Floating offshore wind turbines (FOWTs) operate in multi-hazard marine environments, contending with winds, waves, strong currents, and earthquakes, which affect their structural integrity, energy conversion efficiency, and long-term stability. To study the dynamic responses of FOWTs subjected to environmental loads, a finite element model of OC3-Hywind Spar-type floating foundation and NREL 5MW wind turbine is established in this paper. Firstly, the dynamic responses of the FOWT under earthquakes with different incident angles are calculated. Subsequently, the dynamic responses of the FOWT subjected to winds and regular waves are analyzed. Finally, the dynamic responses of the FOWT considering the combination effect of different loads are presented. The results show that the directionality of loads is a non-ignorable variable in the performance assessment of FOWT. For waves and earthquakes, the most critical incident angle of FOWT is 90°. The combined wind, wave, current and earthquake actions should be carefully considered in the design of FOWT. In addition, it is also found the mooring system possesses an “isolating” effect, which could reduce the earthquake energy transferred upward.
This study systematically investigates polycyclic aromatic hydrocarbons (PAHs) in central Beibu Gulf surface sediments. Total PAHs ranged from 81.23 to 117.93 ng·g⁻1 (mean 99.32 ng·g⁻1), indicating low-to-moderate pollution. Spatial heterogeneity shows highest concentrations at BZ06 (117.93 ng·g⁻1, influenced by industrial discharges and shipping) and lowest at BZ17 (81.23 ng·g⁻1, diluted by open sea). Three-ring (40.79%) and four-ring (32.89%) compounds dominate, with phenanthrene (7.80 ng·g⁻1) and pyrene (10.04 ng·g⁻1) as major contributors. Source apportionment via diagnostic ratios and PCA (cumulative variance 74.36%) confirms 60% origin from biomass/coal combustion and 40% from petroleum processes. Risk assessments show all concentrations below ERL, mean TEQ of 4.29 ng·g⁻1, and low ecological risk, though pyrene’s RQs approach moderate thresholds. This study provides critical data for marine environmental protection and insights into PAHs pollution in semi-enclosed bays.
Small bedrock islands represent the most prevalent and widely distributed island type, particularly in China, where they serve as a dominant geomorphological feature with fragile ecosystems. To assess their ecological status, this study established a comprehensive assessment framework based on an analysis of the eco-environmental characteristics and key influencing factors of small bedrock islands. Using methodologies such as the AHP and fuzzy mathematics, we conducted an empirical assessment of Yuan Island in Dalian. The results indicated that Yuan Island’s overall eco-environmental quality fell within the “Medium” range. Specifically, the surrounding marine area exhibits favorable conditions, while the island’s ecosystem is subhealthy, highlighting the need for enhanced ecological management measures. The proposed assessment framework and methodology not only objectively reflect the current status and challenges of island eco-environments but also provide a theoretical and technical foundation for the scientifically informed conservation of small bedrock islands.
In order to further explore the ecology, structure and topography of the deep-sea hydrothermal zone, a series of image data obtained by manned submersible for close observation of the hydrothermal zone are of high research value. This paper proposes a method for image stitching of deep-sea hydrothermal vent areas based on observations from manned submersibles. Firstly, it corrects color deviations in deep-sea images using red channel compensation and gray world algorithm. Then, it adjusts the brightness and contrast of the images globally and locally by combining improved gamma correction and the CLAHE algorithm, resulting in enhanced images. An adaptive weighted fusion algorithm is utilized to merge the images. Key frames are extracted from the video based on the structural similarity of inter-frame images, reducing the impact of manual operations such as hovering and varying speeds during the submersible exploration on the stitching quality. The SURF algorithm is employed to extract feature points, and then KD tree algorithm is used for coarse matching and KNN classification algorithm to refine matching points, from which motion vectors are calculated. Transformation matrices are derived from these motion vectors, and images are stitched iteratively to obtain the overall morphology of deep-sea hydrothermal vent areas. The experimental data used in this study were obtained from a certain voyage of the ‘Jiaolong’ manned submersible. Experimental results demonstrate the effectiveness of the proposed method.
