Wave Dissipation Research Articles

Gradient Bi-layer coating for reducing energy consumption and improving electromagnetic wave dissipation: Elucidating the role of interfaces and interfacial polarization

The implementation of smart and logical design for absorbers, along with careful selection of components, has proven to be a successful strategy in creating efficient electromagnetic wave (EMW) absorbers. By utilizing novel nanocomposite materials that integrate various loss mechanisms, including enhanced magnetic and dielectric loss, multiple scattering and reflection, and polarization loss, the fabrication of a gradient bi-layer absorber holds great promise for superior EMW absorption. By employing chemical methods, a novel dielectric-magnetic compound comprising of Co2FeAl Heusler Alloy and MWCNTs@NiSe2 was produced. Subsequently, a gradient bi-layer absorber was developed using these components to optimize impedance matching and bolster low-frequency absorption. Abundant hetero-interfaces within this ternary bi-layer nanocomposite absorber give rise to Schottky junctions and heightened interfacial polarization between its layers, components, and matrix. Notably, the utilization of Co2FeAl Heusler Alloy nanoparticles has been shown to lead to the manifestation of magnetic loss phenomena due to their inherent magnetic properties. Through the strategic utilization of the unique layer structure, in conjunction with the incorporation of multiple loss mechanisms, the ternary bi-layer nanocomposite was able to achieve an impressive reflection loss value of -29 dB, despite having a mere 1.4 mm total thickness. Our study offers a fresh framework for creating innovative bilayer gradient absorbers suitable for low frequency applications.

How do various forces affect pressure waves in bubbly flows?

This study investigated the weakly nonlinear propagation of pressure waves in compressible, flowing water with spherical microbubbles, considering various forces. Previous theoretical studies on nonlinear pressure waves in bubbly flows did not consider the forces acting on the bubbles, although the validity of ignoring these forces has not been demonstrated. We focused on every possible force such as drag, gravity, buoyancy, and Bjerknes (acoustic radiation) forces acting on bubbles and studied their effects on pressure waves in a one-dimensional setting. Using a singular perturbation method, the Korteweg–de Vries–Burgers equation describing wave propagation was derived. The following results were obtained: (i) Bjerknes force on the bubbles enhanced the nonlinearity, dissipation, and dispersion of the waves; (ii) Drag, gravity, and buoyancy forces acting on the bubbles increased wave dissipation; (iii) Thermal conduction had the most substantial dissipation effect, followed by acoustic radiation, drag, buoyancy, and gravity. We confirmed that the dissipation due to forces on gas bubbles was quantitatively minor.

Numerical Study on Wave Dissipation and Mooring Force of a Horizontal Multi-Cylinder Floating Breakwater

A three-dimensional numerical model was established based on ANSYS-AQWA (R19.0) software for the purpose of analyzing the hydrodynamic characteristics of a floating breakwater. This study examines three distinct floating breakwaters with different cross-sectional designs in order to evaluate their respective wave dissipation capabilities. It is suggested that the horizontal multi-cylinder floating breakwater exhibits a superior ability to dissipate waves when compared to both the single-cylinder and square pontoon configurations and can be deemed the most advantageous shielding strategy for potential engineering applications. Subsequently, this study examines the effects of influential parameters, including a large cylinder diameter, a small cylinder diameter, the angular position of the small cylinder, and the height and period of the incident wave, on the wave transmission coefficient. An empirical formula for the wave transmission coefficient was derived based on the numerical results. Additionally, the effects of influential parameters, including wind speed, current velocity, incident wave height and period, and water depth, on the maximum total mooring force were investigated. Furthermore, an empirical formula for the maximum total mooring force is proposed for practical implementation in engineering.

