To address the challenges of preventing non-random multiple concurrent faults caused by cable aging in shipboard power grids through preventive reconfiguration, and to resolve the issue of unreasonable weight coefficient settings in multi-objective reconfiguration models, thereby enhancing the safety and reconfiguration efficiency of shipboard power grids, a predictive fault reconfiguration method for shipboard power grids based on a double-level optimization strategy is proposed.

A cable aging fault prediction model for shipboard grids was constructed based on Markov chains and thermo-electro-mechanical multi physics analysis. This model was integrated as a constraint into the reconfiguration framework to avoid high-risk branches. A dual-layer optimization strategy was proposed: the upper layer dynamically solves multi-objective weight coefficients using the whale migration algorithm (WMA), while the lower layer determines the optimal switch configuration for grid reconfiguration using a multi-strategy-improved dung beetle optimizer (MSDBO).

After integrating the fault prediction model, the reconfiguration strategy achieved 100% avoidance of high-risk branches (fault probability ≥0.5) proactively. Compared to the conventional two-step passive reconfiguration strategy, convergence speed improved by 47.06%. The dual-layer optimization framework enabled adaptive dynamic adjustment of weight coefficients and increased reconfiguration convergence speed by 56.25%.

The integration of the cable aging fault prediction model and the dual-layer optimization framework effectively enables predictive reconfiguration of shipboard power grids. This approach proactively mitigates non-random faults while significantly improving reconfiguration efficiency and rationality. It offers a novel solution for addressing predictive reconfiguration challenges in non-random multiple-fault scenarios.

The information obtained through forced detection is often inaccurate, and targets frequently change course unpredictably. This degrades the performance of target maneuver detection and hampers the analysis of the target motion pattern. Therefore, this paper proposes a detection method for maneuvering maritime targets based on prior knowledge.

The method incorporates two types of prior knowledge derived from expert experience. The first is that significant differences in target heading occur before and after maneuvering, whereas the target heading remains relatively stable during non-maneuvering periods. The second is that the heading difference before and after maneuvering reaches a local extremum. The maneuvering point in the trajectory tends to maximize the heading difference between adjacent sub-trajectories. Based on the definition of trajectory smoothness metric, a calculation method is proposed to calculate the course maneuver evaluation factor based on principal component analysis (PCA). This factor enables preliminary screening of potential maneuvering points. In order to find trajectory points that satisfy the second prior knowledge, a maximum filtering-based maneuvering point screening method is proposed.

Simulation results show that, compared with the mainstream interactive multiple model (IMM) algorithm and information entropy-based algorithm, the target maneuver inflection points detected by the proposed method are closer to the actual inflection points, with the lowest false detection rate and missed detection rate. Moreover, when track compression is performed using the maneuver positions extracted by this method, the distance error relative to the original track is minimized.

The findings confirm the superiority of the proposed algorithm, which can effectively improve the accuracy and robustness of target maneuver detection and provide strong support for target behavior analysis and operational decision-making at sea.

This study aims to investigate the shock load characteristics during implosion and the thermodynamic response mechanisms of a ceramic pressure hull in the extreme deep-sea environment. A numerical simulation method for the implosion of a deep-sea ceramic pressure hull is proposed using a compressible multiphase flow model that ensures pressure-velocity-temperature equilibrium and adaptive mesh refinement (AMR).

The proposed method enables accurate prediction of shock waves and precise capture of the flow field. Then, underwater implosion experiments of the ceramic pressure hull are conducted to verify the effectiveness of the numerical method. Finally, a numerical study on the implosion of a ceramic pressure hull at a depth of 10 000 m reveals the characteristics of the shock load and thermal effects during implosion. The implosion of a deep-sea ceramic pressure hull at different water depths and temperatures is studied numerically, and the effects of these factors are analyzed.

The implosion of a deep-sea ceramic pressure hull releases shock waves outward and produces a significant thermal effect when the gas is highly compressed. As the ambient pressure increases, the peak overpressure of the implosion shock wave decreases, and the shock wave attenuation rate increases. However, the ambient water temperature has little effect on the implosion characteristics of the ceramic pressure hull.

This study provides insights into the implosion characteristics of deep-sea ceramic pressure hull, offering valuable theoretical insights and engineering implications for the assessment and mitigation of underwater implosion effects.

