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Based on the second-order harmonic potential theory, the characteristics of the second-order harmonic field generated at the solid-liquid interface induced by P wave incidence are analyzed. A planar model of the solid-liquid interface is established to study the variation of the second-order displacement field versus the incident angles. The homogeneous solution coefficient matrix, refraction and reflection coefficient matrix are introduced. According to the boundary conditions and Lagrange's various parameters method, the second-order displacement field is obtained, and its dependence on the solid-liquid interface is investigated. The different effects of boundary on the tangential displacement and normal displacement are demonstrated. Numerical simulation shows that the complete solution varies slightly at the incident angle, and the tangential displacement and the normal displacement change sharply at a mutation angle θ

Structural health monitoring (SHM) is a revolutionary and innovative technique for determining structural integrity. It has broad application prospects in industrial equipment and infrastructure such as aircrafts, bridges and buildings. SHM system is used to monitor and diagnose the damages of these large structures, and it requires to install large sensor networks in or on large structures such as aircraft wings and airframes. The large number of sensors results in a very large amount of data for excited and received signals, especially for ultrasonic guided wave-based SHM with high frequency signals. According to the traditional Nyquist sampling theorem, the sampling rate is at least 2 times higher than the highest frequency of the received signal. The high sampling rate and the large amount of data pose a serious challenge on the signal acquisition, transmission, storage, and processing equipment, especially in the case that the signal needs to be transmitted to the base station for processing in real time. Therefore, how to compress and sample signals obtained by large sensor networks to improve monitoring efficiency and reduce costs is a research hotspot in current SHM. This paper adopts compressive sensing (CS) theory which has appeared in recent years to solve the big data and high frequency acquirement problem of SHM. The random demodulation system is chosen to realize CS, and the corresponding hardware and software systems are designed, which are achieved to compress and sample signal and reduce the sampling rate and the amount of data at the same time. The active and passive SHM signals based on piezoelectric sensor networks are compressed and sampled, and the new method are compared with the traditional Nyquist sampling in the experiment. The results show the effectiveness of the proposed method.

Effectively sizing inclined cracks inside material is a difficult issue in ultrasonic non-destructive testing. To size the length, depth and orientation of inclined crack, a modified ultrasonic time-of-flight diffraction testing with double receivers (DR-TOFD) using Barker code excitation is proposed. The DR-TOFD technique is excited by Barker code, which has accurate time precision, and the diffraction wave of the crack tips is received by two receivers. The diffraction signals are compressed by matched filter to obtain desired detecting signals, which are used to estimate the length, depth and orientation of crack. Finite element method, which simulates wave propagation in specimen with a 6 mm crack with different inclination angles, is used to evaluate the detecting ability of the DR-TOFD with Barker code excitation. The simulation results show that the time precision of the proposed technique is up to 0.01 μs. Experiment is also performed to verify the detecting ability of DR-TOFD. The experiment results show that the proposed technique is able to expediently and accurately size inclined crack.

To study the leakage situation of a liquid-filled pipe in long-term service, a model of a liquid-filled pipe embedded in an infinite porous medium as well as in a finite porous medium is designed. The principal motivation is to perform detailed quantitative analysis of the longitudinal guided wave propagating in a liquid-filled pipe embedded in a saturated porous medium. The problems of pipeline leakage and porosity as well as the media outside the pipe are solved to identify the characteristics of the guided wave in a more practical model. The characteristics of the guided wave are investigated theoretically and numerically, with special emphasis on the influence of porous medium parameters on the dispersion properties. Assuming the pipe is a cylindrical shell buried in an isotropic, homogeneous, and porous medium, the dispersion equations are established based on the elastic-dynamic equations and the modified Biot liquid-saturated porous theory. The characteristics of dispersion, time-domain waveform and attenuation curves varying with porous medium parameters, wrapping layer material, and thickness, are all analyzed. The increase in porosity decreases the partial mode phase velocity in the liquid-filled pipe embedded in the finite porous medium. The characteristics of attenuation are in good agreement with the dispersion curves and the time-domain waveform results.

