Cavitation plays a crucial role in the reliability of components in refrigeration systems. The properties of refrigerants change significantly with temperature, thereby amplifying the impact of thermodynamic effects. This study, based on the Large Eddy Simulation (LES) method and the Schnerr-Sauer (S-S) cavitation model, investigates the transient cavitating flow characteristics of the R134a refrigerant in a Venturi tube (VT). The bubble number density in the S-S model was improved based on the experimental data of pressure and temperature. Simulation results indicate that there are two shedding modes of cavitation clouds in R134a refrigerant. One is induced by the combined action of reentrant flow and the vortices centrifugal force, while the other is generated by the central jet of the mainstream and the reverse jet produced by the collapsing cavitation bubbles. Furthermore, the thermodynamic effects of the refrigerant exert a certain inhibitory effect on cavitation, revealing the causes of instability in the refrigerant cavitation interface and the shedding characteristics of cavitation clouds. The relationship between local sound speed, flow velocity, and heat conduction rate in the cavitation region was studied, unveiling a time-lag in temperature changes relative to pressure changes in the intensive cavitation region. This study provides insights into the complex cavitation dynamics, especially in R134a refrigerant systems, and provides an approach for accurately predicting and managing cavitation in various industrial applications.
Johanna Fuchte, Felix Wachter, Merle Claßen
et al.
Cystic fibrosis (CF) affects the gastrointestinal tract, but assessing gastrointestinal transit usually requires invasive procedures or exposure to ionizing radiation. Contrast-enhanced multispectral optoacoustic tomography (CE-MSOT) offers a novel, non-invasive, and radiation-free approach to assess gastrointestinal function by orally administered dyes. In this clinical pilot-study five patients with cystic fibrosis and four healthy volunteers received CE-MSOT before and 6-times hourly after a standardized breakfast with Indocyanin green (ICG) as dye. The gastric antrum, terminal ileum and sigmoid colon were recorded and MSOT signals spectrally unmixed to detect ICG signals to determine the transit time. ICG excretion was confirmed by fluorescence imaging of stool samples. MSOT ICG signals were detected earlier in the terminal ileum of CF patients, reaching a maximum after 120 min (p = 0.0079), compared to 240 min (p = 0.0286) in healthy controls after ICG intake (p = 0.0159). In CF patients, ICG signal was further detected in the sigmoid colon from 240 min onwards (p = 0.0079 after 300 min). But, no significant changes in the ICG signal were observed in the sigmoid colon of controls. Furthermore, signals of ICG were verified in 12 of 19 stool samples by fluorescence imaging. In this study, we demonstrated the potential of CE-MSOT for functional imaging of the intestine in CF patients and revealed faster intestinal transit in CF patients compared to healthy controls.
Because of containing the same double 6-ring (D6R) building unit, the pure zeolite CHA with lower framework density (FDSi = 15.1 T/1000 Å3) has been transformed from zeolite T with higher framework density (FDSi = 16.1 T/1000 Å3) through ultrasonic-pretreated hydrothermal synthesis in MOH (KOH and NaOH) solution without adding organic template or seed crystals. Ultrasonic pretreatment facilitates the transformation rate and generates high-quality zeolite CHA. The ultrasound condition should be precisely controlled because that CHA phase is metastable, which is inclined to transform to other more stable phase. The ultrasonic conditions at 313 K and 333 K have been investigated in detail. In KOH solution, the ultrasonic treatment at 313 K can effectively restrain the generation of MER phase, however, it is hard to avoid the existence of MER phase when ultrasound temperature is 333 K. In NaOH solution, the samples with ultrasonic treatment of 313 K show the small particles size of about 1 μm, and the GIS framework topology starts to grow with the ultrasonic treatment of 333 K. The products prepared with the appropriate ultrasonic pretreatment represents smaller particles size, larger mesopore volume and higher CO2 adsorption capacity than the sample without the ultrasonic pretreatment. The structural evolution of interzeolite transformation has been explored by XRD, FT-IR and SEM observations. With the assistance of ultrasound, the parent zeolite T can quickly decompose into intermediate phase and then regenerate into CHA phase.