Laboratory data linking the reconfiguration of and drag on individual plants to the velocity structure and wave dissipation over a meadow of salt marsh plants under waves with and without current

Abstract. Salt marshes provide valuable ecosystem services, which are influenced by their interaction with currents and waves. On the one hand, currents and waves exert hydrodynamic forces on salt marsh plants, which shapes the distribution of species within the marsh. On the other hand, the resistance produced by the plants can shape the flow structure, turbulence intensity, and wave dissipation over the canopy. Because marsh plants are flexible structures, their reconfiguration modifies the drag felt by the plants and the flow. While several previous studies have considered the flexibility of the stem, few studies have considered the leaf component, which has been shown to contribute the majority of plant resistance. This paper reports a unique dataset that includes laboratory measurements of both the force on an individual plant and the flow structure and wave energy dissipation over a meadow of plants. In the individual plant experiment, the motion of the plant and plant drag, free-surface displacement, and velocity profile were measured. The individual plant experiments considered both a live marsh plant (Spartina alterniflora) and a mimic consisting of 10 leaves attached to a central stem. For the meadow experiment, velocity profiles were measured both upstream and within the meadow, and free-surface displacement was measured along the model marsh plant meadow with high spatial and temporal resolution. These experiments used five water depths (covering both submerged and emergent conditions), three wave periods (from long wave to short waves), seven wave heights (from linear to nonlinear waves), and six current conditions (including pure current, pure wave, and combined current and wave). In summary, there are 102 individual plant tests and 58 meadow tests. The drag, free-surface displacement, and velocity are reported in the SMCW.mat and SMCW.nc files including the raw data, the phase averages, and the statistical values. A link to the plant motion videos is also provided. This dataset provides high-quality measurements that can be used to develop and validate models of plant motion, hydrodynamic drag on individual plants, vegetation-generated turbulence, the evolution of flow structure through a meadow, and the transformation and dissipation of waves over natural salt marshes. The dataset is available from Figshare with detailed instructions for reuse (https://doi.org/10.6084/m9.figshare.24117144; Zhang and Nepf, 2023a).

A Helly Model-Based MPC Control System for Jam-Absorption Driving Strategy against Traffic Waves in Mixed Traffic

Traffic waves in traffic flow significantly impact road throughput and fuel consumption and may even lead to severe safety issues. Currently, in connected and autonomous environments, the jam-absorption driving (JAD) strategy shows good performance in dissipating traffic waves. However, the previous JAD strategy has mostly focused on wave dissipation without adequately assessing traffic efficiency and safety. To address this gap, an optimal control problem for JAD in mixed traffic is proposed to reduce traffic waves. The prediction model is developed using the car-following model within a model predictive control (MPC) framework. The Helly model is selected for the manual vehicle. This is because the Helly model is a linear model that describes the car-following phenomenon accurately without delay effect. In addition, the objective function of the prediction model considers both traffic safety and efficiency while satisfying mechanical and safety constraints. Simulation results indicate that the proposed methodology can effectively reduce traffic jams and improve traffic performance on a one-lane freeway. The optimal method is more applicable to complex traffic wave scenarios, providing a new perspective for reducing traffic jams on the freeway.

High-frequency dissipative MHD waves in straight magnetic cylindrical plasma: Coronal loops heating application

The theoretical model for analyzing the waves and oscillatory behavior in the structured solar corona using straight magnetic cylindrical geometry filled with uniform low-β plasma has been recognized as the most preferable classical model for the last few decades. A number of observations, since the first observation of the transition region and coronal explorer to the latest ones, have been adequately explained by adopting this model. In order to analytically formulate the oscillatory characteristics of magnetohydrodynamic (MHD) waves, most of the studies have considered the nature of plasma as an ideal fluid, particularly in the context of solar physics. However, a departure from ideal plasma consideration to non-ideal may lead to a number of modifications in the characteristics of the MHD waves, including its damping too. In what follows, we derive a more general analytical dispersion relation by extending the classical dispersion relation of [Edwin and Roberts, “Wave propagation in a magnetic cylinder,” Sol. Phys. 88, 179–191 (1983)] taking into account the effect of plasma viscosity as a non-ideal term in the existing formulations of the classical model. Consequently, the effects of viscosity on the damping of sausage and kink modes are examined in detail. Multiple trapped body waves of different frequencies exist for both kink and sausage modes in which trapped sausage body wave of comparatively high frequency is damped potentially to generate enough energy to balance the radiative losses of the coronal loop regions. For the coronal loop's plasma parameters, it is found that trapped first radial overtone body wave of sausage type is able to balance the radiative losses of coronal loop structure provided magnetic field strength does not exceed its value of more than 20G.

