Wave Action Research Articles

Investigation on the Optimization Strategy of DWA Algorithm for Path Planning of the USVs with the Consideration of Environmental Factors

Unmanned surface vessels (USVs) are generally subjected to wind force, wave and undercurrent action. Some unidentified objects such as underwater obstacles and submerged reefs should be monitored and evaded with converged communication, autonomous control and network system so as to achieve autonomous and automatic avoidance of danger and real-time control of flight path. Next, based on performing interference mechanics analysis on the USVs under the disturbance of wind force and wave on water surface, the relationship parameters between the bow angle, the deviation angle, safety evaluation function and the external force were obtained, and the comprehensive information of water surface environment was evaluated in combination with the dynamic window approach (DWA) algorithm. Further, the related model was established for simulation by using the simulation software MATLAB, and both reliability and stability of the modified DWA algorithm were designed and examined. Accordingly, the modified DWA algorithm can enhance the safety of the USVs in autonomous path planning and achieve rapid obstacle avoidance and autonomous path planning of the USVs. Our simulation revealed that the modified DWA algorithm can safely and rapidly correct the bow angle and the deviation angle, optimize the path trajectory and reduce the risk of roll-over of the USVs under sudden external force.

Modelling of KdV-Soliton Through Fractional Action and Emergence of Lump Waves

Modelling of KdV-Soliton Through Fractional Action and Emergence of Lump Waves

Research on comprehensive assessment of coastal erosion intensity based on multi index method

The intensity of coastal erosion is a measure of the strength of erosion processes affecting coastal areas. Traditionally, assessments of coastal erosion intensity have relied on singular indices, such as the rate of shoreline retreat or erosion, often prioritizing higher rates over lower ones. This approach, however, lacks comprehensive consideration and scientific rigor. In this study, we adopt a more holistic approach by examining the Qionghai-Wanning coast on the eastern side of Hainan Island. We selected four indices that reflect local conditions and influence coastal erosion strength: Annual rate of shoreline change (T1), Beach annual down-cutting rate (T2), Beach slope (T3), Average particle size of the beach (T4). These indices were used to comprehensively evaluate the erosion intensity of the Qionghai-Wanning coast. The evaluation results categorized the study area into six grades: serious erosion (3.45%), strong erosion (6.90%), erosion (20.69%), micro erosion (44.38%), stabilization (20.69%), and accretion (3.45%). The findings indicate that, under the broader environmental trends of global warming and rising sea levels, most sandy coasts exhibit micro-erosion intensity. Areas experiencing strong and serious erosion are predominantly influenced by human activities, such as those occurring in promenade bays, artificial islands, and harbors. To further understand the relationship between these factors and erosion intensity, we employed the Spearman correlation coefficient method. The analysis revealed that the T1 and the T2 are the primary factors influencing coastal erosion intensity, with the T4 serving as a secondary factor. These factors collectively impact the force and energy absorption of the coast through wave and tidal actions, ultimately determining the intensity of coastal erosion. The multi-index assessment method for coastal erosion intensity demonstrated an accuracy of 82.75%, providing a scientific basis for the management, protection, and restoration of coastal areas.

Frequency distribution of different joint slopes containing ceramic soil under seismic wave action

The dynamic response characteristics of high and steep slopes under the action of earthquakes and blasting was focused on, especially the frequency distribution and propagation laws, which are crucial for slope stability assessment. Using stress wave theory as the theoretical basis and advanced FLAC3D numerical simulation technology, we systematically analyze the frequency response of slope under different joint conditions under seismic waves. The nonlinear characteristics of reflected P-wave coefficient and the significant sensitivity of joint to incident wave frequency are revealed when the Angle of incident P-wave changes. The results show that with the increase of the incidence Angle of the incident P-wave, the reflection coefficient of the reflected P-wave decreases slowly at first and then increases sharply to 1.0. The reflection coefficient of the wave at the joint is more sensitive to the frequency of the incident wave. In a biplanar rock mass, multiple reflections of waves between structural planes produce transmitted waves with different time differences.

