Wave Attack Research Articles

Wave Conversion, Decay, and Heating in a Partially Ionized Two-fluid Magneto-atmosphere

A ray-theoretic phase-space description of linear waves in a two-fluid (charges and neutrals) magnetized plasma is used to calculate analytic decay rates and mode transmission and conversion coefficients between fast and slow waves in two dimensions due to finite ion–neutral collision frequencies at an arbitrary ionization fraction. This is relevant to partially ionized astrophysical plasmas, in particular solar and stellar atmospheres. The most important parameter governing collisional effects is the ratio of the wave frequency to the neutral–charges collision frequency, ϵ = ω/ν nc, with secondary dependence on ionization fraction and wave attack angle. Comparison is made to the one-fluid magnetohydrodynamic case, and it is found that acoustic-to-acoustic and magnetic-to-magnetic transmission through the Alfvén-acoustic equipartition layer is decreased by a term of relative to one-fluid (infinite collision frequency), and correspondingly acoustic-to-magnetic and magnetic-to-acoustic conversion is increased. The neutral-acoustic mode is shown to dissipate rapidly as ν nc → ∞. Away from the mode conversion region, dissipative decay along the remaining magneto-acoustic rays scales as and is found to be much more effective on magnetically dominated rays compared to acoustically dominated rays. This produces a steep jump in dissipation in mode conversion regions, where the rays change character, and can produce localized heating there and beyond. Applications to the solar chromosphere are discussed.

Numerical Analysis on The Effect of Barge Motion to Jacket Lifting Process During Decommissioning

Offshore structure decommissioning is mandatory when an offshore oil and gas platform reaches the end of its service life. There are no less than 450 fixed offshore steel structures in Southeast Asia, and by 2030, more than 200 offshore fields will be terminated and need to be decommissioned. From an operational aspect, the decommissioning process is simply an inverse of installation. However, due to the structures' age and the uncertainties of the structural performance, the simple operation can be an obfuscating process. This paper discusses one of the most crucial processes during decommissioning: lifting. The dynamic performance of a lifted jacket in several rigging variations is investigated. We use a standard stern crane HLV (Heavy Lift Vessel) to simulate the process, with several wave attack angles. Sea condition is according to DNVGL benign wave during marine operation, with random waves generated using the JONSWAP spectrum. Coupled dynamics of HLV and jacket motion are analyzed .

Near‐continuous monitoring of a coastal salt marsh margin: Implications for predicting marsh edge erosion

AbstractMechanisms that control marsh edge erosion include wind‐generated waves, vegetation productivity, land use and land change, and geotechnical properties of sediments. However, existing models for predicting marsh edge evolution focus primarily on edge retreat rates as a function of wave energy while accounting for other controlling factors as empirical constants. This simplification arises from a lack of high‐frequency monitoring of marsh evolutions. In particular, marsh erosion is timescale dependent, and conducting field observations on short temporal and spatial scales could elucidate the progression of erosion, which may improve marsh erosion predictive models. This study developed and validated a near‐continuous camera and erosion pin monitoring system to document marsh edge erosion at a high frequency (i.e., daily) in Terrebonne Bay, Louisiana. This was supplemented with daily wave power to explore the relationships between daily erosion and wave power. Long‐term average erosion rates derived from satellite and aerial imagery from 1989 through 2019 compare similarly to rates derived from longer‐term site visits (i.e., monthly) at approximately 2.2 m/yr. High‐magnitude erosion events (>20 cm/day) are driven by a buildup in wave energy over a 7‐day time period coupled with a strong 1‐day wave event, indicating a gradual reduction in marsh edge resistance with continued wave attack. Long‐term erosion monitoring methods, including monthly field visits, provide results that align well with previously reported relationships between wave power and erosion. High‐frequency measurements, however, illustrate that the previously published trends smooth over the large‐magnitude short‐term erosion events, potentially obscuring the physical processes of marsh edge erosion. For example, satellite and aerial imagery provide a long period of record, but they may underestimate the average annual erosion rate in the region, the effect of which may become exasperated over the varying temporal scales considered in coastal planning efforts across the USA and worldwide.

