Phase Velocity Research Articles

Numerical analysis of blood flow in the abdominal aorta under simulated weightlessness and earth conditions

Blood flow through the abdominal aorta and iliac arteries is a crucial area of research in hemodynamics and cardiovascular diseases. To get in to the problem, this study presents detailed analyses of blood flow through the abdominal aorta, together with left and right iliac arteries, under Earth gravity and weightless conditions, both at the rest stage, and during physical activity. The analysis were conducted using ANSYS Fluent software. The results indicate, that there is significantly less variation in blood flow velocity under weightless conditions, compared to measurement taken under Earth Gravity conditions. Study presents, that the maximum and minimum blood flow velocities decrease and increase, respectively, under weightless conditions. Our model for the left iliac artery revealed higher blood flow velocities during the peak of the systolic phase (systole) and lower velocities during the early diastolic phase (diastole). Furthermore, we analyzed the shear stress of the vessel wall and the mean shear stress over time. Additionally, the distribution of oscillatory shear rate, commonly used in hemodynamic analyses, was examined to assess the effects of blood flow on the blood vessels. Countermeasures to mitigate the negative effects of weightlessness on astronauts health are discussed, including exercises performed on the equipment aboard the space station. These exercises aim to maintain optimal blood flow, prevent the formation of atherosclerotic plaques, and reduce the risk of cardiovascular complications.

Nonlinear wave propagation in homogenized strain gradient 1D and 2D lattice materials: Applications to hexagonal and triangular networks

AbstractThis work aims to analyze the propagation of fully nonlinear waves, encompassing shear, extension, and bending deformation modes, within homogenized periodic nonlinear hexagonal and triangular networks, successively considering 1D and 2D situations. The wave analysis is conducted from the expression of the effective strain energy density of periodic hexagonal and triangular lattices in the nonlinear regime by a continualization of the discrete lattice equations, considering all forms of energy. We incorporate strain gradient effects into the continuous model to account for the wave‐dispersive nature. The resulting second‐gradient nonlinear continuum exhibits subsonic and supersonic propagation modes. We first examine in a 1D situation the dynamical response of the hexagonal and triangular lattices, considering varying levels of nonlinearity quantified by a single scalar valued parameter. We further evaluate the impact of a fully nonlinear analysis compared to an analysis solely based on the shear energy, regarding both supersonic and subsonic modes. The nonlinear wave propagation analysis is then extended to a 2D situation for the same two lattices. It is shown that the longitudinal mode exhibits a higher frequency at a low degree of nonlinearity; however, as the degree of nonlinearity increases, the shear mode surpasses the longitudinal mode in terms of frequency. As the wavenumber increases, the nonlinearity has a lesser impact on the frequency behavior, and the phase velocity is more influenced by other factors, such as the second gradient contributions of the effective constitutive law. Such a behavior indicates a transition from a highly nonlinear behavior at lower wave numbers to a more linear behavior at higher wave numbers.

High-Resolution Two-Phase Velocimetry Of Aspherical Particles Using Wavelet-Based Optical Flow Velocimetry (WOFV) Benchmarked With Fully Resolved Direct Numerical Simulations

Several techniques exist to measure the carrier and dispersed phases in multi-phase flows. Particle image velocimetry (PIV) analyzes the carrier phase by cross-correlating particle images, but its resolution is limited by the size of the interrogation window, making it difficult to resolve fine-scale turbulent structures. Particle tracking algorithms capture translational motion of dispersed particles well, but struggle with rotational motion, especially for irregular and aspherical particles. Currently, there is no method that universally measures both the carrier phase velocity field and the translational and rotational motions of dispersed particles. This study evaluates wavelet-based optical flow velocimetry (wOFV) for motion estimation in multi-phase flows, focusing on dispersed ellipsoidal particles and their surrounding turbulent carrier flow using synthetic image data. The research proceeds in two phases: first, the rigid motion of ellipses, including translational and rotational components, is analyzed using wOFV-generated dense motion fields. The results highlight the critical role of the regularization weighting parameter λ. Higher λ values improve translational motion estimation, while an optimal λ avoids under-regularization and non-physical structures in rotational motion. wOFV maintains accuracy in combined motion scenarios with optimal λ values. In the second phase, wOFV captures the turbulent carrier flow around an aspherical particle, benchmarked against DNS data and compared to PIV. wOFV outperforms PIV in resolving finer structures near the particle surface and in accurately representing the wake region. Error analyses confirm wOFV’s superior performance, with optimal results within a specific λ range. In conclusion, wOFV is a highly effective tool for the analysis of multi-phase flow dynamics, providing greater resolution and accuracy than PIV, especially in complex scenarios involving aspherical particles.

