Search Results (254)

Siltation in semi-enclosed basins is commonly ascribed to the combined action of horizontal entrainment, tidal filling/emptying, and density flow, yet the interplay among these processes complicates a mechanistic understanding of siltation in artificially modified macrotidal bays. In this study, Dyer’s decomposition method for suspended sediment flux (SSF) and end-member analysis (EMA) were applied, combined with in situ hydrodynamic, suspended sediment concentration (SSC), and surface sediment grain-size measurements. Using Wuyuan Bay (Xiamen, China) as a case study, we examined its sediment dynamics and siltation patterns from a tidal-cycle perspective. Results show that the contribution of density flow is negligible. A recirculating gyre, formed during flood and suppressed during ebb, creates flood–ebb velocity asymmetry and net landward sediment transport, producing a central siltation body (CSB) that accounts for 45% of the total deposition. Near the entrance, Eulerian residual transport (gyre advection) dominates, with a notable contribution from tidal pumping. Further landward, tidal pumping weakens and gyre-induced Eulerian transport prevails. Grain-size analysis and EMA decomposition reveal uniform sedimentary dynamic conditions in this zone, with flood-phase deposition averaging 83% of the total siltation. Full article

Quartz purity is essential for reliable optically stimulated luminescence (OSL) dating, yet the mineralogical evolution of sediment samples during extraction is rarely documented at each preparation stage. This study uses scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) to characterise two loess samples from the Urluia section, Dobrogea, Romania, across sixteen successive stages of a standard OSL quartz extraction protocol. Four compositional indices—the Quartz Purity Index (QPI), Feldspar Contamination Index (FCI), Heavy Mineral Index (HMI), and Carbonate Index (CI)—are introduced to quantify purification efficiency. Each preparation stage played a different role: HCl treatment primarily removed carbonates, grain-size separation and density fractionation reduced heavy minerals by ~99%, and feldspar removal resulted from the combined effects of density separation and HF etching. Despite identical protocols, two samples collected from stratigraphically adjacent positions showed markedly different HF etching efficiencies, reaching ~94% and ~66% quartz purity, respectively. However, luminescence measurements showed similarly weak feldspar signals in both samples, with intensities substantially lower than the quartz OSL signal. These results demonstrate that purification efficiency cannot be assumed to be uniform across loess samples in Romania and highlight SEM-EDS as a practical quality-control tool for OSL sample preparation. Full article

Ocean current energy is abundant, yet its exploitation is severely constrained by the low-velocity conditions typical of most marine environments, where conventional lift-type turbines exhibit poor self-starting capability and low efficiency. This review provides the first comprehensive synthesis of research on free-stream Archimedes spiral hydrokinetic turbines (ASHTs), a class of drag-dominated rotors developed specifically for low-velocity kinetic energy harvesting. A unified classification is introduced, dividing ASHTs into single-blade long-axis (SL-ASHT) and three-blade short-axis (TS-ASHT) configurations. The energy conversion mechanisms, governed by pressure difference and hydrodynamic force synergy within helical passages, are elucidated, and the influence of critical geometric parameters is assessed. For SL-ASHTs, the analysis highlights exceptional self-starting capability (cut-in velocity: 0.1 m/s), a starting torque coefficient of 0.52, a maximum power coefficient of 0.51, and passive yaw adaptability that limits efficiency variation to below 2% over yaw angles of 0–40°. TS-ASHTs feature a compact architecture and higher rotational speed, facilitating direct generator coupling. With variable blade-angle distributions, thin airfoils, and non-uniform gap ratios, the power coefficient reaches 0.312. Performance-enhancement measures, including multi-parameter optimization, ducts, and winglets, deliver power gains of up to 35%, 122%, and 12%, respectively. This review further identifies critical barriers to engineering deployment: sediment erosion, cyclic fatigue, performance degradation under large yaw angles, and wake interactions. Future priorities include multi-objective optimization, advanced materials and flow control, full-scale sea trials, multiphysics coupling, array layout optimization, and hybrid energy system integration. By establishing a coherent classification and performance-evaluation framework, this work demonstrates that ASHTs offer strong potential as core devices for large-scale utilization of low-velocity ocean current and river hydrokinetic energy. Full article

