The eigenfrequencies of a part play an important role in the process of creating a new design.
The eigenfrequency optimisation is added as an experimental function in this release. The option can be activated and set-up with the Advanced User Settings as a separate event and therefore additionally to a static load case.
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 environment variable has to be set manually:
EMENDATE_SERVICE_NASTRAN | C:\Program Files\MSC.Software\MSC_Nastran\2023.2\bin\nast20232.exe |
Initializing the frequency event in the Advanced User Settings:
event.EventFA.strategy=conditionBasedFrequencyAnalysis event.EventFA.frequencyTarget=170 event.EventFA.safetyFactor=1 |
The Frequency Target (in Hz) is the target for the first occurring eigenfrequency of the part.
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.
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 entered.
Known Limitations
Symmetry
Symmetry and a Frequency Event cannot be set up together. Some of the Eigenfrequency modes will be asymmetric.
Frequency Target
If the Frequency Target 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 or by entering the following command to the Advanced User Settings:
schedule.iterations.~.operator.optloop_loop_analysis_EventFA_extractLocalFailures.useMetricGoalFactor=1 |
Point Masses
It has been found that comparable heavy point masses can cause that the optimisation does not achieve the Frequency Target. 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.EventFA.impact=1.5 |
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.
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