11.2 Adding an Analysis Step¶
An analysis step is added using the Physics → Add Step menu. Alternatively, you can also add a step by right-clicking on the Steps item in the Model Editor and select Add from the popup menu. A new step will be added to the Steps item in the model tree.
After the step was added, many settings can be modified to control how FEBio will solve the analysis step. Below, some of the most important settings are discussed. For more details, please consult the FEBio User Manual.
The analysis settings allow you to choose the specific analysis type. For instance, for structural mechanics problems, users can choose between steady-state or dynamic.
These settings control the basic time stepping and allows users to set the number of time steps and the size of each time step size. If no time step controller is specified, FEBio will use a fixed time stepping approach to solve the model.
Auto-time stepper
The auto-time stepper provides a way to adaptively adjust the time step size depending on how the solution progresses. The “default” auto-time stepper provides the following parameters.
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Max retries: the maximum number of times that a particular timestep will be retried.
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Optimal iterations: The expected average number of iterations required to converged a single time step.
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Min stepsize: the minimum stepsize that may be taken by the auto timestep controller.
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Max stepsize: the maximum stepsize that may be taken by the auto time step controller. Note that a load curve may be attached to this parameter. This load curve is often referred to as a must point curve. In addition to setting the max time step size, the must point curve also defines points through which the solution must pass. Also note that when a must curve point is defined, FEBio will ignore the value of max step (dtmax) variable.
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Aggressiveness: When set to 1, the time step size will be scaled by the cutback parameter.
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Cutback: scale factor for reducing time step size. Only used when aggressiveness is set to 1.
This property allows users to select from a list of solvers that can be used to solve the analysis. For example, for structural mechanics models, users can choose between an implicit and and explicit solver. Each solver has additional parameters and properties. Please consult the FEBio User Manual for details of the particular solvers.
Output settings
The output generated by FEBio can be controlled by the user. In general, FEBio produces a plot file, which contains the results of the FE analysis, and a log file. The log file stores the screen output from FEBio, but can be customized to store additional data. Alternatively, this additional can be written to separate files. See chapter 11 for more details on how to customize the FEBio output files.
The output settings of the step allow users to control the intervals at which FEBio will generate output during the step.