Wave Propagation Phenomena Research Articles

High resolution wavenumber analysis for investigation of arterial pulse wave propagation

The propagation of the pulse wave along the artery is relatively fast (several m/s), and a high-temporal resolution is required to measure pulse wave velocity (PWV) in a regional segment of the artery. High-frame-rate ultrasound enables the measurement of the regional PWV. In analyses of wave propagation phenomena, the direction and propagation speed are generally identified in the frequency-wavenumber space using the two-dimensional Fourier transform. However, the wavelength of the pulse wave is very long (1 m at a propagation velocity of 10 m/s and a temporal frequency of 10 Hz) compared with a typical lateral field of view of 40 mm in ultrasound imaging. Therefore, PWV cannot be identified in the frequency-wavenumber space owing to the low resolution of the two-dimensional Fourier transform. In the present study, PWV was visualized in the wavenumber domain using phases of arterial wall acceleration waveforms measured by high-frame-rate ultrasound.

Wave propagation characteristics of helically orthotropic cylindrical shells and resonance emergence in scattered acoustic field. Part 1. Formulations

The method of wave function expansion is adopted to study the three dimensional scattering of a plane progressive harmonic acoustic wave incident upon an arbitrarily thick-walled helically filament-wound composite cylindrical shell submerged in and filled with compressible ideal fluids. An approximate laminate model in the context of the so-called state-space formulation is employed for the construction of T-matrix solution to solve for the unknown modal scattering coefficients. Considering the nonaxisymmetric wave propagation phenomenon in anisotropic cylindrical components and following the resonance scattering theory which determines the resonance and background scattering fields, the stimulated resonance frequencies of the shell are isolated and classified due to their fundamental mode of excitation, overtone and style of propagation along the cylindrical axis (i.e., clockwise or anticlockwise propagation around the shell) and are identified as the helically circumnavigating waves.

On Invariant-Preserving Finite Difference Schemes for the Camassa-Holm Equation and the Two-Component Camassa-Holm System

AbstractThe purpose of this paper is to develop and test novel invariant-preserving finite difference schemes for both the Camassa-Holm (CH) equation and one of its 2-component generalizations (2CH). The considered PDEs are strongly nonlinear, admitting soliton-like peakon solutions which are characterized by a slope discontinuity at the peak in the wave shape, and therefore suitable for modeling both short wave breaking and long wave propagation phenomena. The proposed numerical schemes are shown to preserve two invariants, momentum and energy, hence numerically producing wave solutions with smaller phase error over a long time period than those generated by other conventional methods. We first apply the scheme to the CH equation and showcase the merits of considering such a scheme under a wide class of initial data. We then generalize this scheme to the 2CH equation and test this scheme under several types of initial data.

Comparison of the Windkessel model and structured-tree model applied to prescribe outflow boundary conditions for a one-dimensional arterial tree model

One-dimensional (1D) modeling is a widely adopted approach for studying wave propagation phenomena in the arterial system. Despite the frequent use of the Windkessel (WK) model to prescribe outflow boundary conditions for 1D arterial tree models, it remains unclear to what extent the inherent limitation of the WK model in describing wave propagation in distal vasculatures affect hemodynamic variables simulated at the arterial level. In the present study, a 1D model of the arterial tree was coupled respectively with a WK boundary model and a structured-tree (ST) boundary model, yielding two types of arterial tree models. The effective resistances, compliances and inductances of the WK and ST boundary models were matched to facilitate quantitative comparisons. Obtained results showed that pressure/flow waves simulated by the two models were comparable in the aorta, whereas, their discrepancies increased towards the periphery. Wave analysis revealed that the differences in reflected waves generated by the boundary models were the major sources of pressure wave discrepancies observed in large arteries. Additional simulations performed under aging conditions demonstrated that arterial stiffening with age enlarged the discrepancies, but with the effects being partly counteracted by physiological aortic dilatation with age. These findings suggest that the method adopted for modeling the outflow boundary conditions has considerable influence on the performance of a 1D arterial tree model, with the extent of influence varying with the properties of the arterial system.

