Article Topic

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Date it appeared in E/T

Sometimes the mode shapes appear to be rotated from what is expected.  Are the modes wrong?

158 KB

Jan/Feb 2008, Vol. 32, No. 1

Bolted joints are common in structures.  Can the frequency change significantly due to joints?

100 KB

Nov/Dec 2007, Vol, 31, No. 6

The stability diagram has poles that are not indicated by the MMIF or CMIF; are they really modes?

206 KB

Sep/Oct 2007, Vol. 31, No. 5

How do you interpret the stability diagram?  And how do data points affect the fit?

171 KB

Jul/Aug 2007, Vol. 31, No. 4

How do you select the reference location for a modal test?  What needs to be considered?

621 KB

May/Jun 2007, Vol. 31, No. 3

What is the difference between all the mode indicator functions?  What do they all do?

248 KB

Mar/Apr 2007, Vol. 31, No. 2

What is MRIT???  I hear people talk about it for impact testing.

240 KB

Jan/Feb 2007, Vol. 31, No. 1

Someone told me that operating modal analysis produces better results, and that damping is much more realistic

180 KB

Nov/Dec 2006, Vol. 30, No. 6

What is a good MAC value so that I know my model is right?

256 KB

Sep/Oct 2006, Vol. 30, No. 5

Is there any problem running a modal test to 2 KHz but only analyzing up to 500 Hz?

212 KB

Jul/Aug 2006, Vol. 30, No. 4

What effect can the test set up and the rigid body modes have on the higher flexible modes of interest?

187 KB

May/Jun 2006, Vol. 30, No. 3

Can modal parameters be extracted for heavily damped modes when you can’t see them in the measured FRFs?

235 KB

Mar/Apr 2006, Vol. 30, No. 2

Should the measurement bandwidth match the frequency range of interest for impact testing?

272 KB

Jan/Feb 2006, Vol. 30, No. 1

I ran a shaker test with a simple beam, but some of the modes don’t look right – What’s wrong?

216 KB

Nov/Dec 2005, Vol. 29, No. 6

Sometimes my impact force is very smooth just as expected, but often it looks like it is oscillating – Why is that?

164 KB

Sep/Oct 2005, Vol. 29, No. 5

Why does my stability diagram of a component on a system show modes that the SUM and MIF don’t show?

293 KB

Jul/Aug 2005, Vol. 29, No. 4

When I perform impact testing, the input spectrum looks distorted – do you think my FFT analyzer has a problem?

190 KB

May/Jun 2005, Vol. 29, No. 3

I know that certain shaker excitations have different characteristics – but, which is the best to use?

372 KB

Mar/Apr 2005, Vol. 29, No. 2

Once I have set up a good measurement, is there any reason to watch the time and frequency results for every FRF?

223 KB

Jan/Feb 2005, Vol. 29, No. 1

Do mode shapes of a plate have any particular predetermined order?

276 KB

Nov/Dec 2004, Vol. 28, No. 6

I find overload and underload of the digitizer and range settings difficult to understand.

210 KB

Sep/Oct 2004, Vol. 28, No. 5

Is there any way to scale mode shapes without a drive point measurement?

177 KB

Jul/Aug 2004, Vol. 28, No. 4

Do I need to have an accelerometer mounted in the X, Y, and Z directions to do a modal test?

311 KB

May/Jun 2004, Vol. 28, No. 3

Number of points needed for a Modal test and the necessity of defining the entire shape.

284 KB

Mar/Apr 2004, Vol. 28, No. 2

What's the difference between local and global curve fitting?

469 KB

Jan/Feb 2004, Vol. 28, No. 1

Why do some measurements have antiresonances and others do not?

348 KB

Nov/Dec 2003, Vol. 27, No. 6

I ran a Modal test on a portion of a structure of concern and many modes look the same! What did I do wrong?

357 KB

Sep/Oct 2003, Vol. 27, No. 5

Must you have multiple references in order to find pseudo repeated roots?

221 KB

Jul/Aug 2003, Vol. 27, No. 4

Is it really necessary to reject a double impact?

440 KB

May/Jun 2003, Vol. 27, No. 3

Why are calibration and mode shape scaling important, and does it make a difference?

