# Multi-step and time-varying settings in dynamics simulation

April 28, 2023

Nowadays, it is often vital to set multi-step conditions and time-varying boundary conditions when modeling real engineering problems. These requirements bring challenges to simulation softwares. Not only does the solver needs to support multiple steps, but the graphical user interface also should provide convenient and easy input methods. WELSIM started supporting multi-step analysis as early as 2019. For details, please refer to the article “Multi-step quasi-static structural finite element analysis”. Recently, with the support of the explicit dynamic analysis software, OpenRadioss, multi-step analysis related features have gained more attention. This article discusses the multi-step and time-varying boundary condition features in WELSIM with a real-world engineering example.

Among various multi-step models, metal sheet forming has both die-casting and separation steps, which is a typical multi-step working case. The example is shown in the figure below. When the punch is pressed down, the sheet metal will bend under force, resulting in plastic deformation. Then, the punch and holder spring back and separate from the deformed sheet. In this instance, molds and fixtures are rigid bodies, and the sheet metal part is an elastic-plastic body. All shapes are meshed as shell elements.

## Multi-steps and time settings

When the meshing is completed, and the contact pairs are defined, it’s necessary to perform multi-step settings for the analysis. Increase the number of steps as needed, set the time for each step, and define the number of substeps for each iteration. Here, we set the model to 5 steps total. However, the total number of sub-steps is set at 1000, so 1000 result files will be generated.

After setting the time, the user can double-click “Study Settings” to display a list of quantities at each step, as shown in the figure below. The time of each step here is 0.3, 0.5, 0.9, 1, and 1.2 seconds respectively. Users can check that the time is set properly. Once he or she is done looking the time table over, the user can click the red “x” to close the tab.

In this model, the boundary conditions that vary with load steps (time) are forces and velocities. Firstly, users need to set the properties of these boundary conditions as Tabular, and then assign table data. As shown in the example below, change the property data type in the lower left area. The table on the right lists the velocity values for each step, and the user can edit the specific values as needed. The Chart window at the bottom shows velocity over time for improved visualization.

The time of each step is uniform and constant, and cannot be adjusted in the current boundary conditions. When changing the time is necessary, the user can modify it in the properties of “Study Settings”.

So far, the multi-step analysis setting is completed.

Once you generate the OpenRadioss solver scripts for this model, it will accurately display the multi-steps and velocity values settings in the input scripts, as shown in the picture below.

Obviously, it is easy and user-friendly to define multi-steps and time-varying boundary conditions in WELSIM, and generate relevant OpenRadioss solver scripts.

The result animation of the given analysis is shown below.

WELSIM has supported multi-step features since 2019. The multi-step OpenRadioss solver script has been added in the 2023R3 development release. The features related to multi-steps will be continuously enhanced in future versions.

WelSim and the author are not affiliated with OpenRadioss. OpenRadioss is used only as a nominative reference to the open-source project and softwares developed and released by these teams or institutions.

WelSim is an independent engineering simulation software provider, located in Greater Pittsburgh, PA. Its flagship product WESLIM is a general-purpose engineering simulation software with an all-in-one graphical user interface and self-integrated features.