Learning Forum

[Balaji Paikrao]

I am performing the MSUP Random Vibration analysis, In the Modal analysis i am getting ratio of effective modal mass to total mass is very less in y and z direction, as per the ANSYS guidelines in MSUP analysis the ratio should be atleast 90% but i am getting arounf 0.1% in y and Z direction. In this situation whether there is any way to make sure that the random vibration aanalysis results are not going to get affected due to this?

Also the working frequency range of Random vibration input is 20 to 2000 HZ, but my  natural frequencies which i am getting in modal analysis are starting from 2700 HZ. What can be done please help?

 

[peteroznewman]

Was the first mode of the structure expected to be between 20 and 2,000 Hz?

Check that the density of your material is correct.

Check that the mass you see in the model equals the mass of the physical part.

Check that the Young's modulus of your material is correct.

If the first mode is above the frequency range of the Random Vibration spectrum, then the response of the structure will be small.

 

[Balaji Paikrao]

Thanks for your reply Sir,

No it is not necessary to have first mode between the 20 and 2000 Hz. I was just concerned that if my modal frequencies are greater than the frequency range in Random vibration then how the MSUP will perform the calculation will it be accurate or not.

I have checked density, mass and Young's modulus all are correct.

Will you please tell me how can I improve my ratio of effective mass to total mass as increasing no of  modes will increase computational efforts

Thanks in advance.