Showing papers on "Sound power published in 2020"

Parameters Affecting Noise Emitted by Ships Moving in Port Areas

Abstract: Only recently has noise been considered in the assessment of the sustainability of port infrastructures, after decades of unawareness. INTERREG Maritime projects unveiled problems that have been neglected so far, such as the lack of proper regulation and noise exposure assessments for citizens. While it is true that a port area includes a huge variety of possible noise sources, very few of them have been characterized from an acoustical point of view. INTERREG projects have boosted research in the field, and previous studies have dealt with noise produced by moving ships in ports. The present work starts from a previous measurement campaign used to obtain broadband and 1/3-octave-band noise emissions of moving ships, and it aims to explain their uncertainties. More than a month’s worth of continuous acoustic measurements and video recordings were deeply analyzed in order to obtain an input database that is as precise as possible. A multiple regression analysis was performed in order to understand the influence that parameters such as minimum distance, speed, and draught have on ships’ noise emissions, which were calculated using pass-by measurements, with a special focus on ferries. The minimum distance of each ship’s passage from the microphone was measured using a video recording with an innovative methodology, providing results with 3 m of uncertainty. Knowing which parameter is more influential would help in planning proper measurements for monitoring or for drafting correct guidelines. Draught was determined to be uninfluential in ferries’ noise emissions, while the minimum distance and speed relations were estimated and accounted for in the calculation of a refined sound power level. From a spectrum point of view, the frequencies from 500 Hz to 2.5 kHz were determined to be those that contributed the most to the noise produced by the transit of a ship, and they vary with speed. With the studied corrections, different ferry models resulted in similar noise emissions. The standard deviation of noise emitted was reduced by 0.5 dB (A), and the average was also improved by positioning the ships’ flow at the correct average minimum distance. Furthermore, the right placement of a source is also important in the acoustic mapping phase for a correct evaluation of the propagation of noise at a distance. The use of more precise input data is important for improving the output of acoustic propagation models during the assessment of port noise in the surrounding areas.

ACAT1 Benchmark of RANS-Informed Analytical Methods for Fan Broadband Noise Prediction: Part II—Influence of the Acoustic Models

Abstract: A benchmark dedicated to RANS-informed analytical methods for the prediction of turbofan rotor–stator interaction broadband noise was organised within the framework of the European project TurboNoiseBB. The second part of this benchmark focuses on the impact of the acoustic models. Twelve different approaches implemented in seven different acoustic solvers are compared. Some of the methods resort to the acoustic analogy, while some use a direct approach bypassing the calculation of a source term. Due to differing application objectives, the studied methods vary in terms of complexity to represent the turbulence, to calculate the acoustic response of the stator and to model the boundary and flow conditions for the generation and propagation of the acoustic waves. This diversity of approaches constitutes the unique quality of this work. The overall agreement of the predicted sound power spectra is satisfactory. While the comparison between the models show significant deviations at low frequency, the power levels vary within an interval of ±3 dB at mid and high frequencies. The trends predicted by increasing the rotor speed are similar for almost all models. However, most predicted levels are some decibels lower than the experimental results. This comparison is not completely fair—particularly at low frequency—because of the presence of noise sources in the experimental results, which were not considered in the simulations.

Acoustic noise computation of electrical motors using the boundary element method

Abstract: This paper presents a numerical method and computational results for acoustic noise of electromagnetic origin generated by an induction motor. The computation of noise incorporates three levels of numerical calculation steps, combining both the finite element method and boundary element method. The role of magnetic forces in the production of acoustic noise is established in the paper by showing the magneto-mechanical and vibro-acoustic pathway of energy. The conversion of electrical energy into acoustic energy in an electrical motor through electromagnetic, mechanical, or acoustic platforms is illustrated through numerical computations of magnetic forces, mechanical deformation, and acoustic noise. The magnetic forces were computed through 2D electromagnetic finite element simulation, and the deformation of the stator due to these forces was calculated using 3D structural finite element simulation. Finally, boundary element-based computation was employed to calculate the sound pressure and sound power level in decibels. The use of the boundary element method instead of the finite element method in acoustic computation reduces the computational cost because, unlike finite element analysis, the boundary element approach does not require heavy meshing to model the air surrounding the motor.

