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Synchronized time-resolved schlieren and far-field pressure measurements were used to examine control of a supersonic multi-aperture rectangular single- expansion ramp nozzle with an aft deck. The design contains core (Mach 1.6) and bypass (sonic) streams mixing behind a splitter plate, generating a high-frequency tone. Control was applied through splitter-plate trailing-edge spanwise waviness (passive), spanwise-arranged microjet blowing actuators (active), and their combination (hybrid). Passive and hybrid control successfully alleviate the tone, whereas active control amplifies and alters the tone frequency. Time-averaged schlieren data show changes to mean shock structures with control. Spectral proper orthogonal decomposition (SPOD) spectra from the raw schlieren data are consistent with the far-field measurements and reveal coherent structural details. Radiation associated with high-frequency structures is inhibited by passive and hybrid control that enhance mixing, but not by active control. Momentum potential theory filtering prior to SPOD application augments the analysis by isolating irrotational content, providing additional clues on acoustic vs hydrodynamic mechanisms. The results indicate shock-shear-layer interaction and shedding as sources of low- and high-frequency content, respectively. As such, through suitable processing, relatively easy-to-obtain high-speed schlieren provides a powerful tool to assess complex flow-control physics. [ABSTRACT FROM AUTHOR]

The primary objective of this paper is to identify the critical components of the acoustic field for a piston-type pressure reducing valve (PRV) with a high pressure reduction ratio, as well as to predict unfavorable noise both experimentally and numerically. The numerical calculations were conducted using a hybrid approach that combines computational fluid dynamics (CFD) and computational aeroacoustics (CAA). Flow-induced pressure fluctuation from unsteady turbulent flow extracted by the throttling cone, the valve body and the baffle in the low-pressure chamber were considered as individual dipole acoustic sources during calculation of the internal acoustic field. The results indicated that the selected three dipole acoustic sources always played a vital role in the response of the acoustic field, and none of them could be ignored. In comparison, the throttling cone had the most salient contribution to acoustic field distribution, the valve body took second place, and the baffle had the least salient contribution. The radiated noise of interest was predicted using the indirect boundary element method (IBEM), incorporating all three components as dipole acoustic sources simultaneously; the numerical noise values showed strong validation against the experimental data. Furthermore, the distribution of sound pressure levels, as well as directional and planar field points, is also presented. This paper provides new insights into the role of each component in flow-induced noise, and offers technical support for noise reduction design and optimization of pressure reducing valves. [ABSTRACT FROM AUTHOR]

Rocket sled test avoids boundary effects in wind tunnel test and inconvenience of flight test, which is one of the feasible options for future single-stage-to-orbit. To analyze potential safety issues during payload separation and optimize the arrangement of testing sensors, different structural layouts and operating speeds of the rocket sled are conducted based on computational fluid dynamics and computational aeroacoustics. The hypersonic winged standard model is utilized as the load for these simulations. The analysis encompasses the evolution of shock waves, the forces exerted on the payload and noise propagation. Variations in flow field and aeroacoustic characteristics of rocket sled are analysed, revealing underlying physical mechanisms. It is observed that placing the payload in front of the thruster can reduce the head pressure, excessive wingspan may have an impact on the structural safety of the wingtip, and the regions of high sound pressure levels mainly exists in the middle and rear sections of the rocket sled. Moreover, as the Mach number increases, the characteristic frequency initially rises and then declines. These researches can serve as a valuable reference for the development of ground test systems and single-stage-to-orbit. [ABSTRACT FROM AUTHOR]

Copyright of Dokuz Eylul University Muhendislik Faculty of Engineering Journal of Science & Engineering / Dokuz Eylül Üniversitesi Mühendislik Fakültesi Fen ve Mühendislik Dergisi is the property of Dokuz Eylul Universitesi Muhendislik Fakultesi Fen ve Muhendislik Dergisi and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Graphene, a promising carbon nanomaterial, has garnered significant attention owing to its chemical stability, exceptional mechanical properties, and remarkable electrical conductivity and is being used in various electrical engineering applications ranging from solar cells to touch screens. The inherent mechanical strength and electric charge capacity of graphene enable efficient designs of diaphragms used in electrostatic loudspeakers, specifically within the high-frequency domain. This study incorporated single-layer and multi-layer graphene sheets, synthesized via chemical vapor deposition, as electrically charged diaphragms in electrostatic loudspeakers paired with an indium tin oxide film electrode to produce Coulomb force. Subsequently, the sound pressure levels of these distinct graphene- based electrostatic loudspeakers were determined through frequency response measurements. Based on our findings, we propose an optimal graphene film configuration for future electrostatic loudspeaker applications. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate an acoustic environment based on spatial configurations. To achieve this objective, two types of data were utilized. First, the urban acoustic data was collected from 96 measurements based on equivalent continuous A-weighted sound pressure levels across three different urban areas in Cairo, Egypt, during weekends and at night. The data was plotted on a contour map in an effort to investigate their distribution in the urban area. Secondly, the data was collected using DepthMapX software, and in this way, spatial analysis was produced with diverse spatial attributes. Moreover, on-site observations of pedestrian and traffic rates were made, and land use distribution was observed.Statistical analysis was also conducted using the Statistical Package for Social Sciences (SPSS). Our statistical analysis showed that the value of sound pressure level (LAeq) is greatly influenced by spatial attributes in highly accessible spatial configurations, with Normalized Angular Integration (NAIN) being the most accurate predictor of sound pressure level. Our findings also verified the existence of a high correlation between commercial and mixed land uses and (LAeq).Additionally, this study revealed that the urban sound model can predict sound pressure level (LAeq) in an urban setting. This dataset functions as a valuable resource for future research, urban designers, and policymakers who are addressing sustainable issues pertaining to soundscape, noise pollution, and urban planning.

