Acoustic Efficiency Research Articles

Optimization of dissipative mufflers

The method of selecting the configuration of dissipative mufflers with the required acoustic efficiency is considered. The peculiarity of the considered approach is the use of an integral indicator of acoustic efficiency and dimensionless geometric parameters. The studies were carried out using finite element calculations. In the finite element model of a dissipative mufflers, acoustic characteristics of a fibrous sound-absorbing material obtained from experimental studies were used.

Acoustic radiation of a fluid-saturated microperforated plate

It is known that fluid-saturated microperforated plates (MPP) dissipate energy and are substantially damped through thermoviscous dissipation taking place in the thermoviscous skin on the solid wall of the perforations. The aim of this work is to explore the acoustic radiation of a microperforated periodic cell to investigate the intercellular coupling and the complexity of near-field radiation, and to derive a criterion related to the near-field far-field transition. A numerical modeling using the finite element method is developed to solve the elastic and thermo-visco-acoustic (TVA) multiphysics problem. The TVA calculates explicitly the thermoviscous losses on the acoustic wave in the periodic cell studied. Numerical results show that the distance of the near-far field transition is significant at low frequencies, passing through a minimum for a frequency depending on perforation parameters (diameter and ratio) before increasing again as a frequency function. The radiated acoustic power and radiation efficiency are compared with those derived from the theoretical MPP vibration model. It is found that the microperforations and resulting added damping, around a characteristic frequency, reduce the acoustic radiation efficiency of the MPP compared to the corresponding non-perforated plate.

Elasticity and modal effects on the optimal performance of micro-perforated multi-layered absorbers

Multi-layered wall-treatments with thin lightweight micro-perforated panels offer a potential solution to achieve broadband noise absorption while complying with mass saving and compactness. This study examines how vibrational effects, often neglected, may impede the wideband acoustical performance of such partitions, made up of a distribution of either periodic or graded micro-perforated membranes or panels. The impedance translation method and a scattering matrix analysis have been implemented. It is found that the elasticity behavior of thin micro-perforated membranes has a beneficial effect on the acoustical efficiency of the partitions. The contributions of the individual acoustical resonances tend to merge if the elasticity effects are accounted for. If the partition is optimized, near-constant high absorption and low transmission values are obtained over a wide frequency range. A more robust design involves partitions made up of micro-perforated panels. It was observed that the first volumetric volumetric mode of the panels modifies the absorption properties of the partition. It cross-couples with the acoustical resonances and redistributes their spectral locations. This structural resonance sets an upper frequency bound, below which the partition achieves a high broadband performance. It should be accounted for when setting the frequency limits of the total dissipation to be optimized.

Acoustic black hole immersed sonoreactor for high-efficiency cavitation treatment

Developing innovative sonoreactors to enhance acoustic processing efficiency holds immense importance in the field of sonochemistry. Traditional immersed sonoreactors (TISs) mainly produce cavitation at the probe tip, with a relatively weak cavitation around the probe, resulting in posing challenges for high-efficiency cavitation treatment. Here we propose an acoustic black hole immersed sonoreactor (ABHIS) in longitudinal-flexural coupled vibration, enabling high-efficiency cavitation treatment by unleashing the cavitation potential of the probe. The symmetrical structure of the probe is altered to introduce a coupling of flexural vibration mode, and an acoustic black hole (ABH) profile is integrated to further enhance both flexural wave number and amplitude. In this paper, we present a systematic theoretical design method for ABHIS and compare its performance with TIS using finite element method (FEM). An ABHIS prototype is fabricated and subjected to experimental tests and cavitation observation. The results demonstrate that our theoretical analysis model accurately predicts the frequency characteristics of ABHIS. The proposed ABHIS exhibits satisfactory dynamic characteristics, with significantly increased vibration displacement and acoustic radiation ability compared to TIS. Importantly, the ABH design significantly expands ultrasonic cavitation regions and enhances acoustic radiation intensity of ABHIS resulting in a substantial improvement in acoustic processing efficiency.

