哈工程振动噪声第7章 机械噪声的分析测量和控制

1、pagepage 1 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering Chapter 7 Noise Analysis,Measurement,and Control 第第7章章 机械噪声的分析测量和控制机械噪声的分析测量和控制 pagepage 2 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and E

2、nergy Engineering The root-mean square (rms) sound pressure Combined sound pressure of p1 and p2 TT e dtpp T dtp T p 0 2 21 0 22 11 TTT dtpp T dtp T dtp T 0 21 0 2 2 0 2 211 1 T ee dtpp T pp 0 21 2 2 2 1 2 22211121 coscostptpppp mm Chapter 7 Noise Analysis,Measurement,and Control 7. 1 Combination of

3、 Sound Levels 1111 cos m ppt 2222 cos m ppt pagepage 3 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering 12121122 00 22 cos()cos() TT mm p p dtppttdt TT 1212121212 0 1 cos()cos() T mm ppttttdt T 121212 0 1 cos()() T mm pptdt T (1) 两列频率相同且以恒定相

4、位差相交的单频率噪声声波的叠加两列频率相同且以恒定相位差相交的单频率噪声声波的叠加 21 tconstan 21 )cos( 2 1221 0 21 mm T ppdtpp T me pp 2 2 )cos(2 1221 ee pp 相干波：频率相同、相位差固定不变的波称为相干波。相干波：频率相同、相位差固定不变的波称为相干波。 Chapter 7 Noise Analysis,Measurement,and Control 7. 1 Combination of Sound Levels pagepage 4 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofC

5、ollege of Power and Energy EngineeringPower and Energy Engineering )cos(2 1221 2 2 2 1 2 eeeee ppppp 0 21 if 2 21 2 eee ppp mm pp 21 1 2 ee pp if 21 2 21 2 eee ppp mm pp 21 0 e p 这两种情况下的平均声能密度分别为这两种情况下的平均声能密度分别为 12 1212 2 0 0 20 ee p p c 12 1212 2 0 0 2 ee p p c Chapter 7 Noise Analysis,Measurement,

6、and Control 7. 1 Combination of Sound Levels pagepage 5 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering (2) 两列不相干噪声声波的叠加两列不相干噪声声波的叠加 2 2 2 1 2 eee ppp 12 0 2 0 T p p d t T 21 or the frequency is same, but the phase angle variation is of ran

7、dom 0 2 0 21 T dtpp T Time is long enough 21 两列具有不同频率，或频率相同但相交时相位差无规律变化的噪 声声波叠加后的合成声场，其平均声能量密度等于每列噪声声波 平均能量密度之和，这两列噪声波称为不相干波，它们的合成声 场将遵守“能量相加法则”。 Chapter 7 Noise Analysis,Measurement,and Control 7. 1 Combination of Sound Levels pagepage 6 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and

8、Energy EngineeringPower and Energy Engineering Noise is emitted usually from more than one source or at different frequencies, and it is necessary to calculate the cumulative or overall sound levels. Obviously, since the sound level scales are logarithmic, they cannot be added algebraically. Combini

9、ng of sound levels may be performed using the energy addition theorem and the overall level L(OA) is determined by Here, each sound level to be combined might be the noise from n individual sources or the sound levels associated with n octave bands. They may be sound power levels or sound pressure l

10、evels. n i Li OAL 1 10/ 10lg10)( Chapter 7 Noise Analysis,Measurement,and Control 7. 1 Combination of Sound Levels pagepage 7 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering 2222 21eneee pppp 2 222 2 2 21 lg10lg10)( r enee r e p ppp p p OAL

11、 2 2 10 10 r ei i p p L 2 2 lg10 r ei p p Li n i L n i i r ei p p OAL 1 10 1 2 2 10lg10lg10)( Chapter 7 Noise Analysis,Measurement,and Control 7. 1 Combination of Sound Levels pagepage 8 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering 12 22

12、22 eeeen npppp Chapter 7 Noise Analysis,Measurement,and Control 7. 1 Combination of Sound Levels 设有n个不同频率，或频率相同但相位差无规律变化的噪声源，则其 平均声压级可推导得到 12 2222 2222 eeeen rrrr pppp n pppp 12 22222 22222 1 11 () eeeenei n i rrrrr ppppp pnpppnp 2 10 2 1 1 10log10log(10 ) i e L n p i r p L pn pagepage 9 授课人柳贡民2021年

