Sound power

About: Sound power is a research topic. Over the lifetime, 6337 publications have been published within this topic receiving 73363 citations. The topic is also known as: acoustic power.

CLEAN Based on Spatial Source Coherence

Abstract: To obtain higher resolution acoustic source plots from microphone array measurements, deconvolution techniques are becoming increasingly popular. Deconvolution algorithms aim at identifying Point Spread Functions (PSF) in source plots, and may therefore fall short when actual beam patterns of measured noise sources are not similar to synthetically obtained PSF's. To overcome this, a new version of the classical deconvolution method CLEAN is proposed here: CLEAN-SC. By this new method, which is based on spatial source coherence, side lobes can be removed of actually measured beam patterns. Essentially, CLEAN-SC iteratively removes the part of the source plot which is spatially coherent with the peak source. A feature of CLEAN-SC is its ability to extract absolute sound power levels from the source plots. The merits of CLEAN-SC were demonstrated using array measurements of airframe noise on a scale model of the Airbus A340 in the 8×6 m2 closed test section of DNW-LLF.

Structure-Borne Sound: Structural Vibrations and Sound Radiation at Audio Frequencies

Abstract: A Little Dynamics- Survey of Wave Types and Characteristics- Damping- Impedance and Mobility- Attenuation of Structure-Borne Sound- Sound Radiation from Structures- Generation and Measurement of Structure-Borne Sound

Noise of polyphase electric motors

Abstract: GENERATION AND RADIATION OF NOISE IN ELECTRICAL MACHINES Vibration, Sound, and Noise Sound Waves Sources of Noise in Electrical Machines Energy Conversion Process Noise Limits and Measurement Procedures for Electrical Machines Deterministic and Statistical Methods of Noise Prediction Economical Aspects Accuracy of Noise Prediction MAGNETIC FIELDS AND RADIAL FORCES IN POLYPHASE MOTORS FED WITH SINUSOIDAL CURRENTS Construction of Induction Motors Construction of Permanent Magnet Synchronous Brushless Motors A.C. Stator Windings Stator Winding MMF Rotor Magnetic Field Calculation of Air Gap Magnetic Field Radial Forces Other Sources of Electromagnetic Vibration and Noise INVERTER-FED MOTORS Generation of Higher Time Harmonics Analysis of Radial Forces for Nonsinusoidal Currents Higher Time Harmonic Torques in Induction Machines Higher Time Harmonic Torques in Permanent Magnet (PM) Brushless Machines Influence of the Switching Frequency of an Inverter Noise Reduction of Inverter-Fed Motors TORQUE PULSATIONS Analytical Methods of Instantaneous Torque Calculation Numerical Methods of Instantaneous Torque Calculation Electromagnetic Torque Components Sources of Torque Pulsations Higher Harmonic Torques of Induction Motors Cogging Torque in Permanent Magnet (PM) Brushless Motors Torque Ripple Due to Distortion of EMF and Current Waveforms in Permanent Magnet (PM) Brushless Motors Tangential Forces vs. Radial Forces Minimization of Torque Ripple in PM Brushless Motors STATOR SYSTEM VIBRATION ANALYSIS Forced Vibration Simplified Calculation of Natural Frequencies of the Stator System Improved Analytical Method of Calculation of Natural Frequencies Numerical Verification ACOUSTIC CALCULATIONS Sound Radiation Efficiency Plane Radiator Infinitely Long Cylindrical Radiator Finite Length Cylindrical Radiator Calculations of Sound Power Level NOISE AND VIBRATION OF MECHANICAL AND AERODYNAMIC ORIGIN Mechanical Noise Due to Shaft and Rotor Irregularities Bearing Noise Noise Due to Toothed Gear Trains Aerodynamic Noise Mechanical Noise Generated by the Load ACOUSTIC AND VIBRATION INSTRUMENTATION Measuring System and Transducers Measurement of Sound Pressure Acoustic Measurement Procedure Vibration Measurements Frequency Analyzers Sound Power and Sound Pressure Indirect Methods of Sound Power Measurement Direct Method of Sound Power Measurement: Sound Intensity Technique Standard for Testing Acoustic Performance of Rotating Electrical Machines NUMERICAL ANALYSIS Introduction FEM Model for Radial Magnetic Pressure FEM for Structural Modeling BEM for Acoustic Radiation Discussion STATISTICAL ENERGY ANALYSIS Introduction Power Flow Between Linearly Coupled Oscillators Coupled Multimodal Systems Experimental SEA Application to Electrical Motors NOISE CONTROL Mounting Standard Methods of Noise Reduction Active Noise and Vibration Control APPENDIX A: BASICS OF ACOUSTICS Sound Field Variables and Wave Equations Sound Radiation from a Point Source Decibel Levels and Their Calculations Spectrum Analysis APPENDIX B: PERMEANCE OF NONUNIFORM AIR GAP Permeance Calculation Eccentricity Effect APPENDIX C: MAGNETIC SATURATION APPENDIX D: BASICS OF VIBRATION A Mass-Spring-Damper Oscillator Lumped Parameter Systems Continuous Systems SYMBOLS AND ABBREVIATIONS BIBLIOGRAPHY INDEX

A New Mechanism for Core-Collapse Supernova Explosions

Abstract: In this paper we present a new mechanism for core-collapse supernova explosions that relies on acoustic power generated in the inner core as the driver. In our simulation using an 11 M☉ progenitor, an advective-acoustic oscillation a la Foglizzo with a period of ~25-30 ms arises ~200 ms after bounce. Its growth saturates due to the generation of secondary shocks, and kinks in the resulting shock structure funnel and regulate subsequent accretion onto the inner core. However, this instability is not the primary agent of explosion. Rather, it is the acoustic power generated early on in the inner turbulent region stirred by the accretion plumes and, most importantly, but later on, by the excitation and sonic damping of core g-mode oscillations. An l = 1 mode with a period of ~3 ms grows at late times to be prominent around ~500 ms after bounce. The accreting proto-neutron star is a self-excited oscillator, "tuned" to the most easily excited core g-mode. The associated acoustic power seen in our 11 M☉ simulation is sufficient to drive the explosion >550 ms after bounce. The angular distribution of the emitted sound is fundamentally aspherical. The sound pulses radiated from the core steepen into shock waves that merge as they propagate into the outer mantle and deposit their energy and momentum with high efficiency. The ultimate source of the acoustic power is the gravitational energy of infall, and the core oscillation acts like a transducer to convert this accretion energy into sound. An advantage of the acoustic mechanism is that acoustic power does not abate until accretion subsides, so that it is available as long as it may be needed to explode the star. This suggests a natural means by which the supernova is self-regulating.

Radiation modes and the active control of sound power

Abstract: Two formulations for calculating the total acoustic power radiated by a structure are compared; in terms of the amplitudes of the structural modes and in terms of the velocities of an array of elemental radiators on the surface of the structure. In both cases, the sound radiation due to the vibration of one structural mode or element is dependent on the vibration of other structural modes or elements. Either of these formulations can be used to describe the sound power radiation in terms of a set of velocity distributions on the structure whose sound power radiation is independent of the amplitudes of the other velocity distributions. These velocity distributions are termed ‘‘radiation modes.’’ Examples of the shapes and radiation efficiencies of these radiation modes are discussed in the cases of a baffled beam and a baffled panel. The implications of this formulation for the active control of sound radiation from structures are discussed. In particular, the radiation mode formulation can be used to provide an estimate of the number of independent parameters of the structural response which need to be measured and controlled to give a required attenuation of the radiated sound power.