Three-dimensional mesoscopic investigation on the dynamic compressive behavior of coral sand concrete with reinforced granite coarse aggregate (GCA)

In the construction of island and reef engineering, coral concrete shows a good application prospect due to its abundant raw materials. However, the porous and fragile mechanical characteristics of coral reefs limit their use as coarse aggregate in the preparation of coral concrete materials. This study utilized hard and dense granite as the coarse aggregate and regarded coral sand concrete as a two-phase composite material consisting of spherical granite coarse aggregate (GCA) and coral mortar. It investigated the enhancement effect of granite on coral concrete from a microscopic perspective. Five 3D mesoscopic models with different GCA contents and randomly distributed aggregates were established to reveal the variation patterns and failure mechanisms of coral sand concrete under impact loading with GCA. The findings demonstrate that the K&C model can effectively simulate the dynamic compression behavior of coral mortar and granite materials. Under the action of a half-sine incident wave, the dynamic compressive strength of the samples increases with the increase in GCA, demonstrating that the addition of GCA can effectively enhance the impact resistance of coral sand concrete. As the content of GCA increases, the sensitivity of the samples to the loading wave amplitude also increases accordingly.

Combined Freak Wave, Wind, and Current Effects on the Dynamic Responses of Offshore Triceratops

Offshore structures are exposed to various environmental loads, including extreme and abnormal waves, over their operational lifespan. The existence of wind and current can exacerbate the dynamic response of these structures, posing threats to safety and integrity. This study focuses on the dynamic responses of offshore triceratops under different environmental conditions characterized by the superimposition of freak waves, uniform wind, and current. The free surface profile of the freak wave was generated using the dual superposition model. The numerical model of the offshore platform designed for ultra-deep-water applications was developed using the ANSYS AQWA 2023 R2 modeler. Numerical investigations, including the free decay tests and time-domain analysis under random sea states, including freak waves, were initially carried out. Then, the combined effects of freak waves, wind, and current were studied in detail under different loading scenarios. The results revealed the increase in structural response under the freak wave action at the focus time. Wind action resulted in a mean shift in responses, while the inclusion of current led to a pronounced increase in the total response of the platform, encompassing deck and buoyant legs, alongside the tether tension variation. Notably, considerable variations in the response were observed after freak wave exposure under the combined influence of wind, freak wave, and current. The results underscore the profound effects induced by wind and current in the presence of freak waves, providing valuable insights for analyzing similar offshore structures under ultimate design conditions.

The wave-current combined effect on the dynamic response of monopile-supported system considering fluid-structure interactions

ABSTRACT The monopile-supported offshore wind turbines (OWTs) are subjected to complex marine environment loads, the dynamic responses of wind turbine structures under wave and current loads are critical for structural safety assessment, which involves the interaction of fluid and structure fields. This study proposed an approach for simulating the two-way (T-W) fluid-structure interaction (FSI), the dynamic responses of the wind turbine support structure under the combined action of wave and current load are investigated. Subsequently, the effect of wave-current interaction, scour depth and flow velocity on the dynamic responses of monopile-supported OWTs are analysed and some useful guidelines are provided. The results indicate that the wave-current interaction can strongly influence the dynamic responses of OWTs, especially for larger scour depth and higher flow velocity. In addition, the displacement amplitude of OWT decreases by 15% under the current load in consideration of the fluid-structure interaction and the bearing performance of the pile improves accordingly.

Predicting rapid adaptation in time from adaptation in space: A 30-year field experiment in marine snails

Predicting the outcomes of adaptation is a major goal of evolutionary biology. When temporal changes in the environment mirror spatial gradients, it opens up the potential for predicting the course of adaptive evolution over time based on patterns of spatial genetic and phenotypic variation. We assessed this approach in a 30-year transplant experiment in the intertidal snail Littorina saxatilis . In 1992, snails were transplanted from a predation-dominated environment to one dominated by wave action. On the basis of spatial patterns, we predicted transitions in shell size and morphology, allele frequencies at positions throughout the genome, and chromosomal rearrangement frequencies. Observed changes closely agreed with predictions and transformation was both dramatic and rapid. Hence, adaptation can be predicted from knowledge of the phenotypic and genetic variation among populations.

The Safety Assessment of Civil Ships against Capsizing Based on the Probability Analysis of Multiple Threshold-crossings of Stochastic Sea Waves

Abstract This paper investigates the impact of threshold-crossing events on ship capsizing through a probabilistic model that predicts random wave heights. Utilizing statistical data from wave height observations, this paper proposes that random waves can be approximated and modeled using the Wiener process, employing autocorrelation function identification and probabilistic statistical verification methods. The threshold-crossing duration of a random wave is just the period of the wave exceeds a given threshold, which can reflect the frequency property of the stochastic sea waves. And the probability distribution of the period can theoretically be determined using the derived probability density function for the time interval between any two adjacent crossings of the Wiener process and a threshold. Based on the above theories, the capsizing probabilities of a civil ship sailing in different wave areas are analyzed under different safety thresholds considering certain ratios of the ship's intrinsic period and wave period. The research results can provide a reference for the anti-overturning design of the ships under the action of random waves.