Experimental and numerical study on nucleate bubble deformation in subcooled flow boiling

Experimental and numerical study was conducted to investigate the bubble behaviors in subcooled flow nucleate boiling. The bubble behaviors in subcooled flow boiling in an upward annular channel were investigated in the range of subcooling degree 5–30K by visualization with high spatial and temporal resolutions using a high speed video camera and Cassegrain tele-microscope. Obvious deformation on the upstream side surface of the bubble during its growth process was frequently observed. This deformation phenomenon was caused by the condensation occurring at the upstream side bottom of the bubble, which results from the Marangoni flow along the bubble surface from the bubble bottom to the top. Since the Marangoni flow cannot be directly observed by the current experiments because it occurs in a very thin interface along the bubble surface, the numerical simulations of bubble growth and departure behaviors in subcooled flow boiling were carried out. As a result, it was confirmed that the bubble deformation was caused by the Marangoni flow along the bubble surface. Moreover, the phenomenon of wave propagation on the bubble surface during the condensation process was observed, and it can enhance the heat transfer between the bubble and the surrounding subcooled liquid.

Complementary Discrete Geometric <inline-formula> <tex-math notation="LaTeX">$h$ </tex-math> </inline-formula>-Field Formulation for Wave Propagation Problems

An electromagnetic wave propagation problem can be formulated according to a pair of complementary formulations, called the ${e}$ -formulation and the ${h}$ -formulation. The two formulations are linked to each other by Maxwell’s curl equations, and, in the continuous setting, they are perfectly equivalent in describing the wave propagation phenomenon. However, this is not true in the discrete setting, where the two formulations, in general, give different solutions. In the past decades, complementary formulations were widely studied for static problems and eddy-current problems, where they were exploited as error estimators for adaptive refinement schemes. Moreover, the so-called bilateral energy bounds arise for some problems whether theoretically or at least numerically. However, to the best of our knowledge, little attention has been given to complementarity in the wave propagation problems. In this paper, we propose an adaptive refinement scheme using the constitutive error as an estimator, and then, we investigate the behavior in terms of bilateral energy bounds.

Identifying Mechanisms Behind the Tullio Phenomenon: a Computational Study Based on First Principles.

Patients with superior canal dehiscence (SCD) suffer from events of dizziness and vertigo in response to sound, also known as Tullio phenomenon (TP). The present work seeks to explain the fluid-dynamical mechanisms behind TP. In accordance with the so-called third window theory, we developed a computational model for the vestibular signal pathway between stapes and SCD. It is based on first principles and accounts for fluid-structure interactions arising between endolymph, perilymph, and membranous labyrinth. The simulation results reveal a wave propagation phenomenon in the membranous canal, leading to two flow phenomena within the endolymph which are in close interaction. First, the periodic deformation of the membranous labyrinth causes oscillating endolymph flow which forces the cupula to oscillate in phase with the sound stimulus. Second, these primary oscillations of the endolymph induce a steady flow component by a phenomenon known as steady streaming. We find that this steady flow of the endolymph is typically in ampullofugal direction. This flow leads to a quasi-steady deflection of the cupula which increases until the driving forces of the steady streaming are balanced by the elastic reaction forces of the cupula, such that the cupula attains a constant deflection amplitude which lasts as long as the sound stimulus. Both response types have been observed in the literature. In a sensitivity study, we obtain an analytical fit which very well matches our simulation results in a relevant parameter range. Finally, we correlate the corresponding eye response (vestibulo-ocular reflex) with the fluid dynamics by a simplified model of lumped system constants. The results reveal a "sweet spot" for TP within the audible sound spectrum. We find that the underlying mechanisms which lead to TP originate primarily from Reynolds stresses in the fluid, which are weaker at lower sound frequencies.

