The finite volume method was applied to numerically simulate the bottom pressure field induced by regular waves, vehicles in calm water and vehicles in regular waves. The solution of Navier-Stokes (N-S) equations in the vicinity of numerical wave tank's boundary was forced towards the wave theoretical solution by incorporating momentum source terms, thereby reducing adverse effects such as wave reflection. Simulations utilizing laminar flow, turbulent flow, and ideal fluid models were all found capable of effectively capturing the waveform and bottom pressure of regular waves, agreeing well with experimental data. In predicting the bottom pressure field of the submerged vehicle, turbulent simulations considering fluid viscosity and boundary layer development provided more accurate predictions for the stern region than inviscid simulations. Due to sphere's diffractive effect, the sphere's bottom pressure field in waves is not a linear superposition of the wave's and the sphere's bottom pressure field. However, a slender submerged vehicle exhibits a weaker diffractive effect on waves, thus the submerged vehicle's bottom pressure field in waves can be approximated as a linear superposition of the wave's and the submerged vehicle's bottom pressure field, which simplifies computation and analysis.

Currently, the International Maritime Organization (IMO) has approved and implemented the assessment requirement for Minimum Propulsion Power (MPP) of ships in adverse sea conditions. The assessment method and relevant influence factors will have a vital impact on ship's design and operation. On the other hand, MPP is essentially a criterion for manoeuvring safety at actual seas. However, the practical assessment methods adopted in IMO guidelines do not directly and accurately account for ship's course-keeping ability in severe seas. A time-domain comprehensive method with supplementary course-keeping ability criteria has been proposed in the authors' preliminary research. Based on an updated mathematical model and criteria, this paper presents more detailed elaborations, results and discussions on the time-domain method, including the comparative analyses with a power line method and two steady-state equilibrium methods based on IMO guidelines and draft. Discussions on the influences of key factors, involving criterion conditions and calculation parameters, are also presented. The results indicate that different methods exhibit varying advantages and complexity in MPP assessment, thus constituting a multi-level assessment framework for MPP. In particular, the time-domain comprehensive assessment has a higher accuracy with more realistic description of manoeuvre behaviors, capable of offering a solution for the ships that cannot meet other assessments, or for the assessment requiring additional course-keeping ability. Furthermore, an expanded range of wave direction sets a stricter but potentially necessary requirement, while using the self-propulsion factors at low speeds can eliminate the unnecessary conservation of assessment result caused by those at design speed.

The accurate assessment and analysis of nonlinear wave loads on ships and the high-frequency vibrational response of ship structures are requisites for determining the safety of ship structures. However, the reliability of numerical simulation and the analysis of their uncertainties have received relatively little attention. This paper presents a segmented keel beam hydroelastic model CFD-FEM simulation and experimental research to simulate and analyze the high-frequency response of a ship model in waves. Uncertainty analysis was performed on the simulation results to evaluate the reliability of the simulation model. The calculation results of numerical uncertainties can provide criteria for judging the convergence of results under different influencing factors and the level of uncertainty. The uncertainty levels of the impact pressure on the ship’s bow, the motion of the ship model, and the high and low-frequency wave bending moments of the ship hull are also clarified. A comparison between numerical simulation and experimental testing reveals that CFD-FEM two-way fluid-structure coupling simulation can accurately capture the high-frequency response of ship structures. The high-frequency bending moment component of the ship under cruising conditions can account for more than 49.95% of the low-frequency wave bending moment. The dynamic response of ships induced by impact loads cannot be ignored, and their influence must be considered in the structural design and safety assessment of such ships. This paper can provide a reference for the uncertainty analysis of high-frequency structural dynamic responses such as ship impact vibration.

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.

To investigate the collision dynamics of a marine rotating machinery integrated with an airbag-raft-limiter system under the influence of heaving motions, a dynamic model of an asymmetric system incorporating a limiter was developed. This model took into account the effect of the ship heaving motion and the limiter gap on the coupled airbag-raft-limiter system. The equations of motion were given dimensionless treatment to facilitate computational analysis. The study examined the influence of rotor speed, heaving amplitude, and limiter gap on the system’s dynamics utilizing nonlinear dynamics analysis techniques including phase diagrams, spectral responses, and energy trajectory diagrams. The findings indicate that an increase in heaving amplitude leads to collisions between the system and the limiter, causing a significant amplitude decrease while triggering a transition of motion from quasi-periodic state to chaotic state. Additionally, the collision alters the energy trajectory of the system, moving from a uniform distribution towards the collision zone.

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.

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.

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.