Coastal marine areas offer significant potential both for the rapidly growing energy industry and for other public development purposes. As the exploitation of these areas increases significantly, the need for efficient management of infrastructure and environment becomes more important. The work presented in this paper aims to advance proactive solutions for the efficient management of coastal and offshore infrastructure and environment. This is achieved by utilizing the advantages offered by digital technologies. An innovative monitoring system is presented, comprising state-of-the-art sensing equipment installed in two key marine areas of Cyprus, providing real-time monitoring data on structural and environmental parameters. Despite many inherent challenges, the impact of this study is significant in terms of research development, while providing substantial benefits to industry stakeholders. The former is strongly reflected in the advancement of scientific knowledge, and the latter has essential practical importance, highlighting the significance of effective collaboration between the scientific research community and industry. The details of this study along with its impact and prospects are presented and discussed through a series of applications and datasets obtained from the established in-field laboratories.
Suspended sediment concentration (SSC) in marine environments is a key parameter for characterizing sediment dynamic processes, ecological environmental changes, and the evolution of the seabed boundary layer. This paper systematically reviews the research progress in electrical observation techniques for suspended sediment concentration in marine environments. By integrating bibliometric results, it further analyzes the development trends and research hotspots in this field and compares the principles, advantages, limitations, and applicable scenarios of optical, acoustic, laser diffraction, differential pressure, image recognition, and electrical observation methods. Particular emphasis is placed on the application advances of electrical methods, including resistivity, conductivity, capacitance, time-domain reflectometry, self-potential, and oxidation-reduction potential, in suspended sediment concentration monitoring, seabed interface identification, and seabed boundary layer observation. The review indicates that electrical observation techniques offer notable advantages in adaptability to highly turbid environments, anti-fouling capability, potential for online continuous monitoring, and cost control. However, their quantitative inversion remains affected by the coupling of multiple factors, and limitations persist in low-concentration monitoring, long-term stability, and field validation in real marine environments. Future research should focus on the coupling mechanisms of multiple parameters, sensor optimization, and intelligent inversion methods.
Seawater-floater interaction significantly impacts floater dynamic response. Taking the floater segment in a high-density polyethylene (HDPE) double-pontoon nearshore fishing net cage as the research object, a two-way cross-coupling algorithm was employed to simulate the fluid-structure interaction (FSI) effects between seawater and the floater. Considering the double-pontoon structural form of the net cage floater and its mooring system, a three-dimensional refined finite element model of the floater segment was established. Various sea conditions that the net cage might encounter in its operational area were investigated, and a numerical wave tank was designed to simulate the dynamic response of the floater segment in the HDPE double-pontoon nearshore fishing net cage. The numerical simulation results show that under wave-current loading, the floater segment undergoes rigid translation, rotation, and torsional deformation, with the torsional deformation synchronizing with the rotation trend. The intersection between the floater segment and connectors is a weak part in the floater structure design. Compared with calculation results that only consider wave-current effects, the FSI effects between seawater and the floater segment induces high-frequency motion of the floater segment, with significant amplitude and resulting structural internal forces. Floater in inner seas or bays can withstand extreme wave-current actions caused by a once-in-ten-year typhoon.