Transient Response of a Fluid-Filled, Thick-Walled Spherical Shell Embedded in an Elastic Medium

The paper addresses the problem of transient elastodynamics analysis of a thick-walled, fluid-filled spherical shell embedded in an elastic medium with an analytical approach. This configuration is investigated at first step for a full-space case. Different constitutive relations for the elastic medium, shell material and filling fluid can be considered, as well as different excitation sources (including S/P wave or plane/spherical incident wave at different locations). With mapmaking visualisation, the wave propagation phenomena can be described and better understood. The methodology is going to be applied to analysis of the tunnels or other shell like structures under the effect of nearby underground explosion.

Blast load estimation using Finite Volume Method and linear heat transfer

From the point of view of people and building security one of the main destroying factor is the blast load. Rational estimating of its results should be preceded with knowledge of complex wave field distribution in time and space. As a result one can estimate the blast load distribution in time. In considered conditions, the values of blast load are estimating using the empirical functions of overpressure distribution in time ( Δp(t) ). The Δp(t) functions are monotonic and are the approximation of reality. The distributions of these functions are often linearized due to simplifying of estimating the blast reaction of elements. The article presents a method of numerical analysis of the phenomenon of the air shock wave propagation. The main scope of this paper is getting the ability to make more realistic the Δp(t) functions. An explicit own solution using Finite Volume Method was used. This method considers changes in energy due to heat transfer with conservation of linear heat transfer. For validation, the results of numerical analysis were compared with the literature reports. Values of impulse, pressure, and its duration were studied.

BUBBLE BURSTING AT A FREE SURFACE IN A CLOSED DOMAIN

When a charge explodes underwater near a free surface, a bubble would be generated and the surface pushed up very high. Experiments have shown that the motion of the spike lags a lot behind the bubble motion. Many studies only focus on the nonlinear interaction between the bubble and free surface while the water waves afterward is mainly studied based on the linear theory. The nonlinear motion of the water wave after the bubble pulsation is seldom studied. In this study, we concerns the interaction between underwater explosion generated bubble and a free surface and its bursting at a free surface in a closed domain. Suppose that the fluid outside the bubble is incompressible, non-viscous and irrotational and the velocity potential satisfies the Laplace equation. Boundary integral method is used to solve the Laplace equation for the velocity potential. The bubble content is described by an adiabatic law. The whole process of the bubble motion and subsequently the water wave propagation will be simulated in this paper. Particular attention will be focused on the phenomenon of water wave propagation in a closed domain.

Modeling for Estimation of Wave Action in Multi-Cylinder Turbocharged SI Engines

Turbocharged, direct-injection SI engines have become a mainstream solution for improving vehicle fuel economy. A central requirement is the ability to precisely estimate the pressure and gas flows in the exhaust manifold for improving the accuracy of air-charge control algorithms. Due to lack of adequate modeling capabilities, today’s model-based charge and exhaust pressure estimators do not consider the influence of the high-frequency wave propagation dynamics in the manifold. This lack of physical consistency limits the robustness of the estimators, and introduces significant calibration effort to achieve acceptable accuracy. This paper presents a system dynamic approach to model the wave propagation phenomena in the exhaust system of a multi-cylinder turbocharged SI engine, to obtain a nonlinear, state-space system that is suitable for fast simulation and estimator design. A model order reduction methodology is applied to the conservation laws for unsteady compressible flows in ID pipes. Specific boundary conditions are then developed to characterize the wave reflection and transmission through various components of the exhaust system. Simulation results in steady-state and transient conditions show that the resulting reduced order model matches the accuracy of commercial ID engine simulation tools with a much simpler mathematical structure, offering an advantage in reducing calibration effort compared to the heuristic mean-value models.

