Difference between revisions of "Modal practical"

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[[category:Modal]]


==Download==
Download the data of the project [https://orossas.sharepoint.com/:u:/g/support/ER5_KKas6Y9Fm2neEIlNXt4BR5N3qnpI_3kIWyGylOCrXA?e=HeBoff here].


==Create a new project==
- Open the software<br>
- Click on `File/New' and give a name to your project `Cantilever'.


===GEOMETRY BUILDING===


The goal of this part is to model the cantilever by the geometry below. The different steps of the procedure are described here.


[[Image:Modal_practical_13.png|framed|none]]


==GEOMETRY BUILDING==


 
* Position in the XY plan by clicking on `Top view<nowiki>’</nowiki> in the toolbar.
 
<font color="#363639">The goal of this part is to model the cantilever by the geometry below. The different steps of the procedure are described here.
 
</font>
[[Image:Modal_practical_13.png|framed|none]]
 
{|border="0" cellspacing="2" width="71%"
|
* <font color="#363639">Position in the XY plan by clicking on `Top view<nowiki>’</nowiki> in the toolbar.
|
[[Image:Modal_practical_14.png|framed|none]]
[[Image:Modal_practical_14.png|framed|none]]


|}


* Line 1
* Line 1
Click on `add line<nowiki>’</nowiki>  
Click on `add line<nowiki>’</nowiki> [[Image:Modal_practical_15.png]]in the geometry toolbar. A line is defined as follow:
[[Image:Modal_practical_15.png|framed|none]]
in the geometry toolbar. A line is defined as follow:


[[Image:Modal_practical_07.png|framed|none]]
[[Image:Modal_practical_07.png|framed|none]]
Line 31: Line 26:
For each line, the software associates a Cartesian coordinates system. The line is defined by the origin of this system, the direction of X axis, the length and the number of segments.
For each line, the software associates a Cartesian coordinates system. The line is defined by the origin of this system, the direction of X axis, the length and the number of segments.


</font>
----


<font color="#363639">To create the line 1, enter the following parameters:</font>
To create the line 1, enter the following parameters:


[[Image:Modal_practical_16.png|framed|none]]
[[Image:Modal_practical_16.png|framed|none]]


==Note: for the local coordinate system parameters, enter parameters about origin point and Euler angles only.==
Note: for the local coordinate system parameters, enter parameters about origin point and Euler angles only.
 
<font color="#363639">Rename  the  point  6  in  point  3  by  opening  `Config  review<nowiki>’</nowiki>  and  make  the  modification  in  the


Rename  the  point  6  in  point  3  by  opening  `Config  review<nowiki>’</nowiki>  and  make  the  modification  in  the
`nodes<nowiki>’</nowiki> window.
`nodes<nowiki>’</nowiki> window.


</font>==Note:  When  the  `config  review<nowiki>’</nowiki>  is  activated,  click  on  `modeling  interface<nowiki>’</nowiki>  button
Note:  When  the  `config  review<nowiki>’</nowiki>  is  activated,  click  on  `modeling  interface<nowiki>’</nowiki>  button [[Image:Modal_practical_17.png]]to display both `geometry<nowiki>’</nowiki> and `config review<nowiki>’</nowiki> windows.
[[Image:Modal_practical_17.png|framed|none]]
to display both `geometry<nowiki>’</nowiki> and `config review<nowiki>’</nowiki> windows.==


* <font color="#363639">Line 2
* Line 2
Click on `add line<nowiki>’</nowiki>  
Click on `add line<nowiki>’</nowiki> [[Image:Modal_practical_18.png]]and enter the following parameters
[[Image:Modal_practical_18.png|framed|none]]
and enter the following parameters


</font>
----


[[Image:Modal_practical_19.png|framed|none]]
[[Image:Modal_practical_19.png|framed|none]]


<font color="#363639">Remove the line between point 18 and 19 by clicking on `select lines<nowiki>’</nowiki> in the toolbar Select the line 18-19 and delete it.</font>
Remove the line between point 18 and 19 by clicking on `select lines<nowiki>’</nowiki> in the toolbar Select the line 18-19 and delete it.


