機械工程專業(yè)英語教程（第２版）Lesson 47

1、Lesson 47 Definitions and Terminology of Vibration TerminologyText tour 8/5/20221機械工程專業(yè)英語教程Terminology8/5/20222機械工程專業(yè)英語教程Reciprocation An alternating back-and-forth movement往復(fù)運動Drag 1The degree of resistance involved in dragging or hauling.拖拉中所受阻力的程度2The retarding force exerted on a moving body by a

2、 fluid medium such as air or water.阻力：流體介質(zhì)，如水或空氣對移動物體施加的阻力3. One that impedes or slows progress; a drawback or burden阻礙：妨礙或減慢進程的事物；拖后腿的事；累贅機械工程專業(yè)英語教程8/5/2022DashpotA device consisting of a piston that moves within a cylindercontaining oil, used to dampen and control motion.阻尼器，緩沖器：由在裝有油的汽缸里活動的活塞構(gòu)成的一

3、種設(shè)備，用來緩沖和控制運動 3The mechanical vibrations dealt with are either excited by steady harmonic forces (i.e. obeying sine and cosine laws in cases of forced vibrations) or, after an initial disturbance, by no external force apart from gravitational force called weight ( i.e. in cases of natural or free vi

4、brations).所討論的機械振動或者是由穩(wěn)態(tài)的諧振力引起的振動（也就是服從正弦或余弦定律的強迫振動），或者是在初始擾動之后，除了被稱為重量的重力之外，沒有其它外力引起的振動（也就是自然或自由振動的情況）。機械工程專業(yè)英語教程8/5/2022Text tour4Random Vibration is the term used for vibration which is not periodic, i.e. has no cyclic basis and is not regularly repetitive.隨機振動是一個用來描述非周期性振動的術(shù)語。也就是說,這種振動不是周期性變化的,是

5、不定期地進行重復(fù)的。機械工程專業(yè)英語教程8/5/20225 Resonance describes the condition of maximum amplitude. It occurs when the frequency of an impressed force coincides with, or is near to a natural frequency of the system. In this critical condition, dangerously large amplitudes and stresses may occur in mechanical syst

6、ems but, electrically, radio and television receivers are designed to respond to resonant frequencies.共振描述了最大振幅的狀況。當(dāng)外力的頻率與系統(tǒng)的固有頻率相同或相近時就會產(chǎn)生共振。在這種臨界條件下, 機械系統(tǒng)中會出現(xiàn)具有危險性的大振幅和高應(yīng)力。但是,電學(xué)方面,收音機和電視機的接收器則被設(shè)計成在共振頻率時工作。機械工程專業(yè)英語教程8/5/20226Damping is the dissipation of energy from a vibrating system, and thus pre

7、vents excessive response. It is observed that a natural vibration diminishes in amplitude with time and, hence, eventually ceases owing to some restraining or damping influence. Thus, if a vibration is to be sustained, the energy dissipated by damping must be replaced from an external source.阻尼是振動系統(tǒng)

8、中能量被消耗的現(xiàn)象,它可以防止過量的響應(yīng)?？梢杂^察到,自由振動的振幅會隨時間而衰減,因而, 振動最終將由于某些限制或阻尼的影響而停止。因此,如果要使振動持續(xù)下去, 一定要有外部的能源對由于阻尼而耗散的能量進行補充。機械工程專業(yè)英語教程8/5/20227One device assumed to give viscous damping is the “dashpot” which is a loosely fitting piston in a cylinder so that fluid can flow from one side of the piston to the other through the annular clearance space. A dashpot cannot store energy