$
$     THIS ALTER IS CONFIDENTIAL AND A TRADE SECRET OF THE 
$     MSC.Software CORP.  THE RECEIPT OR POSSESSION OF
$     THIS ALTER DOES NOT CONVEY ANY RIGHTS TO REPRODUCE OR
$     DISCLOSE ITS CONTENTS, OR TO MANUFACTURE, USE, OR SELL
$     ANYTHING HEREIN, IN WHOLE OR IN PART, WITHOUT THE 
$     SPECIFIC WRITTEN CONSENT OF THE MSC.Software CORPORATION.                                
$

Alter to Evaluate the Ability of the Obtained Modes to
Represent the Solution to Applied Loadings


Alter Name     modevala.alt


Purpose

To determine if the modes obtained are capable of representing the
solution to a set of applied loadings.  A common practice in modal
solutions is to assume that if the modes are capable of representing
the static solution to an applied loading, they contain sufficient
information to represent the high frequency response of the structure
to a dynamic application of the loading.  This DMAP Alter provides
that information without having to perform a dynamic solution.


Solution Sequence

SOL 103.


Input
 
Executive Control

Include 'modevala.alt'
 
Case Control

Standard Case Control with a DISP request to find the
displacements of any points represented on the DMIG for the
static solutions.
 
Bulk Data

PARAM,EVAL,xx

         0  =     no evaluation 
        -1  =     perform evaluation and give summary of results.
        -2  =     perform evaluation and give results for each mode
                  (preferred).(default) - changed April, 1999
        -3  =     perform evaluation with intermediate output (not
                  recommended).

DMIG,UGVEXT entries for the static solutions.  These should
contain one column for each static loading.  These can be
created by using pchdispa.v68 as shown in file
modeval1.dat.


Output

In addition to the standard SOL 103 output, a summary of the ability of
the modes to represent the strain energy in the static deformed
shapes is printed.  If EVAL = -1, then only the fraction of the total is
printed.  If EVAL = -2, then the individual modal contributions is
printed.  (This is valuable in determining which modes are important
to the dynamic response.)


Limitations

The calculations in this alter are based on your eigenvectors being scaled
to unit generalized mass (the default scaling). If you choose MAX 
normalization, the results of this alter will be incorrect.

This DMAP only evaluates the ability of the modes to represent the
static solution.  This should give a good indication of the quality of the
modal solution but does not guarantee it.  In order to improve the
quality of the dynamic solution, you might obtain additional modes
(see appenda.v68), try using static residual vectors (resflexa.v68),
or use the mode-acceleration method of data recovery.


Sample Files

modeval1.dat    Creates DMIG entries for four static loadings on the
sample model.

modeval2.dat    Solves for system modes and evaluates their ability to
represent the static solutions.


Additional Documentation

T. Rose, "Some Suggestions for Evaluating Modal Solutions," 1992
MSC World Users' Conference Proceedings, Vol. 1, Paper No. 10,
May 1992.