Modeling HDD viberation in promchanica

[sh63]

Hi,
I am
trying to model the HDD affect on a chassis and I am having trouble defining
the rotational/vibrational energy into the model. Basically, I have designed a
mounting bracket that holds the hard disk drive running at 7200 RPM. This
subassembly will be connected to a bigger sheet metal part using three screws.
Four of this subassembly will be mounted on the big sheet metal part next to
each other. I have experimental data of HDD vibrating in units of g^2/HZ.
What I want to be able to determine is how much stress and displacement the
bracket and the entire assembly will experience (I

 

[mechg]

Hi SH,

If you have an g^2/Hz input, then you should use Dynamic Random. Make sure that the modal analysis has captured sufficient modes and use a realistic damping value - I tend to use around 5% critical for most metallic structures. If you are using N-mm-s units then put 9810 in the base excitation multiplier, then define the PSD as a table. Mechanica does the maths for you. Make sure to make plenty of measures before doing the run. I would be a good idea to start off with a very simple model to get the hang of the process before setting up the detailed model.

The results from a dynamic random will be the RMS levels of stress, so the von Mises stress is meaningless, and so too are the max. prin. plots. Plot graphs of stress and acceleration using the measures. Plot the acceleration first. Check that the value corresponds to the RMS acceleration of your input at the constraint surfaces. The RMS stress value is roughly 1 standard deviation, so multiply the result by 3 to get the 3sigma result - compare this stress to the allowable.

Regards,

Rod Giles