Search Results (3)

The flexible fire hose and net (hose net) is a novel fish-hauling device developed for set-net fishery. The hose net is placed inside the box chamber net, air is injected from one edge of the hose net, the hoses are inflated, and the buoyancy force is increased. The net floats up gradually, cornering the fish on the other edge. In previous studies, we have conducted a series of floating-up and sinking-down experiments to evaluate the performance of the hose net in calm water. In this study, aimed at the practical implementation of the hose net fish-hauling system, we conducted a water tank experiment and a semi-field test to confirm the operation of the hose net, which was installed inside a box chamber net model. The results demonstrated that the net could float up gradually in an ideal form and stretched on the surface of the box net. The time taken to float up processes varied with the air injected into the auxiliary hose and hose net, so that the motion of the hose net could be controlled by adjusting the air at different parts of practical operation. Furthermore, semi-field trials were conducted to verify its performance in the natural marine environment and its ability to capture schools of fish. Overall, this innovative hose net fish-hauling device is expected to be valuable for next-generation set-net fishing. Full article

The successful operation of a large-diameter cold water pipeline installation is crucial for harnessing the potential of ocean thermal energy conversion. However, there is a shortage of research focused on mechanical performance analysis during installation. This study establishes a pipeline response analysis model based on a nonlinear beam theory to elucidate the underlying mechanical behaviour. Employing the method of singular perturbation, the general solution for the exterior region of the pipeline, the solution at the boundary layer, and the valid solution across the entire domain are derived. A comparison with numerical solutions is conducted to validate the accuracy and effectiveness of the theoretical model. Based on the theoretical analysis, the influence of installation depth and pipeline curvature on the pipeline’s shape, tension, curvature, and stress is discussed. The results indicate that increasing the installation depth leads to intensified pipeline bending and significant deformation, reaching a maximum bending moment of 3.92 MN∙m at a distance of 50~100 m from the bottom of the pipeline. The results also show that, as the pipeline’s arc length increases from 0 to 100 m, the bending curvature, Von Mises stress, and bending stress exhibit a trend of initial growth followed by a decline, peaking at 7.45 MPa, and 6.83 Mpa, respectively, while the actual tension and axial tension decrease initially and then increase, reaching −0.17 MN and −0.17 MPa, respectively, at the maximum arc length. The findings of this study provide valuable insights for practical cold-water pipe installation and laying. Full article

This paper elaborates on a new composite bucket foundation (CBF) structural system for offshore wind turbines. The proposed CBF consists of a special force transition section, a beam system structure upper steel bucket cover and a large-scale steel bucket with honeycomb structure rooms. It can be prefabricated onshore, self-floated on the sea and then towed to the appointed sea area before sinking to the sea soil under negative pressure. This is called the “one-step” installation technology. Arc- and line-type bucket foundations are calculated by both theory and the finite element method to discuss their force transfer paths and bearing modes. Owning to the special structural form, the transition section can effectively convert the huge load and bending moment into controllable tension and compressive stress, as well as adjust the structure balance. The bearing model and percentage of each part of the composite foundation under monotonous and ultimate load conditions are also calculated. Results indicate that the bearing mode of CBF is a typical top cover mode. In addition, the curvature impact of arc-type is studied and the results reveal that the structure type of the transition section is more important than the diameter ratio between the bottom transition section and the bucket. Full article