Calculation Of Sound Power Research Articles

Development of an Experimental Acoustic Noise Characterization Setup for Electric Motor Drive Applications

This paper presents the development of an experimental setup for acoustic noise characterization of electric motors. It describes the sound measurement microphones utilized in the setup and discusses the application of octave bands and A-weighting in noise measurement. Various methods for acoustic noise measurement and sound power calculation, including those based on sound pressure and sound intensity, are also covered. Given the relatively noisy test environment and restricted access around the test setup, discrete point sound intensity measurement is selected for sound power calculation. Initially, a stationary probe-holding fixture is designed and fabricated for sound intensity measurements. To enhance the fixture’s flexibility and the accuracy of the measurements, a transportable fixture is subsequently designed and fabricated. The necessary hardware and software settings for acoustic noise characterization are then developed. Finally, the setup is used to conduct acoustic noise characterization of an IPM motor, validating the application of the transportable probe-holding fixture.

Integrated CFD-FEM approach for external gear pump vibroacoustic field prediction

In this work, a three-dimensional fluid-structural and vibro-acoustics coupled model of a gear pump is presented. Gear pumps represent the majority of the positive displacement machines used for flow generation in fluid power systems. Typically, the dynamics of gear pumps are dependent on the characteristics of the fluid dynamics inside the pump, which translates into vibrations to the housing. These vibrations then propagate to the surrounding medium and emit sound. The purpose of this study is to propose a three-dimensional fully integrated computational model to simulate the complete gear pump behaviour from the fluid dynamics to the structural vibrations, up to the vibroacoustic response. In this hybrid configuration, a transient CFD (Computational Fluid Dynamics) model is first developed to simulate the 3D flow field with a deforming and re-meshing approach to take into account the variation of the volume between the gears. Second, the internal pressure field calculated at each time step is then used as a loading into a structural FEM (Finite Element Method) model of the gear pump to compute the actual stresses and deformations of the housing. Third, the results of the structural response are used as excitation in a vibroacoustic sub-model to simulate the radiated noise using a high-order FEM technique. The comparison between the numerical and experimental flow curves validates the CFD model. The sound power calculations from the vibroacoustic model show good comparison with the sound intensity measurements around the pump casing, confirming the validity of the proposed coupled model. The described CFD-FEM approach proves to be a powerful gear pump design tool: it provides a reliable estimate of gear pump working parameters such as fluid power and vibroacoustic characteristics, starting from the CAD (Computer-Aided Design) geometry of the components. Furthermore, being one of the first multi-domain simulation models of a gear pump, this work can be useful to researchers as a starting point to correlate the noise emitted with the internal flow in full 3D conditions.

The art of clinical trial design in pulmonary fibrosis

The design of clinical trials is an art on its own. There are numerous, partially conflicting aspects a clinical trial has to satisfy. First and most importantly, the trial, especially in phase III trials, should ideally demonstrate a statistically significant effect of the drug under investigation on a clinically relevant primary endpoint. To accomplish this task, several aspects need to be considered. A crucial aspect at this stage is the expected effect size of the drug and the known variation of the primary endpoint measure, which together govern the power calculation and the sample size needed. As any treatment effect will need time to develop, time is also an important component: if the study is too short important effects or relevant but rare adverse events may be missed; if the study is too long patient retention may be difficult and dropouts may lead to missing data. A realistic estimate of the expected treatment effect on the primary endpoint and a sound power calculation are the mainstay of a successful study. Eligibility criteria for clinical trials need critical consideration <https://bit.ly/3mWl8Lz>

Improved efficiency of vibration-based sound power computation through multi-layered radiation resistance matrix symmetry.

Computing sound power using complex-valued surface velocities involves using a geometry-dependent acoustic radiation resistance matrix multiplied by a velocity vector to compute sound power for a given frequency range. Using a laser scan grid with constant spacing and a scalar radiator area approximation, a multi-layered Toeplitz symmetry exists in the radiation resistance matrix. An innovative approach was developed to exploit this Toeplitz symmetry. This approach preserved accuracy and resulted in a maximum of ∼1300% computation time reduction for curved plate calculations and a ∼9600% computation time reduction for cylindrical shell sound power calculations.

