Determination of Acoustic Radiation Efficiency via Particle Velocity Sensor with Applications (original) (raw)
Related papers
Evaluation of machinery acoustic properties using the acoustic radiation efficiency parameter
2019
Acoustic radiation efficiency is a parameter which characterizes the sound radiation effectiveness of a vibrating surface. It can be useful in describing the coupling between a vibrating element and the origin of its structure-borne noise. This paper discusses the possibilities of using acoustic radiation efficiency parameter as an indicator applied to assess the noise emitted by power machinery. Acoustic methods, including intensity scanning, Laser Doppler Vibrometry (LDV) and numerical analyses, were used to determine the vibration velocity and, subsequently, calculate and evaluate the radiation efficiency values. Results of measurements and FEM simulations are presented along with comparison of the methods.
A particle velocity sensor to measure the sound from a structure in the presence of background noise
2005
The performance (or quality) of a product is often checked by measuring the radiated sound (noise) from the vibrating structure. Often this test has to be done in an environment with background noise, which makes the measurement difficult. When using a (pressure) microphone the background noise can be such that it dominates the radiated sound from the vibrating structure. However, when using a particle velocity sensor, the Microflown [1,2], near the vibrating structure, the background noise has almost no influence (it is almost cancelled) and the sound from the structure is measured with a good S/N ratio. The experimental results are explained in terms of the different boundary conditions at the surface of the vibrating structure for the pressure and the particle velocity.
The design of structural acoustic sensors for active control of sound radiation into enclosures
This paper introduces a design method for polyvinylidene fluoride (PVDF) structural acoustic sensors for the active control of sound radiation into enclosures. It combines genetic algorithms and the quadratic optimal approach to search for a sensor configuration capable of detecting vibration components with strong sound-radiation ability. In this research, one PVDF sensor is not limited to one single piece of continuous PVDF film. It can consist of a cluster of small PVDF pieces, which could be discrete. Therefore, the parameters to be optimized are the number and the locations of PVDF pieces involved in a sensor. The design method is applied to a cylindrical shell with a floor partition. The general design guidelines are discussed. To show the effectiveness of the method, the control performance of an optimal sensor arrangement is compared with that of non-optimal ones. Physical insights are obtained using structural modal response analysis, modal spectrum analysis of the PVDF sensor output, and structural acoustical coupling analysis. The performance of a PVDF sensor configuration designed at one acoustic resonant frequency is also investigated for other disturbance frequencies below 500 Hz, showing that a significant reduction of acoustic potential energy can be achieved over a wide frequency range. It is demonstrated that, with PVDF sensors optimally designed using the proposed method, the active control of sound radiation into enclosures can be achieved without using acoustic transducers.
FE based measures for structure borne sound radiation
The sound emission of thin-walled radiating components is a common objective of structural optimisation. Acoustic measures are not implemented in common FE-codes. Thus, different velocitiy based measures will be compared: the kinetic energy, the equivalent radiated power (ERP) and the lumped parameter model (LPM). The most common approach-the ERP-is based on the sound intensity in normal direction and the sound pressure on the radiating surface. Assuming a unit radiation efficiency all-over the surface and neglecting local effects, this is a common approach for an upper bound of structure borne noise. Therein, the sound power finally results from the squared velocity integrated over the radiating surface and the constant fluid impedance. As ERP usually requires extra post processing to consider the velocity in normal surface direction, the kinetic energy is essential in common FEA results including all velocity components apart from the normal direction, too. Thus, it is less accurate but maybe usable for optimisation abilities. In contrast, LPM is a simplification of the Rayleigh-integral and thus gives quite accurate results but requires significant higher computational costs than ERP. Possibilities and limits of estimating the emitted sound power by these three methods will be shown.
Direct sound radiation testing on a mounted car engine
For (benchmark) tests it is not only useful to study the acoustic performance of the whole vehicle, but also to assess separate components such as the engine. Reflections inside the engine bay bias the acoustic radiation estimated with sound pressure based solutions. Consequently, most current methods require dismounting the engine from the car and installing it in an anechoic room to measure the sound emitted. However, this process is laborious and hard to perform. In this paper, two particle velocity based methods are proposed to characterize the sound radiated from an engine while it is still installed in the car. Particle velocity sensors are much less affected by reflections than sound pressure microphones when the measurements are performed near a radiating surface due to the particle velocity's vector nature, intrinsic dependency upon surface displacement and directivity of the sensor. Therefore, the engine does not have to be disassembled, which saves time and money. An array of special high temperature particle velocity probes is used to measure the radiation simultaneously at many positions near the engine of a compact class car. The particularities of these probes, the mountings used, and the actions taken to cope with disturbances such as airflows are described in this paper. The effective sound pressure is calculated with a particle velocity based transfer path analysis method and a novel sound power based method. To validate these techniques, the data obtained is compared to the results acquired in an anechoic room with a dismounted engine. It is shown that similar results can be obtained with both methods but that the sound power based methodology seems more practical. It is a straightforward and fast approach to characterize the average sound pressure level at certain distance.
Radiation and power flow characteristics of plate-like structures which constitute the bodies of the well-known engineering applications like cars and household appliances is a primary research field in vibroacoustics. In this study, representative radiation characteristics of plates is examined on the surface of a 300 mm x 300 mm steel square plate excited by a shaker at its midpoint. Two-microphone sound intensity measurement with a probe utilizing side-by-side configuration is used to analyze the near-field radiation characteristics. Surface intensity is simultaneously measured on the plate with another probe consisting of a condenser microphone and an eddycurrent non-contact displacement transducer to compare the results with the twomicrophone sound intensity measurement. Structural intensity technique is utilized for visualization of the power flow throughout the plate's surface. Sound power levels and radiation efficiencies are determined by these two acoustical methods and results are compared with those obtained from an analytical model of the radiating plate. In this particular model, the plate is modeled by a collection of small baffled pistons with equal areas functioning in their own true phases. It is also shown that both experimental methods yield reasonably close results, at especially low frequencies, and analytical results obtained from the model display a similar trend with the experimental results.
On Acoustic Emission Sensor Characterization
Journal of acoustic emission, 2016
We examined calibration methods for acoustic emission (AE) sensors. In spite of the self-evident needs of reliable calibration, the current state is deplorable globally. The only primary standard at NIST (US) is non-operational, yet no other standard has emerged. Widely practiced face-to-face calibration methods have no validated foundation. Reciprocity calibration methods are invalid for the lack of reciprocity and sensor dependent reciprocity parameters. This work provides three workable solutions based on laser-based displacement measurement, which leads to "direct" method using the face-to-face arrangement. This leads to the second "indirect" method of mutually consistent determination of transmitting and receiving sensitivities of sensors/transducers. For all ultrasonic and AE sensors examined, their receiving and transmitting sensitivities are found to be always different and non-reciprocal. Displacement vs. velocity calibration terminology is clarified, correlating the "V/ bar" reference to laser-based calibration. We demonstrate the validity of the direct and indirect methods and the third one based on Hill-Adams equation, called Tri-Transducer method. This uses three transducers as in reciprocity method, but incorporates experimentally determined reference sensor sensitivities ratio without a transfer block and can get both transmitting and receiving sensitivities. These three methods provide consistent calibration results for over 30 AE sensors.