Wave Motion最新文献

We investigate counterpropagating optical solitary waves – nematicons – in non-homogeneously oriented nematic liquid crystals. A non-symmetric angular distribution of the optic axis versus beam propagation provides the solitons with direction-dependent trajectories. By performing numerical experiments in realistic planar samples, we launch nematicons in opposite directions and examine the resulting non-specular transmission in terms of optical nonreciprocity and isolation.

This paper concerns the derivation of radiative transfer equations for acoustic waves propagating in a randomly fluctuating slab (between two parallel planes) in the weak-scattering regime, and the study of boundary effects through an asymptotic analysis of the Wigner transform of the wave solution. These radiative transfer equations allow to model the transport of wave energy density, taking into account the scattering by random heterogeneities. The approach builds on the method of images, where the slab is extended to a full-space, with a periodic map of mechanical properties and a series of sources located along a periodic pattern. Two types of local effects, both on the (small) scale of the wavelength, are observed: one within one wavelength of the boundaries of the slab, and one inside the domain (at a distance from the boundaries large compared to the wavelength). The former impacts the entire energy density (coherent as well as incoherent) and is also observed in half-spaces. The latter, more specific to slabs, corresponds to the constructive interference of waves that have reflected at least twice on the boundaries of the slab and only impacts the coherent part of the energy density.

This article examines the soliton-type solutions, their interactions, and the integrable properties of a non-autonomous perturbed Gardner KP (NPGKP) equation. For the NPGKP equation under consideration, a bilinear structure, and a Bäcklund transformation are designed explicitly, which claim the integrability of the system under some constraints. The stability of the obtained solutions is discussed using modulation instability. The bilinear form demonstrates the dynamic characteristics of multiple solitons, breathers, and their interactions in response to external impulses. Furthermore, it allows for determining the solitons’ amplitudes and velocities. The two-soliton solution yields a first-order breather solution. At the same time, the analytical investigation focuses on the interaction between a single breather and a single-soliton within the multi-soliton solution. This investigation also identifies the resonance of $Y$-shaped solitons and examines the dynamical characteristics of the interaction between resonant $Y$-shaped solitons and $M$-fissionable pulses. The multi-shock solutions and the collisions between shocks are analyzed in the presence of external influences. Graphical representations of the relationships between different sorts of achieved solutions are provided explicitly.

This study presents a mathematical model of transmission loss (TL) for finite-sized corrugated-core sandwich panels subjected to aerodynamic pressure. The aerodynamic pressure is calculated using a cross-power spectral density function. The propagation of sound waves within a corrugated sandwich-panel structure is described using the wave propagation method. The corrugated-stiffened panel is equivalently represented using translational and rotational springs. Fluid‒structure coupling is considered by enforcing interface velocity continuity conditions at the fluid‒solid interface. A modal superposition method is used to establish the dynamic equations of the corrugated-core sandwich panel. The velocity response, radiated power, and TL of the corrugated-core sandwich panel are obtained by solving dynamic equations. A mathematical model is employed to investigate the acoustic characteristics of corrugated-core sandwich panels. Subsequently, the distinctions in the TL of a corrugated sandwich panel under acoustic and aerodynamic pressures (turbulence) are discussed. The influences of the flow velocity, corrugated-core sandwich-panel thickness, and corrugated-stiffener angle on the TL performance of the panel are investigated. This analysis contributes to a deeper understanding of the acoustic design of corrugated-core sandwich panels.

Clusters of wave-scattering oscillators offer the ability to passively control wave energy in elastic continua. However, designing such clusters to achieve a desired wave energy pattern is a highly nontrivial task. While the forward scattering problem may be readily analyzed, the inverse problem is very challenging as it is ill-posed, high-dimensional, and known to admit non-unique solutions. Therefore, the inverse design of multiple scattering fields and remote sensing of scattering elements remains a topic of great interest. Motivated by recent advances in physics-informed machine learning, we develop a deep neural network that is capable of predicting the locations of scatterers by evaluating the patterns of a target wavefield. We present a modeling and training formulation to optimize the multi-functional nature of our network in the context of inverse design, remote sensing, and wavefield engineering. Namely, we develop a multi-stage training routine with customized physics-based loss functions to optimize models to detect the locations of scatterers and predict cluster configurations that are physically consistent with the target wavefield. We demonstrate the efficacy of our model as a remote sensing and inverse design tool for three scattering problem types, and we subsequently apply our model to design clusters that direct waves along preferred paths or localize wave energy. Hence, we present an effective model for multiple scattering inverse design which may have diverse applications such as wavefield imaging or passive wave energy control.

