Acoustic Medium Research Articles

Tracking Rayleigh–Bloch waves swapping between Riemann sheets

Rayleigh–Bloch waves are modes localized to periodic arrays of scatterers with unbounded unit cells. Here, Rayleigh–Bloch waves are studied for line arrays of sound-hard circular scatterers embedded in a two-dimensional acoustic medium, for which it has recently been shown that Rayleigh–Bloch waves exist for higher frequencies than previously thought. Moreover, it was shown that Rayleigh–Bloch waves can cut off (disappear) and cut on (reappear), and additional Rayleigh–Bloch waves can cut on and interact with the existing ones. These complicated behaviours are reconsidered using a family of quasi-periodic Green’s functions that allow particular plane-wave components to become unbounded away from the array. The Green’s function formulation is combined with the block Sakurai–Sugiura method to trace the trajectories of the Rayleigh–Bloch wavenumbers as they swap between Riemann sheets that are categorized according to the unbounded plane wave(s). A detailed analysis is presented for three different scatterer radius values, and contrasting qualitative behaviours are identified. The findings are consistent with those published previously, extend to higher frequencies than allowed by the previous approach, and provide new understanding of Rayleigh–Bloch waves around the critical frequency intervals where they cut on/cut off/interact.

Framework of acoustic analysis and shape optimization for three-dimensional doubly periodic multilayered structures

In this research, a framework of acoustic analysis and shape optimization, based on isogeometric boundary element method (IGA-BEM), is proposed for three-dimensional doubly periodic multilayered structures. The study addresses a gap in the literature by focusing on the shape optimization of such structures, which has not been extensively explored previously. The interface between different acoustic media is an infinite doubly periodic surface, which can be constructed by an open non-uniform rational B-splines. A periodic IGA-BEM is developed for the sound field analysis of the doubly periodic multilayered structure, in which the Ewald method is used to accelerate the calculation of periodic Green function. Furthermore, the shape derivative of the doubly periodic multiple boundaries is derived by imposing boundary perturbation and using the adjoint variable method. The control points of the NURBS surfaces are defined as the shape design variables, and all shape sensitivities can be quickly calculated by discretizing the shape derivative formula. Finally, in according with shape sensitivities, the corresponding shape optimization problem is solved by the method of moving asymptotes, so that the optimized shape design can be obtained. A series of numerical examples validates the accuracy and applicability of the proposed approaches.

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.

Image-domain least-squares imaging in an elastic vertically transversely isotropic medium: Multiparameter point-spread function deconvolution

By solving a linear inverse problem, least-squares migration (LSM) can provide higher-precision images of complex subsurface structures than traditional adjoint-operator-based migration. LSM can be conducted in the data domain and the image domain (IDLSM). IDLSM in acoustic media has been extensively studied, commonly using single-parameter point-spread function (PSF) deconvolution. For high-accuracy imaging of complex media, we develop an image-domain elastic least-squares imaging method using multiparameter PSF deconvolution for vertically transversely isotropic (VTI) media. The multiparameter PSFs, including P-P, P-S, S-P, and S-S components, are calculated on a sparse grid using elastic VTI wave equation Born modeling and migration. The traditional migration result is then decomposed into individual local results, each corresponding to the size of a single PSF, through unit partitioning. Finally, a set of filters is derived from four elastic VTI PSF components to approximate the Hessian inverse, which are subsequently assembled to reconstruct an entire deconvolved image. The numerical experiments confirm that our method can significantly decrease multiparameter crosstalk artifacts and improve spatial resolution and amplitude fidelity.

Synchronization of bowhead whales

Inferring animal behavior from irregular tracking data is a challenging area of research. It is particularly difficult to determine if whales, who intermittently explore different depths while staying in the same acoustic medium, synchronize their days with their prey and each other over kilometer-scale distances. Here, we aim to better understand the diving behavior of bowhead whales () in Disko Bay, West Greenland, using the largest high-frequency dive-depth dataset to date (144 days at 1 Hz from 12 different whales) and nonlinear dynamics, whereby we consider the whales to be chaotic (aperiodic) oscillators. We find that foraging whales dive deeper during the daytime in spring, with this diving behavior being in apparent synchrony with their vertically migrating prey. Furthermore, we demonstrate that bowhead whales can synchronize their behavior with each other for up to a week while staying within a range of up to ∼100km. This discovery agrees with the acoustic herd theory of long-range signaling in baleen whales. On the other hand, the synchrony might emerge when animals experience similar ecological conditions, which are, however, difficult to name because targeted depths and locations were separated for hundreds of meters and tens of kilometers, respectively. In this paper, we identify a framework for studying the sociality and behavior of such chaotically moving, unrestrained marine animals and call for more simultaneous tagging campaigns. Published by the American Physical Society 2024