Understanding the physical properties of the seabed is crucial for effective marine engineering. The free-fall penetrometer, driven by gravity, offers a cost-effective and convenient method for assessing the undrained shear strength of the seabed in situ. However, due to the rapid penetration rate and intense interaction between the penetrometer and seabed, the penetration mechanism becomes complex, leading to varying results with different data interpretation methods. This study consolidates calculation approaches for undrained shear strength using acceleration and dynamic cone penetration resistance data. Through in-situ experiments in the Yellow Sea, a systematic quantitative analysis of penetration behavior was conducted. Comparative analysis of computed undrained shear strengths using acceleration and dynamic cone penetration resistance data reveals the strengths and weaknesses of both methods, prompting refinement. Findings indicate that in soft sediments, dynamic cone resistance increases significantly while acceleration remains relatively constant. Conversely, in consolidated sediments, acceleration sharply increases while dynamic cone resistance rises slowly. Thus, the acceleration-based method is unsuitable for ultra-soft sediments like seabed silt or unconsolidated mud. However, in higher seabed strength conditions, it aligns with dynamic cone resistance results. Acceleration data uniquely aids in identifying seabed layering characteristics, while dynamic cone resistance helps determine mud or silt strength, albeit with less sensitivity to sediment layering characteristics.
Multi-cellular revetment blocks exhibit excellent flow reduction and sediment trapping performance and have been gradually applied in ecological shoreline engineering in recent years. In this study, the flow velocity, turbulent kinetic energy, and sediment erosion changes in a new type of hexagonal multi-cellular block and frame grid fence were analyzed using FLOW-3D numerical simulations. The results showed that compared to traditional frame grid fences, the hexagonal multi-cellular blocks exhibited stronger flow reduction and turbulence suppression effects. In specific locations, the flow velocity and turbulent kinetic energy in the multi-cellular blocks were reduced by 58 and 75%, respectively. The weak flow velocity and low turbulent kinetic energy in the hexagonal multi-cellular blocks greatly reduced sediment scouring, making it more conducive for habitats, organism reproduction, and the construction of coastal ecological environments.
Large-scale marine resource development and utilization projects will disturb sediment, cause sediment resuspension, and furtherly cause the release of heavy metals, threatening the safety of ecosystems and biodiversity. This study described the sources of heavy metals in marine sediment, sorted out the simulation devices of heavy metal release caused by the external disturbance and sediment resuspension, detailed the influencing factors and rules of heavy metal release, summarized the kinetic models of heavy metal release, pointed out the current research progress and problems of heavy metal release from sediment, and put forward suggestions. It is found that the current researches on the release of heavy metals in sediment are limited to indoor simulation, and the simulation disturbance devices cannot accurately judge the quantitative relationship between the simulated disturbance intensity under experimental conditions and the one under natural conditions, such as wind wave and current. Among them, particle entrainment simulator (PES) device, EROMES device and Y-type resuspension device are more suitable for simulating the hydrodynamic sediment resuspension process in shallow water. The annular flume device can better simulate the marine environment. Studies on the factors influencing the release of heavy metals mainly focus on the physical and chemical properties of sediment and overlying water conditions, among which the physical and chemical properties of sediment, dissolved oxygen (DO), redox potential (Eh) and pH of overlying water are the main regulatory factors for the release of heavy metals from sediment resuspension. Elovich model and double constant model have a wide range of application in describing the release kinetics of heavy metals. It is pointed out that in the future, in-situ test experiments combined with indoor physical model tests and numerical simulation can be carried out to build a dynamic model of heavy metal release from sediment that is closer to the natural situation, which can provide references for the study of heavy metal release in marine sediment caused by ocean engineering and the formulation of relevant protection and restoration schemes.
The Gaolan Port National Economic Development Zone, located on the northern flank of Gaolan Island in Zhuhai City, holds substantial economic and strategic importance. Since the initial 1990 Gaolan Island Connection Seawall project, successive large-scale reclamation activities have led to pronounced ground subsidence. To address this, we developed a predictive model for soft soil settlement in reclamation areas by integrating coupling theory for fluid-saturated porous media with the 1D-EVP constitutive model to account for creep consolidation. We derived a finite difference discretization scheme, implemented a numerical code, and conducted rigorous model validation. Utilizing stratigraphic architecture interpreted from borehole, the model was applied to quantitatively predict the ultimate settlement magnitudes and temporal evolution at six sites. The results identify the thickness of the artificial soil layer and the underlying mud layer as the dominant factors controlling final settlement which ranges from 1.09 to 2.77 m. The model projects that settlement rates at all sites decline to between 1.03–2.60 cm/year within 14 years and 0.67–1.70 cm/year within 21 years post-reclamation. These predictions align with current InSAR measurements, which show rates below 3 cm/year. While the projected decrease in settlement rates enhances long-term geotechnical suitability, the spatial variability of strata necessitates ongoing monitoring to mitigate risks from differential settlement. This study provides a critical scientific basis for territorial spatial planning and infrastructure risk management in the area. The validated methodology establishes a transferable theoretical framework for forecasting settlement in coastal reclamation projects worldwide.