13、7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering L1-L2012345678910 Lc-L13.02.52.11.81.51.21.00.80.60.50.4 Another easy and useful method for combining sound levels is to utilize the table as bellow. The combined effect of sounds depends on the differen

14、ce in their decibel levels. 实际计算表明，两列声压级相同的噪声叠加后，总声压级仅增加 3dB；两列噪声的声压级相差10dB以上，则声压级低的那列噪声 对总声压级的贡献可以忽略不计，总声压级近似等于声压级高的 那个值. Chapter 7 Noise Analysis,Measurement,and Control 7. 1 Combination of Sound Levels pagepage 10 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPowe

15、r and Energy Engineering (1) Octave Band and 1/3 Octave Band Spectral Analysis In noise control engineering, the bands are related by the following relationship n lu ff2 n=1, octave band n=1/3, one-third-octave band The center frequency of any such band is defined as the geometric mean ulc fff The l

16、ower and upper limit frequencies may be determined from the center frequency as 2 2 n lc ff 2 2 n uc ff Chapter 7 Noise Analysis,Measurement,and Control 7. 2 Spectral Analysis of Noise pagepage 11 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Enginee

17、ring Octave Band1/3 Octave Band Lower Limit Frequency (Hz) Center Frequency (Hz) Upper Limit Frequency (Hz) Lower Limit Frequency (Hz) Center Frequency (Hz) Upper Limit Frequency (Hz) 2231.544 22.42528.2 28.231.535.5 35.54044.7 446388 44.75056.2 56.26370.8 70.88089.1 88125177 89.1100112 112125141 14

18、1160178 177250355 178200224 224250282 282315355 355500710 355400447 447500562 562630708 Chapter 7 Noise Analysis and Measurement 7. 2 Spectral Analysis of Noise pagepage 12 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering 7101,0001,420 70880

19、0891 8911,0001,122 1,1221,2501,413 1,4202,0002,840 1,4131,6001,778 1,7782,0002,239 2,2392,5002,818 2,8404,0005,680 2,8183,1503,548 3,5484,0004,467 4,4675,0005,623 5,6808,00011,360 5,6236,3007,079 7,0798,0008,913 8,91310,00011,220 11,36016,00022,720 11,220 12,500 14,130 14,130 16,000 17,780 17,780 20

20、,000 22,390 Chapter 7 Noise Analysis and Measurement 7. 2 Spectral Analysis of Noise pagepage 13 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering (1) Octave Band and 1/3 Octave Band Spectral Analysis Band Number 1 2 3 4 5 6 7 8 Center Freq.

21、(Hz) 63 125 250 500 1000 2000 4000 8000 SPL at 3 ft (dB) 126 132 128 119 115 108 98 90 133 134.3 134.4 Overall SPL 134 dB Chapter 7 Noise Analysis and Measurement 7. 2 Spectral Analysis of Noise 128.5115.898.6 115.9 L1-L2012345678910 Lc-L13.02.52.11.81.51.21.00.80.60.50.4 pagepage 14 授课人柳贡民2021年7月24

22、日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering 60 70 80 90 100 110 120 130 140 631252505001000200040008000 Octave Center Frequency (Hz) SPL (dB) Chapter 7 Noise Analysis and Measurement 7. 2 Spectral Analysis of Noise pagepage 15 授课人柳贡民2021年7月24日星期六 动力与能

23、源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering (2) Constant Bandwidth Narrow Band Spectral Analysis 在倍频程分析中，中心频率越高，对应的带宽越大，得出的数据越 粗糙。在恒定窄带分析中，在高频域仍能保持同样的带宽，可达到 很高的分析精度。但其代价是大大增加了分析的工作量。 If the noise has frequencies evenly distributed throughout the audible freque

24、ncy range it is known as white noise. Chapter 7 Noise Analysis and Measurement 7. 2 Spectral Analysis of Noise pagepage 16 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering Frequency (Hz) Relative response (dB) Frequency (Hz) Relative respons

25、e (dB) 25 31.5 40 -44.7 -39.4 -34.6 800 1,000 1,250 -0.8 0 +0.6 50 63 80 -30.2 -26.2 -22.5 1,600 2,000 2,500 +1.0 +1.2 +1.3 100 125 160 -19.1 -16.1 -13.4 3,150 4,000 5,000 +1.2 +1.0 +0.5 200 250 315 -10.9 -8.6 -6.6 6,300 8,000 10,000 -0.1 -1.1 -2.5 400 500 630 -4.8 -3.2 -1.9 12,500 16,000 20,000 -4.

