Self-excited oscillation

Japanese: 自励振動 - じれいしんどう（英語表記）self-excited oscillation

Vibration that is excited, grows, and continues in a system when a non-periodic external force is applied. For example, friction can be induced when the string of a violin is pressed against the string with a bow and pulled in a certain direction at a certain speed, causing vibration. The reeds of wind instruments and the squeal of electric wires caused by wind are also examples of self-excited vibration caused by friction when air passes through a narrow space. Abnormal vibrations in machines, turbines, automobiles, aircraft, etc. are often caused by this phenomenon. Self-excited vibration is a phenomenon in which vibrations whose amplitude increases when negative resistance is applied, and is the inverse of damped vibrations in which amplitude decreases when positive resistance is applied. The nonlinear term of negative resistance plays an important role in oscillations in electrical oscillatory circuits and time-delay vibrations in automatic control systems, and research into this phenomenon led to the development of nonlinear vibration theory.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

周期的でない外力が加えられた系に励起され，成長し，持続する振動。たとえば，バイオリンなどの弦を弓で押しつけて一定の方向へ一定の速さで引き，摩擦によって誘起させる弦の振動がある。管楽器のリード，風による電線の鳴きなども空気が狭いところを通るときの摩擦が起す自励振動である。機械，タービン，自動車，航空機などの異常振動もこれに起因することが多い。自励振動は，負の抵抗が働くときに振幅が増大する振動を生じる現象であり，正の抵抗が働いて振幅が減少する減衰振動の逆振動である。電気振動回路の発振，自動制御系の時間遅れ振動などは，負抵抗の非線形項が発振に重要な役割を果し，その研究は非線形振動論の発展の契機となった。

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