Cascadia Earthquake-Triggered Rockslide Burial of Beeswax Galleon Wreck Timbers in a Sea Cliff Wave-Cut Platform Site, North Smuggler Cove, Oregon, USA

Shipwreck timbers (n=27) from the Spanish galleon Santo Cristo de Burgos, also known as the Beeswax Wreck (lost in 1693), are examined for origins of multiple, simultaneous rockslide burials that protected and preserved the timbers on an intertidal wave-cut platform in the small Smuggler Cove in the Northern Oregon coast. The rockslides (n=3–4) that buried the shipwreck timbers are compared to nearby historic rockslide analogs to better establish the mechanisms of boulder distributions on the wave-cut platform. Large boulders (n=20), generally ≥1.0 m intermediate diameter, in the North Smuggler Cove (NSC) timber burial site were measured for estimated mass (1–41 t) and alongshore distribution below small gullies that routed the boulders to the wave-cut platform from overlying short (~100 m distance) but steep hillslopes (40–60% gradient). The multiple independent rockslides in the NSC site, dated to ~300 years by the buried Beeswax Wreck timbers, showed catastrophic, simultaneous activation by a widespread trigger. Anomalous rainfall and/or storm wave attack are unlikely mechanisms for these rockslide activations due to 1) hillslope protections from extended-upslope surface water discharge and 2) sea cliff protection from direct storm wave impacts. The most likely widespread trigger for rockslide activation in the NSC site is seismic ground shaking from an earthquake in the Central Cascadia subduction zone. Modern storm wind velocities (>10 s-1 sustained velocity and 170–225° bearing) and storm surge generated rip currents (≥0.5 km offshore distance) indicate that Beeswax Wreck timbers could have been transported north (1–10 km) to Smuggler Cove, within several winter seasons after the breakup of the Santo Cristo de Burgos. The most likely seismic trigger that could have activated the multiple rockslides in the NSC site, shortly after the brief accumulation of shipwreck timbers on the narrow, intertidal wave-cut platform in Smuggler Cove, is the 1700 Cascadia great earthquake (Mw~9.0). Additional sea cliff rockslide sites (n=8) in the central Cascadia margin are suggested for further investigations of seismically activated slope failures by the 1700 Cascadia great earthquake.

Reevaluating the wave power-salt marsh retreat relationship

Salt marshes are threatened by rising sea levels and human activities, and a major mechanism of marsh loss is edge retreat or erosion. To understand and predict loss in these valuable ecosystems, studies have related erosion to marsh hydrodynamics and wave characteristics such as wave power. Across global studies, erosion is reported to be largely linearly related to wave power, with this relationship having implications for the resilience of marshes to extreme events such as storms. However, there is significant variability in this relationship across marshes because of marsh heterogeneity and the uniqueness of each physical setting. Here, we investigate the results of individual studies throughout the world that report a linear relationship and add a new dataset from the Great Marsh in Massachusetts (USA). We find that most marsh wave power and erosion data are not normally distributed and when these datasets are properly plotted to account for their distributions, the resulting relationships vary from previously published curves. Our Great Marsh data suggest that events from specific wind directions can have an outsized impact on edge erosion due to their larger fetch and wind speeds. We also find that factors other than wave attack such as edge erosion along tidal channels, can have a measurable impact on retreat rates. We show the importance of maintaining statistical assumptions when performing regressions, as well as emphasize the site-specificity of these relationships. Without calibration of a marsh erosion-wave power relationship using robust regressions for each individual marsh, such a relationship is not fully constrained, resulting in unreliable predictions of future marsh resilience and response to climate change.

A laboratory study of wave-induced local scour at an emergent pile breakwater

A pile breakwater is a row of closely-spaced piles, placed in a side-by-side arrangement, to dissipate wave energy and prevent coastal erosion. It is important to understand the local scour at a pile breakwater for its foundation design. This paper reports a set of wave-flume tests on the local scour around the piles in regular waves. A laser scanner was used to measure the change in the three-dimensional bed elevation. Five values of Keulegan–Carpenter number were examined in this study. Scour holes near the pile breakwater were developed due to the oscillatory jet flow through the gaps between adjacent piles, and sand ripples were observed on both sides of the structure. The migration of the sand ripples was either onshore or offshore, depending on the wave conditions. The maximum scour-hole depth had an exponential growth with the duration of wave attack, and the equilibrium depth was found to be deeper than that for a standalone pile. Both the scour-hole depth and length were found to be scaled by the pile diameter. The ripple length and steepness were in general agreement with recent empirical formulas in the literature in spite of the presence of a pile breakwater.

