Free-free Modal and Pre-stressed Modal Analysis — Lesson 5

Given a windmill blade, which we discussed in a previous module, it should not be a problem for us to understand the modal analysis of this blade attached to the windmill hub. However, what about a modal analysis of an airplane freely flying in the sky instead of a windmill fixed to the ground? What is the main difference between the two modal analyses? Similarly, how about a wind turbine or oil platform floating in the ocean? Can you tell the different features of such systems?

Unlike the windmill fixed to the ground, an airplane as a holistic body does not have boundary conditions. It's an unconstrained body flying in the sky. The same is true for a floating wind turbine and an oil platform. Modal analysis of such an unconstrained system is called free-free modal analysis.

Now, let's take a break and enjoy a piece of guitar music.

Have you considered the relationship between the musician's hand pressing on the guitar strings and the beautiful music produced? In fact, it's because of the change of the natural frequency of the strings that the musician can create the variation of sounds that make up a song.

In this lesson, we will further explore the topics of free-free modal and prestress modal analysis.

Lecture

Alternate video link.

Handout

Here are the accompanying handout slides for this lesson.