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.

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 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.

A structural reliability analysis method based on synthetic minority over-sampling technique (SMOTE) algorithm and Bayesian optimization (BO) neural network was proposed in this paper to improve the calculation accuracy and analysis efficiency of the impact resistance reliability of lubricating oil cooler. Firstly, the uniform design (UD) method and SMOTE algorithm were used to improve the utilization efficiency of the sample points. Secondly, the Bayesian optimization algorithm was used to optimize the hyperparameters, initial weights and initial biases of the BP neural network to improve the fitting accuracy and generalization ability of the model. Finally, the optimized surrogate model was combined with the Monte Carlo (MC) method to calculate the structural reliability. The results show that, compared with the traditional surrogate model method, the proposed method has the advantages of higher accuracy, shorter analysis time and lower calculation cost. The analysis method proposed in this paper has great applicability in the impact resistance reliability analysis of lubricating oil cooler. The analysis results provide technical guidance and theoretical support for the impact resistance design of lubricating oil cooler.

To study the time-averaged flow field characteristics of a cylinder under the action of periodic oscillating flow, the time-varying flow field around the cylinder was obtained by numerically solving the Navier-Stokes equations. The time-averaged flow field was obtained by averaging the velocity field over time. The time-averaged flow fields with different K_C numbers under a given Stokes number β=20 for Reynolds number Re< 200 were compared and analyzed. It is found that: (1) when K_C< 7 (Re<140), the oscillating flow vorticity source is always attached to the cylinder wall and gradually stretches along the oscillating flow direction; (2) the corresponding time-averaged flow field consists of four small-scale internal vortices with strong stable flow and four large-scale external vortices with weak flow; (3) the flow structure is of axisymmetric distribution; (4) when K_C> 7 (140<Re<200), the symmetry of the vorticity distribution around the cylinder is destroyed, while the oblique vortex street and dissipative behavior appear, the corresponding time-averaged flow field structure is seriously distorted, and the flow field structure is closely related to the vortex shedding mode around the cylinder, (5) the strength of the time-averaged flow field increases exponentially with the increase of K_C number, and (6) for double cylindrical tubes, the time-averaged flow fields under different arrangements and spacing ratios show rich flow field characteristics, and the gap flow intensity between tubes increases with the decrease of spacing ratio.

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.

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.

An accelerated creep test method for deep-sea equipment viewport window was proposed in this paper based on the sensitivity of PMMA (Polymethyl methacrylate) to temperature and stress. A modified creep constitutive equation based on aging theory was proposed by introducing the influence function of temperature. The uniaxial compressive creep tests at different temperature and stress levels were carried out, and the creep constitutive relation of PMMA was obtained by stepwise fitting method. The conversion relationship of the creep behavior of the viewport under different temperatures and pressures was obtained by the finite element creep analysis. The accelerated creep test method of the viewport model under the condition of raised temperature and increased pressure was proposed, and the comparison between the test results and the calculated results was completed. It is shown that the stress sensitivity of the uniaxial compressive creep behavior of PMMA is related to temperature. The finite element solution of the conversion coefficient of viewport’s creep deformation under different temperatures and pressures is different from the calculated value. The results of the viewport model are in good agreement with those of finite element creep analysis. In conclusion, in a certain temperature and stress range, the creep constitutive relation of PMMA obtained in this paper can well describe the law of uniaxial compressive creep behavior, and that of the viewport can be well simulated by the finite element creep analysis. The calculation results show that the conversion coefficient of viewport’s creep displacements between conditions of 25 °C & 26.6 MPa and 3 °C & 20 MPa is 12.2, and this coefficient can provide a basis for the accelerated creep test.

Suppressing incipient cavitation in an underwater body is of great importance to reducing the adverse effects caused by cavitation. For the method of suppressing incipient cavitation by changing the surface roughness, the research on the optimal design of the rough band parameters based on surrogate model methods was conducted. Firstly, numerical calculation methods were used to analyze the influence mechanism of the rough band parameters on the incipient cavitation characteristics at the head of the underwater body, and an initial design range for the rough band parameters was established. Then, the surrogate model method was used for parameter optimization analysis. The results show that setting a rough band on the head surface of the body can change the pressure distribution. The front and rear boundaries of the roughness may cause slight pressure fluctuations, which can change the minimum pressure value and thereby affect the incipient cavitation characteristics. Through sensitivity analysis of the surrogate model, it can be observed that compared with the position and width of the rough band, its height has a greater influence on incipient cavitation. The final optimization results obtained were verified by numerical calculation, which can obviously reduce the incipient cavitation and achieve a better effect in suppressing it.

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.