Foredune growth and storm surge protection potential at the Eiderstedt Peninsula, Germany

In the context of climate change and associated sea level rise, coastal dunes can provide an essential contribution to coastal protection against wave attack and flooding. Since dunes are highly dynamic systems, their potential safety levels are related to their long-term development, varying in time and space, however pertinent research that ties those aspects together are generally scarce. The objective of this study is to analyze the long-term development of a young coastal foredune at the Eiderstedt peninsula, Germany and assess its coastal protection potential. This research presents (i) a novel semi-automated Dune Toe Tracking (DTT) method to systematically extract dune toes from cross-shore elevation profiles; (ii) established tools to derive the extraction of characteristic dune parameters and (iii) a newly defined Critical Storm Surge Level (CSSL) to relate spatio-temporal dune growth with coastal storm surge protection. Based on geospatial survey data, initial dune formation was identified in the 1980s. By 2015, the foredune had developed over a 6.5 km coastal stretch with a mean annual growth of 7.4m³/m. During the course of dune evolution, the seaward dune toe shifted seaward by an average of 2.3m/yr, while simultaneously increasing in height by an average of 1.1 cm/yr. Overall, the foredune formation established a new line of defense in front of an existing dike/dune line that provides spatially varying protection against a mean CSSL of 3.4m + NHN and can serve as an additional buffer against wave attack during severe storm events.

Characteristics of Sediment Transport After Morphological Changes at Palu Estuary, Sulawesi, Indonesia as The Impact of 2018 Tsunami

The tsunami triggered by the 2018 Palu Earthquake has not only caused the collapse of public infrastructure, but also damaged beaches along Palu Bay. Based on direct investigation along the beaches, the coastlines have shifted inland up to 30 meters. This shoreline change was caused by the attack of the tsunami waves at high speed followed by massive abrasion. Another impact of the wave attackis a change in the morphology of the beach bed, including in the Palu Estuary. This study aims to investigate the impact of changes in bed morphology around the Palu Estuary as a result of the tsunami attack on transport sediment characteristics, as one of the determinants of bed morphology. Quantitative analysis was carried out by numerical simulation based on 2D hydrodynamic modeling using the Surface-water Modeling System (SMS). The geometry of the model is formed from the mesh generated from the bed elevation based on the after-tsunami bathymetry survey. Two boundary conditions and one main input data are applied to this model: discharge data, tidal data and bed load data. Discharge data as an upstream boundary condition consists of minimum discharge, average discharge and maximum discharge. The downstream boundary is defined by a tidal curve predicted from 15 daily data. The bed load data is presented in the form of a gradation curve that describes the distribution of sediment grains. The simulation output indicates that sediment settles intensively downstream of the river mouth at high discharge and low tide. At low discharge and high tide, sediment tends to settle before the flow reaches the river mouth. Referring to the results of previous studies, the direction and velocity of sediment motion changed slightly after the tsunami. Changes in the direction and speed of movement are related to changes in bed morphology at the river mouth due to the 2018 Palu Tsunami.

On Formulae for Wave Transmission at Submerged and Low-Crested Breakwaters

Submerged and low-crested breakwaters are nearshore barriers with an underwater or slightly emergent crest, designed to reduce the energy of wave attacks and, consequently, to protect the coast from erosion and flooding. Their performance in reducing the wave energy can be evaluated by the value of the wave transmission coefficient, which thus requires accurate prediction. In the last few decades, several experimental investigations allowed the development of several formulae to predict this coefficient that agreed well within the given range of validity. In the present study, a comprehensive review of the existing formulae has been reported and the influence of input design variables has been highlighted. Moreover, an extensive set of experimental data has been collected and critically examined and re-analyzed to obtain a homogenous up-to-date database. Special attention has been addressed to the assessment of the reliability of each existing formula for and to evaluate its performance beyond the validity limits for which it was developed.