A cell-centered implicit finite difference scheme to study wave propagation in acoustic media: A numerical modeling

In the present paper, we present a Cell-Centered Implicit Finite Difference (CCIFD) operator-based numerical scheme for the propagation of acoustic waves that is very effective, accurate, and small in size. This scheme requires fewer estimation points than the traditional central difference derivative operator. Any numerical simulation is significantly impacted by the precision of a numerical derivative. Long stencils can deliver excellent accuracy while also minimizing numerical anisotropy error. However, a long stencil requires a lot of computational resources, and as these derivatives get bigger, they could start to look physically unrealistic due to contributions from nodes located extremely far, wherein the derivative is local in nature. Furthermore, using such lengthy stencils at boundary nodes may result in errors. The present article investigates a cell-centered fourth order finite difference scheme to model acoustic wave propagation which utilizes a lesser number of nodes in comparison to the traditional Central Difference (CD) operator. However, in general the implicit derivative operator has high computational cost and therefore despite its significant advantages it is generally avoided to be implemented in applications. This serves as a motivation for the present paper to explore a technique called CCIFD that significantly decreases the computational expense by nearly fifty percent. Additionally, spectral characterization of the CCIFD derivative operator has been analyzed and discussed. Finally, the wave propagation has been numerically simulated in 2-dimensional homogeneous and Marmousi model using CCIFD scheme to validate the applicability and stability of the scheme.

Valley edge states with opposite chirality in temperature dependent acoustic media

The valley degree of freedom in phononic crystals and metamaterials holds immense promise for manipulating acoustic and elastic waves. However, the impact of acoustic medium properties on valley edge state frequencies and their robustness to one-way propagation in valley topological phononic crystals remains unexplored. While significant attention has been devoted to scatterer design embedded in honeycomb lattices within acoustic and elastic media to achieve valley edge states and topologically protected nontrivial bandgaps, the influence of variations in acoustic medium properties, such as wave velocity and density affected by environmental temperature, has been overlooked. In this study, we investigate the effect of valley edge states and topological phases exhibited by topological phononic lattices in a temperature-dependent acoustic medium. We observe that a decrease in wave velocity and density, influenced by changing environmental temperature, shifts the topological valley edge states to lower frequencies. Therefore, alongside phononic lattice design, it is crucial to consider the impact of acoustic medium properties on the practical application of acoustic topological insulators. This issue becomes particularly significant when a topological phononic crystal is placed in a wave medium that transitions from incompressible to compressible, where wave velocity and density are no longer constant. Our findings offer a novel perspective on investigating topological insulators in variable acoustic media affected by changing thermodynamic and fluid properties.

Effect of Acoustic Enclosure on the Sound Transmission Loss of Multi-Layered Micro-Perforated Plates

This study presents an examination of the transmission properties of multilayered partitions made up of multiple micro-perforated plates (MPPs) coupled to acoustic enclosures with general impedance boundaries. Multi-layered MPPs can lower the transmission while minimizing reflection in the source and receiving enclosure. Previous research has mainly focused on the double MPPs or triple MPPs partition itself. However, it is vital to analyze the in-situ sound transmission loss of the multi-layered MPP and their efficiency in a complex vibro-acoustic environment. The case when the multilayered MPPs are coupled to a receiving enclosure or coupled to both a source and receiving enclosure is investigated. The objective is to provide an analytical method to evaluate the transmission properties of multilayered MPPs coupled to acoustic enclosures while being computationally more efficient than the finite element method (FEM). Using the modified Fourier series for the acoustic pressure, a variational form for the acoustic and structure medium yields a completely coupled vibroacoustic system. A comparison between the sound transmission loss of the double MPPs, when mounted on an impedance tube and coupled to acoustics enclosures, shows the modal effect of the enclosures. The effect of enclosure shape, impedance boundary, perforation ratio, air gap thickness on the sound transmission properties of the double MPPs structure is examined for both cases. Finally, in both situations, the performance of triple MPP structure insulation is evaluated.