Marine silt is characterized by a high content of fine particles and low permeability, which often result in uneven urease diffusion, local enrichment, and significant variations in solidification performance during soybean urease-induced calcium carbonate precipitation (SICP) treatment. To address these issues, this study experimentally investigated both the preparation of marine silt mechanical specimens and the injection uniformity of the SICP technique. A cylindrical transparent acrylic mold together with a matching grouting device was developed to enable the observable and standardized preparation of marine silt specimens. On this basis, a series of experiments were conducted, including measurements of urease distribution under single SICP grouting, unconfined compressive strength (UCS) tests of solidified specimens, and quantification of calcium carbonate production. The effects of injection direction, injection volume, and injection rate on solidification uniformity and mechanical strength were systematically examined. The results show that the grouting direction governs the stratification characteristics of urease within the specimens. Increasing the grouting volume significantly enhances the total urease content and improves its distribution uniformity. The UCS of the solidified specimens was found to be closely related to the uniformity of urease distribution. Among the tested methods, the multi-round alternating injection mode from both the top and bottom produced the best overall strength performance. The maximum UCS reached 93.81 kPa at a grouting volume of 150 mL and a grouting rate of 5 mL/min. This study clarifies how injection parameters can be optimized to improve the solidification uniformity of fine-grained marine sediments and provides technical support and parameter references for the standardized preparation of SICP-solidified soil mechanical specimens. Full article

River regulation often leads to uniform conditions within the river channel, alters sediment dynamics, and contributes to the degradation of aquatic habitats. Deflectors are increasingly used as habitat-forming elements in river restoration projects. However, the interaction between hydraulic conditions, sediment inflow, deflector location, and surface roughness and their effects on the spatial extent of sediment removal remain insufficiently studied. Laboratory experiments were conducted in a flow channel using three geometrically identical deflectors arranged according to the configuration observed in the Flinta River in western Poland. The studies were conducted for the following combinations: three discharges (Q = 0.40, 0.64, and 1.70 dm³ s⁻¹), three water depths (h = 0.03, 0.06, and 0.09 m), three cumulative surrogate-sediment masses (R_um = 0.5, 1.0, and 1.5 kg), three dimensionless longitudinal positions (ξ = 0.21, 0.61, and 1.00), and two deflector roughness specifications—smooth or rough. The two-dimensional extent of the sediment-free zone was quantified based on aerial photographs using the normalized surface index A^∗. Dimensionless water depth and dimensionless discharge were the dominant factors χ > Q^∗ > R^∗ ≫ ξ, and their interaction $Q^{\ast }\times \chi$ constituted the strongest two-way effect, whereas sediment mass had a significant but secondary influence. Surface roughness did not independently affect the mean $A^{\ast }$ value but altered the spatial characteristics: longitudinal position was non-significant for smooth deflectors but became significant for rough deflectors, particularly through interactions between depth and location and between depth, location, and surface. These findings indicate that deflector roughness should not be specified as an isolated design parameter but should be selected jointly with the expected flow-depth regime and the longitudinal placement of successive structures. In practical terms, the results can support the preliminary design and positioning of habitat-forming deflectors intended to create or maintain spatially differentiated sediment-cleared zones in regulated channels, thereby contributing to more evidence-based and sustainable river restoration. Full article

