Excitation of the entropy mode in the field of intense sound, that is, acoustic heating, is theoretically considered in this work. The dynamic equation for an excess density which specifies the entropy mode, has been obtained by means of the method of projections. It takes the form of the diffusion equation with an acoustic driving force which is quadratically nonlinear in the leading order. The diffusion coefficient is proportional to the thermal conduction, and the acoustic force is proportional to the total attenuation. Theoretical description of instantaneous heating allows to take into account aperiodic and impulsive sounds. Acoustic heating in a half-space and in a planar resonator is discussed. The aim of this study is to evaluate acoustic heating and determine the contribution of thermal conduction and mechanical viscosity in different boundary problems. The conclusions are drawn for the Dirichlet and Neumann boundary conditions. The instantaneous dynamic equation for variations in temperature, which specifies the entropy mode, is solved analytically for some types of acoustic exciters. The results show variation in temperature as a function of time and distance from the boundary for different boundary conditions.
Ultrasonic processing in the cavitation mode is used to produce the composite materials based on the metal matrix and reinforcing particles of micro- and nano-sizes. In such a case, the deagglomeration of aggregates and the uniform distribution of particles are the expected effects. Although the particles can not only fragment in the acoustic field, they also can coagulate, coarsen and precipitate. In this paper, a theoretical study of processes of deagglomeration and coagulation of particles in the liquid metal under ultrasonic treatment is made. The influence of various parameters of ultrasound and dispersion medium on the dynamics of particles in the acoustic field is considered on the basis of the proposed mathematical model. The criterion of leading process (coagulation or deagglomeration) has been proposed. The calculated results are compared with the experimental ones known from the scientific literature.
For the purpose of making of a solid body of an electric guitar the acoustic- and mechanical properties of walnut- (Juglans regia L.) and ash wood (Fraxinus excelsior L.) were researched. The acoustic properties were determined in a flexural vibration response of laboratory conditioned wood elements of 430 × 186 × 42.8 mm used for making of a solid body of an electric guitar. The velocity of shearand compression ultrasonic waves was additionally determined in parallel small oriented samples of 80 × 40 × 40 mm. The research confirmed better mechanical properties of ash wood, that is, the larger modulus of elasticity and shear modules in all anatomical directions and planes. The acoustic quality of ash wood was better only in the basic vibration mode. Walnut was, on the other hand, lighter and more homogenous and had lower acoustic- and mechanical anisotropy. Additionally, reduced damping of walnut at higher vibration modes is assumed to have a positive impact on the vibration response of future modelled and built solid bodies of electric guitars. When choosing walnut wood, better energy transfer is expected at a similar string playing frequency and a structure resonance of the electric guitar.
Many business offices around the world are organized as open plan offices. Therefore, studies about the acoustic comfort of the people who work in them have become increasingly important. The focus of this work is the acoustic evaluation of an open plan office combining several architectural characteristics and levels of ambient noise. This evaluation was performed through a computational model calibrated from a real office. The rate of spatial decay of sound pressure levels per distance doubling (DL2) and the speech transmission index (STI) were simulated for the acoustic evaluation of the office, allowing for the determination of the radius of distraction (rD). These parameters were simulated for 6 situations using different floor and ceiling covering materials and inserting or withdrawing screens between workstations. In addition, STI and rD were simulated under two conditions of ambient noise. The results indicated that the DL2 and rD are adequate acoustic parameters for the acoustic evaluation and improvement of an open plan office. The DL2 was strongly influenced by the presence or absence of screens between workstations and by the ceiling covering material. The rD was more sensitive to changes in ambient noise.
A method for precise sound sources detection and localization in interiors is presented. Acoustic vector sensors, which provide multichannel output signals of acoustic pressure and particle velocity were employed. Methods for detecting acoustic events are introduced. The algorithm for localizing sound events in the audience is presented. The system set up in a lecture hall, which serves as a demonstrator of the proposed technology, is described. The accurracy of the proposed method is evaluated by the described measurement results. The analysis of the results is followed by conclusions pertaining the usability of the proposed system. The concept of the multimodal audio-visual detection of events in the audience is also introduced.