The objective of this study is to investigate an acoustic environment based on spatial configurations. To achieve this objective, two types of data were utilized. First, the urban acoustic data was collected from 96 measurements based on equivalent continuous A-weighted sound pressure levels across three different urban areas in Cairo, Egypt, during weekends and at night. The data was plotted on a contour map in an effort to investigate their distribution in the urban area. Secondly, the data was collected using DepthMapX software, and in this way, spatial analysis was produced with diverse spatial attributes. Moreover, on-site observations of pedestrian and traffic rates were made, and land use distribution was observed. Statistical analysis was also conducted using the Statistical Package for Social Sciences (SPSS). Our statistical analysis showed that the value of sound pressure level (L Aeq) is greatly influenced by spatial attributes in highly accessible spatial configurations, with Normalized Angular Integration (NAIN) being the most accurate predictor of sound pressure level. Our findings also verified the existence of a high correlation between commercial and mixed land uses and (L Aeq). Additionally, this study revealed that the urban sound model can predict sound pressure level (L Aeq) in an urban setting. This dataset functions as a valuable resource for future research, urban designers, and policymakers who are addressing sustainable issues pertaining to soundscape, noise pollution, and urban planning. [ABSTRACT FROM AUTHOR]

In this paper, a sound quality subjective evaluation method for the high-speed train compartments using semantic scoring method with equal even intervals is proposed. The acoustic metrics in the compartment was studied at different positions and under different operating conditions, and two subjective evaluation experiments using selected sound samples were carried out. The least square method was used to point-fit the sound pressure level values of the original signal, so as to select the appropriate short-term intercepting samples. To avoid the unclear distinction between samples evaluated with the unit interval scoring table, a novel evaluation method that equals even interval semantic scoring method was designed by increasing the interval between adjacent scoring numbers in the scoring table. The results show that the proposed method distinguishes the perceived auditory differences between samples more clearly compared with the unit interval semantic scoring table. And the correlation of the evaluation results obtained by using the equal even interval scoring method between participants is also higher, so the proposed method is suitable for evaluating the sound quality of the interior high-speed train compartments. Psychoacoustic attribute metrics such as loudness, roughness, and sharpness were calculated for the various samples, and loudness was found to have a strong correlation with the subjective evaluation results obtained using the proposed equal even interval method. This further verifies that, compared with unit interval scoring, the proposed method facilitates the sound quality evaluation of the interior high-speed train compartments. [ABSTRACT FROM AUTHOR]

Designing an efficient muffler for single-cylinder IC engines is not an easy task due to the limitation in designing a large muffler and the possibility of engine suffocation. In this regard, this research aims to experimentally investigate the feasibility of inexpensive muffler modification of a small portable two-stroke engine to reduce noise pollution. In experiments, the default muffler as a control treatment and a modified muffler together with a redesigned muffler have been examined to investigate the effect of muffler internal geometry and muffler design on sound emission characteristics. Based on the obtained results, the sound pressure level (SPL) of the modified and redesigned mufflers decreased by 5.31 and 6.86 percent compared to the default muffler, respectively. Meanwhile, installing the modified and redesigned mufflers increased the transmission loss (TL) equal to 8.62 % and 10.08 % compared to the default muffler, respectively. Also, the outcome of Discrete Fourier Transform (DFT) revealed that the intensity and amplitude of output frequencies from the redesigned muffler was significantly reduced in the frequency range of 2–6 kHz. As a general conclusion of this study, by installing the redesigned muffler, the maximum working times of the operator increased by 12.1 h at 5000 rpm.

Simple Summary: The use of sound wave technology on different plant species has revealed that variations in the Hz, sound pressure intensity, treatment time, and type of setup of the sound source significantly impact the plant performance. For example, a study conducted on cotton plants treated by Plant Acoustic Frequency Technology (PAFT) highlighted improvements across various growth parameters. In particular, the treated samples showed increases in the height, leaf area, and number of boll-bearing branches, as well as other plant anatomical parts. In other cases, such as in transgenic rice plants, GUS expression was upregulated or downregulated concerning the Hz employed. This paper presents a complete, rationalized and updated review of the literature on the effects of sound waves on the physiology and growth parameters of sound-treated plants. The application of sound wave technology to different plant species has revealed that variations in the Hz, sound pressure intensity, treatment duration, and type of setup of the sound source significantly impact the plant performance. A study conducted on cotton plants treated with Plant Acoustic Frequency Technology (PAFT) highlighted improvements across various growth metrics. In particular, the treated samples showed increases in the height, size of the fourth expanded leaf from the final one, count of branches carrying bolls, quantity of bolls, and weight of individual bolls. Another study showed how the impact of a 4 kHz sound stimulus positively promoted plant drought tolerance. In other cases, such as in transgenic rice plants, GUS expression was upregulated at 250 Hz but downregulated at 50 Hz. In the same way, sound frequencies have been found to enhance the osmotic potential, with the highest observed in samples treated with frequencies of 0.5 and 0.8 kHz compared to the control. Furthermore, a sound treatment with a frequency of 0.4 kHz and a sound pressure level (SPL) of 106 dB significantly increased the paddy rice germination index, as evidenced by an increase in the stem height and relative fresh weight. This paper presents a complete, rationalized and updated review of the literature on the effects of sound waves on the physiology and growth parameters of sound-treated plants. [ABSTRACT FROM AUTHOR]

