Accurate determination of the mechanical properties of Arctic sea ice during the melting season is essential for navigation safety assessment in Arctic routes, prediction of ship icebreaking resistance, and ice-load design of polar engineering structures. In this study, uniaxial compression, three-point bending, temperature-salinity-density testing, and microstructural observations were conducted based on laboratory experiments, field trials, and ice-crystal image analysis. The results indicate that, under laboratory conditions, the uniaxial compressive strength of sea ice exhibits a pronounced ductile-to-brittle transition with varying strain rates, and reaches a peak value of 2.41 MPa at approximately 4.8×10⁻⁴ s⁻¹. The field results of three-point bending tests revealed a marked layered strength profile along the ice thickness; the central columnar ice exhibited relatively higher strength, whereas the lower layer showed significantly reduced bending strength due to seawater melting and compromised structural integrity. Differences between laboratory and field test results are consistent with the difference in temperature conditions; under the test conditions of this study, ice strength obtained in the low-temperature laboratory environment (−10 ℃) was generally higher than that of field tests. Observations of ice crystals and pores indicated distinct layered microstructural variations within melting-season sea ice, offering microstructural evidence for interpreting the variability of mechanical properties, crack initiation paths, and mechanisms of structural weakening. This study may provide a reference for the selection of mechanical parameters of Arctic sea ice during the melting season and for the cross-validation of laboratory and field test results.

For the frequency domain hydrodynamic problems of ship sailing in waves, the influence of steady wave potential and waterline integral terms on ship hydrodynamic calculation is explored. The boundary integral equation is solved using the three-dimensional translating and pulsating (3DTP) source Green's function method, and the background flow field is linearized using two schemes: double-body (DB) flow and Neumann-Kelvin (NK) uniform flow. A numerical program is developed and hydrodynamic calculations on Wigley I, Wigley III, S60, and S175 ships are performed. The results show that taking into account the steady potential can significantly improve the calculation accuracy of ship motion response on the resonance band of frequency. In addition, directly adding the waterline integral term to the boundary integral equation can easily lead to unstable numerical results. When the waterline is sunk to the centroid of the adjacent panel, the numerical results converge and are generally consistent with the results when the waterline integral is neglected, From an engineering perspective, in the 3DTP method, considering the influence of steady potential enhances the accuracy of the results, whereas neglecting the waterline integral is more practical.

The water ingress of damaged compartments alerts the mechanical characteristics of floating bridge, and the corresponding analysis of dynamic response of the floating bridge becomes highly complex. To investigate this kind of problem, a hydrodynamic analysis model of floating bridge under moving loads accounting for the flooding process of the broken compartment was established based on the Kane method and the modified Bernoulli equation. Having developed the corresponding solution procedure, the accuracy of the proposed model were testified through the comparison between of the relevant model experimental data and numerical results. Next, the influences of parameters such as opening size, load velocity and connection gap on the dynamic responses of the floating bridge with damaged opening in static water were investigated through case studies. The results indicate that the maximum values of vertical displacement, shear force and bending moment would go up when the compartment is flooded, but the size of the opening has little effect upon the dynamic response of the pontoon when the opening size is relatively small. With the increment of the load velocity, the maximum values of the vertical displacements of the pontoon, the shear forces and bending moments at the connections go up nonlinearly. The maximum bending moment decreases firstly and then rises with the increase of the longitudinal connection gap.

The wave glider is a long-endurance unmanned surface vehicle driven by wave energy, widely used in hydrological and meteorological observations as well as oceanographic surveys. However, its low speed due to a single driving mechanism limits its adaptability at sea. To improve speed, this paper proposes a method of sail-assisted wave glider. First, the aerodynamic parameters of the sail were obtained through CFD numerical simulation. Next, a multi-body dynamics coupling model for the wave and sail-assisted wave glider was established. Finally, the synergistic driving effects under typical sea conditions were simulated and analyzed. The results show that, except for headwind and tailwind angles within 30°, the speed increases, with the optimal enhancement observed under crosswind conditions. Under a second-level sea state and a wind speed of 20 kn, the speed can increase by up to 28%. Furthermore, the synergistic propulsion effect and the motion response characteristics of the twin-body structure exhibit strong coupling with wave and wind fields. The research findings provide important theoretical support and design foundations for the optimization of the propulsion system and navigation control strategies of sail-assisted wave gliders.

