Wave Dissipation Research Articles

Multifunctional phase-change composites for green electromagnetic interference shielding and thermal response prepared under the guidance of an impedance matching strategy.

With the advent of the information age, electromagnetic hazards are becoming more serious. In view of environmental protection, green electromagnetic interference (EMI) shielding materials with little or no secondary reflection have become the ideal choice. In this paper, by freeze-drying, high-temperature carbonization, coating and impregnation backfilling, we prepared carbonized Ni-MOF/reduced graphene oxide/silver nanowire-polyimide@polyethylene glycol composites (Ni@C/r-GO/AgNW-PI@PEG) with gradient conductivity based on impedance matching. The impedance matching layer Ni@C/r-GO-300 reduces the reflection of electromagnetic waves from the surface of the material, the dissipation layer Ni@C/r-GO-600 provides excellent electromagnetic wave dissipation capability, and the reflection layer AgNW-PI ensures that the electromagnetic waves are reflected back into the material. Meanwhile, the EMI shielding performance value of Ni@C/r-GO/AgNW-PI@PEG reaches 62.3 dB with an ultra-low reflectivity (R) of 0.04. In CST simulations, the intrinsic mechanism of electromagnetic energy loss within the material is revealed by energy loss density cloud maps. In addition, heat from high-temperature objects is transferred through the highly thermally conductive AgNW-PI membrane to the long-channel Ni@C/r-GO backbone. Therefore, the composites prepared on the basis of impedance matching will accelerate the use of EMI shielding materials for the thermal management of portable electronic devices and battery heat dissipation packaging.

N-doped carbon layer cladded carbon sphere for broadband and boosted microwave attenuation capacity.

Structural construction and heteroatom doping are deemed effective strategies for designing a high-performance microwave absorbing composite to eliminate electromagnetic hazards. Herein, a series of core-shell structural carbon@N-doped carbon (C@NC) nanospheres were successfully fabricated without employing additional modifying agents and sophisticated operation. After incorporating them into a polyvinylidene fluoride (PVDF) matrix, the C@NC/PVDF composites possess tunable wave attenuation capacity obtained by regulating the coating layer thickness and filler loading. Benefitting from the design strategy of the core-shell structure and N-doped C, the C@NC-2/PVDF composites displayed the broadest effective absorption bandwidth of 6.29 GHz (11.71-18 GHz) under a filler content of only 10 wt% at 2.01 mm. Additionally, the minimum reflection loss value of C@NC-3/PVDF composites achieves -62.87 dB within the same mass ratio at a thickness of 2.35 mm. The excellent wave dissipation ability is attributed to the combination of optimized impedance matching and synergistically enhanced multiple loss mechanisms including conduction loss, interfacial polarization as well as dipolar polarization. This work offers a ponderable paradigm for the deeper exploitation of high-efficiency carbon absorbers.

Impact Responses and Wave Dissipation Investigation of a Composite Sandwich Shell Reinforced by Multilayer Negative Poisson's Ratio Viscoelastic Polymer Material Honeycomb.

This analysis investigated the impact wave response and propagation on a composite sandwich shell when subjected to a low-velocity external shock, considering hygrothermal effects. The sandwich shell was crafted using face layers composed of functional gradient metal-ceramic matrix material and a core layer reinforced with negative Poisson's honeycomb. The honeycomb layer consisted of a combination of viscoelastic polymer material and elastic material. The equivalent parameters for the functional gradient material in the face layers were determined using the Mori-Tanaka and Voigt models, and the parameters for the negative Poisson's ratio honeycomb reinforcement core layer were obtained through Gibson's unit cell model. Parameters relevant to a low-velocity impact were derived using a modified Hertz contact law. The internal deformations, strains, and stress of the composite sandwich shell were described based on the higher-order shear deformation theory. The dynamic equilibrium equations were established using Hamilton's principle, and the Galerkin method along with the Newmark direct integration scheme was employed to calculate the shell's response to impact. The validity of the analysis was confirmed through a comparison with published literature. This investigation showed that a multilayer negative Poisson's ratio viscoelastic polymer material honeycomb-cored structure can dissipate impact wave energy swiftly and suppress shock effectively.