The research focuses on measuring body wave by continuous laser scanning along the surface of aluminum plate. The model of aluminum plate was established by finite element method. The temperature near the upper edge rises, and the temperature rise is small. In infinite large aluminum plates, there are transverse and longitudinal wave front, and the wave front velocity is affected by the velocity of the scanning laser source. Finally, the wave front in plate bottom is used to identify the wave front type, which is generated by scanning laser and determined by combining the relationships between wave velocity and scanning velocity and Bscan diagram.

A two-component lattice Boltzmann method (LBM) with a multiple-relaxation-time (MRT) collision operator is presented to improve the numerical stability of the single relaxation time (SRT) model. The macroscopic and the momentum conservation equations can be retrieved through the Chapman-Enskog (C-E) expansion analysis. The equilibrium moment with the diffusion term is calculated, a diffusion phenomenon is simulated by utilizing the developed model, and the numerical stability is verified. Furthermore, the binary mixture channel model is designed to simulate the sound attenuation phenomenon, and the obtained simulation results are found to be consistent with the analytical solutions. The sound attenuation model is used to study the numerical stability and calculation accuracy of the LBM model. The simulation results show the stability and accuracy of the MRT model and the SRT model under different viscosity conditions. Finally, we study the influence of the error between the macroscopic equation of the MRT model and the standard incompressible Navier–Stokes equation on the calculation accuracy of the model to demonstrate the general applicability of the conclusions drawn by the sound attenuation model in the present study.

The investigation focuses on analyzed the influence of periodic V-defects on wedge waves by laser ultrasound technique. Usually, wedge tip is almost non-perfect, which may bring in break and enormous economic losses. The wedge waveguide models with different periodic V-defects were established by using finite element method. We have observed multiple mode wedge waves in 20° wedge. The depth of defect is 0.1mm, and the periodic number are 1, 6, 12, and 24, respectively. Both reflected and transmitted waves are observed. And the low order reflected wave and transmitted wave modes separate from high order mode. As periodic number increase, the amplitude of reflected wave and transmitted wave decreased. By integrating the power spectra of the wedge waves, the energy distribution of these wedge waves of different periodic are analyzed. It is found that the energy has a fluctuation, which could be determined the location of defect. The energy has a gradually increase as the propagation before defect, and dramatic decrease after the defect. The results of this study can provide theoretical guidance for the positioning and size estimation of wedge defects.

Understanding the dynamic characteristic of the cavitation bubble near a solid wall is a fundamental issue for the bubble collapse application and prevention. In the present work, an improved three-dimensional multi-relaxation-time pseudopotential lattice Boltzmann model is adopted to investigate the cavitation bubble collapse near the solid wall. With respect to thermodynamic consistency, Laplace law verification, the three-dimensional pseudopotential multi-relaxation-time lattice Boltzmann model is investigated. By the theoretical analysis, it is proved that the model can be regarded as a solver of the Rayleigh–Plesset equation, and confirmed by comparing the results of the lattice Boltzmann simulation and the Rayleigh–Plesset equation calculation for the case of cavitation bubble collapse in the infinite medium field. The bubble collapse near the solid wall is modeled using the improved pseudopotential multi-relaxation-time lattice Boltzmann model. We find the lattice Boltzmann simulation and the experimental results have the same dynamic process by comparing the bubble profiles evolution. Form the pressure field and the velocity field evolution it is found that the tapered higher pressure region formed near the top of the bubble is a crucial driving force inducing the bubble collapse. This exploratory research demonstrates that the lattice Boltzmann method is an alternative tool for the study of the interaction between collapsing cavitation bubble and matter.

Many problems in measurement data are the physical quantities which are used to reconstruct an image for non-destructive testing. Time of flight data ultrasonic computed tomography is used in concrete non-destructive testing. Here the maximum likelihood expectation maximization (MLEM) algorithm and ultrasonic time of flight data is used to evaluate concrete filled steel tubes. When the image is reconstructed with the measurement data, the image shows many artifacts and therefor it is difficult to find useful information from the reconstruction image. To obtain a high quality image, time of flight data interpolation and normalization are proposed for image reconstruction system. Experimental results indicate the successful identification of the steel tube position and shape, which is not filled with concrete. The results imply that the time of flight data for ultrasonic computed tomography as an effective method of using the time of flight tomography to enhance the soundness of evaluation for concrete filled steel tubes.