Maria Campo-Valera, Isidro Villo-Perez, Alejandro Fernandez-Garrido
et al.
Nonlinear acoustics is a critical area of study with practical applications in fields such as underwater communications, medical imaging, non-destructive testing, and sonar. This paper offers a comprehensive analysis of the Westervelt and Burgers equations, along with their related boundary problems, and investigates the characteristics of parametric generation, thereby making substantial advancements in the theoretical comprehension of nonlinear acoustic waves. Our analysis sheds new light on the dynamics of nonlinear acoustic waves and their behavior in various media, providing valuable insights into the physics of sound propagation. Finally, parametric effects can be intelligently exploited for communication applications. Thus, through the appropriate selection of encodings, it is possible to develop underwater acoustic communication systems with greater directivity and range than classical systems.
Owing to a steep rise in urban population, there has been a continuous growth in construction of buildings, public or private transport like cars, motorbikes, trains, and planes at a global level. Hence, urban noise has become a major issue affecting the health and quality of human life. In the current environmental scenario, architectural acoustics has been directed towards controlling and manipulating sound waves at a desired level. Structural engineers and designers are moving towards green technologies, which may help improve the overall comfort level of residents. A variety of conventional sound absorbing materials are being used to reduce noise, but attenuation of low-frequency noise still remains a challenge. Recently, acoustic metamaterials that enable low-frequency sound manipulation, mitigation, and control have been widely used for architectural acoustics and traffic noise mitigation. This review article provides an overview of the role of acoustic metamaterials for architectural acoustics and road noise mitigation applications. The current challenges and prominent future directions in the field are also highlighted.
The objective of this study is to explore the effect and mechanism of ultrasound on chitin extraction from shrimp shells powder (SSP) by the co-fermentation of Bacillus subtilis and Acetobacter pasteurianus. After pre-treating the SSP with high-intensity ultrasound (HIU) at 800 W, the protease activity in the fermentation solution reached 96.9 U/mL on day 3, which was significantly higher than for SSP that had not been pre-treated with ultrasound (81.8 U/mL). The fermentation time of the chitin extraction process was 5.0 d without ultrasound pre-treatment, while it was shortened to 4.5 d when using ultrasound at 800 W to treat SSP. However, there were no obvious differences when we applied ultrasound at low power (200 W, 400 W). Furthermore, chitin purified from shrimp shells pre-treated with HIU at 800 W exhibited lower molecular weight (11.2 kDa), higher chitin purity (89.8%), and a higher degree of deacetylation (21.1%) compared to SSP with no ultrasound pre-treatment (13.5 kDa, 86.6%, 18.5%). Results indicate that HIU peels off the protein/CaCO3 matrix that covers the SSP surface. About 9.1% of protein and 4.7% of Ca2+ were released from SSP pre-treated with HIU at 800 W. These figures were both higher than with no ultrasound pre-treatment (4.5%, 3.2%). Additionally, the amount of soluble protein extracted from SSP through HIU at 800 W was 50% higher than for the control sample. SDS-PAGE analysis indicated that the soluble protein was degraded to the micromolecule. It also revealed that HIU (600, 800 W) induced the secondary and tertiary structure destruction of protein extracted from SSP. In conclusion, HIU-induced degradation and structural damage of protein enhances the protein/CaCO3 matrix to be peeled off from SSP. Also, in the co-fermentation process, an increase of protease activity further accelerates deproteinization.
