英语翻译Examples of periodic sources and broadband sources are,respectively,rotating machinery such as turbines,fans,etc.,and aerodynamic noise associated with jets or flow past a solid surface.In fact,the two types often occur together with a se

英语翻译Examples of periodic sources and broadband sources are,respectively,rotating machinery such as turbines,fans,etc.,and aerodynamic noise associated with jets or flow past a solid surface.In fact,the two types often occur together with a se
英语翻译
Examples of periodic sources and broadband sources are,respectively,rotating machinery such as turbines,fans,etc.,and aerodynamic noise associated with jets or flow past a solid surface.In fact,the two types often occur together with a series of pure tone peaks above a broadband spectrum.An example is where a large machine with several random sources has a strong periodic mode of operation.For more specific detail on the frequency spectra and appropriate analysis required for different kinds of sources see section 3.3.3.
图2.4及其说明
2.1.3 Wavelength
A wavelength is defined as the distance between analogous points on successive waves of a pure tone signal; it is most easily assessed by measuring the distance between adjacent maxima or minima on the pressure spatial distribution (see figure 2.3a,above).Wavelength is denoted by the symbol X and is numerically equal to the ratio of the speed of sound in a medium to the frequency:
公式
where c is the speed of sound,m/s
f is the frequency,Hz.
2.1.4 Speed
For very high amplitude waves,which occur either when the ambient speed of sound is exceeded (see section 7.1.1) or with strong source radiation as in certain severe impact situations,shock formation occurs,and the waveform is distorted into nonlinear behavior.Essentially,this means that sounds of different frequencies propagate at different speeds through the transmitting medium.However,for most commonplace situations in industry this will not be so,and the speed of sound can be regarded as being the same for all frequencies.
For propagation in a gas,the general expression for the velocity of sound waves,c,is given by
c = _fTrT m/s
where
λ is the ratio of specific heat of gas at constant pressure to that at constant volume
r is the constant dependent on gas involved and equal to the ratio of the gas constant and molecular weight of the gas,J/kg.K
T is the absolute temperature,K.
The velocity is directly proportional to the square root of the absolute temperature,the other terms being constant.Pressure changes and nonuniformity of gas composition are of much less significance in affecting the velocity.For air at atmospheric pressure,the relationship simplifies to
公式：c = 20.05x/T m/s
More complex relationships exist for liquids and solids 1:
Liquids:公式
Solids:公式
(large cross section)
Solids公式
(small cross section)
where
Bbt is the isothermal bulk modulus,N/m 2
0o is the density,kg/m 3

英语翻译Examples of periodic sources and broadband sources are,respectively,rotating machinery such as turbines,fans,etc.,and aerodynamic noise associated with jets or flow past a solid surface.In fact,the two types often occur together with a se
周期源和宽带源的例子分别是旋转机械,如涡轮,风扇等,以及和喷气式飞机或流过一个固体表面有关的空气动力噪声.实际上,这两种类型经常和宽带频谱上一系列纯音质峰值一起发生.一个例子是,一些具有随机来源的大型机器有很强的周期性的运作模式.关于不同类型源的频谱和分析的细节见第3.3.3节.
图2.4及其说明
2.1.3波长
波长定义为一个连续波形的纯音信号,两个相似点之间的距离.通过测量空间压力分布的相邻极大或极小值之间距离,它是最容易给出的（见上图2.3a ） .波长用符号X表示,数值等于声音在媒质中的速度与频率的比值：
公式
其中C是音速,m/s(米/秒)
F 是频率,Hz (赫兹)
2.1.4 速度
对一个高幅波,它通常在环境声速超出（见7.1.1部分）或者在一定的剧烈碰撞情形下,伴随着强烈的辐射而发生.波形也就变为非线性,实质上是不同频率的声波以不同的速度穿越传播介质.然而,在工业场合,通常并非这样.所有频率的音速被认为速度是相等的.
在大气中传播时,通常声波的表达式为：c = _fTrT m/s
此处,λ 是大气在一定比热条件下,压强对体积的比值.

实例定期来源和宽带来源分别是旋转机械，如发电机，风扇等，以及气动噪声与飞机或流过去固体表面。事实上，这两种经常发生一起一系列纯音以上的高峰宽带频谱。一个例子是，与一些大型机器随机来源具有很强的周期性的运作模式。为更具体的细节和适当的频谱分析所需的各种不同的来源见第3.3.3节。
图2.4及其说明
2.1.3波长
波长是指之间的距离相似点连续的纯音信号，它是最容易评估之间...

全部展开

实例定期来源和宽带来源分别是旋转机械，如发电机，风扇等，以及气动噪声与飞机或流过去固体表面。事实上，这两种经常发生一起一系列纯音以上的高峰宽带频谱。一个例子是，与一些大型机器随机来源具有很强的周期性的运作模式。为更具体的细节和适当的频谱分析所需的各种不同的来源见第3.3.3节。
图2.4及其说明
2.1.3波长
波长是指之间的距离相似点连续的纯音信号，它是最容易评估之间的距离测量相邻极大或极小的压力空间分布（见图2.3a ，段） 。波长是指由符号X和数值等于比音速在一个中等的频率：
公式
其中C是音速，米/秒

收起