Cavitation bubble collapse near rough solid wall is modeled by the multi-relaxation-time (MRT) pseudopotential lattice Boltzmann (LB) model. The modified forcing scheme, which can achieve LB model’s thermodynamic consistency by tuning a parameter related with the particle interaction range, is adopted to achieve desired stability and density ratio. The bubble collapse near rough solid wall was simulated by the improved MRT pseudopotential LB model. The mechanism of bubble collapse is studied by investigating the bubble profiles, pressure field and velocity field evolution. The eroding effects of collapsing bubble are analyzed in details. It is found that the process and the effect of the interaction between bubble collapse and rough solid wall are affected seriously by the geometry of solid boundary. At the same time, it demonstrates that the MRT pseudopotential LB model is a potential tool for the investigation of the interaction mechanism between the collapsing bubble and complex geometry boundary.

The thermodynamic of cavitation bubble collapsing is a complex fundamental issue for cavitation application and prevention. The pseudopotential and thermal multi-relaxation-time lattice Boltzmann method (MRT-LBM) is adopted to investigate the thermodynamic of collapsing cavitation bubble in this paper. The simulation results satisfy the maximum temperature equation of the bubble collapse, which derived from the Rayleigh-Plesset (R-P) equation. The validity of thermal MRT-LBM in simulating the collapse process of cavitation bubble is verified. It shows that the temperature evolution of vapor-liquid phase is well captured. Furthermore, the two-dimensional (2D) temperature, velocity and pressure field of the bubble near a solid wall are analyzed. The maximum temperature inside the bubble and wall temperature under different position offset parameters are discussed in details.

The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect. The complexity of this topic is that the cavitation bubble collapse includes many extreme physical phenomena and variability of different solid surface properties. In the present work, the cavitation bubble collapse in hydrophobic concave is studied using the pseudopotential multi-relaxation-time lattice Boltzmann model (MRT-LB). The model is modified by involving the piecewise linear equation of state and improved forcing scheme. The fluid–solid interaction in the model is employed to adjust the wettability of solid surface. Moreover, the validity of the model is verified by comparison with experimental results and grid-independence verification. Finally, the cavitation bubble collapse in a hydrophobic concave is studied by investigating density field, pressure field, collapse time, and jet velocity. The superimposed effect of the surface hydrophobicity and concave geometry is analyzed and explained in the framework of the pseudopotential LBM. The study shows that the hydrophobic concave can enhance cavitation effect by decreasing cavitation threshold, accelerating collapse and increasing jet velocity.

A multicomponent thermal multi-relaxation-time (MRT) lattice Boltzmann method (LBM) is presented to study collapsing cavitation bubble. The simulation results satisfy Laplace law and the adiabatic law, and are consistent with the numerical solution of the Rayleigh–Plesset equation. To study the effects of the non-condensable gas inside bubble on collapsing cavitation bubble, a numerical model of single spherical bubble near a solid wall is established. The temperature and pressure evolution of the two-component two-phase flow are well captured. In addition, the collapse process of the cavitation bubble is discussed elaborately by setting the volume fractions of the gas and vapor to be the only variables. The results show that the non-condensable gas in the bubble significantly affects the pressure field, temperature field evolution, collapse velocity, and profile of the bubble. The distinction of the pressure and temperature on the wall after the second collapse becomes more obvious as the non-condensable gas concentration increases.

The dynamics of the bubble collapse near a rigid boundary is a fundamental issue for the bubble collapse application and prevention. In this paper, the bubble collapse is modeled by adopting the lattice Boltzmann method (LBM) and is verified, and then the dynamic characteristics of the collapsing bubble with the second collapse is investigated. The widely used Shan-Chen model in the LBM multiphase community is modified by coupling with the Carnahan-Starling equation of state (C-S EOS) and the exact difference method (EDM) for the forcing term treatment. The simulation results of the bubble profile evolution by the LBM are in excellent agreements with the theoretical and experimental results. From the two-dimensional pressure field evolution, the dynamic characteristics of the different parts during the bubble collapse stage are studied. The role of the second collapse in the rigid boundary damage is discussed, and the impeding effect between two collapses is demonstrated.

