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.
This study investigates methods to enhance the bearing capacities of pile foundations in coral sand through vertical bearing capacity model tests on coral sand samples. The tests examined single piles and pile groups with varying expansion agent dosages and pile spacings using high-performance calcium sulfoaluminate (HCSA)-based self-compacting expansion piles. The research proposes a combined systematic calculation and numerical simulation method for evaluating the bearing capacities of single piles and pile groups, with results validated through field testing. The findings demonstrate that pile end and side resistances increased significantly when incorporating appropriate HCSA expansive agent. A single pile with 15
A thin-walled liner is widely employed to rehabilitate deep-buried pipelines. This bi-material lined-pipeline system may be situated in geohazard-prone regions, posing significant risks to structural integrity. This study proposes a systematic theoretical methodology to assess the seismic response of lined-pipelines subjected to strike-slip fault displacements. The strain distribution within the deformed system is determined by introducing an admissible transverse displacement function, while the onset of yielding in the lined pipeline is explicitly predicted using the classical beam-yield criterion. The formulated solutions are validated effectively against numerical simulations. Parametric studies subsequently evaluate the influence of the thickness ratio and fault plane inclination on strain development and yielding behavior. Results indicate that a greater fault plane inclination induces higher yield displacement in the lined-pipeline, while the yield strength of the liner exerts minimal influence on system-level yielding.
The power take-off (PTO) mechanism, a crucial component in wave energy converters (WECs), plays an essential role in controlling motion and power conversion. This article examines the control mechanisms of the point-absorber wave energy converter, specifically addressing the multiple constraints related to damping and displacement. To optimize energy capture efficiency, a Model Predictive Control (MPC) framework is implemented and its performance is evaluated. Through reformulation of the time-lag function and derivation of the state-space equation, a predictive model and objective function for the control algorithm are established. A comprehensive model combining theoretical analysis with numerical simulations is constructed to simulate converter behavior under various sea conditions. This methodology enables the identification of optimal control strategies under different constraints, thereby enhancing wave energy conversion. The simulation results demonstrate that without external constraints, MPC and optimal damping control perform similarly in energy conversion optimization. However, when subject to external constraints such as PTO damping force and displacement, MPC demonstrates superior performance than optimal damping control in both regular and irregular waves, particularly near the absorber’s natural frequency.
This study proposes a fence-type permeable breakwater composed of multiple strategically arranged fences along the wave barrier. A wave-generating and absorbing boundary condition is implemented within the OpenFOAM framework—an open-source computational fluid dynamics (CFD) platform—to accurately simulate wave propagation and minimize spurious reflections. A numerical wave flume is developed to model regular wave conditions and investigate wave-structure interactions under controlled scenarios that replicate physical model tests. Transmission, reflection, and dissipation coefficients, along with the porosity of various perforated fence configurations, are evaluated and compared, supported by detailed flow field analysis. Results indicate that fence installation significantly reduces the reflection coefficient and enhances wave energy dissipation. Perforated fences effectively reduce both wave transmission and reflection while increasing energy dissipation. Optimal dissipation performance is achieved when perforations are positioned on the front face of the fence at a porosity of 10
This study establishes a numerical model for simulating coupled interactions of floating offshore wind turbine (FOWT) with large-scale ocean waves and wind. The volume of fluid model combined with the 6-DOF solver efficiently resolves the fluid-induced dynamic motion of FOWT in a multi-phase flow comprising air and water using Fluent. A fluid-structure interaction (FSI) analysis for FOWT integrating the k–ω Shear Stress Transport (SST) turbulent model and a structural dynamic model is conducted. The study first simulates the floating platform’s motion effects on FOWT aerodynamic performance, including surge, pitch, and yaw. Subsequently, a fully coupled calculation of the FOWT is executed using the established numerical model. The aerodynamic hydrodynamic interactions of the FOWT under combined wind and wave effects are simulated. The complex unsteady flow fields considering blade and tower interference effects among blade-tip vortices, shedding vortices, and turbulent wakes are numerically visualized and examined in detail. Additionally, the study investigates the effects of inflow wind conditions, wave conditions, and blade and tower flexibility, calculating time series of aerodynamic loads and aeroelastic responses through one/two-way FSI modeling.