Oblique Propagation of Dissipative Ion-Acoustic Solitary Waves in a Magnetized Viscous Plasma With κ-Gurevich Distributed Electrons

Oblique Propagation of Dissipative Ion-Acoustic Solitary Waves in a Magnetized Viscous Plasma With κ-Gurevich Distributed Electrons

The role of roughness geometry in frictional wave dissipation

Bottom friction dissipation is a key factor for wave attenuation in nearshore environments presenting complex geomorphological structures, such as rocky or coral shores. The present paper reports on a series of laboratory experiments performed in a wave flume with controlled wave conditions and seabed structures. Using the frequency-integrated short-wave analysis and classical models for bottom friction and breaking dissipation, the wave friction factor and the hydraulic roughness parameter were estimated from the experimental data. The former varies from 0.17 to 98 while the latter varies from 0 to 0.291 m. The observations reveal the combined influence of several topographical metrics, including the standard deviation, the skewness, the directionality and the effective slope of the seabed elevation. A metric-based multi-varied model for the hydraulic roughness parameter is proposed and confronted with other field data recovered on coral and rocky shores.

Semigroup theory and finite element method applied to a non-linear dissipative wave equation

We study the wave equation with a non-linear dissipative term associated to a bidimensional membrane with fixed boundary. We use the semigroup theory to consider the existence and uniqueness of solutions to the problem and we implement the finite element method to analyse the vibrating evolutionary equation. In particular we use Comsol Multiphysics software with a rectangular mesh to analyze the corresponding evolutionary system. We mention that this system can appear, for example, in the diaphragm of a centrifugal pump in mining processes.

Effect of entropy waves on the thermoacoustic instability of choked outlet combustion chambers

Thermoacoustic instability is a major issue in aero-engine and gas turbine combustion chambers, especially for the case of lean premixed combustion. The instability is caused by the interaction of acoustic waves with unsteady heat release. As considering the accelerated entropy waves in the system, the entropy effect on the acoustic waves cannot be ignored, which will further modify the thermoacoustic instability. Recent researches have shown that the entropy waves can be generated by the steady heat sources or temperature gradients, which can exclude the interference of unsteady heat release factors in instability analysis. In this study, the effect of entropy waves on the thermoacoustic instability of the combustion chamber model with choked outlets is investigated by constructing a low-order acoustic network model. New modes introduced by entropy waves, called as the entropy acoustic modes (EA modes), are investigated by a steady heat source. Then the unsteady heat release is considered, and the effect of entropy waves on different modes and the coupling behavior of these modes are analyzed comprehensively. It is found that some modes are jointly affected by the flame, entropy waves as well as the acoustic waves, which are called as the entropy thermoacoustic modes (ETA modes). Moreover, the modal frequencies of the intrinsic thermoacoustic instabilities modes (ITA modes) are changed remarkably due to the introduction of entropy waves. In addition, the entropy wave dispersion and dissipation show a non-negligible effect on the thermoacoustic instability.

Experimental and numerical study on hydrodynamic characteristics of a bottom-hinged pitching flap breakwater under regular waves

A bottom-hinged flap breakwater is proposed for the wave attenuation and coastal protection. A series of laboratory experiments and a CFD numerical model were conducted to investigate the hydrodynamic characteristics in regular waves. The hydrodynamic coefficients, dimensionless maximum point pressure and average pitching amplitude of flap were examined with the parameters of incident waves and flap property. As the incident wave steepness increased, the wave reflection coefficient Kr, wave transmission coefficient Kt, dimensionless maximum point pressure pmax/ρwgh, and average pitching amplitude of flap θa increased for a given wave period; however, the wave dissipation coefficient Kd decreased. As the flap relative height increased, Kr and θa increased for a given wave period; whereas, Kt decreased. Furthermore, as the flap density ratio increased, Kr, pmax/ρwgh, and fitted Kd increased; however, Kt and θa decreased. As the equivalent damping coefficient ratio increased, Kr and pmax/ρwgh increased; however, Kt and θa decreased. Additionally, a series of dimensionless parameters of incident waves and flap property were used to derive formulas for Kr, Kt and Kd, which were validated using the related data.

