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A community-driven effort in Cedar Key, Florida, USA, resulted in the construction of three living shoreline retrofits intended to bolster failing coastal infrastructure and restore habitat functions in Daughtry Bayou. A multi-year monitoring program tracked changes in elevation and vegetation communities across the entire shoreline profile from lower-intertidal to upland/transitional zones and measured wave attenuation during typical and extreme (hurricane) conditions. Overall, these living shoreline retrofits served to soften more than 30% of the bayou’s shoreline, dramatically reducing the extent of armored shoreline in direct contact with tidal influence. The extent of vegetated habitat area has increased at all three sites, despite sediment export from higher elevation zones driven largely by repeated impacts from hurricanes and tropical storms. These living shorelines reduced wave energy by 33 to 79% in typical conditions and by up to 28% in hurricane conditions, consistently outperforming armored shorelines, even during an extreme event (Hurricane Idalia). Our monitoring efforts were sufficient to capture project trajectories and assess performance relative to project goals, but our program had limitations that could have been overcome with additional resources and increased focus on capturing spillover effects. The living shoreline retrofit projects assessed here have persisted through and shown signs of recovery after multiple tropical storms and hurricanes, while providing important energy reduction services. Thus, living shoreline retrofits continue to be a cost-effective shoreline management strategy in the short term for this area. However, our analyses suggest that persistence of these shorelines could be threatened by the combination of sea-level rise (by 2040), upland armoring, and an increasing risk of more intense tropical systems. Therefore, future interventions should more carefully consider these threats in conjunction with habitat enhancement goals. [ABSTRACT FROM AUTHOR]

ABSTRACT The dynamic pile‐soil interaction significantly affects the accuracy of pile vibration response analysis. However, currently, there is no well‐established method for simulating pile toe soil under high‐strain dynamic loading (HSDL), which presents a major challenge for pile driving analysis. This paper proposes a fictitious soil pile model to simulate reactions and stress wave propagation in the base soil under HSDL. The pile toe soil was regarded as a fictitious soil pile extending downward to the bedrock at a certain cone angle, considering the non‐linear soil stiffness, radiation damping, and hysteretic damping. The solution of the soil responses was given by differential iterative method combined with MTLAB programming. The model's accuracy was validated against a three‐dimensional (3D) finite element model and the Smith model. Sensitivity analysis was performed on parameters such as discreteness, time interval, cone angle, and non‐linear stiffness. The model shows advantages in simulating stress wave propagation in pile toe soil under HSDL, with attenuation rates decreasing with depth and wave speeds stabilizing after an initial decrease. The soil elastic modulus, pile diameter, cone angle, and impact loads influence the attenuation rate, while only the elastic modulus significantly affects wave speed. The results could be helpful for the simulation of the pile toe soil under HSDL and the study of the attenuation of stress waves in the soil. [ABSTRACT FROM AUTHOR]

Acoustofluidics is a promising technology that leverages acoustic waves for precise manipulation of micro/nano‐scale flows and suspended objects within microchannels. Despite many advantages, the practical applicability of conventional acoustofluidic platforms is limited by irreversible bonding between the piezoelectric actuator and the microfluidic chip. Recently, reconfigurable acoustofluidic platforms are enabled by reversible bonding between the reusable actuator and the replaceable polydimethylsiloxane (PDMS) microfluidic chip by incorporating a PDMS membrane for sealing the microchannel and coupling the acoustic waves with the fluid inside. However, a quantitative guideline for selecting a suitable PDMS membrane for various acoustofluidic applications is still missing. Here, a design rule for reconfigurable acoustofluidic platforms is explored based on a thorough investigation of the PDMS thickness effect on acoustofluidic phenomena: acousto–thermal heating (ATH), acoustic radiation force (ARF), and acoustic streaming flow (ASF). These findings suggest that the relative thickness of the PDMS membrane (t) for acoustic wavelength (λPDMS) determines the wave attenuation in the PDMS and the acoustofluidic phenomena. For t/λPDMS ≈ O(1), the transmission of acoustic waves through the membrane leads to the ARF and ASF phenomena, whereas, for t/λPDMS ≈ O(10), the acoustic waves are entirely absorbed within the membrane, resulting in the ATH phenomenon. [ABSTRACT FROM AUTHOR]

An important technical task is to develop methods for recording the phase transitions of water to ice. At present, many sensors based on various types of acoustic waves are suggested for solving this challenge. This paper focuses on the theoretical and experimental study of the effect of water-to-ice phase transition on the properties of Lamb and quasi shear horizontal (QSH) acoustic waves of a higher order propagating in different directions in piezoelectric plates with strong anisotropy. Y-cut LiNbO3, 128Y-cut LiNbO3, and 36Y-cut LiTaO3 plates with a thickness of 500 μm and 350 μm were used as piezoelectric substrates. It was shown that the amplitude of the waves under study can decrease, increase, or remain relatively stable due to the water-to-ice phase transition, depending on the propagation direction and mode order. The greatest decrease in amplitude (42.1 dB) due to glaciation occurred for Lamb waves with a frequency of 40.53 MHz and propagating in the YX+30° LiNbO3 plate. The smallest change in the amplitude (0.9 dB) due to glaciation was observed for QSH waves at 56.5 MHz propagating in the YX+60° LiNbO3 plate. Additionally, it was also found that, in the YX+30° LiNbO3 plate, the water-to-ice transition results in the complete absorption of all acoustic waves within the specified frequency range (10–60 MHz), with the exception of one. The phase velocities, electromechanical coupling coefficients, elastic polarizations, and attenuation of the waves under study were calculated. The structures "air–piezoelectric plate–air", "air–piezoelectric plate–liquid", and "air–piezoelectric plate–ice" were considered. The results obtained can be used to develop methods for detecting ice formation and measuring its parameters. [ABSTRACT FROM AUTHOR]