A novel hybrid SBM-MFS methodology for acoustic wave propagation problems

In this paper, a novel hybrid meshless approach that combines the singular boundary method (SBM) and the method of fundamental solutions (MFS) to deal with two-dimensional (2D) exterior acoustic wave propagation problems is proposed and studied. The methodology is particularly devised to solve problems with complex boundary geometries containing geometric singularities such as corners and sharp edges. It employs the SBM to model intricate segments of these geometries and the MFS for the smooth ones. The proposed hybrid SBM-MFS method is studied in a 2D context in the framework of three benchmark examples involving acoustic radiation problems of circular-, square- and L-shaped objects in a full-space acoustic medium. In addition, the applicability of the proposed hybrid SBM-MFS methodology to predict the acoustic performance of a T-shaped thin barrier is also investigated. These examples are specifically designed to assess the feasibility, validity and accuracy of the hybrid SBM-MFS approach in comparison with the available analytical solutions and alternative numerical strategies such as the MFS, the SBM and the boundary element method (BEM). Numerical simulations demonstrate that the proposed method can match the level of accuracy of the MFS while keeps the robustness of the SBM when dealing with complex geometries, overcoming one the most important drawbacks of the traditional MFS. Moreover, the proposed hybrid SBM-MFS naturally avoids the non-uniqueness problem arising at the fictitious eigenfrequencies associated with the corresponding interior problems, a feature that neither the SBM nor the BEM inherently possesses.

Vibroacoustic analysis of submerged fluid-filled cylindrical shell

This study presents a comprehensive Chebyshev-Fourier spectral method for analyzing the free and forced vibroacoustic characteristics of submerged fluid-filled cylindrical shells in heavy fluids. The vibroacoustic interaction system of submerged cylindrical shells consists of three discrete regions: The Sanders shell theory is applied for the shell structure, whereas the wave equation is used to determine the fluid inside. The external fluid pressure on the shell is described using the Helmholtz boundary integral equation. The governing equations for the shell's motion, the formulation of the external fluid pressure on the fluid-structure-interaction (FSI) surface using first-class Chebyshev polynomial and Fourier series expansions, and the internal sound pressure employing two-dimensional Chebyshev polynomial and Fourier series expansions, are seamlessly integrated with Gauss-Chebyshev-Lobatto sampling techniques. Artificial springs are implemented to replicate the boundary conditions of the cylindrical shell. The precision of the proposed methodology is corroborated by comparisons with existing literature and finite element method (FEM) results. Furthermore, the research examines how the properties of the acoustical medium on the vibroacoustic responses of the cylindrical shell. Results indicate that the presence of air inside the shell slightly influence on its acoustic radiation. However, replacing the internal medium with water significantly alters the shell's original radiation characteristics.

On the singularity point in acoustic orthorhombic media

Abstract The acoustic orthorhombic model is widely used in seismic modeling and processing of P-wave data. However, the anisotropic acoustic models have so called S-wave artifacts (1 artifact in transversely isotropic acoustic medium and two artifacts in orthorhombic acoustic medium). I show that S-wave artifacts can have one singularity point that results in complications in polarization field and the group velocity surface. The conditions of the existence of this point are defined in terms of anellipticity parameters. This singularity point and its group velocity image are the objects of my analysis.

