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Accurate partial discharge (PD) measurement is critical to ensure the stable operation of transformers. The ultrasonic method is a low-cost, safe, and reliable technology that is widely available and provides real-time monitoring capability. The PD ultrasonic signals propagation is complex and severely attenuated in the transformer, which greatly affects the measurement accuracy of the sensor. In order to improve the accurate monitoring of PD in complicated transformer environments, an optimization monitoring method based on sub-scene detection and quantitative analysis and evaluation is proposed in this paper. Firstly, to address this concern, a sub-scene monitoring method is designed and explores the optimal monitoring points separately. In addition, establish the partition model of an oil-immersed power transformer, and compare the ultrasonic wave propagation characteristics and sound pressure attenuation characteristics of different monitoring points. Then, analyzed by wavelet transform algorithm and Pearson correlation coefficient to determine the best monitoring point location for each scene. Finally, we further tested the proposed method through extensive experiments based on simulations, testbed, and trial deployment. The experimental results have demonstrated the feasibility and accuracy of the proposed method in transformer PD monitoring under complicated environments. [ABSTRACT FROM AUTHOR]

The main goal of this work is to develop a novel boundary element method (BEM) model for analyzing ultrasonic wave propagation in three-temperature anisotropic viscoelastic porous media. Due to the problems of the strong nonlinearity of ultrasonic wave propagation in three-temperature porous media, the analytical or numerical solutions to the problems under consideration are always challenging, necessitating the development of new computational techniques. As a result, we use a new BEM model to solve such problems. A time-stepping procedure based on the linear multistep method is obtained after solving the discretized boundary integral equation with the quadrature rule. The calculation of a double integral is required to obtain fundamental solutions, but this increases the total BEM computation time. Our proposed BEM technique is used to solve the current problem and improve the formulation efficiency. The numerical results are graphed to demonstrate the effects of viscosity and anisotropy on the nonlinear ultrasonic stress waves in three-temperature porous media. The validity, accuracy, and efficiency of the proposed methodology are demonstrated by comparing the obtained results to a corresponding solution obtained from the finite difference method (FDM). [ABSTRACT FROM AUTHOR]

In this paper, we proposed a data-driven spatio-temporal deep learning (SDL) model, to simulate forward and reflected ultrasonic wave propagation in the 2D geometrical domain, by implementing the convolutional long short-term memory (ConvLSTM) algorithm. The SDL model learns underlying wave physics from the spatio-temporal datasets. Two different SDL models are trained, with the following time-domain finite element (FE) simulation datasets, by applying: (1) multi-point excitation sources inside the domain and (2) single-point excitation sources on the edge of the different geometrical domains. The proposed SDL models simulate ultrasonic wave dynamics, for the forward ultrasonic wave propagation in the different geometrical domains and reflected wave propagation phenomenon, from the geometrical boundaries such as curved, T-shaped, triangular, and rectangular domains, with varying frequencies and cycles. The SDL is a reliable model, which generates simulations faster than the conventional finite element solvers. [ABSTRACT FROM AUTHOR]

This paper proposes a three–dimensional (3D) local boundary element model based on meshless moving least squares (MLS) method for ultrasonic wave propagation fractional order boundary value problems of functionally graded anisotropic (FGA) fiber-reinforced plates. The problem domain is split into several circular sub-domains. The nodal points are randomly distributed across the examined region. Each node is the focal point of a circular sub-domain that encircles it. The Laplace-transform approach is used to solve dynamic issues. In the local weak form of the governing equations for the converted quantities, a unit test function is utilized. The Gauss divergence theorem to the weak-form is used to produce local boundary-domain integral equations. A meshless approximation is achieved using the MLS method. To find time-dependent solutions, an inverse Laplace-transform approach is used. The effects of the fractional order parameter, functionally graded material, anisotropy, and the time characteristic of the laser pulse are investigated. The proposed method's validity and performance are demonstrated for a two-dimensional problem with excellent agreement with the finite element method. [ABSTRACT FROM AUTHOR]