Floating breakwaters are widely applied on the ocean water surface to protect human infrastructure from the destructive power of waves. This study designs and investigates the performance of a novel symmetric-pontoon floating breakwater with a symmetric pair of hydrofoils. Based at the Cranfield Ocean Systems Laboratory, the system was constructed and tested in various wave conditions using different fin configurations. The floating structure was anchored using a symmetric four-point mooring system. The tested waves were regular and symmetric perpendicular to the propagating direction. Key parameters, including the attenuated wave amplitude, motions of the breakwater, and the mooring forces, were measured. The wave parameters utilised for testing covered 1.61–5.42 relative wavelength to structural length, with wave heights of 3 c m and 5 c m . Results showed the 90° fin configuration can reduce wave transmission by up to 74 % , with the lowest mooring forces at 3.05 relative wavelength, enhancing the performance of wave energy dissipation and structural seakeeping. At 90° setup, the mooring force was lowest at 2.41 relative wavelength. This research can inform novel designs of breakwaters to improve protection abilities for coastal cities and offshore infrastructures, especially renewable energy systems. [ABSTRACT FROM AUTHOR]

Floating breakwaters (FBs) play an important role in protecting coastlines, marine structures, and ports due to their simple construction, convenient movement, cost-effectiveness, and environmental friendliness. However, the traditional box-type FBs are flawed due to their requiring large sizes for wave attenuation and their overly high level of wave reflection. In this paper, a novel partial T special-type FB with wave attenuation on the surface and flow blocking below the water has been presented. First, the User-Defined Function (UDF) feature in ANSYS Fluent was employed to compile the six degrees of freedom (6-DOF) motion model. A two-dimensional viscous numerical wave flume was developed using the velocity boundary wave-generation method and damping dissipation wave-absorption method, with fully coupled models of the FBs developed. A VOF multiphase flow model and a RANS turbulence model were employed to capture the free flow of gas–liquid two-phase flow. Then, the performance of wave attenuation of the new FB was compared with that of the traditional box-type FB of the same specifications. The simulation results showed that the transmission coefficient of the new FB is significantly lower than that of the box-type FB, and the dissipation coefficient is notably higher, demonstrating excellent performance of wave attenuation, particularly for long-period waves. As wave height increases, the novel FB benefits from its wave attenuation mechanism, with a lower reflection coefficient compared to the box-type FB. Finally, through parametric analysis, some design recommendations of the novel FB suitable for practical engineering applications in deep-sea aquaculture are presented. [ABSTRACT FROM AUTHOR]

Nature‐based solutions, through conservation or (re)creation of vegetated shorelines, are recognized to mitigate the impact of waves and erosion risks on shorelines. Wave attenuation is known to be dependent on plant traits, resulting in increasing wave attenuation rates with increasing shoot density, shoot thickness, height, and stiffness. However, following the allometric scaling theory, we hypothesize that increasing shoot density (a canopy‐scale trait) may be associated with decreasing shoot thickness and stiffness (a shoot‐scale trait), with potential opposing effects on overall wave attenuation.This study investigates (1) the presence of such allometric relations across intertidal shore plant species via existing literature and (2) the trade‐off effects on the overall wave attenuation capacity of shore vegetation through a flume experiment.Our results reveal for the first time the presence of allometric relationships between shoot‐scale and canopy‐scale plant properties in perennial intertidal plant species. Across different species, increasing shoot densities are indeed associated with decreasing shoot thickness and shoot stiffness.Next, we performed a wave flume experiment with plant mimics, showing that wave attenuation rate follows a logarithmic increase with increasing shoot density, even though the increasing shoot density was associated with thinner and more flexible individual shoots.Synthesis and applications. We conclude that wave attenuation is predominantly governed by canopy‐scale properties, but a trade‐off with shoot‐scale properties mediates the overall wave attenuation capacity of the vegetated shore. Our findings imply that nature‐based projects (re‐)creating vegetated shorelines should account for potential trade‐off effects of species‐specific plant traits at the canopy scale and individual shoot scale. [ABSTRACT FROM AUTHOR]

The narrow attenuation bands of traditional marine structures have long been a challenge in mitigating water waves. In this paper, a metastructure (MS) composed of floating periodic pontoons is proposed for broadband water wave attenuation. The interaction of surface gravity waves with the MS is investigated using linear wave theory. The potential solutions of water waves by the MS with a finite array are developed by using the eigenfunction expansion matching method (EEMM), and the band structure of the MS is calculated by the transfer matrix method (TMM), in which the evanescent modes of waves are considered. The solution is verified against the existing numerical result for a special case. Based on the present solution, the association between Bragg resonance reflection and Bloch bandgaps is examined, the effects of pontoon geometry are analyzed, and the comparison between floating MS and bottom-mounted periodic structures is conducted. A computational fluid dynamics (CFD) model is further developed to assess the structures in practical fluid environments, and the floating MS presents excellent wave attenuation performance. The study presented here may provide a promising solution for protecting the coast and offshore structures. [ABSTRACT FROM AUTHOR]

Coastal protection solutions can be categorised as grey, hybrid or natural. Grey infrastructure includes artificial structures like dykes. Natural habitats like seagrasses are considered natural protection infrastructure. Hybrid solutions combine both natural and grey infrastructure. Evidence suggests that grey solutions can negatively impact the environment, while natural habitats prevent flooding without such adverse effects and provide many ecosystem services. New types of protective solutions, called biomimetic solutions, are inspired by natural habitats and reproduce their features using artificial materials. Few studies have been conducted on these new approaches. This study aims to quantify wave dissipation observed in situ above a biomimetic solution inspired by kelps, known for their wave-dampening properties. The solution was deployed in a full water column near Palavas-les-Flots in southern France. A one-month in situ experiment showed that the biomimetic solution dissipates around 10% of total wave energy on average, whatever the meteo-marine conditions. Wave energy dissipation is frequency-dependent: short waves are dissipated, while low-frequency energy increases. An anti-dissipative effect occurs for forcing conditions with frequencies close to the eigen mode linked to the biomimetic solution's geometry, suggesting that resonance should be considered in designing future biomimetic protection solutions. [ABSTRACT FROM AUTHOR]

