Wave Propagation Process Research Articles

Assessing safety conditions in underground excavations after a methane-air mixture explosion

A technique for evaluation of shock wave impulse after a methane-air mixture explosion is elaborated. The numerical model developed in previous studies has been verified in the laboratory by using laser initiation of explosives and measuring the pressure impulses of explosion products on a ballistic pendulum. To evaluate the mechanical impulse the functional correlations between its magnitude, the swing angle, and the pendulum characteristics have been derived analytically. The reliability of experimental results is ensured by calibrating the sensor that measures the pendulum swing angle and estimating the impulse measurement errors caused by specifics of angle measurements by a digital voltmeter, pendulum axis friction, and the pauses between measurements. Testing the developed technique to evaluate the shock wave impact showed satisfactory consistency of experimental and theoretical results with the momentum deviation below 9%, which confirms model applicability and correct reproducibility of the shock wave propagation process.

EFFECTS OF HYPERCONCENTRATION-RELATED DRAG REDUCTION ON TIDAL PROPAGATION IN THE QIANTANG ESTUARY

The Qiantang Estuary (QE) in the east coast of China is famous for its hyperconcentrated tidal bore with the highest sediment concentration up to about 80 kg/m3 (Pan et al., 2013). Recent research for some European estuaries has indicated that hyperconcentrated environment may affect tidal propagation through hydraulic drag reduction, resulting in an enlarged tidal range and even a regime shift in the estuary (Winterwerp and Wang, 2013). However, this water-sediment interactions have not been considered in the tidal prediction of the Qiantang Estuary in the past. Instead, a bed roughness even smaller than that of glossy glass has often been used to fit the observed tidal data in the mathematical modelling.
 
 Therefore, the present study aims to reveal whether the hyperconcentration-related drag reduction can explain the mechanism of very small bed roughness in the Qiantang Estuary and to what extent it can affect the tidal propagation especially for the tidal range. First, an analytical model is used to predict the tidal range along the QE (from Wenyan to Ganpu stations) for different methods of bed friction. Then, mathematical modelling is conducted to shed light on the processes of tidal wave propagation for the corresponding approaches. The results of the two models are compared together with the field observations to further verify the ability of the analytical model and the significance of the effects of hyperconcentration-related drag reduction.

The vertical wave number spectra of potential energy density in the stratosphere deduced from the COSMIC satellite observation

The present study investigates the global vertical wave number spectra of potential energy density in the stratosphere by utilizing the COSMIC temperature data in the period January 2007 to February 2014. The statistical analysis shows that the spectral amplitude (defined as the maximum spectral energy density) varies from 0.1 × 104 m2 s−2 (cycle/m)−1 to 3.2 × 104 m2 s−2 (cycle/m)−1, generally smaller than the theoretical saturated spectral amplitude, with remarkable temporal and spatial variations. Due to the latitudinal and seasonal variations of the background winds and wave sources, the amplitude exhibits obvious quasi‐biennial, annual and semi‐annual cycles at low latitudes, and the annual cycle at middle and high latitudes. The spectral slope, ranging from −1.6 to −3.0, is systematically less negative than the canonical value of −3, and exhibits a quasi‐biennial cycle at low latitudes, annual cycle at middle and high latitudes, and semi‐annual cycle at boreal high latitudes. Different from the amplitude, the slope shows weaker temporal and latitudinal variations, strongly indicating a more universal feature of the slope, which mainly results from the wave propagation process (such as the wave–wave or wave–background flow interactions) rather than the wave source characteristics. Furthermore, we statistically study the longitudinal variation of the spectral parameters. The spectral amplitude at different latitudes shows an obvious and distinctive longitudinal distribution, which is attributed to the latitude‐dependent jet and front mechanisms and/or orography. However, the slope has no evident longitudinal distribution except over around 120°W, 67°W and 85°E. This may be accounted for by the fact that orography‐excited gravity waves are easily influenced by the background winds due to their low frequencies. Interestingly, the amplitude and slope have negative correlation at most latitudes. Larger spectral amplitudes could mean that the gravity wave spectrum is more strongly saturated, resulting in a spectral slope closer to the theoretical value of −3.

Characterization of laser-driven shock compression by time-resolved Raman spectroscopy

To characterize the laser-driven shock wave propagation process in anthracene molecules, the time-resolved Raman spectroscopy experiments were performed. After establishing a pressure distribution formula and using Lorenz profile to simulate the experimental Raman spectrum, the pressure distribution in the gauge layer during the pressure loading and unloading processes will be clarified in real time. The velocity of shock wave in the gauge layer, calculated through the shock front location at various delay time, is about 2.99 km s−1. Noticing that the relative intensity of compressed Raman mode is proportional to the velocity of the shock wave, in this work, this relationship was identified in a new mathematical expression after establishing a physical model. The velocity of shock wave calculated from the new formula is about 3.02 km s−1, which was in great agreement with the previous method and both methods are corresponded to practice.

