The eigenfrequencies of a part play an important role in the process of creating a new design.
The eigenfrequency optimisation is added as an new function in this release. The option can be activated for a separate event and therefore additionally to static load cases.
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 path to the 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 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.
The frequency constraint can directly set in the GD Scenario:
The Frequency Constraint (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 with the Advanced User Settings.
Known Limitations
Symmetry
Symmetry and a Frequency Event cannot be set up together. Some of the Eigenfrequency modes will be asymmetric.
Frequency Constraint
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
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:
event.Event_2.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.
0 Comments