This study experimentally investigated the wave attenuation coefficient and wave number of the heated granite after water cooling (W-C) and air cooling (A-C) treatments. The granite specimens heated to five temperatures (25 °C, 100 °C, 200 °C, 300 °C and 400 °C) were subjected to the W-C and A-C treatments, respectively. The pendulum impact test was performed on the cooled granite at room temperature to obtain the separated stress pulse. The wave attenuation ratio in the cooled granite was investigated. Propagation coefficients (attenuation coefficient and wave number) were introduced to describe the harmonic wave attenuation in the cooled granite. The effects of W-C and A-C treatments on the attenuation coefficient and wave number were discussed. The results show that the P-wave velocity decreases as temperature increases, while the wave attenuation ratio increases as temperature increases. The P-wave velocity of the granite after the W-C treatment is smaller than that of the granite after the A-C treatment. The wave attenuation ratio, attenuation coefficient and wave number of the stress pulse in the granite after the W-C treatment are larger than those of the stress pulse in the granite after the A-C treatment. The differences of P-wave velocity, wave attenuation ratio, attenuation coefficient and wave number after two cooling treatments increase as temperature increases. [ABSTRACT FROM AUTHOR]

The interest in phononic crystals and acoustic metamaterials has been an intensive subject of research in recent years. Finding a robust way to significantly expand or actively control the bandgap has received extensive attention. In this study, we propose a prestressed metamaterial beam attached with multiply local resonators connected by actively tunable piezoelectric springs. The Euler–Bernoulli beam theory and Timoshenko beam theory are applied in the theoretical analysis of the system. Further, the spectral element method is utilized to analytically compute the dispersion relation and transmission ratio and excellent agreement with reference to the benchmark is reported. The influences of an external axial force on the bandgap range and attenuation behavior are further studied. Subsequently, the effect of resonator number and mass on the local resonance bandgap structure is investigated in two parametric studies. The active control of bandgap range and frequency is then verified. By analyzing frequency response function, the tunable transmission ratio of a supercell can be observed. To conclude, this paper not only provides a guideline for designs of wave attenuation with multiple frequency regimes in a one-dimensional system, but it can also be extended to sub-wavelength wave manipulation designs. [ABSTRACT FROM AUTHOR]

In unbounded media, the acoustic attenuation as function of frequency is related to the frequency-dependent sound velocity (dispersion) via Kramers–Kronig dispersion relations. These relations are fundamentally important for better understanding of the nature of attenuation and dispersion and as a tool in physical acoustics measurements, where they can be used for control purposes. However, physical acoustic measurements are frequently carried out not in unbounded media but in acoustic waveguides, e.g., inside liquid-filled pipes. Surface acoustic waves are also often used for physical acoustics measurements. In the present work, the applicability of Kramers–Kronig relations to guided and surface waves is investigated using the approach based on the theory of functions of complex variables. It is demonstrated that Kramers–Kronig relations have limited applicability to guided and surface waves. In particular, they are not applicable to waves propagating in waveguides characterised by the possibility of wave energy leakage from the waveguides into the surrounding medium. For waveguides without leakages, e.g., those formed by rigid walls, Kramers–Kronig relations remain valid for both ideal and viscous liquids. Examples of numerical calculations of wave dispersion and attenuation using Kramers–Kronig relations, where applicable, are presented for unbounded media and for waveguides formed by two rigid walls. [ABSTRACT FROM AUTHOR]

This study aims to examine the impact of areca microfiber and corn cob carbon quantum dots (CQD) magnetic filler particles on the EMI shielding capabilities of PVA composites. The areca fiber was used to improve the mechanical properties whereas the CQD was added to improve the conductivity of composite. The solution casting technique was used to determine the dielectric, magnetic, EMI shielding, and mechanical characteristics of the PVA composite with areca microfiber reinforcement and CQD particles. According to the findings the composite designator RFC4, the highest dielectric constant values measured by inclusion of areca microfiber at 30 vol.% and CQD particles at 0.4 vol.% are around 4.4, 4.8, 2.1, 3.5, and 0.34 at 8, 12, 16, and 20 GHz, respectively. The highest recorded magnetic permeability for composite designation RFC4 is 3.16, 3.76, 4.24, and 5.15 at 8, 12, 16, and 20 GHz, respectively. This was made possible by the addition of areca microfiber at a volume percentage of 30vol. % and CQD particles at a volume percentage of 0.4. In addition, the addition of areca microfiber by 30% volume and CQD particles by 0, 1, 2, 3, and 4% volume for the composite designations RFC1, RFC2, RFC3, and RFC4 accordingly has gradually improved EMI shielding properties. The composite designation RFC4 has the highest measured EMI shielding values about 12.5 (8GHz), 20.8 (8GHz), 31.1 (8GHz), and 50.8 (8GHz). The greatest tensile strength value obtained up to 56.8 MPa after 30 vol.% of areca microfibers and 1 vol.% of CQD particles were added. The maximum hardness of the composite material RFC4 with areca microfiber at 30% volume and CQD particles at 4.0% volume is around 76 shore-D, while the elongation % is up to 72%. [ABSTRACT FROM AUTHOR]