Simulasi karakteristik mesin termoakustik pembangkit listrik dengan penambahan model kerugian minor dari dua segmen konis

Acoustic energy output level from regenerator segment of a thermoacoustic engine model is attenuated along it’s loop due to several conditions including minor losses. This article discusses the result of Delta EC simulation of a thermoacoustic engine model acting as simple electric power generator that inserted with two conical segments. The cone segments are capable to lower the energy loss which in turn improve the overall performance of the engine in term of nett heat to acoustic energy conversion efficiency. Combined acoustic energy loss induced by both cones is equivalent to 4.94 watts minor losses. At this condition, regenerator segment amplifies the incoming acoustic energy flow of 57.02 watt up to 93.57 watt, which is equals to 36.55 watts acoustic amplification. It leads to increasing of overall engines heat to acoustic efficiency into 14.05%, which is 1.29% higher than those at the case of without cones. This engine performance improvement addressed to smoother streamline of working fluid flow inside the loop.

Optimization of acoustic porous material absorbers modeled as rigid multiple microducts networks: Metamaterial design using additive manufacturing

This research presents a strategy to enhancing sound absorption in porous acoustic metamaterials through the optimization of micro-duct networks. The study employs a combination of analytical and numerical methods, systematically adjusting micro-duct diameters within a 2D grid to optimize absorption coefficients at specific frequency bands. The Finite Element Transfer Method (FETM) is utilized for modeling, supported by a multi-objective function influenced by the surface impedance of the network. This approach ensures practical applicability and manufacturability of the designed metamaterial. A significant aspect of the study is the development of an analytical mobility matrix for each microduct, integrated through the Transfer Matrix Method using the visco-thermal dissipation theory. This integration results in a physically coherent model, for which a semi-analytical sensitivity analysis related to the microduct diameters can be directly performed. The optimization employs the Method of Moving Asymptotes (MMA), effectively managing the complexity associated with a large number of design variables. Subsequently, the optimized structure is adapted into a 3D grid, facilitating prototype creation using Additive Manufacturing Technology (AMT) with a specific polymer material. The research methodology is validated through four distinct test cases, each demonstrating the efficacy and adaptability of the optimization tools and techniques. Experimental validation, conducted using an impedance tube, indicates a significant shift in the first absorption maximum from 2500 Hz to 1000 Hz, achieved without altering the material thickness. Additional validation through 3D Finite Element Method (FEM) modeling, which includes visco-thermal effects, further confirms the acoustic efficiency of the final designs. While the potential for achieving lower sub-wavelength conditions is recognized, the study opts for simpler structures, considering the current limitations of 3D printing technology. This study contributes to both theoretical understanding and practical application in acoustic material design, emphasizing the potential for customizing materials to specific frequency ranges. The integration of FETM modeling with MMA provides a systematic and effective approach for optimizing acoustic materials, particularly in enhancing absorption at lower frequencies.

Simulation Analysis of Thermoacoustic Effect of CNT Film with Metasurface-Enhanced Acoustic Autofocusing.

This study introduces a novel thermoacoustic (TA) focusing system enhanced by Airy beam-based acoustic metasurfaces, significantly improving acoustic focusing and efficiency. The system integrates a TA emitter, fabricated from carbon nanotube (CNT) films, with a binary acoustic metasurface capable of generating quasi-Airy beams. Through finite element simulations, the system's heat conduction, acoustic focusing, and self-healing properties were thoroughly analyzed. The results demonstrate that the system achieves superior sub-wavelength focusing, tunable focal length via frequency control, and robust self-healing, even in the presence of obstacles. These findings address current limitations in TA emitters and suggest broader applications in medical ultrasound and advanced technology.