This study aims to systematically quantify the effects of fin-hull geometric configuration on the propulsion performance of bionic undulating-fin vehicles employing media and/or paired fin propulsion (MPF). It addresses the lack of a unified analysis of geometric parameters across different bionic underwater vehicles in existing research.

To this end, a universal parametric geometric model incorporating the hull and a pair of undulating fins was developed. The model innovatively introduces the ratio of fin width to hull width β as the core dimensionless geometric parameter. Based on this model, high-fidelity CFD numerical simulations were conducted to analyze the propulsion performance and flow field structure of the vehicle under different β values.

The results indicate that β has a nonlinear and significant influence on propulsion performance, and that an optimal range of β values exists for maximizing propulsion efficiency. Excessively small β values lead to insufficient thrust generation, whereas excessively large β values increase drag due to intensified fin-hull interactions that induce flow separation. Furthermore, β significantly modulates the magnitude of the pitching moment, imposing a critical constraint on the vehicle's attitude stability.

This study clarifies the design trade-off between efficiency and stability governed by the β parameter. The established parametric model and the identified underlying mechanisms provide a quantitative theoretical basis for the shape design of bionic underwater vehicles and lay a solid foundation for future research on multi-parameter coupling optimization and self-propulsion performance.

This paper addresses the path tracking control problem for underactuated unmanned surface vehicles (USVs) under the conditions of lumped disturbances, input saturation, and limited onboard energy. These factors complicate the path tracking process and reduce the effectiveness of traditional control methods. The aim of this study is to propose an event-triggered fixed-time path tracking control strategy that improves robustness, energy efficiency, and tracking precision in complex environments.

The proposed control strategy integrates several key components to address the challenges mentioned. First, a longitudinal speed guidance law and a fixed-time line-of-sight (SGFTLOS) guidance law are designed to provide the desired longitudinal speed and heading angle for the USV, ensuring it follows the trajectory with optimal speed and heading. Next, to handle model uncertainties and external disturbances (such as wind and current), a Fixed-Time Extended State Observer (FESO) is introduced. The FESO estimates and compensates for lumped disturbances, improving the system's robustness in uncertain environments. To address input saturation, an auxiliary dynamic system is designed to smooth inputs and maintain stable path tracking, even when saturation occurs. Finally, to overcome onboard energy limitations, a periodic event-triggered mechanism based on relative threshold is proposed. This mechanism adjusts control signal update frequency based on system states, minimizing unnecessary actuator activity and energy consumption.

The stability of the system is proven to be fixed-time stable using Lyapunov's fixed-time stability theory, which also eliminates Zeno behavior (infinite triggering in finite time) that could otherwise cause instability. SimuNPS simulation results demonstrate that the tracking error converges within a fixed time, verifying the effectiveness of the proposed method. Compared to existing methods, the proposed strategy exhibits faster transient response, smaller steady-state errors, and superior robustness in the presence of lumped disturbances. Furthermore, the introduction of the FESO provides accurate real-time disturbance estimation, allowing the controller to compensate for disturbances and maintain precise path tracking. Additionally, the event-triggered mechanism significantly reduces the number of control signal updates and actuator actions, improving the system's energy efficiency.

The proposed event-triggered fixed-time path tracking control strategy effectively addresses the challenges of lumped disturbances, input saturation, and limited onboard energy in underactuated USVs. By integrating event-triggered mechanisms, innovative guidance laws, and robust disturbance compensation, the strategy provides a reliable solution for path tracking in complex and uncertain environments. The fixed-time convergence property ensures that the USV achieves desired performance within a fixed time, making the strategy suitable for real-time applications requiring stability, precision, and energy efficiency. This method offers a robust, efficient, and reliable solution for USV path tracking control under difficult operational conditions.

This study investigates the motion characteristics of deep-sea vehicles during deep vertical transit under vectored propulsion.

First, the motion equations were established to obtain preliminary solutions for the parameters of helical diving. Subsequently, a series of lake trials were conducted using a vectored-propulsion deep-sea vehicle prototype, including steady-state turning diameter tests, heeling angle measurements, and powered helical diving experiments under multiple control parameters, in order to analyze the diving motion characteristics. Finally, a 3 650 m powered diving test was performed under real operating conditions at a depth of 3 700 m in the South China Sea.