Wellbore instability poses a significant challenge to the safe and long-term production of natural gas hydrates (NGHs). Characterizing the geometry of the wellbore-adjacent plastic zone is critical for evaluating geomechanical risks during hydrate exploitation. In this paper, an elastic–plastic analytical model incorporating the Mohr–Coulomb failure criterion is developed to describe the stress distribution around the borehole under non-uniform in situ stress conditions. Particular attention is paid to the role of hydrate saturation, which is integrated into the constitutive framework to reflect the cementation effect of NGH-bearing sediments (GHBS). Analytical solutions for the stress fields in both the elastic and plastic regions are derived, which are accompanied by a computational scheme for determining the plastic zone radius. Using site-specific mechanical parameters from the Shenhu area in the South China Sea, a parametric analysis is conducted to quantify the influences of hydrate saturation, reservoir depressurization, and stress anisotropy on the evolution of the plastic zone shape. The results indicate that elevated hydrate saturation enhances the load-bearing capacity of the formation, whereas depressurization significantly expands the plastic region, leading to severe wellbore instability. These findings provide theoretical insights for optimizing drilling strategies in deep-water hydrate reservoirs. Full article

To address the problems of disordered flow patterns, wall-separated recirculation, and sediment deposition that commonly occur in the forebay of forward-facing pumping stations on sediment-laden rivers, the first-stage Xin Zhuangji Pumping Station in Ningxia was selected as the study case. A three-dimensional numerical simulation was conducted using the Realizable k–ε turbulence model coupled with the Mixture two-phase flow model for water–sediment flow. The regulation effects of splayed guide walls with different guide-wall deflection angles on the velocity distribution, vortex structures, and sediment deposition in the forebay were investigated. The results show that large-scale recirculation zones exist on both sides of the prototype forebay, accompanied by uneven velocity distribution and severe sediment deposition within the recirculation regions. The installation of splayed guide walls can effectively suppress lateral recirculation, expand the mainstream flow region, and reduce the deposition area. However, the regulation effect of the diffusion-type guide wall varied significantly with the guide-wall deflection angle. Since the main objective of this study was to control sediment deposition rather than to maximize a single hydraulic indicator, a multi-criteria screening method oriented toward sediment-reduction control was adopted. Under the (θ = 25°) scheme, the reduction ratio of the overall potential deposition area based on the primary threshold criterion reached the maximum value of 53.67%, the recirculation area on plane Z1 decreased by 23.23%, the global recirculation coefficient increased to 68.69%, and the sediment deposition efficiency decreased to 0.033. The axial velocity uniformities at the suction-pipe sections of pumps B# and C# were 71.23% and 80.61%, respectively. Although the (θ = 30°) scheme produced the highest velocity uniformity for pump B# and showed a slightly better reduction effect on local high-concentration sediment-enrichment regions, the (θ = 25°) scheme exhibited a more balanced improvement in overall sediment-deposition control and flow-pattern regulation. Therefore, under the investigated operating condition, the (θ = 25°) scheme is recommended as the guide-wall deflection angle oriented toward sediment-reduction control. Full article

Semi-arid wetlands are highly sensitive to changes in hydrological regimes, as strong evaporation often exceeds limited natural recharge. Ecological water replenishment is widely used to restore these systems, but schemes designed only to meet water-volume targets may cause excessive hydrodynamic disturbance, promote sediment resuspension, and increase the release of internal pollutants. In this study, we developed an ecological water-replenishment assessment framework for Chahannaoer Wetland that incorporates ecological water-demand thresholds, suspended-solids disturbance, and an AHP–entropy weight–TOPSIS decision model. Using hydrological and meteorological data from 2014 to 2024, six replenishment scenarios were evaluated in terms of water-balance recovery, disturbance control, and habitat suitability. The results show that Chahannaoer Wetland experienced a persistent evaporation-dominated water deficit. The mean annual natural recharge was 0.225 × 10⁸ m³, with a mean annual ecological water shortage of 1.03 × 10⁸ m³ and an evapotranspiration-to-recharge ratio of 3.42–4.56. Based on the previous comprehensive water-quality assessment using DO, COD, NH₃-N, TN, and TP, the minimum water volume required to maintain Class IV water quality was 0.86 × 10⁸ m³, whereas the suitable ecological water demand ranged from 1.27 × 10⁸ to 1.56 × 10⁸ m³. With the total replenishment volume held constant, centralized replenishment met the required water volume but substantially increased near-bed disturbance and sediment resuspension risk. By contrast, decentralized uniform replenishment performed best, with the highest relative closeness coefficient of 0.9105, a disturbance index of approximately 0.32, and water depths maintained within the suitable habitat range of 30–50 cm. These findings suggest that ecological restoration in semi-arid wetlands should move beyond volume-based water supplementation and pay greater attention to the timing, pathway, and hydrodynamic effects of replenishment. The proposed framework provides a quantitative basis for optimizing ecological water replenishment in evaporation-dominated wetlands and other inland lakes in arid and semi-arid regions. Full article