• Tube arrangement of electronic expansion valves affects throttling noise. • Large inclination angle of inlet tube is beneficial to reduce throttling noise. • Refrigerant flowing into an expansion valve should be vertical to the needle. The two-phase throttling noise in electronic expansion valves (EEVs) of a multi-split air conditioner may exhibit different intensities due to the variable EEV tube arrangements. The purpose of this study is to experimentally investigate the influence of EEV tube arrangement on the throttling noise, and to find a suitable tube arrangement for noise reduction. A throttling noise testing rig is constructed to investigate the influence of tube arrangement including the inclination angle of inlet tube and the refrigerant flow direction. The test conditions for tube arrangement include an inlet tube inclination angle of 0°–90° as well as the flow direction from tube P (parallel to the valve needle direction) to tube V (vertical to the valve needle direction) and from tube V to tube P ; and the test conditions for refrigerant include a mass flow rate of 30–90 kg h−1 and an inlet quality of 0.02–0.4. The experimental results show that, the increase of inlet tube inclination angle may weaken the throttling noise, and the sound pressure level (SPL) of throttling noise is decreased by 20.1 % as the inlet tube inclination angle increases from 0° to 90°; and the refrigerant flow direction from V – P (tube V to tube P) instead of P – V (tube P to tube V) may attenuate the throttling noise. The tube arrangement with inlet tube inclination angle of 90° and flow direction from V – P is suggested for minimizing the throttling noise in multi-split air conditioners. [ABSTRACT FROM AUTHOR]

Kulning , a loud, high-pitched vocal calling technique pertaining to the Scandinavian herding system, has attracted several researchers' attention, mainly focusing on cultural, phonatory and musical aspects. Less attention has been paid to the spectral and physiological properties that characterize Kulning tones, and also if there is a physiologically optimum pitch range. We analyzed tones produced by ten participants with varying experience in Kulning. They performed a phrase, pitch range G5 to C6 (784 to 1046 Hz), in three different conditions: starting (1) on pitch A5, (2) on the participant's preferred pitch, and (3) after the deepest possible inhalation, also on the participant's preferred pitch subglottal pressure (P sub) was measured as the oral pressure during /p/-occlusion. The quality of the Kulning was rated by a group of experts. The highest-rated tones all had a sound pressure level (SPL) at 0.3 m exceeding 115 dB and a pitch higher than 1010 Hz, while the SPL of the lowest rated tones was less than 108 dB at a pitch below 900 Hz. A multiple regression analysis was performed to evaluate the relationship between the ratings and P sub), SPL, level of the fundamental and the frequency at which a spectrum envelope dip occurred. Highly rated tones were started at maximum lung volumes, and on participants' preferred pitches. They all shared a high frequency of the spectrum envelope dip and a high level of the fundamental. In decreasing order of ratings, Condition 3 showed the highest values followed by Condition 2 and Condition 1. Each singer seemed to perform best within an individual P sub and pitch range. The relevance of the results to voice pedagogy, artistic, and compositional work is discussed. [ABSTRACT FROM AUTHOR]

Acoustic measurements were performed using microphone downstream of a 2-D wind turbine blade section in wind tunnel. The experiments have been carried out in both static and oscillatory pitching cases. The latter is usually experienced by the blades in actual circumstances. The microphone was 1.5 chords downstream of the airfoil and the measurements were conducted at three transverse positions, i.e. behind the trailing edge, midway between the trailing edge and the ground and very close to the ground. A CFD simulation of the flowfield has also been conducted using Fluent to correlate the acoustic behavior to the phenomena observed in the flowfield around the blade. The results show that the acoustic noise heard by a listener located on the ground is higher and stronger than that positioned downstream of the trailing edge, showing the ground effect on acoustic noise reverberation. The aerodynamic noise heard by the listener, changes from a treble to bass sound as the angle of attack increases. Beyond stall, the flow is dominated by the vortices shed into wake and the acoustic noises would be at very low frequencies which would result in a bass sound accompanied by structural vibration. In high angle of attack range, such noises can hardly be heard by a normal person but have a very destructive role on blade structure. [ABSTRACT FROM AUTHOR]