A double double-porosity model for wave propagation in patchy-saturated tight sandstone with fabric heterogeneity

In natural reservoir rocks, fabric heterogeneity can further induce heterogeneous geometrical distribution of immiscible multi-phase fluid mixture, since fluid migration may be affected by lithological variation (mainly permeability) in geological time scales, causing patchy saturation of fluids. Both structure heterogeneity and patchy-saturation can lead to strong seismic wave dispersion and attenuation. In this work, a double double-porosity model is presented to describe the overlapping effect of the two heterogeneities on wave dispersion and attenuation. The wave propagation equations are derived from the Hamilton’s principle, and the numerical results for a tight sandstone are compared with corresponding low-frequency experimental data, which shows good agreements. This new model allows for a comprehensive description of wave propagation process in highly complex reservoirs.

Numerical study on interface debonding detection mechanisms with 2D spectral element method for concrete-filled steel tube using embedded PZT sensor

Interface debonding detection approaches based on stress wave measurement for concrete-filled steel tube (CFST) members have received a great deal of attention in civil and infrastructural engineering societies. The development of efficient computing approaches to investigate the mechanisms of the interface debonding detection approaches and the effect of interface debonding on wave propagation within CFST members is critical. In this study, the wave propagation within the cross section of CFST members with and without interface debonding under a single point excitation force is simulated with a two-dimensional (2D) spectral element method (SEM) at first and that of CFST models coupled with a surface-mounted piezoelectric lead zirconate titanate (PZT) actuator and an embedded PZT sensor in the concrete core under continuous and sweep sinusoidal signals is simulated with the 2D SEM and a piezoelectric spectral element. The debonding defect is modeled by removing concrete elements between the steel tube and the concrete core. Results show that interface debonding affects the wave propagation process, the output potentials of the embedded PZT sensors as well as the displacement responses at different locations of CFST specimens obviously. Rayleigh damping identified from experiments is introduced to the SEM models to reflect wave attenuation in the coupled models. The effect of interface debonding on the amplitude, the Fourier spectra and the wavelet packet energy of stress waves are analyzed. For comparison, another numerical model in which the PZT actuator is not located near the interface debonding defect is studied numerically and the effect of the debonding defect on the response of the embedded PZT sensor is illustrated. SEM provides an efficient way to simulate stress wave propagation and to understand the mechanisms of interfacial debonding defect detection for CFSTs with PZT technique.

Numerical Investigation of Combustion Characteristics of a Wave Rotor Combustor Based on a Reduced Reaction Mechanism of Ethylene

To improve simulations of the flame and pressure wave propagation process and investigate the combustion characteristics of a wave rotor combustor (WRC), direct relation graphs with error propagation (DRGEP), quasi-steady-state assumption (QSSA), and sensitivity analysis were used to establish a reduced reaction mechanism comprised of 23 species and 55 elementary reactions, based on the LLNL N-Butane mechanism. The reduced reaction mechanism of ethylene was combined with an eddy dissipation concept (EDC) model to simulate the flame propagation characteristics in a simplified WRC channel. The effects of spoilers with different blockage ratios and hot-jets of different species on combustion characteristics of flame propagation and pressure rise in the WRC channel were investigated. When the heated inert air was used as hot-jet, the ignition delay time of WRC would increase, which indicated that the activity of the burned gas from the hot-jet igniter would affect the ignition delay time. The spoiler facilitates the coupling of flame and shock waves to reduce the coupling time and distance. With the blockage ratio of the spoiler increasing, the coupling time and distance would be reduced.

Proxy mineral magnetic and elemental analyses for 2004 tsunami impact deposit along the Muttukadu backwater, East Coast of India: Scope of the palaeotsunami studies