The main focus of this work is the echogenicity of a 3D-printed synthetic composite material that mimics the acoustic properties of cardiac biological tissues to provide ultrasound images similar to those obtained during interventional cardiology procedures. The 3D-printed material studied is a polymer-based composite with a matrix-inclusion microstructure, which plays a critical role in ultrasound response due to ultrasound-microstructure interaction at the involved medical echography wavelengths. Both numerical simulations and experimental observations are carried out to quantitatively establish the relationship between the 3D-printed microstructure and its ultrasonic echogenicity, considering different microstructure characteristics, namely area fraction and size of the inclusion, and its actual printed shape. A numerical evaluation based on finite element modeling is carried out to characterize the acoustic properties of the 3D-printed synthetic tissue: phase velocity, attenuation coefficient, and B-mode ultrasound images. Moreover, a morphological experimental study of the shape of the real 3D-printed inclusions is carried out. It shows a significant deviation of the final printed inclusions compared to the input spherical shape delivered to the 3D printer. By simulating and comparing numerically generated microstructures and 3D-printed real microstructures, it is shown that the actual shape of the inclusion is significant in the scattering of the ultrasonic wave and the echogenicity of the printed material., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

In this paper, we proposed a data-driven spatio-temporal deep learning (SDL) model, to simulate forward and reflected ultrasonic wave propagation in the 2D geometrical domain, by implementing the convolutional long short-term memory (ConvLSTM) algorithm. The SDL model learns underlying wave physics from the spatio-temporal datasets. Two different SDL models are trained, with the following time-domain finite element (FE) simulation datasets, by applying: (1) multi-point excitation sources inside the domain and (2) single-point excitation sources on the edge of the different geometrical domains. The proposed SDL models simulate ultrasonic wave dynamics, for the forward ultrasonic wave propagation in the different geometrical domains and reflected wave propagation phenomenon, from the geometrical boundaries such as curved, T-shaped, triangular, and rectangular domains, with varying frequencies and cycles. The SDL is a reliable model, which generates simulations faster than the conventional finite element solvers.

• New multiphysics model for structural health monitoring (SHM) systems for alternative material specifications. • The problem of ultrasonic guided waves (UGWs) propagation in fluidstructure interface features the NDT principle. • Modeling the UGWs propagation with/without the fluid-structure interaction (FSI) problem in the ALE framework. • The double-loop linear solving technique applied for the time-dependent coupled models using monolithic approach. • Numerical simulations of multiphysics problems, contrasted against the approximate experimental data. In the present study, we propose a novel multiphysics model that merges two time-dependent problems – the Fluid-Structure Interaction (FSI) and the ultrasonic wave propagation in a fluid-structure domain with a one directional coupling from the FSI problem to the ultrasonic wave propagation problem. This model is referred to as the "eXtended fluid-structure interaction (eXFSI)" problem. This model comprises isothermal, incompressible Navier–Stokes equations with nonlinear elastodynamics using the Saint-Venant Kirchhoff solid model. The ultrasonic wave propagation problem comprises monolithically coupled acoustic and elastic wave equations. To ensure that the fluid and structure domains are conforming, we use the ALE technique. The solution principle for the coupled problem is to first solve the FSI problem and then to solve the wave propagation problem. Accordingly, the boundary conditions for the wave propagation problem are automatically adopted from the FSI problem at each time step. The overall problem is highly nonlinear, which is tackled via a Newton-like method. The model is verified using several alternative domain configurations. To ensure the credibility of the modeling approach, the numerical solution is contrasted against experimental data. [ABSTRACT FROM AUTHOR]

Linear ultrasonic testing (LUT) has been extensively used as a tool for the evaluation of damage processes in various materials ranging from synthetic metals to natural geomaterials, such as rocks. A key limitation of LUT‐based damage studies to date is the lack of explicit evidence used in associating material damage with the changes in measured LUT attributes (e.g., ultrasonic wave amplitude and velocity). In this study, the evolution of the full‐field strains in brittle rock specimens (Lyons sandstone) subjected to failure are analyzed in real time and linked with the changes in the ultrasonic wave amplitude in localized areas illuminated by ultrasonic beams, termed as the ultrasonic image areas. The noncontact optical full‐field displacement measurement method of 2‐D digital image correlation is implemented in combination with the LUT procedure to continuously track changes in the ultrasonic wave amplitude with the evolution of strains across the surface of the uniaxially loaded intact rock specimens. The ultrasonic amplitude showed near‐linear correlation with the intensity of inelastic tensile strain recorded in the rock specimens. The results from the study corroborate that the ultrasonic changes are in fact influenced by the regions of tensile cracking, which is the primary inelastic deformation mechanism in brittle rocks. Key Points: Compressional ultrasonic wave attenuation was explicitly correlated with the stress‐induced extensile microcracks in brittle rock specimensThe intensity of extension was analyzed in the UIA by the total and nonelastic apparent tensile strain based on the critical strain limitUltrasonic amplitude showed consistent near‐linear correlation with nonelastic apparent strains above the crack initiation threshold [ABSTRACT FROM AUTHOR]