An analytic solution for gust-cascade interaction noise including effects of realistic aerofoil geometry

Abstract: This paper presents an analytic solution for the sound generated by rotor–stator interaction for aerofoils with small camber and thickness subject to a background flow with small angle of attack. The interaction is modelled as a convected, unsteady vortical or entropic gust incident on an infinite rectilinear cascade of staggered aerofoils in a background flow that is uniform far away from the cascade. Applying rapid distortion theory (RDT) and transforming to an orthogonal coordinate system reduces the cascade of aerofoils to a cascade of flat plates. By seeking a perturbation expansion in terms of the disturbance of the background flow from uniform flow, leading- and first-order governing equations and boundary conditions are obtained for the acoustic potential. The system is then solved analytically using the Wiener–Hopf method. The resulting expression is inverted to give the acoustic potential function in the entire domain, i.e. a solution to the inhomogeneous convected Helmholtz equation with inhomogeneous boundary conditions in a cascade geometry. The solution significantly extends previous analytical work that is restricted to flat plates or only calculates the far-upstream radiation, and as such can give insight into the role played by blade geometry on the acoustic field upstream, downstream and in the important inter-blade region of the cascade. This new solution is validated against solutions that only account for flat plates at zero angle of attack. Various aeroacoustic results, including the scattered pressure, unsteady lift and sound power output, are discussed for a range of geometries and angles of attack.

Approximate Simulations for the Non-linear Long-Short Wave Interaction System

Abstract: This research paper studies the semi-analytical, and numerical solutions of on the nonlinear long-short wave interaction system which represents an optical field that does not alter through multiplication due to a sensitive balance between linear and nonlinear impacts in the elastic medium that is defined as the medium which can adjust in the figure as a consequence of a deforming strength and come back its shape to its original form when the force eliminates. In this medium, the wave is produced by vibrations that are a consequence of acoustic power and is known as a sound wave or acoustic wave. The Adomian decomposition method and cubic\,\&\, septic B-spline method are applied to the suggested system to obtain distinct types of solutions that are used to explain the novel physical properties of this system. These novels' features are described by different types of figures that show more physical properties of this model. Also, the convergence between the obtained solutions is discussed by some tables that show the values of absolute error between them.

EAgLE: Equivalent Acoustic Level Estimator Proposal.

Abstract: Road infrastructures represent a key point in the development of smart cities. In any case, the environmental impact of road traffic should be carefully assessed. Acoustic noise is one of the most important issues to be monitored by means of sound level measurements. When a large measurement campaign is not possible, road traffic noise predictive models (RTNMs) can be used. Standard RTNMs present in literature usually require in input several information about the traffic, such as flows of vehicles, percentage of heavy vehicles, average speed, etc. Many times, the lack of information about this large set of inputs is a limitation to the application of predictive models on a large scale. In this paper, a new methodology, easy to be implemented in a sensor concept, based on video processing and object detection tools, is proposed: the Equivalent Acoustic Level Estimator (EAgLE). The input parameters of EAgLE are detected analyzing video images of the area under study. Once the number of vehicles, the typology (light or heavy vehicle), and the speeds are recorded, the sound power level of each vehicle is computed, according to the EU recommended standard model (CNOSSOS-EU), and the Sound Exposure Level (SEL) of each transit is estimated at the receiver. Finally, summing up the contributions of all the vehicles, the continuous equivalent level, Leq, on a given time range can be assessed. A preliminary test of the EAgLE technique is proposed in this paper on two sample measurements performed in proximity of an Italian highway. The results will show excellent performances in terms of agreement with the measured Leq and comparing with other RTNMs. These satisfying results, once confirmed by a larger validation test, will open the way to the development of a dedicated sensor, embedding the EAgLE model, with possible interesting applications in smart cities and road infrastructures monitoring. These sites, in fact, are often equipped (or can be equipped) with a network of monitoring video cameras for safety purposes or for fining/tolling, that, once the model is properly calibrated and validated, can be turned in a large scale network of noise estimators.

Nonlinear effects in high-intensity focused ultrasound power transfer systems

Abstract: In the context of wireless acoustic power transfer, high-intensity focused ultrasound technology aims at the reduction of spreading losses by concentrating the acoustic energy at a specific location. Experiments are performed to determine the impact of nonlinear wave propagation on the spatially resonant conditions in a focused ultrasonic power transfer system. An in-depth analysis is performed to explain experimental observations. The results show that the efficiency of energy transfer is reduced as nonlinear effects become more prominent. Furthermore, the maximum voltage output position shifts away from the focal point and closer to the transducer as the source strength is increased. The results and analysis are relevant to the development of efficient ultrasonic power transfer devices when using focused sources.