CFD simulations of flow past a circular cylinder at subcritical Reynolds numbers pose several challenges, including the accurate prediction of shear-layer Kelvin-Helmholtz (K-H) instabilities, low-frequency unsteady behavior, and the formation mechanisms of V-shaped and U-shaped wake velocity profiles. In this study, a novel wall-modeled hybrid turbulence model, termed TNT WM-XLES, is developed by reconstructing the turbulent kinetic energy (k) equation of the Transitional k–ω Turbulence (TNT) model, thereby significantly enhancing the resolution of turbulent kinetic energy within the shear layer. Numerical validations demonstrate that the proposed model not only accurately reproduces the first- and second-order wake statistics, but also successfully captures three characteristic spectral features: the high-frequency peak associated with shear-layer K–H instability, the dominant peak corresponding to vortex shedding, and the low-frequency peak related to recirculation-zone oscillations. By introducing the instantaneous recirculation-zone length parameter, L_r(t), a quantitative consistency is observed between its dominant spectral frequency and the low-frequency signal. This finding establishes, for the first time, a direct link between the low-frequency instability of cylinder wake flows and the periodic contraction–expansion dynamics of the recirculation zone through a dynamic characteristic parameter. The proposed model overcomes the limitations of conventional RANS/LES approaches in capturing low-frequency flow features and provides an effective and practical tool for high-fidelity simulations of complex bluff-body flows in engineering applications.

Due to its cylindrical configuration and distinctive motion characteristics, the cylindrical FPSO faces significant challenges in offloading operations under complex marine conditions characterized by high-frequency variations in wind, waves, and currents. To address these challenges, particularly under the persistent northeastern and southwestern monsoon conditions in the eastern South China Sea, this study proposes a novel offloading system featuring dual offloading points, bow loading, and position-mooring configuration, intended as a cost-effective alternative to high-cost DP shuttle tankers. The proposed solution integrates a bow thruster on the shuttle tanker and dual stern tugs to enable coordinated control of heading and position, thereby enhancing operational safety and adaptability. To verify the feasibility of the proposed system, a combination of numerical simulations and full-mission maneuvering experiments was conducted. The study systematically investigates key technical aspects such as the selection of shuttle tankers and tugs, bow thruster configuration, and mooring hawser design. Results confirm the feasibility of employing a 75 000 DWT shuttle tanker for position-mooring offloading at the Liuhua oilfield in the South China Sea. Findings indicate a positive correlation between the tension and angle of mooring hawsers and the shuttle tanker's displacement and length. This study provides technical guidance and risk assessment insights for cost-effective offloading operations of cylindrical FPSOs in complex marine environments.

In order to explore the change of propulsion performance of propeller after biological fouling, the full-scale KP505 propeller was taken as the research object. The geometric modeling of fouling was carried out according to the fouling attachment law on the propeller surface, and then the numerical simulation of full-scale propeller under smooth and different fouling attachment conditions was carried out based on viscous fluids Computational Fluid Dynamics (CFD) method and roughness function model. The results show that the attached biofouling has a greater effect on the open water performance. Specially different fouling conditions lead to a reduction in propeller thrust, an increase in torque, a reduction in propulsion efficiency, a reduction in the strength of the wake vortex and the faster dissipation. The more severe the foulings is, the more obvious the change is. Although fouling can increase the loss of flow field energy and cause many adverse effects, fouling can shorten the wake length of the flow field behind the propeller, thereby mitigating its disturbance on the far-field flow.