In this work, computational fluid dynamics (CFD)—based simulations and linear diffraction analysis are carried out to investigate the interaction between water waves and metamaterials composed of an array of C-shaped cylinders. The flow visualization by CFD-based simulations reveals that local resonance is a result of constructive interference between the incident wave and the wave radiated from the cavity of the C-shaped cylinder. The wave-induced water motion inside the cavity acts as a source of generating this radiated wave, which has the same angular wave frequency and wavenumber but opposite propagation direction as the incident wave. In addition, it is found from the CFD-based simulations that the energy dissipation increases as the opening of the C-shaped cylinder becomes shorter and sharper, along with an increase in its outer radius, and the variation trend of energy dissipation is only affected by the outer radius. Meanwhile, except for very small opening lengths, variations in opening length, width, and outer radius do not significantly impact the wave attenuation effect of the C-shaped cylinder array. Moreover, the results obtained by CFD and the linear potential flow model are compared. The linear potential flow theory is proven to be a reliable approach for accurately predicting the local resonant frequency and transmission coefficients within the local resonant band across a range of geometric parameters. However, it is noted that this theory may have limitations when applied to cases with extremely small opening lengths, where it struggles to accurately predict the local resonant frequency and the intensity of local resonance. [ABSTRACT FROM AUTHOR]

A set of laboratory experiments are carried out to investigate the effect of following/opposing currents on wave attenuation. Rigid vegetation canopies with aligned and staggered configurations were tested under the condition of various regular wave heights and current velocities, with the constant water depth being 0.60 m to create the desired submerged scenarios. Results show that the vegetation-induced wave dissipation is enhanced with the increasing incident wave height. A larger velocity magnititude leads to a greater wave height attenuation for both following and opposing current conditions. Moreover, there is a strong positive linear correlation between the damping coefficient β and the relative wave height H0/h, especially for pure wave conditions. For the velocity profile, the distributions of Umin and Umax show different patterns under combined wave and current. The time-averaged turbulent kinetic energy (TKE) vary little under pure wave and Uc = ±0.05 m/s conditions. With the increase of flow velocity amplitude, the time-averaged TKE shows a particularly pronounced increase trend at the top of the canopy. The vegetation drag coefficients are obtained by a calibration approach. The empirical relations of drag coefficient with Reynolds and Keulegane-Carpenter numbers are proposed to further understand the wave-current-vegetation interaction mechanism. [ABSTRACT FROM AUTHOR]

This study employs the XBeach surfbeat model (XBSB) to explore the effects of vegetation on wave attenuation and dune erosion in a case study of Mexico Beach during Hurricane Michael. The XBSB model was validated against laboratory experiments of wave-induced dune erosion and wave attenuation by vegetation. In the case study of vegetation on dunes in Mexico Beach during Hurricane Michael, different vegetation drag coefficients were evaluated to investigate the effects of vegetation on wave attenuation and dune erosion. LiDAR data of dune profiles before and after Hurricane Michael were used for model validation. The findings reveal that vegetation on dunes significantly affects wave attenuation and dune erosion. Under vegetated conditions, as the vegetation drag coefficient value increases, wave attenuation also increases, leading to a reduction of dune erosion. An increase in vegetation density enhances wave attenuation in the vegetated area, including reductions in significant wave height and flow velocity. However, the rate of change in attenuation decreases as the vegetation density increases. Through simulations under regular wave condition on Mexico Beach, an optimal vegetation density was identified as 800 units/m2. Beyond this density, additional vegetation does not substantially improve wave attenuation. Furthermore, the position of the dune crest elevation is related to the location where the alongshore flow velocity begins to decrease. The findings highlight the essential role of coastal vegetation in enhancing coastal resilience against hurricanes. [ABSTRACT FROM AUTHOR]

In unbounded media, the acoustic attenuation as function of frequency is related to the frequency-dependent sound velocity (dispersion) via Kramers–Kronig dispersion relations. These relations are fundamentally important for better understanding of the nature of attenuation and dispersion and as a tool in physical acoustics measurements, where they can be used for control purposes. However, physical acoustic measurements are frequently carried out not in unbounded media but in acoustic waveguides, e.g., inside liquid-filled pipes. Surface acoustic waves are also often used for physical acoustics measurements. In the present work, the applicability of Kramers–Kronig relations to guided and surface waves is investigated using the approach based on the theory of functions of complex variables. It is demonstrated that Kramers–Kronig relations have limited applicability to guided and surface waves. In particular, they are not applicable to waves propagating in waveguides characterised by the possibility of wave energy leakage from the waveguides into the surrounding medium. For waveguides without leakages, e.g., those formed by rigid walls, Kramers–Kronig relations remain valid for both ideal and viscous liquids. Examples of numerical calculations of wave dispersion and attenuation using Kramers–Kronig relations, where applicable, are presented for unbounded media and for waveguides formed by two rigid walls.

Brett, J.; Samuell, M.; Augstein, B.; Parra, S.; Hancock, E.; Saunders, C.; Wunsch, S.; Winstead, N., and Boothby, J., 2024. Nature-based coastal protection: Measuring and modeling flow reduction by oysters. Journal of Coastal Research, 40(4), 647–660. Charlotte (North Carolina), ISSN 0749-0208. Natural coastal infrastructure protects coast lines from climate hazard impacts, such as erosion and flooding. Laboratory and modeling studies presented here examine the utility of oyster reefs as a form of natural coastal protection. Oyster reefs are known to provide both water quality improvements and erosion protection. Experiments were conducted to determine the effects of oysters on flow parameters in a recirculating flow channel. A cage of eastern oysters, Crassostrea virginica, was placed in the flow channel, blocking a portion of the flow, to imitate cultured oysters in the ocean. Particle image velocimetry was used to measure the flow behind the oyster cage to examine the impact of the oysters compared with a control test with an empty cage. Average velocities were reduced by 15%, with velocities directly behind the cage reduced 70% in fresh water and reversed in salt water. A setup similar to the laboratory experiments was simulated in a Coupled Ocean–Atmospheric–Wave–Sediment Transport (COAWST) model. In the COAWST model, the oyster reef was simulated as stiff vegetation with a drag coefficient of 8, reproducing the 70% reduction measured in the lab experiments. Finally, a regional model is presented, which demonstrates the impact of an oyster reef on waves and currents at a larger scale with a drag coefficient of 1.5, the highest numerically stable value found. Within the oyster vegetation patch, depth-averaged currents were reduced 14% and bottom currents were reduced 97%. Significant wave heights were reduced by 62% above the reef and 23% shoreward of the reef. The results here suggest that regional modeling such as COAWST can be an effective tool for assessing the impact of potential coastal resilience strategies to mitigate climate hazard impacts in a climate-changed world. [ABSTRACT FROM AUTHOR]