Abstract 6331: A novel automated platform for rapid manufacturing of CAR T cells

Abstract Autologous cell therapy using genetically modified T cells to express chimeric antigen receptor (CAR) has yielded durable responses in cancers patients. However, currently only a small portion of patients are privileged to receive the treatment. High cost and long manufacturing time contribute to the key limitations prohibiting cell therapy broad adoption. Researchers discovered that reducing ex vivo culture improves anti-tumor activity of CAR T cells1 and recently demonstrated the process of generating functional CAR T cells within 24 hours2. This rapid process provides great promise in cost reduction of CAR T therapy and opportunity to have cells manufactured in close-to-patient settings. CART cell manufacturing process involves: (1) collection of peripheral blood; (2) isolation of T cells; (3) performing transduction via viral vector; (4) washing CAR T cells to remove viral vector, and (5) harvesting CAR T cells in IV fluid. Conventional process uses magnetic separation and serial centrifugation technologies on multiple platforms with manual operations. Here we demonstrate the feasibility of rapid manufacturing CAR T cells on an automated platform with closed fluidics without centrifugation steps. The platform, MARS® Atlas, is built with innovative technologies in immune-magnetic cell isolation and acoustic cell washing and implemented as a modular system. In this feasibility test, T cells were isolated from peripheral blood from a healthy donoron MARS® magnetic module. eGFP expressing lentivirus were added to the enriched T cells. After short incubation, cells and virus were washed with fresh medium on the MARS® acoustic module and cells were incubated with virus overnight without activation. Infected cells were washed on the acoustic module to remove free virus. Product CAR T cells were harvested in saline solution and ready for QC analysis. Starting from 20mL of peripheral blood, magnetic T cell separation was done 2mL/min achieving 90% T cell purity, 90% recovery. In the first acoustic wash, medium exchange of the mixture of cells and virus took place at 0.9mL/min flow rate. As a result, 90% removal of contaminating molecule and 99.6% recovery of T cells were achieved. The second acoustic wash completed medium exchange of transfected cells at 0.9mL/min with 96.7% removal of virus and 90% CAR T cell recovery. As a result, 18 million GFP expressing T cells were produced. In this study we have demonstrated the feasibility of rapidly manufacturing CAR-T cells on an automated platform MARS® Atlas. This result indicates the MARS® Atlas being a potential CAR T manufacturing platform to be used in close-to-patient settings to enable low-cost cell therapy. 1 Saba Ghassemi, Reducing Ex Vivo Culture Improves the Antileukemic Activity of Chimeric Antigen Receptor (CAR) T Cells, Cancer Immunol Res; 6(9) September 2018 2 Saba Ghassemi, Rapid manufacturing of non-activated potent CAR T cells, Nature Biomedical Engineering | VOL 6 | February 2022 | 118-128 Citation Format: Silin Sa, Ethan Nguyen, Jie Pan, Liping Yu. A novel automated platform for rapid manufacturing of CAR T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6331.

On seismic gradiometric wave equation inversion for density

SUMMARY Material density remains poorly constrained in seismic imaging problems, yet knowledge of density would provide important insight into physical material properties for the interpretation of subsurface structures. We test the sensitivity to subsurface density contrasts of spatial and temporal gradients of seismic ambient noise wavefields, using wave equation inversion (WEI), a form of seismic gradiometry. Synthetic results for 3-D acoustic media suggest that it is possible to estimate relative density structure with WEI by using a full acoustic formulation for wave propagation and gradiometry. We show that imposing a constant density assumption on the medium can be detrimental to subsurface seismic velocity images. By contrast, the full acoustic formulation allows us to estimate density as an additional material parameter, as well as to improve phase velocity estimates. In 3-D elastic media, severe approximations in the governing wave physics are necessary in order to invert for density using only an array of receivers on the Earth's free surface. It is then not straightforward to isolate the comparatively weak density signal from the influence of phase velocity using gradiometric WEI. However, by using receivers both at the surface and in the shallow subsurface we show that it is possible to estimate density using fully elastic volumetric WEI.

Ocean bottom dual-sensorQ-compensated elastic least-squares reverse time migration based on acoustic and separated-viscoelastic coupling equations

The ocean bottom dual-sensor (OBD) observation system places water detectors (pressure sensors) and land detectors on the irregular seabed interface to receive acoustic pressure fields and elastic wavefields, respectively. These data are usually applied to effectively remove ghost waves and ringing interference in the seawater layer, rather than being jointly used for migration. We propose an ocean bottom dual-sensor viscoacoustic and separated-viscoelastic coupled Q-compensated least-squares reverse time migration (OBD-VSV- QLSRTM) in curvilinear coordinates. In this method, to solve the Q-compensated elastic inverse problem, we jointly use the recorded acoustic pressure and elastic multicomponent seismic data from the OBD observation system. A new misfit function in the sense of least-squares inversion is constructed based on viscoacoustic and separated viscoelastic wavefields. Acoustic and separated viscoelastic equations are used to describe the acoustic wavefield in the acoustic medium and the Q-compensated P and S wavefields in the underlying viscoelastic medium, respectively. On the acoustic-viscoelastic interface, we implement a stable governing equation to ensure continuous and steady transmission of Q-compensated stresses in the subseabed and pressure in the seawater. To address the irregular seabed problem, we mesh the acoustic-viscoelastic models onto curvilinear grids and apply coordinate transformations to map the models and equations to a new curvilinear coordinate system. We derive viscoacoustic and separated-viscoelastic coupled adjoint and demigration operators in the curvilinear coordinates, enabling linear acoustic-viscoelastic modeling and stable receiver-side back-propagated wavefield continuation. Numerical examples conducted on two typical acoustic-viscoelastic models demonstrate that our proposed OBD-VSV- QLSRTM in curvilinear coordinates can produce highly accurate P- and S-wave images efficiently.

