03_Radiation_Efficiency.pdfVIP

1Radiation Efficiency D. W. Herrin, Ph.D., P.E. University of Kentucky Department of Mechanical Engineering Slides ? 2006 by A. F. Seybert 2 Radiation Efficiency Dept. of Mech. Engineering University of Kentucky Noise and Vibration Short Course Stamped Steel Oil Pan (.084”) Sand-Cast Aluminum Oil Pan (0.42”) Example 23 Radiation Efficiency Dept. of Mech. Engineering University of Kentucky Noise and Vibration Short Course Average Vibration 1.00E-04 1.00E-03 1.00E-02 0 1000 2000 3000 4000 Frequency (Hz) A ve ra ge V el oc ity (m /s ) Alum. pan Steel pan 4 Radiation Efficiency Dept. of Mech. Engineering University of Kentucky Noise and Vibration Short Course Sound Power Contribution 60 65 70 75 80 85 90 95 0 500 1000 1500 2000 2500 3000 Frequency, Hz S ou nd P ow er (d B ) ALUM STEEL 35 Radiation Efficiency Dept. of Mech. Engineering University of Kentucky Noise and Vibration Short Course Sound Radiation from Structures Structural FRF Radiation Efficiency Forces Vibration Sound × ×= = Force Transfer Function Vibration Radiation Efficiency Sound Power 6 Radiation Efficiency Dept. of Mech. Engineering University of Kentucky Noise and Vibration Short Course Radiation Efficiency ? Shape of the source ? Deflection pattern ? Frequency ? Excitation (mechanical or airborne) But does not depend on vibration amplitude Radiation efficiency depends on: 47 Radiation Efficiency Dept. of Mech. Engineering University of Kentucky Noise and Vibration Short Course Radiation Efficiency = 2 n rad rad vcS W ρ σ vn2 — space-time average mean-square vibration velocity actual power equiv. power (baffled piston) 8 Radiation Efficiency Dept. of Mech. Engineering University of Kentucky Noise and Vibration Short Course Radiation Efficiency Oversimplified λa λs λs λa Inefficient Radiator sa λλ Efficient Radiator as λλ ≥ 59 Radiation Efficiency Dept. of Mech. Engineering University of Kentucky Noise and Vibration Short Course Why? Cancellation of sound when λs λa λa λs - - + + - - + +