Mediating coherent acoustic phonon oscillation of a 2D semiconductor/3D dielectric heterostructure by interfacial engineering

Abstract Coherent acoustic phonon (CAP) oscillation of 2D layered semiconductor/3D dielectric heterostructure generated by femtosecond laser pulse excitation can realize ultrafast photoacoustic conversion, while the photoacoustic conversion efficiency suffers from interfacial phonon scatterings of simultaneously laser-induced lattice heat. Here, taking advantage of graphene’s high thermal conductivity and large acoustic impedance, we demonstrate that phonon scatterings can be markedly mediated in a MoS$_2$/graphene/glass heterostructure via femtosecond laser pump-probe measurements. Equilibrium temperatures of MoS$_2$ lattice have been cooled down by about 45 %. As a benefit, both lifetime of CAP oscillations and pump pulse-picosecond acoustic pulse energy conversion efficiency have been enhanced by a factor of about 2. Our results constitute insights into CAP manipulations via interfacial engineering, that are fundamentally important for ultrafast photoacoustics based on 2D layered semiconductors.

Isogeometric modeling and vibro-acoustic analysis of flow-excited irregular cavity-plate-exterior space coupled system

The flow-induced noise has become an important noise source in marine sonar self-noise, which can adversely affect the normal operation of sonar. The marine sonar cabin is simplified as a cavity-plate-exterior space coupled system whose flow-induced vibro-acoustic characteristics are investigated in this paper. An isogeometric vibro-acoustic formulation is proposed in which the cavity with an irregular geometry is precisely described by adjusting the control points and corresponding weights. The flow-induced vibro-acoustic response is obtained by transferring the turbulent pressure data from computational fluid dynamics into the isogeometric vibro-acoustic model. Imposing turbulent pressure into the isogeometric control points is proposed to achieve this objective using a node-based interpolation method. The vibro-acoustic modeling is validated and compared with previous experimental results. These comparisons demonstrate that the developed formulation accurately predicts the vibro-acoustic characteristics of the fluid-excited coupled system. The influences of flow speed, acoustic medium, and cavity shape on flow-excited vibration and sound radiation are discussed. Results show a decrease in radiated acoustic power and radiation efficiency in the exterior space, and a shift in the plate-exterior space coupling modal frequency to lower frequencies when the cavity changes from convex to concave.

Nondestructive evaluation of debonding in composites using air-coupled coda wave analysis and local defect resonance techniques

Abstract Low acoustic energy conversion efficiency is a major challenge for air-coupled ultrasonic technology. In the determination of the lift-off distance of air-coupled sensors, there is a balance between the acoustic energy attenuation and the difficulty of extracting defect information. In this study, an air-coupled local defect resonance (LDR) technique with coda wave analysis is proposed for the nondestructive evaluation of debonding in composites. A sensor consisting of 19 elements was used to simultaneously excite and receive ultrasonic waves. Air-coupled LDR experiments were conducted on the two types of composite structures. The effects of sensor lift-off distance and coda wave analysis on the performance of the LDR technique were investigated. It was found that the sensor lift-off distance and the coda wave analysis had a significant effect on the defect detection capability of the LDR technique. For composites, the optimal sensor lift-off distance was found to be between 3.5λ and 5.5λ, where λ is the wavelength. Compared to multiple reflection echoes, the coda waves are more suitable for identifying the damage in composites. The proposed non-contact ultrasonic technique effectively reduces the required incident acoustic energy and can be used for efficient detection of debonding in composites.

Acoustic Radiation Characteristics of a Forced Vibrating Elastic Panel Under Thermal Environments

This paper presents the thermo-acoustic frequency response of an un-baffled rectangular panel subjected to an external excitation load. A boundary element method BEM has been employed taking into account the Kirchhoff-Helmholtz K-H integral equation for the acoustic pressure and with the fluid-plate interface boundary condition the acoustic pressure jump over the panel is calculated. The thermal effects are considered regarding in the form of a uniform increment of temperature of the panel and are analysed in order to prevent the buckling phenomena. The excitation force considered is in the form of a concentrated load at some point of the panel and the deformation modes correspond to the vacuum case. Applying a collocation method for the panel equation, a frequency transfer function is obtained that relates the deflexion of the panel with the applied load. The effect of several geometric parameters, different thermal loads and location of the load applied on the acoustic radiated power and the acoustic efficiency spectrum are evaluated. Furthermore, the influence of the excitation frequency on the sound directivity is evaluated. The verification of the method is proven with other works.