Hidden corrosion monitoring via phase shift evaluation of lamb wave modes

Abstract Lamb wave inspection is a promising candidate for real-time monitoring of hidden corrosion in thin-walled metallic structures. The time-of-flight (ToF) which represents the variation of group velocity due to thickness reduction is commonly used, but its sensitivity is limited at the early stage of corrosion. To address this issue, the phase shift as a function of the phase velocity is defined and evaluated for corrosion detection in this paper. Specifically, the analytic cross-correlation method is applied, which estimates the group delay and the phase shift between two Lamb wave responses before and after the existence of corrosion simultaneously. The simulated examples show that the phase shift performs an obvious improvement on corrosion sensitivity compared to the ToF, and its value increases nearly monotonically as the corrosion gets deeper. Ultimately, an experimental example is also introduced, where an active sensor network is deployed and a probabilistic imaging algorithm is introduced. The imaging results demonstrate that the proposed method could successfully identify and accurately localize the hidden corrosion.

Uncertainty Quantification in Radial Anisotropy Models Based on Transdimensional Bayesian Inversion of Receiver Functions and Surface-Wave Dispersion: Case Study Sri Lanka

ABSTRACT In geophysical inference problems, quantification of data uncertainties is required to balance the data-fitting ability of the model and its complexity. The transdimensional hierarchical Bayesian approach is a powerful tool to evaluate the level of uncertainty and determine the complexity of the model by treating data errors and model dimensions as unknown. In this article, we take account of the uncertainty through the whole procedure, thus developing a two-step fully Bayesian approach with coupled uncertainty propagation to estimate the crustal isotropic and radial anisotropy (RA) model based on Rayleigh and Love dispersion as well as receiver functions (RFs). First, 2D surface-wave tomography is applied to determine period-wise ambient noise phase velocity maps and their uncertainty for Rayleigh and Love waves. Probabilistic profiles of the isotropic average VS and RA as a function of depth are then derived at station sites by inverting the local surface-wave dispersion and model errors and RFs jointly. The workflow is applied to a temporary seismic broadband array covering all of Sri Lanka. The probabilistic results enable us to effectively quantify the uncertainty of the final RA model and provide robust inferences. The shear-wave velocity results show that the range of Moho depths is between 30 and 40 km, with the thickest crust (38–40 km) beneath the central Highland Complex. Positive RA (VSH>VSV) observed in the upper crust is attributed to subhorizontal alignment of metamorphic foliation and stretched layers resulting from deformation. Negative RA (VSV>VSH) in the midcrust of central Sri Lanka may indicate the existence of melt inclusions and could result from the uplift and folding process. The positive RA in the lower crust could be caused by crustal channel flow in a collision orogeny.

Enhanced Harmonic Suppression for a Miniaturized Hairpin-Line Bandpass Filter with Meander Spurline

The design of a fourth-order centrally corrugated double-folded hairpin line bandpass filter with a broad stopband and enhanced selectivity is demonstrated in this article. Initially, a double-folded hairpin-line bandpass filter (DFHLBF) is designed from a fourth-order conventional hairpin-line bandpass filter (CHLBF), which is centred at 2.5 GHz and has a fractional bandwidth of 3%. This results in a 68% size reduction. With this folding mechanism, the filter's skirt characteristic is only enhanced at the upper passband edge, resulting in an attenuation level of 40 dB at 2.65 GHz. The capacitive loading has then been incorporated by periodic rectangular corrugations that have disturbed the folded arms. Because of the high capacitive coupling between the folded arms, a symmetrical passband with an attenuation level better than 40 dB at both edges has been observed. Besides, a size reduction of 14% than that for the DFHLBF has been achieved. However, because of the imbalance of the modal phase velocities in the inhomogeneous microstrip filter construction, the stopband's attenuation level climbs to 8 dB. Rectangular meander spurlines have been added between the connected arms of the neighbouring centrally corrugated cells of the filters as a way to lower the attenuation levels of the harmonics. This creates a slow-wave effect between the odd- and even-modes of the propagating signals. This results in an overall size reduction of 81% over the standard hairpin-line filter and an enlarged stopband of up to 4.36f0 with a rejection level of 42 dB.

