Training:

Relevant data for this tutorial:

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Step 1: MSC Nastran preparation

To be able to use the Eigenfrequency Optimisation a MSC Nastran version with a valid license must be installed on the same machine.

The path to the MSC Nastran executable can be set manually in the application settings:

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Please use nast20233(.exe) (or the matching executable for your installed nastran version) for frequency analysis.

If you want to run the optimisation also via the command line you need the set up the following environment variable

Step 2: Open an already existing optimisation model / Set up a model as you are used to

The Eigenfrequency Optimisation is activated additionally to static events. Thus, the model can set up as every other optimisation.

For this Tutorial a beam model is used. The model is already completely set-up (Design Space, Interfaces, Loads & Boundary Conditions, Material assignment, optimisation parameters and static Events) for a static optimisation and in the following the Eigenfrequency Optimisation gets activated.

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Step 3: Frequency Event Creation

A frequency Event should only consists of displacement constraints without any loads or moments.

Step 4: Frequency Constraint

As soon as one Event exists with only displacement constraint the frequency constraint can directly set in the GD Scenario:

In this case the Frequency Constraint is set to 210 Hz as the target for the first occurring eigenfrequency of the part. Per default the first 10 eigenfrequencies in a range up to 3 times the frequency constraint value are considered. Based on these eigenmodes the part is stiffened to push the the first eigenfrequency upwards.

Step 5: Starting the Optimisation

The optimisation can be started as usual. In the background MSC Nastran will be called to calculate the eigenfrequencies and eigenmodes.

Step 6: Post Processing

In the Post Processing the first eigenfrequency for each iteration can be displayed in a chart.

The optimization achievement index for the frequency Event (Event_2) shows the influence of the eigenfrequencies on the design creation. Purple to red areas show the areas which need to grow to increase the eigenfrequency of the part.

To check the final eigenfrequencies of the part, please run a Re-Analysis with Apex structures.

Creation of a Point Mass

Step 7: Creating Point Masses for the Eigenfrequency Optimisation

Point Masses play an important role in the calculation of eigenfrequencies. Therefore, Point Masses can be created directly in Apex GD.

In this case a Point Mass of 0.1 kg is attached to the same spot (0; 402.50; 25.00) as the remote Force.

By default it is connected with a compliant connector (RBE3). Point Masses are after the creation automatically considered for a frequency optimisation. They are also considered for static load cases if an acceleration is active. For Frequency Optimisations the connector can also be changed to a rigid one (RBE2) with the Advanced User Settings.

Please have a look at all known limitations!

The complete MSC Apex GD project with all results can be downloaded here:

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