Difference between revisions of "Modal Theorical FAQ"
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[https://orossas.sharepoint.com/:b:/g/support/ESHPvhJIsCBHijgwBeffvcABU-VZCt6ZON1OMcguK2sGoQ?e=qsLNUI Could you explain modal analysis for me.] | |||
==Windowing== | |||
[https://orossas.sharepoint.com/:b:/g/support/ESeXYLSIKetIp7v1LyevBO0BI0hStYqFdzah5aO9kzgGIA?e=MTVQsF When impact testing, can the use of the exponential window cause any problems?] | |||
[https://orossas.sharepoint.com/:b:/g/support/EUw3GiSkKIdBmFAZLE5vw-IBZ6-2-Yczz7zz4i3cTda2iQ?e=btozQG Which window is most appropriate for the various types of modal tests performed?] | |||
[https://orossas.sharepoint.com/:b:/g/support/EZmiM-le4zpDvsyTb1Kfmc0B7AymLe5HB810BiQ2jtsxhQ?e=vJbs0G I heard someone say Pete doesn't do windows. Whets the scoop.] | |||
==Acquisition== | |||
[https://orossas.sharepoint.com/:b:/g/support/ERUU4dr0usxHiAn1Ih8FTAcBwQYcRPpNEMnUTsmT7JBCTg?e=Ag9Nit 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 ?]<br> | [https://orossas.sharepoint.com/:b:/g/support/ERUU4dr0usxHiAn1Ih8FTAcBwQYcRPpNEMnUTsmT7JBCTg?e=Ag9Nit 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 ?]<br> | ||
[https://orossas.sharepoint.com/:b:/g/support/ESAbTQrm4yFKi0RMb2BVRTYBexWVHZewsr7hvDLPuEtUSQ?e=AZTle9 Is it really necessary to reject a double impact?] | [https://orossas.sharepoint.com/:b:/g/support/ESAbTQrm4yFKi0RMb2BVRTYBexWVHZewsr7hvDLPuEtUSQ?e=AZTle9 Is it really necessary to reject a double impact?] | ||
[https://orossas.sharepoint.com/:b:/g/support/Ee9ZZy7KqVxLjWURcjNtKSYBwxXFR_QjQVKhJofS9c4xKA?e=wdtfHO Do I need to have an accelerometer mounted in the X, Y and Z directions to do a modal test?] | [https://orossas.sharepoint.com/:b:/g/support/Ee9ZZy7KqVxLjWURcjNtKSYBwxXFR_QjQVKhJofS9c4xKA?e=wdtfHO Do I need to have an accelerometer mounted in the X, Y and Z directions to do a modal test?] | ||
[https://orossas.sharepoint.com/:b:/g/support/EVWdcqfwhc9Mshv8R6M5BKYB_I8x96uro6ItAhVah31wGA?e=qqb8So Is there a difference between a roving hammer and roving accelerometer test?] | |||
[https://orossas.sharepoint.com/:b:/g/support/EVxxlCgPltJHslo8IlH2Y0wB5T_Z1Mn9mpXMiOhaIRWV8Q?e=h9dWZR Can the test setup have an effect on the measured modal data ? Do the setup boundary conditions and accelerometers have an effect?] | |||
[https://orossas.sharepoint.com/:b:/g/support/EV4GFjhvcStErAqtxUDAFcUBU6db28UlUtckHR2l09Ad7A?e=3DHX1C is it better to collect averaged FRF data for a modal test? Or collect time data and process it afterwards?] | |||
[https://orossas.sharepoint.com/:b:/g/support/EfDJXZ2NsXBIpNnOPouoJLIBlqBNBjgTfnKQ4OUMay4R6g?e=igvjzh How many points are enough when running a modal test] | |||
[https://orossas.sharepoint.com/:b:/g/support/EZfWJLtRuCtDpCkrd09zwEUBz2GXFlFjmWmBjBPJ7O1igw?e=o5c75e We talked about the number of points needed for a modal test before.] | |||
[https://orossas.sharepoint.com/:b:/g/support/EV3I4RVyqhtInP82-HGjH2gBff6U72IhA7orXLTNWH5LLg?e=JGOeAo Is there any benefit to using multiple references?I thought only one reference was need.] | |||
[https://orossas.sharepoint.com/:b:/g/support/ | [https://orossas.sharepoint.com/:b:/g/support/EQKjRyGlsShNg14lgX6gUtwBSq9W2VdBEwiDQ4jTvI8trg?e=1bCxCc Could you please explain the basic steps to acquire data for modal test] | ||
[https://orossas.sharepoint.com/:b:/g/support/ | [https://orossas.sharepoint.com/:b:/g/support/ET7xJmNNuyNGnpoX_E0s9MIB7BfU3wKfDjv3gtZlsjGGZA?e=M0mIrO Someone told me that you must have multiple references to identify pseudo repeated.] | ||