Following the line of approach enumerated in the tsunami toolkit of Chagué-Goff et al. (2011), ‘Expanding the proxy toolkit to help identify past events - Lessons from the 2004 Indian Ocean Tsunami and the 2009 South Pacific Tsunami, Earth Sci. Rev. 107 (1–2), 107–122’, measurements of elemental and mineral magnetic properties coupled with textural parameters have been used to evaluate the 2004 Indian Ocean Tsunami (IOT) induced sediments on the Muttukadu backwaters, East Coast of India. To investigate the sediment provenance, specific Fe, Mn and Pb elemental concentrations were measured in surface sediments and compared with the previously published pre-tsunami database of backwater/inner continental shelf sediments. We found the enrichment of Fe and Pb, against depletion of Mn concentration in present tsunami sediments as compared with pre-tsunami Muttukadu sediments, reflecting the variation of the sediment source area. However, the present data of Fe and Pb enrichment and Mn depletion correlates well with continental shelf sediments hinting at sedimentary routes, processes of erosion and wave propagation. The studied tsunami deposits are characterized by dominant ∼40–85% coarse sand fractions and higher proportion of detrital low and high coercivity Fe-Ti oxides, such as magnetite, titanomagnetite and hematite, reflected by magnetic concentration (magnetic susceptibility (χ), anhysteretic remanent magnetization (ARM)) and coercivity-dependent parameters (soft isothermal remanent magnetization (Soft IRM), Hard IRM, magnetomineralogical S-Ratio and saturation IRM (SIRM)). So, it can be shown that the random spatial variability and the inverse relationship between magnetic concentration χ, ARM and SIRM parameters and grain-size ARM/χ, SIRM/χ and ARM/SIRM ratios as diagnostic criteria for the tsunami impacted the distribution of magnetic parameters in coastal backwater environments. Contrasting mineral magnetic and geochemical properties together with more sand (mean 65%) when compared with silt (mean 25%) content in tsunami sediments indicates that the area was affected by high-energy tsunami waves. The study validates environmental magnetism as a proxy, which is fast and robust for identifying the tsunami or palaeotsunami deposits.

Terahertz wave generation from liquid water films via laser-induced breakdown

Understanding the physics of terahertz (THz) wave generation from water is essential for developing liquid THz sources. This letter reports detailed experimental measurements of THz wave emission by focusing intense laser pulses onto water films. The simulation based on a ponderomotive force-induced dipole is supported by the observation of the THz intensity dependence on the laser incidence angle. This work provides fundamental insights into the THz wave generation process in water and an alternative perspective for studying laser-induced breakdown in liquids.

Transition from the Wave Equation to Either the Heat or the Transport Equations through Fractional Differential Expressions

We present a model that intermediates among the wave, heat, and transport equations. The approach considers the propagation of initial disturbances in a one-dimensional medium that can vibrate. The medium is nonlinear in such a form that nonlocal differential expressions are required to describe the time evolution of solutions. Nonlocality was modeled with a space-time fractional differential equation of order 1 ≤ α ≤ 2 in time, and order 1 ≤ β ≤ 2 in space. We adopted the notion of Caputo for the time derivative and the Riesz pseudo-differential operator for the space derivative. The corresponding Cauchy problem was solved for zero initial velocity and initial disturbance, represented by either the Dirac delta or the Gaussian distributions. Well-known results for the conventional partial differential equations of wave propagation, diffusion, and (modified) transport processes were recovered as particular cases. In addition, regular solutions were found for the partial differential equation that arises from α = 2 and β = 1 . Unlike the above conventional cases, the latter equation permits the presence of nodes in its solutions.

Numerical investigation on combined wave damping effect of pneumatic breakwater and submerged breakwater

This paper attempts to combine the pneumatic breakwater and submerged breakwater to increase the effectiveness of wave damping for long-period waves. A series of physical experiments concerning pneumatic breakwater, submerged breakwater and their joint breakwater was conducted and used to validate a mathematical model based on Reynolds-averaged Navier-Stokes equations, the RNG k-ε turbulence model and the VOF method. In addition, the mathematical model was used to investigate the wave transmission coefficients of three breakwaters. The nonlinear wave propagation behaviors and the energy transfer from lower frequencies to higher frequencies after the submerged breakwater were investigated in detail. Furthermore, an optimal arrangement between pneumatic breakwater and submerged breakwater was obtained for damping longer-period waves that cannot be damped effectively by the pneumatic breakwater alone. In addition, the reason for the appearance of the combination effect is that part of the energy of the transmitted waves over the submerged breakwater transfers to shorter-period waves. Finally, the impact of the joint breakwater on the wave field during wave propagation process was investigated.

Application of Spectral Methods to Inverse Dynamic Problem of Seismicity of a Stratified Medium

Under study is the wave propagation process in the half-space y3 = 0 with the Cartesian coordinates y1, y2, and y3 which is filled with an elastic medium. The parameters of the medium are discontinuous and depend only on the coordinate y3. The wave process is induced by an external perturbation source that generates a plane wave moving from the domain y3 > h > 0. It is proved that the direct dynamic problem is uniquely solvable in the corresponding function space, and a special presentation is found for the solution. The problem of determination of the acoustic impedance of the medium from the wave field measurements on the surface is investigated by the spectral methods of the theory of differential equations.

