Frequency Response Function output from Algor Simulation Professional 2011

[Anonymous]

Hi everybody,

I'm Matteo, an engineering student.

I've made a modal analysis in order to study natural frequencies of a mechanical structure with Algor Simulation Professional 2011.

I would like to ask to you how can I exctract FrequencyResponseFunction as output of my modal analysis.

I've made also an accelerometer acquisition so my intrest is to compare two results, experimental one and FEM one.

Especially i would like to compare both FRF.

Thank you

G'day to everyone

Matteo

[PipePakPat]

I wonder if your request could also be re-phrased to request the "transmissibility" of the applied load through the model measured at a specific point?  Autodesk Simulation (Algor) does not output the accelerations required to determine the transmissibility.

[Stefan2653]

Is this something that might be considered as a future capability? We also have a frequent need to compare analytic predictions of vibration tests with actual accelerometer response functions (FRFs) from the tests. In order to satisfy this requirement, we must use an alternate application to generate the FRFs, which involves model translation, correction, etc.

Thanks.

Stefan

[PipePakPat]

I have documented your request and have forwarded to development.  Please let me know if you have further questions.

[John_Holtz]

Hi Matteo,

As I understand FRF, it is a graph of displacement/force versus forcing frequency. (Or velocity/force or acceleration/force.) So you need to apply a sinusoidal force to the model. That can be done with a "Linear > Frequency Response" analysis to calculate the displacements. Then, can you take the second derivative of displacement to get the acceleration? (displacement = A*sin(w*t+phi), acceleration = d^2 displacement/dt^2?) You know the force and frequency, so you can do the calculations to make the graph.

I suggest you start with the example in the documentation to familiarize yourself with the Frequency Response analysis: Help > Autodesk Simulation > Examples > Linear and Dynamic Stress > Ground Motion -Vibrating Support. (This link goes to the online wiki which is for the current software, 2012. The Help in your product has the version of the example appropriate for your software, 2011.)

The other option is to perform a "Linear > Transient Stress (Direct Integration)" simulation. This analysis type calculates and outputs the acceleration (to the .AO4 file) in addition to the displacements and stresses. Just two disadvantages with this approach:

1. In Transient stress, you apply a force and then define how the force changes with time. How many cycles of F are required to reach a quasi-steady state solution? So, the analysis time will be longer than the Frequency response analysis.
2. Although the processor calculates the accelerations (.AO4), the software does not display those results. This is easy to take care of: Rename the displacement file (.DO4) so that you do not lose it, and rename the acceleration file to .DO4. (ds.ao4 becomes ds.do4). Then the software will display the acceleration results by using the "Displacement" commands.

[Stefan2653]

Thanks for the information. With respect to the first option, to calculate absolute displacement of any particular node over a range of exiting frequencies (typically 20 - 2,000 Hz in our case), I believe you would need the phase information of every node in the model for every exciting frequency. Is that information contained in any of the output files?

Stefan