Purdue ME 56300 - Exhaust Noise & Vibration (17 pages)

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Exhaust Noise & Vibration



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Exhaust Noise & Vibration

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Pages:
17
School:
Purdue University
Course:
Me 56300 - Mechanical Vibrations
Mechanical Vibrations Documents

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Exhaust Noise Vibration System level structure borne vibration problem Loud noise in rear passenger seat at cruising speed is believed to be due to exhaust resonance Neon RT exhaust test bed as an example of a complex system level N V problem Exhaust Noise Vibration Contradictions in diagnosing the problem An increase in the spring rate of the Neon suspension introduces a system level noise problem in the 300 350 Hz frequency range Why does a change in the suspension subsystem create a vibration problem in the exhaust subsystem in the first place How and why does a stiffness change in the exhaust system inlet pipe affect the vibration problem Exhaust Noise Vibration Simplified model An increase in the spring rate of the vehicle suspension subsystem causes the exhaust subsystem resonances to shift upward due to perturbed boundary condition Certain modes are affected by increase in suspension stiffness K2 Increase in K2 Test Setup Electro dynamic shaker testing PCB 288D01 102 24 mV lbf 98 36 mV g 356A08 A356B18 92 102 907 1042 mV g Electro dynamic 50 lb skewed shaker excitation at bellows to excite bending and torsional modes of exhaust Neon RT exhaust subsystem 10 tri axial accelerometer measurements and impedance sensor Agilent E1432 51 2 kHz DAQ with MATLAB based MIMO MRIT testing interface 51 2 kHz clock speed 800 Hz bandwidth 2048 sampling freq 4096 BS 50 overlap 0 5 Hz f Experimental Modal Analysis Modal frequencies and shapes X direction Y direction Z direction Modal Deflection Mode near 312 Hz appears in all three directions with strongest motion in Y Degree of freedom Results of Design Change Removal of problem frequency Accel Force Accel Force Problem mode in the 300 350 Hz range is displaced by the reduction in stiffness at the inlet as shown below Frequency Hz Frequency Hz Structural Modification Structural Modification Windowed 41 Hz Windowless 90 Hz Concentrate inertia reduce stiffness Suction Gas Pulsation Model Annular volume w const cross section For



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