Analysis on Conservation of Energy in Microwave Power Synthesizer

Instead of using the traditional method of scattering matrix analysis, this paper uses a method similar to optical waveguide propagation. The basic theory of electromagnetic waves is used to analyze the amplitude and power of microwaves. Proved Conservation of energy is satisfied in microwave power synthesizer. Meanwhile, explained the different electromagnetic wave propagation phenomenon between divider and synthesizer.

Excitation and propagation of X-ray fluorescence through thin devices with hollowed ordered structures: comparison of experimental and theoretical spectra.

The lack of models describing the propagation of X-rays in waveguides and the interference mechanism between incident and reflected radiation waves hamper the understanding and the control of wave propagation phenomena occurring in many real systems. Here, experimental spectra collected at the exit of microchannel plates (MCPs) under the total X-ray reflection condition are presented. The results are discussed in the framework of a theoretical model in which the wave propagation is enhanced by the presence of a transition layer at the surface. The angular distributions of the propagating radiation at the exit of these MCPs with microchannels of ∼3 µm diameter will also be presented and discussed. These spectra show contributions associated with the reflection of the primary monochromatic beam and with the fluorescence radiation originating from the excitation of atoms composing the surface of the microchannel. The soft X-ray fluorescence spectra collected at the exit of microcapillaries were analyzed in the framework of a wave approximation while diffraction contributions observed at the exit of these hollow X-ray waveguides have been calculated using the Fraunhofer diffraction model for waves in the far-field domain. Data collected at the Si L-edge show that in glassy MCPs the fluorescence radiation can be detected only when the energy of the primary monochromatic radiation is above the absorption edge for grazing angles higher than half of the critical angle of the total reflection phenomenon. Experimental data and simulations of the propagating radiation represent a clear experimental confirmation of the channeling phenomenon of the excited fluorescence radiation inside a medium and point out that a high transmission can be obtained in waveguide optics for parameters relevant to X-ray imaging.

Coupled seismogenic geohazards in alpine regions

COupled seismogenic GEohazards in Alpine Regions (COGEAR) is an interdisciplinary natural hazard project investigating the hazard chain induced by earthquakes. It addresses tectonic processes and the related variability of seismicity in space and time, earthquake forecasting and short-term precursors, and strong ground motion as a result of source and complex path effects. We study non-linear wave propagation phenomena, liquefaction and triggering of landslides in soil and rock, as well as earthquake-induced snow avalanches. The Valais, and in particular parts of the Rhone, Visper, and Matter valleys have been selected as study areas. Tasks include detailed field investigations, development and application of numerical modeling techniques, assessment of the susceptibility to seismically induced effects, and installation of different monitoring systems to test and validate our models. These systems are for long-term operation and include a continuous GPS and seismic networks, a test installation for observing earthquake precursors, and a system to study site-effects and non-linear phenomena in two test areas (Visp, St. Niklaus / Randa). Risk-related aspects relevant for buildings and lifelines are also considered.

誘起衝撃波による薄板内伝播衝撃波挙動計測

誘起衝撃波による薄板内伝播衝撃波挙動計測

Wave propagations through jointed rock masses and their effects on the stability of slopes

Seismic behavior in rock slopes with discontinuities is largely governed by the geometrical distribution and mechanical properties of the discontinuities. Particularly, high and steep rock slopes, which are dominated by bedding and toppling discontinuity joints, are likely to collapse and cause serious damage to structures near the slopes. Because the composition of geological materials and discontinuities becomes more complex, and depending on the specifics of the ground motion caused by the earthquake, slope stability becomes very complicated under earthquake loadings. Special attention should be paid to the study of wave propagation phenomena in rock masses and their effects on the stability of rock mass slopes. This research first focuses on the analysis of the wave propagation phenomenon using numerical methods. The wave propagation characteristics in rock mass slopes with bedding and toppling discontinuity joints are assessed using two-dimensional, dynamic FEM analyses. An analytical result is obtained in the time domain and allows one to consider multiple wave reflections between joints. Next, a series of shaking table tests are conducted on a scaled model of a high and steep rock slope with bedding discontinuity joints. The shaking table tests are performed to evaluate the influence of wave propagation on the stability of the slope. These tests show that an amplification area will form at the top of the slope. When the amplitude of the input acceleration reaches a certain value, an area at the top of the slope completely collapses along a slide surface, which is simulated using Teflon tape in the experiments.