This study evaluates the effectiveness of artificial Kandelia obovata forests in wave attenuation through physical model experiments conducted in a wave flume. The experiments meticulously replicated real-world hydrodynamic conditions and mangrove movement responses using the principles of gravitational and motion similarity, with a scaled 1:10 model of Kandelia obovata. Our approach included comparative experiments against a 1:100 gradient concrete slope to isolate the effects of seabed friction and flume wall reflections. The wave height was measured using strategically placed wave gauges. The findings indicated that the artificial Kandelia obovata forests significantly attenuated waves, with a decrease in the total attenuation capacity as the water depth increased from 2.75 m to 3.28 m under both regular and irregular waves. The elastic mangrove model with a canopy effect led to a 15% increase in wave attenuation over cylindrical models. Predictive models using multivariate nonlinear regression and back propagation neural networks showed that the latter provided a superior accuracy in estimating wave transmission coefficients [ABSTRACT FROM AUTHOR]

Curve beams are widely used in structural engineering like civil engineering and aircraft structures. Due to their coupling effects of bending, shear, and torsion, curve beams have a significant role in wave propagation fields as complete bandgaps can be generated. With the miniaturization of devices, it becomes increasingly imperative to investigate wave characteristics of curve beams at the nanoscale, taking into account the flexoelectric effect. In this study, a theoretical model for the periodic flexoelectric curve beams is established under the strain-gradient electro-elasticity theory. Subsequently, a customized state-space-based transfer matrix method for flexoelectric curve beam is specifically proposed, referred to as FCB-TMM. According to the Floquet-Bloch theorem, the dispersion relations for the periodic flexoelectric curve beams with intriguing coupling characteristics can be obtained and verified. Additionally, the influence of the flexoelectric effect and strain gradient effect on its complete bandgaps is analyzed. The results indicate that the flexoelectric effect plays a vital role in wave propagation at small scales, causing a shift in the bandgaps towards higher frequencies. Ultimately, the synergistic effects of significant geometric and material parameters combined with the flexoelectric effect on the bandgaps are systematically discussed. It is discovered that changing flexoelectric coefficients may alter the pattern of bandgap variation with these geometric and material parameters, while the influence of flexoelectric coefficients on bandgaps varies depending on the values of these parameters. Our investigation offers an insight into understanding the wave propagation of the curve nanobeams, and thus further guides the application and development of flexoelectric wave components in MEMS/NEMS. • A state-space-based transfer matrix method is proposed for the flexoelectric curve nanobeams. • Complex band properties of the periodic flexoelectric curve nanobeams are investigated. • The synergistic effect between flexoelectric effect and significant parameters are systematically discussed. • The findings benefit the application and development of flexoelectric wave components in MEMS/NEMS. [ABSTRACT FROM AUTHOR]

AbstractIn this paper, impact attenuation and blast-wave mitigation are effectively realized by the dissipative stratified metamaterials with negative mass mechanism due to the coupling of the different resonators. To create a broad bandgap of the metamaterials, the dispersion curve and effective negative mass property are investigated. It is found that the coupling effect of different resonators produced by the relative movement of different main masses can create a broad bandgap and make the original bandgap by starting with a lower frequency, and thus impact input waves could be blocked effectively. Simulation results show that a stratified elastic metamaterial containing 25 units can reduce the amplitude of the load by two thirds under impact loading and almost completely impede its further propagation. Furthermore, the bandgap is broadened by optimization of the structure parameters and dissipative coefficient for blocking transient shock waves propagation. It is shown in numerical experiment that the wider bandgap produced by the new elastic metamaterials can effectively absorbed the energy of the blast and impact waves. Therefore, the results of this study provide a remarkably novel strategy for the design of new blast-resistant materials. [ABSTRACT FROM AUTHOR]

A novel three-dimensional mechanical metamaterial with low frequency bandgaps and negative Poisson's ratio is designed, consisting of a conventional three-dimensional reentrant structure and periodic resonators, with the aim of achieving vibration isolation and impact mitigation. The bandgap characteristic of the proposed metamaterial is determined computationally, and its dispersion diagram exhibits both partial bandgaps and a complete bandgap within a frequency band of interest. The mechanism for bandgap occurrence is characterised as the local resonance of ligaments and resonators, according to a vibration mode analysis. The wave attenuation capacity of the proposed metamaterial is derived numerically and experimentally from semi-infinite and finite-size metamaterial models, showing a good agreement with the predicted bandgap. Additionally, a thorough study on the design flexibility indicates that the bandgap characteristic can be directly tailored by changing the geometrical parameters of the proposed metamaterial. This allows further optimisation of the metamaterial for potential applications. The dynamic performance of the proposed metamaterial under an impact load is investigated by a finite element model. This demonstrates that the metamaterial reduces the transmitted force by a factor of 1.6 (for peak value) and 2.0 (for root mean square value) under a pulse impact with a duration of 0.88 ms. The impact mitigation result obtained from the impact test confirms that the metamaterial shows a mitigation capacity which is approximately 20% better than that of the conventional reentrant structure. [ABSTRACT FROM AUTHOR]