• Computationally efficient simulation of transcranial ultrasound for fast focus corrections using hybrid boundary integral methods and finite element methods. • The coupling of boundary integrals and finite elements using dual interpolations. • Reduced computational domain including only the heterogeneous region. Transcranial focused ultrasound is a novel technique for the noninvasive treatment of brain diseases. The success of the treatment greatly depends on achieving precise and efficient intraoperative focus. However, compensating for aberrated ultrasound waves caused by the skull through numerical simulation-based phase corrections is a challenging task due to the significant computational burden involved in solving the acoustic wave equation. In this article, we propose a promising strategy using the coupling of the boundary integral equation method (BIEM) and the finite element method (FEM) to overcome the above limitation. Specifically, we adopt the BIEM to obtain the Robin-to-Dirichlet maps on the boundaries of the skull and then couple the maps to the FEM matrices via a dual interpolation technique, resulting in a computational domain including only the skull. Three simulation experiments were conducted to evaluate the effectiveness of the proposed method, including a convergence test and two skull-induced aberration corrections in 2D and 3D ultrasound. The results show that the method's convergence is guaranteed as the element size decreases, leading to a decrease in pressure error. The computation times for simulating a 500 kHz ultrasound field on a regular desktop computer were found to be 0.47 ± 0.01 s in the 2D case and 43.72 ± 1.49 s in the 3D case, provided that lower–upper decomposition (approximately 13 s in 2D and 2.5 h in 3D) was implemented in advance. We also demonstrated that more accurate transcranial focusing can be achieved by phase correction compared to the noncorrected results (with errors of 1.02 mm vs. 6.45 mm in 2D and 0.28 mm vs. 3.07 mm in 3D). The proposed strategy is valuable for enabling online ultrasound simulations during treatment, facilitating real-time adjustments and interventions. [ABSTRACT FROM AUTHOR]

Abstract Three sets of synthetic shale samples with different clay minerals were prepared to study the effects of mechanical compaction stress on the physical and elastic properties of shales. The results suggest that the physical and elastic properties (i.e., porosity, density, acoustic velocity, etc.) of the mudstones vary greatly the compaction stress, and the type of clay minerals. For a given compaction stress, the synthetic shale with kaolinite exhibits the smallest density and a highest porosity, while the sample with smectite shows the highest density and the smallest porosity. Further, the velocity demonstrates a considerable dependence to compaction stress, both P- and S-wave velocities in different directions increase with the compaction stress. We also find that the velocity anisotropy parameters increase with the compaction stress, and the S-wave anisotropy is more sensitive to the compaction stress compared to the P-wave anisotropy. With respect to the mechanical properties, the dynamic Young's modulus increase with the compaction stress, while the Poisson's ratio decrease with the compaction stress. This can be attributed to the decrease in the porosity. The results also indicate that the mechanical properties display obvious anisotropic behaviours. Finally, strong correlations are observed between the porosity and the velocity anisotropy and mechanical anisotropy for all the prepared samples, providing a means of estimating seismic anisotropy from porosity in shales. Highlights • The correlations between porosity and elastic anisotropy can be exploited for estimating the seismic anisotropy. • The physical properties of the mudstones varied greatly with the compaction stress and the type of clay mineral used. • Using the cold-pressing method, we constructed three sets of synthetic shale samples with different clay minerals. • We study effects of mechanical compaction stress on the physical and elastic properties of shales. [ABSTRACT FROM AUTHOR]

To address difficulties in treating large volumes of liquid metal with ultrasound, a fundamental study of acoustic cavitation in liquid aluminium, expressed in an experimentally validated numerical model, is presented in this paper. To improve the understanding of the cavitation process, a non-linear acoustic model is validated against reference water pressure measurements from acoustic waves produced by an immersed horn. A high-order method is used to discretize the wave equation in both space and time. These discretized equations are coupled to the Rayleigh-Plesset equation using two different time scales to couple the bubble and flow scales, resulting in a stable, fast, and reasonably accurate method for the prediction of acoustic pressures in cavitating liquids. This method is then applied to the context of treatment of liquid aluminium, where it predicts that the most intense cavitation activity is localised below the vibrating horn and estimates the acoustic decay below the sonotrode with reasonable qualitative agreement with experimental data. [ABSTRACT FROM AUTHOR]