The liner of mechanically lined pipe (MLP), which depends on mechanical residual contact pressure for attachment to the carrier pipe, risks wrinkling when subjected to large curvatures. A novel type of MLP, termed adhesively bonded mechanically lined pipe (ABMLP), has been recently developed to address this limitation. Beyond the residual contact pressure generated during manufacturing, ABMLP incorporates additional adhesive strength between the liner and carrier. To evaluate the ultimate bending capacity of ABMLP, this research established bending models utilizing both finite element methods and theoretical analysis. The adhesive layer was simulated using an element-based cohesive zone model (CZM). Results indicate that the adhesive in ABMLP effectively delays liner separation compared with MLP; however, substantial curvatures may still induce localized adhesive damage. Furthermore, sensitivity analyses examined critical adhesive layer parameters, including cohesive stiffness, strength, and fracture energy. The findings reveal that stiffness influences circumferential damage distribution in the adhesive layer, while cohesive strength and fracture energy substantially impact damage extent. Moreover, early adhesive layer failure diminishes the pipeline’s load-bearing capacity.
The turning maneuver performance of multi-body towing systems is crucial for navigation safety and efficiency, particularly in polar regions where ice floes impair turning capability. This paper presents a numerical model for simulating towing system turning operations in broken ice using the discrete element method (DEM). Numerical ice fields comprising polygon-shaped ice floes are generated randomly using the centroidal Voronoi tessellation (CVT) algorithm. The towline connecting the tug and towed structure is modeled as a catenary system. The Newmark-beta method resolves the coupled motions of tug, towed structure, and ice floes incrementally. The analysis examines turning processes for single and multiple tug configurations in ice-infested waters. Additionally, the study investigates how ice and towing characteristics—including ice concentration, thickness, floe size, and towline length—influence turning performance through numerical simulations, contributing insights to ice towing maneuverability.
The hybrid pile-bucket foundation represents an innovative alternative to conventional monopile foundations for supporting offshore wind turbines (OWTs). Given the significant horizontal loads experienced by OWTs, this study comprehensively examines the horizontal ultimate bearing capacity of hybrid pile-bucket foundations in clay through model testing, finite element analysis, and upper bound limit analysis. The study analyzes how varying height-to-diameter (H/D) ratios affect the horizontal bearing capacity through model testing, revealing characteristic failure patterns and instability mechanisms. Finite element analysis validates the experimental results and elucidates the failure mechanism and velocity field of pile-bucket foundations under horizontal loading. Upper bound solutions for horizontal ultimate bearing capacity are derived using the virtual work equation, with detailed analysis of energy dissipation rate contributions from each component. The calculated upper bound solution demonstrates reasonable agreement with experimental and literature values, validating the proposed failure mode and methodology. These findings establish a theoretical foundation for the design and optimization of pile-bucket foundations.
This study focuses on the hydrodynamic analysis and optimization of an integrated break water and wave energy converter system designed to mitigate long-period wave effects. It advances hydrodynamic analysis methods and explores the mechanisms within an integrated oscillating buoy-type wave energy converter and breakwater system. Based on linear potential flow theory and eigenfunction expansion method, a three-dimensional semi-analytical hydrodynamic model is established. The model employs a boundary discretization approach to handle the bottom flow domain of wave energy buoys with complex geometries. A floating breakwater incorporating vertical perforated plates is proposed. Dynamic water pressure difference conditions and artificial velocity potential are introduced to simulate the perforation effect. The mechanisms of wave dissipation, energy capture, and energy loss within the system are investigated theoretically. Key findings indicate an optimal balance between attenuation (KR > 0.5, KT < 0.1 and η > 20
This study presents a systematic experimental investigation into the erosion properties of kaolinite and calcium bentonite, two primary clays with distinct physicochemical characteristics. Erosion tests were conducted across a broad range of dry bulk densities using a small-scale conduit flow apparatus. The results demonstrate that dry bulk density significantly influences the erodibility of both clays. Specifically, increased density leads to a non-linear increase in critical shear stress and a concomitant reduction in erosion rate. Distinct mineralogical behaviors were identified: calcium bentonite exhibited significantly lower erosion thresholds than kaolinite at comparable densities, yet displayed a more gradual increase in erosion rate under rising shear stress. By applying a power-law erosion model, empirical formulations for the erodibility coefficient M and exponent n were developed; both parameters showed a strong inverse correlation with the critical shear stress τcr. Notably, the separation of data clusters for these parameters underscores the profound influence of mineral composition on erosion dynamics. Furthermore, the model proposed by Chen et al. (2021) provided a more fundamental and robust description of the erosion threshold than traditional density-based power relationships, with the cohesion-related coefficient A effectively reflecting the relative cohesive strength of specific clays.