Electric discharge in and in contact with water can accompany ultraviolet (UV) radiation and electron impact, which can generate a large number of active species such as hydroxyl radicals (OH), oxygen radical (O), ozone (O3) and hydrogen peroxide (H2O2). In this paper, a nonthermal plasma processing system was established by means of dielectric barrier discharge (DBD) arrays in water mist spray. The relationship between droplet size and water content was examined, and the effects of the concentrations of oxides in both treated water and gas were investigated under different water content and discharge time. The relative intensity of UV spectra from DBD in water mist was a function of water content. The concentrations of both O3 and nitrogen dioxide (NO2) in DBD room decreased with increasing water content. Moreover, the concentrations of H2O2, O3 and nitrogen oxides (NOx) in treated water decreased with increasing water content, and all the ones enhanced after discharge. The experimental results were further analyzed by chemical reaction equations and commented by physical principles as much as possible. At last, the water containing phenol was tested in this system for the concentration from 100 mg/L to 9.8 mg/L in a period of 35 min.

A method is presented that combining the Mcclements suspension model with the cylindrical model to solve the complexity of calculating the scattered acoustic pressure around the cylinder, when suspended particles are contained in the water. The scattered acoustic pressure of an infinitely long cylinder in water is derived based on the boundary conditions. Then, the wave number of the particle-containing suspension is calculated by the Mcclements suspension model, which is combined with the scattered acoustic pressure of an infinitely long rigid cylinder in water. The scattered acoustic pressure of an infinitely long rigid cylinder in suspension is obtained. The results show that the content of sediment particles has a greater impact on the distribution of scattered acoustic pressure. The scattered acoustic pressure is more directional with the increase of the content of sand particles, laying a foundation for further research on other target objects in suspension.

In the ultrasonic testing of submarine pipelines by using guided waves, wave energy leakage is a main reason of signal decay. For overcoming the decrease of energy attenuation, the propagation of guided waves of immersion plates is studied in this paper. The dispersion equations of guided waves is numerically solved. Then the appropriated modes of which phase velocity are small or large are selected for optical Schlieren visualization and propagation of leaky waves is discussed. It is shown that selecting some modes of which imaginary part are small can retard guided wave decay and extend length of testing.

Bars or tubes are widely used in all kinds of equipment such as automobile shafts or power plant boilers. Effective detection of internal transverse defects is very important to the security of the equipment. In this paper, the time-delay algorithm for the detection by using the combination of a phased array ultrasonic probe and a wedge was discussed. Firstly, a coordinate system was established and the position of each element was calculated. The focal point position of phased array ultrasonic wave was specified. Secondly, based on the geometric acoustics assumption, the equation of the sound wave incident location of each element and its scope on the interface between wedges and artifacts were deduced by using Fermat's principle. The numerical method was implied to solve the equations. And the delay time of each element of the array was computed. Finally, the computed delay time of each element was imported to the finite element model and the acoustic beam was simulated. The result shows that the detecting waves can be focused to the specified position by using the calculated delay time. This paper provides a method to calculate the delay time of each element of phased array probes for detecting the transverse defects of cylindrical surface artefacts.

The research focuses on measuring the influence of V-defect on wedge waves propagating along line wedge tip by using laser ultrasound technique. Generally, wedge has more or less defect or damage on the tip, which may result in break and bring economic losses. Thus it is necessary to investigate characteristic of wedge waves propagating along line wedge with defect. The wedge waveguide models with different defect depth were built by using finite element method. Multiple mode wedge waves were observed through B-scan. The open of defect is 0.1mm, and the depth is 0.01mm, 0.05mm, 0.1mm, 0.2mm, and 0.3mm, respectively. It was seen that both reflected and transmitted waves were observed. Due to the dispersion characteristics, we observed the reflected and transmitted A 1 mode separated from A 2 mode, which can be used to determine the width of V-defect. Meanwhile, models of V-defect with different depth are also built. We had found that wedge waves are totally reflected and there is no transmitted wave observed as the depth is bigger than 0.3mm.

