The real-time prediction of ship motion is one of the key technologies to ensure safe and efficient navigation of ships. Based on the Higher Order Dynamic Mode Decomposition (HODMD) algorithm, this paper constructs an improved Reduced-Order Model (ROM) for real-time prediction of ship maneuvering motion. The improved ROM enhances the correlation between maneuvering motion parameters of similar frequencies by separately incorporatng the parameters into high-frequency and low-frequency input samples according to their frequency features. The prediction of ship maneuvering motion under environmental influences is conducted by using the ship motion data of a 35° turning circle maneuver of the ship YUKUN at sea. The comparative analysis of prediction accuracy between the improved ROM and the original ROM shows that the improved ROM exhibits significantly higher accuracy in predicting low-frequency motion and a slight improvement in predicting high-frequency motion compared to the original ROM.

In this paper, the large eddy simulation and level-set/volume-of-fluid (CLSVOF) coupled interface capture method is used to calculate the ventilated cavity flow of porous flat plate under two wall contact angles (90° and 160°), and the influence of wall superhydrophobicity on the development characteristics of ventilated cavity fusion of flat plate is studied. The results show that compared with the typical experimental results, the numerical calculation method can better simulate the shape of ventilated cavitation and the wall superhydrophobicity. Compared with the flat plate with a contact angle of 90°, it is found that the flat plate with a contact angle of 160° will have a near-wall velocity slip phenomenon, which will increase the spanwise velocity of the cavity and promote the fusion of the cavity, so that the position of the cavity fusion is advanced by 41%. The pressure fluctuation of the cavity after fusion is smaller, and the resistance of the plate with a contact angle of 160° is smaller than that of the plate with a contact angle of 90°.

The propulsion shaft system of a ship is a critical component of the powertrain, subjected to direct contact between the shaft and bearing under various operating conditions, such as low speed, heavy load, and startup/shutdown phases. These conditions can lead to friction-induced vibrations and even result in issues such as flutter and noise. In this paper, a four-degree-of-freedom coupled model of the ship propulsion shaft system is developed on the basis of modal coupling theory to investigate the modal coupling phenomenon in detail. A combined complex modal analysis and the fourth-order Runge-Kutta method are applied to analyze modal coupling instability and identify the critical friction factor. The results indicate that the minimum critical friction coefficient is a crucial parameter influencing the stability of the system. The impact of both proportional and non-proportional damping conditions on the critical friction coefficient is examined. Furthermore, the effects of various damping parameters on the modal coupling instability of the system is summarized. These findings provide important theoretical support for vibration control and stability optimization in propulsion shaft systems, significant value for advancing theoretical models and optimizing practical engineering applications.

The classical finite element method (FEM) is known to suffer from significant accuracy degradation under large wavenumber conditions due to dispersion error effects. Furthermore, the reliability of FEM solutions heavily depends on mesh quality, particularly in regions with steep gradient fields or complex geometric features. While high-quality meshes are essential for obtaining credible results, their generation remains computationally intensive and time-consuming. To address these limitations, this study proposes a modified radial point interpolation meshless method (MRPIM) for three-dimensional acoustic-structure interaction analysis. By introducing a novel interpolation node selection scheme, the method constructs continuous approximation functions within individual integration cells, effectively reducing numerical integration errors. Results demonstrate that the modified method achieves notable improvements in computational accuracy compared to the conventional method (RPIM) while exhibiting superior efficiency. Additionally, the computational overhead of MRPIM is comparable to that of FEM, highlighting its promising potential for engineering applications.

Flow-Induced Vibration (FIV) energy harvesting is an effective approach for harnessing low-velocity ocean currents. Using a maglev support system to replace traditional metal springs enables better stiffness adjustment and improves underwater operation and maintenance performance. To enhance energy output and stability, dual-oscillator designs are widely used in vortex-induced vibration energy harvesters. However, the vibration characteristics of dual oscillators supported by maglev systems remain underexplored. This study establishes a coupled numerical model that integrates the FIV of rigid cylindrical oscillators with a maglev support system to investigate the influence of the spacing ratio (G/D) on their vibration responses. Results show that a smaller spacing ratio (G/D=2) intensifies hydrodynamic interactions, leading to a downstream oscillator's amplitude reaching over twice that of a single oscillator. The oscillation frequencies decrease monotonically with increasing spacing ratios, and distinct frequency variation patterns are observed between upstream and downstream oscillators. Vortex analysis reveals that the upstream wake reconstructs the flow field and strengthens the excitation forces on the downstream oscillator, thereby amplifying its vibration response. The maglev effect enhances the oscillators' responsiveness to flow field changes through nonlinear magnetic forces, further improving vibration performance and system stability. This study provides theoretical insights for optimizing dual-oscillator FIV energy harvesters with maglev support.

