Difference between revisions of "Modal Theorical FAQ"
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[[File:modal.png|900px]] | [[category:Modal]] | ||
== | [[File:modal.png|900px|none]] | ||
The following articles have originally been published in SEM Experimental Techniques. It is write by Dr Peter Avitabile head of [http://macl.caeds.eng.uml.edu/umlspace/mspace.html The Structural Dynamics and Acoustic Systems Laboratory (SDASL) at the University of Massachusetts] | |||
==Modal Generality== | |||
[https://orossas.sharepoint.com/:b:/g/support/ESHPvhJIsCBHijgwBeffvcABU-VZCt6ZON1OMcguK2sGoQ?e=qsLNUI What is modal analysis?.]<br> | [https://orossas.sharepoint.com/:b:/g/support/ESHPvhJIsCBHijgwBeffvcABU-VZCt6ZON1OMcguK2sGoQ?e=qsLNUI What is modal analysis?.]<br> | ||
[https://orossas.sharepoint.com/:b:/g/support/ETV5oBwxLjFHnsfVSL1hit0Bigt_2FuSJIbVmoHjAMPNug?e=Kb0vHk Common mistakes.] | [https://orossas.sharepoint.com/:b:/g/support/ETV5oBwxLjFHnsfVSL1hit0Bigt_2FuSJIbVmoHjAMPNug?e=Kb0vHk Common mistakes.] | ||
| Line 6: | Line 8: | ||
==Acquisition== | ==Acquisition== | ||
===Generality=== | ===Generality=== | ||
[https://orossas.sharepoint.com/:b:/g/support/EQKjRyGlsShNg14lgX6gUtwBSq9W2VdBEwiDQ4jTvI8trg?e=1bCxCc | [https://orossas.sharepoint.com/:b:/g/support/EQKjRyGlsShNg14lgX6gUtwBSq9W2VdBEwiDQ4jTvI8trg?e=1bCxCc Basic steps to acquire data]<br> | ||
[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/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?]<br> | ||
[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/EfDJXZ2NsXBIpNnOPouoJLIBlqBNBjgTfnKQ4OUMay4R6g?e=igvjzh How many points are enough when running a modal test] <br> | ||
[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/EV4GFjhvcStErAqtxUDAFcUBU6db28UlUtckHR2l09Ad7A?e=3DHX1C is it better to collect averaged FRF data for a modal test? Or collect time data and process it afterwards?]<br> | ||
[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/EZfWJLtRuCtDpCkrd09zwEUBz2GXFlFjmWmBjBPJ7O1igw?e=o5c75e We talked about the number of points needed for a modal test before.]<br> | ||
===Sensor and reference=== | ===Sensor and reference=== | ||
[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/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?]<br> | ||
[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/EVWdcqfwhc9Mshv8R6M5BKYB_I8x96uro6ItAhVah31wGA?e=qqb8So Is there a difference between a roving hammer and roving accelerometer test?]<br> | ||
[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/ET7xJmNNuyNGnpoX_E0s9MIB7BfU3wKfDjv3gtZlsjGGZA?e=M0mIrO Someone told me that you must have multiple references to identify pseudo repeated.]<br> | ||
[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/EV3I4RVyqhtInP82-HGjH2gBff6U72IhA7orXLTNWH5LLg?e=JGOeAo Is there any benefit to using multiple references?I thought only one reference was need.]<br> | ||
[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] | [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]<br> | ||
[https://orossas.sharepoint.com/:b:/g/support/ESAbTQrm4yFKi0RMb2BVRTYBexWVHZewsr7hvDLPuEtUSQ?e=AZTle9 double impact question] | [https://orossas.sharepoint.com/:b:/g/support/ESAbTQrm4yFKi0RMb2BVRTYBexWVHZewsr7hvDLPuEtUSQ?e=AZTle9 double impact question] | ||
==Shacker== | ==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/EZ0xK6BALQlMgiXqGEh1UNkBJfsAo4aPmTwE7UKcLSppEg?e=NpNUPs Is there any difference between a modal test with a shaker excitation or impact excitation?]<br> | ||
[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?]<br> | ||
[https://orossas.sharepoint.com/:b:/g/support/EUR6b2uoMXFDkHczw0ZVizwBTKY2otdmB3CNUz2t7-eAvw?e=hw0ffo Which shaker excitation is best? Is there any difference?]<br> | |||
[https://orossas.sharepoint.com/:b:/g/support/EUR6b2uoMXFDkHczw0ZVizwBTKY2otdmB3CNUz2t7-eAvw?e=hw0ffo Which shaker excitation is best? Is there any difference?] | |||
==results interpretation.== | ==results interpretation.== | ||
| Line 31: | Line 31: | ||
==Modal theorical== | ==Modal theorical== | ||
===Windowing=== | ===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/ESeXYLSIKetIp7v1LyevBO0BI0hStYqFdzah5aO9kzgGIA?e=MTVQsF When impact testing, can the use of the exponential window cause any problems?]<br> | ||
[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/EUw3GiSkKIdBmFAZLE5vw-IBZ6-2-Yczz7zz4i3cTda2iQ?e=btozQG Which window is most appropriate for the various types of modal tests performed?]<br> | ||
[https://orossas.sharepoint.com/:b:/g/support/EZmiM-le4zpDvsyTb1Kfmc0B7AymLe5HB810BiQ2jtsxhQ?e=vJbs0G I heard someone say Pete doesn't do windows. Whets the scoop.] | [https://orossas.sharepoint.com/:b:/g/support/EZmiM-le4zpDvsyTb1Kfmc0B7AymLe5HB810BiQ2jtsxhQ?e=vJbs0G I heard someone say Pete doesn't do windows. Whets the scoop.]<br> | ||
===Curvfitting=== | ===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!]<br> | ||
[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/Ebec28JEGMVMvyRfvQZt0GgBOROstYIXhuvGDcWinV9r7A?e=HiXoPC What's the difference between local and global curvefitting ?]<br> | ||