This study investigated the impacts of students' mood states and background sound levels on students' sound perceptions and academic performance in four library rooms. The background sound level was measured for five days. Meanwhile, around 300 students were invited to participate in a survey of questions about their acoustic perceptions and mood states and a concentration test. Pearson correlation, one-way ANOVA, and two-way ANOVA were applied to establish the relationships between the LAeq, students' mood states, acoustic perceptions, and concentration levels on both the individual level and the room level and to identify the interaction effect between the background sound levels and mood states on students' acoustic perception and concentration. The results indicated that LAeq in learning spaces significantly impacted students' acoustic satisfaction, but only at the room level. In contrast, mood states mainly influenced students' sound perception and concentration at the individual level. Furthermore, this study reports significant interaction effects between mood state and LAeq on students' sound perceptions and reveals different impacts of mood states due to different sound levels. These results could help improve occupants' acoustic perceptions and performance in learning spaces in the future. [ABSTRACT FROM AUTHOR]

Svalbard is a Norwegian province in the Arctic, covering the Svalbard archipelago and islands within 71°-- 81° N and 10°-- 35° E. The largest town on the largest island -- Spitsbergen -- is Longyearbyen, with a population of around 2100. It is the main centre of administration for the governor's office, and there are many public buildings, housing estate, a harbour, and an airport. This paper presents the results of acoustic measurements conducted at selected popular tourist destinations near Longyearbyen. The sites for this study were chosen based on the analysis of a survey aimed at identifying preferences in tourism activities in the Longyearbyen area. Based on the responses, three groups of tourist activities were identified: (1) Longyearbyen activity: a round trip to town, a visit to the Svalbard Museum, historic Coal Mine no. 3 and the University Centre in Svalbard UNIS, (2) Snowmobile trips: to Barentsburg, East Cost and Elveneset, (3) Nature hikes: trips to the summits of the Sarkofagen and Trollsteinen peaks, hiking on the Lars Glacier, the Longyear Glacier and the Tell Glacier and visits to glacier caves. Of these sites, acoustic analyses (sound pressure level -- time and frequency characteristics) were conducted at the following locations: Longyear Valley: UNIS area and city centre, Advent Valley: dog sleds and snowmobile rides, Nature hike: Sarkofagen peak and caves in the Lars Glacier and the Longyear Glacier. [ABSTRACT FROM AUTHOR]

Detection of sound pressure level is an important factor for individuals working in noisy environments. When noise occurs in large quantities, it threatens the health and working safety of individuals working in that environment. Since it is necessary to determine periodic pressure changes to measure sound intensity, many mathematical analyzes and experimental studies have been carried out on this subject. Logarithmic equations are used in the intensity measurements of the sound and in the distribution, reduction and exposure analyzes of the sound depending on the distance. In this study, Galerkin Weighted Residues Method (WRM) and Spherical Harmonic Functions, which have been used frequently in sound problems in recent years, are used for the solution of sound wave equations in spherical coordinates, which have not been observed in the literature before, in determining the periodic pressure values of sound. Based on the directivity coefficient and spherical harmonic functions in detecting sound pressure levels in the near field, The Critical Distance Threshold, r_cri, was defined and combined with data from WRM. In this way, it was determined that the numerical sound pressure values obtained were very close to the values used in the classical logarithmic approach, and as a result of the logarithmic consistency analysis made for these numerical data. [ABSTRACT FROM AUTHOR]

The high-speed freight electric multiple unit (EMU) is one of the important development directions for railway freight transportation. To investigate the bridge radiation noise induced by the freight EMU, a noise prediction model consisting of the containers–vehicle–track–bridge dynamic model, finite element model, and boundary element model are established and validated. Through simulation, the bridge radiation noise under different train loading conditions is compared, and the noise radiation mechanism is revealed. Moreover, the noise reduction effect of the noise wall is studied, and the influences of noise wall heights and sound absorption materials are investigated. Results indicate that the bridge sound power and the sound pressure levels (SPLs) of near-field points increase slightly with train loads in the frequency range below 20 Hz and above 125 Hz, with a maximum increase of about 6.8 dB. The structure resonance, intense local vibration, and high acoustic radiation efficiency cause strong bridge radiation noise. The noise wall can realize a good overall noise reduction effect in the sound shadow zone; nevertheless, SPLs increased in areas between the bridge and the noise wall. The ground reflection affects the superposition of transmitted, reflected, and diffracted sound waves, which causes nonlinear relationships of noise reduction effects with the noise wall height. From the perspective of human hearing sensitivity, the loudness levels of typical field points increase with the frequency in the range of 20~80 Hz, and SPLs below 25 Hz are less than the threshold of hearing. Setting the noise wall can effectively reduce the loudness levels, and the reduction effect increases with the noise wall height. [ABSTRACT FROM AUTHOR]

Individuals exposed to elevated noise levels experience heightened emotional intensity, leading to increased cognitive disruption and a higher likelihood of accidents. This study seeks to investigate the impact of noise exposure on human cognitive performance, and the moderating role of emotion. Twelve healthy male college-age students underwent exposure to three noise conditions, each characterized by different sound pressure levels and sharpness. Each condition included an initial acoustic/thermal adaption period lasting approximately 40 min, followed by intermittent questionnaire tests and a battery of computerized cognitive tests. Statistical analysis revealed that reducing noise levels proved advantageous, enhancing perceived sound quality, positive emotions, and auditory perception abilities, while concurrently reducing false alerts and accelerating execution speed. Many of these effects were found to be counteracted by elevated sharpness. Correlation analyses and partial least squares structural equation modeling (PLS-SEM) results suggested that human emotions mediate the relationship between noise exposure and cognitive performance. The potential underlying mechanism suggests that negative feelings towards noise contribute to poor emotional states, subsequently influencing cognitive processes and impairing executive function. The outcomes of this study provide valuable insights into the mechanism of noise exposure and its effects on human cognition and subjective perceptions. [ABSTRACT FROM AUTHOR]