Thermoacoustic performance of 100 kHz wide-band packaged projector in water tank with three-dimensional graphene

This paper presents the demonstration of underwater thermoacoustic (TA) sound generation using three-dimensional graphene (3D-C). 3D-C is able to interface with water as the immediate acoustic medium, resulting in reduced attenuation across solid packaging encapsulation due to favorable acoustic impedance matching. This is shown using array configurations of 2*2 and 4*4 individual 3D-C elements prepared onto printed circuit boards and secured within a watertight cuboid Delrin container with deionized water. Comparisons of underwater acoustic performance between internal medium of water and air shows significant improvement in measured sound pressure level (SPL) with internal water medium, in contrast with internal air medium where SPL were below noise floor. This demonstration opens up new possibilities of 3D-C for underwater acoustic applications. Simulations are conducted using 3D finite element model generated with COMSOL Multiphysics and validated with experimental results. A revised formulation of transmission voltage response (TVR) specific to TA sound generation is proposed due to the difference in power scaling of TA sound generation and subsequently validated using simulation.

Modelling the Propagation of Underwater Acoustic Signals of a Marine Energy Device Using Finite Element Method

Today a large number of marine based energy devices are been deployed rapidly across coastal areas of the world’s oceans to harness the huge natural energy and power potential provided by nature. These devices produce sound signals at high sound pressure levels across a wide range of frequencies that could be detrimental to the health and livelihood of marine animals. This paper proposes a computer model that simulates the emission of acoustic signals produced by a wave energy device. It analyses these signals with the aid of the audiogram of marine mammals, in this case the Harbour seal. This enables us to estimate the levels of acoustic noise experienced by marine mammals due to the presence of ocean deployed devices. Propagation of the acoustic signals underwater was modelled with boundary conditions using the finite element method. These include the bathymetry (features of underwater terrain) of the deployment site and properties of the propagation media. The type of spreading of the acoustic signals, and their interaction with the bottom surface interface of the acoustic enviroment was also taken into consideration. The effect of the bottom surface of the acoustic medium was seen to affect the sound pressure level (SPL) values as the sound receiver moves away from the source.

Carbon nanofibers/liquid metal composites for high temperature laser ultrasound

As the demand for clean energy becomes greater worldwide, there will also be an increasing demand for next generation nuclear power plants that incorporate advanced sensors and monitoring equipment. A major challenge posed by nuclear power plants is that, during normal operation, the reactor compartment is subjected to high operating temperatures and radiation flux. Diagnostic sensors monitoring such structures are also subject to temperatures reaching hundreds of degrees Celsius, which puts them at risk for heat degradation. In this work, the ability of carbon nanofibers to work in conjunction with a liquid metal as a photoacoustic transmitter was demonstrated at high temperatures. Fields metal, a Bi-In-Sn eutectic, and gallium are compared as acoustic mediums. Fields metal was shown experimentally to have superior performance over gallium and other reference cases. Under stimulation from a low fluence 6 ns pulse laser at 6 mJ/cm2 with 532 nm green light, the Fields metal transducer transmitted a 200 kHz longitudinal wave with amplitude >5.5 times that generated by a gallium transducer at 300 °C. Each high temperature test was conducted from a hot to cold progression, beginning as high as 300 °C, and then cooling down to 100 °C. Each test shows increasing signal amplitude of the liquid metal transducers as temperature decreases. Carbon nanofibers show a strong improvement over previously used candle-soot nanoparticles in both their ability to produce strong acoustic signals and absorb higher laser fluences up to 12 mJ/cm2.

