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Difference between revisions of "Modal practical"
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→MODAL ANALYSIS USING EMA BROBAND
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In the operation tree: | In the operation tree: | ||
* select EMA Broband (A red icon appears near the method), | |||
* the MIF is displayed, | |||
* Select a large frequency band by positioning the cursors and double click to fix them (a black line between the 2 cursors appears), | |||
* click on start identification | |||
[[Image:Modal_practical_12.png|framed|none]] | [[Image:Modal_practical_12.png|framed|none]] | ||
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* Preliminary determination of the number of modes in the selected frequency band according to the MIF plot, and fill it in the edit box of "Preset Modes No." Then the BroBand software will calculate a default "minimum order" according to this number. The relationship between "Preset Modes No." and "Minimum Order" is: minimum order = (preset modes No)*Ni/2, where Ni means the number of input. Change the number of "Order Span" if necessary. The BroBand software will estimate the poles with a range of system order from "Minimum Order" to "Maximum Order", where Maximum order= Minimum order <nowiki>+</nowiki> Order Span-1. The default order span is 12. | |||
* Modal identification | |||
Press the button of "Start Modal ID" to obtain frequency stability diagram. This operation might take a little longer time to finish a complex structure with large number of modes and measurement coordinates. In the stability diagram, a shape symbol represents one pole. A pole in this diagram may represent a physical (i.e. structural) mode or a spurious (or noise) mode. It is normally not difficult to distinguish physical/structural) mode from spurious/noise mode by the distribution of poles. Generally speaking, a physical/structural mode can be identified in each proper number of order, while for a spurious/noise pole it usually is not the case. There are five kinds of symbols to indicate the poles: | Press the button of "Start Modal ID" to obtain frequency stability diagram. This operation might take a little longer time to finish a complex structure with large number of modes and measurement coordinates. In the stability diagram, a shape symbol represents one pole. A pole in this diagram may represent a physical (i.e. structural) mode or a spurious (or noise) mode. It is normally not difficult to distinguish physical/structural) mode from spurious/noise mode by the distribution of poles. Generally speaking, a physical/structural mode can be identified in each proper number of order, while for a spurious/noise pole it usually is not the case. There are five kinds of symbols to indicate the poles: | ||
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[[Image:Modal_practical_25.jpg|framed|none]] | [[Image:Modal_practical_25.jpg|framed|none]] | ||
* Auto selection of structural modes | |||
Press the button of "Auto Selection" or | Press the button of "Auto Selection" or [[Image:Modal_practical_26.png]], the OM2 selects the physical/structural modes automatically. While move the mouse cursor on a pole, the modal frequency and damping ratio corresponding to this pole will be shown. You can move the mouse on different poles to check the stability via small change of the modal frequency and/or damping ratio. | ||
[[Image:Modal_practical_26.png | |||
, the OM2 selects the physical/structural modes automatically. While move the mouse cursor on a pole, the modal frequency and damping ratio corresponding to this pole will be shown. You can move the mouse on | |||
[[Image:Modal_practical_27.jpg|framed|none]] | [[Image:Modal_practical_27.jpg|framed|none]] | ||
[[Image:Modal_practical_11.png|framed|none]] | [[Image:Modal_practical_11.png|framed|none]] | ||
Note: Manual selection of structural modes: a pole can also be manually selected by clicking it or deselected it by same operation. A selected pole will be marked with a shape symbol | Note: Manual selection of structural modes: a pole can also be manually selected by clicking it or deselected it by same operation. A selected pole will be marked with a shape symbol | ||
* Mode shapes calculation | |||
Press the button of "Calc. Modeshape" to confirm the pole section and BroBand software start to estimate the mode shapes and to calculate the synthesized FRFs. | Press the button of "Calc. Modeshape" to confirm the pole section and BroBand software start to estimate the mode shapes and to calculate the synthesized FRFs. | ||
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[[File:animate.png|framed|none]] | [[File:animate.png|framed|none]] | ||
== MODAL VALIDATION == | == MODAL VALIDATION == | ||