Total Sound Power Level Research Articles

Sound Power Measurement of Tyre/Road Noise Using the Close-Proximity (CPX) Trailer Enclosure

The present paper reports a new methodology for measuring the sound power level (SWL) of tyre/road noise, using a modified Close-Proximity (CPX) trailer enclosure. Specially designed diffuser panels are implemented to cover the absorption materials on the interior walls and ceiling of the CPX enclosure to create a reverberant chamber. Through numerical simulations, the optimal reverberant chamber design, which holds the least acoustic resonance and most uniform acoustic energy distribution, is determined to guide fabrication. The SWL of a reference sound source (RSS) is determined first. The sound pressure level (SPL) distributions inside the reverberant chamber with the RSS switched on are then obtained under static conditions and road tests. The relationships between the SWL of the RSS and the SPL it produces inside reverberant chamber with various RSS inputs signals show great consistency with theory. Using the linear regression of SWL with respect to spatially averaged SPL reverberant chamber obtained in static condition, the total SWL and its spectrum at a specific vehicle speed can be deduced from the captured SPL information inside the chamber during road tests with the RSS switched off.

Acoustic Radiation of a Beam Subjected to Transverse Load

In this paper, the dynamic response of a Euler–Bernoulli beam subjected to transverse harmonic forces is calculated. The method of separation of variables combined with the mode shape superposition method, which includes the determination of eigenvalues, is used to define the velocity field of the beam surface. The Rayleigh integral was used to calculate the sound radiation and the beam was placed in an infinite baffle. Additional actuators are introduced in order to minimize the sound radiation, or, more specifically, the total sound power level of the vibrating beam, and their optimal position and force amplitude are determined; the conclusions were drawn from the optimization results. This paper proposes a method for faster determination of the optimal actuator parameters in order to achieve the minimum total sound power level. The validity of the obtained results is demonstrated with examples, whose solutions are compared to the results in the published literature.

Parametric Analysis of Structural Noise of Steel-Concrete Composite Slab Beams

In this study, the vibration acceleration and radiation structure noise in specific points, 30 cm away from the center surface of each plate of the concrete deck, web, and flange of the steel beam, are measured via the hammering test. The test is conducted on the middle concrete deck of an 8.5 m steel-concrete composite slab beam. The accuracy of the numerical model is then carefully justified. The influence of the number of shear studs, spacing, and arrangement of ribs on the concerning results is methodically examined and discussed by employing the numerical model. In the center frequency of 10–1000 Hz, the total sound power level of the structure can be lessened by improving the concrete deck thickness as well as the number of shear studs. The reduction of the rib spacing can effectively lessen the sound power level as well. The noise reduction of the plate with rib arrangement in the midspan zone is more influential than the case with uniform layout in the whole span.

Effect of the rotor blade installation angle on the structure-borne noise generated by adjustable-blade axial-flow fans

The effect of rotor blade installation angle on the structure-borne noise of adjustable-blade axial-flow fans is analyzed based on the fluid–solid coupling method. The co-simulation environment ANSYS Workbench is adopted to perform one-way fluid–solid coupling analysis. Following this, the properties of the flow field and noise field with different installation angles are simulated. The flow field simulation results reported significant vorticity near the rotor and stator, and a larger installation angle may cause higher pressure fluctuation. The sound field results showed that the frequency spectrum characteristics for the sound pressure level and the sound power level are almost the same while the installation angle changes from −8° to 8°, and the peaks of frequency spectrum occur at the blade passing frequency and its harmonics. The total sound pressure level (TSPL) and the total sound power level (TPWL) all show increasing trends ranging from −8° to +8°. The maxima of TSPL and TPWL reach 134.1 and 176 dB, while their minima reach 123.1 and 163 dB, respectively. Thus, reduction of the installation angle can reduce the structure-borne noise. Besides, the structure-borne noise generated by adjustable-blade axial-flow fans is low-frequency noise, which lies in the range of 0–500 Hz.