26、3 -6.6 -9.3 A electrical weighting networks for sound level meter Chapter 7 Noise Analysis and Measurement 7. 3 Weighted Sound Levels pagepage 17 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering Band Number 1 2 3 4 5 6 7 8 Center Freq. (Hz)

27、63 125 250 500 1000 2000 4000 8000 SPL at 3 ft (dB) 126 132 128 119 115 108 98 90 A-weighting -26.2 -16.1 -8.6 -3.2 +0 +1.2 +1.0 -1.1 A-weighted SPL 99.8 115.9 119.4 115.8 115 109.2 99 88.9 116 121 116 99.4 122.2 116.1 123.2 Overall A-weighted SPL 123 dB(A) Chapter 7 Noise Analysis and Measurement 7

28、. 3 Weighted Sound Levels pagepage 18 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering Home Works 距离发动机距离发动机3米处测得的米处测得的1/3倍频程声压级列于表倍频程声压级列于表A，试画出，试画出倍频程倍频程频谱图，并频谱图，并 计算总的计算总的A声压级。声压级。 频率(Hz)506380100125160200250 SPL(dB)1089811311912011511011

29、2 频率(Hz)315400500630800100012501600 SPL(dB)104102100989910310099 频率(Hz)200025003150400050006300800010000 SPL(dB)9794959285787570 表A. 1/3倍频程声压级的测量值 pagepage 19 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering Types of sound-absorbing material

30、s Sound-absorbing materials are utilized in almost all areas of noise control engineering. The porous sound-absorbing materials are available in the form of mats, boards, mineral fibers, open cell foams. They have open pores with typical dimensions below 1 mm that are very smaller than the wavelengt

31、h of sound. Here, each can be treated as a lossy homogeneous medium. Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.1 Porous Sound-Absorbing Materials（多孔吸声材料） pagepage 20 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower a

32、nd Energy Engineering Full reticulated plastic foam, Partially reticulated plastic foam, Glass fiber, Mineral wool. Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.1 Porous Sound-Absorbing Materials（多孔吸声材料） pagepage 21 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College o

33、fCollege of Power and Energy EngineeringPower and Energy Engineering How porous materials absorb sound Owing to the acting sound pressure, the air molecules oscillate in the interstices int:stis (空隙)of a porous material with the frequency of exciting sound wave. The oscillations result in frictional

34、 losses, and they convert the sound energy into heat. Changes in flow direction and expansions and contractions of the flow through irregular pores result in loss of momentum in the direction of wave propagation. Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7

35、.4.1 Porous Sound-Absorbing Materials（多孔吸声材料） pagepage 22 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering Physical properties of porous sound-absorbing materials Many experimental studies of the behaviour of common sound-absorbing material

36、of which the structural skeletons are effectively rigid has shown that there are three gross parameters that principally control their sound absorption characteristics. Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.1 Porous Sound-Absorbing Materials（多孔吸声材料

37、） pagepage 23 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering Porosity （孔隙率） Porosity is defined as the ratio of the volume of voids to the total volume occupied by the porous structure: it is symbolized herein by h. sgm VVV m s m g V V V V

38、 h1 where Vg is the volume of gas phase, Vs is the volume of solid phase, Vm is the volume of material Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.1 Porous Sound-Absorbing Materials（多孔吸声材料） pagepage 24 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of P

39、ower and Energy EngineeringPower and Energy Engineering Porosity s m h 1 3 /50mkg m 3 /2550mkg s %98 2550 50 1h s is density of the solid (frame) and m is bulk density(容积密 度) of the porous material. Consider a fiberglass insulation product: It is generally in excess of 95% in mineral and glass wools

40、 and porous plastic foams. Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.1 Porous Sound-Absorbing Materials（多孔吸声材料） pagepage 25 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering (2) Flow Resistivity

41、 (比流阻） 4 1 /(/) p N s mRayls m vx where p is the steady pressure differential across a homogeneous layer of thickness x , is face velocity of the flow through the material (actually it is the average velocity within the material). Flow resistivity (specific flow resistance) is a most important physi

42、cal characteristic of a porous material. It is defined as Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.1 Porous Sound-Absorbing Materials（多孔吸声材料） pagepage 26 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy E