The expansion of island infrastructure contributes to an increase in impermeable surfaces, adversely affecting the replenishment of freshwater lenses and thereby posing a threat to the water security of island residents. To counteract this, cut-off walls—a traditional method for preventing seawater intrusion—have proven effective in enhancing the volumes of freshwater aquifers. Employing a site-scale numerical model, this study investigates the influence of impervious surfaces on the morphology and distribution of island freshwater lenses and assesses the effectiveness of cut-off walls in preserving freshwater reserves in such contexts. Findings suggest that an increase in the extent of impermeable surfaces correlates with a decrease in the thickness of freshwater lenses and a displacement of their central point away from the impervious surface. Furthermore, the placement and depth of cut-off walls significantly influence their efficacy in increasing freshwater lens volumes and mitigating the negative impacts of impermeable surfaces on underground freshwater resources. The greatest effectiveness is achieved when these walls are positioned closer to the shoreline and at an optimal depth—identified in this study as 15 m for scenarios with 150 m of impermeable surface length. Beyond this depth, the increase in freshwater volume becomes marginally reduced.
Exploitation of methane gas from hydrate bearing sediments (HBS) can be achieved by altering thermodynamic stability conditions in the hydrate stability zone (HSZ) by resorting to various dissociation techniques. This process, which alters geomechanical properties (viz., shear strength, stiffness, and permeability) of the HBS might also trigger instability of submarine slopes, reservoir subsidence, sand migration, wellbore instability, etc. To alleviate such a situation, replacing CH4 from HBS, by injecting CO2, a process designated as CH4-CO2 replacement, and which is in line with SDGs 7 (Affordable & Clean Energy) & 13 (Climate Action), seems to be a panacea. However, to achieve this, it is imperative to understand the thermodynamic feasibility, pore-scale mechanisms, and variations in geomechanical properties of HBS during and after the replacement. With this in view, data available in the literature that focus on the thermodynamic conditions, pore-scale mechanisms and geomechanical stability of the HBS, were critically synthesized. It has been noticed an insignificant difference in the normalized peak shear strength for CH4 HBS and CO2 HBS with hydrate saturation (SH). Furthermore, the shear strength parameters (viz., cohesion and angle of internal friction) of both CH4 HBS and CO2 HBS, which predominantly influence geomechanical stability of HBS during CH4-CO2 replacement, are directly dependent on SH. In addition to this, the pore-scale mechanisms that would provide an insight into CH4-CO2 replacement have been conceived to demonstrate how replacement facilitates geomechanical stability of HBS. Based on the analysis of the data, empirical relationships between the cohesion and SH for both CH4 HBS and CO2 HBS have also been proposed. It is our hunch that such an exercise would provide a preliminary insight for field scale implementation of CH4-CO2 replacement successfully by maintaining the stability of HBS.
The most direct manifestation of changes in submarine microtopography is the formation and evolution of different types of microtopography, such as the formation and evolution of sand ripples and potholes. However, accurate measurement of microtopographic changes is extremely challenging. In this study, a set of in-situ observation systems for submarine microtopography was established, and in-situ observations were conducted in the Zhoushan Sea area. The study found that under the action of reciprocating currents, the height of the seabed surface undergoes periodic changes, with a maximum height variation of 10.45 cm. However, at the end of the observation period, only 2.6 cm of sediment deposition was measured. In general, the microtopography in the observation area is controlled by tidal currents, and the morphology of sand ripples is determined by the magnitude and direction of the currents. During high-energy events, the microtopography is influenced by the combined effects of waves and tides, increasing the steepness of sand ripple waves and a decrease in asymmetry coefficient.
