Small Amplitude Pressure Research Articles

Controlled mean dynamics of red blood cells by two orthogonal ultrasonic standing waves

A computational model is developed to study the time-averaged mean dynamics of red blood cells (RBCs) driven by the time-averaged mean stress generated by two phase-shifted orthogonal ultrasonic standing waves in a viscous fluid. The cell is modelled as an ellipsoidal viscoelastic membrane enclosing the viscous fluid cytoplasm, the motion of which is described by the inclination angle of the ellipsoidal cell shape and the phase angle of the potential membrane cycle. Based on the acoustic perturbation method, the acoustic field and acoustic streaming field are solved to obtain the time-averaged mean stress, and then the temporal evolution equations of the inclination and phase angles of the cell are determined considering the torque balance and energy conservation. At a small acoustic pressure amplitude, this model reproduces the experimentally observed features of cell motion in orthogonal standing waves: the transition from steady stationary orientation to unsteady tumbling with the increase of the phase difference between the two standing waves. By turning up the acoustic pressure amplitude above a critical value, it is further predicted that the previously observed motions can be accompanied by the membrane tank-treading rotation. Observations of these motions, combined with the present computational model, can help to evaluate the mechanical properties of RBC membranes in an automated and high-throughput manner by acoustic methods.

Kiel Probes for Stagnation Pressure Measurement in Rotating Detonation Combustors

Kiel probes have the potential to be a versatile tool for determining stagnation pressure gain in rotating detonation combustors (RDCs), accompanying the commonly used equivalent available pressure method. Although average pressure gain values determined with Kiel probes are comparable to those from thrust stand experiments, one can expect several sources of measurement error from the unsteady trans- and supersonic environment. This work investigates the response of a Kiel probe in highly unsteady flow, similar to what would be encountered in an RDC. The probe is subjected to an underexpanded starting jet behind an incident shock with Mach numbers of 1.6–2.7, emanating from a shock tube with a reservoir ratio of about 394. The incidence angle of the probe is varied between 0 and 90 deg, as is the probe’s axial location with respect to the tube’s exit plane. High-speed schlieren images reveal the Mach number of the moving shock wave and the structure of the detached bow shock at the Kiel head, which is similar to that of a bluff body. It is shown that the measured stagnation pressure signal is independent of inflow angle over a range of , and that signal attenuation is caused by gas processing through the bow shock and viscous losses in the probe’s capillary. The frequency response of the Kiel probe to sinusoidal, small-amplitude pressure fluctuations is determined in an acoustic calibration facility up to 5500 Hz, confirming linear behavior and that no unwanted resonance is present in the probe. A Berg–Tijdeman representation delivers amplitude ratio and phase lag of comparable magnitude. An assessment of representative boundary conditions reveals that the average stagnation pressure measurement error is of the order of 1%.

Investigation of the turbulent structure in a flame and the effect of small infrasonic exposure on it using IR thermography methods

The paper presents the results of studies of gasoline and diesel fuel diffusion combustion using IR thermography methods. Experimental results of the effect of small amplitude pressure pulsations with various frequencies on the spectra of temperature changes in the flame and other characteristics are obtained. It is shown that the effect of pressure pulsations with certain frequencies leads to a change in the flame height, fuel burning-up rate and the appearance of characteristic frequency maximum in the spectra of temperature changes in the flame.

Forced convection with unsteady pulsating flow of a hybrid nanofluid in a microchannel in the presence of EDL, magnetic and thermal radiation effects

An unsteady force convection flow of a hybrid nanofluid flow driven in a microchannel by an applied time-dependent periodic pressure gradient in the presence of electric double layer, magnetic field, and thermal radiation effects is studied. Few attentions have been paid to investigate such pressure driven flow in micro-scale though they could be very important in practical applications. In our configuration, the Boltzmenn-Poisson's equation is employed to describe the electrostatic potential, while the reduced Navier-stokes equations based on small pressure amplitude assumption are applied to depict the conservations of momentum and thermal energy. Analytical solutions for all fields are obtained. The influences of physical parameters such as the Debye-Hückel parameter, the Hartmann number, the angular velocity, and the thermal radiation parameter on both steady and unsteady components of the velocity and temperature profiles are presented and discussed. Results show that hybrid nanofluids hold almost the same behaviours as conventional nanofluids. Therefore it is expected to replace conventional nanofluids by hybrid nanofluids for design of cheaper and higher performance heat exchangers or cooling systems and so on.

