Learning Forum

[AR]

Hello,

 

I'm trying to perform a random vibration for an assembly that serves as an interface between a motor and a baseplate. I want to apply the PSD to a body, the motor, and NOT to the supports. To do this I'm using APDL commands.

Although the PSDUNIT can apply acceleration in the form of acceleration (accel) and Gs (accg), I haven't been able to apply it to a body with the pfact,1,node. With the PSDUNIT,1,forc (PSD with force units) I've managed to apply the PSD to the motor. I'm leaving the code in case it's useful to someone:

f,NodosMotor,Fx,1
PSDUNIT,1,forc
PSDFRQ,1,,10.,30.,31.69,2000.
PSDVAL,1,3.15e-3,3.15e-3,3e-003,3e-003
pfact,1,node

However, now I don't know how to convert my data from g^2/Hz to N^2/Hz. This post says that the acceleration must be divided by the mass of the motor. However, it doesn't make sense since F=m*a.

1) How can I convert a value of 0.0025 g^2/Hz to x N^2/Hz?
2) Is there any way to apply the PSD in the form of acceleration to a body?

[dlooman]

The usual way is to apply the acceleration in the modal which will create a nodal force vector based on the acceleration and then read the nodal force vector in the PSD with the LVSCALE command.  

[AR]

Hello Dlooman,

I have already tried to create an acceleration in the modal applied to the body I want using CMACEL,BODY1,9.81,9.81,9.81 and then use LVSCALE,1 in the Random vibration to apply the PSD. However, I obtained results as 0.

Looking at the solution information I saw that it interprets that all the participation factors are 0 when they are not.

How could I do this?