Acoustic Wave Speed Research Articles

Analysis of Pressure Wave Model Predictions Considering Diesel Fuel Properties

Diesel fuel pressure wave inside Combination Electronic Unit Pump (CEUP) pipeline has been investigated using a 1D viscous damped mathematical model considering the effect of four key fuel properties including density, viscosity, acoustic wave speed and bulk modulus. Wave equation (WE) based mathematical model has been developed in MATLAB using finite difference method. Mathematical model results at various operating conditions of diesel engine have been verified by comparing with those of AMESim numerical model of CEUP and quantified through Root Mean Square Errors (RMSE) and Index of Agreements (IA). Dynamic variations of these fuel properties during fuel injection cycles have also been incorporated in mathematical model by utilizing empirical formulas. Predicted results show that simulated results which consider fuel properties dynamic variations as a function of pressure are more coherent to AMESim numerical model results.

Inviscid incompressible limits on expanding domains

We consider the inviscid incompressible limit of the compressible Navier–Stokes system on a large domain, the radius of which becomes infinite in the asymptotic limit. We show that the limit solutions satisfy the incompressible Euler system on the whole physical space R3 as long as the radius of the domain is larger than the speed of acoustic waves inversely proportional to the Mach number. The rate of convergence is estimated in terms of the Mach and Reynolds numbers and the radius of the family of spatial domains.

Feasibility Study of High Data Rate Underwater Optical Wireless Network

The present technology of acoustic underwater communication is a legacy of technology that provides low data rate transmission for medium range communication. In addition the speed of acoustic waves in the ocean is approximately 1500 m/sec so that long range communication involves high latency which poses a problem for a real time response and synchronization. In addition acoustic waves could distress marine mammals such as dolphins and whales. So the acoustic technology needs high data rate communication networks in real time. The growing need for underwater observation and subsea monitoring systems has stimulated considerable interest in advancing the enabling technologies of underwater wireless communication and underwater sensor networks. This communication technology is expected to play an important role in investigating climate change, in monitoring biological, biogeochemical, evolutionary and ecological changes in the sea, ocean and lake environments and in helping to control and maintain oil production facilities and harbours using unmanned underwater vehicles UUVs, submarines, ships, buoys and divers.

Localized micro- and nano-scale remodelling in the diabetic aorta

Diabetes is strongly associated with cardiovascular disease, but the mechanisms, structural and biomechanical consequences of aberrant blood vessel remodelling remain poorly defined. Using an experimental (streptozotocin, STZ) rat model of diabetes, we hypothesized that diabetes enhances extracellular protease activity in the aorta and induces morphological, compositional and localized micromechanical tissue remodelling. We found that the medial aortic layer underwent significant thickening in diabetic animals but without significant changes in collagen or elastin (abundance). Scanning acoustic microscopy demonstrated that such tissue remodelling was associated with a significant decrease in acoustic wave speed (an indicator of reduced material stiffness) in the inter-lamellar spaces of the vessel wall. This index of decreased stiffness was also linked to increased extracellular protease activity (assessed by semi-quantitative in situ gelatin zymography). Such a proteolytically active environment may affect the macromolecular structure of long-lived extracellular matrix molecules. To test this hypothesis, we also characterized the effects of diabetes on the ultrastructure of an important elastic fibre component: the fibrillin microfibril. Using size exclusion chromatography and atomic force microscopy, we isolated and imaged microfibrils from both healthy and diabetic aortas. Microfibrils derived from diabetic tissues were fragmented, morphologically disrupted and weakened (as assessed following molecular combing). These structural and functional abnormalities were not replicated by in vitro glycation. Our data suggest that proteolysis may be a key driver of localized mechanical change in the inter-lamellar space of diabetic rat aortas and that structural proteins (such as fibrillin microfbrils) may be biomarkers of diabetes induced damage.

Extracting effective medium properties for fish schools from resonator and free-field measurements

Resonator and free-field measurements were performed with both real and model fish schools in order to determine the relationship between fish school density and sound speed and absorption of acoustic waves. The results are compared to effective medium models for sound propagation through fish and encapsulated bubbles. The current species under study is Danio rerio (zebrafish); however, this technique can be extended to other fish species. [Work supported by ONR.]

