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1 – 10 of 714Fang Ji, Xiongliang Yao, Aman Zhang and Xi Ye
Laying the acoustic decoupling material on the surface of underwater structures is an effective noise reduction technology. The underwater sound radiation experiment of finite…
Abstract
Purpose
Laying the acoustic decoupling material on the surface of underwater structures is an effective noise reduction technology. The underwater sound radiation experiment of finite stiffened double cylindrical shell with separate‐sound and decoupled tile is carried out with the aim of finding out the most effective laying condition.
Design/methodology/approach
The segmentation power function interpolation method and vertex extreme value envelope continuation method are introduced into basic theory of empirical mode decomposition (EMD). The original measured sound pressure signals are decomposed to intrinsic mode function (IMF) group through EMD, and the high‐frequency components are filtered out. Because the mechanical noise of submarine is mainly at low frequency, the IMFs in low frequency are researched through power spectrum analysis. The noise reduction effects of different separate‐sound and decoupled tile laying conditions are compared.
Findings
The sound pressure signal components' amplitudes, periods and phases are obtained through EMD. The test data show that the double cylindrical shell entirely covered with separate‐sound and decoupled tile is the most effective laying condition in noise reduction.
Originality/value
With reference to the case study, this is believed to be the first application of the EMD in sound radiation time‐frequency characteristics of double cylindrical shell. The evaluation of separate‐sound and decoupled tile laying conditions is of great importance in engineering applications.
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Xi Ye, Longquan Sun and Fuzhen Pang
The purpose of this paper is to research the interaction between multiple bubbles and their noise radiation considering the influence of compressibility. The influences of bubble…
Abstract
Purpose
The purpose of this paper is to research the interaction between multiple bubbles and their noise radiation considering the influence of compressibility. The influences of bubble spacing, initial inner pressure, buoyance and phase difference are presented with different bubbles arrangements.
Design/methodology/approach
Based on wave equation, the new boundary integral equation considering the compressibility is given by the matching between prophase and anaphase approximation of bubble motion and solved with boundary element method. The time-domain characteristics of noise induced by multiple bubbles are obtained by the moving boundary Kirchhoff integral equation. With the surface discretization and coordinate transformation, the bubbles surface is treated as a moving deformable boundary and noise source, and the integral is implemented on the surface directly.
Findings
Numerical results show the manner of jet generation will be affected by the phase difference between bubbles. With the increasing of phase difference, the directive property of noise becomes obvious. With the enlargement of initial inner pressure, the sound pressure will arise at the early stage of expanding, and the increasing of buoyance parameter will reduce the sound pressure after the generation of jet. Since the consideration of compressibility, the oscillation amplitude of bubbles will be weakened.
Originality/value
The paper could provide the reference for the research about the dynamics and noise characteristics of multiple bubbles in compressible fluid. And the new method based on boundary integral equation to simulate the multiple bubbles motion and noise radiation is presented.
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The bulk of jet engine noise developed at high powers arises from the turbulent mixing of the jet efflux in the surrounding air, as judged from model experiments, and has a…
Abstract
The bulk of jet engine noise developed at high powers arises from the turbulent mixing of the jet efflux in the surrounding air, as judged from model experiments, and has a continuous spectrum with a single flat maximum. The high frequency sound arises from fairly close to the orifice, and reaches its maximum intensity at fairly large acute angles to the jet direction. Lower frequency noise arises from lower down stream and its maxima make smaller acute angles with the jet axis. The possible origins are briefly discussed in view of Lighthill's theory and refraction effects. The most intensesound has a wave‐length of the order of three or four exit diameters, and originates between five and ten diameters from the orifice. A semi‐empirical rule of noise energy depending on the jet velocity to the eighth power and the jet diameter squared gives a rough estimate of the noise level for both cold and heated jets. Further noise from heated or supersonic jets may occur through eddies travelling at supersonic speed and so producing small Shockwaves. Model experiments have shown that interaction between shock‐wave configurations in choked jets and passing eddy trains generates sound and this initiates further eddies at the orifice. The directional properties of this sound are quite distinctive, the maximum being in the upstream direction. Methods of reducing jet noise are briefly discussed.
Reproducible images of human fingertips' induced glow (Kirlian radiation) were captured despite extremely unstable nature of living systems' emission. The matrix of correlations…
Abstract
Purpose
Reproducible images of human fingertips' induced glow (Kirlian radiation) were captured despite extremely unstable nature of living systems' emission. The matrix of correlations between fingertips' radiation in the electromagnetic field of high frequency and systemic features of human organism has been studied.
Design/methodology/approach
Weak natural emission of biological object is enhanced and transformed into visual images by gas discharge processes, which proceed in the electromagnetic field of high frequency. Such secondary radiation was found to be reproducible only when special polyethylene membrane is placed between the glass surface of the camera screen and target fingertip (or other living object). Resulting images of fingertips' discharge coronas provide comprehencible information on the whole living system.
