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.

Ice load on underwater vehicles breaking through ice covers from underneath is a significant concern for researchers in polar exploration, and the research on this problem is still in its early stages. Both mechanical experimental measurement and numerical simulation pose research challenges. This study focuses on the ice load of a cylinder structure breaking upward through the ice sheet form underneath in the Small Ice Model Basin of China Ship Scientific Research Center (CSSRC SIMB). A high-speed camera system was employed to observe the ice sheet failure during the tests, in which, with the loading position as center, local radial cracks and circumferential cracks were generated. A load sensor was used to measure the overall ice load during this process. Meanwhile, a numerical model was developed using LS-DYNA for validation and comparison. With this model, numerical simulation was conducted under various ice thicknesses and upgoing speeds to analyze the instantaneous curves of ice load. The calculation results were statistically analyzed under different working conditions to determine the influence of the factors on the ice load of the cylinder. The study explores the measurement method about ice load of objects vertically breaking through model ice sheet and is expected to provide some fundamental insights into the safety design of underwater structures operating in ice waters.

In the past few decades, the navigation performance of ships and structures in ice-covered waters has not been fully studied, especially the influence of ice mechanical properties on icebreaking ability. Ice bending strength is a key ice parameter for predicting ship ice loads, and accurate ice bending strength is also the key to scaling model tests results to real ship. However, numerical simulation studies on model ice bending strength of ice tanks are often neglected. In this paper, an explicit finite element method model is used to simulate the ice cantilever beam test, and the failure load and bending strength of the ice are obtained. In this model, the Tsai-Wu failure criterion is used as the material constitutive model, and the required simulation parameters are obtained from the model ice test in ice tank. Parameter sensitivity analysis shows that the cantilever beam size of the model ice has a significant effect on the flexural strength. The results show that proper rounding at the root of the cantilever beam is beneficial to reduce stress concentration and obtain more accurate bending strength; the thickness, width and length of the cantilever beam should conform to a certain ratio, and consistent with the ITTC recommended reference. Therefore, the results of this study can promote model ice experiments and numerical studies and provide ice strength data support for ship design and polar ship maneuvering.

With the increase of international trade activities and the gradual melting of the polar ice cap, the importance of the Arctic route for marine transportation has been emphasized. Prediction of the polar navigation window period is crucial for navigating in the Arctic route, which is of great significance to the selection of the route and the optimization of navigation. This paper introduces the establishment of a risk index system, determination of risk index weight, establishment of a risk evaluation model, and prediction algorithm for the window period. In addition, data sources of both environmental factors and ship factors are introducted, and their shortcomings are analyzed, followed by introduction of various methods involved in window prediction and analysis of their advantages and disadvantages. The quantitative risk evaluation and window period algorithm can provide a reference for the research of polar navigation window period prediction.

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.

The completion of the first ever floating nuclear plant, “Academic Lomonosov” provided a practical solution for energy supply in high latitudes. There may be ice floes in the sea at high latitudes, and if the floating nuclear plant collides with them, it may lead to damaged flooding, threatening the safety of operation. In this study, based on the Euler multiphase flow model combined with the discrete element theory, a numerical simulation method was proposed to simulate damaged flooding of a ship in the crushed ice area. This method was used to numerically simulate damaged flooding and the navigation resistance in the crushed ice area, and the simulation results were compared with the model test results to verify the accuracy of the simulation method. Taking the independently-designed ship-type nuclear power platform of a ship type as the research object, considering the randomness of the distribution of broken ice, the above method was used to simulate its damaged flooding in the crushed ice area. Finally, the influence of crushed ice flowing into the cabin on the flooding process and the impact load on the hull structure were analyzed. The research results can provide a reference for relevant research on the damage flooding process of ships sailing in ice regions.

Currently, when predicting the ship maneuvering motion in waves based on the mathematical model of ship maneuvering motion, hydrodynamic coefficients are mostly obtained through the model test or numerical prediction in still water, without considering the influence of waves on ship maneuvering hydrodynamics. Therefore, establishing the prediction method of ship maneuvering motion hydrodynamics in waves is essential for accurately predicting ship maneuvering motion. In this paper, the multi-degree-of-freedom motion of ship in waves was numerically modeled based on the overset grid method. The hydrodynamic modeling, free surface treatment and wave simulation methods were presented. The numerical simulation method of ship maneuvering hydrodynamic forces in waves was established. The hydrodynamic model test and numerical prediction of S175-ship in regular waves were carried out, and the influence of waves on ship hydrodynamics was evaluated. The numerical prediction results were compared with the model test results to verify the reliability and practicability of the numerical simulation method. The research in this paper can provide a guidance for the improvement of the ship maneuvering prediction in waves.

