Acoustic Treatment Research Articles

CHANGE OF RHEOLOGICAL PARAMETERS OF HIGH-PARAFFIN OIL UNDER MULTI-FACTOR IMPACT IN A ROTOR-STATOR DEVICE

Background The energy consumption of oil transportation through pipelines significantly depends on the rheological properties of the pumped medium. Positive results in reducing the viscosity of oil were obtained during hydro-mechanical and acoustic treatment of oil, which is carried out in a rotor-stator device, the acoustic impulse effect on oil in which is carried out due to pressure pulsations in the stator channels, which generate cavitation. Aims and Objectives Investigation of the physicochemical and rheological characteristics of oil during its processing in a rotor-stator device Results The possibility of changing the rheological properties of highly paraffinic oil due to hydromechanical and acoustic effects in a rotor-stator device has been experimentally investigated. A mechanism is proposed that explains the change in the structure of complex structural units of oil as a result of processing in the rotor-stator device. Analysis of the rheological characteristics showed that the reduction in the viscosity of the treated highly paraffinic oil reaches 50 %.

Exposure to Excessive Sound Volume: A Major Challenge in the South-Western Nigeria Church Auditoria

The study examines the exposure to excessive sound volume as a major challenge to grapple with in church auditoria in South-western Nigeria. This exposure to excessive sound has become a source of noise pollution and it is dangerous to human health. Data for this paper were gathered through participant observation of musical acoustics in worship auditoria using a Virtual Instrument; a Sound Pressure Level mobile application installed on a mobile phone for sound volume measurement. The equivalent noise level using A-weighting was taken for twenty minutes per day, this was observed for the three different worship services at different dates and time in each of the selected church auditoria during each worship service. The LAeq, T, of each musical session was calculated. Findings show that the worshippers are exposed to average noise levels of 90.29 dB (Threshold of Pain) at every worship service which is higher than the recommended 60dB for normal human ear by World Health Organization (WHO). It was also observed that all the selected church auditoria lack appropriate acoustic treatment which led to sound reflections and severe echo. The paper concludes that the culture of noise pollution has become a social phenomenon in the Nigerian society especially, in church auditoria where loud musical sound is arrogated to power and domination of space. This paper recommends that acceptable optimal standards for sound production either in enclosures or in open spaces be emphasized by the Nigerian local, state and federal governments to effectively control noise for human and societal wellbeing.

Antimicrobial effects of airborne acoustic ultrasound and plasma activated water from cold and thermal plasma systems on biofilms

Bacterial biofilms are difficult to inactivate due to their high antimicrobial resistance. Therefore, new approaches are required for more effective bacterial biofilm inactivation. Airborne acoustic ultrasound improves bactericidal or bacteriostatic activity which is safe and environmentally friendly. While, plasma activated water (PAW) is attracting increasing attention due to its strong antimicrobial properties. This study determined efficacy of combined airborne acoustic ultrasound and plasma activated water from both cold and thermal plasma systems in inactivating Escherichia coli K12 biofilms. The application of airborne acoustic ultrasound (15 min) alone was significantly more effective in reducing E. coli counts in 48 and 72 h biofilms compared to 30 min treatment with PAW. The effect of airborne acoustic ultrasound was more pronounced when used in combination with PAW. Airborne acoustic ultrasound treatment for 15 min of the E. coli biofilm followed by treatment with PAW significantly reduced the bacterial count by 2.2—2.62 Log10 CFU/mL when compared to control biofilm treated with distilled water. This study demonstrates that the synergistic effects of airborne acoustic ultrasound and PAW for enhanced antimicrobial effects. These technologies have the potential to prevent and control biofilm formation in food and bio-medical applications.

Evaluation of Acoustic Similarities in Two Italian Churches Honored to S. Dominic

This paper compares two acoustical projects, applied to the S. Dominic church of Foligno and Imola, which are subject to a permanent and temporary conversion respectively, to places dedicated for listening to live music. Sets of measurements have been undertaken before the acoustical treatments in order to calibrate the digital model; in Foligno, the measurements have also been performed after the installation of the acoustical features, to check if the aims have been achieved. Between the proposed acoustical projects, only one has been realized in Foligno, with the artistic activity still running inside the auditorium. The challenge to adjust the acoustics of reverberant rooms like churches to host musical venues has been achieved with a good quality of sound perception. In particular, in S. Dominic church of Foligno, the goal has been hit after many digital simulations that calibrated the redirection of the sound towards the sitting areas.