Findings
Present research resulted in the discovery of previously unknown phenomenon, which turned out to be specific for living systems. It is demonstrated that Kirlian radiation of fingertips can display almost exact replicas (holograms) of organism's internal organs and tissues. Each part of the body is able to provide holographic information on any problematic element of dynamic system. Holodiffractional nature of discovered phenomenon has been confirmed experimentally.
Originality/value
The discovery of new natural phenomenon represents a major step forward regarding both theoretical disciplines and practical biomedicine. Secondary holodiffractional radiation of body parts provides previously unavailable information on dynamic organization of the whole living system. Bioholographic information is already widely used for diagnostics of body/mind pathology.
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This article aims to propose a new measurement method for ultrasonic power based on self-reciprocity theorem which turns the estimation of ultrasonic power to the measurement of…
Abstract
Purpose
This article aims to propose a new measurement method for ultrasonic power based on self-reciprocity theorem which turns the estimation of ultrasonic power to the measurement of first echo current and open-circuit voltage of the driving source.
Design/methodology/approach
The formula for ultrasonic power is derived which has corrected the position of pressure reflection coefficient on the interface of water and steel. The diffraction correction for focusing transducers is evaluated using numerical computation of the Rayleigh integral. One way to estimate the reflection coefficient of focusing beams on heterogeneous interface is also depicted.
Findings
Comparison experiment with radiation force balance method demonstrates that ultrasonic power measurement using self-reciprocity is sound in theory and feasible in practice.
Originality/value
It has a better capability of anti-environmental interference and, thus, can be extended to low-level and high-frequency power measurements.
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David Franck, Michael van der Giet and Kay Hameyer
Nowadays, the determination of the acoustic radiation of electric machines is of particular interest, because legal regulations restrict the maximum audible noise radiated by…
Abstract
Purpose
Nowadays, the determination of the acoustic radiation of electric machines is of particular interest, because legal regulations restrict the maximum audible noise radiated by technical devices such as electrical machinery. The purpose of this paper is to analyze the electromagnetic excited structure‐borne sound and air‐borne noise of an AC servo drive.
Design/methodology/approach
This paper presents the required steps for the multiphysics acoustic simulation of electrical machines to evaluate its noise behaviour. This numerical approach starts with the electromagnetic force‐wave simulation. The computation by a structure dynamic model determines the deformation of the mechanical structure due to the force‐waves. The final step of the simulation approach consists of the computation of the acoustic radiation.
Findings
For the electromagnetic simulation analytical and numerical methods are combined to gain some acceleration of the entire multiphysics simulation approach. This combination offers additionally a detailed understanding of the noise generation mechanism in electrical machines.
Originality/value
Particular attention is paid to the structural‐dynamic model. Modelling of microstructures, such as the laminated iron core or insulated coils, is memory and computational expensive. A systematic material homogenisation technique, based on experimental‐ and numerical modal analyses, yields a higher accuracy at lower computational costs when compared to standard numerical approaches. The presented multiphysics simulation is validated by measurements. The methods are presented by means of a case study.
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Jiaru Shao, Xueping Mo, Zijun Zheng and Yu Yang
This study aims to improve the survivability and maneuverability of the fighter,and study the stealth performance of fighter in the jet noise of aeroengine, it is of great…
Abstract
Purpose
This study aims to improve the survivability and maneuverability of the fighter,and study the stealth performance of fighter in the jet noise of aeroengine, it is of great significance to study the jet noise characteristics of double S-bend nozzles.
Design/methodology/approach
The multiparameter coupling and super-ellipse design methods are used to design the cross section of double S-bend nozzle. Taking unsteady flow information as the equivalent sound source, the noise signal at the far-field monitoring points were calculated with Ffowcs Williams–Hawkings (FW–H) method, and then, the sound source characteristics of the double S-bend nozzle are analyzed.
Findings
The results show that the internal flow of the S-bend nozzle with rectangular section is smoothed and the aerodynamic performance is better than super-ellipse section, the shear layer length of rectangular section is longer, the thickness is smaller and the mixing ability is stronger. The sound pressure level of the two S-bend nozzles decreases with the increase of the monitoring angle, and the sound pressure on the horizontal plane is greater than the vertical plane. In the direction of 40°–120°, the jet noise of rectangular nozzle is smaller, and the multiparameter coupled rectangular cross section structure is more applicable.
Practical implications
It is beneficial to reduce the jet noise of the engine tail nozzle and improve the stealth performance of the aircraft.
Originality/value
There is very little research on the jet noise characteristics of the double S-bend nozzle. The multiparameter coupling and the super-ellipse method are used to design the nozzle flow section to study the aerodynamic performance and jet noise characteristics of the double S-bend nozzle and to improve the acoustic stealth characteristics of the aircraft.
