Modal Theorical FAQ

I ran one test with an x-excitation and can see some modes and another test with a y-excitation and see some different modes could I use an oblique angle instead ?

When impact testing, can the use of the exponential window cause any problems?

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

Is it really necessary to reject a double impact?

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

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

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

I still don't understand curvefitting ...

Someone told me SDM will never work

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

I ran a modal test on a portion of a structure of concern and many modes look the same!

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

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

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

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

is it better to collect averaged FRF data for a modal test? Or collect time data and process it afterwards?

What's the difference between local and global curvefitting ?

Which shaker excitation is best? Is there any difference?

I'am still overwhelmed by all this modal stuffLaplace, Fourier, FRFs, and all that!

I showed some mode shapes to someone. They asked me if the structural design was ok. What should I tell them ?

Does it make any sense to use the actual operating loadsas the excitation force for a modal testif the force is a random signal ?

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

Why is calibration and mode shape scaling important?And does it make a difference?

We talked about the number of points needed for a modal test before. feb05