This review paper provides a comprehensive analysis of utilizing coastal vegetation as a mitigation strategy against tsunamis. It begins with an introduction to the historical impact of tsunamis on coastal vegetation and explores various types of trees known for their tsunami defense characteristics. The paper examines how vegetation can effectively protect against tsunamis based on past events, supported by both experimental and numerical studies. It also delves into innovative concepts proposed by researchers, including hybrid defense systems and optimized plantation layouts, to enhance the protective capabilities of coastal vegetation. Case studies from Aceh and South Java illustrate practical applications of reforestation efforts aimed at tsunami mitigation. Additionally, the paper discusses the challenges and limitations associated with implementing coastal vegetation strategies, emphasizing crucial factors such as maintenance and long-term sustainability.

Combining periodic layered structure with three-dimensional cylindrical local resonators, a hybrid metastructure with improved wave isolation ability was designed and investigated through theoretical and numerical approaches. The metastructure is composed of periodic rubber layers and concrete layers embedded with three-dimensional resonators, which can be freely designed with multi local resonant frequencies to attenuate vibrations at required frequencies and widen the attenuation bandgap. The metastructure can also effectively attenuate seismic responses. Compared with layered rubber-based structures, the metastructure has more excellent wave attenuation effects with greater attenuation and wider bandgap.

Based on field observation at the north coast of the Zhanjiang Bay in southern China, the characteristics of wave attenuation due to the drag force of one mangrove species, Avicennia marina (Forsk.) Viern., were quantitatively analyzed. The results demonstrated that the mean significant wave height decreased by ~62% within a forest belt up to 80 m due to various bio-physical interactions. Affected by the unique vertical configuration of vegetation, the wave attenuation rate is positively correlated with water depth. The drag force within the forest can be approximated by the function Cd=0.7344e0.1409Am, where Am is the projected area of the submerged obstacle at a certain water depth. The wave attenuation rate and the vegetation density (ρveg) in volume (‰) satisfy the fitting relationship of r=5×10−4·ρveg−3.6×10−3. These findings can accumulate quantitative information for studying the influence of mangrove vegetation on wave attenuation characteristics and provide necessary basic data for modeling studies to investigate the processes contributing to the attenuation capacity of mangroves.

Floating breakwaters (FBs) play an important role in protecting coastlines, marine structures, and ports due to their simple construction, convenient movement, cost-effectiveness, and environmental friendliness. However, the traditional box-type FBs are flawed due to their requiring large sizes for wave attenuation and their overly high level of wave reflection. In this paper, a novel partial T special-type FB with wave attenuation on the surface and flow blocking below the water has been presented. First, the User-Defined Function (UDF) feature in ANSYS Fluent was employed to compile the six degrees of freedom (6-DOF) motion model. A two-dimensional viscous numerical wave flume was developed using the velocity boundary wave-generation method and damping dissipation wave-absorption method, with fully coupled models of the FBs developed. A VOF multiphase flow model and a RANS turbulence model were employed to capture the free flow of gas–liquid two-phase flow. Then, the performance of wave attenuation of the new FB was compared with that of the traditional box-type FB of the same specifications. The simulation results showed that the transmission coefficient of the new FB is significantly lower than that of the box-type FB, and the dissipation coefficient is notably higher, demonstrating excellent performance of wave attenuation, particularly for long-period waves. As wave height increases, the novel FB benefits from its wave attenuation mechanism, with a lower reflection coefficient compared to the box-type FB. Finally, through parametric analysis, some design recommendations of the novel FB suitable for practical engineering applications in deep-sea aquaculture are presented.

Coastal protection solutions can be categorised as grey, hybrid or natural. Grey infrastructure includes artificial structures like dykes. Natural habitats like seagrasses are considered natural protection infrastructure. Hybrid solutions combine both natural and grey infrastructure. Evidence suggests that grey solutions can negatively impact the environment, while natural habitats prevent flooding without such adverse effects and provide many ecosystem services. New types of protective solutions, called biomimetic solutions, are inspired by natural habitats and reproduce their features using artificial materials. Few studies have been conducted on these new approaches. This study aims to quantify wave dissipation observed in situ above a biomimetic solution inspired by kelps, known for their wave-dampening properties. The solution was deployed in a full water column near Palavas-les-Flots in southern France. A one-month in situ experiment showed that the biomimetic solution dissipates around 10% of total wave energy on average, whatever the meteo-marine conditions. Wave energy dissipation is frequency-dependent: short waves are dissipated, while low-frequency energy increases. An anti-dissipative effect occurs for forcing conditions with frequencies close to the eigen mode linked to the biomimetic solution’s geometry, suggesting that resonance should be considered in designing future biomimetic protection solutions.

Mangroves offer vital ecological advantages including air and water filtration, coastal and estuarine habitat provision, sediment stabilization, and wave energy dissipation. Their intricate root systems play a key role in safeguarding shorelines from tsunamis and erosive storms by dissipating wave energy. Moreover, mangroves shield against boat wakes and wind-waves, thus naturally bolstering shoreline defense. Wave dissipation is a function of forest width, tree diameter, and forest density. Restoration efforts of juvenile mangroves in Florida's Indian River Lagoon (IRL) aim to reduce wave energy in areas vulnerable to erosion. Physical model testing of wave dissipation through mangroves is limited due to the complexity in representing the mangrove structure, where prop roots are non-uniform in both diameter and location. Previous studies have quantified wave-dissipating effects through the use of scaled and parameterized mangrove structures. This study measures the dissipation effects of live mangroves in a wave flume, forced by conditions representative of the IRL. These measurements are used to validate a parameterized dowel model. Error between wave attenuation factors for the live mangrove and dowel system was on average 2.5%. Validation of the modularized dowel system allowed for further parameterized testing to understand forest structure effects, such as sediment stabilization and wave attenuation. Maximum wave attenuation achieved in this study was 27–35% corresponding to a 40–60% reduction in wave energy depending on the configuration of the system. The wave reduction resulted in a 50–70% decrease in sediment erosion from the berm. The dowel tests indicate a target minimum thickness for mangrove root systems of 0.6 m for shoreline stabilization and restoration in the IRL. [ABSTRACT FROM AUTHOR]

