
This task shows you how to insert a
frequency case.
Inserting a frequency case allows you to create objects
sets for the new environmental specifications, and to implicitly require a
normal modes solution procedure for the computation of the system
vibration frequencies and normal modes for a given nonstructural mass
distribution under given restraints. 

This capability is only available with the ELFINI
Structural Analysis (EST) product (except for inserting a first Frequency
Analysis Case).
Remember that if you do not have the ELFINI Structural
Analysis product license, your Finite Element Model can simultaneously
contain at most one Static Analysis Case and one Frequency Analysis Case.


Open the
sample00.CATAnalysis document from the samples directory. 


Select Insert > Frequency Case
.
The Frequency Case dialog box is displayed.
For each type of objects set (Restraints,
Masses, Static Case Solution), you can
require that your new Frequency Case contains either an empty
objects set or an objects set existing in a previously defined
Analysis Case.
The New and Reference
switches for Restrains and Masses objects sets
allow you to choose between these two options:
 New: the new objects set is empty.
 Reference: the new objects set is a copy of an
objects set existing in a previously defined Analysis Case.

If you clear the Restraints check
box, you create a Free Frequency Analysis Case that is to
say you require a computation of eigen frequencies by
referencing only nonstructural masses (no restraint). 
 Static Case Solution option allows you to perform a
preloaded frequency computation by selecting a static solution.
The frequency computation will then take the corresponding loads
into account and generate a (nonlinear, loaddependent) preloaded
frequency computation.

Only available with the
ELFINI Structural Analysis (EST) product. 


Set the switch for each type of objects set.

Click OK.
A new Frequency Case template (objects sets set)
appears in the Finite Element Model specification tree template
displayed on the left.
The new Frequency Analysis Case representation
consists of the following (empty) object sets:

Restraints

Masses

Solution


Edit the solution.
To do this, doubleclick Frequency Case
Solution.1 in the specification tree.
The Frequency Solution Parameters dialog box appears.

Number of Modes

Method (Iterative subspace, Lanczos)
(only available if you have ELFINI Structural Analysis (EST)
product installed, otherwise, the default method is Iterative
subspace).
If you select the Lanczos Method,
the Shift option appears: compute the modes beyond
a given value: Auto, 1Hz, 2Hz
and so forth. Auto means that the computation is
performed on a structure that is partially free.


Dynamic Parameters (Maximum iteration number,
Accuracy)

Mass Parameter: lets you take into
account or not the structural mass.
Select this check box lets you exclude the structural mass from the
total mass summation when computing the solution of a frequency
case with additional mass.

If you exclude the structural mass parameter in
a frequency case without additional masses (frequency case
without masses set), an error occurs while computing the
solution.
If the frequency case does not contain any
masses set, do not select this option. 


Change the desired parameters.

Click OK.


By default, the last created (inserted) Analysis Case is
set as current, and the corresponding objects set is underlined in the
analysis features tree.
A right mouse click (key 3) on a Frequency Case objects set
further allows the following action:
Set as Current: allows you to define the Frequency Analysis Case
as being the currently active one. The Frequency Case is then underlined in
the features tree and all subsequent actions refer to it.
If you inactivate the Hide Existing Analysis Cases
switch in the Frequency Case dialog box, the symbols of objects created in
previous Analysis Cases will remain displayed.
Once a New Analysis Case has been inserted, its
Definition parameters cannot be changed.
To modify the Analysis Case Definition parameters you can
only replace it (Delete followed by Insert) in the
analysis specification tree.


To compute free vibration modes, you need a Frequency
Analysis Case containing no Restraints set. This means that you
must first delete the existing Frequency Analysis Case and insert a new
Frequency Analysis Case without Restraints.
To subsequently compute supported (nonfree) vibration
modes, you must delete the previous, Restraintsless (free vibration modes)
Frequency Analysis Case and insert a new (supported) Frequency Analysis
Case with Restraints. 