On-Board Fuel Property Identification Method Based on High-Pressure Common Rail Pressure Signal

This paper investigates the impact of fuel property variations on the common rail pressure fluctuation in high-pressure common rail (HPCR) system and explores the possibility of identifying the fuel types based on the measurement of rail pressure for internal combustion engines. Fluid transients, particularly the water hammer effect in a HPCR system, are discussed and the 1D governing equations are given. A typical HPCR system model is developed in GT-Suite with the injectors, three-plunger high-pressure pump, and pressure control valve being modeled in a relatively high level of detail. Four different fuels including gasoline, ethanol, diesel, and biodiesel are modeled and their properties including density, bulk modulus, and acoustic wave speed are validated against data in the literature. Simulation results are obtained under different conditions with variable rail pressures and engine speeds. To reduce the excessive rail pressure oscillation caused by multiple injections, only four main-injections are enabled in each engine revolution. The results show that the natural frequency of a common rail varies with the type of fuel filled in it. By applying the fast Fourier transform (FFT) to the pressure signal, the differences of fuel properties can be revealed in the frequency domain. The experiment validation is conducted on a medium-duty diesel engine, which is equipped with a typical HPCR system and piezo-electric injectors. Tests results are given for both pure No. 2 diesel and pure soybean biodiesel at different rail pressure levels and different engine speeds. This approach is proved to be potentially useful for fuel property identification of gasoline-ethanol or diesel-biodiesel blends on internal combustion engines.

Scanning acoustic microscopy of biological cryosections: the effect of local thickness on apparent acoustic wave speed

ABSTRACTScanning acoustic microscopy (SAM), when applied to biological samples has the potential to resolve the longitudinal acoustic wave speed and hence stiffness of discrete tissue components. The heterogeneity of biological materials combined with the action of cryosectioning and rehydrating can, however, create variations in section topography. Here, we set out to determine how variations in specimen thickness influence apparent acoustic wave speed measurementsCryosections (5μm nominal thickness) of human skin biopsies were adhered to glass slides before washing and rehydrating in water. Multiple regions (200x200 μm; n = 3) were imaged by SAM to generate acoustic wave speed maps. Subsequently co-localised 30x30 μm sub-regions were imaged by atomic force microscopy (AFM) in fluid. The images were then registered using Image J. Each pixel was allocated both a height and wave speed value before their relationship was then plotted on a scattergram. The mean section thickness measured by AFM was 3.48 ± 1.12 (SD) μm. Regional height variations influenced apparent wave speed measurements. A 3.5 μm height difference was associated with a 400 ms-1 increase in wave speed. In the present study we show that local variations in specimen thickness influence apparent wave speed. We also show that a true measure of wave speed can be calculated if the thickness of the specimen is known at each sampling point.

Pressure Modeling of Combination Electronic Unit Pump Fuel Pipeline with Rapeseed Methyl Ester

An alternate biodiesel fuel Rapeseed Methyl Ester (RME) has been evaluated for diesel engine Combination Electronic Unit Pump (CEUP) fuel injection system. Pressure wave modeling of CEUP high pressure fuel pipeline using viscous damped wave equation has been done in MATLAB at various operating conditions of diesel engine. Finite Difference method has been used to model and simulate wave equation at eleven equidistant locations along fuel pipeline. Results show increase in pressure, density, acoustic wave speed and bulk modulus amplitudes with RME fuel as compared to conventional diesel fuel.

Nonlinear Modeling and Analysis of Pressure Wave inside CEUP Fuel Pipeline

Operating conditions dependent large pressure variations are one of the working characteristics of combination electronic unit pump (CEUP) fuel injection system for diesel engines. We propose a precise and accurate nonlinear numerical model of pressure inside HP fuel pipeline of CEUP using wave equation (WE) including both viscous and frequency dependent frictions. We have proved that developed hyperbolic approximation gives more realistic description of pressure wave as compared to classical viscous damped wave equation. Frictional effects of various frequencies on pressure wave have been averaged out across valid frequencies to represent the combined effect of all frequencies on pressure wave. Dynamic variations of key fuel properties including density, acoustic wave speed, and bulk modulus with varying pressures have also been incorporated. Based on developed model we present analysis on effect of fuel pipeline length on pressure wave propagation and variation of key fuel properties with both conventional diesel and alternate fuel rapeseed methyl ester (RME) for CEUP pipeline.

