Category: (((—Acoustics Engineering—))))
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Metal Cutting
Many industrial processes involve cutting metals. Metal‐cutting processes can either be continuous or impulsive in character. Examples of continuous processes include sawing, drilling, milling, and grinding. Additional continuous cutting processes include use of water jets for cutting steel plates up to 300‐mm thickness and plasma and laser cutting techniques. Examples of impulsive processes include punching, piercing, and shearing [50].…
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Fans and Blowers
Fans and blowers are used in appliances, in buildings, in air distribution systems for heating and cooling, and in industry for a variety of purposes. Fan noise, its generation, and control are discussed in detail in Ref. [31] and Chapter 13 in the present book. There are two main types of fan designs: axial and centrifugal (see Figure…
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Bearings
There are two main types of bearings: (i) rolling contact and (ii) sliding contact [6, 7]. Rolling contact bearings are more commonly used, but sliding contact bearings are usually quieter than rolling contact bearings, if properly manufactured, installed, and maintained. Proper lubrication is essential for both rolling and sliding contact bearings. Reference [26] presents a detailed…
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Machine Element Noise and Vibration Sources and Control
11.2.1 Gears Gears are used in a number of applications where mechanical power is transmitted. Gears can emit annoying and harmful noise levels when a fraction of the transmitted power is converted to noise [16]. Most modern gear teeth have an involute profile, although some have circular‐arc profiles [1, 2]. Figure 11.1a shows some of the terms…
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Introduction
Many different machine components are used in appliances, vehicles, aircraft, and industry. Some machine components including bearings, gears, fans, burners, cutters, and valves are used in machines built from several of these components such as pumps, compressors, electric motors, and internal combustion (IC) engines. It is impossible to discuss every type of machine and machine component here;…
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Parallel‐Baffle Mufflers
Power generation plants around the world often employ gas turbines and other industrial equipment, which need to be muffled. The inlets and exhausts of large fans and blowers in buildings must also be muffled. Very often large industrial mufflers have to be designed individually for specific applications to achieve optimum performance and acceptable physical size.…
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Historical Development of Dissipative Mufflers and Lined Duct Theories
Rayleigh made the earliest study of the acoustical performance of sound‐absorbing materials in 1883 [125]. That was followed by a theoretical study of the propagation of sound in rectangular lined ducts by Sivian in 1937 who used the impedance of the lining material as the acoustical boundary condition for his model [126]. Morse [127] extended…
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Dissipative Mufflers and Lined Ducts
Porous sound‐absorbing materials are used to control the noise of heavy equipment and machinery in industry and to line air‐conditioning ducts in buildings. Both intake and exhaust noise of the equipment normally needs to be muffled. Improved sound‐absorbing materials are also now being used to increase the NR of reactive mufflers.
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Measurements of Source Impedance
Figure 10.72 shows that it is very important to have knowledge of the source impedance if narrow‐band predictions of the IL of an automobile muffler are desired. In many cases, such as automobile engines, compressors and blowers, the mechanical sound source is not constant, but varies over restricted frequency range. Figure 10.73 shows that the IL is largely…
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Reactive Muffler IL
The effect of source impedance on IL of an automobile muffler was investigated theoretically in 1970 by Young [45]. Some results are shown in Figures 10.70 and 10.71. In Figure 10.70 it is seen that there is a large difference between the IL curves for the muffler for the three different source impedances investigated: Ze = 0, ρc/S, and ∞, when the prediction…