Parametric Study

A Parametric Study is used to optimize the design of your models. A typical goal is to minimize the weight of a part or assembly while staying within allowable stress and displacement criteria.

For models originating in Autodesk® Inventor®, you can automatically run a batch of linear static stress analyses using the Parametric Study feature. Parameters are dimension variables defined in Inventor. You can choose one or more parameters that you would like to vary in an attempt to optimize your design. Every combination of the specified parameter values is then analyzed and the weight, stress, and displacement results compared.

Attention: There is currently a known limitation in the interoperability between Autodesk Inventor and Simulation Mechanical that affects whether a Parametric Study will be successful:

• When PUSHING the CAD model from Inventor to Simulation Mechanical 2014, the model must be pushed from Inventor 2014. A Parametric Study cannot be run on a model pushed from Inventor 2013 to Simulation Mechanical 2014.
• However, a Parametric Study can be run successfully for an Inventor 2013 model if the CAD file is PULLED into Simulation Mechanical 2014. That is, you must open the CAD file from the File Open dialog box within Simulation Mechanical rather than initiating the model transfer from within Inventor.

Prior to executing the Parametric Study command, you must complete the following tasks:

• Apply the loads and constraints upon which the results will be based.
• Specify the mesh settings and optionally apply mesh refinement if desired. The specified mesh size, options, and refinement will be used as the basis for all Parametric Study iterations.

In addition, you may wish to perform the following optional tasks:

• Mesh the model.
• Run the simulation based on the initial geometry, as-imported.

These mesh and simulation tasks will be automatically performed multiple times as part of a Parametric Study. However, it is useful to visualize the mesh size and quality in order to determine if different settings or local refinement would be beneficial. Also, running an initial simulation gives you some baseline results, which may help you to determine a suitable range of values for your parametric study.

To begin a Parametric Study, click the Setup Model Setup Parametric Study () command. The procedure for completing the study is outlined below.

Step 1 – Choose the Parameters to Vary

The first window contains a list of all model parameters, arranged into the following columns:

• Name: The names of the parameters are listed in this column, grouped according to the assembly part and feature to which each parameter belongs. For example, within a given part, the feature Extrusion2 would be followed by a list of the parameters that comprise this feature. Then, the next feature (such as Circular Pattern1 ) would appear, followed by the parameters that comprise it. Each parameter name is preceded by a checkbox. Activate the checkbox for each parameter that you wish to vary for your study.
  Tip: It is usually best not to vary too many parameters in a single study, for two reasons...
  • It is more difficult to gauge the sensitivity of the results to changes in a particular parameter when other parameters are also being changed.
  • The study may take a long time to complete because of the large number of combinations of parameter values. For example, if four parameters are varied and each has five possible values specified, the number of combinations of values for the study is 625 (5⁴). This means that the model would have to be meshed and solved 625 times to complete the parametric study.
• Value: The current value of the parameter, as specified in the CAD model.
• Units: The units of the parameter (for example, mm or degrees).

Press the Next button to proceed to step 2, or click Setup/Run in the navigation frame along the left side of the dialog box.

Step 2 – Modify the Parameters and Start the Analysis

In this step, the parameters to vary, as selected in the previous step, are now listed in the dialog box. You can specify the values for each parameter using one of the following four methods:

1. Enter a single numerical value (such as 37.5).
2. Enter a list of discrete numerical values, separated by semicolons (such as 2.5;2.75;3;3.5).
3. Enter a range of values and the total number of values using the syntax...

   StartValue-StopValue:NumberOfValues

   Example: 5-10:3

   Equivalent to: 5;7.5;10)

4. Enter a range of values and the increment using the syntax...

   StartValue-StopValue|Increment

   Example: 10-16|2

   Equivalent to: 10;12;14;16

Notes:

• For discrete lists and ranges (methods 2 through 4 above), the values must be in ascending order.
• For method 4, the increment cannot exceed the difference between the start and stop values. For example, 5-10|6 is not a legal input since the increment (6) exceeds the range of values (10-5 = 5).