Dynamic behavior of intermittent combustion oscillations in a model rocket engine combustor

We experimentally study the dynamic behavior of intermittent combustion oscillations by time series analysis in terms of nonlinear forecasting, symbolic dynamics, and statistical complexity, including the detection of the change in dynamical state based on symbolic dynamics and graph networks. We observe sudden switching back and forth between irregular small-amplitude and regular large-amplitude pressure fluctuations. The nonlinear local prediction method, permutation spectrum test, and the Rényi complexity–entropy curve clearly identify the possible presence of chaotic dynamics in small-amplitude pressure fluctuations during intermittent combustion oscillations. The network entropy in ordinal partition transition networks allows us to capture a significant change in dynamical state switching between chaotic oscillations and noisy limit cycle oscillations.

Early detection of thermoacoustic combustion oscillations using a methodology combining statistical complexity and machine learning.

We conduct an experimental study on early detection of thermoacoustic combustion oscillations using a method combining statistical complexity and machine learning, including the characterization of intermittent combustion oscillations. Abrupt switching from aperiodic small-amplitude oscillations to periodic large-amplitude oscillations and vice versa appears in pressure fluctuations. The dynamic behavior of aperiodic small-amplitude pressure fluctuations represents chaos. The complexity-entropy causality plane effectively captures the subtle changes in the combustion state during a transition to well-developed combustion oscillations. The feature space of the complexity-entropy causality plane, which is obtained by a support vector machine, has potential use for detecting a precursor of combustion oscillations.

Fragmentation of cavitation bubble in ultrasound field under small pressure amplitude.

In the present study, dynamic behavior and fragmentation mechanism of acoustic cavitation bubbles are investigated under relatively small pressure amplitudes of ultrasonic wave through a three-dimensional compressive multiphase flow simulation and experimental observations. It is found that the oscillating bubble takes a non-spherical shape soon after occurring the Rayleigh collapse following the sound pressure distribution around the bubble. Then, the amplitude of non-spherical deformation is enhanced during small high-frequent oscillations after the Rayleigh collapse due to the fluid inertial effect. Finally, the oscillating bubble is fragmented into two smaller ones with the Laplace pressure gradient becoming the final trigger of bubble fragmentation. Besides, the results reveal that the temperature of bubble surface is varied when the non-spherical bubble deformation is large, while during spherical bubble oscillations the surface temperature remains almost unchanged.

Влияние технологических параметров на прочность изделий из АБС-пластика при ультразвуковой сварке

An ultrasonic welding method for round-shaped products made from ABS plastic is described in this paper. This method can eliminate roughness and waviness on the contact surface between the planimetric waveguide and the welded part, increase heat removal from the surface of the welded part in the subwaveguide zone and improve the efficiency of ultrasonic welding as well as the strength and quality of the welded joint. It is shown that a mushroom-shaped waveguide is the optimal choice for planimetric ultrasonic welding of ABS parts of the fan wheel type with regard to the uniformity of the oscillation amplitude distribution along the perimeter of the waveguide’s working end face. The optimal form of the waveguide’s working end face is defined that entails fixing the connecting parts relative to the waveguide’s axis along their diameter. It is established that at a certain combination of the ultrasonic welding modes for ABS plastic the rate of deformation at large welding pressures can turn out to be higher than at small pressures. This is caused by the competition of three factors: temperatures, static welding pressure and concentration of energy on the welded surfaces. It is determined that for welding ABS plastic the so-called soft modes of ultrasonic welding with small static welding pressure and oscillation amplitude of the waveguide’s end face should be used. In this case welding occurs only due to the distribution of microroughness, without dents from the waveguide on the surface of the welded material. Optimal welding parameters for ABS plastic are determined.