Influence of acoustics on the collective behaviour of a shoaling freshwater fish

Abstract Understanding how collective behaviour of animals is influenced by anthropogenic activity is important for their conservation in an increasingly urbanised world. River infrastructure, e.g. for transport and electricity generation, and associated construction and operation, produces sound that can disrupt ecological processes. Adopting a reductionist manipulative experimental approach using Eurasian minnow (Phoxinus phoxinus) as a model shoaling species, we compared the response of individuals and groups of five fish to a broadband acoustic stimulus in a tank containing still water. Four metrics were calculated 10 min immediately before (control–sound stimulus absent) and during the acoustic treatment: (1) swimming speed, (2) persistence of swim paths, (3) cohesion of the group, and (4) orientation of group members. On presentation of the stimulus, groups exhibited a consistent escape response compared to individuals for which behaviour was more variable. Thereafter, individuals swam faster and their swim paths were less persistent than during the control; no difference was observed for groups. Conversely, group integrity became more cohesive and members were more likely to orient in a common direction during the treatment compared to the control. This study provides insight into the importance of collective behaviour of fish in relation to antipredator‐like response to anthropogenic noise. Short‐term shifts in behaviour are context specific and depend on whether fish are members of a shoal or solitary. The results indicate the potential for negative impacts of unnatural sound on the ecology of shoaling species that inhabit engineered freshwater environments.

Non-cuboid iterative room optimizer

In past years, various iterative optimization programs emerged to separately determine optimal room ratios, sources and listening positions in perfectly reflective cuboid rooms, using the image source model. This approach fails to account for scattering, phase change at the boundary and cannot be extended to non-cuboid rooms. The present work presents a solution, using the boundary element method (BEM) to compute the frequency response at low frequencies, considering the effects of the complex admittances of the boundaries and all acoustical elements inside the room. With BEM as its engine, a genetic algorithm was developed to optimize source and receiver positions simultaneously with the room geometry, within architectural restraints. Given real-world limitations, optimizing source and listener positioning and room geometry is not always an option. Therefore, a damper module was added, which addresses low frequency acoustic treatment. By using different transfer matrix models, the acoustical behavior of different low-frequency pressure absorbers can be modeled and inserted into the BEM simulation, to evaluate the change in the room's acoustic field and frequency response at the receiving positions of interest. 3-D waterfalls are used to illustrate the modal decay following optimization. Examples will be presented.

The mixture material of dried straw and kapok for acoustic treatment for UTeM mosque

The acoustical requirements in terms of intelligibility and liveliness are dissimilar for both of sounds-recitation and speech on religious subjects at UTeM mosque. To attain an overall satisfactory acoustical performance, it is significant to find an optimum Reverberation Time (RT) and the best directivity, which is the major factors affecting intelligibility and liveliness. This experiment is conduct to gauge the effect of RT by making it a variable, while keeping other factors as non-variable and fulfilling ideal conditions for maximum intelligibility. Bearing in mind, the acoustical problems always occurred in any communication building. To improve the problem, this paper presents the new idea of improvement by using biodegradable sound absorber materials which is the mixture of dried rice straw and kapok.

Impedance modelling of acoustically treated circumferential grooves for over-tip-rotor fan noise suppression

Experimental investigation of Over-Tip-Rotor circumferential groove liners has shown potential for fan noise suppression in turbofan engines whilst providing minimal penalty in fan aerodynamic performance. The validation of Over-Tip-Rotor liner analytical prediction models against published experimental data requires the modelling of an equivalent impedance for such acoustic treatments. This paper describes the formulation of two analytical groove impedance models as semi-locally reacting liners, that is locally reacting in the axial direction and non-locally reacting in the azimuthal direction. The models are cross-verified by comparison with high-order FEM simulations, and applied to a simplified Over-Tip-Rotor configuration consisting of multiple grooves excited by a monopole point source located close to the grooved surface.