In response to the problems of excessive measurement points and low nonlinear segment reconstruction efficiency in the deformation field reconstruction of ship structures, this paper proposes a deformation field reconstruction method (iFEM-PSO) based on dynamic measurement field optimization combining inverse finite element method (iFEM) and particle swarm optimization algorithm (PSO). Taking three typical hull plate structures of flat plates, open flat plates and open reinforced plates as objects, different order buckling modes are applied as initial defects to obtain different failure characteristics, and the reconstruction accuracy under the input of optimized measurement points and full measurement points is compared and analyzed. The results show that the iFEM-PSO method can reduce the number of required strain sensors by about 75%, and the overall reconstruction error remains within 15%, effectively verifying its accuracy and efficiency in nonlinear deformation reconstruction. The optimized measurement points are mainly concentrated in areas with large initial defects, structural boundaries and stress concentration areas (such as the periphery of the opening, the connection between the ribs and plates), and the reconstruction accuracy is proportional to the degree of failure, revealing the inherent correlation between the failure characteristics and the sensitive areas of the measurement point, and providing theoretical basis and technical support for the optimization arrangement of the reconstruction measurement points of the typical structural deformation field of the ship.

To address the structural safety issues of polar ships subjected to collisions with extreme ice ridges, this study proposes a predictive framework for extreme ice ridge geometries corresponding to a 50-year return period. The model is developed based on the environmental contour method and statistical analysis of measured data from representative polar sea areas. A finite element model simulating the collision between a PC3-class icebreaker and ice ridges is established, incorporating variations in ridge scale and impact velocity. The study investigates the time histories of ice-induced impact forces, energy absorption of the hull outer plating, and stress responses of critical structural components. The results demonstrate that the consolidated layer thickness is the key parameter influencing structural response; an increase in this thickness significantly amplifies the hull’s energy absorption and stress levels. The outer plating and transverse frames are identified as the primary vulnerable components, with localized stress levels exceeding the material yield strength under the most severe scenarios. The proposed methodology, which integrates extreme ice condition modeling with structural response prediction, provides a valuable basis for the safety assessment and risk analysis of polar ships operating in harsh ice-infested environments.

To address the issues of hypervelocity impact on composite sandwich panels and the evaluation of their post-impact residual strength, this study established a numerical calculation method for the hypervelocity impact behavior of composite sandwich panels and their post-impact residual strength, which incorporates multiple failure modes. A single-point impact case was designed, and hypervelocity impact tests were conducted using 7.5 mm cubic 45# steel fragments with an impact velocity of 1200 m/s ± 5%. Subsequent axial compression tests were performed on the impacted panels to determine their residual strength. The proposed numerical calculation method was implemented in the finite element software ABAQUS for simulation. The results indicate that the errors between the experimental and simulated values of residual velocity and maximum compressive load are both within 10%, thus verifying the effectiveness of the developed numerical calculation method. Based on this validated numerical method, the influence of the number of fragments on the post-impact residual strength of the sandwich panels was further investigated. Comparative analysis across different test cases reveals two key findings: first, the position of a single impact-induced breach has no significant effect on the residual strength of the composite sandwich panels; second, as the number of breaches increases from 1 to 3, the residual strength ratio decreases progressively, with the rate of decrease accelerating.

Line-heating with water cooling is the primary forming process used in shipbuilding to manufacture steel plates with complex double curvature. Owing to its high computational efficiency and reduced trial-and-error cost, finite element simulation has become an essential tool for process optimization and forming-quality control in the fabrication of complex curved plates. However, the Gaussian surface heat source model commonly adopted in existing finite element analysis neglects the transient heat-transfer effect induced by water cooling, leading to large errors in predicted plate deformation and insufficient forming accuracy for engineering applications. To address the thermomechanical modelling challenges in the simulation of line-heating with water cooling, the full-field temperature distribution during the forming process was first measured using an infrared camera. Based on the expectation-maximization algorithm for solving Gaussian mixture models, a Gaussian mixture heat source model incorporating both the heat input and the heat extraction was established. In addition, the material hardening behavior caused by accumulated plastic deformation under repeated thermal loading was considered, accounting for the gradual increase in yield strength and tensile strength. On this basis, a simulation method capable of accurately predicting both the temperature field and deformation of plates formed by line-heating with water cooling was developed, thereby improving the accuracy of existing process simulations. Comparisons between numerical and experimental results show that, relative to the conventional Gaussian heat source model, the proposed Gaussian mixture heat source model effectively captures the rapid heat-transfer process associated with water cooling and reduces the temperature prediction error in the water-cooled region from 200 ℃ to 20 ℃. When combined with the material hardening model, the maximum prediction deviations of transverse and longitudinal deformation are reduced to 2.0% and 1.6%, respectively. The proposed method provides a reliable technical basis for high-precision ship manufacturing.