Hydro‐micromechanical modeling of wave propagation in saturated granular crystals

SummaryBiot theory predicts wave velocities in a saturated granular medium using the pore geometry, viscosity, densities, and elastic moduli of the solid skeleton and pore fluid, neglecting the interaction between constituent particles and local flow, which becomes essential as the wavelength decreases. Here, a hydro‐micromechanical model, for direct numerical simulations of wave propagation in saturated granular media, is implemented by two‐way coupling the lattice Boltzmann method (LBM) and the discrete element method (DEM), which resolve the pore‐scale hydrodynamics and intergranular behavior, respectively. The coupling scheme is benchmarked with the terminal velocity of a single sphere settling in a fluid. In order to mimic a small amplitude pressure wave entering a saturated granular medium, an oscillating pressure boundary on the fluid is implemented and benchmarked with the one‐dimensional wave equation. The effects of input waveforms and frequencies on the dispersion relations in 3D saturated poroelastic media are investigated with granular face‐centered‐cubic crystals. Finally, the pressure and shear wave velocities predicted by the numerical model at various effective confining pressures are found to be in excellent agreement with Biot analytical solutions, including his prediction for slow compressional waves.

Study on connecting way of gas reservoir in a double-cold-finger pulse tube refrigerator

Double-cold-finger pulse tube refrigerator (PTR) driven by a linear compressor possesses important application values. To research the influences on the performance of a double-cold-finger PTR under different connecting ways between inertance tubes and reservoirs, an experimental system of the double-cold-finger PTR was built. Comparing with the double-cold-finger PTR with two gas reservoirs, the double-cold-finger PTR with a common reservoir would have smaller pressure amplitude at the inlet of cold finger and bigger phase angle between velocity and pressure, which would bring more losses in regenerator and further weaken cooling performance. With the same operating parameters, the cooling temperatures of two cold fingers with a common reservoir are higher than that of two cold fingers with two reservoirs. The gas flow in reservoir was simulated to explain the test results. It is important to choose a good connecting way between common reservoir and inertance tube to match cold load.

Attenuation of the Acoustic Signal Propagating Through a Bubbly Liquid Layer

The acoustic signal dynamics in a five-layer medium containing two liquid layers with polydisperse gas bubbles has been investigated. Calculations have been made for the interaction between the pulse perturbation of smallamplitude pressure and a multilayer sample containing two layers of industrial gel with polydisperse air bubbles. It has been shown that a small content of bubbles (about 0.1 vol. %) in a thin gel layer decreases tenfold or more the amplitude of acoustic waves with frequencies close to the resonance frequency of natural oscillations of bubbles. There are frequency ranges thereby where the influence of the bubbly layer is insignificant.

The influence of non-uniform blockages on transient wave behavior and blockage detection in pressurized water pipelines

Blockages in piping systems are formed from potentially complex combinations of bio-film build up, corrosion by-products, and sediment deposition. Transient-based methods seek to detect blockages by analyzing the evolution of small amplitude pressure waves. In theory, such methods can be efficient, nearly non-intrusive and economical but, thus far, studies have only considered symmetrical blockages, uniform in both the radial and longitudinal directions. Laboratory experiments are described here that involve pipe blockages with various levels of irregularity and severity; the way the transient response is affected by a non-uniform blockage is investigated. The differences between uniform and non-uniform blockages are quantified in terms of the rate that wave envelopes attenuate and the degree that phases are shifted. Two different methods for modeling these impacts are compared, namely through an increase in pipe roughness and through a wave scattering model. Wave scattering is shown to play a dominant role in explaining both wave envelope attenuation and phase shift. The accuracy of existing transient-based methods of blockage detection in the frequency domain is also examined, and is found that the predictions of rough blockage locations and sizes by current method are in good agreement with data, with relatively larger discrepancies for rough blockage lengths.