Offshore heavy oil production is transitioning from steam flooding to in-situ combustion (ISC). To accurately evaluate the risk boundary of the combustion-zone casing section in injection wells during the ignition-combustion process, a dynamic risk assessment framework is proposed by integrating a time-dependent Kriging model with stress-strength interference theory. Thermo-mechanical finite element simulations are first conducted, alongside high-temperature tensile and creep tests on TP110H casing steel, which is widely used in offshore thermal recovery wells. These tests are performed over a temperature range from ignition to peak combustion temperatures to characterize the temperature-dependent mechanical behavior of casing materials under ISC conditions. A Kriging model is then constructed to extrapolate these data and characterize material behavior under continuously varying bottom-hole temperatures. Subsequently, Monte Carlo simulation is employed to sample random operating conditions, and the dynamic casing failure probability is evaluated using stress-strength interference theory. The results indicate that the failure probability of the combustion-zone casing section remains below 0.1
Ice sheets present significant challenges for underwater high-speed projectiles during water exit processes in cold regions.This study investigates the water exit process of an underwater high-speed projectile through ice-covered water using the structured arbitrary Lagrangian-Eulerian(S-ALE)method in LS-DYNA.The ice material model is validated against high-speed impact tests,and the fluid-structure interaction(FSI)model is verified through ice-free water exit experiments.Comparative analyses between ice-free and ice-covered conditions examine projectile motion,cavity evolution,ice forces,and damage patterns.Numerical simulations demonstrate that ice thickness and size significantly influence projectile behavior during water exit.At a launch velocity of 60 m/s with a 0.1 m thick ice sheet,the velocity loss ratio reaches 36.4%,which is 4.28 times larger than that under ice-free conditions.Thin ice(0.05 m)generates larger cavities and extensive cracking,while thicker ice(0.1-0.15 m)constrains crack propagation and reduces cavity dimensions.Size-dependent phenomena indicate that smaller ice blocks(0.14-0.42 m)exhibit crushing failure with higher peak forces,while larger ice sheets(5 m)demonstrate bending-dominated failure with lower force magnitudes.Cavity development shows an inverse relationship with ice size.These findings contribute to underwater projectile design for polar environments and establish groundwork for future studies of environmental-structure interactions in cold regions.
Internal solitary waves (ISWs), characterized by their nonlinearity, large amplitude, and destructive potential, pose significant risks during propagation, potentially causing riser fracture and anchor dragging. This paper presents an alternative to the conventional conservative emergency approach of immediate riser disconnection upon ISW detection. The proposed methodology integrates quantitative dynamic model calculations with Petri-net modeling for contingency plan design. The dynamic model of the deepwater drilling riser coupled system facilitates the identification of failure structures and critical failure time points. Through the incorporation of temporal factors into Petri net modeling, the optimal timing for each action step can be precisely determined, preventing resource wastage and structural damage from premature or delayed operations. A case study demonstrates the emergency response process. The analysis yielded five contingency plans during ISW propagation. Dynamic catastrophic analysis indicates prioritization should focus on the lower flex joint angle, followed by platform trajectory and mooring line tension. Certain ISW scenarios necessitate concurrent monitoring of mooring tension adjustment and emergency disconnection. The developed contingency plan effectively reduces operational time and costs while maintaining safety standards.
Dredging is a critical approach for estuary improvement and development and remains one of the most practical solutions to sedimentation problems. Dredged sediments are typically transported by suction hopper dredgers and disposed of at designated offshore dumping sites. Accurate prediction of the formation and evolution of subaqueous sediment mounds is therefore essential for minimizing the ecological and environmental impacts associated with secondary sediment transport. This study conducts a series of experimental tests examining the morphology and classification of sediment subaqueous mounds formed through continuous release of coarse sediment under static and dynamic flow conditions. Observations indicate that mounds can be classified as regular cones or oblique elliptic cones under hydrodynamic forces. Based on diffusion theory, this research develops a theoretical model describing the subaqueous mound formation process. Four key characteristic parameters are identified to characterize mound shape: peak height, radiation length, peak offset distance, and turbulence-induced diffusion length. These parameters are expressed as functions of dimensionless numbers: sand Reynolds number, flow Reynolds number, density Froude number, and characteristic length. The findings demonstrate that the process model incorporating peak offset distance and diffusion length more accurately predicts drift characteristics and skew distribution of sediment subaqueous mounds.
This study presents a precision analysis of underwater docking control for marine vehicles considering coupled random factors through Monte Carlo simulations. The analysis of how various random factors and input parameters affect docking accuracy is essential, given the stochastic nature of sensor measurement errors, ocean currents, and wave forces. Initially, a vehicle model incorporating uncertainties and randomness composed of coupled random variables is established. Subsequently, the research presents a robust controller for three-stage underwater docking and a systematic framework for docking accuracy analysis. Furthermore, an enhanced sampling system is developed to effectively decouple the coupled random factors for the Monte Carlo simulations. Comprehensive statistical tests validate its substantial advantages over traditional sampling approaches. The comparative simulation results demonstrate that coupling relationships among random factors in precision analysis result in increased docking errors compared with uncoupled scenarios. Additionally, the proposed sampling method demonstrates improved efficiency in computational time while minimizing both decomposition and docking errors.