Knowledge of the uncertainty of measurement of testing results is important when results have to be compared with limits and specifications. In the measurement of sound insulation following standards ISO 140-4 and 140-5 the uncertainty of the final magnitude is mainly associated to the average sound pressure levels L1 and L2 measured. However, the study of sound fields in enclosed spaces is very difficult: there are a wide variety of rooms with different sound fields depending on factors as volume, geometry and materials. A parameter what allows us to quantify the spatial variation of the sound pressure level is the standard deviation of the pressure levels measured at the different positions of the room. Based on the analysis of this parameter some results have been pointed out: we show examples on the influence of the microphone positions and the wall characteristics on the uncertainty of the final magnitudes mainly at the low frequencies regime. In this line, we propose a theoretical calculus of the standard deviation as a combined uncertainty of the standard deviation already proposed in the literature focused in the room geometry and the standard deviation associated to the wall vibrational field.
The paper presents the possible applications of using acoustic diagnostics in inspecting the technical condition of an internal combustion engine with autoignition on the example of the Fiat drive unit with common rail system. As a result of measuring the sound pressure level for specific faults and comparing the noise generated by the motor running smoothly, the detailed maps of changes in the acoustic spectrum are possible to generate. These results may be helpful in the future diagnostics of internal combustion engines. In the paper, the results of scientific work in the area of research, design and operation of internal combustion engines, conducted at the Department of Automotive Engineering, in cooperation with the Laboratory of Hydraulic Drives & Vibroacoustics of Machines at the Wroclaw University of Technology are included.
The pump performance and occurrence of cavitation directly depends on different operating conditions. To cover a wide range of operation conditions for detecting cavitation in this work, investigations on the effect of various suction valve openings on cavitation in the pump were carried out. In order to analyse various levels of cavitation in different operation conditions, the effect of the decrease in the inlet suction pressure of the centrifugal pump by controlling the inlet suction valve opening was investigated using this experimental setup. Hence, the acoustic and pressure signals under different inlet valve openings and different flow rates, namely, 103, 200, 302 l/min were collected for this purpose. A detailed analysis of the results obtained from the acoustic signal was carried out to predict cavitation in the pump under different operating conditions. Also, the acoustic signal was investigated in time domain through the use of the same statistical features. The FFT technique was used to analyse the acoustic signal in the frequency domain. In addition, in this work an attempt was made to find a relationship between the cavitation and noise characteristics using the acoustic technique for identifying cavitation within a pump.
The increment in the number of automobiles and the densification of the city has increased noise pollution rates. In addition, the lack of regulation in Chile regarding the acoustic insulation of façades is a problem of a growing concern. The main objective of the present study was to obtain a model of the Sound Insulation of housing, façades, stratified in Santiago, Chile, based on constructive variables. It is expected to serve as a basis for one future regulation for acoustic façades of houses. In the present study, tests based on the international ISO 140-5 standard were carried out in situ. An estimation model of the Standardized Level Difference Dls,2m,nT,w + C, was obtained based on the opening/façade proportion, and the type of glass used for the windows.
The aim of this publication is to design a procedure for the synthesis of an IDT (interdigital transducer) with diluted electrodes. The paper deals with the surface acoustic waves (SAW) and the theory of synthesis of the asymmetrical delay line with the interdigital transducer with diluted electrodes. The authors developed a theory, design, and implementation of the proposed design. They also measured signals. The authors analysed acoustoelectronic components with SAW: PLF 13, PLR 40, delay line with PAV 44 PLO. The presented applications have a potential practical use.
The paper discusses acoustic problems in the contemporary Catholic church, and presents a study of the influence of the ceiling structure on acoustics in the interior for two types of ceiling structures, i.e. the truss type and the reinforced concrete one. The investigations involved six contemporary churches: three buildings with a truss type ceiling and three buildings with a reinforced concrete ceiling. The results reveal that in churches with a truss type ceiling, acoustic parameters reach values close to recommendations. In contrast, churches with a concrete ceiling create very unfavourable acoustic conditions. The investigations rendered it possible to calculate the sound absorption coefficient α for the truss type cover.