Effect of thin vertical porous barrier with variable permeability on an obliquely incident wave train

The present paper is concerned with a study of wave propagation due to incidence of an obliquely incident wave on a thin porous vertical barrier with variable porosity. Two different configurations of the barrier are considered: 1. partially immersed barrier 2. bottom standing barrier in water of finite depth. The problem is formulated in terms of a Fredholm integral equation of the second kind, where the unknown function represents the difference of potentials across the barrier. The integral equation is then solved using two methods: the boundary element method and the collocation method. Using the solution of the integral equation, the reflection coefficient and amount of energy dissipated are determined and depicted graphically. It is observed that a barrier with variable porosity induces more reflection than a barrier with constant porosity. Also the energy dissipation for barrier with variable porosity is in general less than a barrier with constant porosity. However for partially immersed long barrier, energy dissipation of waves with certain wavelength is more for barrier with variable porosity than a barrier with constant porosity. For both configurations of the barrier, a long barrier induces more reflection and dissipation of wave energy. The inertial force coefficient of the porous material of the barrier reduces the reflection and dissipation of wave energy. Also, for an obliquely incident wave, the presence of porous barrier reduces reflection and dissipation of energy as compared to a normally incident wave.

Energy and dissipation spectra of waves propagating in the inner surf zone

The spectral behaviour of random sawtooth waves propagating in the inner surf zone is investigated in this study. We show that the elevation energy spectrum exhibits a universal shape with an $\omega ^{-2}$ tendency in the inertial subrange and an exponential decay in the diffusive subrange ( $\omega$ being the angular frequency). A theoretical spectrum is derived based on the similarities between sawtooth waves in the inner surf zone and Burgers wave solutions. Very good agreement is shown between this theoretical spectrum and laboratory experiments covering a large range of incident random wave conditions. Additionally, an equation describing the universal shape of the dissipation spectrum is derived. It highlights that the dissipation spectrum is nearly constant in the inertial subrange, consistent with prior laboratory observations. The findings presented in this study can be useful to improve broken wave dissipation parametrizations in stochastic spectral wave models.

A simplified consistent nonlinear mild-slope equation model for random waves propagation and dissipation

The model for ocean surface wave propagation can be formulated either in the form of deterministic models or stochastic models. The stochastic models appear to be particularly attractive in the global domain due to their computational efficiency. However, in the nearshore region, the phase becomes highly correlated, and the phase information therefore becomes critical. Therefore, a simplified consistent nonlinear mild-slope equation model has been developed in order to take advantage of the deterministic model for handling phase information, as well as the stochastic model for numerical simplicity. We demonstrate the advanced performance of the present model for random waves by comparing it with laboratory data and previous models.

Tidal Dissipation in Stably Stratified and Semiconvective Regions of Rotating Giant Planets: Incorporating Coriolis Forces

We study how stably stratified or semiconvective layers alter tidal dissipation rates associated with the generation of inertial, gravito-inertial, interfacial, and surface gravity waves in rotating giant planets. We explore scenarios in which stable (nonconvective) layers contribute to the high rates of tidal dissipation observed for Jupiter and Saturn in our solar system. Our model is an idealized spherical Boussinesq system incorporating Coriolis forces to study effects of stable stratification and semiconvective layers on tidal dissipation. Our detailed numerical calculations consider realistic tidal forcing and compute the resulting viscous and thermal dissipation rates. The presence of an extended stably stratified fluid core significantly enhances tidal wave excitation of both inertial waves (due to rotation) in the convective envelope and gravito-inertial waves in the dilute core. We show that a sufficiently strongly stratified fluid core enhances inertial wave dissipation in a convective envelope much like a solid core does. We demonstrate that efficient tidal dissipation rates (and associated tidal quality factors )—sufficient to explain the observed migration rates of Saturn's moons—are predicted at the frequencies of the orbiting moons due to the excitation of inertial or gravito-inertial waves in our models with stable layers (without requiring resonance locking). Stable layers could also be important for tidal evolution of hot and warm Jupiters and hot Neptunes, providing efficient tidal circularization rates. Future work should study more sophisticated planetary models that also account for magnetism and differential rotation, as well as the interaction of inertial waves with turbulent convection.

Hierarchical Flower-like Sulfides with Increased Entropy for Electromagnetic Wave Absorption.

