Determines the optimal shaker locations and orientations for a modal test.
[shaker,candidate] = shaker_locator(sg,aset[,fem][,OPTARGS])
SHAKER_LOCATOR determines the optimal shaker locations and orientations for a modal test from supplied mode shapes and test DOF. The theory behind its operation is documented in
Napolitano, Blelloch, "Automated Selection of Shaker Locations for Modal Tests," Proceedings from the XXI IMAC Conference, Kissimmee, FL, 2003.
SG is an imat_shp containing all of the shapes used to calculate the frequency response. The shape coefficients must be in the Basic or Displacement coordinate system. All of the shapes must use the same coordinate systems, and the input and output angles are defined in the coordinate system(s) of the shapes.
ASET is an imat_ctrace containing the test measured DOF (ASET).
FEM is an optional input argument containing the imat_fem related to the shapes. If supplied, the shaker locations and orientations will be displayed on this FEM. Otherwise, you can use PLOT_SHAKER_LOCATIONS to display the locations.
Several optional input arguments are supported. They must each be specified as a string containing the argument type, followed by the argument. The valid arguments are listed below. If an argument is not specified, the default listed below will be used.
String | Value | ||||||||||||||
'target_modes' |
Vector of mode shape numbers that are defined as Target Modes (default: use all modes in SG) |
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'force_loc' |
Column vector containing node numbers to use as force location candidates, or matrix containing node numbers and angles. Angles are specified in the coordinate system of the shape coefficients in SG. [Node XY_start XY_end DeltaXY Z_start Z_end DeltaZ]
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'nmif_level' | Scalar of vector containing the required NMIF levels for optimization to be determined successful. Default is 0.2. | ||||||||||||||
'coupling' |
Minimum required cross-MAC (or cross-ortho between imaginary portion of operating deflected shape (ODS) and mode shape to ensure that one shaker excites only one of N modes with repeated roots. MAC: (Recommend >= 55). Default is 55. Ortho: (Recommend >= 71). Default is 80. |
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'niter' |
Number of times optimization is run for each number of shakers (Recommend >= 10). Default is 20. |
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'mass' | Substructure containing a mass matrix and ASET DOF. If provided, orthogonality will be used instead of MAC. |
Two output arguments are available.
SHAKER is an Nx1 structure containing the optimal shaker location information. It contains these fields:
Node | Optimal Shaker Nodes for the specified NMIF level. |
XY_angle | Optimal Shaker Angle in the XY plane. |
Z_angle | Optimal Shaker Angle from the XY plane. |
Nmodes | Number of modes with NMIF values below NMIF level. |
fn_MIF | imat_fn containing NMIF at the natural frequencies for the optimal shakers for the specified NMIF level. |
NMIF_level | NMIF level used for this iteration. |
Not_Found | Target modes with NMIF below the NMIF level. |
Found | Target modes with NMIF below the specified NMIF level. |
shp | imat_shp that contains vectors showing the location and orientation of the shakers. |
dircos | Direction cosines for each shaker. |
CSType | Coordinate system in which the direction cosines and angles are defined (Basic or Displacement). |
CANDIDATE contains a data for all of the candidate shaker locations and directions evaluated.
fn_MIF | Calculated NMIF for all candidate shaker locations and directions at natural frequencies |
Node | Candidate shaker node(s) |
XY_angle | Candidate shaker orientation in the XY plane |
Z_angle | Candidate shaker orientation from the XY plane |
>> [shaker,candidate]=shaker_locator(sg,TAM.aset)
shaker_frfs, plot_shaker_locations