Assessing Drivers of Coastal Tundra Retreat at Point Hope, Alaska

AbstractShoreline erosion over the last few decades along the Point Hope, Alaska, USA coastline has led to considerable loss of tundra behind the beach. Analysis of available remote sensing, morphology, and hydrodynamic datasets are used to inform the time scales and mechanisms of coastal land loss at Point Hope, in part through integration of these data into an analytical retreat model originally developed for coastal foredunes. At shorter time scales, these analyses indicate that steeper local beach slopes influence higher wave runup that can enhance the scale of tundra retreat at a particular section of coast. Coastal stretches that are most vulnerable to wave attack of the tundra scarp appear to shift with time related to complex spatio‐temporal variability in shoreline change rates. These local beach erosion rates primarily control the retreat of the tundra at decadal scales. However, independent of the fronting beach morphology, the largest erosion events throughout the region generally occur when there is the coincidence of both high wave energy and elevated still water levels. Additional exploratory modeling results indicate that future changes to sea level and changes in wave energy will further enhance the magnitude of tundra erosion.

New insights in the probability distributions of wave-by-wave overtopping volumes at vertical breakwaters

Advances in the development of prediction tools for wave overtopping allow now for overtopping volumes to be estimated with good accuracy, with the combined use of mean overtopping rates and maximum wave by wave overtopping volumes in a sequence of wave overtopping events. While previous literature has tended to focus on mean overtopping rates at coastal structures, limited studies have investigated the wave by wave overtopping volumes at coastal sea defences; in particular, a paucity of studies have focussed on the prediction of the shape parameter in the Weibull distribution (i.e., Weibull b) of overtopping volumes. This study provides new insights on the probability distribution of individual wave overtopping volumes at plain vertical seawalls by analysing the measured Weibull b values derived from a series of laboratory experiments on seawalls performed on a wide range of wave conditions and crest freeboards. The influence of wave conditions (wave steepness, significant wave height), structural parameters (crest freeboard, toe water depth), impulsiveness, probability of overtopping waves, and overtopping discharge on Weibull b parameter were examined, and then compared with the well-established empirical formulae. For the conditions covered within this study, it was found that the probability distribution of wave-by-wave overtopping volumes follow a 2-parameter Weibull distribution. No apparent differences in Weibull b values were reported with the variation of incident wave steepness and impulsiveness parameter. Results of this study revealed that Weibull b values at vertical walls, subjected to non-impulsive wave conditions, can be predicted reasonably well using relative freeboard and relative overtopping rates. A new unified formula is proposed for the estimation of Weibull b values at vertical walls under impulsive and non-impulsive wave attack.

Hydraulic Stability of BPPT – lock on Breakwater Head

Breakwater is one of the coastal buildings built by humans to protect coastal areas such as ports, settlements, and tourist attractions from wave attacks. This test aims to determine the condition damage of BPPT – lock in one- and two-layers placements in the head of the rubble mound breakwater. The method used to conduct this research was physical model test and carried out at laboratory of Balai Teknologi Infrastruktur Pelabuhan dan Dinamika Pantai (BTIPDP) Yogyakarta – Indonesia. The armour unit model used BPPT–locks were 66.048 grams or equivalent to 2.268 tons in prototype and tested in various wave heights, starting from 7.5 cm, 9.2 cm, and 11.4 cm with period 1.5 S or equal to 4 meters of wave height in the prototype. Based on the laboratory results of testing, installing a double armour layer was recommended because the percentage of damage of the double armour layer was lower, and the coefficient of damage was higher.

Wave overtopping discharges at rubble mound breakwaters including effects of a crest wall and a berm

Physical model tests have been performed to study wave overtopping at rubble mound breakwaters, including breakwaters with a crest wall, breakwaters with a berm, and breakwaters with a crest wall and a berm. For rubble mound structures with a protruding crest wall or with a stable berm, limited information is available in literature even though protruding crest walls and berms clearly affect wave overtopping discharges. Adding a crest wall to an existing structure, increasing the height of a crest wall, adding a berm, or increasing the width or height of a berm, can be effective measures to account for effects of sea level rise if the sea level rise appears to be more severe than the amount of sea level rise for which the structure was designed for. The present wave flume tests were used to develop guidelines for rubble mound breakwaters, including breakwaters with a crest wall or with a berm. The relative height of the protruding part of a crest wall dominates the effect of a crest wall. The berm width, berm level and wave steepness all affect the influence of a berm on the wave overtopping discharge. Moreover, it was confirmed that the wave steepness also affects wave overtopping discharges for rubble mound breakwaters without a berm or without a crest wall. The developed set of expressions for rubble mound structures has also been validated based on existing data for oblique wave attack on rubble mound breakwaters with a crest wall. • The reduction in wave overtopping due to a protruding crest wall, a berm, and the combination of both, has been studied. • The wave steepness affects wave overtopping at rubble mound breakwaters. • The width and level of a berm affect the reduction in wave overtopping and their influences increase for a higher steepness. • A method to account for the wave steepness, a protruding crest wall, and a berm on wave overtopping has been proposed. • The new method also accurately describes the influence of oblique wave attack on rubble mound breakwaters with a crest wall.