ACOUSTIC MODELS OF THE MAIN SOURCES OF NOISE OF MULTI-SPINDLE DRILLING WOODWORKING MACHINE

The harmful factors in the woodworking industry include the increased noise level in the workplace. This is especially true when working with multi-spindle drilling woodworking machines. The main sources of noise include the constant speed of drills, the geometric shape of the motor and the body of the cutting units, as well as the pneumatic feed mechanism of the cutting units or workpieces. The article presents a theoretical justification of noise sources, which allowed us to obtain the equation of sound power of noise sources in general form. The acoustic calculation of the main noise sources was performed using the obtained formulas. The obtained acoustic models of the main noise sources showed that the practical calculation of sound pressure levels or sound power is actually reduced to determining the vibration rates on the natural vibration forms of the sources.

Sound power of vibrating cylinders using the radiation resistance matrix and a laser vibrometer

Research has shown that using acoustic radiation modes combined with surface velocity measurements provide an accurate method of measuring the radiated sound power from vibrating plates. This paper investigates the extension of this method to acoustically radiating cylindrical structures. The mathematical formulations of the radiation resistance matrix and the accompanying acoustic radiation modes of a baffled cylinder are developed. Computational sound power calculations using the vibration-based radiation mode (VBRM) method and the boundary element method are then compared and shown to have good agreement. Experimental surface velocity measurements of a cylinder are taken using a scanning laser Doppler vibrometer and the VBRM method is used to calculate sound power. The results are compared to sound power measurements taken using ISO 3741.

A uniform theory of diffraction formulation for acoustic radiation modes

Acoustic radiation modes have recently regained the attention of the literature, with applications ranging from active structural acoustic control to acoustical holography. Typically the calculation of these modes requires boundary element methods for all but flat plate and full sphere geometries. This paper presents a radiation mode formulation for cylindrically curved structures with small curvature, based on the uniform theory of diffraction. This formulation shows promise, as it produces analytical expressions for the radiation resistance matrix, leading to computationally efficient radiation mode calculation. Radiation modes are shown for cylindrically curved plates, and the calculation of sound power with these modes is compared to that calculated using boundary element methods. The extension of this formulation to other curved structures is discussed.

Acoustic Response of Thin Plate with Discrete Patches with Variable Thickness in Water Medium

This paper analyses acoustic response of thin plate with discrete patches with variable thickness in water medium. Finite-element method and Rayleigh integral method are used for sound power calculation in water medium. For low-frequency range up to 50 Hz, the peak sound power level (SPL) is achieved at higher taper ratio of 0.9 with parabolically increasing–decreasing thickness variation with one patch. In the frequency range of 70–180 Hz and 260–290 Hz, a taper ratio of 0.6 with four patches on the plate with parabolically increasing–decreasing variation is preferred for minimum SPL. It is observed that SPL is influenced by redistribution of patches, thickness variations, and taper ratios.

Sound Power Estimation for Beam and Plate Structures Using Polyvinylidene Fluoride Films as Sensors.

The theory for calculation and/or measurement of sound power based on the classical velocity-based radiation mode (V-mode) approach is well established for planar structures. However, the current V-mode theory is limited in scope in that it can only be applied to conventional motion sensors (i.e., accelerometers). In this study, in order to estimate the sound power of vibrating beam and plate structure by using polyvinylidene fluoride (PVDF) films as sensors, a PVDF-based radiation mode (C-mode) approach concept is introduced to determine the sound power radiation from the output signals of PVDF films of the vibrating structure. The proposed method is a hybrid of vibration measurement and numerical calculation of C-modes. The proposed C-mode approach has the following advantages: (1) compared to conventional motion sensors, the PVDF films are lightweight, flexible, and low-cost; (2) there is no need for special measuring environments, since the proposed method does not require the measurement of sound fields; (3) In low frequency range (typically with dimensionless frequency kl < 4), the radiation efficiencies of the C-modes fall off very rapidly with increasing mode order, furthermore, the shapes of the C-modes remain almost unchanged, which means that the computation load can be significantly reduced due to the fact only the first few dominant C-modes are involved in the low frequency range. Numerical simulations and experimental investigations were carried out to verify the accuracy and efficiency of the proposed method.

Measurement Precision Under Repeatability Conditions of a Batch of Sound Power Assessment for Blenders in Reverberation Room

Abstract A set of sound power assessments was performed to determine measurement precision in specified conditions by the comparison method in a reverberation room with a fixed position array of six microphones. Six blenders (or mixers) and, complementary, a reference sound source were the noise sources. Five or six sound power calculations were undertaken on each noise source, and the standard deviation (sr) was computed as “measurement precision under repeatability conditions” for each octave band from 125 Hz to 8 kHz, and in dB(A). With the results obtained, values of sr equal 1.0 dB for 125 Hz and 250 Hz, 0.8 dB for 500 Hz to 2 kHz, and 0.5 dB for 4 kHz and 8 kHz. Those can be considered representative as sound power precision for blenders according to the measurement method used. The standard deviation of repeatability for the A-weighted sound power level equals 0.6 dB. This paper could be used for house or laboratory tests to check where their uncertainty assessment for sound power determination is similar or not to those generated at the National Metrology Institute.