Effect of Reduced Graphene Oxide on Microwave Absorbing Properties of Al1.5Co4Fe2Cr High-Entropy Alloys.

The microwave absorption performance of high-entropy alloys (HEAs) can be improved by reducing the reflection coefficient of electromagnetic waves and broadening the absorption frequency band. The present work prepared flaky irregular-shaped Al1.5Co4Fe2Cr and Al1.5Co4Fe2Cr@rGO alloy powders by mechanical alloying (MA) at different rotational speeds. It was found that the addition of trace amounts of reduced graphene oxide (rGO) had a favorable effect on the impedance matching, reflection loss (RL), and effective absorbing bandwidth (EAB) of the Al1.5Co4Fe2Cr@rGO HEA composite powders. The EAB of the alloy powders prepared at 300 rpm increased from 2.58 GHz to 4.62 GHz with the additive, and the RL increased by 2.56 dB. The results showed that the presence of rGO modified the complex dielectric constant of HEA powders, thereby enhancing their dielectric loss capability. Additionally, the presence of lamellar rGO intensified the interfacial reflections within the absorber, facilitating the dissipation of electromagnetic waves. The effect of the ball milling speed on the defect concentration of the alloy powders also affected its wave absorption performance. The samples prepared at 350 rpm had the best wave absorption performance, with an RL of -16.23 and -17.28 dB for a thickness of 1.6 mm and EAB of 5.77 GHz and 5.43 GHz, respectively.

N atoms regulate heterogeneous crystal phase engineering of mesoporous magnetic FexN nanofibers to promote electromagnetic wave dissipation of magnetic composite aerogel absorbers

One dimensional (1D) soft magnetic nanomaterial and its lightweight porous composites are highly needed in promoting electromagnetic wave absorption for the high-frequency magnetic response and low density. In this study, lightweight magnetic composite aerogels were fabricated through the process of heterogeneous crystal phase, involving the modulation of 1D mesoporous magnetic FexN nanofibers with N atoms. The promotion of electromagnetic wave dissipation was achieved through meticulous composition design and interface optimization. The multi-mode magnetic resonance of 1D heterogeneous crystal FexN magnetic nanofibers, along with the N-doped reduced graphene/amorphous carbon three-dimensional conductive network, greatly enhances electromagnetic wave dissipation through the magnetic-dielectric synergistic effect. Consequently, the resulting composite absorber demonstrates remarkable microwave absorption capabilities, achieving a maximum effective absorption bandwidth (EABmax) of 6.63 GHz at a thickness of 2.13 mm, and a minimum reflection loss (RLmin) of −63.3 dB. In addition, the composite magnetic aerogel with the best microwave absorption performance shows a low density of 11.25 mg/cm3. This electromagnetic synergy approach is anticipated to serve as a guide for the development of highly efficient lightweight magnetoelectric composite for wideband microwave absorption in the future.