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Maria Barbarosou, Ioannis Paraskevas and Amr Ahmed
– This paper aims to present a system framework for classifying different models of military aircrafts, which is based on the sound they produce.
Abstract
Purpose
This paper aims to present a system framework for classifying different models of military aircrafts, which is based on the sound they produce.
Design/methodology/approach
The technique is based on extracting a compact feature set, of only two features, extracted from the frequency domain of the aircrafts’ sound signals produced by their engines, namely, the spectral centroid and the signal bandwidth. These features are then introduced to an artificial neural network to classify the aircraft signals.
Findings
The current system identifies the aircraft type among four military aircrafts: Mirage 2000, F-16 Fighting Falcon, F-4 Phantom II and F-104 Starfighter. The experimental results show that the aforementioned types of aircrafts can be accurately classified up to 96.2 per cent via the proposed method.
Practical implications
The proposed system can be used as a low-cost assistive tool to the already existing radar systems to avoid cases of missed detection or false alarm. More importantly, the same method can be used for aircrafts that use stealth technology that cannot be detected using radar devices.
Originality/value
The proposed method constitutes a novel approach to classifying military aircrafts based on their sound signature. It utilizes only two spectral features extracted from the sound of the aircraft engine; these features are then introduced to a neural network classifier.
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Fang Ji, Xiongliang Yao and Aman Zhang
The structure‐borne sound generated by power equipment can be isolated effectively through vibration absorber under hull base structures. The practical vibration isolation…
Abstract
Purpose
The structure‐borne sound generated by power equipment can be isolated effectively through vibration absorber under hull base structures. The practical vibration isolation performance is limited due to the weight, size and cost. The dramatic attenuating wave propagation characteristic of hull base without adding weight is essential to the vessel acoustic stealth.
Design/methodology/approach
The characteristics of vibration wave propagated from typical shape base link structures have been investigated according to impedance mismatch and wave conversion in non‐homogeneous structure. The hull base is simplified to three degrees of freedom damped system through the mechanical impedance method. The influence of blocking mass weight, as well as location properties to the base vibration isolation performance have been discussed. Furthermore, the structure‐borne sound design of a typical hull base is carried out.
Findings
The impedance mismatch of the hull base is further increased by the comprehensive use of high transmission loss base link structures, blocking mass as well as damping layer. The effectiveness of structure‐borne sound design is verified through numerical calculation together with underwater model test. The test data show that the noise has been reduced larger than 3 dB.
Originality/value
The paper describes what is believed to be the first application of the high transmission loss base in hull structures based on the literature survey. The method of structure‐borne sound design of a typical hull base can be applied in different types of vessels.
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Seyed Hamid Delbari, Amir Nejat, Mohammad H. Ahmadi, Ali Khaleghi and Marjan Goodarzi
This study aims to carry out numerical modeling to predict aerodynamic noise radiation from four different Savonius rotor blade profile.
Abstract
Purpose
This study aims to carry out numerical modeling to predict aerodynamic noise radiation from four different Savonius rotor blade profile.
Design/methodology/approach
Incompressible unsteady reynolds-averaged navier-stokes (URANS) approach using gamma–theta turbulence model is conducted to obtain the time accurate turbulent flow field. The Ffowcs Williams and Hawkings (FW-H) acoustic analogy formulation is used for noise predictions at optimal tip speed ratio (TSR).
Findings
The mean torque and power coefficients are compared with the experimental data and acceptable agreement is observed. The total and Mono+Dipole noise graphs are presented. A discrete tonal component at low frequencies in all graphs is attributed to the blade passing frequency at the given TSR. According to the noise prediction results, Bach type rotor has the lowest level of noise emission. The effect of TSR on the noise level from the Bach rotor is investigated. A direct relation between angular velocity and the noise emission is found.
Practical implications
The savonius rotor is a type of vertical axis wind turbines suited for mounting in the vicinity of residential areas. Also, wind turbines wherein operation are efficient sources of tonal and broadband noises and affect the inhabitable environment adversely. Therefore, the acoustic pollution assessment is essential for the installation of wind turbines in residential areas.
Originality/value
This study aims to investigate the radiated noise level of four common Savonius rotor blade profiles, namely, Bach type, Benesh type, semi-elliptic and conventional. As stated above, numbers of studies exploit the URANS method coupled with the FW-H analogy to predict the aeroacoustics behavior of wind turbines. Therefore, this approach is chosen in this research to deal with the aeroacoustics and aerodynamic calculation of the flow field around the aforementioned Savonius blade profiles. The effect of optimal TSR on the emitted noise and the contribution of thickness, loading and quadrupole sources are of interest in this study.
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