Search Results (409)

Synthesis of published and new data from the Govorov and Kocebu guyots provide geochemical and chronostratigraphic constraints on hydrogenetic cobalt-rich Fe-Mn crusts from the Western Pacific Magellan Seamount Trail (MST). The history of the crusts began about 65–60 Ma, when the relict layer R was deposited in the Campanian—Maastrichtian and Late Paleocene along the shores of guyots. The growth of the old-generation crusts continued in the Late Paleocene—Early Eocene (Layer I-1) and in the Middle—Late Eocene (Layer I-2) in a shallow-water shelf environment. The younger layers formed in the Late Oligocene—Early Miocene (Layer I-2b), Miocene (Layer II), and Pliocene—Pleistocene (Layer III) at depths about the present sea level. The precipitation of Fe and Mn oxyhydroxides from seawater was interrupted by several times, with the longest gap from 38 to 26.5 Ma between the old (R, I-1, and I-2) and young (I-2b, II, and III) layers. Fe and Mn oxyhydroxides in the crusts were affected by two global events of phosphogenesis in the Pacific: Late Eocene—Early Oligocene, from 43 to 39 Ma (Layers R, I-1, I-2) and Late Oligocene—Early Miocene, from 27 to 21 Ma (Layer I-2b). The trace element patterns in different layers of the Co-rich Fe-Mn crusts are grouped using factor analysis of principal components (varimax raw) into four factors: (1) +(all REEs except Ce and La); (2) +(Ce, La, Ba, Mo, Sr, Pb); (3) +(Zr, Hf, Nb, Rb, As)/-Pb; (4) +(U, Th, Co, As, Sb, W)/-Y. The factor score diagrams highlight fields which are especially contrasting for Layers I-1, I-2, and II + III according to factors 2 and 4. Consistent REE and Y variations in Layers I-2b → II → III of the crust from Pallada Guyot correlate with gradual ocean deepening between the Late Oligocene—Early Miocene and Present when the MST guyots were submerging. Large variations in the trace element contents across coeval layers may be due to the hydrodynamics of currents on the guyot surfaces. Furthermore, the geochemistry of the crusts bears effects from repeated episodes of Cenozoic volcanism in the MST region of the Pacific Plate. Higher contents of Nb, Zr, As, Sb, and W in the younger layers II and III may result from large-scale volcanism, including Miocene eruptions of petit-spot volcanoes. Full article

This study investigates the hydrodynamic loads of “Ningde No. 1” offshore aquaculture under current-only conditions using a fluid–structure interaction (FSI) approach with the computational fluid dynamics (CFD) solver OpenFOAM. A porous-media-based model is applied to simulate net-induced drag, while the rigid framework is resolved using a large eddy simulation (LES) turbulence model. A comprehensive set of 350 CFD simulations is performed, with varying flow velocities, flow directions, draft depths, and existence of nets. The results reveal that the load on this fishing facility in the streamwise direction (Fx) increases monotonically with flow velocity, direction, and draft. The lateral (Fy) and vertical (Fz) loads exhibit non-linear trends, peaking at a specific flow direction (approximately 60°) and draft levels (around 11.5 m). The fishing nets substantially increase the streamwise load by up to 80%, while their influence on the lateral forces is dependent on submergence depth. To efficiently predict hydrodynamic loads without performing additional and lengthy CFD simulations, a physics-informed neural network (PINN) is trained using the simulated data. The PINN model is found able to accurately reproduce the hydrodynamic force across a wide range of current conditions, offering a practical and interpretable surrogate approach for structural design optimization and mooring system development in offshore aquaculture industry. Full article