To study the influence of classical phononic crystal (PC) structures on the acoustical characteristics of a sound source, a combined acoustics/perceptual analysis is conducted on a PC specially designed to exhibit several spectral and wave vector properties in different audible frequency ranges. The properties, confirmed by both numerical calculations and experiments, consist in both partial and absolute band gaps, as well as a negative refraction band. A psychoacoustic feature, namely the loudness in third-octave bands, is estimated from numerical simulations of the acoustic field behind the crystal. Additional perceptual tests are conducted to evaluate the efficiency of the PC slab. In the frequency range of the band gaps, sound stimuli filtered by the PC’s impulse response are perceived as softer than stimuli resulting from a free-field propagation (FF), they also are perceived as equally (or close to equally) loud than sounds attenuated by a free-standing rigid wall (FS). In the frequency range of the focalization (negative refraction), PC sound stimuli sound louder than both FS and FF sound stimuli. The possibility of designing an efficient sound barrier based on the considered PC is finally discussed.
Acoustics in engineering. Acoustical engineering, Acoustics. Sound
In this work, the spraying of ethanol solution containing phenolic acid (ferulic acid or caffeic acid) was performed before subjecting to contact ultrasound-assisted air drying of blackberry. The mass transfer modeling results revealed that sonication intensified both internal water diffusion and external water exchange during drying, and ethanol pretreatment enhanced the effective diffusivity of water. Compared with air drying alone, the drying time for sequential ferulic acid pretreatment and drying with sonication was shortened by 89.2%. Owing to the co-pigmentation between phenolic acid and anthocyanins, the retention of anthocyanins was significantly enhanced after dehydration. At the end of drying, the total anthocyanin contents in the ultrasound-dried samples pretreated with ferulic acid and caffeic acid were 25.3% and 10.5% higher than the sonicated samples without pretreatments, respectively. Furthermore, drying simultaneously with sonication promoted the preservation of non-anthocyaninic soluble phenolics including catechin, phloretic acid, rutin in blackberry compared to air drying alone. Besides, bound phenolics in blackberry were less influences by the applied dehydration treatments. This study demonstrates that the combination of phenolic acid co-pigmentation pretreatment and ultrasound drying could be a promising method to protect anthocyanin pigments during dehydration of berry fruits.
Jian Jin, Ogadimma D. Okagu, Abu ElGasim Ahmed Yagoub
et al.
The present work investigated the effects of sonication at different amplitudes and durations on the in vitro digestibility of buckwheat protein isolates (BPIs). The conformation, particle size and microstructures of the BPIs were also studied to explicate the possible mechanisms of the sonication-induced changes. The results showed that sonication conditions of 20 kHz, pulsed on-time 10 s, off-time 5 s, amplitude of 60% and duration of 10 min (SA6T10) improved the digestibility of BPIs from 41.4% (control) to 58.2%. The tertiary structure analysis showed that sonication exposed the hydrophobic core buried inside the protein molecules and broke the intramolecular crosslinks, based on the increase in the surface hydrophobicity and intrinsic fluorescence and the decrease in the disulphide content. The secondary structure analysis showed that SA6T10 decreased the content of β-turn and β-sheet by 40.9% and 22.4%, respectively, and increased the content of anti-parallel β-sheet, random coil, and α-helix by 40.9%, 30.6%, and 25.5%, respectively. The particle size of the control BPIs (427.7 ± 76.7 nm) increased to 2130.8 ± 356.2 nm in the SA6T10 sonicated sample with a corresponding decrease in the polydispersity index from 0.97 ± 0.04 to 0.51 ± 0.13. Moreover, scanning electron microscopy indicated that sonication broke the macroparticles into smaller fragments and changed the surface state of the proteins. Taken together, sonication has proven to be a promising approach for improving the digestibility of buckwheat proteins, which can be explored as a source of plant-based alternative protein for food applications.