The concept of high entropy is considered promising to enhance electromagnetic wave absorption properties. However, preparing high-entropy sulfides with unique structures for high-performance electromagnetic absorption remains a challenge. In this study, hierarchical porous flower-like dual-phase sulfides were designed with increased entropy and fabricated using a versatile approach. The porous flower configuration enhanced the scattering of electromagnetic waves and the impedance-matching characteristics. Additionally, the effect of high entropy induced diverse defects that were favorable for electromagnetic wave dissipation in dual-phase sulfides. The design of the dual-phase structure generated strong interface polarization, and the composition and content of the phases exhibited clear changes with the increase in the number of metal elements. Interestingly, apparent lattice distortions, defects, and shear strains were directly observed near the dual-phase interface of millerite (102) and pyrite (220) planes, facilitating the occurrence of dipole polarization. Consequently, the developed dual-phase high-entropy sulfide exhibited outstanding microwave absorption properties. The minimum reflection loss value of (FeCoNiCuZn)S was -45.8 dB at a thickness of 1.5 mm, and the optimal effective absorption bandwidth was 3.8 GHz at a thickness of 1.4 mm thickness. Thus, the design of high-entropy sulfides brings meaningful guidance for tuning the wave absorption properties in sulfides.

Exploring variable coefficient models: Insights into nonlinear wave behavior and soliton solutions in physical systems

The KdV-Burgers equation, featuring time-varying coefficients is a fundamental equation in the domain of wave propagation for wave propagation, dispersion, and dissipation in different physical systems. This equation is particularly useful for coastal engineering studies, flow analysis in rivers, open channels, and nonlinear phenomena across different physical systems. In this article, we derive feasible soliton solutions to the stated equation with time-varying coefficients through the tanh-expansion, exp (-φ(τ))-expansion, and modified simple equation approaches. The obtained solutions provide insightful information on wave and solitons behavior in diverse physical systems. The wave profiles in soliton shapes, including 3D and 2D waves, are significantly influenced by the variable wave velocity function and associated parameters. Such variations are not visible when the parameters are held constant. This study emphasizes the critical role of nonlinear evolution equations with time-dependent coefficients, leading to an exploration of an intriguing and challenging field of study.

Effect analysis of wooden fence width on wave transmission by SWASH model

Wooden fences, a permeable structure, have become a nature-based solution for supporting traditional structures to restore mangrove forests along the Mekong deltaic coasts. Even though prior studies have explored a number of hydraulic functions of these fences, an in-depth investigation into the influence of fence width on wave dissipation and damping is needed to consider. Therefore, this paper employs a numerical approach to thoroughly examine the impact of fence width on wave damping. The findings illustrate the substantial role of fence width in governing the dissipation of incoming waves. The correlation between the transmission coefficient and the fence width is established. This relationship also concludes that the larger the fence thicknesses, the lower the transmission coefficients. Notably, the study also identifies that the transmission coefficient experiences a slight decline beyond a certain width threshold.

Wave dissipation by vegetation for coastal defense in the Western Mekong Delta under climate change

The combination of the Mekong Delta dyke-mangrove system effectively protects the hinterland against flooding and erosion in extreme conditions for decades since they could dissipate waves and currents efficiently. However, literature and satellite data indicate that severe erosion happens along the Western sea-dykes of the Ca Mau coast caused by increased intensity of storms due to climate change. State-of-the-art wave transformation models are used to predict the influences of wave propagation and wave overtopping discharge over sea dykes and/or associated with mangrove ecosystems under extreme typhoons, which cooperates with both high – frequencies (HF) and low – frequencies (LF) waves. Results confirm that the HF wave quickly dissipates in shallow water, whereas the LF wave is dominant and penetrates over a longer distance. At dyke toe, the wave height through vegetation is substantially diminished, approximately ten times less than that in the sea-dyke solely. However, the modelling wave overtopping discharge seems to be overestimated compared with the standard-based formula.

Micro-perforated mufflers based on the Acoustic Black Hole effect

Attenuation of acoustic disturbance with compact and low-weight acoustical devices is a demanding requisite in industries such as vehicle exhaust mufflers, turbofan liners or ventilation systems. Acoustic Black Holes (ABH) is a concept that has been studied originally in the field of vibration control for the design of a structure based on a power-law thickness profiles along its edges. The idea of wave trapping and dissipation has been extended to the field of duct acoustics using compact devices that avoid blocking the air flow. Based on this idea, in this work we propose the study of a micro-perforated silencer that should prevent reflection and transmission of the sound waves over a wide range of audible frequencies. The use of micro-perforations over the facing cavities should help to extend performance towards the low frequency range. The acoustic behavior of the ABH is assessed from theoretical and numerical modeling. The performance can be greatly improved when the physical constituting parameters are optimized simultaneously. Particle swarm optimization is a computational method inspired by the behavior of natural systems that is able to provide a satisfactory solution with enhanced total dissipation.