This paper presents a novel submersible seaweed cultivation infrastructure designed to enhance seaweed growth through deep cycling. The system consists of a square grid of ropes for growing seaweed, supported by buoys, mooring lines, and innovative SubTractors—movable buoys that enable controlled submersion. The grid ropes are stabilized by four SubTractors, an array of small buoys, intermediate sinker weights and mooring lines anchored to the seabed. The SubTractors facilitate dynamic positioning, allowing the seaweed rope grid to be submerged below the thermocline—at depths of 100 m or more—where nutrient-rich deep water accelerates seaweed growth in offshore sites with low surface nutrient levels. Small buoys attached to the grid provide buoyancy, keeping the seaweed rope grid planar and near the surface to optimize photosynthesis when not submerged. This paper first describes the seaweed cultivation infrastructure, then develops a hydroelastic model of the proposed cultivation system, followed by a hydroelastic analysis under varying wave and current conditions. The results provide insights into the system’s dynamic behaviour, informing engineering design and structural optimization. Full article

As the environmental regulations of the International Maritime Organization (IMO) become more stringent, the accurate prediction of ship propulsion performance has become essential. Under ballast conditions where the draft is shallow, the propeller approaches the free surface, causing complex phenomena such as ventilation and surface piercing, which reduce propulsion efficiency. The conventional virtual disk (VD) method cannot adequately capture these free-surface effects, leading to deviations from model propeller results. To resolve this, a correction formula that accounts for the advance ratio (J) and submergence ratio ($h/D$) has been proposed in previous studies. In this study, the correction formula was simplified and implemented in a CFD environment using a field function, enabling dynamic adjustment of body force based on time-varying submergence depth. A comparative analysis was conducted between the conventional VD, modified VD, and model propeller using POW and self-propulsion simulations for an MR tanker and SP598M propeller. The improved method was validated in calm and regular wave conditions. The results showed that the modified VD method closely matched the performance trends of the model propeller, especially in free surface-interference conditions (e.g., $h/D$ < 0.5). Furthermore, additional validations in wave-induced self-propulsion confirmed that the modified VD method accurately reproduced the reductions in wake fraction and thrust deduction coefficient, unlike the overestimations observed with the conventional VD. These results demonstrate that the modified VD method can reliably predict propulsion performance under real sea states and serve as a practical tool in the early design stage. Full article

Ground-penetrating radar surveys on structures have a wide range of applications, and they are very useful in solving engineering problems: from detecting reinforcement, studying concrete characteristics, unfilled joints, analyzing brick elements, detecting water content in building bodies, and evaluating structural deformation. They generally pursued small investigation areas with measurements made in direct contact with target structures and for small depths. Detecting deep piles presents specific challenges, and surveys conducted from the ground level may be unsuccessful. To reach great depths, medium-low frequencies must be used, but this choice results in lower resolution. Furthermore, the pile signals may be masked when they are located beneath massive reinforced foundations, which act as an electromagnetic shield. Finally, GPR equipment looks for differences in the dielectric of the material, and the signals recorded by the GPR will be very weak when the differences in the physical properties of the investigated media are modest. From these weak signals, it is difficult to identify information on the differences in the subsurface media. In this paper, we are illustrating an exploration on plinth foundations, supported by drilled piles, submerged in soil, extensive, deep and uninformed. Pulse GPR prospecting was performed in common-offset and single-fold, bistatic configuration, exploiting the exposed faces of an excavation around the foundation. In addition, three velocity tests were conducted, including two in common mid-point and one in zero-offset transillumination, in order to explore the range of variation in relative dielectric permittivity in the investigated media. Thanks to the innovative survey on the excavation faces, it is possible to perform profiles perpendicular to the strike direction of the interface. The electromagnetic backscattering analysis approach allowed us to extract the weighted average frequency attribute section. In it, anomalies emerge in the presence of drilled piles with four piles with an estimated diameter of 80 cm. Full article

Carbon Fiber Reinforced Composite (CFRP) is widely used in deep-sea pressure-resistant structures. With the increase in submergence depth demand leading to the increase in the thickness of the CFRP shell plate, there is a significant thickness effect on its compression performance. In order to study the mechanism of the decrease in compression performance of the laminate, uniaxial compression tests, interlaminar shear tests, out-of-plane tensile tests, damage characterization, and FEM analysis were carried out on three thicknesses of laminates. The results showed that the compressive strength, interlaminar shear strength, out-of-plane tensile strength of laminates and FEM compression model decreased by 10.3%, 12.7%, 23.6%, and 13.6% when the thickness of the laminate was increased from 2 mm to 12 mm. Concurrently, the compression failure mechanism is transformed from the overall strength failure to the instability–crush failure mode caused by the initial delamination. The effects of out-of-plane tensile strength and interlaminar shear strength on compressive properties were also considered. It provides support for the regulation of compression performance of large-thickness laminates and the safety of deep-sea pressure-resistant structures in service. Full article

