Query on High Frequency Analysis with AutoSEA

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

Saurabh Chhablani - 21 Jan 2004 08:30 GMT

Hi All,
I am working for a machine, which produces high frequency noise.
(2000Hz & above). I am using AutoSEA for this analysis. I don't have
any measurement data. One electromagnetic load of some magnitude at
50Hz is the only input available. My queries are:

1.As in low frequency analysis we can get velocities at surfaces
(nodes) by harmonic analysis of structure. This velocity in turn gives
the SPL and so on. Can we use this approach for high freq analysis as
well?
2.If answer of above query is yes, then how do we do harmonic analysis
of a structure for higher frequency? If model is very big.
3.Is the approach of doing harmonic analysis is not at all correct for
high frequency? Do we need to have some information about source
characteristics? Which in turn we can get only via measurement.

Please throw some light

Saurabh
Hi All,
i am working for a machine which produces high frequency noise.
(2000Hz n above). i m using AutoSEA for this analysis . i dont have
any measurement data. one electromagnetic load of some magnitude at
50Hz is the only input available. my queries are:

1. As in low frequency analysis we can get velocities at
surfaces(nodes) by harmonic analysis of structure. This velocity
inturn gives the SPL and so on.
can we use this approach for high freq analysis as well.
2. If answer of above query is yes, then how do we do harmonic
analysis of a structure for higher frequency.
3. Is the approach of doing harmonic analysis is not at all correct
for high frequency? do we must need to have some information about
source characteristics, which inturn we can get only via measurement.

Please thro some light

Saurabh

Reply to this Message

Greg Locock - 22 Jan 2004 05:32 GMT

> Hi All,
> I am working for a machine, which produces high frequency noise.
> (2000Hz & above). I am using AutoSEA for this analysis. I don't have
> any measurement data.

Big problem

>One electromagnetic load of some magnitude at
> 50Hz is the only input available.

If it is a linear system then exciting it at 50 Hz will not produce any
noise at 2000 Hz. Either your nput signal must have some high frequency
content, or your system is non-linear. If the latter then I think SEA
may be the incorrect approach.

My queries are:

> 1.As in low frequency analysis we can get velocities at surfaces
> (nodes) by harmonic analysis of structure. This velocity in turn gives
> the SPL and so on. Can we use this approach for high freq analysis as
> well?

What do you mean by harmonic analysis? Experimental Modal Analysis? FEA?
In either case SEA basically uses an average modal response in a given
bandwidth, to determine the response of the structure in that bandwidth.
So, yes, it is a viable approach. However, you should be aware that a
computational model (whether by hand or FEA) at high frequencies will be
increasingly less accurate with increasing frequency, so far as
particualr modes go, although admittedly if you are merely trying to
estimate an average mobility per bandwidth then this may not matter.

> 2.If answer of above query is yes, then how do we do harmonic analysis
> of a structure for higher frequency? If model is very big.

Experimentally? Modal Analysis. Analytically? FEA

> 3.Is the approach of doing harmonic analysis is not at all correct for
> high frequency? Do we need to have some information about source
> characteristics? Which in turn we can get only via measurement.

An uncorrelated model is worth no more than a back of envelope
calculation in many respects.

Of course you need to know the source characteristics.

Cheers

Greg Locock

Reply to this Message

Natural Science Forum / Physics / Acoustics / January 2004

Query on High Frequency Analysis with AutoSEA