This study evaluates the ecological impacts of seawater desalination discharge on coastal marine ecosystems through a sequential analytical framework linking systematic literature synthesis, field-monitoring evidence, spatial analysis, and predictive ecological modeling. The novelty of the study lies in combining multi-regional evidence from Mediterranean coastal zones, Persian Gulf waters, and Pacific coastal environments with threshold-based ecological risk assessment, thereby linking discharge-related environmental stressors with biological responses and ecosystem-function alterations. The systematic review first retained 750 studies published between 2004 and 2024 for qualitative synthesis. On this basis, 59 high-quality references with sufficient numerical information were selected for the main quantitative meta-analysis, while field-monitoring data were used to support the interpretation of distance-based discharge gradients. Spatial interpolation and hierarchical modeling were then applied to evaluate exposure–response patterns and ecological threshold behavior. The results showed that desalination facilities generated measurable ecological impacts mainly within 50–200 m of discharge points, with a critical transition distance of approximately 127 m where hypersaline conditions, typically 1.5–2.0 times ambient seawater levels, were associated with marked changes in marine community structure. Benthic assemblages showed taxon-specific responses, with mollusks and echinoderms exhibiting greater sensitivity than polychaetes and small crustaceans. Marine vegetation declined strongly under combined salinity, thermal, and chemical stress, while phosphonate-based antiscalants accumulated in filter-feeding organisms and produced bioaccumulation factors up to 42.1 times ambient levels. Ecosystem-function indicators, including microbial community composition and sediment organic matter processing, remained altered up to 300 m from discharge points, indicating that functional impacts may extend beyond the primary hypersaline plume. The predictive modeling framework further demonstrated that ecological risk decreased nonlinearly with distance and varied according to discharge intensity, local hydrodynamics, and biological sensitivity. These findings indicate that conventional uniform buffer-based assessment may underestimate the ecological footprint of desalination discharge. Sustainable desalination management should therefore adopt site-specific monitoring, species-sensitive protection thresholds, improved brine-management technologies, and adaptive mitigation strategies based on real-time environmental feedback. Full article

Flexible capacitive pressure sensors have garnered significant attention in wearable electronics and robotic tactile sensing due to their high flexibility and simple structure. However, non-uniform distribution of conductive fillers in composite dielectric layers often compromises dielectric stability and sensing performance. In this work, a Cu/PDMS composite dielectric layer was fabricated using ultrasonic-assisted homogenization to enhance Cu particle dispersion and suppress sedimentation. A theoretical model and finite element simulations were employed to investigate the effects of particle distribution on permittivity, capacitance, electric field, and current density. The results indicate that uniform Cu dispersion improves dielectric stability and mitigates local electric-field concentration. Compared with conventionally prepared sensors, the ultrasonically treated sensor demonstrated higher sensitivity, enhanced dielectric stability, and a broader working range. Specifically, the sensor achieved a sensitivity of 0.157 kPa⁻¹ within 0–1 kPa and maintained stable performance over 1000 loading cycles. These findings confirm that ultrasonic-assisted homogenization is an effective approach for improving the dielectric and sensing performance of flexible capacitive pressure sensors. Full article

