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Alter to Perform Pre-Test Analysis


Alter Name     premaca.alt


Purpose

To compute the cross-orthogonality between modes of a full model
and modes of a reduced model.  Three cross-orthogonality checks are
made:  modal assurance criterion (MAC) and two types of mass
orthogonality (ORTHOA and CHECKIT).

Define:

PHIG    g-set mode shapes from full model
PHIA    a-set mode shapes from reduced model
PHIT    PHIG partitioned to a-set degrees of freedom
MAA     a-set mass

Compute:        MAC(i,j), ORTHOA(i,j), CHECKIT(i,j)

This procedure can be used, for example, to help select the best
measurement locations for a modal test by letting the a-set represent
the proposed measurement locations.


Solution Sequence

SOL 103.


Input
 
Executive Control

Include 'premaca.alt'
 
Case Control

No special Case Control is required.
 
Bulk Data

Several inputs are required:

1.  
Input for the reduced model with a specified a-set.

2.  
DMIG entries representing the displacements punched
from the large model.  These are the displacements at
the DOF corresponding to the a-set for the reduced
model.


Output

There are several outputs:

        1.  
MAC.  This is in the form of a line of output for each set of
modes that are compared.

ANALYTICAL MODE 1 COMPARED TO INPUT MODE 1  - MAC = 1.00
ANALYTICAL MODE 1 COMPARED TO INPUT MODE 2  - MAC = 0.10
ANALYTICAL MODE 1 COMPARED TO INPUT MODE 3  - MAC = 0.00

"Analytical modes" are the modes computed from the reduced
model, and "input modes" are the modes from the full model. 
There are i times j lines of output where i is the number of
analytical modes and j is the number of input modes.

        2.  
Matrix CHECKIT.

        3.  
Matrix ORTHOA.

        4.  
Punched a-set mode shapes (PHIEXT) and mass (MAAEXT)
in DMIG format.  These are used in post-test model
verification (see Alter postmaca.v68).


Limitations

None.


Sample Files

premac1.dat   10-bar cantilever beam full model that includes an
alter (pchdispa.v68), which punches the g-set modal
displacements onto file premac1.pch.

premac2.dat   10-bar cantilever beam model with an a-set for axial
and longitudinal translation of grid points 3, 5, 7, 9,
and 11.  This run includes the punched g-set
displacements (premac1.pch) from above.  MAC,
CHECKIT, and ORTHOA are computed.  "a-set"
modal displacements (PHIEXT) and mass (MAAEXT)
are punched onto file premac2.pch.


Additional Documentation

K. Blakely and T. Rose, "Cross-Orthogonality Calculations for Pre-Test
Planning and Model Verification," 1993 MSC World Users'
Conference Proceedings, May 1993.