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Modal Space — Back to Basics


To see the complete list of Modal Space articles which includes the most recent articles, please go to:

Article Topic


File Size

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



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