Tidal dissipation in rotating and evolving giant planets with application to exoplanet systems

ABSTRACT We study tidal dissipation in models of rotating giant planets with masses in the range 0.1–10MJ throughout their evolution. Our models incorporate a frequency-dependent turbulent effective viscosity acting on equilibrium tides (including its modification by rapid rotation consistent with hydrodynamical simulations) and inertial waves in convection zones, and internal gravity waves in the thin radiative atmospheres. We consider a range of planetary evolutionary models for various masses and strengths of stellar instellation. Dissipation of inertial waves is computed using a frequency-averaged formalism fully accounting for planetary structures. Dissipation of gravity waves in the radiation zone is computed assuming these waves are launched adiabatically and are subsequently fully damped (by wave breaking/radiative damping). We compute modified tidal quality factors Q′ and evolutionary time-scales for these planets as a function of their ages. We find inertial waves to be the dominant mechanism of tidal dissipation in giant planets whenever they are excited. Their excitation requires the tidal period (Ptide) to be longer than half the planetary rotation (Prot/2), and we predict inertial waves to provide a typical Q′ ∼ 103(Prot/1d)2, with values between 105 and 106 for a 10-d period. We show correlations of observed exoplanet eccentricities with tidal circularization time-scale predictions, highlighting the key role of planetary tides. A major uncertainty in planetary models is the role of stably-stratified layers resulting from compositional gradients, which we do not account for here, but which could modify predictions for tidal dissipation rates.

Tuning Electromagnetic Parameters Induced by Synergistic Dual-Polarization Enhancement Mechanisms with Amorphous Cobalt Phosphide with Phosphorus Vacancies for Excellent Electromagnetic Wave Dissipation Performance

The understanding of amorphous and heterojunction materials has been widely used in the field of electromagnetic wave absorption due to their unique physical and chemical properties. However, the effectiveness of individual strategies currently used is still limited. Well-designed compositions and amorphous structures simplify the effect of different polarization mechanisms on the absorption of electromagnetic waves. In this work, through the carbonization and controlled phosphating of one-dimensional Co Metal–Organic Framework (Co-MOF) nanorods, the synthesis of complex components and amorphous CoPx with phosphorus vacancies is successfully accomplished, thus adjusting the optimization of electromagnetic parameters. Phosphorus-vacancy-induced defective polarization loss and enhanced-electronegativity-differences-induced dipole polarization loss synergistically as a dual-polarization strategy significantly improved the electromagnetic parameters and impedance matching. In conclusion, the electromagnetic parameters of the Co@CoPx@C composites are indeed significantly regulated, with reflection losses of −55 dB and a bandwidth of up to 5.5 GHz. These innovative research ideas provide instructive thinking for the development of amorphous absorbers with vacancies.

Modulational instability of dust-ion acoustic waves in generalized (r, q) distributed electron dissipative plasmas

The modulational instability of the dust-ion acoustic waves in a dissipative dusty plasma system containing warm ions, generalized ( r , q ) distributed electrons, and immobile dust grains has been studied. The Krylov–Bogoliubov–Mitropolsky (KBM) perturbation method is employed to analyze the amplitude modulation of a monochromatic plane wave through the derivation of a nonlinear Schrödinger equation. This equation is solved analytically to determine the modulational instability region, and the corresponding dissipative rogue wave solution is obtained. The effects of various system parameters, such as the kinematic viscosity of the ions (υ), the wavenumber (k), the ion to electron temperature ratio ( σ i ), the unperturbed ion to electron density ratio (γ) as well as the electron distribution parameters: r and q, are investigated. The dependence of the amplitude of dissipated rogue waves on υ is discussed. It is found that various system parameters have significant effects on the features of dissipated rogue waves. The present investigation can be relevance to the electrostatic rogue structures in various cosmic dust-laden plasmas such as Saturn's F-ring.

Mathematical model of wave diffraction for multiple concentric segmented arc-shaped breakwaters

The problem of regular wave diffraction from segmented arc-shaped breakwater (ASB) structures was studied. Based on the linear potential flow theory, the velocity potential of the entire fluid domain was derived using the characteristic function expansion method. The accuracy of the current model was verified by comparing the results of this study with published computational results. The numerical results revealed variations in the wave load and wave surface of the segmental ASB with the gap width between the arcs, opening angle, wave incidence angle, porosity coefficient, and number of segments of the segmental ASB. The results showed that the segmented ASB reduced the wave load on the breakwater, and the proper gap width between the arcs significantly increased the wave dissipation capacity of the breakwater. This study will be of guidance to actual marine engineering.