The main purpose of the presented research is to investigate the partial discharge (PD) phenomenon variability under long-term AC voltage with particular consideration of the selected physical quantities changes while measured and registered by the acoustic emission method (AE). During the research a PD model source generating surface discharges is immersed in the brand new insulation mineral oil. Acoustic signals generated by the continuously occurred PDs within 168 hours are registered. Several qualitative and quantitative indicators are assigned to describe the PD variability in time. Furthermore, some longterm characteristics of the applied PD model source in mineral oil, are also presented according to acoustic signals emitted by the PD. Finally, various statistical tools are applied for the results analysis and presentation. Despite there are numerous contemporary research papers dealing with long-term PD analysis, such complementary and multiparametric approach has not been presented so far, regarding the presented research. According to the presented research from among all assigned indicators there are discriminated descriptors that could depend on PD long-term duration. On the grounds of the regression models analysis there are discovered trends that potentially allow to apply the results for modeling of the PD variability in time using the acoustic emission method. Subsequently such an approach may potentially support the development and extend the abilities of the diagnostic tools and maintenance policy in electrical power industry.
The locally resonant sonic material (LRSM) is an artificial metamaterial that can block underwater sound. The low-frequency insulation performance of LRSM can be enhanced by coupling local resonance and Bragg scattering effects. However, such method is hard to be experimentally proven as the best optimizing method. Hence, this paper proposes a statistical optimization method, which first finds a group of optimal solutions of an object function by utilizing genetic algorithm multiple times, and then analyzes the distribution of the fitness and the Euclidean distance of the obtained solutions, in order to verify whether the result is the global optimum. By using this method, we obtain the global optimal solution of the low-frequency insulation of LRSM. By varying parameters of the optimum, it can be found that the optimized insulation performance of the LRSM is contributed by the coupling of local resonance with Bragg scattering effect, as well as a distinct impedance mismatch between the matrix of LRSM and the surrounding water. This indicates coupling different effects with impedance mismatches is the best method to enhance the low-frequency insulation performance of LRSM.
Choral singers are among intensive voice users whose excessive vocal effort puts them at risk of developing voice disorders. The aim of the work was to assess voice quality for choral singers in the choir at the Polish-Japanese Academy of Information Technology. This evaluation was carried out using the acoustic parameters from the COVAREP (A Collaborative Voice Analysis Repository For Speech Technologies) repository. A prototype of a mobile application was also prepared to allow the calculation of these parameters. The study group comprised 6 male and 19 female choir singers. The control group consisted of healthy non-singing individuals, 50 men and 39 women. Auditory perceptual assessment (using the RBH scale) as well as acoustic analysis were used to test the voice quality of all the participants. The voice quality of the female choir singers proved to be normal in comparison with the control group. The male choir singers were found to have tense voice in comparison with the controls. The parameters which proved most effective for voice evaluation were Peak Slope and Normalized Amplitude Quotient.
The airflow in the mouth of an open and closed flue organ pipe of corresponding geometrical proportions is studied. The phase locked particle image velocimetry with subsequent analysis by the biorthogonal decomposition is employed in order to compare the flow mechanisms and related features. The most significant differences lie in the mean velocity distribution and rapidity of the jet lateral motion. Remarks on the pressure estimation from PIV data and its importance for the aeroacoustic source terms are made and a specific example is discussed.
