Step controls is a very tough business in ANSYS® Mechanical analyses. It is very important to adjust the steps of analyses according to the loads, conditions, and response frequencies of a system. You can use step options in transient structural analyses and static structural analyses in ANSYS®.
You can adjust the application of loads and conditions by turning them on and off on time steps. This gives very good control to obtain the exact physical phenomenon in ANSYS® Mechanical.
Please do not forget that at the end of each step, solutions to the conditions defined in these steps are obtained. In the following steps, the solutions of previous steps are used with new conditions and loads.
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How To Adjust Time Steps In ANSYS® Mechanical Analyses?
Steps are generally used in transient analyses in ANSYS®. To make transient analyses in ANSYS®, you need to know how to adjust step controls.
In an analysis in ANSYS® Mechanical, click on ‘Analysis Settings’ as shown by the red arrow above, you will see all step controls as shown in the green box above.
- Number Of Steps: This is the first option in ‘step controls’. You can enter a value to define how many steps that you will use in your analysis.
- Current Step Number: You can make discrete adjustments on each step in ANSYS® Mechanical. For example, if you enter a number inside ‘Current Step Number’, you can make adjustments to that step. The step controls after this option related to the current step number.
- Step End Time: This is the time that the selected step in ‘Current Step Number’ when it will over.
- Auto Time Stepping: This is a very important adjustment that you can turn on or off in ANSYS® Mechanical. If you have a physical system that has nonlinear and dynamic loads and responses, the use of the auto time stepping option can be very useful. If you turn the auto time stepping option on, there will three values appear that you need to adjust for that current step number.
- Initial Time Step: This is about the starting of the selected step. When the step starts, the loads or conditions will be applied and solved at the end of this initial time step. These sub-solutions will be used in the next sub-step.
- Maximum Time Step: Auto time-stepping divides the selected step in ‘Current Step Number’. This is the biggest increment of time inside a step that auto time stepping will make. You can define a value inside it.
- Minimum Time Step: This will be the minimum time step value inside the selected step in ‘Current Step Number’.
The accuracy of nonlinear, dynamic analyses performed in ANSYS® Mechanical depends on the definition of smaller minimum time steps allowed.
Definition of time step properly is very important. In general applications, the time step is defined as 1/(20*f) in which ‘f’ is the response frequency of a system.
If your system has contacts, it is recommended from ANSYS® to use 1/(30*fc), in which fc is contact frequency.
These auto time stepping options are important for where there are abrupt changes in loads and nonlinear responses from a system. In other steps that there are no these kinds of abrupt changes, you do not need to use strict time stepping options.
If you make the ‘Auto Time Stepping’ option off, you can directly define one value called ‘Time Step’ for a selected step.
Also, you can define the ‘Auto Time Stepping’ as sub-steps instead of time. It has the same logic with adjusting it as time.
- Time Integration: This is an option in transient analyses in ANSYS®. By default, this is ‘On’. With this, you can include transient effects such as inertial effects. It is recommended to be ‘On’ to find out all the results related to inertial effects. Otherwise, they will be 0 in solution.
- Carry Over Time Step: If you are using substeps and multiple steps, this option will be available. If you do not want abrupt changes on loads and conditions between steps, you can turn it on. If you want to initial time step is equal to the minimum time step, you can use this option also.
Conclusion For Time Step Options In ANSYS® Analyses
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So, it is very important to adjust steps according to your physical model in ANSYS® Mechanical. According to your physical requirements, proper optimization of steps with the guide of the information above in ANSYS®.
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NOTE: All the screenshots and images are used for educational and informative purposes. Images used courtesy of ANSYS, Inc.