250 KB

Mar/Apr 2003, Vol. 27, No. 2

Is it better to collect averaged FRF data for a Modal test, or collect time data and process it afterwards?

591 KB

Jan/Feb 2003, Vol. 27, No. 1

What are some of the major mistakes people make in Modal tests so I don't make the same ones.

189 KB

Nov/Dec 2002, Vol. 26, No. 6

Is there any real advantage to MIMO testing?  Why not just use SISO and then move the shaker?

254 KB

Sep/Oct  2002, Vol. 26, No. 5

Can you explain the basic steps to acquire data for Modal testing?

257 KB

Jul/Aug 2002, Vol. 26, No. 4

What's the difference between a complex mode and a real normal mode?

236 KB

May/Jun 2002, Vol. 26, No. 3

Which window is most appropriate for the various types of Modal tests performed?

282 KB

Mar/Apr 2002, Vol. 26, No. 2

Can the test setup have an effect on the measured Modal data?  Do the setup boundary conditions and accelerometers have an effect?

258 KB

Jan/Feb 2002, Vol. 26, No. 1

Should I use all collected measurements when estimating modal parameters? Let's discuss this.
 

 223 KB

Nov/Dec 2001, Vol. 25, No.6

What are some of the most important things to consider when impact testing? Let's discuss this.
 

296 KB

Sep/Oct 2001, Vol. 25, No.5

Is there any benefit to using multiple references? I thought that only one reference was necessary.  Let's discuss this.
 

 495 KB

Jul/Aug 2001, Vol. 25, No.4

When impact testing, can the use of the exponential window cause any problems? Let's discuss this.
 

 647 KB

May/Jun 2001, Vol. 25, No.3

Does it make any sense to use the actual operating load as excitation force for modal test if the force is a random signal?
 

489 KB

Mar/Apr 2001, Vol. 25, No.2

I hear about SVD all the time. Could you explain it simply to me?
 

456 KB

Jan/Feb 2001, Vol. 25, No.1

Why is mass loading and data consistency important for modal parameter estimation?
 

338 KB

Nov/Dec 2000, Vol. 24, No.6

Someone told me SDM will never work because you don't have all the mode shapes of the system.
 

220 KB

Sep/Oct 2000, Vol. 24, No. 5

How many points are enough when running a modal test? 
 

463 KB

Jul/Aug 2000, Vol. 24, No.4

I ran one test with an X-excitation and can see some of the modes, and another test with a Y-excitation and see some different modes. Could I use an oblique angle instead?
 

458 KB

May/Jun 2000, Vol. 24, No. 3

I showed some mode shapes to someone and they asked if the design was OK.
 

 537 KB

Mar/Apr 2000, Vol. 24, No. 2

I'm still overwhelmed by all this modal stuff - give me the big picture!
 

 682 KB

Jan/Feb 2000, Vol. 24, No. 1

I heard someone say "Pete doesn't do windows" What's the scoop?
 

243 KB

Nov/Dec 1999, Vol. 23, No. 6

Are you sure you can get mode shapes from one row or column of H?
 

203 KB

Sep/Oct 1999, Vol. 23, No. 5

What's the difference between operating deflection shapes and mode shapes?
 

483 KB

Jul/Aug 1999, Vol. 23, No. 4

I still don't understand curvefitting. How do I get mode shapes from FRFs?
 

443 KB

May/Jun 1999, Vol. 23, No. 3

Curvefitting is so confusing to me! What do all the different techniques mean?
 

421 KB

Mar/Apr 1999, Vol. 23, No. 2

Which shaker excitation is best? Is there any difference?
 

491 KB

Jan/Feb 1999, Vol. 23, No. 1

Should I always use a hard tip for impact testing so the input spectrum is flat over all frequencies?
 

522 KB

Nov/Dec 1998, Vol. 22, No. 6

Is there any difference between a roving hammer and roving accelerometer test?
 

445 KB

Sep/Oct 1998, Vol. 22, No. 5

Is there any difference between a modal test with a shaker excitation or impact excitation?
 

484 KB

Jul/Aug 1998, Vol. 22, No. 4

Could you explain the difference between the time domain, frequency domain and modal space?
 

487 KB

May/Jun 1998, Vol. 22, No. 3

Could you explain modal analysis for me?
 

640 KB

Mar/Apr 1998, Vol. 22, No. 2