Pneumatic desilting technology provides a non-contact solution for mitigating asymmetric sediment accumulation beneath pile-supported wharves, where conventional mechanical dredging is often restricted. However, the multiphase dynamics governing this process remain poorly understood. This study combines multiphase fluid dynamics experiments with theoretical analyses to systematically elucidate the mechanisms of bed morphology evolution, suspended sediment sorting, and synergistic sediment transport induced by submerged air jets. Based on the principle of gas expansion work, a macroscopic prediction equation for the ultimate desilting volume is established. To evaluate sediment suspension, a modified Rouse equation is employed to quantify the vertical attenuation of suspended sediment concentration. Experimental results indicate that high-energy gas input significantly coarsens the particle size distribution of suspended sediments. Building on these physical findings, a flux matching theory linking pneumatic sediment suspension to natural flow transport is proposed. A globally optimal parameter control trajectory is derived, clearly delineating zones of excess gas energy and ineffective dissipation of flow transport capacity. These results provide a theoretical basis for selecting gas parameters for pneumatic scouring equipment in field desilting operations.
Metal materials are widely used in vehicle hulls owing to their high strength and toughness; however, their high density increases overall mass, reducing maneuverability, and they are susceptible to oxidation and corrosion. In contrast, composite materials offer significant advantages through their lightweight nature and high specific strength, making them promising candidates for applications such as ships and underwater vehicles. This study employs the coupled Eulerian-Lagrangian method to investigate the water entry of an autonomous underwater vehicle (AUV) fabricated from T700/M21 composite materials. A numerical model of a carbon fiber-reinforced epoxy resin composite AUV is established to evaluate the effects of different stacking sequences and entry angles on hydrodynamic loads, dynamic deformation, and failure mechanisms. The Hashin failure criterion is incorporated into the VUMAT subroutine. Results reveal a distinctive “hump” indentation on the AUV nose during water entry, accompanied by substantial matrix damage in the head region, while the fibers remain largely intact. The surface matrix fails first under high stress, whereas deeper layers experience lower stress levels. A 45° interlaced stacking sequence demonstrates superior impact resistance. Moreover, decreasing the entry angle intensifies material damage, underscoring the critical importance of optimizing entry angles to ensure the structural safety of composite AUVs.
Wake interactions significantly influence the aerodynamic performance and energy efficiency of wind farms, yet their complex dynamics under realistic atmospheric conditions remain insufficiently resolved. This study employs large-eddy simulation (LES) with full-geometry overset grids to investigate the wake characteristics of the NREL 5 MW wind turbine under varying turbulence intensities and shear inflow conditions. Numerical validations against experimental data and established LES results confirm the reliability of the model. The analysis focuses on wake velocity distribution, recovery dynamics, vortex evolution, and turbulence intensity fields. Results demonstrate that increasing turbulence intensity markedly accelerates wake recovery by enhancing convective mixing, reducing the recovery distance by approximately 25
This study investigates the flow characteristics around a newly designed offshore groin in the basin behind a pile-supported wharf to facilitate effective silt dredging. Detailed flow measurements are conducted around the groin in a current flume during peak ebb and flood tides. Laboratory results document the flow acceleration regime between the groin and the wharf. The Reynolds-Averaged Navier-Stokes (RANS) equations with a k–ε turbulence closure are implemented to establish a numerical flume using the computational fluid dynamics (CFD) tool FLOW-3D. The numerical model is validated through experimental flow measurements. The horizontal mean flow field, turbulent kinetic energy, and vorticity field around the groin are examined numerically under both tidal conditions. The effects of design parameters, including groin length, orientation, location, and incoming tidal current on flow acceleration around the groin are analyzed through numerical simulations. Results indicate that flow acceleration around the groin head and the extent of the effective accelerating region increase significantly with greater groin length and alongshore orientation angle, while remaining relatively unaffected by incoming tidal current variations. As the groin shifts shoreward from the wharf to the shoreline, flow deceleration persists around the groin head, while the effective accelerating region reaches its maximum at a specific distance from the wharf.
This study establishes a nonlinear surge motion model of a tension-leg platform wind turbine (TLPWT) under combined aerodynamic and hydrodynamic loads in the form of a Duffing type oscillator. The nonlinear restoring force is derived by considering stretching tendons and platform set-down motions, with the analytical solution obtained through the harmonic balance method (HBM). The motion stability is analyzed using stability algorithms, and the boundary is determined through Floquet theory. The research examines the effects of system dynamic parameters and environmental loads on the TLPWT surge model. Analysis of the Duffing oscillator model reveals that TLPWT surge exhibits an unstable region characterized by multiple coexisting periodic solutions due to nonlinear stiffness. This instability manifests in both low-frequency and high-frequency regions, with saddle-node bifurcation occurring at the stable boundary. Reduced damping expands the unstable region, while increased linear stiffness shifts it toward higher frequencies. Greater nonlinear stiffness reduces response amplitudes but expands the unstable region while compressing the high-frequency stable region. Wave force significantly affects resonance peak and vibration amplitude in the low-frequency region, whereas wind force shows minimal impact on motion amplitude and stability. The study also investigates bifurcation characteristics under failure conditions, including tendon and blade pitch failures.
