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The eigenfrequency optimisation is added as an experimental new function in this release. The option can be activated and set-up with the Advanced User Settings as for a separate event and therefore additionally to a static load casecases.
The eigenfrequencies for each iteration of the optimisation process are calculated by MSC Nastran. Therefore, MSC Nastran has to be installed on the same machine and a valid license is required.
The
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path to the MSC Nastran executable can be set manually in the application settings:
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
EMENDATE_SERVICE_NASTRAN | C:\Program Files\MSC.Software\MSC_Nastran\2023.2\bin\nast20232.exe |
Initializing the frequency
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event.EventFA.strategy=conditionBasedFrequencyAnalysis event.EventFA.frequencyTarget=170 event.EventFA.safetyFactor=1 |
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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 . By default the first 10 eigenmodes are considered to an upper frequency limit of 3 times the frequency target.
event.EventFA.frequencyMax=4500 |
Advanced User Settings to copy Boundary Conditions from an already existing Event:
Since the eigenfrequency optimisation isn’t integrated into the GUI yet, Boundary Conditions (Fixations) can be copied from a static event. Therefore, the following command needs to be added:
event.EventFA.condition.\.include = event.Event_1.condition |
Event_1 is the static Event from which the BCs will be copied.
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Advanced User Settings to create a Point Mass:
pointMass.pointMass1.geometryName=ModelLoadEvent_Force_-_Moment_1 |
Point Masses can also be considered in a frequency event. A Point Mass can only be attached to surfaces where a Force is already applied to. The geometry name has to be linked correctly.
Furthermore, the coordinate point of the Point Mass, the mass itself and the connection type (RBE2, RBE3) to the surface need to be enteredwith 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
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Constraint
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If the Frequency Target 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 Target Constraint or by entering the following command to the Advanced User Settings: |
schedule.iterations.~.operator.optloop_loop_analysis_EventFAEvent-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 TargetConstraint. 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: |
event.EventFAEvent_2.impact=1.5 |
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RBE2 can be used as a connection type, but the RBE2 connection won’t be considered in a static load case. This can occur if a Point Mass is added in combination with acceleration. In this case, the static load of the point mass will be considered with a RBE3 connection.. |
pointMass.PointMassInertia_Point_Mass_1.type=RBE2 |