Theoretical modeling of triboelectric receiver transducer for mechanic-electrical transformations

In recent years, receiver transducers have gained extensive attention in both research and industrial fields. In particular, the triboelectric receiver transducer (TE-RT) stands out due to their self-powered capability, low cost, and excellent output performance. While theoretical methods for analyzing the output performance are still lacked, which may limit the further development of this field. In this study, we propose an equivalent electromechanical conversion circuit that couples the acoustic field and electric field to predict the performance characteristics of the TE-RT. Specifically, the relationship between the deformation of the diaphragm and output performance of the TE-RT is analyzed through theoretical modeling and clarification of governing equations. Subsequently, a specific transformer revealing the mechanical-electrical conversion mechanism for the TE-RT was proposed using the equivalent circuit method (ECM), and an ECM model was established to analyze the performance of TE-RT quickly and accurately. To further improve the output performance of the TE-RT, piezoelectric materials are integrated into the model to enhance its capacity for converting acoustic energy. Verification for the two types of receiver transducer was conducted using the finite element method (FEM), and the equivalent circuit model fit the simulation results well. The acoustic energy conversion efficiency of the TE-RT can also be further evaluated by the number of turns (n) in the specialized transformer. This study can provide a solid theoretical foundation for the design and development of receiver transducer.

Analysis of a standing wave thermoacoustic engine with multiple unit stages

The thermoacoustic engine is an eco-friendly technology capable of harnessing solar and waste energy for electricity generation, in conjunction with a linear alternator, and can function as a heat pump. This engine type holds significant appeal due to its simplistic design, devoid of any mechanical moving components, comprising only a stack sandwiched between heat exchangers within a resonator. When the temperature gradient across the stack reaches the critical threshold (onset temperature), the working gas undergoes spontaneous oscillation. Typically, a high onset temperature is necessary to induce gas oscillation in a thermoacoustic engine due to viscous losses within the system. A method to lower the onset temperature by increasing the number of unit stages consisting of stacks and heat exchangers so that the engine can utilize low-grade thermal sources has been developed to overcome this challenge. However, this method has only been applied to traveling-wave thermoacoustic engines. Its application in standing-wave engines, which offer a more compact and straightforward structure, remains unexplored. This research aims to examine how the number of unit stages in a standing-wave thermoacoustic engine influences the onset temperature and acoustic field. The onset temperature is estimated using a fundamental hydrodynamics equation and the investigation of the acoustic field throughout the engine using DeltaEC software. Results showed that the strategic positioning of multiple unit stages is essential to achieve a low onset temperature. The minimum onset temperature, approximately 92°C, is obtained when three- or four-unit stages are installed. Additionally, increasing the number of unit stages does not affect the acoustic impedance and phase difference between pressure and velocity in the stack, while simultaneously enhancing both acoustic power output and thermal efficiency.

Akustična svojstva drvnih i nedrvnih materijala za izradu kućišta klavira

This article presents the possibilities of substituting expensive and scarce wood materials in the construction of piano cases, especially the front panels of upright pianos. Three-layer blockboard, multi-layer plywood, medium-density fibreboard (MDF), and Purenit were selected for the study. These materials were long-time climatised at 20 °C and 50 % relative air humidity. Their frequencies, damping coefficient and relative amplitude were measured. The density r, sound velocity v, dynamic modulus of elasticity E´, sound impedance Zn, and Acoustic Conversion Efficiency (ACE) were calculated. With the materials used to make the front panels of an upright piano, a subjective assessment of the instrument’s acoustic response was made. The presence of front panels of any type was found to have a negative effect on the sound except at low frequencies. With panels fitted, the best acoustic properties were achieved by blockboard, followed by plywood, MDF and Purenit panels in that order; this was affirmed by the subjective assessment. The best acoustic performance was achieved by blockboard and plywood. Taking both price and performance into consideration, MDF presented the best compromise. Purenit was ruled out due to its high damping properties.

