Page 29 - Using ANSYS for Finite Element Analysis Dynamic, Probabilistic, Design and Heat Transfer Analysis

16 • using ansys for finite eLement anaLysis
1.2.1.4 Using the Reduced Method for Modal Analysis

This method employs the use of MDOFs. These are DOFs that govern
the dynamic characteristics of a structure. For example, the MDOFs for
the bending modes of cantilever beam are:

Master degrees of freedom (MDOFs)

For this option, a detailed understanding of the dynamic behavior
of a structure is required. However, going this route means a smaller
(reduced) stiffness matrix, and thus faster calculations.
The steps for using this option are quite simple.
Instead of specifying the Subspace method, select the Reduced
method and specify 5 modes for extraction.
Complete the window as shown in the following:

Note: For this example both the number of modes and frequency range
was specified. ANSYS then extracts the minimum number of modes
between the two.
Select Solution > Master DOF > User Selected > Define
When prompted, select all nodes except the left-most node (fixed).