Hydraulic stability of cube-armored mound breakwaters in depth-limited breaking wave conditions

Armor erosion due to wave attack has been studied intensively since it is considered the main failure mode of mound breakwaters. Cube-armored mound breakwaters in depth-limited breaking wave conditions are common in practice but have received limited attention in the literature. In this study, 2D physical tests were performed on non-overtopped double-layer randomly-placed cube-armored mound breakwater models with armor slope cotα = 1.5 and bottom slope m = 2% in breaking wave conditions. Using the experimental results, a new hydraulic stability formula was derived with a coefficient of determination R2 = 0.85 based on a power relationship between the armor damage and the stability number and the dimensionless water depth. A lower hydraulic stability was found for the front slope of non-overtopped cube-armored structures in breaking wave conditions when compared to formulas given in the literature.

The Unique Ability of Fine Roots to Reduce Vegetated Coastal Dune Erosion During Wave Collision

Vegetated coastal sand dunes can be vital components of flood risk reduction schemes due to their ability to act as an erosive buffer during storm surge and wave attack. However, the effects of plant morphotypes on the wave-induced erosion process are hard to quantify, in part due to the complexity of the coupled hydrodynamic, morphodynamic, and biological processes involved. In this study the effects of four vegetation types on the dune erosion process under wave action was investigated in a wave flume experiment. Sand dune profiles containing real plant arrangements at different growth stages were exposed to irregular waves at water levels producing a collision regime to simulate storm impact. Stepwise multivariate statistical analysis was carried out to determine the relationship of above- and below-ground plant variables to the physical response. Plant variables included, among others, fine root biomass, coarse root biomass, above-ground surface area, stem rotational stiffness, and mycorrhizal colonization. Morphologic variables, among others, included eroded sediment volume, cross-shore area centroid shift, and scarp retreat rate. Results showed that vegetation was able to reduce erosion during a collision regime by up to 37%. Although this reduction was found to be related to both above- and belowground plant structures and their effect on hydrodynamic processes, it was primarily accounted for by the presence of fine root biomass. Fine roots increased the shear strength of the sediment and thus lowered erosional volumes and scarp retreat rates. For each additional 100 mg/L of fine roots (dry) added to the sediment, the erosional volume was reduced by 6.6% and the scarp retreat rate was slowed by 4.6%. Coarse roots and plant-mediated mycorrhizal colonization did not significantly alter these outcomes, nor did the apparent enhancement of wave reflection caused by the fine roots. In summary, fine roots provided a unique ability to bind sediment leading to reduced dune erosion.

Quantitative consideration in selection of breakwater concrete armor unit based on unit’s internal tensile stress response

Concrete armor units are essential for the protection of rubble mound breakwaters, yet their selection is generally not based on structural integrity considerations. In this study, the authors used static finite element simulations, as implemented by Ansys software, to compare the structural integrity of five armor units: Accropode, A-Jack, BPPT-Lock, tetrapod, and dolos. All armor units have a mass of around 11,500 kg and have the same quality of concrete at f’c of 30 MPa. The study involves two different loading cases: Armor units were (1) arranged on a breakwater slope subjected to their own weight and (2) placed on a horizontal ground subjected to idealized wave attacks. In Case #1, the armor units were modelled fixed to the ground and bonded to each other. In Case #2, the wave attack was modelled as a unidirectional and uniform pressure. From the simulation results, the authors compare the highest tensile stresses which could be found on the corner regions of the armor units—their most vulnerable region. In both cases, armor units with stocky shapes experience lower tensile stresses compared to those with slender shapes. These results confirm that Accropode, BPPT-Lock, and tetrapod are structurally safer than dolos and A-Jack.