Mechanical and electromagnetic wave dissipation features of bilayer absorber filled with hierarchical porous CoNi magnetic alloy and BiVO4/VOOH nanocomposite

Designing absorbers with efficient critical parameters is required to address the problems caused by electromagnetic pollution. In this context, this study focuses on the chemical synthesis of hierarchical mesoporous microspheres CoNi magnetic alloy particles, and BiVO4/VOOH nanocomposite as a source of dielectric dissipation for constructing bilayer absorbers that are optimized in their absorption properties using MATLAB simulation. Single layer and constructed bilayer absorber sample's mechanical and X band microwave absorption performance were investigated, compared, and optimized. It is found that the prepared bilayer absorber sample's mechanical characteristics are comparable to those of the two bulk single-layer samples of CN and BVH, indicating that the interface in the double-layer sample not only has little to no effect on the majority of BVH or CN samples but also enhances the dissipation feature. Bilayer absorber sample with reasonable design and layer thickness optimization outperform single layer samples in terms of absorption efficiency, with the ideal sample having a minimum reflection loss (RLmini) of −37.5 dB and an effective absorption bandwidth (EAB) of 3.6 GHz with only a total thickness of 1.6 mm. The exceptional microwave absorption capabilities of the bilayer absorber sample are the consequence of the beneficial impacts of interfacial polarization between layers.

The Dominant Role of the Summer Hemisphere in Subtropical Lower Stratospheric Wave Drag Trends

AbstractIt is well established that the shallow branch of the Brewer‐Dobson circulation accelerates in a warming climate due to enhanced wave drag in the subtropical lower stratosphere. This has been linked to the strengthening of the upper flanks of the subtropical jets. However, the seasonality of the zonal wind trends, peaking in the winter hemisphere, is opposite to that of the Eliassen‐Palm flux convergence trends, peaking in summer. We investigate the seasonality in the wave drag trends and find a different behavior for each hemisphere. The Shepherd and McLandress (2011, https://doi.org/10.1175/2010jas3608.1) mechanism, involving transient wave dissipation at higher levels following the rise of the critical lines, is found to maximize in austral summer. On the other hand, in the Northern Hemisphere the wave drag increase peaks in summer primarily due to the changes in the stationary planetary waves (monsoonal circulations) associated with enhanced deep convection.

AWSoM Magnetohydrodynamic Simulation of a Solar Active Region. II. Statistical Analysis of Alfvén Wave Dissipation and Reflection, Scaling Laws, and Energy Budget on Coronal Loops

The coronal heating problem has been a major challenge in solar physics, and a tremendous amount of effort has been made over the past several decades to solve it. In this paper, we aim at answering how the physical processes behind the Alfvén wave turbulent heating adopted in the Alfvén Wave Solar atmosphere Model (AWSoM) unfold in individual plasma loops in an active region (AR). We perform comprehensive investigations in a statistical manner on the wave dissipation and reflection, temperature distribution, heating scaling laws, and energy balance along the loops, providing in-depth insights into the energy allocation in the lower solar atmosphere. We demonstrate that our 3D global model with a physics-based phenomenological formulation for the Alfvén wave turbulent heating yields a heating rate exponentially decreasing from loop footpoints to top, which had been empirically assumed in the past literature. A detailed differential emission measure (DEM) analysis of the AR is also performed, and the simulation compares favorably with DEM curves obtained from Hinode/Extreme-ultraviolet Imaging Spectrometer observations. This is the first work to examine the detailed AR energetics of our AWSoM model with high numerical resolution and further demonstrates the capabilities of low-frequency Alfvén wave turbulent heating in producing realistic plasma properties and energetics in an AR.

To simple waves and small-amplitude perturbations in radiation gasodynamics

The paper analyzes one-dimensional simple waves and small-amplitude perturbations in radiating and scattering gray gas. The governing equation of radiation acoustics describing the dynamics of simple waves is derived. The conditions of radiation-thermal dissipation and radiation resistance force are introduced into this equation to describe the propagation with dissipation and attenuation of various radiation perturbation waves. The phenomenological approximate Whitham method is used to investigate non-equilibrium wave phenomena in radiative medium. This method is an effective way to analyze fundamental modes when more than one velocity appears in the governing equation. The use of this method is demonstrated in this paper by considering the evolution of one-dimensional harmonic waves caused by a short-wave initial perturbation of the equilibrium state of the radiating and scattering medium. Analytical solutions are obtained for all wave modes, which allow us to interpret their physical meaning. These solutions can be, in particular, an additional test for radiative hydrodynamic codes operating in the radiative acoustics regime. The presented approach may be useful in detailing higher-order numerical Godunov schemes for radiation acoustics problems.