Simulation of Gaussian wave packets used to illustrate elementary quantum mechanics scenarios

In this paper we numerically solve the time dependent Schrödinger equation for scenarios using wave packets. These examples include the free wave packet, which we use to show the difference between group and phase velocities, the packet in a harmonic oscillator potential with non-trivial initial conditions in one and two dimensions, which is compared with their classical analogs to show how Ehrenfest theorem holds. We also include simulations of the diffraction through the single and double slit potentials, the refraction with a step potential and the dispersion by a central potential. The aim of this paper is to illustrate with simulations, nowadays easy to implement, scenarios that can help explaining the basics of the wave-particle duality.

Deformable baffles coupled with pulsatile flow improve mixing in microfluidic devices

An important objective for many microfluidic mixer devices is to attain a high level of mixing efficiency at low Reynolds numbers. Previous research incorporating rigid obstacles into microchannels has shown enhanced chaotic advection and improved mixing index; however, the increased pressure drop and corresponding shear forces within the fluid domain can create issues in biological applications. In this paper, we show how an innovative micromixer strategy, i.e., incorporating deformable baffles and utilizing pulsatile flow, results in a high level of mixing efficiency at low Reynolds numbers (Re =1.25), where diffusion is the pure mechanism of mixing. The numerical investigation involved solving the continuity, Navier-Stokes, solid mechanics, and fluid-solid interaction equations alongside a convection-diffusion model to analyze species concentration. To find the best conditions of the micromixer, the mixing index as the objective function was optimized, and various parameters, including phase difference, velocity ratio, Strouhal number, baffle distance, and Reynolds number, were investigated. Through optimization of these parameters, we show a notable improvement in the mixing index (increase from 21.7% to 78.86%) at a Reynolds number of 1.25 with 2 mixing units, more than 92% mixing efficiency by using 6 mixing units, and more than 95% mixing efficiency at a Reynolds number of 0.1. Moreover, the incorporation of deformable baffles and pulsation results in a lower pressure drop. These conditions are optimal for biological applications that require thorough mixing of the sample inputs.

Weakly anelliptical traveltime analysis: Ambiguity between subsurface and elasticity

The building of a subsurface and (anisotropic) velocity model from a single gather of reflection traveltime (kinematic) data is inherently ambiguous because the processing of such data can only determine a horizontal slowness component, not a vertical one. Based thereon, I derive a simple algorithm that generates an infinite series of combinations of the subsurface-velocity models, all of which will show nearly the same seismic kinematic response, as further demonstrated by simulating wave propagation through a model with different interface dips. This algorithm assumes, first, that all interface dips remain constant over the distance considered and, second, that an approximation of the elasticity model — that is, the linearization of a phase velocity — valid for weak anisotropy can be used. Furthermore, when applied to the classic and analytically solvable case of traveltime analysis for a stack of flat layers with weak transverse isotropy, the algorithm theoretically explains the combination of anisotropy parameters that govern the nonhyperbolic term of a traveltime series: the established [Formula: see text] and its new counterpart [Formula: see text] for a [Formula: see text] and [Formula: see text] wave, respectively.

Identification method of the hydrodynamic and acoustic natures of wall pressure fluctuation based on dynamic mode decomposition