Investigation on residual stress distribution in thin plate subjected to two sided laser shock processing

Two sided laser shock processing (TSLSP) has been an innovative process to impart the favorable compressive residual stresses into thin components without producing excessively detrimental deformation. In this paper, the investigations focus on the residual stresses distribution in the 7075-T7351 alloy plate with thickness of 2 mm, whose both side surfaces are subjected to shock waves with peak pressure 2 GPa induced by laser with duration 24 ns. The dynamic propagation and attenuation process of stress waves in thickness direction of the plate is also investigated, and the critical factors on residual stresses field are further discussed. The results reveal that the whole thickness section between the irradiated areas is distributed with the compressive residual stresses, while the surrounding of the region distributed with compressive residual stresses is accompanied by the tensile residual stresses. The distribution characteristic of residual stresses in the processed plate is closely related to the exact values of the applied parameters in TSLSP treatment.

Assessment of Pluvial Floods Potential on the Rivers of the Republic of Moldova

Abstract Present study is dedicated to assessment and mapping of generation and propagation potential of flash flood and river floods on the rivers of the Republic of Moldova. Main methods applied in the research are Flash Flood Potential Index (FFPI) and Flooding Potential Index (FPI). Additionally, a new index for estimation of flood propagation potential (FPPI) is proposed in order to evaluate impact of main factors (natural and human) on propagation of flood wave through the floodplain of small and medium-sized rivers of Moldova. In total, assessment of FFPI an FPI was performed for 789 elementary river basins (basin area less than 200 km2) and also was considered for 983 elementary territorial-administrative units (communes). Estimation of FPPI was made for 50 main small and medium sized rivers of Moldova. All index parameters (7 for FFPI, 6 for FPI and 12 for FPPI) were integrated, analyzed and combined in GIS environment. As a results, it was found that the FFPI is average for mostly all basins and communes but is characterized by significant differences in spatial representation on local level. FPI is high in basins and communes situated in the floodplains of large and medium sized rivers, in flood-prone areas, and is low in those with high altitudes and steep slopes (Codri and Nistru heights). Flood propagation potential was estimated with average values for 56% of total number of rivers, high for 34% and very high for 6%. The results can be used for future estimation of flood generation and flood wave propagation processes and for improvement and optimization of flood management practices and strategies on rivers weakly studied from hydrology point of view.

A Numerical Landslide-Tsunami Hazard Assessment Technique Applied on Hypothetical Scenarios at Es Vedrà, Offshore Ibiza

This study presents a numerical landslide-tsunami hazard assessment technique for applications in reservoirs, lakes, fjords, and the sea. This technique is illustrated with hypothetical scenarios at Es Vedrà, offshore Ibiza, although currently no evidence suggests that this island may become unstable. The two selected scenarios include two particularly vulnerable locations, namely: (i) Cala d’Hort on Ibiza (3 km away from Es Vedrà) and (ii) Marina de Formentera (23 km away from Es Vedrà). The violent wave generation process is modelled with the meshless Lagrangian method smoothed particle hydrodynamics. Further offshore, the simulations are continued with the less computational expensive code SWASH (Simulating WAves till SHore), which is based on the non-hydrostatic non-linear shallow water equations that are capable of considering bottom friction and frequency dispersion. The up to 133-m high tsunamis decay relatively fast with distance from Es Vedrà; the wave height 5 m offshore Cala d’Hort is 14.2 m, reaching a maximum run-up height of over 21.5 m, whilst the offshore wave height (2.7 m) and maximum inundation depth at Marina de Formentera (1.2 m) are significantly smaller. This study illustrates that landslide-tsunami hazard assessment can nowadays readily be conducted under consideration of site-specific details such as the bathymetry and topography, and intends to support future investigations of real landslide-tsunami cases.

The effects of microstructure on wave velocity and wavefront in granular assemblies with binary-sized particles

The nonlinear behavior of highly ordered granular materials is due to their inability to transfer tensile loads and the Hertzian contact between particles. We investigated the propagation of stress waves excited by impulsive loadings in granular assemblies composed of an uncompressed, centered square array of spherical particles the radii of which are gradually increased. Systematic variations in the radius ratio of the surrounding and intruder particles lead to large variations in the characteristics of the wave velocity and propagating stress wavefronts traveling through the system. By assuming the dissipating rate of the contact interface, the pulse energy dissipation is obtained, which provides a solution to the calculation of the frictional energy consumption. The relationship between the microstructure and the wavefront shape is of concern. Finally, equations of the wavefront in hexagonal assemblies were analytically given which substantiated reasonable prediction of the wave propagation process through the assemblies.