The advancement of ocean observation technology has confirmed that submarine canyons are important sedimentary sites for microplastics. Turbidity currents serve as a medium for transporting microplastics through submarine canyons to the deep sea. However, the transport and deposition of microplastics in these canyons by turbidity currents remain unclear. This study, through physical model experiments, explores how the initial conditions of turbidity currents affect the distribution of microplastics in a canyon topography. Results reveal that different concentrations of turbidity currents create varying depositional patterns along the middle to the upper reaches of the canyon. At low concentrations, uniformly distributed crescent-shaped structures are formed, whereas at high concentrations, the deposits are irregularly shaped and tend to migrate toward the head of the canyon. Microplastics are predominantly deposited in areas with wavy sedimentary topography, and in situations with low turbidity current concentrations, abundant microplastics are exposed and accumulated. Additionally, the retention rate of microplastics in 6% volume concentration of turbidity currents is considerably higher than that in 1% volume concentration, and high flow rates promote the migration of microplastic enrichment areas along the canyon. The maximum enrichment zones of microplastics are always located in areas with wave-shaped topography where the sediment particles are large, making them the main deposition zones for microplastics. This research provides valuable insights for predicting the accumulation sites of microplastics in submarine canyons and their effects on the ecological environment.
Based on numerical simulations of triaxial tests, this paper investigates the effects of stress histories on the strength and deformation of marine clay from both macro and micro scales. By introducing the Elastic-Plastic Cemented contact model (EPC model) and a servo wall combination method, an extended DEM model is presented in our study. This novel method can effectively investigate the mechanical properties of marine clay. The validation and applicability of this simulation are achieved by comparing the numerical results and experimental data. The results indicate that the servo wall combination method effectively simulates the mechanical behavior and deformation characteristics of the soil in triaxial simulations. The EPC model accurately captures the stress-strain characteristics of soil stress history through plastic deformation. To investigate the influence of stress histories on the mechanical and deformation characteristics of soil, a consolidated drained triaxial DEM simulation of marine clay incorporating various over-consolidation ratios (OCRs) is conducted. It is observed that as the OCR increases, the soil sample experiences shear shrinkage, accompanied by a continuous increase in peak strength and a reduction in maximum volume shrinkage. Additionally, the porosity of the soil sample decreases while the coordination number of particles increases with an increase in OCR. Such macro and micro analyses demonstrate that increasing OCR enhances the total number of particle contacts and promotes the formation of more adhesion forces between particles. Consequently, the density and structural integrity of the soil are improved.
In this paper, the physical mechanism and evaluation methods of the sinking of small heavy objects into a wave-induced liquefied seabed are particularly investigated. First, the sinking patterns and mechanisms of an object under different forms of liquefaction (i.e., residual liquefaction and momentary liquefaction) are analyzed. Then, a viscous approach for estimating the sinking of the object into a wave-induced liquefied seabed is proposed. The framework, the procedures, and the influencing factors of the approach are discussed in detail. Finally, cases are discussed to assess the performances of the models. Results and analysis indicate that the object sinks continuously to the rigid bottom of the residual liquefied seabed at a constant velocity, while the object alternately sinks and stops sinking in a momentarily liquefied seabed because the seabed alternates between liquefied and non-liquefied states during every wave period. The process of objects sinking into a wave-induced liquefied seabed can be well represented by solving the mechanical equilibrium equations for objects sinking in an isotropic dense viscous fluid. For the residual liquefaction case, the final sinking depth of object can be obtained by multiplying the sinking velocity by the liquefaction duration, with its value not exceeding the liquefaction depth. While for wave-induced momentary liquefaction case, the possible sinking depth in a single wave period is calculated by multiplying the sinking velocity by the liquefaction duration, if the initial sinking position is shallower than the maximum liquefaction depth during the wave period, this product is added to the total sinking depth, the final sinking depth is obtained by adding the sinking depths during each wave period together. Two viscosity regions of the liquefied soil are delineated as 1–10 kPa·s and 100–5000 kPa·s based on the comprehensive summary of the experimental data and the case analysis of objects sinking in a wave-induced liquefied seabed. The viscosity can be approximately taken as 10 kPa·s in Region I and 1000 kPa·s in Region II for regular-shaped objects sinking in wave-induced residual and momentarily liquefied seabed, respectively. Equations for a spherical object with an equivalent diameter and a more concentrated viscosity in the vicinity of 10 kPa·s are suggested to enable better evaluation of the sinking of irregularly shaped munitions in a wave-induced momentarily liquefied seabed.