[https://orossas.sharepoint.com/:b:/g/support/Ea9f9MN6HDRFsZpwejhz7NwBmCNR8dXZvc-vuCLIVoNGww?e=k2ATuM I still don't understand curvefitting ...] | [https://orossas.sharepoint.com/:b:/g/support/Ea9f9MN6HDRFsZpwejhz7NwBmCNR8dXZvc-vuCLIVoNGww?e=k2ATuM I still don't understand curvefitting ...] | ||
===others questions=== | ===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/EXQqztDPrmdAnJ9kU9OVB80B0oGkUjtqvwZwg9M29HfWzA?e=tpRaTG What's the difference between a complex mode and a real normal mode?]<br> | ||
[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/EXaI-C0co7lNrKrXwfquUAgBNBKd7GQf1CvSFvyuk-ywfQ?e=T9MACh Could you explain the difference between time domain, frequency domain and modal space?]<br> | ||
[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/EdcRQK9hbXlJnDYwtTpT-PIBLpl_qPzNmgGtAEsUjqJqVw?e=EJ9Lzi I ran a modal test on a portion of a structure of concern and many modes look the same!]<br> | ||
[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/EYn8VMAjMoVHqynlrHcaI-wBd7Oi5A55fjkyKHZAyPBeQg?e=rUffYN Someone told me SDM will never work]<br> | ||
[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/EVTrvk3ZJQNKkGlX6NmVl9cBDZMOI2kPc4vnKpUW2G9swA?e=ylkpgg Are you sure you can get mode shapes from one row or column of the H matrix?]<br> | ||
[https://orossas.sharepoint.com/:b:/g/support/EZrt0mNRSxdBtew4xoQjLTgB0evFRtDOgnhDzuOYIXLE7w?e=3ziz3G I hear about SVD all the time Could you explain it simply to me?]<br> | |||
[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/EamEoIefNl5Pg0zVmkDUv_4Bh3TXKPJz991K65nXTbuxdg?e=3KQWga I'am still overwhelmed by all this modal stuff Laplace, Fourier, FRFs, and all that!]<br> | ||
[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 ?]<br> | |||
[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?]<br> | |||
[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/EQbt6Vnt4KVMo4ma2i2aVsQBqd1-nHRGjmpaOzymCT2seg?e=KjIRqC Mode shape scaling requires a drive point measurement.Is there any way to scale shapes without this ?]<br> | ||
[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/ESajfBbFfnhMvEhmiI5e1BQBAniHZiFbHOyjOslbWLViDQ?e=R096s2 What's the difference between operating deflection shapes and mode shapes? sometimes they look the same to me!]<br> | ||
[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/EbOrZLh9ciJFut6vhJF-ZUcB3uMpxjtPEWgXYKqITdGVhA?e=4rQILL Why is mass loading and data consistencyimportant for modal parameter estimation?]<br> | ||
[https://orossas.sharepoint.com/:b:/g/support/EdfeqFk3QiVCtOnH7pR4v70BIt91qGFZeKYnAcXNkoiX2A?e=LFHkTg Should I use all collected measurements when estimating modal parameters ?]<br> | |||
[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 ?] | |||
[https://orossas.sharepoint.com/:b:/g/support/ESajfBbFfnhMvEhmiI5e1BQBAniHZiFbHOyjOslbWLViDQ?e=R096s2 What's the difference between operating deflection shapes and mode shapes? sometimes they look the same to me!] | |||
[https://orossas.sharepoint.com/:b:/g/support/EbOrZLh9ciJFut6vhJF-ZUcB3uMpxjtPEWgXYKqITdGVhA?e=4rQILL Why is mass loading and data consistencyimportant for modal parameter estimation?] | |||
[https://orossas.sharepoint.com/:b:/g/support/EdfeqFk3QiVCtOnH7pR4v70BIt91qGFZeKYnAcXNkoiX2A?e=LFHkTg Should I use all collected measurements when estimating modal parameters ?] | |||
[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 ?] | ||
Latest revision as of 09:55, 10 September 2020
The following articles have originally been published in SEM Experimental Techniques. It is write by Dr Peter Avitabile head of The Structural Dynamics and Acoustic Systems Laboratory (SDASL) at the University of Massachusetts
Modal Generality
What is modal analysis?.
Common mistakes.
Acquisition
Generality
Basic steps to acquire data
Can the test setup have an effect on the measured modal data ? Do the setup boundary conditions and accelerometers have an effect?
How many points are enough when running a modal test
is it better to collect averaged FRF data for a modal test? Or collect time data and process it afterwards?
We talked about the number of points needed for a modal test before.
Sensor and reference
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 ?
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?
Someone told me that you must have multiple references to identify pseudo repeated.
Is there any benefit to using multiple references?I thought only one reference was need.
Should I always use a hard tip for impact testing . . .so the input spectrum is flat over all frequencies
double impact question
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
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.
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?
Mode shape scaling requires a drive point measurement.Is there any way to scale shapes without this ?
What's the difference between operating deflection shapes and mode shapes? sometimes they look the same to me!
Why is mass loading and data consistencyimportant for modal parameter estimation?
Should I use all collected measurements when estimating modal parameters ?
Why do some measurements have anti-resonances and others not ?