In this study, an analysis method is proposed to explain the dynamic mode decomposition (DMD) mode of wall fluctuating pressure from the perspective of hydrodynamics and acoustics. According to the phase velocity, the wavenumber–frequency spectrum is divided into hydrodynamic, acoustic, and subconvective regions. Multiple DMD modes of the pressure field are calculated to obtain the wavenumber–frequency spectrum of the reconstructed pressure, which is characterized by the fact that the energy is concentrated at different wavenumber positions of the same frequency. This behavioral feature enables the DMD mode to be identified as a hydrodynamic, acoustic, and hybrid property according to the wavenumber position where the energy spot appears. This method can realize the classification and contribution analysis of the hydrodynamic and acoustic properties of the wall pressure DMD mode, and establish the mapping relationship between the acoustic mode and the eddy current characteristics through the eigenvalues. The coherent structure of the trace acoustic energy radiation in the incompressible fluid is observed from the statistical perspective, which increases understanding of the flow noise. The zero-pressure gradient wall flow experiment of Abraham is numerically analyzed using the aforementioned method. The results indicate that most of the DMD modes are identified as hydrodynamic, and only the nineteenth-order DMD mode is identified as acoustic. The frequency of the acoustic mode is 23.9 Hz, which has obvious wave-packet characteristics, whereas the hydrodynamic mode exhibits nonradiative convection characteristics, and its eddy current structure is closer to the wall transfer.

Thermal transport characteristics of fluid-particle suspension in a vertical uniform tube: A computational study on Rabinowitsch fluid with uniform heat source

Problem statement The thermal transport of fluid-particle suspension in Rabinowitsch fluid is discussed theoretically in a vertical uniform tube under the consideration of a uniform heat source. Methodology The fluid and particle phase models are used to develop the mathematical model in the form of partial differential equations which are solved through the symbolic software MATHEMATICA version 12.0 and present the exact solution of temperature distribution, velocity of fluid and particle phases, wall shear stress, pressure gradient, pressure rise, and stream function, etc. Computational results and findings The volume fraction density of the particles slows down the motion of the fluid particles. The velocity of Newtonian fluid is maximum as compared to pseudo-plastic and Dilatant fluids. The fluid phase velocity is superior to particle phase velocity distribution for all pertinent parameters of the analysis. The pressure rise increases in the case of Newtonian and pseudo plastic fluid and decreases in Dilatant fluid. The trapping phenomena are strongly associated with the volume fraction density of the particle. The shear stress shows a decreasing trend against the volume fraction density of the particles, Grashoff number, and heat source parameter. Special case The current fluid model (Rabinowitsch fluid) can be reduced in Newtonian, pseudo plastic, and Dilatant fluid for taking κ → 0 , κ < 0 , and κ > 0 , respectively. Applications The current analysis can be useful in biomedical engineering to observe the blood supply through the arteries, the removal of kidney stones, and also the passage of urine to the bladder from the ureter. Originality The present research is original and has not been published before.

Piezoelectric layer guided in-plane surface waves with flexoelectricity and gradient effects

With the rapid advancement of 5 G technology, the demand for surface acoustic wave (SAW) devices is experiencing exponential growth. Precisely forecasting the speed at which Rayleigh waves propagate, taking into account size effects and flexoelectric properties, is vital for enhancing SAW device design. To address this need, the study explores Rayleigh wave propagation in a stratified system consisting of a nanoscale piezoelectric guiding layer atop an isotropic elastic substrate. The governing equations, boundary conditions, and interface continuity conditions between the guiding layer and substrate are established through the Hamiltonian principle. Following this, the dispersion equations for Rayleigh waves under electric open-circuit and electric short-circuit conditions are derived and solved numerically. Additionally, the effects of flexoelectricity, inertial gradients, strain gradients, electric field gradients, and the piezoelectric guiding layer thickness on the phase velocity of Rayleigh waves are extensively explored. Our findings indicate that flexoelectricity and strain gradients elevate the phase velocity, while inertial gradients and electric field gradients result in a decrease in the phase velocity. As the frequency of Rayleigh waves increases, the impact of these factors becomes more prominent. In addition, it is observed that electric field gradients play a less significant role compared to inertial gradients and strain gradients. The findings of this study could offer valuable insights for the advancement of miniaturized SAW devices designed for high-frequency service.