Submerged vanes offer a promising solution for reducing scour depth around hydraulic structures such as bridge piers by modifying near-bed flow patterns. However, temporal changes in bed profiles around a cylindrical pier remain insufficiently quantified. This study employs three machine learning models (MLMs), gene expression programming (GEP), support vector regression (SVR), and an artificial neural network (ANN), to simulate the temporal evolution of the bed profile around a cylindrical pier under constant subcritical flow. We use a published laboratory flume dataset (106 observations) obtained for a pier of diameter $D=6\mathrm{cm}$ and uniform sediment with median size $D_{50}=0.43\mathrm{mm}$. Geometric/layout parameters of the submerged vanes (number n, transverse offset z, longitudinal spacing e, and distance from the pier base a) were fixed at their reported optima, and subsequent tests varied installation angles $\alpha$ to minimize scour. Models were trained on $70\%$ of the data and tested on $30\%$ using dimensionless inputs $(t/t_e,{\alpha }_1,{\alpha }_2,{\alpha }_3)$ with t the elapsed time from the start of the run and $t_e$ the equilibrium time at which scour growth becomes negligible and response $s/D$ with s the instantaneous scour depth at time t. The GEP model with a three-gene structure achieved the best accuracy. During training and testing, GEP attained $(\mathrm{RMSE}, \mathrm{MAE}, R^2, {(D_s/D)}_{\mathrm{DDR}\left(\max \right)})=(0.0864,0.0681,0.9237,4.25)$ and $(0.0729,0.0641,0.9143,4.94)$, respectively, where $D_s$ denotes scour depth at equilibrium state, D is the pier diameter, and $\mathrm{DDR}\left(\max \right)\equiv max(D_s/D)$ is the maximum dimensionless depth ratio observed/predicted. Full article

Flow past bluff bodies (e.g., circular cylinders) forms a canonical context for teaching external flow separation, vortex shedding, and the coupling between surface pressure and hydrodynamic forces in offshore engineering. Conventional laboratory implementations, however, often fragment local and global measurements, delay data feedback, and omit intelligent modeling components, thereby limiting the development of higher-order cognitive skills and data literacy. We present a low-cost, modular, data-enabled instructional hydrodynamics platform that integrates a transparent recirculating water channel, multi-point synchronous circumferential pressure measurements, global force acquisition, and an artificial neural network (ANN) surrogate. Using feature vectors composed of Reynolds number, angle of attack, and submergence depth, we train a lightweight AI model for rapid prediction of drag and lift coefficients, closing a loop of measurement, prediction, deviation diagnosis, and feature refinement. In the subcritical Reynolds regime, the measured circumferential pressure distribution for a circular cylinder and the drag and lift coefficients for a rectangular cylinder agree with empirical correlations and published benchmarks. The ANN surrogate attains a mean absolute percentage error of approximately 4% for both drag and lift coefficients, indicating stable, physically interpretable performance under limited feature inputs. This platform will facilitate students’ cross-domain transfer spanning flow physics mechanisms, signal processing, feature engineering, and model evaluation, thereby enhancing inquiry-driven and critical analytical competencies. Key contributions include the following: (i) a synchronized local pressure and global force dataset architecture; (ii) embedding a physics-interpretable lightweight ANN surrogate in a foundational hydrodynamics experiment; and (iii) an error-tracking, iteration-oriented instructional workflow. The platform provides a replicable pathway for transitioning offshore hydrodynamics laboratories toward an integrated intelligence-plus-data literacy paradigm and establishes a foundation for future extensions to higher Reynolds numbers, multiple body geometries, and physics-constrained neural networks. Full article