Concrete is utilized in a wide range of civil engineering applications specifically in infrastructure projects. In general, as with any construction material, it may be subjected to deterioration over time because of various reasons such as excessive loading and so on. In this research, two reinforced concrete beams on a large scale (length 2400 mm, depth 350 mm, and width 250 mm) are cast and tested under static load using the ultrasonic pulse velocity (UPV) technique consisting of three pairs of transducers (54 kHz, 150 kHz, and 250 kHz). During the loading, the signals are sent and captured through the used transducers at selected loading steps. Two new proposed procedures based on signal peaks in time and frequency domains are used to monitor the crack progress induced in concrete beams under concentrated load. The findings of this study revealed the suitability of the proposed two approaches to detect the propagation of cracks to evaluate damage induced in concrete beams. [ABSTRACT FROM AUTHOR]

Near-source κ s , along-path κ ~ , and near-site κ 0 contributions to the spectral parameter kappa (κ ) were studied from earthquakes located along the Canal de Ballenas-Guaymas fault system and recorded by stations sited around the central-north Gulf of California, Mexico. The dataset consists of 26 earthquakes (M 3.4-6.0) recorded by six stations with hypocentral distances ranging from 31 to 270 km. We used the Anderson and Hough (1984) approach to estimate κ , followed by a one-step least-squares inversion to separate κ contributions. We found that κ has a range of 0.0260 to 0.1012 s, with a mean of 0.0600 ± 0.0170 s, while κ s and κ 0 exhibit means of 0.0088 ± 0.0059 s and 0.0200 ± 0.0205 s, respectively. We also observed significant inter-event κ s and inter-station κ 0 variabilities. The d κ ~ / d r regional average is 0.00023 ± 0.00001 s, equivalent to a regional quality factor of 1242 ± 54 for an S-wave velocity of 3.5 km/s. Furthermore, our results suggest that d κ ~ / d r tends to decrease with distance. We demonstrate that a well-designed least-squares inversion scheme can effectively address the limitations associated with estimating κ 0 using the Anderson and Hough approach in situations where recordings per station have a narrow distance range and where no recordings at small source-site distances are available for most stations. We found no correlation of κ s with earthquake magnitude. Instead, relatively higher κ s values tend to cluster along the ridge flanks of the Canal de Ballenas Basin, where hydrothermal fluid circulation is expected. [ABSTRACT FROM AUTHOR]

Designing materials that mitigate impacts effectively are crucial for protecting people and structures. Here, a single-resonator metamaterial with negative mass characteristics is proposed for impact mitigation, and numerical analysis of wave propagation shows explicitly how the spring stiffness and number of unit cells influence that mitigation. The results show clearly that a metamaterial with differing microstructural stiffness is better at mitigating the effect of a shock wave than one with a unique stiffness. Also, there is a critical number of unit cells beyond which the shock wave is not attenuated further, but the fabrication complexity increases. In the 40 groups of microstructural regions in this example, the attenuation effect no longer increases when there are more than 35 groups. This work offers guidance for microstructure designs in metamaterials and provides new ideas for using metamaterials to mitigate shock waves. [ABSTRACT FROM AUTHOR]

Ultra‐rough oceanic surfaces, such as oyster reefs, are characterized by densely‐packed, sharp‐edged roughness elements that induce high frictional resistance on the ambient flows. To effectively employ, for example, oyster reefs as a nature‐based solution in coastal protection, a detailed understanding of the frictional wave energy dissipation processes is necessary. This work reports on an experimental study in which six surrogates of very to ultra‐rough oceanic bed surfaces were subjected to regular waves. The influences of different sharpness' of roughness elements (bluntly‐shaped, sharp‐edged, and a combination thereof) and relative spacing between elements compared to the near‐bed horizontal excursion amplitude, λ/ab, on the wave attenuation have been investigated. Turbulence is 2–27 times larger for sharp‐edged surfaces and 1 to 18 times larger for mix surfaces than those of bluntly‐shaped surfaces. Maximum bed shear stresses, hydraulic roughness lengths, and wave friction factors are likewise significantly larger for sharp‐edged compared to bluntly‐shaped surfaces. These observations indicate that the sharp edges are crucial for frictional energy dissipation. Comparing the maximum bed shear stresses determined from wave height reductions to those determined from velocity measurements indicates that in addition to turbulent kinetic energy (TKE), periodic form‐induced stresses significantly contribute to the overall bed shear stresses. This study provides new insight into the frictional dissipation processes of oscillating flows encountering ultra‐rough surfaces. Plain Language Summary: Oyster reefs and other ultra‐rough bed surfaces near a shore significantly reduce wave heights of passing waves. Integrated into a nature‐based coastal protection system, they can reduce the requirement for artificial structures (e.g., seawalls and breakwaters). However, the processes causing the wave height reductions have not been comprehensively investigated. Oyster reefs have ultra‐rough surfaces, with edges so sharp they can cut rubber boots. As a model of those surfaces, we investigated the influence of different shapes of elements (sharp, blunt, and a combination thereof) on wave height reductions to address this feature of ultra‐rough surfaces. We found that the sharp‐edged elements cause significantly stronger turbulence in the surrounding flow, which leads to more substantial wave height reductions. We also found that the spacing between the elements in relation to the wave length influences the wave height reduction. Furthermore, we compared two methods of estimating the shear stress near the bed and found similar trends but different magnitudes of the results for the sharp‐edged surfaces. The results improve the understanding of underlying processes of wave height reductions caused by ultra‐rough bed surfaces. It is suggested to consider the bed roughness more prominently when designing oyster reefs as a coastal protection measure. Key Points: Physical modeling is used to investigate the influence of the sharpness of ultra‐rough surfaces on wave energy dissipationSharp‐edged roughness elements induce stronger turbulence production rates and wave height reductions compared to bluntly‐shaped elementsBoth turbulent and wake kinetic energy are necessary for an accurate estimation of bed shear stress for ultra‐rough surfaces [ABSTRACT FROM AUTHOR]

