During maritime operations, ships are subject to wave-induced disturbances, resulting in complex multi-degree-of-freedom motions that severely affect the stability of ships during offshore operations. To address this challenge, this study proposes a CNN-BiLSTM hybrid prediction model for real-time ship attitude forecasting and designs a dual-layer Stewart platform compensation mechanism to mitigate ship motion effects. To overcome sensor latency and noise interference, 2011 ship attitude samples collected in the South China Sea were first filtered using a Savitzky-Golay (SG) filter. The processed data were then fed into the CNN-BiLSTM hybrid prediction model, which significantly improved the accuracy of attitude prediction. Furthermore, a platform kinematic model was established using the closed-loop vector method. The predicted data were utilized to compensate the dual-layer Stewart platform, enabling coordinated control between the lower platform (simulating wave disturbances) and the upper platform (performing dynamic compensation). Experimental results demonstrate that the proposed approach achieves effective ship attitude compensation and provides a feasible solution for stable landing operations of unmanned aerial vehicles (UAVs) at sea.

In order to predict the second-order force and moment of ships sailing in waves, the fluid domain is decomposed into two parts (where the steady flow effects are considered in the internal one), and a multi-domain coupled hydrodynamic model is established based on the continuity of the flow field. Then a higher-order coupled method is developed, in which nine-node quadratic elements are employed to discretize the boundary, Rankine source is adopted to deal with the complex boundary condition near the ship and higher-order translating-pulsating panel source Green’s function (i.e., analytical integral of the Green’s function over the higher-order panel) is derived over the control surface. On this basis, formulas for second-order force and moment in oblique waves are established under the weak scattering assumption. A numerical program is developed to calculate and analyze the second-order wave forces in surge/sway and yaw moment of various ships advancing in different wave directions. The results show that the present method is more stable and accurate than the traditional higher-order translating-pulsating source method based on Gaussian quadrature formula, as well as the lower-order constant panel method. It is generally applicable to different ship types sailing in both head and oblique waves.

In turbulent channel flows, traditional Detached Eddy Simulation (DES) methods suffer from significant deficiencies in capturing detailed turbulent structures due to the improper allocation of modeling scales. DDES models fail to accurately predict the streamwise mean velocity and are prone to the problem of logarithmic layer mismatch. Although IDDES provides some improvements, it still shows considerable discrepancies in the prediction of second-order statistical quantities. As an improved hybrid approach, the Wall-Modelled Hybrid RANS-LES (WM-HRL) framework addresses this limitation by employing a predefined partitioning strategy to rationally allocate modeling scales between RANS and LES regions. This study systematically investigates the performance of the WM-HRL model in turbulent channel flow and compares its results with those obtained from DDES, IDDES, and direct numerical simulation (DNS) data. The findings demonstrate that the WM-HRL model can more accurately predict near-wall turbulent structures and Reynolds stress distributions, effectively overcoming the limitations of traditional DES methods in the near-wall region.

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.

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.

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.

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.

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.