43、ngineering (2) Flow Resistivity The flow resistance of a sheet of material of thickness x is given by x . The flow resistivity of common absorbing materials typically lies in the range 2 to 2 Ns/(m4). For a given material bulk density, flow resistivity increases strongly as fiber diameter is decreas

44、ed. Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.1 Porous Sound-Absorbing Materials（多孔吸声材料） pagepage 27 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering (3) Structure Factor （结构因子） The various inf

45、luences of the geometric form of the skeleton on effective density and compressibility are lumped together into a structure factor symbolized by s. The structure factor decreases with increasing frequency and ranges from extreme high value of s=6 down to s=1 but generally falls in the range of s=1.3

46、 . Most numerical calculations use s=1. Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.1 Porous Sound-Absorbing Materials（多孔吸声材料） pagepage 28 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering (1) The

47、 modified plane wave equation 22 0 22 0 spph p xtx Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.2 Plane Wave Sound Propagation in Porous Materials where is the effective bulk modulus of the gas. pagepage 29 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege

48、of Power and Energy EngineeringPower and Energy Engineering (2) Harmonic solution of the modified plane wave equation ( , )( )e j t p x tp x 0)(/ )( 0 2 2 2 xphjs x xp 0)( )( 2 2 2 xpk x xp Setting Substituting it into the modified wave equation yields or / 0 hjsk is called complex wavenumber. Chapt

49、er 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.2 Plane Wave Sound Propagation in Porous Materials pagepage 30 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering (2) Harmonic solution of the modified plane

50、wave equation xk jxk j BeAexp )( )( 1 )( xk jxk j c BeAe z xu ) exp()(xk jAxp jk For a harmonic progressive wave, . We write the complex wavenumber , in which is the attenuation constant and is the propagation constant. Therefore, the general solution of the modified plane sound wave equation may be

51、 expressed as Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.2 Plane Wave Sound Propagation in Porous Materials pagepage 31 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering (2) Harmonic solution of

52、the modified plane wave equation The spatial distribution of instantaneous pressure is illustrated by the followed Figure. Exponential attenuation of a progressive harmonic wave: instantaneous pressure distribution Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption

53、 7.4.2 Plane Wave Sound Propagation in Porous Materials pagepage 32 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering AC BD x= -t x=0 Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.3 Large Plat Absor

54、bers Sound energy absorption coefficient 2 1R E E i a where Ea and Ei are the absorbed and incident energies, respectively, R is the reflection coefficient defined as the ratio of the reflected and incident sound pressure at the interface. pagepage 33 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege

55、of Power and Energy EngineeringPower and Energy Engineering jkxjkx BeAexp )( jkxjkx BeAe z xu 0 1 )( )( xk jxk j DeCexp xk jxk j c DeCe z xu 1 )( Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.3 Large Plat Absorbers The sound pressures and particle velociti

56、es in the air and porous materials are expressed as At x=0, the particle velocity is zero, yields C=D pagepage 34 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering jktjktjktjkt AeBeCeCe 0 11 jktjktjktjkt c AeBeCeCe zz cos()sin()1tan() cos()si

57、n()1tan() cc cc tj ztj ztB R Atj ztj zt bbb bbb - = + 0 zzz cc Where Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption 7.4.3 Large Plat Absorbers At x= -t , the continuities of sound pressure and particle velocity give Combining above expressions, one obtain the s

58、ound pressure reflection coefficient as 2 1R E E i a kj pagepage 35 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering Sound absorption characteristics of finite thick layer of porous material 超细玻璃棉归一化吸声系数曲线 Chapter 7 Mechanical Noise Control

59、Techniques 7.4 Noise Reduction by Sound Absorption 7.4.3 Large Plat Absorbers 下限频率 下半频带宽度 a 2a pagepage 36 授课人柳贡民2021年7月24日星期六 动力与能源工程学院 College ofCollege of Power and Energy EngineeringPower and Energy Engineering Chapter 7 Mechanical Noise Control Techniques 7.4 Noise Reduction by Sound Absorption

60、 7.4.3 Large Plat Absorbers Principle factor influencing sound absorption characteristics of finite thick layer of porous material: Density of material Thickness of material 容重增加，低频吸声系数变大，但高频吸声系数降低；容重过大 会使总的吸声效果明显降低。一般超细玻璃棉容重大约可取15 25kg/m3，矿渣棉为120 130kg/m3。 如前页图，增加吸声材料厚度会使材料吸声系数曲线向低频方向 移动。 pagepage