Experimental study of noise mitigation measures on a slab track

Slab track is generally noisier than conventional ballasted track, so noise control measures that can be applied to a slab track are of great importance. Several noise control treatments have been studied under controlled conditions through experiments on a 1:5 scale model slab track with and without the presence of a train body. These treatments consist of absorptive rubber mats applied to the surface of the slab and a low noise barrier introduced close to the track. The noise reduction is evaluated experimentally by using a reciprocal method and compared with the results of numerical simulations. The insertion loss spectra of these treatments have been combined with predicted train pass-by spectra to determine the potential overall noise reductions. It has been found that the absorptive treatment alone has only a small effect on the radiated noise from the track. This is increased by the presence of the train body leading to a reduction of up to 2–3 dB at a standard receiver height of 1.2 m, which suggests that the absorptive layer controls reflections between the car body and the track. All the treatments considered have a greater effect on the noise radiated by the lateral vibration of the rail than on that from the vertical vibration. Their effectiveness mostly increases, by between roughly 0.5 and 1.5 dB, as the train speed is increased from 80 to 300 km/h. As expected, the noise barrier is more effective at lower receiver positions than at higher ones but its effectiveness is reduced by 1–2 dB by the presence of the train body. However, in combination with the absorptive treatment, its effectiveness increases when the train body is present. This shows the importance of including of the presence of the train body in evaluating the effects of acoustic treatments in the track.

Estimation of efficiency of ultrasonic cavitation processing of technological media on energy criteria

The paper presents the energy evaluation of cavitation treatment of technological environments with the aim of establishing such parameters that implement the optimal conditions to maximize the transfer of energy to the stages in cavitation generation, development and slam shut bubbles. Accounting multiple transformation of energy of ultrasonic vibrations, as the need to improve the efficiency of the process based on the gradual definition of qualitative and quantitative picture of the energy in the contact zone of cavitation and technological environment and conditions of transfer of energy to the technological environment. Definition and consistent calculation of the energy conversion chain for the implementation of this idea used existing and developed new criteria for evaluating methods of acoustic treatment of technological environments: the intensity, the ratio of energies, a synergistic coefficient, coefficient of energy absorption, the rate of change of pressure in time; the wave resistance of the medium in the regimes of cavitation resistance of the initial state of the environment and others. This approach, as the process of improving existing or establishing new systems and technologies is synergistic systems. On the basis of research and evaluation of these criteria formulated synergistic principles of perfecting of conditions and parameters of the system “ultrasonic installation – technology environment”.

Experimental Research on Noise Reduction for Continuous Transonic Wind Tunnel Loop

The noise level of wind tunnel test section is respected as one of the most important performance specifications to represent the flow field quality, especially for large scale wind tunnel. According to the acoustic experimental research conducted in the 0.6 m continuous transonic wind tunnel of CARDC, main noise sources in the tunnel loop included the compressor, the high-speed diffuser and the test section. To reduce the noise in the test section, it is necessary to prevent the test section from the compressor noise propagated both forward and backward. In 0.6 m wind tunnel loop, acoustic treatments were installed on both the compressor rear cone and the fourth corner to prevent the noise emitted from the compressor from propagating forward. The vanes in the forth corner were filled with glass fibers and covered with perforated panels. And the compressor rear cone was covered with three layers of micro-perforated panels. With acoustic treatment in the tunnel loop and the second throat throttling, the fluctuation pressure coefficient (ΔCp) is lower than 0.8%, which is close to the international advanced level.

Reverberation time recommendations for noisy industrial workshops

Industrial workshops or any other industrial premises where noisy machines are operated should be as acoustically absorbent as possible. On the other hand, acoustic treatments are expensive (especially when correcting existing premises), messy, and not always compatible with the implemented production processes. Therefore, there is a need for acoustic specifications to find the best compromise between cost and efficiency. In France, for noisy industrial workshops to be compliant, the regulation requires the rate of decay of sound per distance doubling (DL2) to exceed compulsory limit values, unless this does not have a significant impact on workers' exposure to noise. However, that rate of decay is difficult and time consuming to evaluate. The purpose of this paper is to provide recommendations based on reverberation time (RT), which is not only easier to measure but is also widely used. The D2L values are conventionally measured in industrial workshops together with RT values and thus a database compiling both RT and DL2 values was available. It has been used to draw up reference limits for RT values consistent with the DL2 regulation limits. These reference limits were validated by comparison with the literature and with a new set of data collected specially for the purposes of performing that comparison. The final limits are divided into four categories: compliant/non-compliant, for furnished/empty industrial workshops, using a 95/99% confidence interval. They are intended to enable the acoustic treatment of a workshop to be evaluated using a simple metric, either at the design stage or for monitoring or occupational inspection purposes.