Study on Structure-Borne Noise Characteristics of Long-Span Steel Truss Bridge in Urban Rail Transit

The application of long-span steel bridge in urban rail transit is becoming more and more extensive, but the structure-borne noise of steel bridge induced by passing train is also prominent. Research on the structure-borne noise problem of long-span steel bridge in urban rail transit has positive significance in promoting the sustainable development of steel bridge, and improving the quality of sound environment along rail transit. In this work, dynamic receptance principle, finite element method and statistical energy method are combined to establish the structure-borne noise prediction model of the long-span steel bridge, and the rationality and validity of the model are verified based on field measurement results. Based on the prediction model, the noise radiation characteristics of large-span steel truss bridge in urban rail transit are studied, and the following conclusions are drawn: The bridge deck has the strongest acoustic contribution ability, with the contribution rate of 33–44%, followed by the longitudinal web and transverse web, with the contribution rate of 23–30%, followed by the truss chord, with the contribution rate of 5–8%, and the truss web, longitudinal wing and transverse wing have weak contribution ability, with the contribution rate of less than 2%. The acoustic radiation efficiency of steel truss bridge components reaches its peak at the critical frequency, and the critical frequency is determined by the thickness of steel bridge plate components when the material parameters are fixed. Under ordinary track structures, the middle-to-high frequency noise distribution characteristics of large-span steel truss bridge structure are obvious. Damping pad floating slab track can effectively suppress the high-frequency noise of steel bridge, and the overall sound level can be reduced by about 11–14[Formula: see text]dB.

Assessment of acoustic shock wave resistance of SiO2 (α-cristobalite): A potential material for aerospace and defense industry applications

In the present research article, the acoustic shock wave-resistant efficiency of silica microparticles (SiO2-α-cristobalite)) has been experimentally evaluated in terms of structural, optical and morphological stability against the impact of shock waves. The required SiO2 particles were synthesized by a hydrothermal method which was subjected to a different number of shock pulses such as 200,400 and 600 with Mach number 2.2. Shocked samples’ structural, morphological and optical stabilities have been evaluated by utilizing a powder X-ray diffractometer (PXRD), Ultraviolet–Diffuse reflectance spectrometer (DRS) while the surface morphological analysis has been scrutinized by the field emission scanning electron microscopic technique (FESEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy techniques are utilized to evaluate oxidation states and crystallographic structural stability. The above-mentioned analytical techniques provide convincing proofs whereby the synthesized SiO2 particles are authentically proven to possess outstanding structural, optical and morphological stability against the impact of shock waves. The implicated experimental results and the arguments strongly suggest that the SiO2 particles are suitable candidates for aerospace and defense industry applications due to their outstanding shock wave-resistant properties.

Calculations of the Acoustic Efficiency of Noise Shields Based on the Numerical Solution of the Sound Diffraction Equation

Calculations of the Acoustic Efficiency of Noise Shields Based on the Numerical Solution of the Sound Diffraction Equation

A rapid prediction model for the radiation efficiency of baffled constrained layer damping plate