This paper proposes a novel protective material that enhances the impact resistance of metaconcrete by integrating rubber aggregates. The study delves into the mesoscopic mechanisms of wave attenuation in this material and the regulation of its performance accordingly. It first explores the effect of various design parameters of engineering aggregates on bandgap formation and then further investigates the influence of material viscoelastic properties on its bandgap width. Mesoscale simulations of spalling tests demonstrate that incorporating rubber aggregates can effectively expand the bandgap range, enhance energy absorption, reduce damage to the mortar matrix, and ultimately improve the impact resistance of metaconcrete. Simulation results in the present study highlight the effectiveness of rubber aggregates in strengthening metaconcrete's impact resistance.

This study employs the XBeach surfbeat model (XBSB) to explore the effects of vegetation on wave attenuation and dune erosion in a case study of Mexico Beach during Hurricane Michael. The XBSB model was validated against laboratory experiments of wave-induced dune erosion and wave attenuation by vegetation. In the case study of vegetation on dunes in Mexico Beach during Hurricane Michael, different vegetation drag coefficients were evaluated to investigate the effects of vegetation on wave attenuation and dune erosion. LiDAR data of dune profiles before and after Hurricane Michael were used for model validation. The findings reveal that vegetation on dunes significantly affects wave attenuation and dune erosion. Under vegetated conditions, as the vegetation drag coefficient value increases, wave attenuation also increases, leading to a reduction of dune erosion. An increase in vegetation density enhances wave attenuation in the vegetated area, including reductions in significant wave height and flow velocity. However, the rate of change in attenuation decreases as the vegetation density increases. Through simulations under regular wave condition on Mexico Beach, an optimal vegetation density was identified as 800 units/m2. Beyond this density, additional vegetation does not substantially improve wave attenuation. Furthermore, the position of the dune crest elevation is related to the location where the alongshore flow velocity begins to decrease. The findings highlight the essential role of coastal vegetation in enhancing coastal resilience against hurricanes.

Concrete is utilized in a wide range of civil engineering applications specifically in infrastructure projects. In general, as with any construction material, it may be subjected to deterioration over time because of various reasons such as excessive loading and so on. In this research, two reinforced concrete beams on a large scale (length 2400 mm, depth 350 mm, and width 250 mm) are cast and tested under static load using the ultrasonic pulse velocity (UPV) technique consisting of three pairs of transducers (54 kHz, 150 kHz, and 250 kHz). During the loading, the signals are sent and captured through the used transducers at selected loading steps. Two new proposed procedures based on signal peaks in time and frequency domains are used to monitor the crack progress induced in concrete beams under concentrated load. The findings of this study revealed the suitability of the proposed two approaches to detect the propagation of cracks to evaluate damage induced in concrete beams.

Background Marine macroalgae ('seaweeds') are a diverse and globally distributed group of photosynthetic organisms that together generate considerable primary productivity, provide an array of different habitats for other organisms, and contribute many important ecosystem functions and services. As a result of continued anthropogenic stress on marine systems, many macroalgal species and habitats face an uncertain future, risking their vital contribution to global productivity and ecosystem service provision. Scope After briefly considering the remarkable taxonomy and ecological distribution of marine macroalgae, we review how the threats posed by a combination of anthropogenically induced stressors affect seaweed species and communities. From there we highlight five critical avenues for further research to explore (long-term monitoring, use of functional traits, focus on early ontogeny, biotic interactions and impact of marine litter on coastal vegetation). Conclusions Although there are considerable parallels with terrestrial vascular plant responses to the many threats posed by anthropogenic stressors, we note that the impacts of some (e.g. habitat loss) are much less keenly felt in the oceans than on land. Nevertheless, and in common with terrestrial plant communities, the impact of climate change will inevitably be the most pernicious threat to the future persistence of seaweed species, communities and service provision. While understanding macroalgal responses to simultaneous environmental stressors is inevitably a complex exercise, our attempt to highlight synergies with terrestrial systems, and provide five future research priorities to elucidate some of the important trends and mechanisms of response, may yet offer some small contribution to this goal. [ABSTRACT FROM AUTHOR]

The global wave model WAVEWATCH III®; works well in open water. To simulate the propagation and attenuation of waves through ice-covered water, existing simulations have considered the influence of sea ice by adding the sea ice concentration in the wind wave module; however, they simply suppose that the wind cannot penetrate the ice layer and ignore the possibility of wind forcing waves below the ice cover. To improve the simulation performance of wind wave modules in the marginal ice zone (MIZ), this study proposes a parameterization scheme by directly including the sea ice thickness. Instead of scaling the wind input with the fraction of open water, this new scheme allows partial wind input in ice-covered areas based on the ice thickness. Compared with observations in the Barents Sea in 2016, the new scheme appears to improve the modeled waves in the high-frequency band. Sensitivity experiments with and without wind wave modules show that wind waves can play an important role in areas with low sea ice concentration in the MIZ. [ABSTRACT FROM AUTHOR]