This study examines the impact of recent climatic trends on the preservation of submerged wooden structures at the Gran Carro archaeological site in Lake Bolsena, Italy. Climatic data from the Bolsena Meteorological Station were analysed alongside in situ water quality measurements collected near the archaeological remains at a depth of 4 m. The key parameters included water temperature (Tw), redox potential (Eh), dissolved oxygen (DO), and total dissolved solids (TDS). Trend analyses using the Mann–Kendall test and Sen’s slope revealed significant increases in air and water temperatures, which were strongly correlated. Although precipitation exhibited an upward trend, its negative correlation with temperature suggests greater variability rather than a stable water supply. Despite increased rainfall, lake levels showed a significant decline, likely due to intensified evaporation and water extraction for irrigation. UAV surveys confirmed recent lowering of the lake’s water surface during drought periods. Among the limnological parameters, dissolved oxygen saturation declined significantly, while redox potential increased, indicating shifts toward more anaerobic conditions. These environmental changes could promote the activity of erosive bacteria that degrade submerged wood. Conversely, increased evaporation might also enhance oxygen penetration at depth, potentially activating decay agents such as soft rot fungi and wood-boring bacteria. Overall, the findings suggest that ongoing climatic changes are adversely affecting the preservation of submerged wooden structures, highlighting the need for adaptive management strategies to protect both the lake ecosystem and its archaeological heritage. Full article

Despite being low-resource environments, sandy beaches can contain diverse bacterial assemblages. In this study we examined the spatial heterogeneity of bacterial communities in sand on a beach on the Mississippi Gulf Coast, USA. 16S ribosomal RNA gene sequencing was used to characterize bacterial communities in surface sand along 10 m transects from dry sand towards the upper beach to fully submerged sand, as well as up to 0.4 m deep into the sand. There were clear gradients in bacterial community structure based on position on the beach and depth, and community richness and diversity was greater in moist sand subject to tidal influence than drier sand. Bacterial communities in sand higher up the beach were characterized by members of the phyla Bacillota and Actinomycetota, whereas there was an increased presence of picocyanobacteria (phylum Cyanobacteriota) in sand closer to the water and greater diversity overall. Along with gradients in community structure, microbial activity also showed spatial patterns, with microbial extracellular enzyme activity being greatest in surface sand at intermediate positions along the beach transects that were subject to tidal influences but not fully submerged. This research supports the idea of beaches containing diverse bacterial communities and demonstrates that the existence of gradients in beach environments means that these communities show clear patterns in their spatial distribution. Full article

Understanding the interaction between submerged water jets and cohesive deep-sea sediment is critical for optimizing deep-sea polymetallic nodule hydraulic mining techniques. This research investigated the distinct erosion behavior of cohesive sediments through laboratory experiments and numerical simulations. Cohesive deep-sea sediments were simulated using bentonite–kaolinite mixtures. A series of laboratory experiments, including vane shear tests and viscosity tests under varying moisture content, were conducted to assess the sediments’ mechanical properties. Experimental submerged water jet erosion tests provided basic data for validating the numerical simulations. A Eulerian multi-fluid (EMF) model was implemented to capture sediment–water jet interactions under varying operational parameters, including jet velocities and nozzle heights. The erosion process was found to comprise three distinct stages, including rapid erosion, steady erosion, and stabilization. Two distinct erosion mechanisms were identified, depending on the jet intensity, which affected the depth and shape of the erosion pits. Quantitative analysis revealed that erosion depth exhibits an approximately linear relationship with jet velocity and nozzle height, whereas the erosion diameter shows nonlinear characteristics. These findings enhance the fundamental understanding of cohesive sediment responses under hydraulic disturbances, providing crucial insights for the design and optimization of efficient deep-sea mining systems. Full article

