Elastoplastic constitutive model considering the filling and cementation effects for gas hydrate-bearing sediments: development and finite element implementation

Dynamic evolution of hydrate filling and cementation effects significantly affects the mechanical behavior of gas hydrate-bearing sediments (GHBS). To analyze the strength and deformation characteristics of GHBS under varying effective confining pressures and hydrate saturations, we use the unified hardening model for clays and sands (CSUH model) as a framework. A compressive hardening parameter is introduced to describe the isotropic compression behavior. Additionally, cementation strength is incorporated to adjust the yield function, while state parameters are used to modify the potential strength. An elastoplastic constitutive model is developed to capture the strength, stiffness, dilatancy, and softening of GHBS. Based on the user-defined subroutine interface provided by ABAQUS and the modified Euler integral algorithm with error control, the user-defined subroutine (UMAT) is embedded in ABAQUS to implement the finite element model. Numerical solutions are obtained, and the accuracy of the model is verified by comparing theoretical solutions with experimental data, showing good agreement. The results demonstrate that the model accurately represents the stress-strain relations and shear dilatancy characteristics of GHBS under various conditions. Furthermore, the model effectively evaluates the mechanical responses of GHBS with different hydrate formation behaviors under various environmental loads. These findings provide a foundation for further engineering applications

A novel edge-feature attention fusion framework for underwater image enhancement

Underwater images captured by Remotely Operated Vehicles are critical for marine research, ocean engineering, and national defense, but challenges such as blurriness and color distortion necessitate advanced enhancement techniques. To address these issues, this paper presents the CUG-UIEF algorithm, an underwater image enhancement framework leveraging edge feature attention fusion. The method comprises three modules: 1) an Attention-Guided Edge Feature Fusion Module that extracts edge information via edge operators and enhances object detail through multi-scale feature integration with channel-cross attention to resolve edge blurring; 2) a Spatial Information Enhancement Module that employs spatial-cross attention to capture spatial interrelationships and improve semantic representation, mitigating low signal-to-noise ratio; and 3) Multi-Dimensional Perception Optimization integrating perceptual, structural, and anomaly optimizations to address detail blurring and low contrast. Experimental results demonstrate that CUG-UIEF achieves an average peak signal-to-noise ratio of 24.49 dB, an 8.41% improvement over six mainstream algorithms, and a structural similarity index of 0.92, a 1.09% increase. These findings highlight the model’s effectiveness in balancing edge preservation, spatial semantics, and perceptual quality, offering promising applications in marine science and related fields

Application of the Navigational Air-Sea Methane Exchange Flux Observation System in the Qiongdongnan Basin of the Northern South China Sea

The sources and sinks of dissolved CH4 in offshore waters are becoming diversified with the rapid increase in human activities. The concentration and air–sea exchange flux of dissolved CH4 present new characteristics of more intense spatiotemporal evolution, and the contribution to atmospheric CH4 continues to increase. Herein, a new model based on navigable air–sea exchange flux observations was proposed, which replaced the traditional station-based sampling analysis and testing method, realizing the synchronous measurement of methane in the atmosphere and surface seawater carried by ships. Based on the Marine Geological Survey project of the China Geological Survey, comprehensive environmental surveys were conducted in April 2018, September 2018, and June 2019 in the Qiongdongnan area in the northern part of the South China Sea, and the dissolved methane content in the sea surface atmosphere and surface seawaters in 2019 were simultaneously obtained. The methane exchange flux ranges of the southeastern sea area were calculated as −0.001~−0.0023 μmol·m−2·d−1 and −0.00164~−0.00395 μmol·m−2·d−1 by using the Liss and Merlivat formula (LM86), the Wanninkhof formula (W92), and the field-measured wind speed. The feasibility of the navigational air–sea methane exchange flux observation system was proven in a sea trial, and the measurement accuracy and observation efficiency of air-sea flux were improved with the designed system, providing a new technical means for further research on multiscale air–sea interactions and global climate change.</jats:p