[https://orossas.sharepoint.com/:b:/g/support/ESRlQH3hGgpLgqwRbYFMOHQBb-J3fkac76JMhSCwgAF_pg?e=qQRnZL Should I always use a hard tip for impact testing . . .so the input spectrum is flat over all frequencies] | |||
==Shacker== | |||
[https://orossas.sharepoint.com/:b:/g/support/EZ0xK6BALQlMgiXqGEh1UNkBJfsAo4aPmTwE7UKcLSppEg?e=NpNUPs Is there any difference between a modal test with a shaker excitation or impact excitation?] | |||
[https://orossas.sharepoint.com/:b:/g/support/EQddAeNBRVdIlU5bh9bZXTEBgLHRYnAduKohW9AovB_rKg?e=jax1z5 Is there any real advantage to MIMO testing? Why not just use SISO and then move the shaker?] | [https://orossas.sharepoint.com/:b:/g/support/EQddAeNBRVdIlU5bh9bZXTEBgLHRYnAduKohW9AovB_rKg?e=jax1z5 Is there any real advantage to MIMO testing? Why not just use SISO and then move the shaker?] | ||
[https://orossas.sharepoint.com/:b:/g/support/EUR6b2uoMXFDkHczw0ZVizwBTKY2otdmB3CNUz2t7-eAvw?e=hw0ffo Which shaker excitation is best? Is there any difference?] | [https://orossas.sharepoint.com/:b:/g/support/EUR6b2uoMXFDkHczw0ZVizwBTKY2otdmB3CNUz2t7-eAvw?e=hw0ffo Which shaker excitation is best? Is there any difference?] | ||
==results interpretation.== | |||
[https://orossas.sharepoint.com/:b:/g/support/EWVXgK-KbPBLn3VMLviBuuQB7XgfOpaAPUzLPe0dbMhe9A?e=AVixDw I showed some mode shapes to someone. They asked me if the structural design was ok. What should I tell them ?] | [https://orossas.sharepoint.com/:b:/g/support/EWVXgK-KbPBLn3VMLviBuuQB7XgfOpaAPUzLPe0dbMhe9A?e=AVixDw I showed some mode shapes to someone. They asked me if the structural design was ok. What should I tell them ?] | ||
==Modal theorical== | |||
===Curvfitting=== | |||
[https://orossas.sharepoint.com/:b:/g/support/EeYfWtoUNHhIgpr2i1_wYkcBZPq3GmF0ETi7I8DtsuWKoQ?e=d5nXIx Curvefitting is so confusing to me!] | [https://orossas.sharepoint.com/:b:/g/support/EeYfWtoUNHhIgpr2i1_wYkcBZPq3GmF0ETi7I8DtsuWKoQ?e=d5nXIx Curvefitting is so confusing to me!] | ||
[https://orossas.sharepoint.com/:b:/g/support/Ebec28JEGMVMvyRfvQZt0GgBOROstYIXhuvGDcWinV9r7A?e=HiXoPC What's the difference between local and global curvefitting ?] | |||
[https://orossas.sharepoint.com/:b:/g/support/Ea9f9MN6HDRFsZpwejhz7NwBmCNR8dXZvc-vuCLIVoNGww?e=k2ATuM I still don't understand curvefitting ...] | |||
===others questions=== | |||
[https://orossas.sharepoint.com/:b:/g/support/EXQqztDPrmdAnJ9kU9OVB80B0oGkUjtqvwZwg9M29HfWzA?e=tpRaTG What's the difference between a complex mode and a real normal mode?] | |||
[https://orossas.sharepoint.com/:b:/g/support/EXaI-C0co7lNrKrXwfquUAgBNBKd7GQf1CvSFvyuk-ywfQ?e=T9MACh Could you explain the difference between time domain, frequency domain and modal space?] | |||
[https://orossas.sharepoint.com/:b:/g/support/EdcRQK9hbXlJnDYwtTpT-PIBLpl_qPzNmgGtAEsUjqJqVw?e=EJ9Lzi I ran a modal test on a portion of a structure of concern and many modes look the same!] | |||
[https://orossas.sharepoint.com/:b:/g/support/EYn8VMAjMoVHqynlrHcaI-wBd7Oi5A55fjkyKHZAyPBeQg?e=rUffYN Someone told me SDM will never work] | |||
[https://orossas.sharepoint.com/:b:/g/support/EVTrvk3ZJQNKkGlX6NmVl9cBDZMOI2kPc4vnKpUW2G9swA?e=ylkpgg Are you sure you can get mode shapes from one row or column of the H matrix?] | |||
[https://orossas.sharepoint.com/:b:/g/support/ | [https://orossas.sharepoint.com/:b:/g/support/EZrt0mNRSxdBtew4xoQjLTgB0evFRtDOgnhDzuOYIXLE7w?e=3ziz3G I hear about SVD all the time Could you explain it simply to me?] | ||