Study on seismic response characteristics of living stumps slope based on large-scale shaking table test

A large-scale shaking table test of a living stump slope with a geometric similarity ratio of 1:7 was designed and completed. The peak acceleration, acceleration amplification factor, and displacement response patterns of living stumps slopes under different types of seismic waves and excitation intensities were obtained. The time-frequency and energy variation characteristics were analyzed using the Hilbert-Huang Transform (HHT). The results showed that: (1) Regardless of the type of seismic wave, the peak acceleration and acceleration amplification factor of the living stumps slope surface are positively correlated with relative height and seismic excitation intensity. When the excitation intensity is ≤ 0.4 g, the acceleration amplification effect is more pronounced; when the excitation intensity is > 0.4 g, the acceleration amplification effect weakens. (2) Under the action of different seismic waves, the peak displacement of slope surface shows amplification effect along the elevation, and increases with the increase of excitation intensity. In addition, the incremental displacement gradually decreases from the toe to the top of the slope, which is expressed as D2 > D3 > D1 > D4 > D5. The peak displacement at the top of the slope is the greatest, but the incremental displacement is the smallest; the peak displacement at the toe of the slope is the smallest, but the incremental displacement is relatively large. (3) Regardless of the type of seismic wave, living stumps slope shows the characteristics of filtering the low-frequency components of the seismic waves and amplifying their high-frequency components. At the same time, the seismic Hilbert energy gradually accumulates along the elevation. PSHEA and PMSA significantly increase with elevation and excitation intensity, and they reach the maximum at the top of the slope. (4) The seismic Hilbert energy is positively correlated with the relative height and excitation intensity, and reaches the maximum at the top of the slope. With the accumulation of seismic Hilbert energy increases, the dynamic response parameters such as peak acceleration, acceleration amplification coefficient and displacement also increase synchronously, reaching the maximum at the top of the slope. The research conclusions can provide an experimental basis for the seismic design of living stumps slopes.

Experimental Study on the Vibration Characteristics of a Wave-Induced Oscillation Heaving Plate Energy Capture Device

In order to develop green energy, reduce carbon emissions, and alleviate global warming and the green energy crisis, many researchers focus on wave energy, using a device to convert wave energy into electricity. The three main types of wave energy converters are the overtopping type, the oscillating water column type, and the oscillating body type, and for most of them, the power generation efficiency is low. The research team in this paper proposed a wave energy converter for a wave-induced oscillation heave plate. The plate vibrates up and down under the action of waves, and the captured energy of the vibrating plate transfers the energy to the generator, so as to generate electricity. There is electricity only when there is vibration; therefore, the vibration characteristic of the converter is crucial to power generation. So, the vibration characteristics of the energy capture structure of the converter were studied experimentally. The test results show that the energy harvesting device can vibrate, and the vibration effect is good, which further indicates that the device can generate electricity. The effects of different wave conditions and system stiffnesses on amplitude and corresponding amplitude were studied, and the amplitude increases with the increase in wave height and period and decreases with the increase in system stiffness. The amplitude response decreases with the increase in wave height and system stiffness. Under the test conditions, the maximum amplitude of the system is 6.23 cm (when the wave period is 1.40 s, the wave height is 0.25 m, and the system stiffness is 1735.62 N/m), and the maximum amplitude ratio is 0.34 (when the wave period is 1.1 s, the wave height is 0.10 m, and the system stiffness is 1735.62 N/m).

Damage mechanism of model arch dam subjected to far-field underwater explosion

The dynamic response and damage modes of arch dams subjected to explosions are key topics having been extensively researched in recent years. However, the majority of research employs numerical simulation, and there is a lack of experimental investigations to further support those numerical simulation results. Given this, small-scale model experiments were conducted on the arch dam to investigate its dynamic response to underwater explosions. The findings of these experiments indicated a potential overall damage mode along the crown cantilever profile. A numerical investigation of the experimental arch dam was executed employing the CEL method in combination with the Concrete Damage Plasticity model. The damage development process and cracking mechanism of the arch dam under a far-field underwater explosion were examined. According to the numerical findings, the damage process to the arch dam resulting from a far-field underwater explosion might be divided into two phases: the shock wave action phase and the overall response phase. During the shock wave action phase, slight damage first appeared on the downstream dam face. Later, during the overall response phase, a crack spread from the dam base to dam crest and from the downstream side to the upstream side, eventually penetrating through the crown cantilever profile. The damage mechanism in the shock wave action phase is the reflected rarefaction wave off the downstream dam face causing localized tensile damage to surrounding concrete. While the cracking mechanism in the overall response phase is structural bending-induced tensile damage driven by the overall response.