Linearized waveform inversion for vertical transversely isotropic elastic media: Methodology and multi-parameter crosstalk analysis

Seismic migration and inversion are closely related techniques to portray subsurface images and identify hydrocarbon reservoirs. Seismic migration aims at obtaining structural images of subsurface geologic discontinuities. More specifically, seismic migration estimates the reflectivity function (stacked average reflectivity or pre-stack angle-dependent reflectivity) from seismic reflection data. On the other hand, seismic inversion quantitatively estimates the intrinsic rock properties of subsurface formulations. Such seismic inversion methods are applicable to detect hydrocarbon reservoirs that may exhibit lateral variations in the inverted parameters. Although there exist many differences, pre-stack seismic migration is similar with the first iteration of the general linearized seismic inversion.Usually, seismic migration and inversion techniques assume an acoustic or isotropic elastic medium. Unconventional reservoirs such as shale and tight sand formation have notable anisotropic property. We present a linearized waveform inversion (LWI) scheme for weakly anisotropic elastic media with vertical transversely isotropic (VTI) symmetry. It is based on two-way anisotropic elastic wave equation and simultaneously inverts for the localized perturbations (ΔVp0/Vp0,ΔVs0/Vs0,Δϵ,Δδ) from the long-wavelength reference model. Our proposed VTI-elastic LWI is an iterative method that requires a forward and an adjoint operator acting on vectors in each iteration. We derive the forward Born approximation operator by perturbation theory and adjoint operator via adjoint-state method. The inversion has improved the quality of the images and reduces the multi-parameter crosstalk comparing with the adjoint-based images. We have observed that the multi-parameter crosstalk problem is more prominent in the inversion images for Thomsen anisotropy parameters. Especially, the Thomsen parameter δ is the most difficult to resolve. We also analyze the multi-parameter crosstalk using scattering radiation patterns.The linearized waveform inversion for VTI-elastic media presented in this article provides quantitative information of the rock properties that has the potential to help identify hydrocarbon reservoirs.

Experimental study of acoustic streaming induced by a sharp edge at different frequencies and vibrating amplitudes

Acoustic streaming is the time-averaged flow induced by acoustic waves inside the fluid medium. Much attention has been paid to the streaming flow at the microscale, with the rapid development of micro-fluidics and significant demand for the microscale manipulation of fluid or particles. Recently, the streaming flow at the audible or lower frequency (10 Hz~10 kHz) has been found to be closely associated with local structures, like a sharp edge in the micro-channel. By its strong magnitude and low cost, this kind of streaming flow has been applied in various fields. However, the mechanisms behind this non-classical Rayleigh streaming are still not very clear, though its high sensitivity to the thickness of the acoustic boundary-layer and unstable streaming pattern under high forcing amplitude have been demonstrated. In this study, experimental work has been conducted, with the help of the particle imaginary velocimetry platform, to reveal the influence of frequency and vibrating amplitude on the streaming flow field around a sharp edge with 90?, and its characterized spatial dimension. The scaling law concerning the vibration amplitude and streaming velocity has been come up with, and the parameter frequency is also included. The expression f ?1/6va2~vsy,max demonstrates a good prediction in terms of the streaming magnitude, in comparison with experimental results.

A meshfree approach for vibro-acoustic analysis of combined composite laminated shells with variable thickness

The vibro-acoustic responses of combined composite laminated shell structures with variable thickness immersed in acoustic medium is investigated by using a meshfree method in this paper. The theoretical model of structural field is established by employing the energy principle in conjunction with the first-order shear deformation theory (FSDT) and the theoretical model of acoustic field are established by using Kirchhoff-Helmholtz integral equation. The displacement components of shell segments and the sound pressure variables of acoustic medium are described by using the meshfree Tchebychev point interpolation (TPIM) shape function and Double Fourier series in meridional and circumferential directions. The non-uniqueness problem of Kirchhoff-Helmholtz integral equation is overcome by adopting CHIEF method. The validation of the presented theoretical model is proved by comparing the results calculated by the proposed model with those results of existing literature and FEM/BEM. Based on the established theoretical model, vibro-acoustic responses of combined composite laminated shell structures with variable thickness immersed in acoustic medium are performed by analyzing the influences of thickness parameter, external load and boundary condition on the sound pressure level (SPL) and sound power level (SWL) of combined composite laminated shell structures. The above investigations can provide the theoretical thesis and technique guidance of preliminary design of combined composite laminated shell immersed in various acoustic medium.