In the paper, the results of investigations on the properties of acoustic emission signals generated in a tested pressure vessel are presented. The investigations were performed by repeating several times the following procedure: an increase in pressure, maintaining a given pressure level, a further increase in pressure, and then maintaining the pressure at new determined level. During the tests the acoustic emission signals were recorded by the measuring system 8AE-PD with piezoelectric sensors D9241A. The used eight-channel measuring system 8AE-PD enables the monitoring, recording and then basic and advanced analysis of signals. The results of basic analysis carried out in domain of time and the results of advanced analysis carried out in the discrimination threshold domain of the recorded acoustic emission signals are presented in the paper. In the framework of the advanced analysis, results are described by the defined by the author descriptors with acronyms ADC, ADP and ADNC. Such description is based on identifying the properties of amplitude distributions of acoustic emission signals by assigning them the level of advancement. It is shown that for signals including continoues AE or single burst AE signals descriptions of such registered signals by means of ADC, ADP and ADNC descriptors and by Upp and Urms descriptors provide identical ordering of registered acoustic emission signals. For complex signals, the description using ADC, ADP and ADNC descriptors based on the analysis of amplitude distributions of recorded signals gives the order of signals with more accurate connection with deformational processes being sources of acoustic emission signals.
A hybrid artificial boundary condition (HABC) that combines the volume-based acoustic damping layer (ADL) and the local face-based characteristic boundary condition (CBC) is presented to enhance the absorption of acoustic waves near the computational boundaries. This method is applied to the prediction of aerodynamic noise from a circular cylinder immersed in uniform compressible viscous flow. Different ADLs are designed to assess their effectiveness whereby the effect of the mesh-stretch direction on wave absorption in the ADL is analysed. Large eddy simulation (LES) and FW-H acoustic analogy method are implemented to predict the far-field noise, and the sensitivities of each approach to the HABC are compared. In the LES computed propagation field of the fluctuation pressure and the frequency-domain results, the spurious reflections at edges are found to be significantly eliminated by the HABC through the effective dissipation of incident waves along the wave-front direction in the ADL. Thereby, the LES results are found to be in a good agreement with the acoustic pressure predicted using FW-H method, which is observed to be just affected slightly by reflected waves.
In this work we present the design and the manufacturing processes, as well as the acoustics standardization tests, of an acoustic barrier formed by a set of multi-phenomena cylindrical scatterers. Periodic arrangements of acoustic scatterers embedded in a fluid medium with different physical properties are usually called Sonic Crystals. The multiple scattering of waves inside these structures leads to attenuation bands related to the periodicity of the structure by means of Bragg scattering. In order to design the acoustic barrier, two strategies have been used: First, the arrangement of scatterers is based on fractal geometries to maximize the Bragg scattering; second, multi-phenomena scatterers with several noise control mechanisms, as resonances or absorption, are designed and used to construct the periodic array. The acoustic barrier reported in this work provides a high technological solution in the field of noise control.
The church of Santa Cruz de Oleiros, Spain (1967) shows architect Miguel Fisac’s perception of sacred space after the Second Vatican Council. In this place of worship, the architect responded to the new liturgical guidelines combining geometry and architectural forms with the material of the moment, concrete. However, ordinary religious celebrations reveal acoustic deficiencies for the main use of the building. This fact is corroborated by acoustic measurements in situ. With a methodology that uses simulation techniques for the sound field, the analysis of the current acoustic behaviour of the room will serve as the basis for an acoustic rehabilitation proposal aimed at improving the acoustic conditions and so, the functionality of the church.
The article presents the results concerning the use of clustering methods to identify signals of acoustic emission (AE) generated by partial discharge (PD) in oil-paper insulation. The conducted testing featured qualitative analysis of the following clustering methods: single linkage, complete linkage, average linkage, centroid linkage and Ward linkage. The purpose of the analysis was to search the tested series of AE signal measurements, deriving from three various PD forms, for elements of grouping (clusters), which are most similar to one another and maximally different than in other groups in terms of a specific feature or adopted criteria. Then, the conducted clustering was used as a basis for attempting to assess the effectiveness of identification of particular PD forms that modelled exemplary defects of the power transformer’s oil-paper insulation system. The relevant analyses and simulations were conducted using the Matlab estimation environment and the clustering procedures available in it. The conducted tests featured analyses of the results of the series of measurements of acoustic emissions generated by the basic PD forms, which were obtained in laboratory conditions using spark gap systems that modelled the defects of the power transformer’s oil-paper insulation.