The research focuses on measuring the influence of defect on wedge waves by using laser ultrasound technique. The wedge waveguide models with defect and different angles were built and calculated by using finite element method. Both reflected and transmitted waves are observed. Meanwhile, angle has the greatest influence on the low-order wedge wave mode, and there is low order reflected wave and transmitted wave modes separate from high order mode. By integrating the power spectra of the wedge waves, the energy distribution of these wedge waves of 20°, 30°, 45° and 60° wedge are analyzed, and the location of defect is determined. The results of this study can provide theoretical guidance for the positioning and size estimation of wedge defects.

Surface breaking cracks pose great risk to the security of steel structure equipment. It is very important to estimate the height and the orientation of surface breaking cracks accurately for the residual life evaluation of equipment. In this paper, a modified phased array ultrasonic absolute arrival time technique (AATT) for this purpose was proposed. It utilizes the absolute position of the tip diffraction echo and the corner reflection echo in a ultrasonic phased array S-scan image to estimate the crack height and the crack inclination angle. The height and the orientation of the surface breaking cracks was deduced with ray acoustic approximation. Both pencil approximation and Kirchhoff approximation were used to simulate the phased array ultrasonic S-scan image of the surface breaking cracks. The echo arrival time extracted from the S-scan image was used to calculate the height and the orientation of surface breaking cracks with AATT technique. The calculated result agree with the size of pre-set cracks in simulation. Proved that the AATT technique can be applied to measure the size of surface breaking cracks, especially in the testing from single side.

The interaction between cavitation bubbles and solid surfaces is an important issue when investigating the mechanism of collapsing cavitation bubbles. The property of a solid surface has a great effect on the inception, development and collapse of the bubbles. In this work, we aim to investigate the effect of wettability on collapsing cavitation bubbles using the multi-relaxation-time lattice Boltzmann model. First, the pseudopotential multi-relaxation-time lattice Boltzmann is improved by involving the piecewise linear equation of state and the improved forcing scheme modified by Li et al. The improved pseudopotential model is verified by the Laplace law. Next, the fluid&ndash, solid interaction in the model is employed to adjust the wettability of the solid surface. Moreover, the simulation of the collapse of the cavitation bubble near the solid surface is compared by the experiment results. Finally, the simulation of the collapsing cavitation bubbles near the solid surface with different wettability is also investigated. We find that the numerical results of the collapsing bubble are in good agreement with the experimental results. The simulation results show that the hydrophobicity of the solid surface can accelerate the cavitation bubble collapse. The hydrophilicity of the solid surface has little effect on the collapsing bubbles.

Authentication is a crucial security service for the wireless sensor networks (WSNs) in versatile domains. The deployment of WSN devices in the untrusted open environment and the resource-constrained nature make the on-chip authentication an open challenge. The strong physical unclonable function (PUF) came in handy as light-weight authentication security primitive. In this paper, we present the first ring oscillator (RO) based strong physical unclonable function (PUF) with high resilience to both the electromagnetic (EM) side-channel attack and the support vector machine (SVM) modelling attack. By employing an RO based PUF architecture with the current starved inverter as the delay cell, the oscillation power is significantly reduced to minimize the emitted EM signal, leading to greatly enhanced immunity to the EM side-channel analysis attack. In addition, featuring superior reconfigurability due to the conspicuously simplified circuitries, the proposed implementation is capable of withstanding the SVM modelling attack by generating and comparing a large number of RO frequency pairs. The reported experimental results validate the prototype of a 9-stage RO PUF fabricated using standard 65 nm complementary-metal-oxide-semiconductor (CMOS) process. Operating at the supply voltage of 1.2 V and the frequency of 100 KHz, the fabricated RO PUF occupies a compact silicon area of 250 μ m 2 and consumes a power as low as 5.16 μ W per challenge-response pair (CRP). Furthermore, the uniqueness and the worst-case reliability are measured to be 50.17% and 98.30% for the working temperature range of −40∼120 ∘ C and the supply voltage variation of ±2%, respectively. Thus, the proposed PUF is applicable for the low power, low cost and secure WSN communications.