Propagation of Cylindrical and Spherical Waves in Two-Layer Soil Media

The process of wave propagation in a two-layer media is studied numerically using a model of nonlinear liquid three-component medium. The cases of cylindrical and spherical symmetries are considered. For description of wave propagation, the equations of continuum mechanics are used. The propagation of a pressure wave in the radial direction in a two-layer soil medium is described. The results are analyzed depending on layer parameters for both cases of symmetry.

Debonding detection for rectangular CFST using surface wave measurement: Test and multi-physical fields numerical simulation

Abstract The interfacial debonding detection approach for concrete-filled steel tubular (CFST) members using surface-mounted piezoelectric-lead-zirconate-titanate (PZT) actuators and sensors is experimentally and numerically investigated. In this study, an interfacial debonding detection approach using surface wave measurement with PZT patches is propoed firstly and experimental investigation on the feasibility of the proposed approach with two CFST specimens with different levels of interface debonding defects is carried out. For comparison, a PZT sensor is also embedded in concrete core to measure the stress wave traveling from the surface-mounted PZT actuator. Experiment results indicate that the voltage amplitude of the embedded PZT sensor representing the wave propagation from the steel plate into the concrete core decreases due to the existence of interfacial debonding defect, but the output signal of the surface-mounted PZT sensor increases accordingly when interface debonding occurs. Moreover, the increment of surface-mounted PZT sensor measurement is related to the dimension of the interface debonding defects. The experimental finding implies that the interface debonding is detectable using surface wave measurement. In order to investigate the mechanism of the proposed approach, numerical study on the wave propagation process in CFSTs is further discussed by using three-dimensional (3D) solid element models and two-dimensional (2D) plane strain models, respectively. Finally, in order to consider the effect of nonhomogeneous meso-scale structure of concrete on the wave propagation, a random aggregate method (RAM) is employed to model the concrete core and multi-physical fields coupling numerical analysis on stress wave propagation of the CFST member with different interface debonding defects is performed. The numerical findings meet well with the experimental observations and the results indicate that the interface debonding of CFST can be detected efficiently using surface wave measurement.

Driving frequency dependent wave modes of point-focusing electromagnetic acoustic transducers.

This article presents a driving frequency dependent wave mode of point-focusing electromagnetic acoustic transducers (PF-EMATs), which is composed of a cylindrical permanent magnet and a concentric meander line (CML) coil with a varying spacing interval for concentring the ultrasound waves to a point. A finite element model is established to simulate the incentive and propagation process of ultrasonic waves so that the focusing characteristic, such as displacement, amplitude profile, and focal offset, can be obtained, allowing for investigation into the driving frequency dependence of wave modes. In addition, the universality of driving frequency dependent wave modes is well demonstrated. Furthermore, the relationship between the focusing performance of the developed PF-EMAT and the coil parameters, inner radius RC and number of turns NC of the CML coil, is explored. Finally, the experimental results show good agreement with the simulated results and indicate that the presented driving frequency dependent wave modes of PF-EMATs employing CML coils could manipulate the wave modes by carefully controlling the driving frequency.

Simulation of induced acoustic emission in fractured porous media

Acoustic/microseismic Emissions (AE) in naturally fractured porous media are the result of local instability along internal interfaces and the sudden release of strain energy stored in the rock matrix. This rapid release of energy, stimulates high-frequency components of the dynamic response of the rock mass, inducing mechanical wave propagation. In this article an enriched finite element model is employed to concurrently simulate the interface instability and the induced wave propagation processes in a fractured porous media. Harmonic enrichment functions are used in the context of the Generalized Finite Element Method (GFEM) to suppress the spurious oscillations that can appear in wave propagation/dynamic modelings using regular finite elements. To model the fractures, the Phantom Node Method (PNM) is employed with the GFEM. The frictional contact condition at material interfaces is modeled using a stable augmented Lagrange multiplier approach. Through various parametric studies it’s shown that (i) decreasing the permeability leads to an increase in the frequency and a decrease in the amplitude of the acoustic signal; (ii) increasing viscous damping leads to narrower frequency spectrum and decreased magnitude of the emitted acoustic signal; (iii) increasing damping leads to a transition from transient wave propagation to diffusion-dominated AE response; (iv) increasing interface friction leads to more pronounced stick-slip behavior and higher amplitude AE-without interface friction there is no AE. Lastly, the numerical illustrations demonstrate the superior capability of the enriched model (in comparison with regular finite element models) in suppressing the spurious oscillations in AE solutions.