Ultrasonic wave propagation in the aqueous magnetic fluid is investigated for different particle concentrations. The sound velocity decreases while acoustic impedance increases with increasing concentrations. The velocity anisotropy is observed upon application of magnetic field. The velocity anisotropy fits with Tarapov’s theory suggests the presence of aggregates in the system. We report that these aggregates are thermodynamically unstable and the length of aggregate changes continuously with increasing concentration and, or magnetic field and resulted in a decrease in effective magnetic moment. The Taketomi's theory fits well with the experimental data suggesting that the particle clusters are aligned in the direction of the magnetic field. The radius of cluster found to increase with increasing concentration, and then decreases whereas the elastic force constant increases and then becomes constant. The increase in cluster radius indicates elongation of aggregate length due to tip-to-tip interaction of aggregates whereas for higher concentration, the lateral alignment is more favorable than tip-to-tip alignment of aggregates which reduces the cluster radius making elastic force constant to raise. Optical images show that the chains are fluctuating and confirming the lateral alignment of chains at higher fields. [ABSTRACT FROM AUTHOR]

• Elevated attenuation of ternary composites found in experiments and FE simulations. • Established quantitative relation between UT results and particle content, frequency. • Proposed a model of energy propagation in multiple-particle reinforced composites. • Explained the mechanism of the interaction among multiple particles. • SiC particles partially compensating for the loss of attenuation among W particles. The study of ultrasonic wave propagation is a crucial foundation for the application of ultrasonic testing in particle-reinforced composites. However, in the presence of the complex interaction among multiple particles, the wave characteristics are difficult to be analyzed and used for parametric inversion. Here we combine the finite element analysis and experimental measurement to investigate the ultrasonic wave propagation in Cu-W/SiC particle-reinforced composites. The experimental and simulation results are in good agreement and quantitatively correlate longitudinal wave velocity and attenuation coefficient with SiC content and ultrasonic frequency. The results show that the attenuation coefficient of ternary composites (Cu-W/SiC) is significantly larger than that of binary composites (Cu-W, Cu-SiC). This is explained by numerical simulation analysis via extracting the individual attenuation components and visualizing the interaction among multiple particles in a model of energy propagation. The interaction among particles competes with the particle independent scattering in particle-reinforced composites. SiC particles serve as energy transfer channels partially compensating for the loss of scattering attenuation caused by interaction among W particles, which further blocks the transmission of incident energy. The present work provides insight into the theoretical basis for ultrasonic testing in multiple-particle reinforced composites. [ABSTRACT FROM AUTHOR]

In this paper, we propose the study of optimizing the hyperparameters of deep learning Data-driven simulation-assisted-Physics learned AI (DPAI) model to simulate the ultrasonic wave propagation for extended depth with a lower error. DPAI model has layers of encoder–decoder structure with modified convolutional long short-term memory (ConvLSTM). DPAI model is trained using the finite element (FE) simulations dataset of distributed single-point to multi-point excitation sources in the 2D domain. The DPAI is the data-driven approach to apprehending the underlying physics of elastodynamic wave propagation. Six different combinations of hyperparameters (hidden dimensions, kernel size, batch size) are used in the DAPI model to study parameter optimization for lowering compounding error. The effectiveness of the trained DPAI models with varying hyperparameters is demonstrated to reduce the compounding error for modeling the deeper simulations of the single-point excitation and multi-point excitation sources. The maximum MAE on amplitude is 5.0 × 10 -2 , and MAPE is 2.64% on time of flight (TOF) between DPAI and FE simulations. • The hyperparameters of the DPAI model are optimized to generate long-term simulations with lower compounding error. • Deeper simulations of reduced compounding error can be generated by increasing the size of hyperparameters. • With high-end computational resources, DPAI can outperform FE modeling in terms of accuracy and computational. [ABSTRACT FROM AUTHOR]

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The paper reports the study of magnetic field induced structures in magnetic nanofluid investigated through ultrasonic wave propagation. Modified Tarapov’s theory is used to study variation in velocity anisotropy with magnetic field. The types of field induced structures depend upon the chemical structure of the carrier in which magnetic nanoparticles are dispersed. Our study indicates formation of fractals and chain respectively, in transformer oil and kerosene based fluid. This difference is explained on the basis of particle–particle interaction and particle–medium interaction. [ABSTRACT FROM AUTHOR]