Multi-wave characteristics associated with January 15, 2022 Hunga-Tonga volcanic eruption: A global observation

The eruption of Hunga-Tonga Volcano on January 15, 2022 has stimulated a wide spectrum of atmospheric waves globally. To probe the surface deformation pattern, Sentinel-1 Synthetic Aperture Radar (SAR) data has been analyzed. It has been approximated that an overall area of about 2.47 square kilometres experienced deformation in conjunction with this event. To characterize the atmospheric wave propagation, barometric pressure data from 1814 stations distributed all around the globe have been examined. This study encompassed with the propagation characteristics of the waves over four zones including Indian and Polar regions for the first time using barometric data. Time-series observations indicate that the waves propagated globally multiple times. Within the Indian region, three minor arc passages and one major arc passage were identified. In Japan, two minor arc passages and one major arc were present. Conversely, in North America, both minor and major arc passages were detected, occurring a minimum of three times. Moreover, the attributes of these waves, such as their propagation speed and periodicity, were compared across these four regions. The estimated phase speed and periodicity fall within the ranges of approximately 291–314 m/s and 10–180 min, respectively including Polar Regions. These speed and periodicity measurements of the observed waves suggest that the dominant mode of wave propagation generated during the Tonga volcanic eruption is that of Lamb waves. In addition, a slower propagation phase speed of about 226.6 m/s was identified in Japan which corresponds to Pekeris mode of waves.

Measurement of phase velocity in the functionally graded concrete systems via improved higher-order shear deformation theory

The measurement of phase velocity (PV) in concrete systems is critically important for civil engineers as it provides essential insights into the material properties and structural integrity of concrete. PV, which refers to the speed at which a wave phase propagates through a medium, is directly related to the stiffness and density of the material. By accurately measuring PV, civil engineers can assess the quality and homogeneity of concrete, detect potential flaws, and predict the material’s behavior under various load conditions. This information is crucial for ensuring the safety and durability of concrete structures, from bridges and buildings to pavements and dams. Moreover, understanding PV helps in the optimization of mix designs and the development of new, advanced concrete materials, ultimately leading to more resilient and cost-effective construction practices. For this issue, in this work, for the first time, the measurement of PV in the concrete doubly curved panel reinforced by graphene oxide powders (GOPs) via improved higher-order shear deformation theory is presented. Hamilton’s principle and analytical method are used for extracting and solving the higher-order equations. Finally, some recommendations for improving the efficiency and stability of the concrete structures are presented for related engineering industries. The findings underscore the potential of combining state-of-the-art theoretical models with cutting-edge material reinforcements to push the boundaries of structural engineering and material performance.

Acoustic radiation force-induced longitudinal shear wave for ultrasound-based viscoelastic evaluation

Acoustic radiation force (ARF) is widely used to induce shear waves for evaluating the mechanical properties of biological tissues. Two shear waves can be generated when exciting with ARF: a transverse shear wave, also simply called shear wave (SW), and a longitudinal shear wave (LSW). Shear waves (SWs) have been broadly used to assess the mechanical properties. Some articles have reported that the LSW can be used to evaluate mechanical properties locally. However, existing LSW studies are mainly focused on the group velocity evaluation using optical coherence tomography (OCT). Here, we report that a LSW generated with ARF can be used to probe viscoelastic properties, including shear modulus and viscosity, using ultrasound. We took advantage of the surface boundary effect to reflect the LSW, named RLSW, to address the energy deficiency of LSW induced by ARF. We systematically evaluated the experiments with tissue-mimicking viscoelastic phantoms and validated by numerical simulations. Phase velocity and dispersion comparison between the results induced by a RLSW and a SW exhibit good agreement in both the numerical simulations and experimental results. The Kelvin-Voigt (KV) model was used to determine the shear modulus and viscosity. RLSW shows great potential to evaluate localized viscoelastic properties, which could benefit various biomedical applications such as evaluating the viscoelasticity of heterogeneous materials or microscopic lesions of tissues.

A machine learning-based simplified collision model for granular flows

This study aims to create an efficient, rapid, and reliable particle collision model utilizing machine learning techniques for granular flow simulations. A simplified surrogate collision model developed in the framework of a Hybrid Euler–Lagrange (HEL) technique was successfully applied to model particle interactions for flows with a low fraction of the granular phase. The precision of the simplified collision model was evaluated using experimental data obtained from the in-house, two-stream particle collision test rig, focusing on solid phase velocity profiles. The implemented model demonstrates strong concordance with the experimental results. The simulations carried out highlight the relation between the simulation time step and the collision rate, which affects the cost of the numerical simulation. The execution time for both the conventional Discrete Element Method (DEM) on a CPU and the streamlined collision HEL model saw a reduction exceeding 70%.

