When an underwater vehicle undergoes a turning maneuver in the horizontal plane, the complex flow due to the vertical asymmetry of its hull shape (especially the sail) causes th vehicle to experience normal forces and pitching moments. This phenomenon can significantly affect the vehicle's maneuverability. In this paper, the SUBOFF model equipped with the E1619 propeller was taken as the research object, and the straight-line self-propulsion and horizontal turning simulation were carried out by combining the CFD method with rigid-body dynamics. The simulation results were in good agreement with the results from relevant literatures. By observing the distribution characteristics of the flow field around the hull, we analyzed the causes of the normal forces and pitching moments experienced by the vehicle during the turning motion, and the variation laws of the normal forces and pitching moments during the dynamic turning process of the vehicle under different rudder angles were discussed.

Using the CFD-DEM numerical simulation method, this paper predicts the hydrodynamic forces and ice forces on a ship sailing obliquely in brash ice region. The results show that, compared with the steady and stable hydrodynamic component, the ice force in the time domain exhibits characteristics of unsteady and random pulse groups. The mechanism of this feature was explained in the paper. Considering the large inertia of the ship, this paper proposed to divide the ice force into low-frequency components for motion prediction and high-frequency components for vibration and structural damage assessment based on the ship's steering frequency. Since the filtered low-frequency ice force remains random, a "random sampling method" was proposed alongside the conventional 'time averaging method', This new method extracts the ice force corresponding to different drift angles or angular velocities from the time-domain curve for analytical representation. Therefore, predicting the ship's maneuvering motion yields not a unique trajectory but a probability band instead. The paper investigates the mechanism of ice force, filtering frequency selection criteria, and a random sampling method of ice force. The findings can serve as a reference for maneuverability prediction in brash ice.

In the field of ship and ocean engineering, fluid dynamics analysis plays a crucial role in the design and optimization of marine structures. With the development of big data technologies, data-driven methods have gradually become mainstream in fluid dynamics analysis. However, existing methods have limitations in handling complex nonlinear relationships. Therefore, this paper introduced complex network science into the field of fluid dynamics, redefined the transient flow field and simplified its description through clustering methods, thus effectively captured key structures and features. Additionally, network theory was applied to describe the fluid flow process, revealing important patterns and interactions within it. Finally, a model for unsteady hydrodynamic coefficients was constructed, enabling accurate prediction and description of unsteady behaviors in fluid dynamics. This research integrates network science with fluid dynamics, providing new ideas and tools for solving complex fluid dynamics problems, particularly in the context of ship and ocean engineering applications.

Turning maneuver is a typical operational condition for underwater vehicles. This paper establishes a self-propulsion numerical simulation method for underwater vehicles based on Computational Fluid Dynamics (CFD) and conducts numerical investigations on the hydrodynamic characteristics during turning maneuvers. The proposed method employs the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations to solve the viscous flow field, while a Proportional-Derivative (PD) control algorithm and overset grid technique are applied to regulate the steering states of the vehicle, thereby enabling simulations of depth-keeping straight-line motion and complex maneuvers. Using this method, the turning maneuver process of an underwater vehicle at ±20° rudder angles was simulated, and an in-depth analysis was performed on the motion responses and flow field characteristics during starboard turning. The results demonstrate that the proposed self-propulsion numerical method effectively captures the motion responses during turning maneuvers, with simulation results agreeing well with experimental data (relative errors of key response parameters within 7%). The turning motion significantly influences the pressure field, velocity field, and vortex structures, particularly near the parallel middle body and wake region. As the heading angle gradually increases, the flow field stabilizes and reaches a quasi-steady state at approximately 180°.

