The flexible boundary constraints have a significant effect on the vibration characteristics of rectangular stiffened plates excited by turbulent boundary layer. In this paper, springs were used to simulate flexible boundary constraints. The response function of an underwater rectangular plate was derived based on the energy principle, combined with the power spectra density expression caused by turbulent boundary layer, and the power spectral density of the plate velocity was obtained. It is shown that the boundary spring stiffness has an effect on the response of the plate. As the spring stiffness of the boundary displacement increases, the vibration response of the plate at low frequencies decreases. The effect of the boundary spring stiffness on the vibration response of plate excited by TBL converges when the boundary displacement spring stiffness k_d is larger than 10¹⁰ N/m². The effect of stiffened rib direction and the number of stiffened ribs on the vibration response of stiffened plate was also studied in this paper. Compared with an unreinforced plate, the vibration response of a stiffened plate at low frequency was effectively reduced. The results can serve as a theoretical reference for the analysis of the vibration characteristics of rectangular stiffened plates excited by turbulent boundary layer under flexible boundary constraints.

There is a strong coherence between random wind and wave environment elements, which not only affects the synchronization and intensities of fluctuating wind and random wave in combined wind-wave propagation process, and but also affects the accurate calculations of combined wind-wave action on offshore structures. Therefore, based on the CFD numerical simulation methods of random wave and fluctuating wind fields, a numerical flume for simulations of combined wind-wave propagation was established, then a series of numerical simulations of combined propagation of fluctuating wind and random wave were carried out. Based on the analysis of numerical results, the influences of wind speed position height, significant wave height, wave peak frequency and basic wind speed on the coherence between wind and wave were explored. According to the influence characteristics of these factors, a calculation function model of wind-wave coherence value of combined wind-wave propagation was proposed. Then, the parameters of the coherence function model were determined by a series of numerical fits according to the numerical results under various influencing factors. Based on this, a concrete calculation expression describing the coherence value of combined wind-wave propagation was established.

Underwater target azimuth estimation is a critical technology in array signal processing, with wide applications in military operations, marine resource development, and environmental monitoring. A comprehensive review of the current development status of underwater target azimuth estimation methods is provided in this paper. Firstly, an introduction to the acoustic mathematical model based on an uniformly distributed sound pressure line array was given. Next, azimuth estimation methods are classified into four categories: classical beamforming, statistical, subspace, and AI-based Direction of Arrival (DOA) estimation methods. Key factors affecting azimuth estimation accuracy, such as array calibration errors, array geometry, signal processing techniques, and underwater acoustic channel characteristics, were also analyzed. Finally, the paper discussed the limitations of current azimuth estimation technologies and proposed future research directions, including multimodal data fusion, integration of deep learning with physical models, and the development of new array structures etc, to enhance the accuracy and robustness of underwater azimuth estimation.

The volume fraction equation is an important control equation for multiphase flow such as cavitation, which is derived from the mass conservation equation in incompressible cases. However, there is currently no universally recognized descriptive form for compressible fluids. The paper uses the body-fixed coordinate system as a reference frame to describe the problem, focusing on local fluid units. Starting from the volume changes of multiphase fluids, the relationship between the body derivative of volume fraction and the local average velocity divergence of each phase fluid is derived. The article also discusses the relationship between the volume fraction equation and the mass conservation equation, as well as the influence of phase transition and compressibility on the evolution of volume fraction. The forms of the volume fraction equations under two-phase pressure equilibrium are provided.

To investigate the turning maneuverability of polar ships in floating ice area, in this study a combined CFD-DEM approach was adopted to numerically simulate the turning motion process of a medium-sized polar ship in floating ice area. In the simulation the ship’s turning motion at different rudder angles and ice concentrations have been considered, and the parameters of the ship’s turning motion have been predicted. The results show that the existence of floating ice will significantly hinder the ship’s turning motion, and the range of the tactical diameter in floating ice area is 1 to 1.5 times than that in open water conditions. The forces and moments acting on the hull exhibit strong randomness, and the instantaneous fluctuations of the ship’s speed and yaw rate are more pronounced. At the same rudder angle, the ice longitudinal force increases with the increase of ice concentration, while the variation of the fluid longitudinal force is not significant. The average total lateral force and total yawing moment are in the same direction as the turning maneuver, while the average ice yawing moment tends to be in the opposite direction.

