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.

This paper presents an investigation on the target-guided coordinated control (TACC) of unmanned surface vehicles (USVs). In the scenario of tracking non-cooperative targets, the status information of the target can only be obtained by some USVs. In order to achieve semi-encirclement tracking of non-cooperative targets under maritime security conditions, a fixed-time tracking control method based on dynamic surface control (DSC) is proposed in this paper. Firstly, a novel TACC architecture with decoupled kinematic control law and decoupled kinetic control law was designed to reduce the complexity of control system design. Secondly, the proposed DSC-based target-guided kinematic control law including tracking points pre-allocation strategy and sigmoid artificial potential functions (SigAPFs) can avoid collisions during tracking process and optimize kinematic control output. Finally, a fixed-time TACC system was proposed to achieve fast convergence of kinematic and kinetics errors. The effectiveness of the proposed TACC approach in improving target tracking safety and reducing control output chattering was verified by simulation comparison results.

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.

Ice-going ships play a crucial role in polar transportation and resource extraction. Different from the existing modeling approach which assumes that ships remain stationary, dynamic overset grid technology and DFBI (Dynamic Fluid-Body Interaction) method are employed in this paper to enable the free-running motion of the ship in modeling. A numerical model capable of simulating a ship navigating through pack ice area is proposed, which uses Computational Fluid Dynamics (CFD) method to solve the flow field and applies the Discrete Element Method (DEM) to simulate ship-ice and ice-ice interactions. Besides, the proposed high-precision method for generating pack ice area can be used in conjunction with the proposed numerical model. By comparing the numerical results with the available model test data and experimental observations, the effectiveness of the numerical model is validated, demonstrating its strong capability of predicting resistance and simulating ship navigation in pack ice, as well as its significant potential and applicability for further studies.

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.

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.

Mooring cable tension is a crucial parameter for evaluating the safety and reliability of a floating platform mooring system. The real-time mooring tension in an actual marine environment has always been essential data that mooring system designers aim to acquire. To address the need for long-term continuous monitoring of mooring tension in deep-sea marine environments, this paper presents a mooring cable tension monitoring method based on the principle of direct mechanical measurement. The developed tension monitoring sensors were installed and applied in the mooring system of the "Yongle" scientific experimental platform. Over the course of one year, a substantial amount of in-situ tension monitoring data was obtained. Under wave heights of up to 1.24 m, the mooring tension on the floating platform reached 16.5 tons. Through frequency domain and time domain analysis, the spectral characteristics of mooring tension, including wave-induced force, slow drift force, and mooring cable elastic restoring force, were determined. The mooring cable elastic restoring force frequency was approximately half of that of the wave signal. Due to the characteristics of the hinge connection structure of the dual module floating platform, under some specific working conditions the wave-induced force was the maximum of the three different frequency forces, and restoring force was the smallest.