[https://orossas.sharepoint.com/:b:/g/support/ | [https://orossas.sharepoint.com/:b:/g/support/EamEoIefNl5Pg0zVmkDUv_4Bh3TXKPJz991K65nXTbuxdg?e=3KQWga I'am still overwhelmed by all this modal stuff Laplace, Fourier, FRFs, and all that!] | ||
[https://orossas.sharepoint.com/:b:/g/support/ETt1D-Wue5BBvDzO5y8GwwgBJGvPz-mNmEBZYT-ifPOK9Q?e=nfQafc Does it make any sense to use the actual operating loads as the excitation force for a modal test if the force is a random signal ?] | |||
[https://orossas.sharepoint.com/:b:/g/support/EQJYwQLkKa9Dp1k-gqlMWlwBJ4wmLrIZyuex9aeee5ftyA?e=cw1KIp Why is calibration and mode shape scaling important? And does it make a difference?] | |||
[https://orossas.sharepoint.com/:b:/g/support/ | [https://orossas.sharepoint.com/:b:/g/support/EQbt6Vnt4KVMo4ma2i2aVsQBqd1-nHRGjmpaOzymCT2seg?e=KjIRqC Mode shape scaling requires a drive point measurement.Is there any way to scale shapes without this ?] | ||
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[https://orossas.sharepoint.com/:b:/g/support/EX4IEP3GWoRPr1V5RTGD5jcBiHNsJ0rJPWpdPaJ_bH_aaQ?e=LIqzlD Why do some measurements have anti-resonances and others not ?] | [https://orossas.sharepoint.com/:b:/g/support/EX4IEP3GWoRPr1V5RTGD5jcBiHNsJ0rJPWpdPaJ_bH_aaQ?e=LIqzlD Why do some measurements have anti-resonances and others not ?] | ||
Revision as of 13:38, 17 July 2020
Could you explain modal analysis for me.
Windowing
When impact testing, can the use of the exponential window cause any problems? Which window is most appropriate for the various types of modal tests performed? I heard someone say Pete doesn't do windows. Whets the scoop.
Acquisition
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 ?
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?
Is there a difference between a roving hammer and roving accelerometer test?
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?
How many points are enough when running a modal test We talked about the number of points needed for a modal test before. Is there any benefit to using multiple references?I thought only one reference was need.
Could you please explain the basic steps to acquire data for modal test
Someone told me that you must have multiple references to identify pseudo repeated.
Shacker
Is there any difference between a modal test with a shaker excitation or impact excitation? Is there any real advantage to MIMO testing? Why not just use SISO and then move the shaker?
Which shaker excitation is best? Is there any difference?
results interpretation.
Modal theorical
Curvfitting
Curvefitting is so confusing to me! What's the difference between local and global curvefitting ? I still don't understand curvefitting ...
others questions
What's the difference between a complex mode and a real normal mode? Could you explain the difference between time domain, frequency domain and modal space? I ran a modal test on a portion of a structure of concern and many modes look the same! Someone told me SDM will never work 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?
I'am still overwhelmed by all this modal stuff Laplace, Fourier, FRFs, and all that!
Does it make any sense to use the actual operating loads as the excitation force for a modal test if the force is a random signal ?
Why is calibration and mode shape scaling important? And does it make a difference?
Why is mass loading and data consistencyimportant for modal parameter estimation?
Should I use all collected measurements when estimating modal parameters ?
What are some of the major mistakes people make in modal tests so I don't make the same one
Why do some measurements have anti-resonances and others not ?