Aiming at the difficuties of fatigue evaluation of slamming stress response for high-speed ships, this study analyzes the stress response and fatigue damage based on the measured data of the bow of a small high-speed aluminum alloy ship, by combining with fatigue tests on two typical longitudinal bulkhead-penetrating structures, with the linear cumulative damage theory. The research confirms that the stress response under slamming pressure exhibits obvious impact characteristics, and the stress amplitude no longer follows the Rayleigh distribution. The results show that fatigue cracks may occur at the measuring points after 212 hours of continuous navigation under the test conditions. This achievement deepens the understanding of the dynamic characteristics of slamming stress and provides a reference for the anti-fatigue design of longitudinal bulkhead-penetrating structures of high-speed aluminum alloy ships.

With the widespread application of composite materials in aerospace, shipbuilding, and automotive fields, optimizing the performance of their connecting structures has become a key challenge. This article focuses on three types of composite connections: adhesive bonding, bolted connection, and adhesive-bolted hybrid. The influence of parameters such as adhesive layer thickness, bolt preload, and porosity on the mechanical properties of joints was systematically analyzed through a combination of experiments and numerical simulations. The key parameters are optimized based on Response Surface Methodology (RSM). The research results indicate that increasing the thickness of the adhesive layer leads to intensified deformation but has no significant monotonic effect on the ultimate bearing capacity. The optimal balance between stiffness and strength is achieved when the pre-tightening force of the bolt is 3.0 N·m, while the ultimate load close to the low porosity structure can still be achieved through deformation compensation mechanism when the porosity is 100%. The adhesive-bolted hybrid joint combines the stress dispersion of adhesive bonding with the anti-stripping characteristics of bolts, and its ultimate load is increased by 17% to 40% compared with a single connection form. The quadratic polynomial model established based on the improved response surface method identified the optimal parameter combination was adhesive thickness of 0.58 mm, pre-tension force of 3.1 N·m, and porosity of 93.0%.

Polymethyl Methacrylate (PMMA) has become a key material for pressure-resistant shells of full-view manned submersibles due to its high transparency, light weight and excellent pressure resistance. However, the viscoelastic creep behavior of PMMA material itself has a significant impact on the long-term reliability of the structure. Therefore, the creep buckling mechanism of PMMA pressure spherical shells and their remaining ultimate load carrying capacity were investigated based on the viscoelastic properties of PMMA. Firstly, the non-linear influence law of stress level and time on the creep behavior of PMMA was revealed through creep tensile tests. Based on short-term test data, creep curves applicable to different stress levels were obtained by applying the time-stress equivalence principle while the applicability of the Burgers model and the modified Burgers model was discussed and analyzed. Subsequently, based on the modified Burgers model and numerical simulations, the influence of key factors, like initial geometric defects, the thickness-to-diameter ratio and working depth on the residual ultimate load of spherical shells after different creep durations was analyzed. The research results can provide certain theoretical basis and data support for the design, safety assessment and life prediction of full-view PMMA pressure-resistant structures.

To improve the efficiency and accuracy of ultimate-bending-moment estimation for complex non-symmetric hull sections, a hybrid method integrating genetic-enhanced Bayesian optimization with an improved Smith stepwise failure procedure was proposed. Firstly, for a given section curvature and increment, Latin hypercube sampling was used to generate an initial design and train a Gaussian process (Kriging) surrogate. Based on the surrogate’s posterior mean and variance, an Expected Improvement (EI) acquisition function was constructed, and a genetic algorithm was then employed to maximize EI and select candidate sampling points, thereby enhancing global search capability while keeping the number of high-fidelity evaluations small. Selected candidates were subsequently refined by a constrained derivative-free local optimizer and their high-fidelity evaluations were incorporated into the training set to iteratively update the surrogate, ensuring accurate local search in regions near global optima. With the Dow 1/3-scale frigate model adopted as a test case, the ultimate bending moments under intact and damaged conditions were computed using the traditional Smith method, a PSO-Smith variant and the proposed approach. Results show that the proposed method could precisely resolve the ultimate bending moments for non-symmetric sections, and that, compared with the PSO-Smith approach, it improves computational accuracy by approximately 2% and increases computational efficiency by about 90%, validating its effectiveness and strong potential for engineering applications.

Accurate prediction of radiated sound fields from underwater structures with limited measurement points is crucial for vibration and noise reduction studies. This paper presents an investigation on a rectangular plate and the proposal of a measurement point arrangement strategy based on Gaussian integration point distribution. The surface vibration velocity field of the structure was reconstructed using an L₁ norm sparse solution, and the acoustic radiation sound field was predicted through vibro-acoustic transfer functions. Under the constraint of limited measurement points, the effects of truncated modal order, number of measurement points, and their arrangement on the prediction accuracy of the radiated sound field were analyzed. Results show that, within the mid-to-low frequency range, the Gaussian integration point distribution strategy optimizes sensor placement. Compared with traditional uniformly distributed measurement methods, the proposed strategy could achieve an accurate prediction of the radiated sound field with fewer measurement points, providing theoretical support for engineering applications involving sound field prediction under limited sensor conditions.

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.