Ultra‐wideband electromagnetic interference shielding properties of parallel expanded graphite/Fe3O4 composites

AbstractThe rapid development of electronic devices in various fields has stimulated an increased demand for electromagnetic interference (EMI) shielding materials working in ultra‐wideband frequencies of gigahertz. However, the aggregation problem and single attenuation mechanism severely limit the broadband shielding applications of nanomaterials. To address these challenges, a novel composite of parallel expanded graphite (EG) embedded in the densified Fe3O4 matrix is designed and successfully synthesized through the in situ chemical coprecipitation followed by pressure sintering. This unique structure creates heterogeneous interfaces by combining the conductive EG and magnetic Fe3O4. The significant dielectric and magnetic loss then arise from conduction and polarization loss, as well as the eddy current and resonance effects. The multiple reflections of electromagnetic waves between the oriented EG sheets further cause the “absorb–reflect–reabsorb” effect that prolongs the propagation paths and enhances the dissipation of electromagnetic waves. Based on these multiple mechanisms over an ultrawide range of frequencies (8.2–40 GHz), the EG/Fe3O4 composites exhibit exceptional EMI shielding performance, with an average shielding effectiveness of 29.3 dB, indicating the potential for multifunctional EMI shielding applications.

Wave statistics and energy dissipation of shallow-water breaking waves in a tank with a level bottom

The present study focuses on two-dimensional direct numerical simulations of shallow-water breaking waves, specifically those generated by a wave plate at constant water depths. The primary objective is to quantitatively analyse the dynamics, kinematics and energy dissipation associated with wave breaking. The numerical results exhibit good agreement with experimental data in terms of free-surface profiles during wave breaking. A parametric study was conducted to examine the influence of various wave properties and initial conditions on breaking characteristics. According to research on the Bond number ( $Bo$ , the ratio of gravitational to surface tension forces), an increased surface tension leads to the formation of more prominent parasitic capillaries at the forwards face of the wave profile and a thicker plunging jet, which causes a delayed breaking time and is tightly correlated with the main cavity size. A close relationship between wave statistics and the initial conditions of the wave plate is discovered, allowing for the classification of breaker types based on the ratio of wave height to water depth, $H/d$ . Moreover, an analysis based on inertial scaling arguments reveals that the energy dissipation rate due to breaking can be linked to the local geometry of the breaking crest $H_b/d$ , and exhibits a threshold behaviour, where the energy dissipation approaches zero at a critical value of $H_b/d$ . An empirical scaling of the breaking parameter is proposed as $b = a(H_b/d - \chi _0)^n$ , where $\chi _0 = 0.65$ represents the breaking threshold and $n = 1.5$ is a power law determined through the best fit to the numerical results.

Atmospheric Wave Radiation by Vibrations of an Ice Shelf

AbstractLidar and radar observations of persistent atmospheric wave activity in the Antarctic atmosphere motivate investigation of generation of acoustic‐gravity waves (AGWs) by vibrations of ice shelves and exploiting their possible ionospheric manifestations as a source of information about the ice shelves' conditions and stability. A mathematical model of the waves radiated by vibrations of a finite area of the lower boundary of the atmosphere is developed in this paper by extending to AGWs an efficient, numerically exact approach that was originally developed in seismology and underwater acoustics. The model represents three‐dimensional wave fields as Fourier integrals of numerical or analytical solutions of a one‐dimensional wave equation and accounts for the source directionality, AGW refraction and diffraction, and the wind‐induced anisotropy of wave dissipation. Application of the model to the generation of atmospheric waves in Antarctica by free vibrations of the Ross Ice Shelf reveals a complex three‐dimensional structure of the AGW field and elucidates the impact of various environmental factors on the wave field. The intricate variation of the wave amplitude with altitude and in the horizontal plane is shaped by the spatial spectrum of the ice surface vibrations and the temperature and wind velocity stratification from the troposphere to the mesosphere. It is found that the waves due to the low‐order modes of the free oscillations of the Ross Ice Shelf, which have periods of the order of several hours, can transport energy to the middle and upper atmosphere in a wide range of directions from near‐horizontal to near‐vertical.

A cVEM-DG space-time method for the dissipative wave equation

A novel space-time discretization for the (linear) scalar-valued dissipative wave equation is presented. It is a structured approach, namely, the discretization space is obtained tensorizing the Virtual Element (VE) discretization in space with the Discontinuous Galerkin (DG) method in time. As such, it combines the advantages of both the VE and the DG methods. The proposed scheme is implicit and it is proved to be unconditionally stable and accurate in space and time.