Shock Spectrum 2

[Tunalover]

Folks-
Our customer has imposed a shock spectrum on the laser product we are developing for him. How does one go about approaching such a problem with pencil and paper? Spreadsheet? MathCAD? FEA?

I know this is a wide-open question but perhaps if someone could just point us to a practical reference I'd be much obliged!


Tunalover

 

[GregLocock]

http://www.knovel.com/knovel2/Toc.jsp?BookID=625

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Tunalover]

Thanks GregLocock-
Thanks but I suppose I should have mentioned the word "free" reference.



Tunalover

 

[xydrex]

There's a free 7 day trial. Get a work experience student to take screen shots for 7 days LOL.

 

[IRstuff]

The free trial allows you to download any and all PDF files you have access to. Unfortunately, it's PDS (PDQ-not), because the files are arbitrarily sectioned.

TTFN

Eng-Tips Policies FAQ731-376

 

[Tunalover]

IRStuff and GregLocock-
Why do you refer me to FAQ731-376?


Tunalover

 

[IRstuff]

We don't. It's part of our signatures.

TTFN

Eng-Tips Policies FAQ731-376

 

[GregLocock]

We're not picking on /you/ tunalover, we pick on everyone!

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Tunalover]

Thanks guys.
I have a copy of Harris but it's hopelessly buried in a box in my garage.
Good Luck!


Tunalover

 

[tomirvine]

The shock response spectrum gives the peak acceleration response for a single-degree-of-freedom system subjected to base excitation. The natural frequency of the item is the independent variable.

You can readily determine the item's peak acceleration for a given natural frequency from the SRS plot. The key is that the natural frequency of item must be known through analysis and/or test. Upper and lower esimates of the natural frequency may be used if the natural frequency is not precisely known.

The relative displacement might also be a concern. The relative displacement is approximately equal to the SRS acceleration divide by (omega sub n)^2, where (omega sub n)is the natural frequency in terms of radians/sec.

On the other hand, a given item may behave as a multi-degree-of-freedom system. There are some techniques available for applying the SRS to such a system. A finite element analysis is usually required to carry this out.

My favorite method is to synthesize a sample time history to satisfy the SRS. Then perform a modal transient analysis via FEA.

For further information, I have posted a free SRS paper at:

http://www.vibrationdata.com/tutorials2/srs_intr.pdf

Additional, papers are available at:

http://www.vibrationdata.com/SRS.htm

Thank you,
Tom Irvine