Piezoelectric wave generation system for condition assessment of field water pipelines

ABSTRACTThe condition assessment of pipelines is central to the management of water systems but is only conducted sporadically due to the limited range and practical constraints of current technologies. This paper describes the successful international field trial of a new condition assessment approach that was tested in live water pipeline networks of large cities during peak water demand and traffic conditions. The system, referred to as PIPE SONAR (PCT/EP2015/059540), uses a piezoelectric actuator capable of generating customized, small amplitude (<0.4 m) pressure signals. The field trial involved 1600 individual field tests covering 31 sites of water networks in New Zealand and China, across nine different pipe materials and pipe diameters ranging from 100 mm to 600 mm. The results of the condition assessment were independently confirmed using hydrant tests, low frequency transient tests, and direct inspection through excavation.

High-frequency linear rheology of hydrogels probed by ultrasound-driven microbubble dynamics.

Ultrasound-driven microbubble dynamics are central to biomedical applications, from diagnostic imaging to drug delivery and therapy. In therapeutic applications, the bubbles are typically embedded in tissue, and their dynamics are strongly affected by the viscoelastic properties of the soft solid medium. While the behaviour of bubbles in Newtonian fluids is well characterised, a fundamental understanding of the effect on ultrasound-driven bubble dynamics of a soft viscoelastic medium is still being developed. We characterised the resonant behaviour in ultrasound of isolated microbubbles embedded in agarose gels, commonly used as tissue-mimicking phantoms. Gels with different viscoelastic properties were obtained by tuning agarose concentration, and were characterised by standard rheological tests. Isolated bubbles (100-200 μm) were excited by ultrasound (10-50 kHz) at small pressure amplitudes (<1 kPa), to ensure that the deformation of the material and the bubble dynamics remained in the linear regime. The radial dynamics of the bubbles were recorded by high-speed video microscopy. Resonance curves were measured experimentally and fitted to a model combining the Rayleigh-Plesset equation governing bubble dynamics, with the Kelvin-Voigt model for the viscoelastic medium. The resonance frequency of the bubbles was found to increase with increasing shear modulus of the medium, with implications for optimisation of imaging and therapeutic ultrasound protocols. In addition, the viscoelastic properties inferred from ultrasound-driven bubble dynamics differ significantly from those measured at low frequency with the rheometer. Hence, rheological characterisation of biomaterials for medical ultrasound applications requires particular attention to the strain rate applied.

Condition of resonant break-up of gas bubbles by an acoustic wave in liquid

The linear theory of damping of radial vibrations of a bubble in a liquid is constructed by taking into account the key dissipative mechanisms: thermal, viscous, and acoustic. The basic approximation of homobaricity made helps to obtain the results in a convenient and simple form. The results obtained for damping are used further in the description of the forced resonant oscillations of a bubble in an acoustic wave with the frequency equal to the eigenfrequency of the radial oscillation mode and twice as high as the frequency of the deformation oscillation mode (resonance 2:2:1). It is shown that the amplitude of deformation oscillations, which is reasonably large for breaking, is developed at a relatively small pressure amplitude of the exciting acoustic wave, and subharmonics arise in the acoustic-emission spectrum. The condition of bubble break-up is obtained for a fast and slow start of the acoustic wave.

Estimation of respiratory impedance at low frequencies during spontaneous breathing using the forced oscillation technique.