Determining reliable noise emission values for machinery is key to successfully implement the Sell and Buy Quiet concept. ISO 11202 is a basic noise emission standard to determine the emission sound pressure level of machines outside of special acoustic test rooms (in situ measurements) and enables machinery manufacturers to determine the noise emission data of their products within their own premises. However, a recent amendment to this standard was made on the basis of an unsatisfactory amount of experimental data. Therefore, this paper systematically examines the validity and accuracy of the amended part of the method. It answers the question, whether the amendment represents an improvement of the existing method. Measurements on a model machine with two configurations allow for an extensive investigation of the effects of the amendment. To that end, the emission sound pressure levels at eight positions near the machine are determined in three different acoustic environments. One finds that the amendment leads to an overestimation of the local environmental correction for the L p A , which, in turn, could lead to an underestimation of the determined emission sound pressure level. [ABSTRACT FROM AUTHOR]

Sound produced by vertical axis wind turbines can reduce their popularity for use in urban and residential areas. In order to reduce the produced sound level the acoustic behavior of hybrid rotor is studied in this research with the help of Computational Fluid Dynamics (CFD). In the investigated rotor structure, conventional-type blades were used as the inner rotor, which was connected to the outer rotor at a zero-degree angle. To ensure the modeling, the validation of the results and the measuring of effect of the time step on the output data were undertaken. The purpose of this research was to investigate the effect of a tip speed ratio and free wind speed on the level of sound produced. The results showed that the sound level produced had a direct relationship with a tip speed ratio and the free wind speed in such a way that the lowest sound pressure level in a tip speed ratio of 1.5 and the free wind speed of 5 m/s was reported by the R4 receiver. Its value was equal to 7.64 dB. Also, by moving away from the rotor, the produced sound level decreasesd. [ABSTRACT FROM AUTHOR]

Determining reliable noise emission values for machinery is key to successfully implement the Sell and Buy Quiet concept. ISO 11202 is a basic noise emission standard to determine the emission sound pressure level of machines outside of special acoustic test rooms (in situ measurements) and enables machinery manufacturers to determine the noise emission data of their products within their own premises. However, a recent amendment to this standard was made on the basis of an unsatisfactory amount of experimental data. Therefore, this paper systematically examines the validity and accuracy of the amended part of the method. It answers the question, whether the amendment represents an improvement of the existing method. Measurements on a model machine with two configurations allow for an extensive investigation of the effects of the amendment. To that end, the emission sound pressure levels at eight positions near the machine are determined in three different acoustic environments. One finds that the amendment leads to an overestimation of the local environmental correction for the LpA, which, in turn, could lead to an underestimation of the determined emission sound pressure level.

Acoustic measurements were performed using microphone downstream of a 2-D wind turbine blade section in wind tunnel. The experiments have been carried out in both static and oscillatory pitching cases. The latter is usually experienced by the blades in actual circumstances. The microphone was 1.5 chords downstream of the airfoil and the measurements were conducted at three transverse positions, i.e. behind the trailing edge, midway between the trailing edge and the ground and very close to the ground. A CFD simulation of the flowfield has also been conducted using Fluent to correlate the acoustic behavior to the phenomena observed in the flowfield around the blade. The results show that the acoustic noise heard by a listener located on the ground is higher and stronger than that positioned downstream of the trailing edge, showing the ground effect on acoustic noise reverberation. The aerodynamic noise heard by the listener, changes from a treble to bass sound as the angle of attack increases. Beyond stall, the flow is dominated by the vortices shed into wake and the acoustic noises would be at very low frequencies which would result in a bass sound accompanied by structural vibration. In high angle of attack range, such noises can hardly be heard by a normal person but have a very destructive role on blade structure.

The demand for electrical machines has been spurred by rising fuel costs, technological advancements, and urbanization. Consequently, there is an increased focus on developing machines with greater power density, improved efficiency, and enhanced vibroacoustic characteristics while promoting a more sustainable supply chain. This paper offers a thorough comparison of three distinct motor topologies: switched reluctance motor (SRM), interior permanent magnet synchronous motor (IPMSM), and induction motor (IM). The study begins with electromagnetic analysis of the motors, covering torque, output power, losses, and efficiency calculations. Subsequently, the investigation delves into radial force density waveforms, extracting the dominant radial force density harmonics and presenting patterns for each motor’s dominant radial force harmonics. Following this, a 3D assembly of the motors is introduced for modal analysis, determining their mode shapes and natural frequencies. Finally, vibroacoustic analysis is conducted for the proposed motors, with observed differences being discussed. These analyses are conducted solely for the rated operating point, as transitioning to other operating points does not alter the pattern of radial force harmonics or the correlation between acoustic noise and radial force harmonics.

