Derived Load Cases

The Loadcase tool allows you to create a derived load case from other load cases, or from a combination of other load cases and simulation steps.

From the Results toolbar, click Derived Load Steps .
Note: You can also select Create > Derived Load Steps from the Results menu.
There are three types of derived load cases available:
  • Steps
  • Linear-Superposition
  • Envelope

Recent enhancements have been made which involve the creation of a Linear-Superposition or Envelope loadcase composed of base and derived loadcases. Finding the minimum or maximum of envelopes, or the maximum value of a set of linear combination loadcases is now possible.

See the Envelope or Linear Superposition of Base and Derived Loadcases section for additional information.

Attention: The Envelope utility is not intended for use with Tensor or Vector plots. If it is used with a Tensor or Vector plot, Altair HyperView will simply draw the last loadstep in the derived loadstep list.
The Type drop-down menu is used to select the desired load case that you would like to create.


Figure 1. Type drop-down menu
The Loadsteps section lists all the loaded results files in the current session, as well as all the loadsteps/simulations corresponding to each result file, in a tree-like structure. You can select simulation steps from the derived loadstep list by selecting them with your mouse or the arrow keys. Use the blue right/left arrows (add/remove buttons), to add or remove the required loadsteps/simulations to or from the derived loadstep. In addition, keyboard shortcuts and a context menu are available for items within the list.
Note: Multiple loadsteps can be selected in the table/list using the standard CTRL/SHIFT+click functionality.
Tip: You can use the All, None, Reverse buttons to quickly select/deselect loadsteps listed in the current view of the tree structure.

In addition, the derived load cases list can be displayed by clicking on the View Derived Load Cases icon.

Derived loadsteps can also be saved or imported as configuration files (*.cfg) using the buttons below:
Use To
Save Save the definition of the current derived loadsteps as a configuration file.
Open Import/read a previously saved derived loadstep configuration file.
Note: Click the following link to see a Sample Derived Loadsteps Configuration File.

Steps

The Steps type is used to create a derived loadstep from other loadsteps. A derived loadstep can contain more than one simulation step, with scale factors optionally applied to them.
The Select loadstep drop-down menu is used to select the derived loadstep that you would like to be active.


Figure 2. Select loadstep drop-down menu
Upon selecting a derived loadstep, the simulation steps contained within that derived loadstep are displayed in the table below the drop-down menu.


Figure 3. Example derived loadstep table
The table contains the following categories:
Label
Displays the loadstep number and the time of each simulation step.
This field is not able to be edited.
Scale
Displays the scale factor that was defined for each loadstep/simulation step.
Note: The scale factor can be manually changed/edited.

Simulation steps can also be removed from a loadstep.

Linear Superposition

The Linear Superposition type is used to create a derived loadstep with only one simulation step, which is a combination of all the selected loadsteps/simulations with scale factors.

The Loadsteps section lists all the loaded results files in the current session, as well as all the loadsteps/simulations corresponding to each result file, in a tree-like structure.

In addition, the derived load cases list can be displayed by clicking on the View Derived Load Cases icon.

This section allows you to specify which loadstep(s), from the currently selected input file, to add to the linear combination definition.

Envelope

The Envelope type is used to identify the most significant loading conditions out of all the selected analysis loadsteps. This creates a derived loadstep with only one simulation step, which compares entity values and stores desired values from selected loadsteps (or animations) based on the Min/Max/Extreme/Range option that is chosen.

The Loadsteps section lists all the loaded results files in the current session, as well as all the loadsteps/simulations corresponding to each result file, in a tree-like structure.

The following envelope types are available:
Min
Finds the minimum values among all the selected loadsteps or simulations (weighted by the appropriate scale factors) defined within the derived loadcase.
Max
Finds the maximum values among all the selected loadsteps or simulations (weighted by the appropriate scale factors) defined within the derived loadcase.
Extreme
Finds the maximum absolute values among all the selected loadsteps or simulations (weighted by the appropriate scale factors) defined within the derived loadcase. The sign of the number is not changed however. For example, the Extreme of 5 and 10 is 10, and the Extreme of 5 and -10 is -10.
Range
Finds the difference between the maximum value and the minimum value among all the selected loadsteps or simulations (weighted by the appropriate scale factors) defined within the derived loadcase.
Note: Selecting this option will disable the Envelope trace plot option in the Contour panel.
The example below shows how the various Envelope types are calculated:


Figure 4.

When a particular layer is selected in the Contour panel, the Envelope value is obtained by cycling through all the loadsteps for that given layer, and the Min/Max/Range value is then reported. When the layer aggregate is set to Min/Max/Extreme/Average/Range, the result is calculated across all the layers including all the loadsteps defined for the Envelope.

It is possible to resolve a contour in global system. The value on the entity (element, node etc.) is first transformed into global system and then the envelope value is obtained by cycling through all the load steps for that entity.

The example table below shows the relation between layer aggregate modes (Min/Max/Range layers within the Contour panel) to an Envelope type of Min/Max/Range for an element with three layers (Top, Mid, and Bottom) across four loadcases (LC1, LC2, LC3, and LC4).


Figure 5.
The image below shows a contour plot with Min, Max, and Range as the Envelope types (the top row shows values from four different loadsteps):


Figure 6.

Envelope or Linear Superposition of Base and Derived Loadcases

In certain use cases, it may be useful to create an envelope or a linear combination of a derived loadcase. As an example of finding the maximum of a set of linearly combined loadcases, or just finding the minimum or maximum of different envelope type loadcases. From the base loadcases provided by the solver, you can create two levels of derived loadcases (as shown in the image below):


Figure 7.
At the second level (Level 2), any combination of base and derived loacases from the first level (Level 1) is allowed. To allow referencing the derived loadcases subsequently, these loadcases are displayed in the Create/Edit Derived Load Case dialog along with the base loadcases. Only the derived loadcase name is displayed in the tree. A full breakdown of a derived loadcase can be viewed by clicking on the View Derived Load Cases icon . You can also easily modify the definition of a derived loadcase by using the left and right arrows located in the middle of the dialog.
Figure 8.

Various checks are performed in order to try and prevent the creation of ill-defined derived loadcases. Among them, a recursive error is displayed when a loadcases is pointing to itself through recursion, or going through more than two levels of derived definition. The error message will be prompted with no action taken. It is also important to note that the newly created IDs for a derived loadcase (at level 2) are stored and restored from the session/report template file (and not necessarily the base loadcase IDs). In the case of envelope derived loadcases, the trace plot in the contour panel will display the derived loadcase ID where appropriate.

If loadcases from multiple result files are referenced, it is recommended that you include all the required result files prior to creating any derived loadcases. See the Result Files section for additional information regarding adding result files.

Note: A linear superposition combination of another set of linearly combined loadcases is not supported for complex data. After the first level of combination, the complex data is extracted and converted to real numbers in the result processing stage, thereby any subsequent combinations (linear additions) are done on the real data and not on complex math. You are advised to verify the results in these cases. The second level of derived loadcases is also disabled with certain file formats of the crash solvers, namely LS-DYNA, PAM-CRASH 2G, and Radioss.