Based on the open source programme OpenFOAM, a numerical model was established to investigate the behavior of the interaction between waves and the newly-developed open breakwaters with elliptical arc-plate. The numerical model was verified by using theoretical wave surface and previous experimental results. Focusing on the three types of open structures, such as double flat plate, flat-elliptical arc-plate and double elliptical arc-plate open breakwater, a total of 90 cases were designed to analyze their wave attenuation performance. Considering the indexes of transmission coefficient, reflection coefficient and energy dissipation coefficient comprehensively, the numerical results indicate that the open breakwater with flat-elliptical arc-plate exhibits a low-level transmitted wave energy and a high-level reflected wave energy, while the open breakwater with double elliptical arc-plate exhibits a high-level transmitted wave energy and a low-level reflected wave energy under most working conditions. Further analysis revealed that when the structure is placed above the hydrostatic level, the open breakwater with flat-elliptical arc-plate has higher wave attenuation performance compared with the double flat plate type and double elliptical arc-plate. Therefore, the open breakwater with flat-elliptical arc-plate could be selected when it is submerged at suitable depths based on hydrodynamic conditions in engineering practice. This research provides design references for the breakwaters which could simultaneously meet the requirements of wave attenuation and water permeability.

In freak wave-related research, the wavelength of the freak wave is generally calculated from the dispersion relation of the Stokes wave or linear wave. The freak wave, however, is a type of short-duration wave, also characterized by strong-nonlinearity. Its energy components are more complex compared to regular waves. Beside the effect of higher-order harmonics, the energy transfer occurs due to the nonlinear wave-wave interaction during the generation of freak waves. In order to check the accuracy of the wavelength of freak waves calculated from the dispersion relation, freak waves were experimentally simulated in a wave tank by focusing a range of component waves. The statistics on wavelength of freak wave were calculated from the time history of wave surface obtained from a wave gauge array. The statistical wavelengths conduted were compared to those of linear wave, 3rd- and 5th-order Stokes wave with identical wave heights and periods. The results from comparison indicate that the wavelengths from the 3rd- and 5th-order Stokes wave dispersion relations have a higher accuracy than that from the 1st-order dispersion relations of linear wave. And the 3rd-order dispersion relation is sufficient to describe the effect of higher-order harmonics on the wavelength. However, without accounting for the nonlinear wave-wave interaction, high-order dispersion relation will overestimate the wavelength of frear wave with longer periods and underestimate that for freak wave with shorter periods. And as a consequence, on the basis of the 3rd-order dispersion relation and regression model, a new improved method for higher accuracy calculation of the wavelengths of the freak wave was proposed. The accuracy of the wavelengths for the new method increases by over 50% compared to the tradional 3rd-order dispersion relation.

The motion of an underwater shaking table will make waves in water. In this paper, a numerical tank including wave maker, wave absorber and underwater shaking table was established and validated. Waves made by the vertical harmonic motion of the underwater shaking table were investigated. The velocity, dynamic water pressure and wave factors were discussed. This study aims to provide reference testing in coupled earthquake-wave-current environment and eliminating tank wave disturbance. The results show that (1) the water velocity of the center of the underwater shaking table in vertical direction increases with the increase of the vertical moving amplitude and the length of the shaking table while the velocity decreases with the increase of the period of the shaking table; (2) the distribution of dynamic water pressure above the center of the underwater shaking table depicts a trend of “decrease-first, increase-second” in the water depth direction; (3) the dynamic water pressure increases with the increase of the vertical moving amplitude of the shaking table; (4) the wave height increases with the increase of the vertical moving amplitude of the shaking table, and decreases with the increase of water depth; (5) and the wave period increases with the increase of the period of the shaking table while the wave length increases with the increase of the period of the shaking table and the water depth.