UPV as non-destructive technique can effectively contribute to the low invasive in situ analysis and diagnosis of masonry elements related to the conservation, rehabilitation and strengthening of the built heritage. The use of non-destructive and non-invasive techniques brings all the times many advantages in diagnostic activities on pre-existing buildings in terms of sustainability; moreover, it is a strong necessity with respect to the conservation constraints when dealing with the historical–architectural heritage. In this work laboratory experiments were carried out to investigate the effectiveness of ultrasonic pulse velocity (UPV) in evaluating physical and mechanical properties of Lecce stone, a soft and porous building limestone. UPV and selected physical–mechanical parameters such as density and uniaxial compressive strength (UCS) were determined. Factors such as anisotropy and water presence that induce variations on the ultrasonic velocity were also assessed. Correlations between the analysed parameters are presented and discussed. The presence of water greatly affected the values of the analysed parameters, leading to a decrease of UPV and to a strong reduction of the compressive strength. A discussion of the role of the water on these results is provided. Regression analysis showed a reliable linear correlation between UPV and compressive strength, which allows a reasonable estimation of the strength of Lecce stone by means of non-destructive testing methods such as the ultrasonic wave velocity. Low correlation between UPV and density was found, suggesting that other factors than density, related to the fabric and composition, also influence the response of the selected stone to the UPV. They have no influence on the UCS, that instead showed to be highly correlated with the packing density. [ABSTRACT FROM AUTHOR]

This study reports on the demonstration and characterisation of a short cavity fibre Fabry‐Perot resonator (FPR) for the detection of ultrasonic waves propagating through a solid medium over a frequency range of 1 kHz–10 MHz. The proposed sensing device has some outstanding features in terms of simple fabrication technique, frequency response and high sensitivity over a wide frequency range. The response of the surface‐mounted FPR sensor showed good agreement with that of a commercially available piezoelectric transducer during ultrasonic excitation. [ABSTRACT FROM AUTHOR]

This study focuses on the use of P-wave propagation measurements in order to evaluate the complex modulus, more specifically for the reversible and dissipated parts of asphalt materials. Both the wave velocity and attenuation factor have been measured by means of an ultrasonic transmission test, at frequencies between 200 and 300 kHz and temperatures ranging from −20 to 40 °C. Based on this wave velocity and attenuation factor, the high-frequency complex modulus and its components are computed by considering a 2D propagation of waves in an isotropic viscoelastic medium. Results are plotted with respect to the master curve, Cole-Cole and Black spaces. The ultrasonic test results agree with results obtained by complex modulus test and then fitted by the 2S2P1D rheological model. This paper shows in Cole-Cole space that ultrasonic data can facilitate the determination of important rheological parameters as one of the two parabolic dashpots ( k) and the glassy modulus E. The phase angle, which is also a key viscoelastic identification parameter, can be determined at high frequency in a Black space representation. [ABSTRACT FROM AUTHOR]

Although techniques to visualize ultrasonic wave propagation help to detect defects, quantitative evaluation using these techniques remains a significant challenge. In this study, a topology-optimization-based damage identification method combined with an ultrasonic wave visualization technique is applied to the experimental results, and its performance is evaluated. This method estimates the target crack as the distribution of 'damage parameters' that reproduces the experimentally visualized ultrasonic wave propagation in an inverse analysis model. The objective function of the optimization was the sum of the squared error between the maximum amplitude distribution obtained in the experiment and finite element analysis. Our results suggest that the crack identification results depend on the incidence angle of the ultrasonic wave to the target crack. This is because the low amplitude in the downstream region of the ultrasonic wave to the crack causes low sensitivity of the objective function. Crack identification was performed using the dataset of ultrasonic wave propagation incident from two directions. The crack could be identified with high accuracy provided the sensitivity of the objective function was high in the entire design domain. Based on this mechanism of crack identification, this study proposes two indices to evaluate the validity of crack identification results in actual inspections. • A crack is identified through topology optimization and ultrasound visualization. • The identification method is applied to experimentally visualized ultrasonic waves. • Crack identification at different ultrasonic incidence angles is validated. • Mechanism of the crack identification is discussed using sensitivity analysis. • Two indices to evaluate the crack identification results are proposed. [ABSTRACT FROM AUTHOR]