Hydrodynamic response characteristics of curved shape trash intercepting net under wave–current combined conditions

Under the influence of waves and ocean currents, the mesh panels of trash nets at nuclear power plants exhibit a curved shape. The combined action of waves and currents creates a Doppler effect that significantly influences the hydrodynamic response of these nets. This paper used OpenFOAM to establish a porous media macroscopic computational fluid dynamics model for analyzing the forces on curved trash nets. Wave–current combined conditions were simulated by introducing a uniform current in the direction of wave propagation. Forces on the nets under wave–current combined conditions were analyzed and compared with forces under separate uniform current and wave conditions. The results indicate that wave run-up on the nets is more significant under wave–current combined conditions than under wave action alone. The dimensionless horizontal force decreases more rapidly with increasing wave steepness (kA) and wave number (kd) under combined conditions than with linear superposition. Specifically, the rate of increase in dimensionless horizontal force with current speed, at the same blockage ratio, is about twice that of linear superposition. Additionally, the tension in the main cable of the nets is 17% higher under combined conditions than with linear superposition.

Numerical study of vehicle motion during water exit under combined lifting force and wave action

During the retrieval process of the deep-sea mining vehicle (DSMV), the stability of the retrieval system is strongly influenced by the interaction between the vehicle body and the surrounding seawater due to the vehicle's complex shape and wave motion. Naturally, the negative side effects of significant changes in the vehicle's attitude and the water exit position can only increase retrieval's challenge. To investigate the characteristic of the flow field of the DSMV, this study employs the computational fluid dynamics method based on the Reynolds-averaged Navier–Stokes equations integrating the volume-of-fluid multiphase flow model with a fifth-order Stokes-wave model to explore the attitude and displacement changes of the vehicle during the water exit process in the ocean wave environment. The results indicate that the wave phase and lifting force are the major effect factors in the DSMV's water exit process. An appropriate lifting force under a specific wave phase can effectively reduce attitude changes and positional drift of the DSMV during water exit, thereby enhancing recovery efficiency and stability.

Performance of an oscillating water column wave energy converter device under random ocean waves and ocean currents

The present study investigates the hydrodynamic performance of an onshore oscillating water column (OWC) device placed over an undulated bottom topography by analyzing its hydrodynamic efficiency under the action of combined wave–current interaction. The classical small-amplitude water wave theory is used to model the physical problem. The constant boundary element method is employed to solve the boundary value problem. Significant attention is devoted to describing the hydrodynamic parameters associated with the OWC device by considering the mutual combination of the random waves and ocean currents in the wave propagation phenomena. To examine the complex dynamics of the combined irregular wave current phenomena, the Det Norske Veritas spectrum accompanied by a suitable sea state has been considered for the present study. Considering the existence of opposing and following currents in wave propagation, a comprehensive analysis is conducted on the interactions of regular and irregular water waves with the OWC device. The simulated results demonstrate that the presence of ocean currents in the wave propagation phenomenon strongly influences the resonating patterns of the efficiency and force curves. Additionally, the Doppler shift in the apparent frequency caused by the following currents in the random wave–current interaction significantly improves the device's efficiency for an appropriate structural design.

Numerical simulation of complex slope dike overtopping wave flow under isolated wave action based on OpenFOAM

Abstract In recent years, a significant number of compound slope dikes have been developed, but research on the over-wave flow of their viewing platforms remains relatively sparse. In this paper, isolated waves are selected to simulate storm surges. Numerical flumes are constructed based on OpenFOAM to explore the thickness and flow velocity of overtopping wave flow impacts and the thickness and flow velocity of backwash flow on viewing platforms on a compound slope dike with three different foreslope gradients. The study finds that both the impact thickness and return thickness of the cross-wave flow show a tendency to decay along the course, and the smaller the relative wave height is, the slower the impact thickness decays along the course, and the faster the return thickness decays along the course.