The Effect on Room Acoustical Parameters Using a Combination of Absorbers and Diffusers—An Experimental Study in a Classroom

Several room acoustic parameters have to be considered in ordinary public rooms, such as offices and classrooms, in order to present the actual conditions, thus increasing demands on the acoustic treatment. The most common acoustical treatment in ordinary rooms is a suspended absorbent ceiling. Due to the non-uniform distribution of the absorbent material, the classical diffuse field assumption is not fulfilled in such cases. Further, the sound scattering effect of non-absorbing objects such as furniture are considerable in these types of rooms. Even the directional characteristic of the sound scattering objects are of importance. The sound decay curve in rooms with absorbent ceilings often demonstrate a double slope. Thus, it is not possible to use reverberation time as room parameter as a representative standalone acoustic measure. An evaluation that captures the true room acoustical conditions therefore needs supplementary parameters. The aim of this experimental study is to show how various acoustical treatments affect reverberation time T20, speech clarity C50 and sound strength G. The experiment was performed in a mock-up of a classroom. The results demonstrated how absorbers, diffusers and scattering objects influence room acoustical parameters. It is shown that to some extent the parameters can be adjusted individually by using different treatments or combination of treatments. This allows for the fine-tuning of the acoustical conditions, in order to fulfill the requirements for achieving a high-quality sound environment.

Processing of dragon fruit beverage by acoustic treatment

Processing of dragon fruit beverage by acoustic treatment

Aeroacustic and Vibroacoustic Advancement in Aerospace and Automotive Systems

This Special Issue highlights the latest enhancements in the abatement of noise and vibrations of aerospace and automotive systems. The reduction of acoustic emissions and the improvement of cabin interior comfort are on the path of all major transportation industries, having a direct impact on customer satisfaction and, consequently, the commercial success of new products. Topics covered in this Special Issue deal with computational, instrumentation and data analysis of noise and vibrations of fixed wing aircrafts, satellites, spacecrafts, automotives and trains, ranging from aerodynamically generated noise to engine noise, sound absorption, cabin acoustic treatments, duct acoustics and vibroacoustic properties of materials. The focus of this Special Issue is also related to industrial aspects, e.g.,: numerical and experimental studies have been performed for an existing and commercialized engine to enable design improvements aimed at reducing noise and vibrations; moreover, an optimization is provided for the design of low vibroacoustic volute centrifugal compressors and fans whose fluids should be strictly kept in the system without any leakage. Existing procedures and algorithms useful to reach the abovementioned objectives in the most efficient way are illustrated in the collected papers.

Electrostatically tunable axisymmetric vibrations of soft electro-active tubes

Due to their unique electromechanical coupling properties, soft electro-active (SEA) resonators are actively tunable, extremely suitable, and practically important for designing the next-generation acoustic and vibration treatment devices. In this paper, we investigate the electrostatically tunable axisymmetric vibrations of SEA tubes with different geometric sizes. We consider both axisymmetric torsional and longitudinal vibrations for an incompressible SEA cylindrical tube under inhomogeneous biasing fields induced by radial electric voltage and axial pre-stretch. We then employ the state-space method, which combines the state-space formalism in cylindrical coordinates with the approximate laminate technique, to derive the frequency equations for two separate classes of axisymmetric vibration of the tube subjected to appropriate boundary conditions. We perform numerical calculations to validate the convergence and accuracy of the state-space method and to illuminate that the axisymmetric vibration characteristics of SEA tubes may be tuned significantly by adjusting the electromechanical biasing fields as well as altering the tube geometry. The reported results provide a solid guidance for the proper design of tunable resonant devices composed of SEA tubes.

Effect of Pyrolysis Temperature on PhysicoChemical Properties and Acoustic-Based Amination of Biochar for Efficient CO2 Adsorption

The present study examined the effect of pyrolysis temperature on the physicochemical properties of biochar, activation process and carbon capture. Two different categories of biochars were synthesized from herbaceous (miscanthus and switchgrass) or agro-industrial (corn stover and sugarcane bagasse) feedstock under four different pyrolysis temperatures- 500, 600, 700 and 800 oC. The synthesized biochars underwent sono-amination activation comprising low-frequency acoustic treatment followed by amine functionalization to prepare adsorbents for CO2 capture. As per the elemental analysis, the elevated pyrolysis temperature resulted in increased %C and %ash contents and reduced %N contents of biochar. The textural analysis exhibited almost 3-times enhancement of micro surface area and pore volume upon increasing the pyrolysis temperature from 500 to 700 oC, though further increase to 800 oC reduced the micro-porosity and the surface area. The intermediate temperatures of 600 and 700 oC revealed the highest interactions with ultrasound-amination, which significantly intensified CO2 adsorption. Accordingly, the CO2 capture capacity of sono-aminated biochars synthesized at 600 and 700 oC were almost 200% greater than that of raw biochars. There were 127-159% and 115-151% increases in adsorption capacity of biochars synthesized at 800 and 500 oC upon ultrasono-amine functionalization. Miscanthus biochar synthesized at 700 oC and treated sono-chemically demonstrated the highest adsorption ability of 2.89 mmol/g at 70 oC and 0.10 atm partial pressure, which is 211% higher than its pristine condition. The superior adsorption capacity of miscanthus (at 700 oC) can be attributed to its large surface area (324.35 m2/g), high carbon content (84%), and low ash content (4.9%), as well as its %N content after sono-amination that was twice that of raw char.