Line heating is a critical process for forming ship hull outer plates, involving complex thermo-mechanical coupling effects. The deformation process is intricate, making real-time, dynamic, and accurate prediction of its spatiotemporal evolution challenging. To address this issue, this paper proposes a CNN-Double-Layer LSTM-AM model that integrates spatiotemporal features. The model uses a single heating line as a time step to dynamically predict transverse shrinkage and angular deformation. The model incorporates key influencing factors of line heating deformation: it employs a Convolutional Neural Network (CNN) to extract spatial features from deformation data, utilizes Double-Layer Long Short-Term Memory (LSTM) networks to model both temporal dependencies among multiple heating lines within a single plate and deformation correlations between multiple plates, and introduces an Attention Mechanism (AM) to enhance feature weights of critical time steps. Results demonstrate that the model achieves a Mean Absolute Error (MAE) of 0.0383 for angular deformation prediction and an R² coefficient of 0.96 for transverse shrinkage prediction, which effectively solves the spatiotemporal dynamic evolution prediction challenge in line heating deformation processes and provides technical support for realizing closed-loop intelligent control of "processing-prediction-feedback".

During the operation of the ship propulsion shafting system, it is often excited by the friction of the water-lubricated stern bearing, which in turn induces self-excited vibration noise. The results of sea trials show that this type of vibration exhibits the characteristics of a certain order of the natural frequency of torsional vibration of the propulsion shafting system and its harmonic frequency components in the vibration spectrum. In order to explore the causes of such vibrations and propose an effective criterion formula, this study employs the finite element method to construct a nonlinear torsional vibration analysis model of the propulsion shafting system under the friction excitation of the stern bearing. The shooting method is applied to explore the influence of key parameters, such as the rotational speed of the shafting system, the structural damping ratio, the inclination degree of the shafting system, and the propeller excitation, on this vibration. The study finds that the root cause of this type of vibration lies in the existence of local torsional vibration modes near the stern bearing. The lower the rotational speed and the greater the friction force, the more likely this type of vibration is to occur. The inclination of the shafting system will increase the local friction force, thereby increasing the probability of this type of vibration. The blade frequency excitation force of the propeller will cause a sideband phenomenon in the spectrum of the self-excited vibration, that is, a series of equally spaced blade frequency components will form on both sides of the self-excited vibration frequency. Through in-depth analysis of a large amount of data, this study proposes a criterion formula to determine whether the propulsion shafting system will undergo frictional torsional self-excited vibration, and verifies the effectiveness through numerical calculations. This criterion formula can provide an important theoretical basis for the design of early fault warning mechanisms of the ship propulsion shafting system.

To address the problem of pipe flow-induced vibration caused by orifice plates, an efficient prediction method is proposed. Based on the idea of the separation solution, combined with the detailed simulation of the time-domain fluctuating pressure of the pipeline using Computational Fluid Dynamics, the time-domain excitation load is mapped through segmented integration and Fourier transformation into the frequency domain. Subsequently, the vibration response is rapidly predicted in the finite element model based on the beam theory. Compared with the three-dimensional model, it is shown that this method significantly reduces the simulation time while maintaining the calculation accuracy. The comparison with the experimental results shows that this method can accurately predict the flow-induced vibration characteristics of the orifice plate. By leveraging the efficient computing advantage of this method, the excitation source is divided into the upstream high-pressure area, the local disturbance area of the orifice plate, and the downstream strong vortex area for qualitative analysis. The results indicate that the axial force at the orifice plate end face and the circumferential force in the strong vortex area are the main excitation sources, and the other loads can be approximately ignored. The proposed method has strong universality and is applicable for the rapid prediction and design evaluation of the orifice plate structure in pipeline systems, and can also be extended to other types of pipeline accessories.