1,721,100 research outputs found
Sound source identification using coherence- and intensity-based methods
No full textVery often in environmental and industrial acoustics, it is necessary to identify the contribution of single sources to global sound levels. Under this perspective, interests arise from the necessity of controlling noise or verifying whether a single source exceeds legal limits while there are other active sources around. Currently available methods are typically based on coherence or expert system techniques. Both approaches have relevant limitations, but for current purposes, coherence methods are usually more robust, particularly if carried out using vibration sensors in vibroacoustic interactions. Nevertheless, when a measurement system has to be based only on microphone measurements, those methods also have too little reliability and unsatisfying accuracy. In fact, it is quite impossible to eliminate in the input signals the effects of other sources, which usually also have some coherence with the output signal. In this paper, a relevant enhancement to coherence-based methods is described and discussed. The proposed approach leverages on the use of an acoustic intensity measurement approach instead of the sound pressure one. Method advantages and limitations are addressed with a theoretical approach; method performances are experimentally verified. © 2007 IEEE
Sound source identification using coherence and intensity based methods
No full textVery often in environmental and industrial acoustics it is necessary to identify the contribution of single sources to global levels. Under this perspective usually interests arise from the necessity of controlling noise or verifying whether a single source exceeds legal limits, although there are other active sources around. Currently available methods are typically based on coherence or expert systems techniques. Both approaches have relevant limitations, but, for current purposes, coherence methods are usually more robust, especially if carried out using vibration sensors in vibro-acoustic interactions. Nevertheless when a measurement system is based only on microphone measurements also those methods have too little reliability and unsatisfying accuracy, since it's quite impossible to eliminate in input signals the effects of other sources, which usually have some coherence also with output signal. In this paper a relevant enhancement to coherence-based methods, obtained by means of an acoustic-intensity measurement approach, is presented
Prediction of data variability in hand-arm vibration measurements
No full textThe long-term exposure to vibrations transmitted to the human upper limb by hand-held powered tools leads to a group of diseases commonly known as hand-arm vibration (HAV) syndrome. The risk deriving from the vibration exposure can be assessed with direct measurements, using data declared by the tool manufacturer or by retrieving measurements from specific databases. The discrepancies between data belonging to each of these three groups were evidenced in several studies. This paper analyzes the causes of the HAV measurements variability following the ISO GUM approach. The work process was modeled with a lumped parameter scheme of the tool-operator-measurement chain interactions. The measurement uncertainty has been identified propagating the uncertainties of the influencing parameters through the model. The soundness of the approach was verified by comparing the predicted and the observed variability in a specific case study. The major outcome of the proposed method is that the uncertainty budget allows understanding which parameters have to be controlled to limit data dispersion. © 2011 Elsevier Ltd. All rights reserved
3-D sound intensity measurements: Accuracy enhancements with virtual-instrument-based technology
No full textThis paper describes a method that allows accuracy and bandwidth enhancements in 3-D sound intensity measurements. Commercial 3-D probes are usually set up with three mutually perpendicular 1-D p-p probes and, thus, arranged with six microphones; although sound intensity can be calculated with 15 independent pairs of transducers, only the three "primary" pairs that are aligned with the coordinate system axes. The other 12 "secondary" pairs consist of mutually perpendicular microphones, which are placed at a distance that is √2 times shorter than the primary one. The main idea of the proposed method is to average the intensity that is measured on primary and secondary pairs. This leads to a larger bandwidth, thanks to the shorter separating distance between secondary pairs. The intrinsic p-p method highfrequency sensitivity loss is partially recovered, starting from the theoretical plane wave expression. Measurements of different axes are weighted with coefficients that are computed by optimizing the measurement uncertainty. Errors that are due to the metrological characteristics of the transducers and the effects of environmental conditions are compensated. Experimental results showed that a p-p probe arranged with half-inch microphones that are placed at a distance of 50 mm allows reliable measurements up to 2.5 kHz, whereas a commercial probe bandwidth with the same configuration is usually 1250 Hz. © 2008 IEEE
Long term WBV measurements on vehicles travelling on urban paths