The submersible waterjet propeller (SMWJP) is more efficient than conventional stern waterjet propulsion, while its thrust will be significantly reduced during high-speed maneuvering. The working process of SMWJP in high-speed yaw maneuvering was simulated under a set of stationary oblique flow conditions. Compared with straight flow, the head and efficiency of SMWJP decreased by 20% and 17.6% for oblique flow with positive oblique flow angle, and by 40% and 23.5% for that with negative oblique flow angle. Based on the entropy generation theory used to evaluate flow loss, the distribution law of entropy generation for each component of SMWJP in oblique flow was derived. Turbulent dissipative entropy generation accounts for the largest proportion of total entropy generation, reaching 60%. And entropy generation in impeller flow passages accounts for 45% of the total. The entropy generation in the inlet duct accounts for the smallest proportion, while it was more easily affected by the oblique flow angle. The oblique flow leads to the formation of low-energy vortices in the inlet tube, which invades the impeller flow channel, resulting in the expansion of the high-entropy generation area on the front edge of the suction and the top of the leaf. The turbulent dissipative entropy generation was then increased. Therefore optimizing the design of the inlet tube and reducing the sensitivity of the inlet tube to oblique flow is the key way to improve the dynamic performance of the submersible propeller.

First, based on the modified Hamiltonian principle, the nonlinear dynamic control equation of the deep-sea coarse-grained ore vertical lifting pipeline system was established. Then, the equation was discretized using the Galerkin method, converting the partial differential equation into a system of ordinary differential equations. Finally, numerical solutions were obtained for the stability characteristics of the pipeline using the eigenvalue method and Newton-Raphson iteration method. The system analyzed the influence of four key dimensionless parameters, namely the particle feed concentration, terminal lumped mass, gravity coefficient of the pipeline, and fluid velocity, on the critical flow velocity of the structure. Results show that when the feed concentration is C_v is 0.1, Hopf bifurcations occur only in the first three modes. When the feed concentration increases to C_v = 0.3, a Hopf bifurcation also occurs in the fourth mode, and the minimum critical flow velocity u_cr decreases significantly. When the internal flow velocity is below the critical value, the imaginary parts of the complex eigenfrequencies remain positive, indicating decaying structural vibrations. Once the internal flow velocity exceeds the critical threshold, the imaginary part of the first complex eigenfrequency becomes negative, signifying flutter instability. When the gravity coefficient α is held constantly, the critical flow velocity u_cr increases progressively with the dimensionless terminal mass κ₅. Conversely, with fixed κ₅, an increase in the gravity coefficient leads to a significant rise in critical flow velocity, exhibiting an approximately parabolic growth trend.

To address the insufficient analytical accuracy of traditional turbulence models in simulating ship maneuvering flow characteristics, this study proposesd a hydrodynamic derivative identification method based on the Elliptic Blending (EB) turbulence model, aiming to improve the prediction accuracy of ship motion under complex maneuvering conditions. Taking the KCS ship as the object, the performance of the k-ε turbulence model, Shear Stress Transport (SST) k-ω turbulence model and EB turbulence model was compared in terms of flow stability and vortex-resolving capability. Based on the EB turbulence model, static drift and pure yaw simulations were conducted to identify hydrodynamic derivatives, which were then input into the MMG model to predict turning motions. The EB turbulence model significantly improves the resolution of flow with strong pressure gradients near the wall by reconstructing the Reynolds stress transport equations. It accurately captures the evolution of bilge vortex clusters and asymmetric stern vortices in static drift conditions. In pure yaw motion, it effectively represents the dynamic coupling between vortex intensity and free-surface fluctuations. For the 35° rudder angle turning prediction, the average deviations of tactical diameter and steady turning diameter are only 3.34% and 1.55%, respectively, representing a maximum accuracy improvement of over 30% compared to the k-ε turbulence model. The EB turbulence model demonstrates high fidelity in simulating ship maneuvering flow characteristics, enables accurate identification of hydrodynamic derivatives, provides reliable prediction of maneuvering motions, and offers a reliable tool for the safety assessment of actual ship navigation.