The goal of this paper is to fabricate innovative diaphragm headphones using graphene oxide paper (GOP) and GOP/epoxy nanocomposites (GOPC). Initially, graphene oxide suspension is fabricated, and the vacuum filtration method is adopted to make GOP. Then, vacuum bag molding is used to fabricate GOPC from GOP. Hot pressing and associated molds are adopted to fabricate line-indented (GOPC-L) or curve-indented patterns (GOPC-C) on the GOPC. The performances of one kind of GOP and three kinds of GOPC diaphragm headphones are analyzed based on their sound pressure level (SPL) curves achieved by the Soundcheck measurement system. There are four important processing parameters that will influence the performance of the diaphragm, including material type GOP versus GOPC, indented pattern type, sonication time on suspension, and graphene weight fraction in suspension. Compliances of various diaphragms are measured by the Klippel LPM laser measurement system. The results indicate that effects of sonication time and graphene weight fraction on SPL of GOP and GOPC headphones are in reverse, and this is associated with their difference on compliance (modulus), mass, damping ratio, and microstructure uniformity. Either GOPC-L or GOPC-C seems to improve the microstructure of the GOPC, and leads to better SPL performance. The correlation between the previous four factors and SPLs of four kinds of diaphragm headphones is proposed by using scanning electron microscope (SEM) to examine the microstructure of these diaphragms. [ABSTRACT FROM AUTHOR]

Airfoil-turbulence interaction noise is a known source of environmental disturbance and acoustic performance loss in aeroacoustics and hydroacoustics. This noise can be predicted using semi-analytical models that require input measurements of the incoming turbulent flow parameters. However, the turbulence parameters are inherently difficult to measure accurately. These parameters, which include the turbulence kinetic energy and its dissipation rate, have a stochastic nature. This study aims to investigate how small variations in the measurements of turbulence parameters affect the uncertainty of the predicted airfoil-turbulence interaction noise. This is achieved by applying polynomial chaos expansion (PCE) to the semi-analytical model of Amiet's theory for airfoil-interaction noise. The validity of the deterministic and stochastic simulations is ensured by comparisons against available experimental data from the literature, and Monte Carlo simulations, respectively. Uncertainty quantification is then performed using a stochastic collocation technique, where the aerodynamic noise is evaluated at specific collocation points to estimate the coefficients required for PCE. Both the individual and combined effects of varying the uncertain input turbulence parameters are simulated to quantify the uncertainty of the output aerodynamic noise. The insights gained from the results suggest it is important to incorporate the stochastic behavior of the incoming turbulent flow in operational models for airfoil-turbulence interaction noise predictions. [ABSTRACT FROM AUTHOR]

The cooling fan is one of the important noise sources for new energy vehicles, and the research on its aerodynamic and aeroacoustic characteristics is of great help to improve the noise, vibration and harshness performance of new energy vehicles. However, most of these studies focus on the impeller, and little consideration has been given to the study of the shroud. Based on the coupling calculation method of large eddy simulation and the Ffowcs-Williams and Hawkings acoustics model, the aerodynamic and aeroacoustic characteristics in a cooling fan with the shroud are investigated at flow rates from 0.623 kg/s to 1.019 kg/s (where 0.865 kg/s is the flow rate corresponding to the best efficiency point). The accuracy of numerical simulation results is verified by the grid independence verification and the comparison of experimental data. Research shows that several large-scale vortex structures are observed in the clearance between the impeller and the shroud. The maximum peak-to-peak values of pressure fluctuation at different flow rates occur in the intermediate section or outlet section of the shroud. Although the shroud contributes relatively less to the far field noise, its different distribution may change the position of the maximum sound pressure level. The dominant frequency of pressure fluctuation equals the blade passage frequency (BPF) and the maximum SPL is around the BPF, both of which are independent of flow rates. The maximum SPL and the amplitude of the dominant frequency decrease as the flow rate increases. [ABSTRACT FROM AUTHOR]

Occupational noise-induced hearing loss prominently occurs due to unavoidable sound frequencies mainly in the range of 3000 to 6000 Hz. This frequency region thus holds great importance for acoustic insulation. Polymeric foams with open cellular frameworks are mostly employed for sound absorption in these frequency regions. To enhance their sound-absorbing ability, nanofillers are integrated with the polymeric matrix. However, the majority of the incorporation methods result in a single-phased porous structure, which limits their potential. Herein, an altered method of modification of multiwall carbon nanotubes (MWCNTs) is explored for the preparation of modified polyurethane foam via a simple one-pot immersion-hydrothermal-evaporation method. A unique self-assembled nanolayered structure with nanopores was fabricated through optimized experimental conditions resembling a double three-dimensional form. This gave rise to an additional resonating-type structure within the porous-type matrix. Thus, a hybrid-type sound-absorbing material with distinctive structure was fabricated which could help achieve focused sound absorption ability at the desired frequency. The sound pressure level evaluated at a frequency of 4000 Hz was found to improve through incorporation of 0.5 wt % modified CNTs. The mean percentage enhancement in sound isolation for treated foam in comparison to untreated foam is 15 to 20% at 4000 Hz. The development of distinctive structures within the polymeric framework opens up a plethora of horizons that could be employed at the industrial level as well, and such structures could be engaged for achieving other eccentric properties, which would further enhance their applicability. [ABSTRACT FROM AUTHOR]