Optimized Perforation Schemes in Railway Wheels Toward Acoustic Radiation Mitigation

Abstract Rolling noise emitted by railway wheels is a problem that affects human health and limits the expansion of the railway network. It is caused by the wheel vibration due to the wheel-rail contact force, and it is important in almost all the vehicle velocity range. The minimization of noise radiation associated with changes on the wheel web is discussed in this work, focusing on potential shape modifications in existing wheels in the form of a perforation distribution over the web. Such a post-manufacturing technique is a cost-effective solution that can be performed in a relatively short term. The implemented objective function is directly related to the overall radiated sound power, which is minimized using a genetic algorithm-based optimizer. In the acoustic model, radiation efficiencies are approximated to unity, the accuracy of this assumption being also studied in the work. The results reflect that an optimized distribution of perforations on the web of a railway wheel can reduce the total sound power level, by about 5 dB(A) and 2 dB(A) for curved and straight web, respectively. The mitigation of the radiated sound power is due to the fact that certain wheel vibration modes are modified and shifted to other frequencies where they are less excited. Finally, the relevance of the cross-sectional curvature of the web is explored by studying two different web geometries, suggesting that it can strongly influence the noise mitigation effects of the perforation pattern.

A novel MPP-NSGA algorithm and its application in optimization for radiated noises in the aircraft cabin

The paper used the AML method to compute transmission loss of aircraft panels and verifies correctness of the numerical simulation model by experimental test. Finally, this paper used an improved genetic algorithm to conduct a multi-objective optimization for the cabin noise. When the analyzed frequency is less than 250 Hz, transmission loss decreased rapidly with the increased analysis frequency, and decreased from the maximum 63.2 dB to 18.5 dB. Within 250 Hz-4000 Hz, the transmission loss gradually increased with the increased analysis frequency. At 250 Hz, the transmission loss had an obvious valley value. Sound radiation power was then computed based on boundary element method, and panel contribution analysis was conducted to find those panels which had an obvious impact on the cabin noise. Therefore, a multi-objective optimization was conducted on these panels and reinforced ribs. In order to further verify effectiveness of the MPP-NSGA method, it was compared with the traditional GA model and NSGA model. Optimization accuracy using MPP-NSGA model is increased, and optimization time is reduced. Through optimization with traditional GA method, the maximum sound power level decreased by 15.4 %, and the total sound power level decreased by 21.9 %. Through optimization with the NSGA method, the maximum sound power level decreased by 21.7 %, and the total sound power level decreased by 29.0 %. Through optimization with the MPP-NSGA method, the maximum sound power level decreased by 46.3 %, and the total sound power level decreased by 36.0 %. Therefore, compared with other two kinds of genetic algorithms, the MPP-NSGA method is obviously superior in noise optimization in the cabin. In the whole analysis frequency band, noise of the optimized cabin panel at each frequency point was smaller than that of the original structure, fully verifying feasibility of the optimization algorithm proposed in the paper. In addition, in the optimized structure, no panel made obvious contributions to the cabin noise, and each panel showed an equivalent contribution level. Transmission loss of the optimized cabin panel was obviously improved. However, the sound insulation valley still appeared at 250 Hz, but it was not so obvious like the original structure. After optimization, the sound insulation valley was 31.6 dB. The sound insulation valley of the original structure was 18.5 dB. Obviously, the sound insulation valley value of the optimized structure was increased by double compared with the original structure. This paper provided a valuable reference for noise reduction in the aircraft cabin.