Based on the 10 MW semi-submersible floating wind turbine foundation OO-Star, this study investigates the influence of wave spectrum characteristics on the dynamic behavior of floating wind turbines. A hydrodynamic analysis model of the floating wind turbine is established in ANSYS/AQWA, and hydrodynamic loads are calculated using Morison’s equation and potential-flow theory. Under identical incident wave height and peak period conditions, the effects of wave spectrum bandwidth on the hydrodynamic performance of the floating platform are analyzed. The surge and pitch responses of the turbine increase significantly with broader wave spectra, with peak amplitudes increasing by over 50%. Meanwhile, surge and pitch motions are distributed over a wider displacement range, indicating greater variability in motion response. Statistical values for heave response show little variation across different spectral bandwidths, suggesting a limited influence of spectrum width on heave motion. As spectral bandwidth increases, mooring line tension rises markedly and exhibits greater variation, potentially, exacerbating fatigue damage in the mooring system.

To establish an intelligent prediction method for internal shock environments of shipboard cabinet-type equipment, this study conducted shock tests on typical shipboard electrical cabinets to verify the reliability of numerical calculation methods. Based on industry survey data, a parametric simplified model of cabinet-type equipment was established. Using Abaqus secondary development, a batch finite element analysis platform was constructed, successfully obtaining 1000 complete datasets containing structural parameters, shock loads, and dynamic responses. To address the limitations of traditional regression models, an innovative deep neural network (DNN) shock response prediction model was developed, creating dedicated prediction networks for spectral acceleration, spectral velocity and spectral displacement. Through grid search algorithm optimization of network topology, a coefficient of determination R² > 0.9 was achieved, with the mean absolute error of spectral acceleration prediction being 0.14, while spectral velocity and spectral displacement prediction errors were both below 0.1. The SHAP (SHapley Additive exPlanations) interpretability analysis method was introduced, revealing that installation frequency, spectral velocity of foundation shock environment and plate thickness are dominant factors in shock responses, clarifying the coupling mechanism between structural parameters and shock loads. The research results provide efficient analysis tools and theoretical support for shock-resistant design of shipboard equipment.

At present, submarine propulsion shafts are gradually developing towards shorter shafts, and they have features such as multi-segment, variable cross-section, and variable bearing oil-film stiffness. The existing analytical methods are mostly based on uniform beam theory, which has limitations in solving multi-segment and variable cross-section shaft systems. To address this issue, this paper proposes an analytical calculation method for the modal and vibration transmission of multi-segment, variable cross-section, and variable stiffness-supported propulsion shaft systems based on the Timoshenko beam vibration theory. This method has high solution efficiency and good agreement with finite element results. Based on this theoretical model and calculation method, the paper studies the influence of bearing stiffness variation, bearing simulation methods and bearing span on the vibration characteristics of complex propulsion shaft systems. The results show that this analytical method is highly practical and can effectively consider the influence of the variation in bearing oil film stiffness on the vibration of the shafting system. The main manifestation is that as the bearing speed and frequency increase, the bearing stiffness decreases and the natural frequency of the propeller shaft reduces. In addition, when modeling the shafting system, it is recommended that the number of simulated springs for the bearing be more than two, and the bearing span should not be too large. It should be selected based on the effective length of the actual bearing; otherwise, the deviation of each natural frequency will increase.