Boiling histotripsy is a High Intensity Focused Ultrasound (HIFU) technique which uses a number of short pulses with high acoustic pressures at the HIFU focus to induce mechanical tissue fractionation. In boiling histotripsy, two different types of acoustic cavitation contribute towards mechanical tissue destruction: a boiling vapour bubble and cavitation clouds. An understanding of the mechanisms underpinning these phenomena and their dynamics is therefore paramount to predicting and controlling the overall size of a lesion produced for a given boiling histotripsy exposure condition. A number of studies have shown the effects of shockwave heating in generating a boiling bubble at the HIFU focus and have studied its dynamics under boiling histotripsy insonation. However, not much is known about the subsequent production of cavitation clouds that form between the HIFU transducer and the boiling bubble. The main objective of the present study is to examine what causes this bubble cluster formation after the generation of a boiling vapour bubble. A numerical simulation of 2D nonlinear wave propagation with the presence of a bubble at the focus of a HIFU field was performed using the k-Wave MATLAB toolbox for time domain ultrasound simulations, which numerically solves the generalised Westervelt equation. The numerical results clearly demonstrate the appearance of the constructive interference of a backscattered shockwave by a bubble with incoming incident shockwaves. This interaction (i.e., the reflected and inverted peak positive phase from the bubble with the incoming incident rarefactional phase) can eventually induce a greater peak negative pressure field compared to that without the bubble at the HIFU focus. In addition, the backscattered peak negative pressure magnitude gradually increased from 17.4 MPa to 31.6 MPa when increasing the bubble size from 0.2 mm to 1.5 mm. The latter value is above the intrinsic cavitation threshold of –28 MPa in soft tissue. Our results suggest that the formation of a cavitation cloud in boiling histotripsy is a threshold effect which primarily depends (a) the size and location of a boiling bubble, and (b) the sum of the incident field and that scattered by a bubble.
Zero index materials where sound propagates without phase variation, holds a great potential for wavefront and dispersion engineering. Recently explored electromagnetic double zero index metamaterials consist of periodic scatterers whose refractive index is significantly larger than that of the surrounding medium. This requirement is fundamentally challenging for airborne acoustics because the sound speed (inversely proportional to the refractive index) in air is among the slowest. Here, we report the first experimental realization of an impedance matched acoustic double zero refractive index metamaterial induced by a Dirac-like cone at the Brillouin zone centre. This is achieved in a two-dimensional waveguide with periodically varying air channel that modulates the effective phase velocity of a high-order waveguide mode. Using such a zero-index medium, we demonstrated acoustic wave collimation emitted from a point source. For the first time, we experimentally confirm the existence of the Dirac-like cone at the Brillouin zone centre. Impedance mismatch between acoustic metamaterials and a surrounding medium hinders efficient applications, especially for zero-index materials. Here, Duboiset al. utilize the Dirac-like dispersion in a double-zero-index material to overcome this problem and to collimate sound.
One of the main issues of design process of HVAC systems and ventilation ducts in particular is correct modelling of coupling of the flow field and acoustic field of the air flowing in such systems. Such a coupling can be modelled in many ways, one of them is using linearised Euler equations (LEE). In this paper, the method of solving these equations using finite element method and open source tools is decribed. Equations were transformed into functional and solved using Python language and FEniCS software. The non-reflective boundary condition called buffer layer was also implemented into equations, which allowed modelling of unbounded domains. The issue, influence of flow on wave propagation, could be adressed using LEE equations, as they take non-uniform mean flow into account. The developed tool was verified and results of simulations were compared with analytical solutions, both in one- and two-dimensional cases. The obtained numerical results are very consistent with analytical ones. Furthermore, this paper describes the use of the developed tool for analysing a more complex model. Acoustic wave propagation for the backward-facing step in the presence of flow calculated using Navier-Stokes equations was studied.
This paper describes the development of a simulator to reproduce gunner’s target tracking tasks in a main battle tank, under whole-body vibration conditions. For specifying the vibration and tracking conditions, three-degree-of-freedom acceleration was measured in a tracked armored vehicle, equipped with a 105 mm cannon, running in a battlefield test track. The electrohydraulic dynamics of the turret systems was experimentally identified as black-box autoregressive functions. A pneumatic actuation system and a real-time control software were designed to reproduce horizontal, single-axis periodic motion with the dominant frequency observed in field measurements. The control software displays the target and sight points and acquires the turret pointing command from an adapted gunner’s handle joystick. The root mean square error between target and simulated turret position allows assessing gunner’s target acquisition and tracking performance under periodic vibration.