The high-power operation or generation in fuel cell vehicle (FCV) generates massive heat in the powertrain. Multiple cooling fans are used to ensure the heat dissipation requirement, causing severe fan noise problems. This study aims to analyze the noise characteristics of multiple cooling fans. Hence, the feasibility of reducing the total sound pressure level is verified by cooling fan control strategy. A numerical calculation model of multiple cooling fans is established for the entire vehicle's internal and external sound fields. Then, this numerical calculation model is verified using experiments. The contribution of multiple cooling fans to the total noise in FCV is analyzed under the same duty cycle of fan. The selection method of cooling fan control strategy is proposed, and the feasibility of reducing noise is verified under three different working conditions. In parking charging working conditions, the total sound pressure level near the driver's ear decreases by 0.6, 1.9, and 2.8 dBA, respectively. In idling conditions, the total sound pressure level near the driver's ear decreases by 0.4, 1.6, and 2.4 dBA, respectively. In constant speed working conditions, the total sound pressure level near the driver's ear decreases by 0.6, 2.2, and 3.1 dBA, respectively. [ABSTRACT FROM AUTHOR]

Cartilage conduction is known widely as a third hearing transmission mechanism after the air and bone conduction methods, and transducers dedicated to the production of cartilage conduction sounds have been developed by several Japanese companies. To estimate the acoustic performance of the five cartilage conduction transducers selected for this study, both airborne sounds and cartilage conduction sounds were measured. Airborne sounds can be measured using a commercial condenser microphone; however, cartilage conduction sounds are impossible to measure using a conventional head and torso simulator (HATS), because the standard-issue ear pinna simulator cannot reproduce cartilage conduction sounds with the same spectral characteristics as the corresponding sounds measured in humans. Therefore, this study replaced the standard-issue simulator with a developed pinna simulator that can produce similar spectral characteristics to those of humans. The HATS manipulated in this manner realized results demonstrating that transducers that fitted the entrance to the external auditory canal more densely could produce greater cartilage conduction sounds. Among the five transducers under test, the ring-shaped device, which was not much larger than the entrance to the canal, satisfied the spectral requirements. [ABSTRACT FROM AUTHOR]

Wind turbines play a major role in the European Green Deal for clean energy transition. Noise is a critical aspect among open technological issues, as it determines the possibility of onshore installations near inhabited places and the possible detrimental effects on wildlife when offshore. This paper assesses the accuracy of different approaches to predicting the sound pressure level (SPL) of a wind turbine. The 2.75 MW Neg Micon NM80 horizontal axis wind turbine (HWAT) was simulated in OpenFOAM, modeling the turbine with the actuator line method (ALM) implemented in the turbinesFoam library. Two different inflow conditions were considered: a stationary inflow with a typical atmospheric boundary layer profile and a time-dependent inflow derived from a precursor channel with fully turbulent conditions. The surrogate model for noise prediction used for this work is based on the synthetic/surrogate acoustics models (SAMs) of Amiet and Brooks-Pope-Marcolini (BPM). This approach allows for blade motion modeling and the prediction of the SPL of the URANS postprocessing results. The SPL spectrum obtained was then compared to the results from the other aeroacoustic solvers of IEA Task 39 participants, showing the best performance in the fully turbulent case. The results demonstrate that coupling between the ALM and surrogate acoustics provides more accurate results than the blade element momentum (BEM) approach. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive investigation of the internal noise characteristics of a mixed-flow pump by combining computational fluid dynamics (CFD) and computational acoustics. The turbulent flow field of the pump is simulated using the unsteady SST k-ω turbulence model in CFD. The contributions of the volute, guide vanes, and impeller to the internal noise are analyzed and compared using the Lighthill theory, FW-H formula, and LMS Virtual Lab software for acoustic simulation. The research findings indicate that the energy of pressure fluctuations in the mixed-flow pump is predominantly concentrated at the blade passing frequency and its low-frequency harmonics. This suggests that the internal noise is mainly in the low-frequency range, with higher energy at the blade passing frequency and its harmonics. Under the 0.6Qdes flow condition, the flow inside the pump becomes more complex, resulting in higher sound pressure levels and sound power levels compared to higher flow conditions. However, for flow conditions ranging from 0.8Qdes to 1.2Qdes, the sound pressure levels gradually increase with increasing flow rate, with the sound pressure level at 1.0Qdes being nearly identical to that at 1.2Qdes. The analysis of sound power level spectra at different flow rates reveals that the distribution characteristics of internal vortex structures directly impact the hydrodynamic noise inside the mixed-flow pump. These research findings provide a significant theoretical basis for noise control in mixed-flow pumps. [ABSTRACT FROM AUTHOR]

Cartilage conduction is known widely as a third hearing transmission mechanism after the air and bone conduction methods, and transducers dedicated to the production of cartilage conduction sounds have been developed by several Japanese companies. To estimate the acoustic performance of the five cartilage conduction transducers selected for this study, both airborne sounds and cartilage conduction sounds were measured. Airborne sounds can be measured using a commercial condenser microphone; however, cartilage conduction sounds are impossible to measure using a conventional head and torso simulator (HATS), because the standard-issue ear pinna simulator cannot reproduce cartilage conduction sounds with the same spectral characteristics as the corresponding sounds measured in humans. Therefore, this study replaced the standard-issue simulator with a developed pinna simulator that can produce similar spectral characteristics to those of humans. The HATS manipulated in this manner realized results demonstrating that transducers that fitted the entrance to the external auditory canal more densely could produce greater cartilage conduction sounds. Among the five transducers under test, the ring-shaped device, which was not much larger than the entrance to the canal, satisfied the spectral requirements.

