Mechanical Vibration

The last two lectures introduced me to the vibration phenomenon, especially in the mechanical engineering field. Vibrations are mechanical oscillations about an equilibrium point. There are three types of vibrations: free vibration, forced vibration and self excited vibration.

Free vibration occurs when the system is given an initial condition where no external vibration is exerted then the system vibrates. An example is when we pull a pendulum or swing then letting go. It will vibrate at one of its natural frequencies. Forced vibration happens when external alternating force is given to vibrate the system. The largest impact caused by forced vibration is when the frequency of the external force is the same as the system’s natural frequency (also called resonance).

Self excited vibration happens when no external oscillating force or vibration is given, instead another form of energy is given to the system and the system vibrates. The system modulates the energy into vibration, and the amplitude of the vibration is proportional to the amount of energy. Self excited vibrations are shown in pianos, violins, many other musical instruments and method of making Hita Pottery.

During the first lab visit, rolling machine was introduced. The machine is mainly used in the pulp and paper industry. When the roller spins, the rubber deforms and vibration occurs (self excited). To produce smooth paper, vibrations should be minimized as much as possible. To do this, they alter rotation speed, damping and use dynamic absorbers.

The second lab visit was to the Venture Business Laboratory. There are research on brake systems and vibration suppression. A new method of avoiding brake squeals is introduced by using dynamic absorbers. A new method of vibration suppression is introduced by using variable stiffness beams. Spinning the rectangular prism changes the stiffness thus the natural frequency of the absorber. By altering the natural frequency of the dynamic absorber, vibrations on the system can be eliminated.

There are many other interesting applications of vibration concepts found in daily life. Cell phone vibrator is constructed by putting mass not on the centre of the spinning motor, therefore creating centrifugal force. In washing machines salt water is used to avoid resonance (self ambivalence). It shows just one fraction of the many contributions of mechanical engineering towards civilization.


Posted on December 7, 2007, in @Japan, Study @ Oita. Bookmark the permalink. Leave a comment.

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