Volumetric MRI-guided, high-intensity focused ultrasound ablation of uterine leiomyomas: ASEAN preliminary experience.

We sought to present our preliminary experience on the effectiveness and safety of magnetic resonance imaging (MRI)-guided, high-intensity focused ultrasound (HIFU) therapy using a volumetric ablation technique in the treatment of Association of Asian Nations (ASEAN) patients with symptomatic uterine leiomyomas. This study included 33 women who underwent HIFU treatment. Tissue characteristics of leiomyomas were assessed based on T2- and T1-weighted MRI. The immediate nonperfused volume (NPV) ratio and the treatment effectiveness of MRI-guided HIFU on the basis of the degrees of volume reduction and improvement in transformed symptom severity score (SSS) were assessed. The median immediate NPV ratio was 89.8%. Additionally, the median acoustic sonication power and HIFU treatment durations were 150 W and 125 min, respectively. At six-month follow-up, the median leiomyoma volume had decreased from 139 mL at baseline to 84 mL and the median transformed SSS had decreased from 56.2 at baseline to 18.8. No major adverse events were observed. The preliminary results demonstrated that volumetric MRI-guided HIFU therapy for the treatment of symptomatic leiomyomas in ASEAN patients appears to be clinically acceptable with regard to treatment effectiveness and safety.

Comparative study of acoustical indices and speech perception of students in two primary school classrooms with an acoustical treatment

Objective acoustical indices and subjective speech perception of students were investigated and compared in two different classrooms before and after an acoustical treatment. The treatment in the present study refers to the installation of sound absorption materials on the ceilings in two primary school classrooms. The results showed that the reverberation time after acoustical treatment was reduced, while the early-to-late sound ratio and the speech transmission index were improved. The subjective speech intelligibility in classrooms was also enhanced. Subjective survey showed that most of the students preferred learning in the classrooms after acoustical treatment. They reported that higher concentration is because the speeches of the teachers were much clear in the treated classroom. However, subjective speech perception of the students has some discrepancies between the two classrooms. The perception of the students in Classroom A was better than that in Classroom B. Sixty-two percent (61.9%) of the students prefer to study in the classroom A after acoustical treatment, but only 46.3% of the students prefer to study in the Classroom B. Results show that exceeding low-frequency reverberation in the classroom may significantly mask speech signals and have effect on the student’s speech perception in classroom, even though the traditional criteria of RT and C50 at mid-frequencies are similar.

Potential acoustic treatment analysis using sabine formula in unoccupied classroom

Effective teaching and learning, not only taking into account the good teaching methodology and facilities but the acoustic level in the classroom should also be addressed. RT-60 is the time required for sound decay in a classroom. The time taken for the sound to decay depends on the absorption coefficients (α) of surface material and the volume of the room. This paper aims to identify potential treatment materials for improving the value of RT-60 of the selected unoccupied teaching hall/classroom at one of the higher learning institution in Malaysia. The value of RT-60 is calculated using Sabine formula and used the same parameter like the surface material, surface area, and room’s volume identified in previous research. The best RT-60 value is 0.6s for the classroom with 10k-20k cubit feet in volume and it coincides with the volume of the selected classroom which is about 14320 cubic feet. To ensure that room has the optimum RT-60 values, the materials used on the ceiling, walls, floors, windows, and doors are assessed for sound absorption rate and then materials with appropriate absorption coefficient are proposed for improvement purposes. As a result, it found that gypsum board is suitable to use for wall and plywood 12mm thick is proposed for ceiling material. By applying this proposed material will then enhance the acoustical performance of the unoccupied teaching hall especially in RT-60 value.