-Length control method and set the Arc-Length completion options where you specify the termination scheme.
- To consider thermal or flow effects, click the Flow/Thermal Effects tab and set the desired options.
- Click OK.
- Define material properties, mesh, loads and restraints. No load or restraint is associated with a time curve.
- Right-click the Result Options folder in the tree to specify result saving options.
- Run the study and view the results as function of the load parameter.