Influence of strong directional sources in ambient seismic imaging using traffic-induced noise

Continuously moving seismic sources, such as vehicles and train cars, play a crucial role as passive sources for nondestructive exploration in urban areas. Seismic interferometry is commonly used in field data acquisition and processing using linear arrays. However, the simultaneous recording of high-energy noise, excited by buildings and factories, cannot be overlooked. We simulate moving-source seismic records with strong noises using orthogonal arrays. When strong noise originates from specific angles, the energy-phase velocity curves of arrays in different directions significantly diverge. We determine that an L-shaped array, formed by orthogonal arrays, can effectively mitigate this effect, yielding more consistent results. Nonetheless, spatial constraints often preclude the deployment of L-shaped arrays. To mitigate this issue, we develop a new parallel observation system. Field tests conducted on a main road validate that the new array is comparable with the L-shaped array in terms of dispersion extraction. Similar to synthetic data, the phase velocity extracted from the linear array field data is found to be unreliable. Drilling data align well with the inversion results of the parallel observation system. Given the challenges of urban traffic-induced signal acquisition, deploying multiazimuth arrays to minimize noise impact is essential. Considering the spatial limitations, the convenient parallel observation system emerges as a good choice.

Experimental evidence for the drift wave nature of the weakly coherent mode in ASDEX Upgrade I-mode plasmas

The improved energy confinement mode (I-mode) is a potential candidate for future fusion power plants, as it combines ELM-free operation with good confinement. The unusual edge transport and turbulence in this regime is still not fully understood. This study analyzes the turbulent structure of the weakly coherent mode (WCM) in ASDEX Upgrade. Measurements from Doppler back-scattering and a thermal helium beam diagnostic are used to determine velocities of the background plasma and the WCM over multiple discharges. A phase velocity of the WCM of the order of 2–5 km s−1 in the electron diamagnetic drift direction is found, quantitatively close to a drift wave assuming negligible temperature fluctuations. A good agreement with a previously proposed mechanism behind the I-mode regime is observed. This marks the first experimental verification of a specific understanding of the WCM and the I-mode regime.

Corrugated waveguide with matched phase and group velocities: an extended regime of wave-beam interaction

We show that it is possible to design corrugated waveguides where phase and group velocities coincide at an inflection point of the dispersion relation, thereby allowing an extended regime of interaction with a charge particle beam. This provides a basis for designing travelling slow-wave structures with a broadband interaction between relativistic charged particle beams and propagating terahertz waves allowing an energy exchange between beam and wave, amplifying terahertz radiation. We employ Fourier-Mathieu expansion, which gives approximate analytic solutions to Maxwell equations in a corrugated waveguide with periodically undulating cross-section. Being analytic, this enables quick design of corrugated waveguides, determined from desirable dispersion relations. We design a three dimensional waveguide with the desired dispersion and confirm the analytical predictions of the wave profile, using numerical simulations. Madey’s theorem is used to analyse the strength of the wave-beam interaction, showing that there is a broad frequency interaction region.

Study on the attributes of transverse surface waves in a layered piezoelectric semi-space with surface elasticity theory and extended stroh formalism

Previous works on surface acoustic wave sensors have shown great limitations in selecting piezoelectric materials and the wave propagation direction. To eliminate such limitations in the technological revolution of SAW sensors, the current paper's main purpose is to explore how wave propagation orientation affects the performance of SAW macro- and nano-sensors. Based on Extended Stroh formalism, the theoretical forms are derived and exploited to present the wavenumber of transverse waves in an arbitrary direction of the piezoelectric medium. Furthermore, we consider surface elasticity theory to acquire the phase velocity equation on the basis of the expression of the wavenumber. More intuitively, a physical model is set up to obtain the horizontal shear stiffness of the surface and bulk layers. Then, the numerical case is carried out to determine the relationship between phase velocity and wave propagation orientation. By comparing the numerical study and the physical model, it can be found that the empirical formula of shear stiffness for bulk and surface layers offers a helpful route to precisely predict the mechanical attributes of SAW macro- and nano-sensors, respectively. The summaries of the current theoretical work benefit the manufacturing of surface acoustic wave sensors with improved performance.