Torsional Vibration of Bar — Lesson 2

This lesson covers the concept of torsional vibration of a bar, focusing on the derivation of the governing differential equations using Newton's second law and Hamilton's principle. It also discusses the natural frequencies and mode shapes in axial vibration, and how force vibration problems can be formulated considering damping. The lesson further explains the principal modes of vibrations in real structures and how to isolate a particular mode of vibration. It also discusses the effects of torsion, the concept of axial torsion, and the disasters caused by torsional motion in structures like elevated water tanks during earthquakes. The lesson concludes with the application of these concepts in solving practical problems related to machine components and structures.

Video Highlights

05:07 - Governing differential equations of torsional vibration derived using Newton's second law and Hamilton's principle.
08:34 - Process of converting the governing differential equations into time-dependent equations using generalized coordinates.
19:24 - Derivation of the equation of motion for torsional vibration using Hamilton's principle.
45:57 - Modal analysis to determine the natural frequencies and mode shapes.

Key Takeaways

- Torsional vibration of a bar can be understood and analyzed using Newton's second law and Hamilton's principle.
- Natural frequencies and mode shapes play a crucial role in the design and analysis of structures and machine components.
- Torsional motion can cause disasters in structures like elevated water tanks during earthquakes.
- The principal modes of vibrations in real structures are axial, torsional, and bending.
- The combination of these modes can occur in real structures, and isolating a particular mode of vibration can be necessary in some cases.