In order to study the interference characteristics between multiple wingsails on sail-assisted vessels during navigation, a lateral arrangement scheme of a two-element wingsail based on the relative wind direction angle was designed. The Reynolds averaged N-S equation was used for numerical simulation under steady conditions. The aerodynamic interference performance of the two-element wingsail was analyzed, and an optimization scheme for the angle of attack and flap deflection angle was proposed to address the stall problem caused by the interference of multi-sails. Furthermore, the interstage interference characteristics of wingsails were obtained. The results show that, in the single row arrangement scheme, the optimal spacing is 1.5c for relative wind angles of 30°, 90°, and 120°. However, the interstage interference can cause the wingsail to stall at the relative wind angles of 90° and 120°. After optimization, the auxiliary thrust coefficient can be increased by more than 5.2%, and the flow separation on the downstream wingsail disappears.

Tip clearance flow is a complex phenomenon that occurs between the rotor blade tip and the inner surface of the duct of a pump-jet propulsor. The tip clearance size significantly influences both the tip clearance flow and the performance of the pump-jet propulsor. Previous studies on tip clearance flow primarily focused on cases with tip clearance sizes less than 4 mm on model scale. Tip clearance flow of pump-jet propulsors with tip clearance sizes of 1 mm and 16 mm were simulated based on large eddy simulation in this paper. The study focuses on the characteristics of tip clearance flow in the large tip clearance pump-jet propulsor and the effects on cavitation inception, hydrodynamic performance, and duct pressure fluctuation. The results indicate that, compared to smaller tip clearance, the starting position of tip-separation vortex of pump-jet propulsor with large tip clearance is closer to the leading edge of rotor, while the intersection position of tip-separation vortex and tip-leakage vortex is closer to the trailing edge of rotor. Furthermore, the propulsion efficiency of the pump-jet propulsor behind SUBOFF is reduced by approximately 10%. The vorticity and circulation of tip-leakage vortex are larger, and cavitation inception of tip-leakage vortex occurs earlier. The amplitude of fluctuating pressure on duct inner surface is significantly decreased by about 80%. Therefore, the design of the pump-jet propulsor should be made based on comprehensive balance of the above-mentioned performance characteristics to find the optimal tip clearance size.

Uniaxial compressive strengths tests were carried out in the field and in the low-temperature laboratory to investigate the mechanical properties of granular sea ice, with a strain rates ranging from 10⁻⁵ s⁻¹ to 10⁻² s⁻¹. The test temperatures were set at −3 ℃, −5 ℃, −7 ℃, −10 ℃, and −15 ℃, respectively. The loading direction was parallel to the ice surface. The test results show that the uniaxial compressive strength of sea ice increases with the strain rate in the ductile zone, decreases with the increase of the strain rate in the brittle zone, and reaches its peak in the ductile-brittle transition zone. Comparing the ice temperature-peak strength curve with historical data, it is found that the peak of compressive strength of granular sea ice in Bohai is relatively low, and increases with the decrease of ice temperature, but its upward trend gradually slows down, which reflects the influence of sea ice crystal structure on ice mechanical properties. The sea ice porosity was introduced to establish the statistical relationship between sea ice uniaxial compressive strength and strain rate, as well as porosity, across a wide strain-rate range. The feasibility of a unified mathematical description for mechanical properties of Bohai Sea ice and polar sea ice was discussed.

In order to study the thrust deduction of waterjet propelled high-speed amphibious platform, the self-propulsion flow field of the platform was solved, based on RANS equations and VOF model. The trim and heave motion of the platform were calculated by adopting overlapping grid method, and the effect of waterjet pump was simplified using body force method to realize the numerical simulation of self-propulsion of waterjet propelled high-speed amphibious platform. The inlet surface of the propeller was obtained by streamline tracing method, and the total thrust of the propeller was calculated by momentum flux method. The results show that the thrust deduction fraction of amphibious platform exhibits different characteristics at different speeds. At low speed, the thrust deduction fraction is positive. Negative thrust deduction occurs at medium and high speeds. In the whole speed range, the resistance increment is always positive and the jet thrust deduction fraction is always negative. The reason for the negative thrust deduction at medium and high speeds is that the resistance increment decreases gradually with the increase of speed and approaches zero.

Ribbed plate structures are widely used in ship structural design due to their high structural stiffness and strength. In this paper, based on the frequency band analysis model of ribbed plates and the statistical energy analysis (SEA) parameter calculation method of the acoustic cavity subsystem, a calculation model of the radiation efficiency between the ribbed plate structure and the acoustic cavity was established, and the influence of fluid load was taken into account, thus the method for calculating the coupling loss factor of an underwater ribbed plate with an acoustic cavity was obtained. Further, the calculation method was verified by using SEA commercial software. The effects of fluid load and structural reinforcement on the coupling characteristics were studied and analyzed. The results show that the fluid load and structural reinforcement mainly affect the radiation efficiency and coupling loss factor in the frequency band below the cut-off frequency of the coupling structure, and have little effect on that in the frequency band above the cut-off frequency. The research results of this paper can provide theoretical support for the prediction of ship cabin noise and acoustic design.