Wave Resonance in the Narrow Gap between Two Boxes under Irregular Wave Actions

Wave Resonance in the Narrow Gap between Two Boxes under Irregular Wave Actions

LOADS ON SUBMERGED WALLS OF PROTECTIVE STRUCTURES

The intensification of military operations on the territory of Ukraine, which are accompanied by missile attacks and bombing of territories, requires the use of reliable protective structures. Modern codes require the provision of each new building with storage facilities that guarantee the safety of life and health of citizens, so the correct determination of all loads on the structural elements of protective structures is an urgent issue. Taking into acoount the fact that the previous codes were somewhat outdated and had limited access for a long time, a significant event was the adoption in 2023 of new codes for the design of protective structures of civil defence. The main requirements and recommendations of SBC B.2.2-5:20023 were taken into account when conducting research on determining the loads on buried walls of bomb shelters. Such structures, as we know, perceive a constant load from the lateral pressure of the soil, which during an explosion is supplemented by an episodic load from the action of an air wave. Modern specialized literature contains rather limited information on scientific research and development in the field of design of protective structures. An actual issue is also the study of the influence of determining factors on the intensity of the load on the walls of buried protective structures and the possibility of its adjustment in order to reduce it. Taking into account the nature of the distribution of loads on the underground walls of bomb shelters, a dependence was obtained to determine the resulting active pressure and quasi-static load caused by the action of an air wave. The pressures from the soil and the blast wave at different orientations of the contact wall and for different types of soil environment were studied. The loads in contact of a smooth and rough wall with sandy, sandy and loamy soils with different indicators of physical and mechanical characteristics were considered. The obtained results indicate a significant influence of the geometric parameters of the wall and the features of the contact soil on the resulting pressure, which can vary depending on the studied factors by 10-20%, which indicates the possibility of reducing the load on protective structures, operating with the considered indicators.

Characterization of Seismic Signal Patterns and Dynamic Pore Pressure Fluctuations Due to Wave-Induced Erosion on Non-Cohesive Slopes

Wave erosion of slopes can easily trigger landslides into marine environments and pose severe threats to both the ecological environment and human activities. Therefore, near-shore slope monitoring becomes crucial for preventing and alerting people to these potential disasters. To achieve a comprehensive understanding, it is imperative to conduct a detailed investigation into the dynamics of wave erosion processes acting on slopes. This research is conducted through flume tests, using a wave maker to create waves of various heights and frequencies to erode the slope models. During the tests, seismic signals, acoustic signals, and pore pressure generated by wave erosion and slope failure are recorded. Seismic and acoustic signals are analyzed, and time-frequency spectra are calculated using the Hilbert–Huang Transform to identify the erosion events and signal frequency ranges. Arias Intensity is used to assess seismic energy and explore the relationship between the amount of erosion and energy. The results show that wave height has a more decisive influence on erosion behavior and retreat than wave frequency. Rapid drawdown may potentially cause the slope to slide during cyclic swash and backwash wave action. As wave erosion changes from swash to impact, there is a significant increase in the spectral magnitude and Power Spectral Density (PSD) of both seismic and acoustic signals. An increase in pore pressure is observed due to the rise in the run-up height of waves. The amplitude of pore pressure will increase as the slope undergoes further erosion. Understanding the results of this study can aid in predicting erosion and in planning effective management strategies for slopes subject to wave action.

A frequency domain analysis method for the dynamic response of a submerged floating tunnel under wave action

To investigate the dynamic response of a submerged floating tunnel (SFT) under the action of waves, a modal superposition method in the frequency domain was established, and the amplitudes of the modals were determined using the generalized wave loads and hydrodynamic coefficients of the structural modals. In this model, the SFT was simplified as a constant-cross-section Euler–Bernoulli beam with multiple anchor cables, and its structural modals were resolved using the finite element method (FEM). The generalized wave loads and generalized hydrodynamic coefficients were obtained using the Fourier expansion strategy of the modal function, by which the hydrodynamic problem can be converted into 2D problems with the modified Helmholtz controlling equation and solved using the matched higher-order boundary element method (HOBEM) and eigenfunction expansion. The effects of the diameter of the anchor cables and length of the SFT on the stiffness of the structure and the dynamic response of an SFT with anchor cables under wave action were investigated. Furthermore, the effects of different added mass calculation methods on the structural response were studied. In addition, the wave exciting forces were calculated using potential flow theory or linearized Morison equations according to the wave scale. Finally, the effects of the incident wave frequencies and incident angles were investigated in detail to reveal the combined resonance mechanism.