Calculation of sound power level of tandem axial fan

A numerical simulation of the flow in axial fans with single and tandem geometrically equivalent blade rows was carried out. During the research, the sound power level of the fans was calculated. The acoustic characteristics of the single fan obtained in the numerical experiment were compared with the results of the physical experiment. The divergence between the results of the physical and numerical experiments on the sound power level for the first harmonic is 0.08 %, for the second harmonic – 0.35 %. In order to reduce the acoustic emission, a 3D model of the axial fan with the geometrically equivalent tandem row was constructed. The results showed that at the fan rotation frequency of 900 rpm, the sound power level on the first two harmonics is reduced by more than 7 dB. Also, the change in the total sound power level for axial single and tandem fans in the rotation frequency range of 900 to 1,500 rpm was investigated. The fan with the geometrically equivalent tandem blade row has the total sound power level by 6.9...7.4 dB lower than the single fan. The use of the tandem axial fan allows improving acoustic characteristics

A combined FEM/BEM model and experimental investigation into the effects of fluid-borne noise sources on the air-borne noise generated by hydraulic pumps and motors

A common assumption about fluid power systems is that the outlet pressure ripple is a primary source for air-borne noise. Fluid pressure fluctuations are caused by flow ripples generated by positive displacement units that are the prime power movers in these systems. The present research aims to leverage previous efforts in the topic of noise generation in hydrostatic units, formulating a method to predict air-borne noise for a particular reference machine. A numerical model has been developed to gain knowledge on the mechanisms of noise generation in external gear machines. The simulated noise sources are then applied to the structure in order to predict the propagation of noise to the surroundings. Also, experimental activity based on an innovative method of interpretation of noise measurements is also accomplished in order to better characterize the dependency between fluid-borne noise and air-borne noise. Measurements are made of total sound power level as well as sound pressure level at representative points to better understand the acoustic performance of external gear machines at a wide variety of operating conditions.

Effect Factors Analysis of Flow Generation Noise from Muffler Element with Inserted Tube

Using orthogonal experimental design method structure parameters of work piece for muffler element with inserted tube are determined. Flow noise regeneration of them is measured on the self development test bench. Relationship model on total sound power of flow regeneration noise and structure parameter and flow velocity is established utilizing Multiple linear regression method, model parameters are solved making use of hyper static least square method. Significance test of the model is performed, the law of total sound power level for muffler element flow regeneration noise changing with the parameters is discussed. Result shows that the established models is all highly significant under 0.01 levels, and inserted length of outlet tube and inn-diameter of inlet tube have higher effect on the flow generation noise, and decreasing the inserted length and the inn-diameter are in favor of reducing flow generation noise. But inserted length of inlet tube and expansion ratio have little effect on the flow generation noise.

Method for modifying axial fan’s guard grill and its impact on operating characteristics

This paper presents the impact of guard grill on aerodynamic integral characteristic, the spectrum of sound pressure level and total sound power level at four characteristic operating points of axial fans with standard guard grill, with optimized guard grill and without guard grill. The study of guard grill’s impact was conducted with measurements at integral level and local outflow velocity field of the axial fan without guard grill. The measurement results of the local outflow velocity field of the axial fan without guard grill at optimal operating point were used to model the optimized guard grill contour. The guard grill of axial fan has a significant impact on aerodynamic integral characteristic at free flow and mostly used operating region. The influence of guard grill is also characteristically reflected in the spectrum of sound pressure level via vortex shedding frequency and consequently at total sound power level of compared axial fans.

Guard grill impact on aerodynamic integral and acoustic characteristics of an axial fan

This paper presents the impact of a guard grill design on the aerodynamic integral characteristic, the spectrum of sound pressure level and total sound power level. Four characteristic operating points of axial fans with a standard guard grill, with an optimized guard grill and without a guard grill were studied. Measurement results of the local outflow velocity vector of the axial fan without a guard grill at an optimal operating point were used to model the optimized guard grill contour. The guard grill of axial fan has a significant impact on the aerodynamic integral characteristic in the mostly used operating region. The influence of a guard grill is more characteristically reflected in the spectrum of the sound pressure levels via the vortex shedding frequency and consequently in the total sound power level of compared axial fans. Flow properties around grill wires were studied using an in-line cylinder cascade in the free velocity field at appropriate Reynolds numbers. Results are presented as power spectra of velocity fluctuations and spectra of sound pressure level and show good agreement with results of fan measurements

