Frequency response Function : Mobility for somepoints

Hallo Group

I want to have value of frequency response function Mobility defined as (Normal velocity/ force) at some points on my structure.

I am doing direct frequency response analysis with optistruct. How do I go about it.

Regards

Pratik

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Altair Forum User

Hi Pratik,

Please refer to Frequency response function tutorial on our help documents.

OS-1300: Direct Frequency Response Analysis of a Flat Plate

OS-1305: Modal Frequency Response Analysis of a Flat Plate

In addition refer to RLOAD2 card (used in above mentioned tutorials) to learn how to apply velocity as a freq function.

Altair Forum User

Step 8: Create a Set of Frequencies to be used in the Response Solution

can you elaborate this steps? does is it calculate the response for only this 49 freqencies (20 hz -1000 hz)

Modal frequency response : does it used some Modal matrix reduction method? any literature for optistruct about this method?

Can i use EIGRA instead to EIGRL for Mode frequency extraction

Altair Forum User

Hi Pratik,

Yes, response is calculated from 20-1000Hz.

You can use EIGRA for modal FRA. You can refer to OptiStruct user guide form more information on FRF analysis.

Altair OptiStruct > User's Guide > Structural Finite Element Analysis > Solution Sequences:

Altair Forum User

Hello Prakash

In Step 5: Create a Unit Load at a Point on the Flat Plate

7 Uncheck all the dof's; except dof3, and click the = to the right of dof3 and enter a value of 20.

what dies the value 20 stand for? Isn,t it unit load?

Regards

Pratik

Altair Forum User

Pratik,

that is the load/exitation you are giving in Z-direction.

If you are giving load type as enforced displacement for instance, then the node will be displaced by 20 units.

Altair Forum User

OS-1305: Modal Frequency Response Analysis of a Flat Plate

Hello Prakash

so what exactly is Modal Frequency Response , how does it differ from drect frequency response

for example If i want velocity response between excitation frequency between say 1000 to 2000 hz , but i want response only at eigen frequncies in this range should i do Modal Frequency response analysis?

Rahul_P1

you will have to provide the excitation frequencies for which you need the response,

The direct method solves the coupled equation of motion in terms of the excitation frequency.

The modal method uses the mode shape of the structure to uncouple the equations of motion and the solution for a particular excitation frequency is obtained by summation of individual modal responses or modal superposition.

see help

OptiStruct > User's Guide > Structural Analysis:

Frequency Response Analysis

Devakar_Altair

Hello Group ,

I want to have value of frequency response function Impedance defined as (Acceleration / force) at some points on my structure.

I am doing modal frequency response analysis with optistruct. How do I go about it

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