Multiphysical numerical (FE–BE) solution of sound radiation responses of laminated sandwich shell panel including curvature effect

Abstract: In this paper, a numerical scheme is prepared using the higher-order shear deformation type of kinematic model with the help of a coupled finite and boundary elements (FE–BE) to evaluate the vibroacoustic responses of laminated composite sandwich curved shell panels The panel is under the influence of a harmonic point load Further, an FE–BE combined technique is utilized to prepare a generic computer code (MATLAB environment) for the numerical prediction via the proposed mathematical formulation The structural frequency and the subsequent sound relevant data are obtained by solving the final form of the multiphysics model In this regard, the structural system equation is derived through Hamilton’s principle and the Helmholtz wave equation for the computation of acoustic responses The performance of the proposed scheme is established initially through the convergence and the corresponding validation studies The comparison cases are made with the available published benchmark frequency (free vibration) as well as the acoustic data Appropriate numbers of numerical examples are solved to draw the meaningful inferences of various factors to show the significant influences on the acoustic radiation responses of the curved sandwich panel type of structural components The curvature ratio is showing the accentuated influences on the sound radiation responses for the low-frequency ranges whereas the increase in the thickness ratio, ie the ratio of core to face leads to an accentuated radiated sound power

Data-Driven Soft Sensor for the Estimation of Sound Power Levels of Refrigeration Compressors Through Vibration Measurements

Abstract: The quality assessment of the sound power generated by refrigeration compressors is an important and costly process for manufacturers, mainly due to the need for acoustic rooms. Hence, very few samples per lot are tested. In this article, an alternative method based on soft sensing is proposed to estimate the sound power of refrigeration compressors. The method uses vibration measurements from the compressor surface as the input and the sound power generated as the output of machine learning (ML) models to create data-driven soft sensors. This method is less restrictive than the traditional ones and allows a test to be done close to the manufacturing line, in a much faster and cheaper way. In order to create the dataset to train the ML models, sound power and vibration levels of compressors were measured simultaneously in a reverberation room. The results from the data-driven soft sensors were compared with the ones obtained using a simple analytic model defined in an ISO technical note and showed that, even with as little as one vibration measurement point, the proposed method presented better results than the ISO analytic model with nine measurement points.

Flow and Noise Characteristics of Centrifugal Fan in Low Pressure Environment

Abstract: The influence of low-pressure environment on centrifugal fan’s flow and noise characteristics was studied experimentally and numerically. A testbed was established to conduct the experimental test on the performance of a centrifugal fan, and the characteristic curve and power consumption curve of the fan under different pressure were obtained. Then the simulation model of the centrifugal fan was established, which was used to simulate the working process of centrifugal fan under different negative pressures. The results showed that the total pressure and static pressure of the fan decrease with the decrease of the ambient pressure. The total and static pressures of the fan under 60 kPa pressure condition decreased by 42.3% and 38.3%, respectively, compared with those of fan under the normal pressure. The main reason for this phenomenon is that the decrease of the environmental pressure leads to the decrease of air density. Besides, with the drop of environmental pressure, the sound pressure and sound power of the fan noise decreases.

Influence of nasal cavities on voice quality: Computer simulations and experiments.

Abstract: Nasal cavities are known to introduce antiresonances (dips) in the sound spectrum reducing the acoustic power of the voice. In this study, a three-dimensional (3D) finite element (FE) model of the vocal tract (VT) of one female subject was created for vowels [a:] and [i:] without and with a detailed model of nasal cavities based on CT (Computer Tomography) images. The 3D FE models were then used for analyzing the resonances, antiresonances and the acoustic pressure response spectra of the VT. The computed results were compared with the measurements of a VT model for the vowel [a:], obtained from the FE model by 3D printing. The nasality affects mainly the lowest formant frequency and decreases its peak level. The results confirm the main effect of nasalization, i.e., that sound pressure level decreases in the frequency region of the formants F1-F2 and emphasizes the frequency region of the formants F3-F5 around the singer's formant cluster. Additionally, many internal local resonances in the nasal and paranasal cavities were found in the 3D FE model. Their effect on the acoustic output was found to be minimal, but accelerometer measurements on the walls of the 3D-printed model suggested they could contribute to structure vibrations.