<font color="#363639">Rename the point 18 in point 1.</font>
[[File:selectline.png|framed|none]]


<font color="#363639">Create the lines 1-19 and 3-7 by clicking on
Rename the point 18 in point 1.


`add lines<nowiki>’</nowiki> in the toolbar
Create the lines 1-19 and 3-7 by clicking on`add lines<nowiki>’</nowiki> in the toolbar and link the points directly on the geometry. (left click on the 2 points and right click to end the operation)


and link the points directly on the geometry. (left click on the 2 points and right click to end the operation)


</font>
[[Image:Modal_practical_20.png|framed|none]]
[[Image:Modal_practical_20.png|framed|none]]


* <font color="#363639">Line 3</font>
* Line 3


<font color="#363639">Click on `add lines<nowiki>’</nowiki>  
Click on `add lines<nowiki>’</nowiki> [[Image:Modal_practical_21.png]] and link point 1 and 3
[[Image:Modal_practical_21.png|framed|none]]
and link point 1 and 3


[[Image:Modal_practical_08.png|framed|none]]
[[Image:Modal_practical_08.png|framed|none]]


To  create  point  2,  click  on  `add  nodes<nowiki>’</nowiki>   
To  create  point  2,  click  on  `add  nodes<nowiki>’</nowiki>  [[Image:Modal_practical_22.png]],  a  grid  is displayed to help you to position new points. Right click to fix a new point and rename it in point 2.
[[Image:Modal_practical_22.png|framed|none]]
,  a  grid  is displayed to help you to position new points. Right click to fix a new point and rename it in point 2.


</font>
* Line 4


----
Create the points 4, 5 and 6 with the grid and add lines to link them.


* <font color="#363639">Line 4</font>
[[File:line4.png|framed|none]]


<font color="#363639">Create the points 4, 5 and 6 with the grid and add lines to link them.</font>
* Experimental coordinates systems


Regarding the axis definition for the acquisition, 2 local coordinates systems should be added respectively on the nodes of line 1 and 2.


* <font color="#363639">Experimental coordinates systems</font>
In the `config review<nowiki>’</nowiki> select the nodes of lines 1. Right click and select `Assign Coord.<nowiki>’</nowiki>
 
<font color="#363639">Regarding the axis definition for the acquisition, 2 local coordinates systems should be added respectively on the nodes of line 1 and 2.</font>
 
<font color="#363639">
[[Image:Modal_practical_02.jpg|framed|none]]
[[Image:Modal_practical_02.jpg|framed|none]]


In the `config review<nowiki>’</nowiki> select the nodes of lines 1. Right click and select `Assign Coord.<nowiki>’</nowiki></font>
To reproduce the experimental conditions, enter the following parameters
 
[[Image:Modal_practical_09.jpg|framed|none]]
[[Image:Modal_practical_09.jpg|framed|none]]


<font color="#363639">To reproduce the experimental conditions, enter the following parameters</font>
In the `Config review<nowiki>’</nowiki> select the nodes of line 2. Right click and select `Assign Coord.<nowiki>’</nowiki> Enter the following parameters
[[File:config.png|framed|none]]


----


<font color="#363639">In the `Config review<nowiki>’</nowiki> select the nodes of line 2. Right click and select `Assign Coord.<nowiki>’</nowiki> Enter the following parameters</font>
Delete the coordinates systems 1 and 2 in `config review<nowiki>’</nowiki> /coordinates


 
<font color="#363639">Delete the coordinates systems 1 and 2 in `config review<nowiki>’</nowiki> /coordinates</font>
*Results
 
* <font color="#363639">
[[Image:Modal_practical_03.png|framed|none]]
[[Image:Modal_practical_03.png|framed|none]]


Results</font>
==DATA IMPORT AND READING==
 
----
 
{|border="0" cellspacing="2" width="90%"
|
## <font color="#FFFFFF">DATA IMPORT AND READING
|</font>
 
|}
 
 
{|border="0" cellspacing="2" width="90%"
|
### <font color="#FFFFFF">DATA IMPORT
|</font>


|}
===Data import===
For  this  demo,  use  the  data  file  `CANTILEVER  HAMMER  DATA.uff<nowiki>’</nowiki>  containing  the  Frequency Response Functions acquired with one impact hammer and 2 accelerometers.