Stream sediment geochemistry is a widely used reconnaissance tool in early-stage mineral exploration, particularly in regions where direct evidence of mineralisation is limited. Because stream sediment anomalies provide indirect geochemical signatures and are typically constrained by limited ground-truth information, labelled datasets are often scarce and spatially biased. This limitation restricts the applicability of supervised learning approaches and highlights the need for robust unsupervised methods. In this study, six unsupervised techniques, Principal Component Analysis (PCA), Non-negative Matrix Factorisation (NMF), Uniform Manifold Approximation and Projection (UMAP), Autoencoder (AE), Deep Embedded Clustering (DEC), and an Averaged Ensemble Index (AVE), were evaluated for integrating multivariate stream sediment geochemical data and delineating gold prospectivity zones. Eight gold-related elements (Au, As, Ag, B, Hg, Mo, Sb, and W) were selected based on regional metallogenic characteristics and previously reported geochemical associations. To facilitate direct comparison, all model outputs were normalised to a fuzzy membership scale ranging from 0 to 1. Model performance was quantitatively assessed using Receiver Operating Characteristic–Area Under the Curve (ROC–AUC) and Matthews Correlation Coefficient (MCC) metrics based on independently verified mineralised and non-mineralised locations. The results indicated that DEC and AE consistently outperformed the other methods investigated, achieving the highest ROC–AUC and MCC values, whereas UMAP exhibited comparatively weaker performance. The findings demonstrated that unsupervised representation learning approaches, particularly DEC and AE, provided a more effective framework for integrating multivariate geochemical data and delineating gold-related anomalies in data-limited exploration environments than conventional dimensionality reduction and heuristic integration methods. Full article

Hydropower is a crucial component of renewable energy, and sediment erosion is a key factor affecting the operation of impulse turbines, with erosion inside the nozzle being particularly prominent and leading to reduced unit efficiency. This paper investigates the distribution patterns of energy dissipation and erosion locations inside the nozzle under varying particle sizes, based on numerical simulation and entropy production theory. The results indicate that small particle sizes (0.02 mm) exhibit good fluidity, uniform flow velocity distribution, and a small high-entropy-production region. As particle size increases (0.1 mm, 0.3 mm), fluidity gradually deteriorates, the flow field becomes more turbulent, and the high-entropy-production region expands. When the turbulent kinetic energy exceeds 10 m²/s², the entropy production rate increases sharply. A significant negative correlation is observed between entropy production rate and erosion rate; smaller particle sizes correspond to more severe erosion. Erosion on the needle is primarily due to friction, while erosion on the nozzle is primarily due to impact. High erosion levels on both the nozzle and needle are concentrated within a particle velocity range of [80, 100], and the erosion rate within this speed range shows a sharp upward trend. Full article

Submarine channels are critical conduits for sediment transport by turbidity currents, yet the quantitative influence of channel geometry on flow dynamics and sediment segregation remains poorly understood. Based on computational fluid dynamics, we constructed six three-dimensional numerical models of submarine channels with varying curvatures (R1–R3) and axial slopes (R4–R6) using ANSYS Fluent 17.2, with model settings informed by seafloor morphology from the South China Sea. The Eulerian–Eulerian multiphase model coupled with the standard k-ε turbulence model was used to simulate density fields, velocity structures, and sediment distributions. Results show that low-curvature channels exhibit symmetric density evolution and uniform sediment distribution, whereas high curvature induces pronounced asymmetry with a steep outer-bank density front and triggers secondary flow reversal. Increasing curvature also enhances flow thickness and radial mass flux. Increasing axial slope markedly elevates downstream velocity (0.09 to 0.16 m/s), reduces flow thickness, and shifts sediment distribution toward the inner bank without inducing secondary flow reversal. This study provides a parametric comparison of curvature versus slope effects on turbidity current dynamics and sedimentation patterns under fixed-bed, rectangular-channel assumptions. The findings offer a qualitative reference for interpreting sedimentary architectures in deep-water systems such as those in the South China Sea and analogous rift basins. Results are hypothesis-generating, pending further validation with field data and morphodynamic modeling. Full article