The sparse regularization has been successfully applied to near-field acoustic holography to provide the reconstruction accuracy of sound field with limited number of measurements. However, most of the applications are concentrated on the reconstruction of the sound pressure and the corresponding sparse bases are designed for the sound pressure. In this study, dictionary learning is introduced and K-SVD is utilized to generate a sparse basis for the velocity. Then the reconstruction of surface velocity of a vibrating structure can be realized in a sparse framework to improve the reconstruction accuracy with limited number of measurements. In the process of data sample selection, the equivalent source method is used to generate the velocity sample according to the feature of the sound field and samples can be obtained by numerical simulations. The results of numerical simulations and experiment demonstrate the validity of the learned dictionary and the advantage of the proposed method.

The present study examines the effects of various edge conditions of a submerged flexible disc on wave propagation for infinite-depth water within the framework of linear water waves theory. Three types of edge conditions (namely Free edge, simply supported edge, and clamped edge) are taken into consideration for the analysis. The governing boundary value problem (BVP) has been solved by reducing it to a two-dimensional hypersingular integral equation. The notion of modal analysis has been adopted to examine the structural response of the disc on the propagation of waves. Later, the two-dimensional hypersingular integral has been transformed into a second kind one-dimensional Fredholm integral equation by applying Fourier series expansion. Finally, the Nystrom technique based on Gauss–Legendre quadrature nodes is used to obtain an approximate solution of the one-dimensional integral equation. The computed solution is used to evaluate the numerical estimates of the physical quantities such as added mass, damping coefficient, hydrodynamic force, and surface elevation for different edge conditions mentioned earlier.

We investigate the simultaneous processes of optical frequency doubling and sum frequency generation in quasi-phase-matched quadratically nonlinear crystals. Specifically, we focus on lattices with domain thicknesses corresponding to the coherence lengths of the two cascaded parametric processes and explore the realistic scenario of a single crystal containing sequential domain segments, each independently satisfying quasi-phase-matching for optical frequency doubling and summing, respectively. We demonstrate that high conversion efficiencies to the third harmonic can be obtained from an arbitrary fundamental wavelength.

The evaluation and localization of micro-cracks in pipelines were studied by combining nonlinear ultrasonic guided wave and the SEResNet50 network in this paper. The nonlinear effects arising from the interaction of ultrasonic guided wave and micro-cracks in different directions, lengths and locations were investigated using the finite element simulation. In the analysis section, the stacked spectrum map which contains more obvious nonlinear features was introduced to analyze and reveal the impact of these three factors on the spectrum of the signal received by the sensor array. During the learning part, in order to further identify the relationships between the micro-crack features and stacked spectrum map, the SEResNet50 network was provided for the training and conducted for further prediction of the micro-crack with a well-trained model. The results show that the accuracy of the validation set is up to 98.57%, and the generated model also performs well on the test set with an accuracy of 97.22%. The outcome can illustrate that it is feasible for the well-trained SEResNet50 network to identify the complex connections between the spectrum of the sensor array and micro-cracks, enabling the simultaneous evaluation and location of micro-cracks. In summary, the method proposed in this paper combining nonlinear ultrasonic guided wave and deep learning provides a new approach for the detection of micro-cracks in pipelines and will further promote the application of artificial intelligence in non-destructive testing.

This study focuses on the dispersive behavior of SH waves in a piezoelectric viscoelastic (PV) layer sandwiched between a magnetoelastic fiber-reinforced viscoelastic (MFRV) layer and a heterogeneous viscoelastic half-space. The linear variation of the downward-pointing space variable introduces inhomogeneity in the viscoelastic half-space. With the help of the variable separation technique, the governing equations of the present model are solved to obtain solutions for the mechanical displacement and electric potential function. A complex frequency equation for the SH waves has been derived by applying appropriate boundary conditions. The results are confirmed by comparison to the classical case of Love wave, and special cases of the problem are also discussed. In the fundamental analytical study, two cases of the PV layer are discussed, and the effects of physical parameters on the phase and damped velocity of SH waves are investigated through numerical calculations and presented graphically. A comparative study has also been carried out to analyze the effects of the viscoelastic parameters, reinforcement parameters, thickness ratio parameter, magnetoelastic coupling parameter, inhomogeneity parameter, and the angle at which the wave intersects the magnetic field on the phase and damped velocity by taking electrically open and short conditions.