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.

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.