Denoising deep brain stimulation pacemaker signals with novel polymer-based nanocomposites: Porous biomaterials for sound absorption

<p>Deep brain stimulation (DBS) pacemakers are sophisticated medical devices that deliver electrical signals to targeted areas of the brain via implanted electrodes, effectively regulating abnormal brain activity and relieving symptoms of treatment-resistant neurological disorders. However, proximity to other electromagnetic equipment may introduce additional noise, which can be disruptive to individuals. To mitigate this issue, we propose a novel polymer-based nanocomposite for pacemakers for signal denoising. This research focused on the development and analysis of nanocomposites comprising polypropylene (PP) combined with montmorillonite nanoclay and graphene nanosheets (GNs). The nanocomposites were created by blending them through melting, using varying ratios of clay to GNs, with a total loading of 4 wt.%. This study focused on enhancing the signal-to-noise ratio for brain pacemakers by using nanocomposites. It investigated the noise reduction properties of PP nanocomposites, specifically in the outlet gate of the pacemaker. This research aimed to find the ideal ratio of clay to GNs in the PP matrix. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were conducted to analyze the crystalline structure and filler dispersion, as well as thermal behavior and filler–matrix interactions in the material. Scanning electron microscopy was employed to observe the dispersion of the nanofillers in the PP, and sound tube testing was conducted to evaluate the noise levels of the composites. The findings indicated that a porous structure of the nanocomposite with dispersed microspheres within the PP matrix and a long pathway facilitated increased dissipation of acoustic waves, making it suitable for denoising in brain pacemakers. Furthermore, the nanocomposite containing 2.75 wt.% of nanoclay and 1.25 wt.% of graphene components within the polypropylene matrix demonstrated a favorable signal-to-noise ratio compared to other evaluated nanocomposites.</p>

Design of broadband metamaterial absorber utilized by flower-shaped unit loaded with lumped-resistor

A metamaterial broadband absorber is designed by means of metal pattern and lumped resistance. The optimal structural parameters and resistance are scanned in certain steps to determine. The maximum absorbing bandwidth can achieve up to 8.2 GHz with 3 mm thickness. Subsequently, the angle stability of the absorber can be improved by adding vertical metal through holes. After optimization, the maximum absorbing bandwidth can be further increased to 9.1 GHz (8.3–17.4 GHz), and the effective absorption bandwidth of 3.7 GHz (9.53–13.25 GHz) can still be achieved when the incident angle is 60°. Further analysis reveals that the dissipation of the electromagnetic wave is achieved by ohmic loss caused by the resistive element and magnetic resonance caused by the induced circular current, rather than by temperature or other factors. Finally, to verify the real performance of the designed metamaterial absorber, a 30 cm × 30 cm sample was fabricated, and the reflection coefficient was tested by the NRL arch test method. The results showed that the measured return loss of the absorber was consistent with the simulation results.

Fabrication of innovative multifunctional dye using MXene nanosheets.

The increasing demand for natural and safer alternatives to traditional hair dyes has led to the investigation of nanomaterials as potential candidates for hair coloring applications. MXene nanosheets have emerged as a promising alternative in this context due to their unique optical and electronic properties. In this study, we aimed to evaluate the potential of Ti3C2Tx (Tx = -O, -OH, -F, etc.) MXene nanosheets as a hair dye. MXene nanosheet-based dyes have been demonstrated to exhibit not only coloring capabilities but also additional properties such as antistatic properties, heat dissipation, and electromagnetic wave shielding. Additionally, surface modification of MXene using collagen reduces the surface roughness of hair and upregulates keratinocyte markers KRT5 and KRT14, demonstrating the potential for tuning its physicochemical and biological properties. This conceptual advancement highlights the potential of MXene nanosheets to go beyond simple cosmetic improvements and provide improved comfort and safety by preventing the presence of hazardous ingredients and solvents while providing versatility.