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.

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.

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.

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.

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.

The aim of this study is to address the issues associated with traditional magnetorheological fluid (MRF) dampers, such as insufficient damping force after power failure and susceptibility to settlement. In order to achieve this, a bidirectional adjustable MRF damper was designed and developed. Magnetic field simulation analysis was conducted on the damper, along with simulation analysis on its dynamic characteristics. The dynamic characteristics were ultimately validated through experimental testing on the material testing machine, thereby corroborating the theoretical simulation results. Concurrently, this process generated valuable test data for subsequent implementation of the semi-active vibration control system. The simulation and test results demonstrate that the integrated permanent magnet effectively accomplishes bidirectional regulation. The magnetic induction intensity of the damping channel is 0.2 T in the absence of current, increases to 0.5 T when a maximum forward current of 4 A is applied, and becomes 0 T when a maximum reverse current of 3.8 A is applied. When the excitation amplitude is 8 mm and the frequency is 2 Hz, with the applied currents varying, the maximum damping force reaches 8 kN, while the minimum damping force measures at 511 N. Additionally, at zero current, the damping force stands at 2 kN, which aligns closely with simulation results. The present paper can serve as a valuable reference for the design and research of semi-active MRF dampers.

In order to accurately forecast the main engine fuel consumption and reduce the Energy Efficiency Operational Indicator (EEOI) of merchant ships in polar ice areas, the energy transfer relationship between ship-machine-propeller is studied by analyzing the complex force situation during ship navigation and building a MATLAB/Simulink simulation platform based on multi-environmental resistance, propeller efficiency, main engine power, fuel consumption, fuel consumption rate and EEOI calculation module. Considering the environmental factors of wind, wave and ice, the route is divided into sections, the calculation of main engine power, main engine fuel consumption and EEOI for each section is completed, and the speed design is optimized based on the simulation model for each section. Under the requirements of the voyage plan, the optimization results show that the energy efficiency operation index of the whole route is reduced by 3.114% and the fuel consumption is reduced by 9.17 t.

To study the rolling motion of a ship in the presence of water on its deck, a linear-plus-quadratic damping term was incorporated into its equation of motion. Ship model tests indicates that the key dynamics of the physical system are preserved in the ship rolling equation with the linear-plus-quadratic type damping term. To take into account the presence of randomness in the excitation and the response, a new method was developed and a Melnikov criterion was obtained to provide an upper bound on the domain of the potential chaotic rolling motion (erratic rocking). Additionally, the Melnikov criterion proposed in this study was verified by the utilization of phase plane diagrams and Poincare maps. Furthermore, this research has made the initial endeavor to systematically modify the system parameters in the rolling equation of motion for ship stability analysis.

In this paper, the failure caused by HRAM loads which were generated by high-speed projectile penetration, and protection technology of the fluid-filled structure were explored. A bubble was preset on the projectile trajectory in a fluid-filled structure. Based on the reflection and transmission phenomena of pressure waves at the gas-liquid interface and the compressibility characteristics of gases, a numerical analysis was conducted on the influence of preset bubble on projectile penetration and structural failure characteristics. The results indicate that the secondary water-entry impact phenomenon occurs when a preset bubble exists on the projectile trajectory, leading to the secondary water entry impact loads. The rarefaction waves reflected on the surface of the preset bubble cause the attenuation ratio of the initial impact pressure peak to reach 68.8% and the total specific impulse attenuation ratio to reach 48.6%. Furthermore, the larger the bubble, the faster the projectile, and the more obvious the attenuation effect. Moreover, due to the compressibility of the bubble, the global deformation attenuation ratio of the front and rear walls can reach over 80%. However, the larger the bubble size, the faster the projectile velocity, the smaller the local deformation attenuation effect of the rear wall, and the more severe the failure at the perforation of the rear wall.

As a typical steel, the fatigue of marine high-strength steels has been emphasized by scholars. In this paper, the fatigue performance and crack growth mechanism of a high-strength steel for ships are investigated by experimental methods. First, the fatigue threshold test and fatigue crack growth rate test of this high-strength steel under different stress ratios were carried out. The influence of stress ratio on the fatigue properties of this steel was analyzed. Secondly, scanning electron microscope was used to analyze the crack growth specimen section of this steel. The crack growth and failure mechanism of this steel were revealed. Finally, based on the above research results, the stress ratio effect of high-strength steel was investigated from the perspectives of crack closure and driving force. Considering the fatigue behavior in the near-threshold stage and the destabilization stage, a fatigue crack growth behavior prediction model of high-strength steel was established. The accuracy of the model was verified by test data. Moreover, the applicability of the modified model to various materials and its excellent predictive ability were verified through comparison with literature data and existing models.