Deepwater mooring systems are critical infrastructure for semi-submersible platforms, directly influencing their operational safety and stable operation. Traditional steel-chain mooring systems are increasingly inadequate for meeting the urgent demands of deepwater and ultra-deepwater marine resource development, primarily due to their inherent limitations such as high self-weight and susceptibility to corrosion. Carbon fiber reinforced polymer (CFRP) composites, which possess exceptional properties including light weight, high strength, high-temperature resistance, corrosion resistance, fatigue resistance and durability, provide a new solution for the configuration design and engineering application of mooring systems for deepwater semi-submersible platforms. Taking a deepwater semi-submersible platform in the South China Sea as the research object, this study proposes a novel three-segment mooring configuration consisting of steel chain–CFRP cable–steel chain, and further constructs two three-segment mooring systems, namely steel chain–CFRP cable–steel chain and steel chain–polyester cable–steel chain. A coupled hydrodynamic analysis model of the large floating platform–mooring system was established, and the dynamic response characteristics of the two mooring configurations including mooring tension, fatigue damage and platform motions were comparatively investigated through numerical simulations. The results indicate that compared with the polyester cable mooring configuration, the CFRP cable mooring configuration exhibits higher overall stiffness and lower natural periods in surge, sway, roll, pitch, and yaw. Under extreme wave conditions, it shows better performance in restraining platform motions, thereby leading to higher platform stability and operational reliability. Notably, the fatigue damage of the CFRP mooring cable is much lower than that of the polyester cable; however, the use of CFRP cable increases the fatigue damage of the steel chains at both ends, especially that of the bottom steel chain. These findings reveal the dynamic response characteristics of a deepwater semi-submersible platform under a CFRP mooring system, preliminarily verify the feasibility and superior performance of CFRP cables in deepwater semi-submersible platform mooring systems, and provide important data support and reference for innovative mooring scheme design and engineering applications.

To address the severe shock protection requirements of marine heavy equipment, this paper proposes a metal rubber impact isolator featuring both high-temperature resistance and corrosion resistance, capable of meeting operational requirements in complex marine environments. The isolator adopts a series-parallel combination of multiple metal rubber components as its cushioning and energy-absorbing elements, which ensures a high load-bearing capacity while achieving a favorable linear elastic working range. Additionally, the stiffness and damping characteristics are adjusted by means of parallel linear springs. A dynamic model of the impact isolator is established to analyze the influence of stiffness and damping on its shock isolation performance. The mechanical properties and impact resistance of the isolator are verified through experimental tests. Experimental results demonstrate that the isolator exhibits excellent linear elasticity within a stroke of ±9 mm, with an average stiffness of 7.45×10⁶ N/m, an equivalent damping ratio of approximately 0.43, and a limit load capacity of 6.5 t. Under the impact of a 2.2 t drop hammer falling freely from a height of 8.6 mm, the impact loss factor reaches 1.03 and the shock transmissibility is 0.0038, indicating excellent impact resistance performance. This study will provide a reference for the design of impact isolators for marine heavy equipment.

Aiming at the ultimate bearing capacity problem of I-type metal sandwich panels under in-plane compressive loads, a series of nonlinear finite element calculations were carried out for I-type metal sandwich panels examples. The typical failure modes and ultimate bearing capacity were analyzed. The calculation results show that the main failure modes are yielding or overall collapse caused by local panel buckling. The compressive ultimate strength is highly correlated with the flexibility of the face plates and core plates. Based on this, a simplified method for calculating the ultimate stress by superimposing the stresses of the face sheets and core plates is proposed. Compared with the nonlinear finite element results, the simplified method yields a mean relative error of −5.53%, and a deviation of 5.45% from published model test data, indicating good accuracy. This method can provide technical support for the rapid prediction of the ultimate strength and the design of configuration parameters of I-type metal sandwich panels.

The prediction accuracy and control effectiveness of hydrodynamic noise for underwater vehicles directly impact their overall performance. Accurately grasping the distribution characteristics of pulsating pressure is the fundamental and critical basis for assessing hydrodynamic noise levels and conducting low-noise design. This study takes an axisymmetric underwater structure as the research object, conducts numerical simulations of pulsating pressures based on Large Eddy Simulation (LES), and analyzes their distribution patterns in different regions. Using the Q-criterion, the vortex structures in various typical regions of the axisymmetric structure are captured and the characteristics of pulsating pressures in each region are analyzed in conjunction with vorticity distribution. By comparing the simulated pulsating pressure results with experimental data, the accuracy of the simulation method was verified. Based on this, research on pulsating pressure control methods in the flank array region of an underwater vehicle was conducted, and it proposes adding a guide fillet at the transition position between the front end of the flank array and the hull. The study shows that this measure can effectively suppress the horseshoe vortex induced by the geometric discontinuity of the flank array, reducing the overall pulsating pressure level at typical locations by over 5 dB.