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Difference between revisions of "Modal Theorical FAQ"
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[[File:modal.png|900px]] | [[File:modal.png|900px]] | ||
== | ==Generalit== | ||
[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.] | ||
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==Acquisition== | ==Acquisition== | ||
===Generality=== | ===Generality=== | ||
[https://orossas.sharepoint.com/:b:/g/support/EQKjRyGlsShNg14lgX6gUtwBSq9W2VdBEwiDQ4jTvI8trg?e=1bCxCc basic steps to acquire data] | [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.== | ||
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==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 ?] | ||