Transport and Mechanical Properties of High-ZT Mg2.08Si0.4−x Sn0.6Sb x Thermoelectric Materials

Mg2(Si,Sn) compounds are promising candidate low-cost, lightweight, nontoxic thermoelectric materials made from abundant elements and are suited for power generation applications in the intermediate temperature range of 600 K to 800 K. Knowledge on the transport and mechanical properties of Mg2(Si,Sn) compounds is essential to the design of Mg2(Si,Sn)-based thermoelectric devices. In this work, such materials were synthesized using the molten-salt sealing method and were powder processed, followed by pulsed electric sintering densification. A set of Mg2.08Si0.4−xSn0.6Sbx (0 ≤ x ≤ 0.072) compounds were investigated, and a peak ZT of 1.50 was obtained at 716 K in Mg2.08Si0.364Sn0.6Sb0.036. The high ZT is attributed to a high electrical conductivity in these samples, possibly caused by a magnesium deficiency in the final product. The mechanical response of the material to stresses is a function of the elastic moduli. The temperature-dependent Young’s modulus, shear modulus, bulk modulus, Poisson’s ratio, acoustic wave speeds, and acoustic Debye temperature of the undoped Mg2(Si,Sn) compounds were measured using resonant ultrasound spectroscopy from 295 K to 603 K. In addition, the hardness and fracture toughness were measured at room temperature.

Quantitative Evaluation of the Effect of Porosity on the Local Young’s Modulus of Isotropic Composites by Using the Laser Optoacoustic Method

An impulse acoustic method with a laser source of ultrasound is proposed and realized experimentally for a quantitative evaluation of the joint effect of porosity (the volume fraction of pores) and the concentration of dispersed filler on the local Young’s modulus of isotropic metal-matrix composite materials. The determination of Young’s modulus is based on the laser thermooptical excitation of ultrasound and measurements of the phase speed of longitudinal and shears acoustic waves in composite specimens. Silumin-matrix composite specimens reinforced with various volume fractions of silicon carbide (SiC) microparticles of the mean size of 14 μm were investigated. It was found that, to provide an effective growth in Young’s modulus by increasing the concentration of SiC, the porosity of a ready specimen should not exceed 2%. The technique developed allows one to carry out a nondestructive local testing of the acoustical and mechanical properties of composites in the actual state, which is necessary for a technological development and improvement of the fabrication process of the materials.

Numerical Simulation of Low Mach Number Steady and Unsteady Flow Past a Circular Cylinder with Preconditioning Method

Preconditioning techniques have become established as a useful technique for optimizing accuracy and efficiency of CFD solutions over a range of flow conditions. Specifically, at low Mach numbers, it is well known that the standard physical time derivatives lead to an ill-conditioned system due to the stiffness between the acoustic and particle wave speeds, which in turn results in degraded convergence and inaccurate discretization. With preconditioning, the pseudo-time derivatives scale the acoustic speeds so that they remain well conditioned at all Mach numbers. A low-diffusion preconditioning Roe scheme by using an adjustable parameter in preconditioning Roe scheme to control the numerical dissipation and the adjustable parameter value rules are proposed. Numerical results show the efficiency of the new scheme and the low Mach/Reynolds number steady and unsteady solutions of viscous flow past a circular cylinder are satisfied.