The degradation of acephate in aqueous solutions was investigated with the ultrasonic and ozonation methods, as well as a combination of both. An experimental facility was designed and operation parameters such as the ultrasonic power, temperature, and gas flow rate were strictly controlled at constant levels. The frequency of the ultrasonic wave was 160 kHz. The ultraviolet-visible (UV-Vis) spectroscopic and Raman spectroscopic techniques were used in the experiment. The UV-Vis spectroscopic results show that ultrasonication and ozonation have a synergistic effect in the combined system. The degradation efficiency of acephate increases from 60.6% to 87.6% after the solution is irradiated by a 160 kHz ultrasonic wave for 60 min in the ozonation process, and it is higher with the combined method than the sum of the separated ultrasonic and ozonation methods. Raman spectra studies show that degradation via the combined ultrasonic/ozonation method is more thorough than photocatalysis. The oxidability of nitrogen atoms is promoted under ultrasonic waves. Changes of the inorganic ions and degradation pathway during the degradation process were investigated in this study. Most final products are innocuous to the environment.

The research focuses on study the influence of truncations on the dispersion of wedge waves propagating along cylinder wedge with different truncations by using the laser ultrasound technique. The wedge waveguide models with different truncations were built by using finite element method (FEM). The dispersion curves were obtained by using 2D Fourier transformation method. Multiple mode wedge waves were observed, which was well agreed with the results estimated from Lagasse’s empirical formula. We established cylinder wedge with radius of 3mm, 20° and 60°angle, with 0μm, 5μm, 10μm, 20μm, 30μm, 40μm, and 50μm truncations, respectively. It was found that non-ideal wedge tip caused abnormal dispersion of the mode of cylinder wedge, the modes of 20° cylinder wedge presents the characteristics of guide waves which propagating along hollow cylinder as the truncation increasing. Meanwhile, the modes of 60° cylinder wedge with truncations appears the characteristics of guide waves propagating along hollow cylinder, and its mode are observed clearly. The study can be used to evaluate and detect wedge structure.

In this paper, a model of elastic rod surrounded by porous media and a model of porous rod surrounded by elastic media are built. Based on the elastic-dynamic theory of liquid-saturated porous solid and numerical computation, the dispersion characteristic of guided waves in this structure with different cylinder radius and porous media parameters are discussed. Results show that the longitudinal guided wave propagation in this structure is dispersive and influenced by the radius of the rod and porosity of the porous media. It suggests that the dispersion curve of L (0,1) shifts to lower frequency with increasing rod radius.The dispersion is mainly influenced by the propertiesof internal rod. When the internal rod is porous media,the dispersion curves of guided waves gradually shift to low speed with the increasing porosity. The static permeability has little effect on dispersion.All these results can provide a theoretical reference for the non-destructive evaluation to the structure of a solid rod surrounded by infinite media.

Underwater pulsed discharge is widely applied in medicine, machining, and material modification. The induced cavitation bubble and subsequent cavitation collapse are considered the major motivations behind these applications. This paper presents an underwater pulsed discharge system. The experimental setup is established to induce and investigate the cavitation bubble assisted with a high-speed camera. Three aspects, including the characteristic of the discharge with different applied voltages and conductivities, the evolution of the cavitation bubble profile, and the energy efficiency of cavitation bubble inducing, are investigated, respectively. Especially, the mechanism of pre-discharge time delay in the low field intensity case is explained using the Joule heat effect. The results show the validity of the underwater pulsed discharger and experimental setup. The present underwater pulsed discharger is proved to be a simple, portable, and easy-to-implement device for the investigation of cavitation bubble dynamics.

The shear waves have been taken into consideration to deduce the theoretical model of the scattering of isotropic circular solid cylinders in a fluid medium. The theoretical analysis has been done based on the wave equation and the three classical boundary conditions. The analytical solution of the far-field pattern for this scattering issue has been derived and the pressure in the scattered wave can be given. And the finite element method (FEM) has been used to solve the underwater acoustic scattering problems. Numerical solution of the resulting was discussed in three directions. The following work is to study the scattering problems of collection of cylinders with arbitrary cross-sections and any numbers. The conclusions drawn in this paper could contribute to explore the acoustic propagation characteristics of the two-phase media.