In recent years, the global exploration and development of marine resources have prompted a surge in geotechnical engineering projects and experiments in oceanic settings. This expansion has necessitated enhanced in-situ testing technologies in marine environments. Traditional methods such as the Cone Penetration Test (CPT) and Piezocone Penetration Test (CPTU) often fail to ensure the reliability of data acquired in ultra-soft soil. Consequently, the Full-Flow Penetration Test has gained prominence in marine geotechnical engineering, offering improved data accuracy. This paper synthesizes findings from a wide array of global literature on in-situ testing technology, delineating the evolution of this technology and concentrating on the latest advancements in marine detection equipment. It provides an in-depth theoretical analysis of the probe penetration process and explores the application of in-situ testing technology in various domains, including soil classification, estimation of undrained shear strength, and sensitivity among others. Summary findings indicate that the increasing human engagement with oceanic exploration and utilization necessitates the development of testing equipment adept at navigating the complexities of seabed environments. The Full-Flow Penetration Test offers significant advantages over the Cone Penetration Test (CPT) and Piezocone Penetration Test (CPTU) when assessing soft and ultra-soft soils. It enables the estimation of undrained shear strength through laboratory-based cyclic testing, which facilitates soil remolding and obviates the necessity for in-situ testing to ascertain seabed soil properties. Nonetheless, the research into Full-Flow Penetration Test instruments is nascent, with scant comprehensive analysis on how strain rate and strain softening impact the penetration resistance coefficient. This area necessitates further empirical validation. Given the escalating global focus on marine resources and the imperative for marine surveys in resource exploitation, the Full-Flow Penetration Test methodology promises extensive utility in forthcoming developments.
Plastic pollution can be attributed to the unsustainable use and disposal of plastic products in today’s civilisation and threatens the economy, the environment, and human health. Plastic in the oceans has emerged as a major cause of marine ecosystem pollution in recent years. However, we believe there are more pressing issues, such as climate change and overfishing. As plastic debris accumulates in the oceans at an unprecedented rate, the demand for efficient and long-term remediation strategies becomes more urgent. Current clean-up approaches attempt to mitigate the harmful effects of plastic pollution but must be sufficient to keep up with the everincreasing amounts of plastic entering the marine environment. This article reviews the sources of ocean plastic pollution, classification, and impacts of plastic pollution on the aquatic environment and discusses the Norwegian and South African scenarios of *Corresponding author email: anekwesmarte@gmail.com plastic pollution. The link between climate change and plastic pollution was established, and challenges and initiatives for effectively mitigating ocean plastic pollution were presented. Based on this study, reducing plastic input into the ecosystem must be pursued as part of a global holistic strategy. The results of this study show that appropriate policy frameworks and mechanisms are needed to address plastic pollution in the oceans effectively. Although a regulatory framework already exists, it needs to be regularly reviewed and improved to limit the amount of plastic in our environment. While immediate action should be taken, new scientific research in various fields will help identify the most effective approaches and develop innovative solutions.