To characterize the transport of the mining-induced sediment plume in the Clarion–Clipperton Zone (CCZ) nodule area, this study introduces a particle relative dispersion (RD) to assess material dispersion in 2D and 3D. In 2D, forward and backward RD results show clear sub-regional differences in particle aggregation and diffusion. Forward RD reaches a maximum ridge value of 40 km in regions of strong shear and strain. Backward RD effectively identifies upstream source regions and convergence pathways. High RD values align closely with strong strain-rate gradients, indicating that particle separation and mixing are primarily driven by transition regions between flow structures rather than uniform high- or low-strain areas. In the 3D, the vertical domain was limited to the 4500–4600 m depth range above the seabed. The overall RD patterns remain broadly consistent with the 2D results, while the maximum RD increases to approximately 80 km due to the inclusion of vertical displacement and local vertical shear effects. Within the 4500–4600 m depth range, horizontal transport remains dominant, whereas vertical variations are comparatively weak, and particle trajectories exhibit only minor local differences. Compared with the 2D case, the deep-layer 3D RD distribution exhibits lower skewness values, suggesting a more spatially balanced particle separation pattern with reduced directional asymmetry. Multi scale quasi-3D RD analysis provides essential insights into material dispersion and convergence patterns, offering valuable information for evaluating transport pathways, potential pollutant spread, and ecological risks associated with deep-sea mining. Full article

The Mugan Syncline in northeastern Yunnan represents a significant relay area for shale gas exploration in China. However, due to the combined effects of tectonic superimposition and sedimentary heterogeneity, systematic investigations into the intervals hosting high-quality shales and the coupling relationships among microfacies, reservoir quality, and gas-bearing properties remain insufficient. The core objective of this study is to establish a high-resolution microfacies framework and to quantitatively elucidate the multi-parameter coupling mechanisms by which microfacies control organic matter enrichment, pore development, and gas storage capacity in this structurally complex, basin-margin setting. By integrating core observations, thin-section petrography, scanning electron microscopy (SEM), whole-rock X-ray diffraction (XRD), total organic carbon (TOC) analysis, trace-element geochemistry, and well-logging data, we establish a stratigraphic subdivision and cross-well correlation framework for the Wufeng (WF) Formation and the Long11 submember. Furthermore, a lithofacies (microfacies) identification scheme based on a “TOC + siliceous (quartz + feldspar)–carbonate–clay” ternary classification is applied. The results reveal the following: (1) Based on the locally developed erosional contact at the boundary between the Longmaxi (LMX) Formation and the underlying Guanyinqiao Formation, the WF Formation in the study area can be subdivided into two submembers, whereas the Long11 submember comprises four sublayers. The thicknesses of the Long11-1 through Long11-3 sublayers range from 21.42 to 25.47 m, exhibiting a subtle northward-thickening trend. In contrast, the Long11-4 sublayer displays a relatively uniform thickness and high stratigraphic continuity of shale deposition. (2) Based on TOC content and ternary mineral composition, the shales are classified into four lithofacies associations and sixteen lithofacies subtypes. The main favorable microfacies assemblages are identified as high-carbon siliceous/calcareous shale (C-1), high-carbon calcareous/siliceous mixed shale (M-1), carbon-rich argillaceous siliceous shale (S-3), and high-carbon siliceous/argillaceous mixed shale (M-2). (3) High-quality shales (TOC > 2%) are predominantly developed in the upper member of the WF Formation and in the Long11-1 through Long11-4 sublayers. Their lateral distribution is markedly controlled by variations in paleotopography and terrigenous sediment supply. (4) The microfacies exert a synergistic control on shale gas enrichment. Carbon-rich argillaceous siliceous and siliceous-rich microfacies generally correspond to higher TOC contents and better-developed organic-matter pores. Siliceous-rich and mixed microfacies exert a positive influence on pore preservation and rock brittleness. The gas-bearing properties are influenced not only by TOC content but also by pore structure, mineral composition, and tectonic preservation conditions. The findings of this study provide a scientific basis for the prediction of shale gas sweet spots and the optimization of target intervals in the Mugan Syncline and other structurally and sedimentologically complex regions of northeastern Yunnan. Full article