哈工程振动噪声一一第7章 机械噪声的分析测量和控制.ppt

Damping factor Young’s modulus Poisson’s ratio Chapter 7 Mechanical Noise Control Techniques 7.5 Noise Insulation 7.5.2 Sound Transmission through a Panel The first resonant frequency is The surface mass is: The critical or wave coincidence frequency is Chapter 7 Mechanical Noise Control Techniques 7.5 Noise Insulation 7.5.2 Sound Transmission through a Panel (a) For this case lies in Region I, the stiffness-controlled region. The specific mechanical compliance may be evaluated The sound power transmission coefficient The transmission loss for a frequency of 63Hz is Chapter 7 Mechanical Noise Control Techniques 7.5 Noise Insulation 7.5.2 Sound Transmission through a Panel (b) For the operating region is Region II, the mass-controlled region. The sound power transmission coefficient for normal incidence is The transmission loss for normal incidence is Chapter 7 Mechanical Noise Control Techniques 7.5 Noise Insulation 7.5.2 Sound Transmission through a Panel (c) For this case lies in Region III, the damping-controlled region. The transmission loss for normal incidence at the critical frequency is The transmission loss for a frequency of 2000 Hz is Chapter 7 Mechanical Noise Control Techniques 7.5 Noise Insulation 7.5.2 Sound Transmission through a Panel A silencer or muffler is a device that allows the gas/air or liquid pass through and can attenuate the noise. Classification: Reactive (reflective) Dissipative (absorptive) Combination reactive/ dissipative The aerodynamic noise generated by gas/air consuming/handling equipments, such as internal combustion engines, gas turbines, blowers, pumps(vacuum pump or other punp), compressors and fans, is controlled through the use of silencers and mufflers. Chapter 7 Mechanical Noise Control Techniques 7.6 Silencers and Mufflers 7.6.1 Aerodynamic Noise and Silencers Noise Reduction Mechanism and characteristics of Reactive Silencer Chapter 7 Mechanical Noise Control Techniques 7.6 Silencer