The lake trial results show that the steady turning diameter of the vector-propelled deep-sea vehicle is only 4 times the overall length of the platform, while the turning heel angle remains within 2.5°. The sea trial results indicate that, under the selected control parameters, the average deep-sea diving speed reaches 0.6 m/s, the standard deviation of the pitch angle is only 0.42°, and the horizontal offset during the 3 650 m diving process is 442 m. These results demonstrate stable and controllable motion characteristics, verifying the feasibility of the powered diving technology for deep-sea vehicles based on vectored propulsion.

The results provide a reference for the research on diving technologies for deep-sea vehicles.

To explore the effect of structural elasticity on the ice-structure interaction process, model tests on the interaction between frozen ice and elastic plates were conducted in a low-temperature laboratory. This study aims to provide a theoretical basis for understanding the ice-structure interaction mechanism and predicting ice loads on ships operating in ice-covered areas.

In the experiments, the stiffness of the elastic plates was adjusted by varying their thickness. Two loading rates within the strain-rate range associated with brittle ice failure were selected. A universal testing machine was used to record load-time history data, and a CCD camera was employed to capture the ice failure modes under different test conditions.

The interaction process consists of two typical phases: the loose contact phase and the tight contact phase. Loose contact results from the uneven contact between the plate and the top of the ice specimen, with maximum displacements generally ranging from 0 to 1.5 mm. In the tight contact phase, about 43.3% of the load-displacement curves show a saw-tooth shape, representing multi-stage failure modes. Stiffer plates are more likely to cause single-stage ice failure, while more flexible plates tend to result in multi-stage failures. Multi-stage failures are associated with ice flaking at a 45° angle due to shear failure. During multi-stage failure, the slope of the load-displacement curve remains nearly constant, suggesting constant stiffness of the ice-elastic plate coupling system in the tight contact phase.

Although the structure in this study is simplified as a plate, the experimental results provide valuable insights for designers of ice-going ships into the complex interaction mechanics between ice and ship structures. This research also provides a foundation for further studies on more complex structures and accurate ice load predictions.

With the increasing diversification of application requirements for unmanned underwater vehicles (UUVs), traditional design methods centered on text-based documentation have revealed numerous limitations in practice, such as scattered design documents, difficulty in maintenance, and low iteration efficiency among systems. Therefore, it is necessary to introduce a novel overall design methodology.

In this study, the model-based systems engineering (MBSE) methodology was incorporated into the design process of UUVs and integrated with traditional design approaches to establish a model-driven design and verification framework. Using the M-Design collaborative research platform, graphical system modeling language (SysML) was employed to construct a comprehensive system model, including the requirements model, logical architecture model, and physical architecture model, thereby forming an integrated design framework. To further validate the feasibility of the framework, multi-system co-simulation technology was adopted, and a distributed simulation platform was developed to perform performance simulation and verification for typical mission scenarios of UUVs. Based on these efforts, a conceptual scheme for an agile design and verification prototype system has been proposed to support agile development requirements.

The results demonstrate that the model-based design methodology can significantly improve the design efficiency and verification capability of UUVs, enabling a closed-loop development process from requirements definition to design implementation.

The proposed design methodology provides effective guidance for the design and specification verification of various manned and unmanned underwater platforms.

To overcome the limitations of conventional wave-absorbing structures, a novel broadband, low-profile multilayer composite absorber was designed.

The proposed design integrates square loop resistive film units to significantly broaden the operational bandwidth and incorporates miniaturized conductor units based on lumped inductance loading. Structural parameters were further optimized to achieve broadband, low-profile wave-absorption, effectively lowering the minimum operational frequency.

Simulation results show that the developed composite absorber achieves over 90% electromagnetic wave absorption across the frequency range of 3.22 to 14.63 GHz, with a relative bandwidth of 127.8% and a low profile height of just 0.068λ_L.

The operational mechanism of the absorber is analyzed using an equivalent circuit model, and potential improvements are discussed. This design offers valuable insights and a solid reference for the development of broadband, low-profile absorbers. Future work will focus on replacing lumped inductors with metal meander-line structures to reduce processing complexity and costs.