Pressure based first-principles study of the electronic, elastic, optic and phonon properties of zincblende InN

Generalized gradient approximation proposed by Perdew–Burke–Ernzerhof (GGA-PBE) is used to determine the effect of pressure on electronic, elastic, acoustic, optical and vibrational properties of zincblende InN along with the Ultra soft pseudopotential method. The structural properties show good consistency and stability at elevated pressures. The zincblende InN displays zero band gap and its metallicity maintains even at high pressures. The density of states appear in a quarterly divided region, where the contribution of different states have been discussed, and it is found that the peak positions are consistent with experimental L1, L3, K absorption and emission edges. The effect of pressure appears in strong hybridization due to which DOS above and below the Fermi level are shifting to the corresponding higher and lower energies due to p–d hybridization. The calculated elastic constants agree well with the literature. Except C44 and Cs, all others show an increasing trend with the pressure. Acoustic wave speeds have been calculated in [100], [110] and [111] directions with the help of elastic constants for the first time. For the optical properties, the main peaks of the imaginary part of dielectric function lie in close vicinity of experiment and shift to higher energies with a reduction in peak intensities when the pressure effects come into play. Similarly the absorption peaks are red shifted with respect to hydro-static pressure. The refractive index is maximum at lower energies and its magnitude reduces with pressure and the maximum value of energy loss function is obtained corresponding to minimum dielectric function. Phonon frequencies in high symmetry directions agree well with the only available first principle study. Except XTA, WTA, and LTA, all the other modes show an increase in phonon frequencies when pressure is exerted, this is further confirmed by Gruneisen parameters calculated for the first time.

Ionospheric disturbances induced by a missile launched from North Korea on 12 December 2012

AbstractIonospheric disturbances caused by a missile launched from North Korea on 12 December 2012 were investigated by using the GPS total electron content (TEC). The spatial characteristic of the front edge of V‐shaped disturbances produced by missiles and rockets was first determined. Considering the launch direction and the height of estimated ionospheric points at which GPS radio signal pierces the ionosphere, the missile passed through the ionosphere at heights of 391, 425, and 435 km at 0056:30, 0057:00, and 0057:30 UT, respectively. The observed velocities of the missile were 2.8 and 3.2 km/s at that time, which was estimated from the traveling speed of the front edge of V‐shaped disturbances. Westward and eastward V‐shaped disturbances propagated at 1.8–2.6 km/s. The phase velocities of the westward and eastward V‐shaped disturbances were much faster than the speed of acoustic waves reported in previous studies, suggesting that sources other than acoustic waves may have played an important role. Furthermore, the plasma density depletion that is often observed following missile and rocket launches was not found. This suggests that the depletion resulting from the missile's exhaust was not strong enough to be observed in the TEC distribution in the topside ionosphere.

A model for determination of effective permeability from acoustic wavespeed and attenuation in a rigid two‐phase porous medium

ABSTRACTWe propose a two‐phase permeability spherical inclusion model of mesoscopic heterogeneity for a rigid, porous acoustic medium, and apply the non‐self‐consistent theory to the scattered wave field from a single spherical inclusion to obtain the dispersion curves of phase velocity and attenuation factor (inverse quality factor) for the composite. We then determine the effective permeability from the wave frequency, complex velocity and other effective material parameters such as bulk modulus, porosity and fluid viscosity. Unlike other rigid double porosity models, our model shows that the host material and its volume fraction determine the acoustic velocity and attenuation, but there are additional attenuation peaks (we call them resonance peaks) in the inverse quality factor responses which are a possible indicator of the size of inclusions. Since the thermal relaxation frequency of the inclusion material actually does not affect the wave behaviour of the composite, the effective dynamic permeability is easily calculated from the velocity and attenuation. This result is compared with other measures of effective dynamic permeability, deduced from the effective hydraulic permeability by replacing the permeability of the components with their dynamic values as determined from the Johnson model. We find that for frequencies lower than the resonance frequency, this dynamic permeability model is very similar to that determined from the scattering model of this paper. However, the model which uses the arithmetic mean of the constituents is not valid for inclusions having higher permeability than the host phase whereas the model which uses the harmonic mean is not valid for inclusions having lower permeability than that of the host material. We have checked the validity of the effective dynamic permeability and its applicability to rocks encountered in both near surface and petroleum seismic exploration.