<font color="#363639">For  this  demo, use  the  data  file  `CANTILEVER  HAMMER  DATA.uff<nowiki>’</nowiki>  containing  the  Frequency Response Functions acquired with one impact hammer and 2 accelerometers.</font>
In the File menu, click on Import/Data files (UFF). The following window is displayed.
[[File:import_modal.png|framed|none]]


<font color="#363639">In the File menu, click on Import/Data files (UFF). The following window is displayed.</font>


<font color="#363639">Select `acceleration<nowiki>’</nowiki> for response type,
Select `acceleration<nowiki>’</nowiki> for response type,


`Frequency domain<nowiki>’</nowiki> for data type.
`Frequency domain<nowiki>’</nowiki> for data type.
Line 148: Line 106:
, select the file `CANTILEVER HAMMER DATA.uff<nowiki>’</nowiki> and click on OK.
, select the file `CANTILEVER HAMMER DATA.uff<nowiki>’</nowiki> and click on OK.


</font>


<font color="#363639">The following window shows all the results contained in the imported file with their characteristics. Information of nodes and directions can be modified if an error occurs.
 
The following window shows all the results contained in the imported file with their characteristics. Information of nodes and directions can be modified if an error occurs.


Any filters are available to import a part of the data only.
Any filters are available to import a part of the data only.


</font>
 


----
----
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[[Image:Modal_practical_24.jpg|framed|none]]
[[Image:Modal_practical_24.jpg|framed|none]]


<font color="#363639">Here all the data will be used, so click on OK. The FRFs are directly displayed in the software.</font>
Here all the data will be used, so click on OK. The FRFs are directly displayed in the software.




<font color="#363639">All the FRFs can be visualized.</font>
[[File:FRF_modal.png|framed|none]]


----
All the FRFs can be visualized.
 
===DATA READING===


{|border="0" cellspacing="2" width="90%"
By using the Control Panel (Series select), all the FRFs can be displayed. For each result, there is information about the DOFs (node, direction).
|
### <font color="#FFFFFF">DATA READING
|</font>


|}
Several types of displayed are available by right clicking on the graph: magnitude/phase, real/imaginary, Nyquist.


<font color="#363639">By using the Control Panel (Series select), all the FRFs can be displayed. For each result, there is information about the DOFs (node, direction).</font>
By  right  clicking  on  the  graph  and  selecting  `Showed  Series…<nowiki>’</nowiki>, you  can  display  several  FRFs on the same graph for comparison.


<font color="#363639">Several types of displayed are available by right clicking on the graph: magnitude/phase, real/imaginary, Nyquist.</font>
==MODAL IDENTIFICATION==


<font color="#363639">By  right  clicking  on  the  graph  and  selecting  `Showed  Series…<nowiki>’</nowiki>, you  can  display  several  FRFs on the same graph for comparison.</font>


{|border="0" cellspacing="2" width="90%"
|
# <font color="#FFFFFF">MODAL IDENTIFICATION
|</font>


|}


===OPERATING DEFLECTION SHAPE===


{|border="0" cellspacing="2" width="90%"
|
## <font color="#FFFFFF">OPERATING DEFLECTION SHAPE
|</font>


|}
In the operation tree, double click on `ODS: Freq Domain  The following interface is displayed.
[[File:ODS.png|framed|none]]