Volcano-tectonic seismic events (VT) are quite rare at Stromboli, numbering about ten events per year and generally with low magnitude. Using a dataset of 98 events from the 2005–2024 period, we report an improved relocation of VT events here. Relocated earthquakes are mainly distributed on the island and in an area located SSW of Stromboli. These VT events are related to the activation of seismogenic structures by a stress increase related to magma ascent. The shallowest seismicity (4–5 km) is positioned under the Stromboli summit, with a high occurrence in 2006–2007 and in 2019–2024, suggesting a major recharge of the HP magma reservoir. The deepest VT seismicity affects a depth of 7–12 km located in the submerged edifice SSW of the summit and is attributable to the dynamics of the LP magma reservoir, which was more active in 2006–2014 and much less so in the successive years. The increase in the occurrence rate of VT shallow seismicity seems to precede the most significant Stromboli activities, such as the 2007 and 2024 lava effusions followed by paroxysms. For these episodes, VT seismicity would appear to indicate a recharging in the first 4–5 km during the months preceding them, thereby representing a medium–short-term warning signal. Full article

Coastal wetlands in the Laurentian Great Lakes of North America are under increasing stress due to numerous threats. Restoration and management of the remaining wetlands are necessary to ensure that ecosystem functions, critical for fisheries, persist. This study used long-term monitoring datasets for one of the Laurentian Great Lakes, Lake Ontario, including 138 sampling events from 31 different wetlands, to examine the relationship between fish community health and select abiotic and vegetation habitat variables. Eight of 13 habitat variables were found to have significant relationships with fish community health, including total, submerged, and emergent vegetation; submerged aquatic vegetation IBI; water depth; turbidity; conductivity; and water-quality index. Ranges for each significant variable were summarized for each fish community health group to provide guidance when diagnosing impairment or setting restoration goals. An ordination of the fish and environmental data revealed high amounts of variation at sites with poor fish community health relative to excellent health, suggesting a multimetric approach provides valuable insight into community variability. The results from this study provide additional information and alternative methods for assessment of current conditions, target setting, and restoration success assessment for coastal wetland managers. Full article

The submerged petrified forest in Sozopol Bay, located along Bulgaria’s southeastern coast in the Black Sea, is an extraordinarily rare natural phenomenon that has remained unexplored in terms of microbial diversity until now. This study focuses on characterizing the microbial communities associated with this unique habitat. Ancient petrified tree remnants located at depths of 18–20 m were sampled in August–September 2024, targeting four tree trunks from different sites within the bay. The quantitative assessment of selected bacterial groups, essential for nutrient cycling, organic matter degradation, and marine ecosystem health, revealed distinct community profiles. 16S rDNA sequencing of cultivated isolates identified a diverse microbial community predominantly composed of γ-Proteobacteria, with key representatives such as Vibrio aestuarianus, Vibrio orientalis, Pseudoalteromonas, and Cobetia sp. The culture-independent approach confirmed the dominance of Proteobacteria, along with other prevalent phyla like Bacteroidetes, Planctomycetes, and Actinobacteria. The most abundant taxa included Woeseia oceani, Ilumatobacter coccineus, Halioglobus maricola, and Vibrio breoganii. Archaea made up about 3% of classified reads. Fungal sequences accounted for less than 2% of the total reads, indicating a low fungal prevalence. These results provide essential baseline data for future monitoring and the conservation of this unique habitat and its diverse microbial communities. Full article

The utilization of ocean wave energy through environmentally sustainable technologies plays a pivotal role in the transition toward renewable energy sources. Among such technologies, the Submerged Horizontal Plate (SHP) stands out as a viable option for clean power production. This study focuses on the system’s application in a region on the southern coast of Brazil, identified as a potential site for future installation. To investigate this system, a three-dimensional numerical wave tank was developed to simulate wave behavior and hydrodynamic loads using the Navier–Stokes framework in the computational fluid dynamics software ANSYS FLUENT 2022 R2. The volume of fluid approach was adopted to track the free surface. The setup for wave generation in the numerical wave tank was verified against analytical solutions to ensure precision and validated under the SHP’s non-oscillating condition. To represent the oscillating condition, boundary conditions constrained motion along the x- and y-axes, allowing movement exclusively along the z-axis. A parametric analysis of 54 cases, with varying geometric configurations, wave characteristics, and submersion depths, indicated that the oscillating SHP configuration elongated perpendicular to wave propagation, combined with specific wave conditions, achieved a theoretical mean efficiency of 76.61%. Full article