Approximate method for obtaining source quantities for calculation of structure-borne sound transmission into lightweight buildings

An approximate approach is described, for obtaining the source quantities required for the calculation of structure-borne sound power from machines into supporting lightweight building elements. The approach is in two stages, which are based on existing international Standards for measurement. The first stage involves direct measurement of the source free velocity at each contact, to give the sum of the square velocities. The second stage is based on the reception plate method and yields the single equivalent blocked force, which approximates the sum of the square blocked forces. The applicability of the source data obtained has been investigated in a case study of a fan unit on a timber joist floor. The approach contains several significant simplifying assumptions and the uncertainties associated with them are considered. For the case considered, the power transmitted into the floor is estimated by the approximate method to within 5 dB of the true value, on average.

Vibro-acoustic behavior of functionally graded carbon nanotube reinforced polymer nanocomposite plates

This paper presents the numerical investigation results carried out on vibro-acoustic behavior of functionally graded carbon nanotube reinforced polymer nanocomposite plate using combined finite element method and Rayleigh integral. Parameter studies are carried out to analyze the influence of nature of functional grading, loading of carbon nanotube, and structural boundary conditions on free and forced vibration and sound radiation characteristics in detail. It is found that natural frequencies are significantly influenced by the nature of functional grading while the mode shapes are insensitive. The resonant amplitude of vibration and acoustic response are significantly influenced with the nature of different functional grading. This reflects in the bandwise calculation of sound power also which recommends the carbon nanotube functional grading with X distribution along the thickness direction for lower frequency level. Similar variation in vibro-acoustic response has been observed with increase in the carbon nanotube loading also.

Numerical Analysis of Structure Acoustic Radiation Based on Wave Superposition Method

To overcome the non-uniqueness of solution at eigenfrequencies in the boundary integral equation method for structural acoustic radiation, wave superposition method is introduced to study the acoustics characteristics including acoustic field reconstruction and sound power calculation. The numerical method is implemented by using the acoustic field from a series of virtual sources which are collocated near the boundary surface to replace the acoustic field of the radiator, namely the principle of equivalent. How to collocate these equivalent sources is not indicated definitely. Once wave superposition method is applied to sound power calculation, it is necessary to evaluate its accuracy and impact factors. In the paper, the basic principle of wave superposition method is described, and then the integral equation is discretized. Also, the impact factors including element numbers, frequency limitation, and distance between virtual source and integral surface are analyzed in the process of calculate the acoustic radiation from the simply supported thin plate under concentrated force. The extensive measures of acoustic field at the thin plate are compared with results obtain using different numerical methods. The results show that: (a) The agreement between the results from the above numerical methods is excellent. The wave superposition method requires fewer elements and hence is faster. But the extensive numerical modeling suggests that as long as the volume velocity matching yields more than adequate accuracy. (b) The equivalent sources should be collocated inside the radiator. And the accuracy of a given Gauss integration formula will decrease as the source approaches the boundary surface. (c) The numerical method is applicable to the acoustic radiation of structure with complicated shape. (d) The method described in this paper can be used to perform effectively sound power calculation, and its application range can be extended on the basis of these conclusions.

Analyzing structure-borne sound by using the forced vibro-acoustic components

At the 158th meeting of the ASA, a numerical study on analyzing structure-borne sound radiation using the forced vibro-acoustic components (F-VACs) established by the Helmholtz equation least squares (HELS) method was presented [Natarajan et al., JASA, 126, 2244 (2009)]. The present paper presents an experimental case study of this approach on a baffled square plate subjected to a point force excitation using random signals. The radiated acoustic pressures are measured by a planar array of microphones at a very close distance to the plate surface. These input data are used to determine the F-VACs of the plate obtained by decomposing the transfer functions into orthogonal space via singular value decomposition. These F-VACs are correlated to sound radiation through sound power calculations. Meanwhile, the F-VACs are expanded in terms of the natural modes of the plate, so the dominant F-VACs that are directly responsible for sound radiation can be correlated to the natural modes of the plate. Using this F-VAC analysis, one can identify the critical natural modes of a structure, which by themselves have no direct relationships to sound radiation. Based on the F-VAC analysis results, the plate is modified and tested to examine its effectiveness in reducing structure-borne radiation.