<font color="#363639">
On the left, the Modal Indication Function (MIF) shows the modes in the frequency band. Position the cursor on the peaks and visualize the corresponding mode shapes on the right.
[[Image:Modal_practical_04.jpg|framed|none]]
[[Image:Modal_practical_04.jpg|framed|none]]


In the operation tree, double click on `ODS: Freq Domain  The following interface is displayed.</font>
==MODAL ANALYSIS USING EMA BROBAND==


<font color="#363639">On the left, the Modal Indication Function (MIF) shows the modes in the frequency band. Position the cursor on the peaks and visualize the corresponding mode shapes on the right.</font>


----
In the operation tree:


<font color="#363639">'''''What is the MIF?'''''</font>
* 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


==MIF can be employed in not only EMA, but also OMA. In EMA case, the number of MIFs equals the number of excitations or references. In OMA case, the number of MIFs equals the minimum number of responses of each setup. The MIFs consist of the singular values of frequency response function matrix (FRF), output power spectral density matrix (OPSD), or half power spectral density matrix (HPSD).==
<font color="#363639">By the powerful singular value decomposition, the real signal space is separated from the noise space. Therefore, the MIFs exhibit the modes effectively. A peak in the MIFs plot usually indicate the existence of a structural mode, and two peaks at a same frequency point means the existence of two repeated modes. Moreover, the magnitude of the MIFs always implies the strength of a mode.</font>
<font color="#363639">Two separated modes</font>
----
<font color="#363639">Weak modes</font>
<font color="#363639">Two pairs of repeated modes</font>
----
<font color="#363639">Sometimes we should note the cross modes. For example, in the below figure, the peak in the second MIF curve doesn<nowiki>’</nowiki>t indicate a mode. It<nowiki>’</nowiki>s formed by the cross of two modes.</font>
----
{|border="0" cellspacing="2" width="90%"
|
## <font color="#FFFFFF">MODAL ANALYSIS USING EMA BROBAND
|</font>
|}
<font color="#363639">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
</font>
[[Image:Modal_practical_12.png|framed|none]]
[[Image:Modal_practical_12.png|framed|none]]


The follwoing windows is displayed:
[[File:modal_id.png|framed|none]]




----
* 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.


# <font color="#363639">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.</font>
* Modal identification
 
# <font color="#363639">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
* 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|framed|none]]
, 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_27.jpg|framed|none]]
[[Image:Modal_practical_27.jpg|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 [[Image:Modal_practical_11.png]].


# Mode shapes calculation
* 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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----
----


# Results visualization
* Results visualization


[[Image:Modal_practical_10.jpg|framed|none]]
[[Image:Modal_practical_10.jpg|framed|none]]
Line 310: Line 220:
To visualize the list of the modes, double click on `EMA: BroBand The list of results will be displayed. By right clicking on a mode and  selecting  `animate<nowiki>’</nowiki>,  the  corresponding  mode  shape  will  be showed.
To visualize the list of the modes, double click on `EMA: BroBand The list of results will be displayed. By right clicking on a mode and  selecting  `animate<nowiki>’</nowiki>,  the  corresponding  mode  shape  will  be showed.


[[File:animate.png|framed|none]]


 
== MODAL VALIDATION ==
{|border="0" cellspacing="2" width="90%"
|
# MODAL VALIDATION
|&nbsp;
 
|}
 
The first way to check the results is to look at the coherence between the experimental FRFs and the synthesized ones in the selected frequency band.
The first way to check the results is to look at the coherence between the experimental FRFs and the synthesized ones in the selected frequency band.


Line 325: Line 229:
Here,  we  have  results  from  Broadband  method.  The  repertory  `Cantilever  modal  demo<nowiki>’</nowiki> contains a file `MIMO1 results<nowiki>’</nowiki> with the modal parameters obtained from MIMO1 method.
Here,  we  have  results  from  Broadband  method.  The  repertory  `Cantilever  modal  demo<nowiki>’</nowiki> contains a file `MIMO1 results<nowiki>’</nowiki> with the modal parameters obtained from MIMO1 method.