The phenomenon of flow-induced vibrations with small amplitude and strong fluid-structure interaction is commonly found in both nature and engineering practice. This paper proposes a frozen boundary method, which keeps the boundary fixed and represents the boundary vibration effects using mass sources and momentum sources. This method is applied to calculate forced vibrations and vortex-induced vibrations of a circular cylinder with a single degree of freedom. The results show that in forced vibrations, the frozen boundary method improves computation speed compared to the dynamic mesh method while ensuring calculation accuracy, thus validating the reliability of the method. For the single degree of freedom vortex-induced vibration of the circular cylinder, the phenomenon of lock-in was successfully computed. Due to the resonance effects within the lock-in region, the lateral fluctuations of the cylinder's wake field are considerable. The wake-vortex lock-in results from the competition between the vibrating vortex system and the detached vortex system. When the vibrating vortex system dominates, it manifests as frequency locking, leading to resonance. The frozen boundary method provides a new perspective and implementation approach for calculating fluid-structure interaction problems.

In order to establish a comprehensive planar Real-Time Nearfield Acoustic Holography (RT-NAH) system and effectively avoid overdependence on the Laplace transform table when deriving impulse response functions, an alternative method based on the Rayleigh integral is proposed. Firstly, the pressure-pressure, normal velocity-pressure, normal acceleration-pressure, and normal displacement-pressure impulse response functions are systematically derived based on the Rayleigh integral. Then, a comprehensive planar RT-NAH system is constructed based on the obtained impulse response functions. Finally, simulation of a simply supported thin aluminum plate is performed to evaluate the correctness of the derived impulse response functions. The analysis of the reconstruction results demonstrates that high accuracy is achieved when reconstructing pressure and normal velocity, whereas relatively lower accuracy is observed for normal acceleration and displacement. The primary factors contributing to the lower accuracy when reconstructing the normal acceleration and displacement are further investigated.

Sloshing experiment is crucial to determine the reaction performance of regeneration columns on an offshore floating platform. A novel type of column motion simulating device and a Marine Predator Algorithm-based Sliding Mode Controller (MPA-SMC) are proposed for such sloshing experiments. The simulator consists of a Stewart platform and a steel framework. The Stewart platform is located at the column's center of gravity (CoG) and supported by the steel framework. The platform's hydraulic servo system is controlled by a sliding mode controller with parameters optimized by MPA to improve robustness and precision. A numerical sloshing experiment is conducted using the proposed device and controller. The results show that the novel motion simulator has lower torque during the column sloshes, and the proposed controller performs better than a well-tuned PID controller in terms of target tracking precision and anti-interference capability.

In order to understand the influence of bow shape on ice resistance and provide guidelines for hull line design in the early design stage, an investigation of the impact of bow shape on ice resistance for the Arctic LNG carriers is carried out based on semi-empirical methods. Firstly, some typical semi-empirical formulas developed for ice resistance estimation of cargo carriers in different ice conditions are summarized. Then, formulas appropriate for ice resistance estimation of Arctic LNG carriers under different ice conditions are verified according to the result comparison between semi-empirical formulas and experimental tests. The comparison result indicates that the Lindqvist formula is appropriate for ice resistance estimation in level ice conditions, Zuev and Dobrodeev formula for ice resistance estimation in broken ice conditions, and Dobrodeev formula for ice resistance estimation in brash ice conditions. After that, the parameters considered in the selected formulas are summarized, and the influence of critical parameters on ice resistance is analyzed. Some parameters describing the ship's bow shape characteristic like ship breadth, waterline angle and stem angle greatly influence the ice resistance. Ice resistance increases with both the growth of ship breadth under all ice conditions and the growth of stem angle in level ice and broken ice conditions while ice resistance decreases with the development of waterline angle under all ice conditions. Finally, the optimization of the bow shape is discussed, and an optimized bow shape with both a large waterline angle and low stem angle is proposed. The optimized bow shape can decrease ice resistance by 9.9% in the level ice condition and reduce ice resistance by 11.3% in the brash ice condition.

High-static-low-dynamic stiffness (HSLDS) vibration isolators have been demonstrated to be an effective means of attenuating low-frequency vibrations, and may be utilized for ship shafting applications to mitigate torsional vibration. This paper presents the construction of a highly compact HSLDS torsional vibration isolator by connecting positive and negative stiffness components in parallel. Based on mechanical model analysis, the restoring torque of negative stiffness components is derived from their springs and connecting rods, while that of positive stiffness components is obtained through their circular section flexible rods. The quasi-zero stiffness characteristics of the HSLDS isolator are achieved through a combination of static structural simulation and experimental test. The torsional vibration isolation performance is assessed by means of numerical simulation and theory analysis. Finally, the frequency-sweep vibration test is conducted. The test results indicate that the HSLDS torsional vibration isolator exhibits superior low-frequency isolation performance compared to its linear counterpart, rendering it a promising solution for mitigating low-frequency torsional vibration in ship shafting.