Overview of Linear Analysis features

What is Linear analysis?

Performing Linear analysis It can be extremely difficult analyzing time domain results even for highly skilled simulation experts. Such experts make extensive use of the frequency domain. In other words they use Linear analysis.

Important tools are: eigenvalues, modal analysis, modal shapes, Bode plot, Nichols plot, Nyquist plot, root locus.

It is very important to realize that use of these tools is meaningless unless the linearization is carried out at an equilibrium position. In addition it is necessary to switch off stick-slip friction (also called dry friction).

• How do I ensure my system is in equilibrium? Do a Stabilizing run or do a long Dynamic run using the Hold inputs constant option in the Run Parameters dialog box.

  However, simple eigenvalue analysis can be useful with the system not in equilibrium, some people working in simulation perform a series of eigenvalue analysis at a very early stage in development of a model, just to get an idea of the system frequencies. If they have some extremely high frequencies, they may try to remove them by altering the model.

Performing Linear analysis

Linear analysis performing

When you click on the Linear analysis mode button ,

• the interface of the component variables window is different,

• a group of options is enabled that is available from the toolbar Figure 12: Linear analysis toolbar entries

  or from the menubar Simulate > Linear analysis Figure 13: Linear analysis menubar entries

In order to perform any sort of linear analysis you must do the following:

• Set linear analysis times using LA Times in the simulation time interval to access the eigenvalues and all the related tools

• Set control and observer variables to use FRF - Modal analysis, Modal shapes, and Frequency diagrams tools

• Perform batch runs to analyze how the dependency of modes on parameter changes in the Root locus plot

• Run a simulation