针对振动的三要素即振幅、频率及相位分别做了介绍；
The analysis of vibration is introduced by its three factors-vibration amplitude, frequency and phase.
正确确定初相和任意时刻的相位，对于解决振动和波动问题至关重要。
It is important for solving the problem of vibration and wave to determine correctly initial phrase and phrase at any moment.
四极声源(30)一种分成四部份而相位交替振动的噪音源。
Quadrupole source (30) a noise source in which four parts vibrate alternately in phase.
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