Computer Simulation Usage For Verification Of Deepened Shaft Artificial Bottom Construction

Abstract The paper presents the design verification methodology for so called artificial bottom of the mining shaft using computer simulation. Artificial bottom serves as the protection of the lower part of the shaft, in which works related to shaft deepening are carried out, against falling to the bottom of the shaft elements transported in its upper, active part. Model describing the phenomenon of artificial bottom stress is complex. In presented case it is a process of collision between object with a mass of 18 Mg model, falling into the shaft from a height of 800 m, and artificial bottom construction and inducted phenomenon of stress and strain wave propagation in various elements of construction. In this case load receiving elements are heavily deformed and many of them has to be destroyed. Therefore for construction verification computer simulation method has been chosen, conducted on the basis of subsequent crash tests, using the LS-DYNA program. The object of the research was an innovative solution of artificial bottom, developed by Central Mining Institute. A series of falling mass impact tests were performed, which had to prove the usefulness of applied solutions, as well as determine the influence of selected construction geometric parameters to effectiveness of transferring the impact load. This way, using the successive approximations method, the assumptions about the number of artificial bottom platforms and plate thickness used for additional coverage of one of the platforms were verified.

Target wave imagery in nonlinear oscillatory systems

Scientists have been familiar with various phenomena of wave propagation for several centuries, such as reflection, diffraction, normal and negative refraction in both linear and nonlinear systems. However, there has been no report about wave imagery in nonlinear systems which is a well-known phenomenon in linear optics. By periodically pacing a small area of a medium in one side of the interface, we reveal target wave imagery in the medium of the other side of the interface. We demonstrate that unlike what happens in linear optics, with certain proper parameter sets, imaging target waves in nonlinear systems can form without apparatus. The imagery process has been discussed in detail. Moreover, the position of the image will move when the core of the pacing-generated target wave changes. This imagery phenomenon provides a new insight into the understanding of the behavior of nonlinear waves, and is helpful to design new functional materials.

Effective medium modelling the effects of saturation on the joint elastic-dielectric properties of carbonates

SUMMARY The effects of saturation on the joint elastic-dielectric properties of porous medium is important for the understanding of elastic and electromagnetic wave propagation phenomena as well as quantifying hydrocarbon content in partially saturated reservoir rocks. We studied theoretically for the first time the crossproperty relations between elastic velocity and dielectric permittivity (the joint elastic-dielectric properties) of carbonates with a unified microstructure. The effects of porosity and water saturation on the joint elastic-dielectric properties were also studied using validated self-consistent effective medium models for elastic velocity and dielectric permittivity. The results offered an important new possibility for estimating in situ carbonate porosity and hydrocarbon saturation using joint velocity-permittivity crossplots from co-located sonic and dielectric surveys.

Pressure wave propagation phenomena in the pipe system of a nuclear power plant

The aim of this research is to compare the experimental data obtained by using PMK-2 test facility which was equipped as an experimental apparatus for water hammering of the pipe system in the KFKI research center in Hungary with some results of numerical calculations (V&V test) based on WAHA3 code on the pressure wave propagation phenomena in a pipe system of a nuclear power plant. In order to simulate pressure wave propagation in the two-phase flow by using WAHA3 code, we used two node systems for numerical calculations: For the first preliminary calculation, we used a simplified node system by assuming all the same area in the entire pipe system. But for the second calculations, we differently used a fully described node system for a real PMK-2 test facility. And then, we finally compare the calculated results using WAHA3 code with the experimental data produced by PMK-2 test facility.