An Inverse Force Measurement Method to Determine the Injected Structure-Borne Sound Power from an Installation into a Building Element

In structure-borne sound problems in buildings, knowledge of the contact forces between vibrating equipment and a receiving element is often required. When multiplying these forces with the simultaneously measured velocities at the contact points of the equipment, the structure-borne sound power can be determined, which is the quantity governing the sound energy transfer from a source space to a receiving space. Measuring contact forces directly is however not straightforward. Therefore, a structural-acoustical method is used to determine the contact forces inversely. This technique is already used in the automotive industry, but applications in buildings are rather rare. The installation used is a vibrating platform, which induces tonal, low-frequency vibrations into the building. Therefore, the used sound source has to perform well for low frequencies. The resulting forces are used for structure-borne sound power calculation and verified by comparing the sound pressure, caused by this injected power, with measured sound pressure.

Study of the road traffic noise prediction method applicable to low-noise road surfaces

In this study, the new road traffic noise prediction method applicable to Japanese and Dutch various road surfaces was developed. Firstly, the A-weighted sound power levels of road vehicles were measured for actual roads in the Netherlands paved with various surfaces. With regard to the levels on dense asphalt concrete, the differences between Dutch and Japanese data were not significant, therefore it was found that the common sound power calculation model can be used in both Japan and the Netherlands. On the other hand, the levels for low-noise road surfaces in the Netherlands were 1 to 7 dB lower than those for dense asphalt concrete, therefore the different sound power calculation models were required to be constructed for such surfaces. Secondly, based on the above results, a sound power calculation model applicable to each road surface was developed. By integrating the model with the dynamic traffic flow calculation model, the new road traffic noise prediction method was constructed. Using the method, the road traffic noise in 32 urban areas including low-noise road surfaces in Japan and the Netherlands was calculated. As a result, the calculated levels correspond well with the measured levels (the differences between them were 1.3 dB on average).

Calculation of sound power of aircraft engine compressor

Проведено порівняльний аналіз методів розрахунку рівня звукової потужності компресора авіаційного двигуна. За допомогою розглянутих методів можна розрахувати залежності рівня акустичної потужності дискретних складових компресора від його геометричних і режимних параметрів, дослідити процес шумоутворення

Measurement of sound power and absorption in reverberation chambers using energy density

Reverberation chamber measurements typically rely upon spatially averaged squared pressure for the calculation of sound absorption, sound power, and other acoustic values. While a reverberation chamber can provide an approximately diffuse sound field, variations in sound pressure consistently produce uncertainty in measurement results. This paper explores the benefits of using total energy density or squared particle velocity magnitude (kinetic energy density) instead of squared pressure (potential energy density) for sound absorption and sound power measurements. The approaches are based on methods outlined in current ISO standards. The standards require a sufficient number of source-receiver locations to obtain suitable measurement results. The total and kinetic energy densities exhibit greater spatial uniformity at most frequencies than potential energy density, thus requiring fewer source-receiver positions to produce effective results. Because the total energy density is typically the most uniform of the three quantities at low frequencies, its use could also impact the usable low-frequency ranges of reverberation chambers. In order to employ total and kinetic energy densities for sound absorption measurements, relevant energy-based impulse responses were developed as part of the work for the assessment of sound field decays.

ON CALCULATION OF ACOUSTIC POWER

The previous work on sound power calculation in the presence of a mean flow has been focused on the casting of the basic acoustic equations in the form of an acoustic energy conservation law from which a definition of the acoustic intensity is extracted. The present paper shows that such definitions of sound intensity are deducible from the physical definition of sound power. Also presented is an expression or the sound power in a narrow pipe with a uniform mean flow.

Case study evaluation of the Rayleigh integral method

The Rayleigh integral is based on the assumption that the vibrating surface is flat and part of an infinite rigid baffle. Though approximate, the Rayleigh integral can evaluate the sound power radiated by a vibrating surface in a fraction of the time required by the boundary element method. Three case studies were conducted to evaluate the reliability of the Rayleigh integral. Specifically, the Rayleigh integral was used to predict the sound power from a wheel-rail structure, a gearbox, and an engine. In each case, Rayleigh integral results were compared with boundary element results. The results indicated that sound power compared well with that obtained using the boundary element method. The differences were less than 5 dB except at low frequencies. However, the Rayleigh integral did not accurately predict the sound pressures at field points. The results suggested that the Rayleigh integral could be used in place of the more time intensive boundary element method for sound power calculations.