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EMENDATE_SERVICE_NASTRAN | C:\Program Files\MSC.Software\MSC_Nastran\2023.2\bin\nast20232.exe |
Initializing the frequency optimisation:
In a first step a frequency Event has to be created. A frequency Event should only consists of displacement constraints without any loads or moments.
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The frequency constraint can directly set in the GD Scenario:
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Frequency Constraint
The Frequency Constraint (in Hz) is 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.
As an optional input the range and the number of frequencies which are taken into account for the optimisation can be modified with the Advanced User Settings.
Post Processing
The calculated first eigenfrequency over the iterations can be observed with a chart in the Post Processing. The frequency Event does not create any visible plots for the Failure Criterion or Stress on the geometry. But the influence of the frequency Event can be observed with the optimization achievement index which shows where material will be added (>0) to increase the first eigenfrequency of the part.
Known Limitations
Symmetry
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Symmetry and a Frequency Event cannot be set up together. Some of the Eigenfrequency modes will be asymmetric. |
Frequency Constraint
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If the Frequency Constraint is higher than the first calculated Eigenfrequency of the whole Design Space in the first Iteration, this can lead to the case that no material will be reduced. This can be resolved by reducing the Frequency Constraint or by entering the following command to the Advanced User Settings: |
schedule.iterations.~.operator.optloop_loop_analysis_Event-2_extractLocalFailures.useMetricGoalFactor=1 |
Point Masses
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It has been found that comparable heavy point masses can cause that the optimisation does not achieve the Frequency Constraint. To address this the impact value can be set up to a value greater than 1. This can be done with the following Advanced User Settings command: |
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pointMass.PointMassInertia_Point_Mass_1.type=RBE2 |