No full textThis paper describes the results of a long-term whole-body-vibration monitoring campaign performed on different cars with different drivers. The weighted and the un-weighted root-mean-square acceleration, the MTVV and the VDV have been monitored on five different cars in regular usage for over one hundred hours of measurements on urban roads and highways. The variability of the above parameters has been statistically analyzed in order to assess the time requested for the convergence of standard indexes to their average values. The aim is to supply a general reliability evaluation so as to minimize the on-field tests and to provide a scientific support to the design of such experiments. A comparison between different vehicles is presented and discussed; the correlation with speed measured by a GPS system is analyzed with probabilistic assessments. Results showed that the minimum time for reliable measurement was approximately 30 min for each driving condition (urban, carriage road, highway). The MTVV/aw ratio was usually larger than 1.5 (even on short measurement periods), thus indicating the unsuitability of the basic ISO 2631 criterion. The 8-h based VDV provided indications compatible with the av criterion
Contribution of airports to noise in surrounding environment; identification and measurement of noise sources
No full textThis paper describes the results of an experimental campaign carried out near the Milan Malpensa airport. Aim of the work was the determination of new parameters or measurements that can be used in order to deeply characterize the acoustic field in aeroportual environment. The most innovative aspect is the use of a three dimensional sound intensity probe, that allows determining the direction of the acoustic energy flow and consequently making assessments about the noise source position. Data has been statistically analyzed with sound intensity polar diagrams, which represent the direction of sound (as a function of frequency) coming from the surroundings toward the experimental site. These diagrams allow determining which is the direction from which most of the acoustic energy comes from and can be used, for example, in order to optimize active or passive noise control procedures
3D-coherent acoustic intensity measurements for source identification in aircraft cabins
No full textThis work describes the results of an experimental campaign carried out to identify the correlation between the vibration of different parts of an aircraft cabin and the sound field parameters (pressure, velocity and intensity) measured at the vicinity. The reverberant cabin of the aircraft was considered as a multiple input, multiple output linear system. The inputs were the vibrations measured on different fuselage positions, while the outputs were the sound pressure, velocity and intensity close to the surface. The coherence between the vibration and the sound intensity vector was used to identify the amount of acoustic energy linearly dependent with the vibration. Experiments were performed inside the mock-up of an ATR 42 at Alenia premises, within the FP-6 framework CREDO project (Cabin noise Reduction by Experimental and numerical Design Optimization). Results showed that the 3D coherent intensity, combined with the vibration data, provides indications on the noise sources location also in reverberant conditions
Factors influencing the hand-arm mechanical impedance
No full textAn experimental campaign was described with the aim to evaluate of the factors affecting the driving point mechanical impedance (DPMI) at different frequencies, using the ANOVA technique. The factorial design of experiments (DOE) was used to identify how the posture of elbow, shoulder, and wrist angles, the grip and the push forces and the vibration level affect the DPMI at different frequencies. An aluminum alloy handle was designed with finite elements methods so as to have a natural frequency above 300 Hz. The resonant frequency decrease due to the hand mass led to a systematic error not compensated by the handle idle mass subtraction. The apparent mass uncertainty in the frequency range 10 Hz-1 kHz is lower than 5% for masses ranging from 10 to 80 g. The effect of the vibration level is found to be limited and this leads to the conclusion that the adoption of a linear model is adequate
A device for the skin-contact thermal resistance measurement
No full textThe skin-contact thermal resistance is a parameter that allows evaluating, in steady condition, the heat flow at the interface between the skin and a rigid surface at a known temperature. At the current state of the art, it is evaluated with empirical equations and is known to be dependent on the contact pressure, on the surface characteristics, and on the skin conductivity. The need to measure skin and contact thermal resistance with low uncertainty led to the realization of the device described in this paper. The instrumentbased on the principle of the thermoflowmeterhas been designed with the goal of minimizing the measurement uncertainty with contact temperatures ranging between 12 C° and 27° and contact areas from 50 to 314 mm2. The device allows varying and controlling the interface pressure and temperature that, according to existing literature studies, are likely to influence the skin thermal properties. The different temperatures needed for the evaluation of the thermal resistance are measured with individually calibrated thermocouples. The metrological characterization of the flowmeter was performed under vacuum, and the effect of convective heat exchanges in normal operation was modeled and compensated. Measurement repeatability and reproducibility were assessed by measuring the thermal resistance of plastic materials in operational conditions. Preliminary tests showed that the skin-contact thermal resistances measured in different conditions are compatible with the theoretically evaluated ones, with improvement in uncertainty due to direct measurement. © 2006 IEEE
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