Apparatus for measurement of acoustic wave propagation under uniaxial loading with application to measurement of third-order elastic constants of piezoelectric single crystals

We describe an apparatus for the measurement of acoustic wave propagation under uniaxial loading featuring a special mechanism designed to assure a uniform mechanical load on a cube-shaped sample of piezoelectric material. We demonstrate the utility of the apparatus by determining the effects of stresses on acoustic wave speed, which forms a foundation for the final determination of the third-order elastic constants of langasite and langatate single crystals. The transit time method is used to determine changes in acoustic wave velocity as the loading is varied. In order to minimize error and improve the accuracy of the wave speed measurements, the cross correlation method is used to determine the small changes in the time of flight. Typical experimental results are presented and discussed.

AlN film deposition as a semiconductor device

AlN films were deposited by pulsed laser deposition (PLD) using an Nd: YAG laser (λ = 1064 nm). The films were deposited in a nitrogen atmosphere as working gas; the cathode was an aluminium high purity (99.99%) target. The films were deposited using 7 J/cm2 laser fluence for 10 minutes on silicon (100) substrates. The working pressure was 9x10-3 mbar and the substrate temperature was varied from 200°C to 630°C. The thickness measured by profilometer was 150 nm for all films. Moreover, surface acoustic wave (SAW) devices with a Mo/AlN/Si configuration have been fabricated using AlN-buffer and Mo Channel. The films’ morphology and composition were studied using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), respectively. The films’ optical reflectance spectra and colour coordinates were obtained by optical spectral reflectometry in the 400-900 cm-1 range using an Ocean Optics 2000 spectrophotometer. The present work found clear dependence on morphological properties, reflectance, dominant wavelength colour purity, frequency response and acoustic wave speed in terms of the temperature applied to the substrate. About 30% reduction in reflectance was observed and increased acoustic wave speed of about 1.3 % when the temperature was increased from 200°C to 630°C.

Electronic, elastic, acoustic and optical properties of cubic TiO2: A DFT approach

The electronic, elastic, acoustic and optical properties of cubic phases TiO2 fluorite and pyrite are investigated using the first principles calculations. We have employed five different exchange–correlation functions within the local density and generalized gradient approximations using the ultrasoft plane wave pseudopotential method. The calculated band structures of cubic-TiO2 elucidate that the TiO2 fluorite and pyrite are direct and indirect semiconductors in contrast to the previous findings. From our studied properties such as bulk and shear moduli, elastic constants C44 and Debye temperature for TiO2 fluorite and pyrite, we infer that both the cubic phases are not superhard materials and the pyrite phase is harder than fluorite. The longitudinal and transversal acoustic wave speeds for both phases in the directions [100], [110] and [111] are determined using the pre-calculated elastic constants. In addition, we also calculate the optical properties such as dielectric function, absorption spectrum, refractive index and energy loss function using the pre-optimized structure. On the observation of optical properties TiO2 fluorite phase turn out to be more photocatalytic than pyrite.

Bohm criterion in a dusty plasma with nonextensive electrons and cold ions

The Bohm criterion in a dusty plasma containing nonextensively distributed electrons and cold ions is investigated within the framework of probe model including the effects of dust charge fluctuation. It is shown that the critical Mach number upshifts with the decrease of electron nonextensive parameter (qe) and the increase of the ion-to-electron number density ratio (Rn) when the effects of dust charge fluctuation are out of consideration. Once the effects of dust charge fluctuation are included, with the increase of Rn, the critical Mach number increases first, then decreases. The slop of the critical Mach number curves in the region Rn≫1 for qe>1 becomes more gradual than that for qe<1. When critical Mach number is defined with respect to modified ion acoustic wave speed, it should be larger than unity in the case free of dust charge fluctuation. Whereas when Rn≫1, it may be smaller than unity due to the effect of dust charge fluctuation.

Ion holes in the hydrodynamic regime in ultracold neutral plasmas

We describe the creation of localized density perturbations, or ion holes, in an ultracold neutral plasma in the hydrodynamic regime, and show that the holes propagate at the local ion acoustic wave speed. We also observe the process of hole splitting, which results from the formation of a density depletion initially at rest in the plasma. One-dimensional, two-fluid hydrodynamic simulations describe the results well. Measurements of the ion velocity distribution also show the effects of the ion hole and confirm the hydrodynamic conditions in the plasma.