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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 preperation
To be able to use the Eigenfrequency Optimisation a MSC Nastran version with a valid license must be installed on the same machine.
The environment variable has to be set once manually:
EMENDATE_SERVICE_NASTRAN | C:\Program Files\MSC.Software\MSC_Nastran\2023.2\bin\nast20232.exe |
Path to your MSC Nastran installation |
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, you can set up your model as every other optimisation and before you start the optimisation the Eigenfrequency Optimisation gets activated with the Advanced User Settings.
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: Advanced User Settings to initialize the Eigenfrequency Optimisation
The following 3 Advanced User Setting commands are mandatory to start a Eigenfrequency Optimisation. With these a additional event for the Eigenfrequencies is added.
event.EventFA.strategy=conditionBasedFrequencyAnalysis event.EventFA.frequencyTarget=210 event.EventFA.safetyFactor=1 |
The Frequency Target (in Hz) is the target for the first occurring eigenfrequency of the part. This value need to be adjusted to your according requirements 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=630 |
Step 4: 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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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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Currently, the influence of the eigenfrequency calculation is displayed in the enveloped plot of the Failure Criterion (even if this isn’t based on a stress value).
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 and using them for the Eigenfrequency Optimisation
Point masses play an important role in the calculation of eigenfrequencies. Therefore, Point Masses can be created with the Advanced User Settings.
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 position has to be entered with three values (x,y,z) regarding the global coordinate system (These can be also reused from a remote force).
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Advanced User Settings to create a Point Mass:
pointMass.pointMass1.geometryName=ModelLoadEvent_Force_-_Moment_1 |
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Be aware that the Unit System in the Advanced User Settings is SI. Thus, you have to enter the position of the point in meters and the mass in kg! |
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Be aware that the Point Mass will also introduce a static load if acceleration is used in one Event. You may want to modify the Remote Load accordingly. |