Research on hydrodynamics of foundation structure of offshore wind turbine under typhoon-wave-current coupling

Offshore wind turbine is facing with extremely complicated climatic environment. The accurate prediction of wave movement caused by strong typhoons and its action on foundation of wind turbine are crucial. To disclose hydrodynamic characteristics of foundation structure of wind turbine under typhoon-wave-current coupling effect on the sea, a 10 MW super-large offshore wind turbine in Wailuo Wind Farm, Guangdong was chosen as a research object and a real-time meso-scale WRF-SWAN-FVCOM (W-S-F) coupling simulation platform was constructed by using Model Coupling Toolkit The spatial-temporal evolution of typhoon-wave-current in the offshore wind farm was simulated when a super typhoon “Rammasun” passed through. Next, the hydrodynamic load distribution characteristics of single pile foundation of wind turbine were analyzed by combining the meso-micro scale nested method. Extreme load model of foundation piles under different wave phases was proposed. Results demonstrated that the constructed W-S-F platform increased the simulation precision of typhoon path by 42.51% than single WRF model. The horizontal wave force of the foundation pile reached the negative and positive peaks at phases T0 and T4 under typhoon-wave-current coupling, and it presented symmetric distribution circumferentially around the 180° angle of wave attack. The phase T4 was the most adverse phase for the strength design of single pile foundation of offshore wind turbine. At the bottom of foundation, the maximum shear reached the 7.68 × 106 magnitude and the maximum bending moment reached the 5.2 × 108 magnitude.

Experimental study of wave force on breakwater head under oblique waves

The head of a breakwater warrants special consideration to achieve the necessary stability at vulnerable part of its structure. To widen the entrance to a harbour, a caisson is used for the breakwater head. Therefore, the wave force on the caisson head under oblique waves was analysed in this study. Physical model tests were performed in a wave tank, where wave loads on two weathering sections (S1 and S2) of the caisson head were measured under oblique-regular and irregular wave attacks. The results have shown that the improved Goda’s method can predict the wave forces on the caisson head. The wave forces on the two sections increased with an increase in the period under different incident angles. The phase lag between the horizontal forces on S1 and S2 was evidently influenced by the incident angle. The relationship between the maximum wave force on one section and its accompanying wave force on another section was described, and the results have demonstrated that under the same incident angle, as the period increased, the maximum wave force of S1/S2 is gradually equal to its accompany wave force of another section.

SSVEP-based brain-computer interfaces are vulnerable to square wave attacks

SSVEP-based brain-computer interfaces are vulnerable to square wave attacks

Antenatal care services utilization during COVID-19 second wave attack in Pasuruan, Indonesia.

Indonesia is currently experiencing the second wave of the COVID-19 pandemic, impacting maternal health services and maternal mortality. This research aims to investigate the use of antenatal care (ANC) during the COVID-19 second wave and the factors that play a role in this situation. A cross-sectional study was conducted during July 2021 on 344 pregnant women in primary, secondary, and tertiary maternal health care facilities in Pasuruan Regency, Indonesia. The data collection technique was simple random sampling, with face-to-face interviews assisted by questionnaires. Logistic regression and adjusted odds ratio with 95% CI and p<0.05 were performed to identify a significant relationship. 136 (39.5%) pregnant women did not use ANC services during the second wave of the COVID-19 outbreak. Husband’s support (AOR=13.814, 95% CI: 8.090–23.588), believing that pregnant women are not afraid of contracting COVID-19 (AOR=6.501, 95% CI: 3.904–10.825), easy access to transportation (AOR=12.145, 95% CI: 6.186–23.846), ease of ANC fees (AOR=4.105, 95% CI: 2.424–6.950), no lockdown policy (AOR=3.130, 95% CI: 1.983–4.940), knowledge regarding COVID-19 (AOR=2.975, 95% CI: 1.793–4.938), COVID-19 information on social media (AOR=3.035, 95% CI: 1.179–7.815), COVID-19 prevention protocols in health facilities (AOR=8.478, 95% CI: 3.611–19.903) were predictors of ANC utilization. This encourages the importance of prioritizing health services for pregnant women during the pandemic, overcoming the fear of contracting COVID-19 through maternal education, husband support, easy access to ANC, and improving the quality of ANC service facilities.