The results of long-term continuous noise measurements in two selected schools are presented in the paper. Noise characteristics were measured continuously there for approximately 16 months. Measurements started eight months prior to the acoustic treatment of the school corridors of both schools. An evaluation of the acoustic climates in both schools, before and after the acoustic treatment, was performed based on comparison of these two periods of continuous measurements. The autonomous noise monitoring stations, engineered at the Multimedia Systems Department of the Gdańsk University of Technology were used for this purpose. Investigations of measured noise, especially its influence on hearing sense, assessed on ground of spectral analyses in critical bands, is discussed. Effects of occupational noise exposure, including the Temporary Threshold Shift simulation, are determined. The correlation of the above said measurement results with respective instantaneous noise levels is discussed, and concluding remarks are presented. Some additional indicators such as air pollution or video analysis aiming at the analysis of corridor occupancy are also measured. It should be remembered that excessive noise, or air pollution may be evidence of a dangerous event and may pose health risks.
Several methods can be applied for analyses of the acoustic field in enclosed rooms namely: wave propagation, geometrical or statistical analysis. The paper presents problems related to application of the boundary elements method to modelling of acoustic field parameters. Experimental and numerical studies have been combined for evaluation of acoustic impedance of the material used for the walls of a model room. The experimental studies have been carried out by implementing a multichannel measuring system inside the constructed model of an industrial room. The measuring system allowed simultaneous measurements of the source parameters - the loudspeaker membrane vibration speed, the acoustic pressure values in reception points located inside the model space as well as phase shifts between signals registered in various reception points. The numerical modelling making use of the acoustic pressure values measured inside the analyzed space allowed determination of requested parameters of the surface at the space boundary.
The church of Santa Ana in Moratalaz, Madrid, Spain (1965-1971), is an emblematic work of the architect Miguel Fisac. In his long career include interventions in the religious field, constituting one of the most important contributions to Spanish religious architecture of the last century. This church is a singular place of worship and architecturally significant, in which the acoustics played an important role in the configuration of the spatiality of the church. This paper studies the acoustic behaviour of the church and its relationship with its unique structural, spatial and coating material characteristics. The analysis of the current acoustic conditions, with high reverberation times (up to 6 seconds) and poor intelligibility on the audience, serve as the basis for making an acoustic rehabilitation proposal that contributes to improving the sound conditions of the building for the intended use, without distorting the spatial, formal and material aspects with which the architect conceived the project.
In the acoustic fatigue experiment for hypersonic vehicle in simulated harsh service environment on ground, acoustic loads on the surface of test pieces of the vehicle need to be measured. However, for the normal microphones without high temperature resistance ability, the near field sound measurement cannot be achieved. In this work, on the basis of previous researches, an acoustic tubes array is designed to achieve the near field measurement of acoustic loads on the surface of the test piece in the supersonic airflow with high temperature achieved by coherent jet oxygen lance. Firstly, the process of designing this acoustic tubes array is introduced. Secondly, the equality of phase differences at the front and at the end of the tubes is stated and proved using a phase differences test with an acoustic tubes array whose design is presented in this text; therefore, the phase differences of signals acquired by microphones can be directly applied to beamforming algorithm to determine the acoustic load source. Finally, using above mentioned acoustic tubes array, measurement of acoustic load, with and without a test piece in the supersonic airflow made by the coherent jet oxygen lance, is conducted respectively, and the measurements results are analyzed.
In this paper a possibility of determining a local velocity of the surface acoustic Rayleigh waves using a transducer, with the rigidly connected emitting and receiving parts, is considered. A problem on spatial resolution of such a transducer for investigation of inhomogeneous specimens is also examined. A high spatial resolution can be obtained due to the transducer displacement by a value less than the distance between the emitting and receiving parts. It is shown that in this case it is not necessary to measure the transducer displacement with a high accuracy for precise determination of the velocity. Such an effect is obtained through measuring the velocity of surface waves in one local region of the specimen with respect to the other. The criterion for optimal spatial resolution selection during spatially inhomogeneous specimens study is also proposed. The proposed criterion use is illustrated on the example of the determination of spatial distribution of the surface acoustic velocity in a steel specimen subjected to inhomogeneous plastic deformation.