The forced oscillation technique (FOT) is a non-invasive method to measure the respiratory impedance Z, defined as the complex ratio of transrespiratory pressure P to the airflow at the airway opening Q as a function of frequency. FOT determines Z by superimposing small amplitude pressure oscillations on the normal breathing and measuring the resulting air flow. In this work a new approach for the analysis of the respiratory impedance Z at low frequencies (0.1-5 Hz) during spontaneous breathing is presented. When the respiratory impedance is measured in frequency ranges that overlap with the frequency of spontaneous breathing (0.1-1 Hz), the measured air flow will contain both the breathing of the patient and the response of the respiratory impedance to the pressure oscillations. A nonlinear estimator is developed which is able to separate the breathing signal from the respiratory response in order to obtain the respiratory impedance. The estimated results are used to obtain accurate estimates of airway and tissue components of a constant phase model.

Converging spherical and cylindrical elastic—plastic waves of small amplitude

Converging spherical and cylindrical elastic—plastic waves in an isotropic work-hardening medium is investigated on the basis of a finite difference method. The small amplitude pressure is applied instantaneously and maintained on the outer surface of a spherical or a cylindrical medium. It is found that for undercritical loading, the induced wave structure is an elastic front followed in turn by an expanding plastic region and an expanding elastic region. For supercritical loading, the elastic front is followed in turn by an expanding plastic region, a narrowing elastic region and an expanding plastic region. After yielding is initiated, the strength of the elastic front is constant and equal to the critical loading pressure. The motion of the continuous elastic—plastic interface is discussed in detail. Spatial distributions of pressure near the axis show the strength of the converging wave is nearly doubled in the reflecting stage.

A Fan-Based, Low-Frequent, Forced Oscillation Technique Apparatus

The forced oscillation technique (FOT) is a noninvasive method to characterize the respiratory impedance (Z). Z is defined as the frequency-dependent ratio between pressure and flow. The FOT determines Z by superimposing small amplitude (in the order of 0.1 kPa) pressure oscillations on the normal breathing. It has been shown that a lot of useful information is contained in the frequency range of spontaneous breathing (0.1-1 Hz). In the current state-of-the-art methods, patient cooperation by means of voluntary apnea or mechanical ventilation is required to obtain the respiratory impedance at low frequencies. This article proposes a fan-based setup driven by a microcontroller. The setup allows to excite the respiratory mechanics at frequencies around the spontaneous breathing rate without requiring any patient effort. However, the (nonlinear) dynamic behavior of the setup and the pressure perturbations introduced by the subjects breathing jeopardize the spectral analysis of the measurement. Therefore, a combination of feedforward compensation of the excitation signal and linear feedback control are applied and discussed using measurements on a prototype device. A high-quality pressure signal is obtained, which makes it possible to obtain the respiratory impedance at low frequencies in a clinically practical way.

Propagation of acoustic waves in two-fraction bubbly liquids with account for phase transitions in each fraction

The propagation of acoustic waves in two-fraction liquid mixtures containing vapor-gas bubbles of different dimensions and composition with phase transitions in each fraction is investigated. The system of differential equations of the mixture motion is presented and the dispersion equation is derived. The evolution of weak pulsed pressure disturbances in the mixture is numerically investigated. The effect of phase transitions in each fraction of the disperse phase on the evolution of a small-amplitude pressure pulse is shown.

Estimation of Small Amplitude Pressure Wave in Gaseous Pipeline Using a Linear Kalman Filter

Measurement of pressure distribution in gaseous pipeline is important from a view point of control or safe management. In the present paper, a linear Kalman filter is developed to estimate the pressure estimation of small amplitude pressure wave in a single straight gaseous pipeline with constant circular cross section. The Kalman filter uses the linear dynamic system of the pipeline derived by using the approximation method of the unsteady friction, high speed and accurate computing method. The inputs to the Kalman filter are inlet and outlet pressures, and the pressure at the point one third of the pipe entrance is used as the observation point for feedback compensation. The performance of the developed method is tested using two experimental results by comparing with calculation results without feedback compensation. The comparison demonstrated that the developed method has better performance in the presences of measurement noise and erroneous boundary condition than does the ordinary calculation. It also showed much higher ability in error reduction than the ordinary calculation in computation with an erroneous initial condition.