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.

Marine operations, such as takeoff and landing of carrier-based aircraft, ship fuel supply, and ship lifting operations, have strict requirements for the movement of ships and need to be carried out within the quiescent period window to ensure operational safety. However, the incidence probability of a quiescent period window under high sea conditions is relatively low. Therefore, it is crucial to assess the probability of the target sea area’s quiescent period in advance for the planning and deployment of offshore operations. This article establishes a ship motion probability model based on the statistical characteristics of ship motion to study the short-term statistical characteristics of quiescent periods. Simulation data is used to verify the statistical characteristics of motion, the joint statistical features of motion amplitude-period, proving the accuracy of the model. Subsequently, the probability of continuous small movements below the operational threshold during the quiescent period have been analyzed. The results indicate that the established ship motion probability model and the ship continuous small amplitude motion probability model can accurately reflect the motion characteristics and probability of quiescent periods of ships under corresponding sea conditions. This study can provide the probability of a quiescent period meeting the operational requirements before the ship enters a certain sea area for operation, and also provide the probability of a quiescent period occurring in a certain period of time before the operation, providing auxiliary decision-making for the navigation operation plan of offshore ships.

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.

This paper investigates the characteristics of the flow field induced by a supersonic jet at the tail of an underwater axisymmetric vehicles under different pressure ratio conditions, based on the volume of fluid (VOF) multiphase flow model. The study analyzes the evolution of the flow field at the tail of the axisymmetric vehicles and explores the morphological distribution of the induced cavity at various time instances under different pressure ratios. The research findings indicate a close relationship between the jet’s tail cavity morphology and the nozzle pressure ratio. When the pressure ratio is relatively low, the tail cavity exhibits a conical shape similar to the supercavitation. As the pressure ratio increases, the influence of the tail vortex on the jet gradually diminishes, and the high-pressure ratio jet evolves into a pulsating jet under the action of shear entrainment driven by the Kelvin-Helmholtz instability. Within the pulsating jet flow field, phenomena such as “back-attack” and pressure disturbances in the water medium lead to a “positive feedback” effect on the pulsation characteristics of the jet. After the high-pressure ratio jet transforms into a pulsating jet, the degree of jet necking fluctuates significantly with time, and the initial bubble breakup results in a random distribution of the jet necking location with time. With a further increase in pressure ratio, the morphology of the pulsating tail cavity tends to stabilize, and the pressure fluctuation amplitude at the bottom of the axisymmetric vehicles decreases.

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.

The grid fins underwater launch technology scheme can increase the motion stability of underwater vehicles, which is one of the effective ways to improve the adaptability of the vehicles to the launch environment conditions. Aiming at the dynamic deployment process of the grid fins underwater application, the mathematical model of the kinematic parameters of the deployment process was established, and the ground deployment mechanism verification test of the grid fins was designed. The scene of the deployment process of the grid fins in the air medium and the water medium, the variation law of the motion parameters and the deployment time were studied. The influence of the water medium on the parameters of the deployment process of the grid fins was obtained, providing useful experience for the analysis of the dynamic deployment process of the underwater grid fins and the analysis of the motion parameters of the deployment process.

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.

The failure analysis of marine brittle materials under dynamic load has always been the focus of academic and engineering fields. A state-based peridynamic (PD) model for the failure in brittle materials was established based on the state-based PD. In the model, a quartic polynomial influence function was introduced to reflect the PD long-range force attenuation, and an energy-based failure criterion was given. The accuracy of the model was verified by comparing a series of numerical results with experimental results. The effects of biaxial load ratio, Poisson’s ratio, central pre-crack length and pre-crack angle on the failure of brittle solids were studied. The results show that the change of biaxial load ratio or pre-crack angle can affect the crack propagation direction; the biaxial load ratio or Poisson’s ratio leads to crack branches in the main crack path. Moreover, the increase of load ratio or Poisson’s ratio improves the dynamic load resistance of the specimen, while the increase of prefabricated crack length or angle reduces the dynamic load resistance of brittle solids.

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.

