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
checkbox in the properties of the study before running.
You must decide what control method to use.
Force
control is the most common and it is the only one available
for dynamic nonlinear studies. However, the Displacement
or Arc-Length control methods
can be more appropriate to use for
some class of problems. Contact is supported with the Force control method
only.
To perform nonlinear analysis using Force
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.
In most cases, you do not
need to click the Advanced Options
button, where you can set the Iterative
method and the Step/Tolerance options.
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.
You can associate
each load and restraint with a different time
curve. The time range for each curve should cover the Start time and End
time.
Define damping.
Applicable for nonlinear dynamic studies only.
Right-click the Result Options
folder in the tree to specify result saving options.
Run
the study and view
the results at different times (solution steps).
When you run a study that
does not have any result folders, the software creates the folders and
plots specified in the Result
Options for the study type. If result folders are present,
the software updates the existing plots.
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.
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.