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This 3 page Class Notes was uploaded by Gerhard Leuschke II on Saturday October 3, 2015. The Class Notes belongs to ME405 at California State Polytechnic University taught by Chuan-ChiangChen in Fall. Since its upload, it has received 83 views. For similar materials see /class/218332/me405-california-state-polytechnic-university in Mechanical Engineering at California State Polytechnic University.
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Date Created: 10/03/15
ME405 HW1 Spring 2011 1 For a plane wave traveling in a medium of density p0 15kgm3 the particle velocity is uxt 05 cos628t 7 2x 002cos628 2x ms nd a the frequency in Hz the characteristic impedance and the bulk modulus 39 ement and intensity for negative x direction waves 39me verag e ergy ensit for positive x direction waves es 3 a a quotD E a art c e e acoustic pressure an e d the condensation amplitude for both positive and negative direction wav 2 The microphone measures a sound pressure with an amplitude of 2828 Pa The medium is air a Determine the magnitude of the piston displacement amplitude and the sound power radiated by the piston b If the frequency is traced to be 300 Hz repeat part a for the same sound pressure State any assumptions you make lulu 39 muznplmsn39 3 Starting with the general solution determine the natural frequencies ofa tube closed at both ends and plot the first three standing wave patterns of sound pressure in the tube Compare this case with example given in class 4 For plane waves of acoustic intensity 1 WmA2 compute the rms values of the sound pressure and particle velocities in air and water Comment on the differences between the two media 5 A inu oidal I 39 r 39 f2Pa ata distance of 5 m from an essentially point source Calculat a the effective rms pressure at a distance 0 m b the intensity at 5 m c the acoustic power radiated by the source Watts d the intensity at 10 m and e the effective rms pressure at a distance of 10 m k In H 39 val J l X Q H gt if 77 W HOMEWORK 2 1 Compute the sound pressures at point t and plot the line spectrum The following arrangement of air compressors is symmetrical Assume that the dynamics of the discharge lines and tank are negligible Hint for each harmonic compute phase difference between the two line pressures gurines 3 I Ark 39 t 62th COMPR sag TAN K q 39 6U T7 ON 6 Line SPOQTWM a39i39 e g a 1201f radsec 3 No 3 me 0 8 Ice 3 Us 39 O J 5o l 3 4 539 6 7 8 n Harmonic index 2 The preliminary step in noise control problems is the source identi cation and measurement of intensity levels If an installation has more than one source then the individual contribution of a source can be determined by isolating it In an air conditioning install t ion the following set of sound pressure levels tweighted decibles were obtain Motor 80 dB Compressor 70 dB Fan 65 dB Duet 60 dB Ambient 55 dB Determine the combined level of the following a i motor and compressor ii motor compressor and fan iii entire installation b If the overall combined noise level of the installation is to be reduced by 5 113 which noise souncc would you attack and what noise level would you recommend c If the combined noise level is to be reduced by IVSMdB what are the possible areas of noise reduction 3 In an indust al plant sound pressure levels at the operator s location due to three machines is shown below The curves have been obtained by turning on one machine at a time a Which machines have the highest dBA 1138 and dBC levels b Plot the combined noise level dBA octave band spectrum 6 Determine the overall dBLIN BA and dBC levels maels tml39 q a I J 45 a machine III lllllll 039135 0 35 06 be 20 40 3 Q octave Bands kHz
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