For ships with large outboard flare structures, severe slamming is likely to occur in rough sea conditions, resulting in short-duration slamming moment in the ship’s midship region with an amplitude comparable to the wave moment. Therefore, it is necessary to conduct research on the dynamic ultimate strength of hull girder under slamming loads. This article focuses on a 5618 TEU container ship and proposes two models for calculating the dynamic ultimate strength of hull girder under slamming loads. Different forms of slamming loads are applied to study the resulting dynamic responses under dynamic loading. The B-H criterion is applied to determine the dynamic ultimate strength of hull girder. Based on the one-span model, the influences of load duration, material strain rate effect, preloading, and combination of high and low frequency bending moments on the dynamic ultimate strength of the hull girder were discussed, laying a solid foundation for the formulation of dynamic ultimate strength design criteria that has considered slamming bending moments.

Single-layer cylindrical shells are common structural form of underwater vehicles, which have more advantages than double-layer cylindrical shells regarding hydrodynamic noise control. With the increase of speed, however, the hydrodynamic noise of single-layer cylindrical shells cannot be ignored. This paper establishes the vibro-acoustic coupling model of a finite cylindrical shell fully immersed in infinite ideal water medium. On the basis of the comb function, the hydrodynamic noise calculation method for finite cylindrical shells under external turbulent boundary layer (TBL) excitation is established using correlation function and power spectral density function. The comb function method and the direct expansion method are used to establish the TBL wavenumber-frequency spectrum, respectively. The influence of the two methods on the excitations and displacements of the cylindrical shell in the calculation are analyzed. Furthermore, the sound radiation powers determined by the two approaches are compared with that of the statistical energy method. The results indicate that the comb function method produces different power spectrum density functions of TBL excitations and cylindrical shell displacements from the direct expansion method. The sound radiation power of finite cylindrical shells calculated by the comb function method has better agreement with the results of the statistical energy method in the medium and high frequencies, indicating that the hydrodynamic noise computation of finite cylindrical shell based on the comb function is more accurate. The effects of various speeds and shell thicknesses on the sound radiation power of finite cylindrical shell under TBL excitations are also compared. The results comply with the general law of hydrodynamic noise.

There exists a two-way vibration transmission between the propulsion shafting system and the shell of an underwater vessel. A single structural dynamics model cannot accurately reflect the vibration coupling effect between the propulsion shafting and the shell. In this paper, a dynamic model of the propulsion shafting-shell coupling system of an underwater vessel was established using an analytical method. The shell was simplified as a combination of underwater conical-cylindrical shell, and the propulsion shafting was modeled as a beam structure. The bearing was simplified as a spring-damper-mass system to serve as the connecting structure between the shafting and the shell. Power flow theory was used to analyze the input power flow at the shafting end and shell end under different directions of excitation, as well as the power flow transmitted through the bearing between the shafting and the shell. In addition, the vibration transfer characteristics of the shafting-shell coupling system solved by the analytical method were verified by the finite element method. The results show that the input power flow of the shafting-shell coupling system is greater under shafting end excitation, the shafting-shell coupling effect can significantly increase the input power flow under shafting end excitation, and the rear stern bearing is the main path for transverse vibration transmission between the shafting and the shell. This research provides theoretical support for vibration reduction and noise optimization design of underwater vessels.

Vibration comfort is one of the key technical indicators to evaluate the passenger experience of large cruise ships. Due to the high superstructure and the large difference from ordinary ship types, there is no mature approximate calculation method for global vibration of cruise ships. According to the stiffness and mass distribution of a large cruise ship, this paper proposes a design method for the steel global vibration test model, and designs two schemes: the equiscale model and the non-equiscale abnormal model. Then the abnormal model is used to complete the modal test in the air and the pool, and the test results of the dry/wet modes under the loading and unloading condition are given. The results show that the ratio of the natural frequencies of the wet mode to the corresponding dry mode is basically unchanged under the loading or unloading condition. For the same order mode, the ratio of the natural frequencies under the loading condition to the corresponding unloading condition also remains basically unchanged. The steel-hull global vibration test model can better consider the influence of added water mass, which can provide a valuable reference for the design of the global vibration model and the natural frequency prediction of special ship types.

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.

The underwater wall effect has a significant impact on the survival activities of aquatic animals and the task execution of underwater vehicles. Reasonable utilization of underwater wall effects can achieve energy conservation and consumption reduction, while improper control can lead to safety accidents. This paper mainly reviews the achievements of underwater wall effects in various research directions, including research on live observations of aquatic animals swimming near the ground, wall effects on simplified biomimetic models and wall effects on underwater vehicles. It also presents the research progress on the application of underwater wall effects in biomimetic engineering. At the end, the main problems and challenges faced by the research of underwater wall effects are proposed.