It’s well-known that constrained layer damping (CLD) can effectively reduce the vibration and radiation noise from the (plate-like or shell-like) thin-walled structures under various of dynamic excitations. As one of the key properties deciding the CLD’s performance, the CLD’s acoustic radiation characteristics has always been a focus of researchers. In this study, an analytical model based on equivalent principle is proposed to predict the acoustic radiation efficiency of the CLD plate. In this model, a laminated CLD plate is equivalent to a single-layer plate and the equivalent stiffness and loss factor are obtained using the strain energy method. The vibration velocity of the plate is calculated using mode-superposition method and the sound pressure on the plate surface is calculated using Rayleigh integral formula. Variable mesh sizes and frequency steps are employed to improve the calculation efficiency. The difference between the base and CLD plates in sound radiation characteristics is investigated using this model. The results indicate that CLD involving a damping layer with a low Young’s modulus can mitigate more vibration at low frequencies. A higher Young’s modulus of the damping layer results in a higher radiation efficiency of the CLD plate between the fundamental and critical frequencies. By increasing the loss factor, the spatially averaged mean square velocity would decrease, more modes would contribute to the response, and the CLD plate can consequently achieve a higher radiation efficiency below the critical frequency. Moreover, the simplified formulae for the average radiation efficiency of the CLD plate is developed to achieve the rapid calculation. Its accuracy is then validated by comparing the results to the more comprehensive model.

Acoustical Efficiency and Physico-Mechanical Characteristics Study for New Composite Material: Ethylene Vinyl Acetate and Wood Sawdust

Developing neoteric composite materials (CM) that improve the acoustic efficiency and mechanical properties become the target of many scientists in the last decade. This paper presents research on developing new CMs using Ethylene Vinyl Acetate (EVA) and sawdust (SD) of different weight concentrations which can be help to improve the acoustic and mechanical properties of the EVA polymer materials. Prototypes of EVA composite in form of flat plates with different weight concentrations of sawdust namely; 0, 2.5, 5, 10, 20 and 30% were produced. One of the interesting applications of this new CMs is to use it as a floor covering in buildings and manufactures. The acoustic efficiency parameters namely, impact noise reduction and sound absorption are experimentally studied. The obtained results articulate that covering floors with the designed composite material of EVA/SD as filler can decrease ISR up to 14 dB. Also, it gives peak sound absorption coefficient about 0.6 for 30 % of SD at mid-frequency band. The greatest proportion of SD aggregate EVA does not entail a higher acoustic performance. The tensile strength of the composite increases to 15.5% when the SD content is 5% and the tensile strength drops with increase the SD content up to 30%. Therefore, SD may be utilized as filler and consolidation in the EVA matrix, which will save expenses and assist the environment.

AS A MEANS OF REDUCING THE LEVEL OF EXTERNAL NOISE CHASSIS KRAZ-6511NE

Ukraine’s full-scale war with its northern neighbor has been going on more than two years now. One of the most important laws of war is: “If you don’t detect it, you don’t hit the target.” It’s about masking. In wartime, the camouflage properties of a military vehicle are especially relevant. There are a number of ways to improve them. One of them is reducing the external noise level of a military vehicle. Using the example of the KrAZ-6511NE chassis, one of the ways to reduce noise is considered. The BM 9P140 “Uragan” antiircraft missile system is placed on this chassis. The developed silencer has the ability to change its frequency response synchronously with the change in the engine crankshaft rotation frequency. The developed muffler is a well-known twochamber reactive muffler, which is modified by the ability to change the effective lengths of the chambers. A diagram showing the operation of the developed noise muffler is given, where the main elements are: two muffler chambers, a connecting tube, piston drive mechanisms of the first and second muffler chambers, respectively, an electric motor, a control unit, and a sensor for determining the frequency of rotation of the crankshaft. The acoustic efficiency of this muffler was determined with fixed geometric parameters (outer diameter, diameters of the inlet and outlet pipes) and variable effective lengths of both chambers, families of frequency characteristics were constructed for various combinations of the muffler’s geometric parameters. To construct graphs, code was written in Python, which uses the NumPy and Matplotlib libraries. As a result of the introduction of the developed noise muffler, it is predicted that the external noise level of the KrAZ 6511НЕ chassis will decrease by 5-7 dBA in the speed range of 45-85 km/h.