Control engineering systems. Automatic machinery (General), Acoustics. Sound
The paper presents the results of measurements of the shear impedance for samples of synthetic oil with different length of molecules for the shear frequencies 10, 30 and 450 MHz over a range of temperatures from –100°C do 50°C. It was found that the results of measurements of the shear impedance are well described by LAMB'S liquid model with the high-frequency approximation for the DAVIDSON-COLE term [...].
It has been shown that the coefficient 2K in this term is a function of the viscosity of the examined liquid. The results obtained have been interpreted as the superposition of two relaxation processes, one of high-frequency viscoelastic relaxation and one of low-frequency retardation related to the three-dimensional orientation of the molecules. The values of the individual relaxation times have been determined with the aid of ROUSE's theory.
Elisabete Fraga FREITAS, Joaquim TINOCO, Francisco SOARES
et al.
The research aimed to establish tyre-road noise models by using a Data Mining approach that allowed to build a predictive model and assess the importance of the tested input variables. The data modelling took into account three learning algorithms and three metrics to define the best predictive model. The variables tested included basic properties of pavement surfaces, macrotexture, megatexture, and unevenness and, for the first time, damping. Also, the importance of those variables was measured by using a sensitivity analysis procedure. Two types of models were set: one with basic variables and another with complex variables, such as megatexture and damping, all as a function of vehicles speed. More detailed models were additionally set by the speed level. As a result, several models with very good tyre-road noise predictive capacity were achieved. The most relevant variables were Speed, Temperature, Aggregate size, Mean Profile Depth, and Damping, which had the highest importance, even though influenced by speed. Megatexture and IRI had the lowest importance. The applicability of the models developed in this work is relevant for trucks tyre-noise prediction, represented by the AVON V4 test tyre, at the early stage of road pavements use. Therefore, the obtained models are highly useful for the design of pavements and for noise prediction by road authorities and contractors.
This paper presents a general-purpose system for recognition of a limited set of words uttered in isolation. Such a system is intended for voice control of robot's movements. In order to minimize the number of operations performed during the recognition process and to limit the memory requirements frequency analysis of the signal was performed in adequately selected bands. Output signals from filters undergo detection and through an A/D converter are introduced into a computer where they undergo further processing logarithmic conversion and linear time standarization, among others. This leads to a reduction of the number range in further calculations. The DTW algorithm was used in the recognition process, while templates of individual words are introduced once, in principle separately for individual operators. The developed system speaker-dependent, in principle was verified experimentally for various vocabularies (containing 20 to 60 words) uttered by 11 voices (including 1 female voice). The average recognition accuracy for a 60 word wocabulary exceeded 98% for individual voices, while in a case of recognition whithout system accomodation to given voice the average error of recognition increased by about 10%.
Hitherto developed algorithms for wow and flutter characteristic determination were found useful in some real-life restoration procedures, however, there was no study of their capabilities in terms of the maximal parasite modulation frequency that can be determined with their application. This paper presents the study for three algorithms, i.e. the power-line hum tracker, high frequency bias tracker, and the center of gravity tracker. The short description of the algorithms is followed by the theoretical study on the maximal modulation frequency determined by the algorithms. Next, the experimental part is given, with simulations which confirm the findings from the theoretical part, and conclusions summarizing obtained results.
Harmonic wave propagation in thick, cylindrical, three-layered shells of infinite length was studied. Both the outer layers and the core are composites made of short strand fiberglass resin, but the planes of isotropy in the outer layers are orthogonal to the plane of isotropy at the core. A closed form solution of the exact linear equations of elasticity was sought in terms of Frobenius power series. The influence of the core thickness on the dynamics of the wave motion is estimated from numerically computed dispersion curves. Prime consideration was given the asymmetric wave motion and the different types of waves which can occur are identified over a wide range of wave numbers.