{|border="0" cellspacing="2" width="100%"
In the operation tree, double click on MAC: [[Image:Modal_practical_28.png]]
|In the operation tree, double click on MAC
|
[[Image:Modal_practical_28.png|framed|none]]
The following window is displayed
The following window is displayed


|}
----


[[Image:Modal_practical_29.jpg|framed|none]]
[[Image:Modal_practical_29.jpg|framed|none]]
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[[Image:Modal_practical_06.jpg|framed|none]]
[[Image:Modal_practical_06.jpg|framed|none]]


[[File:Mac.png|framed|none]]


== SAVE/EXPORT==


----
{|border="0" cellspacing="2" width="90%"
|
# SAVE/EXPORT
|&nbsp;
|}


The project can be saved in a workspace containing data, geometry, results… It<nowiki>’</nowiki>s also possible to save independently each part of a project.
The project can be saved in a workspace containing data, geometry, results… It<nowiki>’</nowiki>s also possible to save independently each part of a project.
Line 359: Line 249:
** Create a file uff 15 containing the geometry by clicking on File/export/geometry,
** Create a file uff 15 containing the geometry by clicking on File/export/geometry,
** Export the modal results by right clicking on the modes list and select `Export Modes…<nowiki>’</nowiki>
** Export the modal results by right clicking on the modes list and select `Export Modes…<nowiki>’</nowiki>
** Create a file .avi with a mose shape by displaying a mode shape and click on  
** Create a file .avi with a mose shape by displaying a mode shape and click on [[Image:Modal_practical_30.png]]in the control panel.
[[Image:Modal_practical_30.png|framed|none]]
in the control panel.

Latest revision as of 09:54, 10 September 2020


Download

Download the data of the project here.

Create a new project

- Open the software
- Click on `File/New' and give a name to your project `Cantilever'.

GEOMETRY BUILDING

The goal of this part is to model the cantilever by the geometry below. The different steps of the procedure are described here.

Modal practical 13.png


  • Position in the XY plan by clicking on `Top view’ in the toolbar.
Modal practical 14.png


  • Line 1

Click on `add line’ Modal practical 15.pngin the geometry toolbar. A line is defined as follow:

Modal practical 07.png

For each line, the software associates a Cartesian coordinates system. The line is defined by the origin of this system, the direction of X axis, the length and the number of segments.


To create the line 1, enter the following parameters:

Modal practical 16.png

Note: for the local coordinate system parameters, enter parameters about origin point and Euler angles only.

Rename the point 6 in point 3 by opening `Config review’ and make the modification in the `nodes’ window.

Note: When the `config review’ is activated, click on `modeling interface’ button Modal practical 17.pngto display both `geometry’ and `config review’ windows.

  • Line 2

Click on `add line’ Modal practical 18.pngand enter the following parameters


Modal practical 19.png

Remove the line between point 18 and 19 by clicking on `select lines’ in the toolbar Select the line 18-19 and delete it.

Selectline.png

Rename the point 18 in point 1.

Create the lines 1-19 and 3-7 by clicking on`add lines’ in the toolbar and link the points directly on the geometry. (left click on the 2 points and right click to end the operation)


Modal practical 20.png
  • Line 3

Click on `add lines’ Modal practical 21.png and link point 1 and 3

Modal practical 08.png

To create point 2, click on `add nodes’ Modal practical 22.png, a grid is displayed to help you to position new points. Right click to fix a new point and rename it in point 2.

  • Line 4

Create the points 4, 5 and 6 with the grid and add lines to link them.

Line4.png
  • Experimental coordinates systems

Regarding the axis definition for the acquisition, 2 local coordinates systems should be added respectively on the nodes of line 1 and 2.

In the `config review’ select the nodes of lines 1. Right click and select `Assign Coord.’