In most vocal fish species, females possess smaller sound‐generating organs and vocalize less than males. In certain cases females lack sonic organs, in others differences between sexes are unknown. This study analyzes in detail the relationship between sexual dimorphism of sonic organs and the characteristics of agonistic behavior and of sounds recorded under the same behavioral conditions in a vocal fish species, the croaking gourami Trichopsis vittata. During agonistic contests both sexes stretch and pluck two enhanced (sonic) tendons when beating pectoral fins alternately, resulting in a series of double‐pulsed bursts, termed croaking sound. The following anatomical, behavioral, and acoustic variables were analyzed: diameter of enhanced tendons in each specimen, duration of same‐sex dyadic contests, number and duration of lateral display bouts and of sounds, number of single‐ and double‐pulsed bursts, burst period, peak‐to‐peak amplitudes of pulses, dominant frequency and sound pressure level (SPLrms). Female sonic tendons were approximately one‐fifth smaller than male's of the same size. Six out of seven behavioral variables did not differ between sexes. Sound characteristics were similar in both sexes except for SPLs, which were on average 5 dB lower in females. The degree of sexual dimorphisms in sonic organs may explain differences in sound characteristics. Sounds differ only in one sound characteristic (SPLrms) in T. vittata, in contrast with the congeneric Trichopsis pumila which possesses a more pronounced sexual dimorphism in sonic organs and in which agonistic sounds differ in all sound properties between sexes. Research highlights: In most vocal fish species females possess smaller sound‐generating organs than males.Not‐pronounced sexual dimorphism in pectoral fin sonic tendons in the croaking gourami results in sex‐specific differences in one out of eight sound characteristic (sound pressure level) in similar‐sized sexes.In the previously studied pygmy gourami the pronounced sexual dimorphism results in sex‐specific differences in all sound properties. [ABSTRACT FROM AUTHOR]

Short takeoff and vertical landing aircraft configurations involve multiple jets that impinge onto the deck surface in tandem and lead to several adverse effects. This study reports on the experimental characterization of supersonic dual-impinging jets by systematically varying their relative jet temperature. A sonic converging and Mach 1.5 converging-diverging (CD) nozzles are employed. The expansion ratio of the converging nozzle is maintained at 0.96, 1.19, and 1.59, and the CD nozzle is operated at a fixed nozzle pressure ratio of 3. The temperature ratio of the jet from the CD nozzle is varied from 1.0, 1.3, and 1.7. For a fixed momentum of the jet pair, an increase in jet temperature intensified the nearfield noise and unsteadiness on the impingement surface. At short impingement heights, resonance in the heated jet was the primary source of unsteadiness. At a fixed impingement height, an increase in jet temperature led to a systematic increase in tonal frequency, while jet instability mode shapes were retained. Furthermore, the mean flowfield of sonic jet and fountain regions remain unaffected, and an increase in supersonic jet velocity is observed. This is also accompanied by an increase in unsteadiness in the fountain upwash. [ABSTRACT FROM AUTHOR]

This study investigates the aeroacoustics of flow around a square cylinder using an in-house OpenFoam solver with Ffowcs Williams' Hawking methodology and the k − ω SST turbulence model. First, the numerical results were validated against experimental data. Then, the effects of a 1 mm thick splitter with different lengths, 2.5 (L / D = 0. 2 5), 5 (L / D = 0. 5), 7.5 (L / D = 0. 7 5) and 10 (L / D = 1), were studied as a passive control method. The findings indicate that the splitter suppresses the vortex shedding, a dipole source of aeroacoustic emission, resulting in a reduction of the noise level by up to 7% for L / D = 0. 2 5 , 9. 7 % for L / D = 0. 5 , 1 3. 6 5 % for L / D = 0. 7 5 and 17.5% for L / D = 1. [ABSTRACT FROM AUTHOR]

Based on the finite element-infinite element theory, the finite element model of a certain type of vehicle was established, and the vehicle near-field monitoring points, far-field monitoring surfaces and infinite element boundary interfaces were set, and the direct frequency response method was used to analyze the sound field characteristics of the key areas of the head car, the middle car and the tail car at different frequencies. The calculation results show that the sound radiation of the smooth area on the top of the car body is small when the head car and tail car area are in the low frequency range (within 100 Hz), and the maximum sound pressure level of the bogie area at the nose tip and below is 153 dB. The sound pressure level and sound radiation range of the rear area of the tail car are larger than that of the head car area, and there is obvious flow field effect, but the overall sound pressure level is uniform and low in the high frequency range. The maximum sound pressure level of the intermediate car in the pantograph area in the low frequency range is 158 dB, especially at the carbon slide plate and underframe, and the sound radiation capacity in the bogie area is relatively large. With the increase of frequency, its energy has a significant attenuation. The research results have certain reference value for the aeroacoustic design of high-speed trains. [ABSTRACT FROM AUTHOR]