The Perforated Panel Resonator with Flexible Tube Bundles and its Appliations

The sound absorptive mechanism and properties of the perforated panel resonator with flexible tube bundles are presented. Based upon that, some practical applications of the sound absorbing structure are introduced as follows. First of all, the perforated panel resonator with flexible tube bundles is used in designing a highly sound absorptive chamber, which is used as an audio-video laboratory. The acoustical performances of the chamber are presented. Second, the perforated panel resonator with flexible tube bundles is used in highly efficient duct silencer. The total noise level of axial fan source is attenuated to background noise level. Not only middle and high frequency noise is reduced, but also low frequency noise is suppressed considerably. Third, the perforated panel resonator with flexible tube bundles is used in a small-type centrifugal fan's casing treatments. The cut-off region of the centrifugal fan's casing is also acoustically treated. After the acoustical treatments, total sound power level of the fan is reduced obviously. Fourth, the perforated panel resonator with flexible tube bundles is used in designing the exhaust ducts and sound absorptive channel walls for an electrical transformer substation. The noise emitted from the transformer substation is reduced to surrounding background noise level.

Modeling and control of sound radiation by simply supported and cantilever beam coupled with smart material

In this paper forced vibration of the beam due to bonded piezoelectric patch is considered. When an external excitation is applied to the beam, it starts to vibrate, and the resulting acoustic response is predicted from the analytical model, which is based on Bernoulli-Euler theory of beam vibration. Analytical research of the sound radiation by a finite elastic beam is done for criteria based on minimal total sound power level. Helmholtz equation and inhomogeneous differential equation for beam transverse motion defines the solution to this problem. Such solutions were found for boundary conditions of simply supported and cantilever beams. In order to solve the task two analytical methods were used for simply supported beam. The solutions received by Fourier transform and Green functions approach give the very similar results, thus, proving methods reliability. At the case studies the exerted voltage, phase, location and piezoelectric actuator length are varied in order to establish their influence on noise attenuation.

Investigation of sound radiation by cantilever beam

The research investigates vibration of a cantilever beam loaded with actuators and load. The equation of motion is based on Bernoulli-Euler-Timoshenko theory of beams with corresponding boundary conditions. This equation is solved by the method of Green functions. A feature of this investigation is taking into account the influence of concentrated force parameters, namely the value, location of actuator and phase difference between load and actuator. In the work represented the contribution of actuator parameters on total sound power level as well as on each mode separately.

Reducing the noise emitted from a domestic clothes-drying machine

In recent years the development of large household appliances has increasingly focused on the reduction of noise. In this paper we report on attempts to reduce the sound-power level of an existing clothes dryer by investigating the aerodynamic noise sources. The critical points were determined on the basis of spatial sound-intensity measurements and sound-pressure-level spectra measurements. The changes to produce the modified dryer, version I, involved corrections to the secondary-flow fan's inlet region. For version II a different design of the heat exchanger was considered. For this, a measurement station was set up in order to analyze the aerodynamic properties of heat exchangers. The velocity and the acoustic properties of the heat exchangers were measured to help in the selection of the heat exchanger in accordance with the aeroacoustics theory that connects turbulent fluctuations and noise generation. After performing all the modifications, the A - weighted total sound-power level was reduced from 76.0 to 66.5 dB for left rotation and from 73.8 to 64.7 dB for right rotation.

