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Goal of this tutorial
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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.
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EMENDATE_SERVICE_NASTRAN | C:\Program Files\MSC.Software\MSC_Nastran\2023.2\bin\nast20232.exe |
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.
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Step 4: Frequency Constraint
As soon as one Event exists with only displacement constraint the frequency constraint can directly set in the GD Scenario:
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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
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In the Post Processing the first eigenfrequency for each iteration can be displayed in a chart.
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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.
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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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