Modal practical 02.jpg

To reproduce the experimental conditions, enter the following parameters

Modal practical 09.jpg

In the `Config review’ select the nodes of line 2. Right click and select `Assign Coord.’ Enter the following parameters

Config.png


Delete the coordinates systems 1 and 2 in `config review’ /coordinates


  • Results
Modal practical 03.png

DATA IMPORT AND READING

Data import

For this demo, use the data file `CANTILEVER HAMMER DATA.uff’ containing the Frequency Response Functions acquired with one impact hammer and 2 accelerometers.

In the File menu, click on Import/Data files (UFF). The following window is displayed.

Import modal.png


Select `acceleration’ for response type,

`Frequency domain’ for data type.

Click on the button

Modal practical 23.png

, select the file `CANTILEVER HAMMER DATA.uff’ and click on OK.


The following window shows all the results contained in the imported file with their characteristics. Information of nodes and directions can be modified if an error occurs.

Any filters are available to import a part of the data only.


Modal practical 24.jpg

Here all the data will be used, so click on OK. The FRFs are directly displayed in the software.


FRF modal.png

All the FRFs can be visualized.

DATA READING

By using the Control Panel (Series select), all the FRFs can be displayed. For each result, there is information about the DOFs (node, direction).

Several types of displayed are available by right clicking on the graph: magnitude/phase, real/imaginary, Nyquist.

By right clicking on the graph and selecting `Showed Series…’, you can display several FRFs on the same graph for comparison.

MODAL IDENTIFICATION

OPERATING DEFLECTION SHAPE

In the operation tree, double click on `ODS: Freq Domain The following interface is displayed.

ODS.png

On the left, the Modal Indication Function (MIF) shows the modes in the frequency band. Position the cursor on the peaks and visualize the corresponding mode shapes on the right.

Modal practical 04.jpg

MODAL ANALYSIS USING EMA BROBAND

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
Modal practical 12.png

The follwoing windows is displayed:

Modal id.png


  • 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 + 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:

Symbol Description
o The pole is not stable. (The poles obtained from the first order are always
considered as unstable.)
f The frequency of the pole does not change within the tolerance of 1%.
v The frequency of the pole does not change within the tolerance of 1%,
and the pole vector does not change within the tolerance of 10%
d The frequency of the pole does not change within the tolerance of 1%,
and the damping of the pole does not change within the tolerance of 10%.
s Both frequency, damping and vector are stable within the tolerances: the frequency of the pole does not change within the tolerance of 1%; the pole vector does not change within the tolerance of 10%;
and the damping of the pole does not change within the tolerance of 10%.
Modal practical 25.jpg
  • Auto selection of structural modes

Press the button of "Auto Selection" or 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.


Modal practical 27.jpg


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 Modal practical 11.png.

  • 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.

Modal practical 05.png
  • Results visualization
Modal practical 10.jpg

To visualize the list of the modes, double click on `EMA: BroBand The list of results will be displayed. By right clicking on a mode and selecting `animate’, the corresponding mode shape will be showed.

Animate.png

MODAL VALIDATION

The first way to check the results is to look at the coherence between the experimental FRFs and the synthesized ones in the selected frequency band.

To go further, results from 2 different methods can be compared using the Modal Assurance Criterion (MAC).

Here, we have results from Broadband method. The repertory `Cantilever modal demo’ contains a file `MIMO1 results’ with the modal parameters obtained from MIMO1 method.

In the operation tree, double click on MAC: Modal practical 28.png The following window is displayed


Modal practical 29.jpg

Click on Import Modes and select the file `MIMO1 results’ and OK

Modal practical 06.jpg
Mac.png

SAVE/EXPORT

The project can be saved in a workspace containing data, geometry, results… It’s also possible to save independently each part of a project.

    • The data (FRFs) are saved in uff 58
    • Create a file uff 15 containing the geometry by clicking on File/export/geometry,
    • Export the modal results by right clicking on the modes list and select `Export Modes…’
    • Create a file .avi with a mose shape by displaying a mode shape and click on Modal practical 30.pngin the control panel.
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