Characterization of the noise emitted by a washing-machine due to the pump

The noise sources during the pump operation of a washing machine are: the electric motor, the water–air impulsion, and the structural radiation of the pump-housing, hose, and cabinet. The determination of the sound power level under different working conditions let us identify that the noise emitted by the cabinet vibration was the more noticeable, being irrelevant the noise emitted by the other elements. In order to know which part of the cabinet is the noisiest, the standard ISO-TR 7849 was applied to calculate the contribution of the noise emitted by the structural radiation of each part of the cabinet to the total sound power level. This experimental procedure relates the noise radiated by a structure with its vibration velocity, and it was found that the kick plate was the more relevant element. Once the noise transmission paths have been characterized, the proposals to reduce noise are focused on a new design of the kick plate to make it more flexible and the modification of the join zone of the pump to the kick plate to reduce the force transmitted between both elements. (To be presented in Spanish.)

Sound power radiated from an inverter-driven induction motor: experimental investigation

The effects of various inverter strategies, switching frequency, random modulation levels and motor speeds on the radiated noise of a 2.2 kW induction motor with and without load were examined by measuring the sound power spectrum, rather than the sound pressure spectrum at a single point in space. Results show that the sound power level due to the aerodynamic and mechanical noise increases at a rate of 12 dB per doubling of the motor speed. For an ideal, almost purely sinusoidal supply, electromagnetic noise dominates at low motor speeds. For a PWM inverter drive, the electromagnetic noise due to the switching harmonics could dominate the total sound power level at low motor speeds; however, the effects of switching harmonics appear to be insignificant at high motor speeds where the noise due to the fundamental frequency is dominant. At high speeds, the variation of sound power level with load is small, whereas at low speeds the total sound power level normally increases due to the low-frequency component.

ETUDE DU BRUIT ENGENDRÉ PAR L'IMPACT D'UN JET SUPERSONIQUE CHAUD SUR UN OBSTACLE

This document presents experimental works on supersonic hot jet impingement noise which have been done in an anechoic wind tunnel. Far field noise directivity measurements were done for a supersonic jet impingement on an axisymmetric obstacle. Source localizations with focused microphone arrays were realized simultaneously. Introduction of a board in a jet increases the sound pressure level upstream of the board. The localizations with focused microphone arrays show that the predominant sources of noise are located near the impingement region. However, this apparition of sound sources does not amount to a large increase of the total sound power level

Sound power level and directivity pattern determination of a space shuttle solid rocket booster

The sound power level and directivity pattern of sound were determined for a space shuttle solid rocket booster motor during a horizontal test firing at the Morton Thiokol Wasatch Test Facility in Utah. Six Bruel & Kjaer type 2230 precision sound level meters were placed at 60‐deg intervals around the rocket motor at a distance of 1000 ft, except the location directly behind the nozzle (2600 ft). These analyzers were used to determine the overall sound‐pressure level, between 20 and 20 000 Hz, at each of the six locations during the test. Two Cetec‐Ivie model IE‐30A audio spectrum analyzers were used to determine the shape of the spectrum at a one‐third octave band resolution. The equipment was turned on approximately 2 h prior to the scheduled test and was unattended during the test. Various adjustments were made to the data to account for topographic and atmospheric effects. The sound produced was predominantly low frequency, and the directivity pattern exhibited major acoustic lobes 60 deg to both sides of the line of fire. A total overall sound power level of 196 dB was determined. [Work funded by NASA Stennis Space Center, Mississippi.]

Sound power level determination for large steam turbine generators

A technique is presented for calculating the approximate total sound power level (PWL) of large steam turbine-generators as well as the PWL of individual turbine-generator components. A near field approximation is used which is similar in structure to the new IEEE test code 85. Modifications are introduced in the test code procedure to reduce the effect of component flanking noise, and noise contributed by extraneous sources. The overall turbine room PWL is also calculated by a reverberant field technique and compared to PWL as calculated by free field methods. Measurements were made around ten large steam turbine generator units ranging in name plate rating from 390 to 1050 MVA. PWL's of turbine-generators were found to increase by approximately 3.5db for each doubling of unit rated MVA. PWL's calculated from indoor near field approximation show a 3 dbA increase over PWL's of outdoor units of equivalent rating. This difference is an indication of the need for further development of methods for determining sound power level.