Once the parameter values have been specified, click the Run button to begin the batch of analyses. Progress bars are provided for the overall study and the current iteration. Annotations to the right of the progress bars indicate how many analyses have been completed, how many are required, the current process running (such as Meshing or Processor solving ), and the percent completion (overall and for the current iteration). Every combination of the specified parameters will be analyzed.

During execution, the Run button will change to a Stop button. Click this button to halt the batch of analyses at the present level of progress.

When the analysis has been stopped, you can click the Restart button to resume the batch of analyses. It will continue from where it was stopped. Already completed iterations do not have to be solved again. The Restart button will be grayed-out if the study has not been stopped or has run to completion.

When run to completion, the study will automatically advance to the step 3 dialog box.

Step 3 – Create Filters and Review the Results

Once all iterations of your parametric study have been completed, a summary of the results appears. For each parametric study iteration, a new set of model files is created and placed in a subfolder named pStudy_x, where x is the iteration number. Each of these subfolders is located in a folder named modelname.pStudy, where modelname is the name of your original model. The modelname.pStudy folder resides in the same location as the original modelname.fem file.

At the top of the dialog box is a table of the upper and lower limits for the following three results:

• Maximum von Mises Stress
• Weight
• Maximum Displacement

By default, the full range of each result is listed in the table.

Below the upper and lower limits table is a summary of the results for each combination of parametric values that was analyzed. The columns contain the following information:

• Index: An identifying number assigned to each parameter combination.
• Maximum von Mises Stress
• Weight
• Maximum Displacement
• Preview: A thumbnail image of the model. If you double-click a preview image, the model representing the specific combination of parameters for this index is opened in a new Simulation Mechanical session.

Important: The von Mises stress magnitudes listed by the parametric study are based on the unsmoothed results. The smoothed stresses are generally shown by default in the Results environment, and these smoothed stresses are smaller in magnitude than the unsmoothed stresses. For the von Mises results contour and legend to match the parametric study results, turn off smoothing—Results Contours Settings Smooth Results ( )

Note: If a combination of parameters results in invalid geometry, or if a particular iteration fails to mesh or solve, the following image will appear in the Preview column:

To Filter Your Results

You can apply a filter to the table to hide iterations with results that are outside of target design guidelines. To apply a filter, take one or more of the following actions and then click the Apply button:

• Decrease the Upper Limit for one or more of the three results.
• Increase the Lower Limit for one or more of the three results.

Any iteration with a result greater than a user-specified Upper Limit and any iteration with a result less than a user-specified Lower Limit will be removed from the results summary table.

Click the Disable button to clear your filters and to return to the full range of results.

Note: When a filter is applied, invalid results are removed from the table. If the filter is then disabled, the invalid results are NOT restored to the table. Once hidden, they remain hidden.

To Save Your Parametric Study Results

If you exit the Parametric Study without saving the results summary, your results comparison table will be lost. However, the models in the modelname.Pstudy folder will remain.

Click the Save button, specify the desired file name and location, and click Save. The results table is saved in a .CSV (comma separated values) text file. The following columns comprise the CSV file:

• Index
• Maximum von Mises Stress
• Weight
• Maximum Displacement
• Path to .fem File
• CAD Parameters

The units are indicated in the header row for applicable columns.

General Notes:

• Use the Next or Prev button to move to the next or previous step of the Parametric Study, respectively.
• You can also jump to any of the three steps of the Parametric Study by clicking on Parameter(s), Setup/Run, or Results in the navigation frame along the left edge of the dialog box.
• You can close the Parametric Study and return to the FEA Editor environment by either clicking the FEA-Editor button or the X icon in the upper-right corner of the dialog box.
• When you close the Parametric Study prior to analyzing all of the iterations, the setup is discarded. You will have to reselect the parameters and redefine the values prior to running a study. The parameter values shown will be the last ones analyzed, if a previous study has been at least partially completed. The original parameter values are overwritten during the study.