This study aims to develop a dynamic model of the longitudinal profile motion of wave gliders by modeling the umbilical cable as multiple hinged rigid rods, and to investigate the effects of environmental and umbilical cable parameters on the longitudinal motion characteristics.

Based on reasonable assumptions and simplifications, the umbilical cable was modeled as a series of homogeneous, multi-segment rigid rods connected by hinges. The Lagrangian method was employed to construct a multi-rigid-body dynamic model of the wave glider in the longitudinal profile. Incorporating calculation methods for wave force, fluid resistance, and hydrofoil external forces, a simulation program was developed on the MATLAB/Simulink platform to solve the model. The model's validity was verified by comparing its results with those of existing studies. Finally, a sensitivity analysis was conducted to examine the influence of environmental and umbilical cable parameters on the system response.

The results indicate that the longitudinal motion response increases with wave height; specifically, when the wave height rises from 0.2 m to 0.4 m, the longitudinal response increases by 78.20%. Under a current disturbance of 0.07 m/s, the longitudinal displacement within 60 s in the downstream condition increases from 1.53 m to 9.11 m compared with the upstream condition. Shorter umbilical cables amplify the longitudinal motion response; when the umbilical cable length decreases from 5 m to 2 m, the longitudinal response increases by 31.97%. Conversely, excessively small wave periods reduce the longitudinal response due to rigid impacts between the multi-segment hinged rigid rods. Changes in umbilical cable density, however, exert only a minor influence on the longitudinal motion response.

The findings of this study provide theoretical support for the structural optimization and motion control strategies of wave gliders.

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 dynamic behavior and flow field characteristics of trans-medium submersibles during underwater straight-line navigation and turning maneuvers.

To this end, computational fluid dynamics simulations were employed, using the VOF multiphase flow model and the SST k–ω turbulence model to establish a numerical model of the underwater navigation of the trans-medium submersibles. The accuracy of the numerical method was validated by comparing the experimental total drag data for the DARPA Suboff submarine model at various speeds with the numerical calculation results. On this basis, numerical simulations and analyses of underwater straight-line navigation and turning maneuvers of the trans-medium submersible were conducted, focusing on the effects of ducted propeller rotation speed and tail fin deflection angle on the underwater straight-line navigation and turning performance of the submersible.

The research results indicate that during straight-line underwater navigation, the forward speed of the trans-medium submersible exhibits an approximately linear relationship with the propeller's rotational speed. For instance, as the propeller speed increases from 600 r/min to 4800 r/min, the forward speed rises from 1.1 m/s to 8.1 m/s. At the same time, the pitch moment becomes less negative with increasing propeller speed (from −0.35 N·m to −0.17 N·m), indicating that the submersible remains stable in pitch during high-speed navigation. The propeller speed has little effect on the surface pressure distribution and the structure of the surrounding flow field. During underwater turning, the turning radius is mainly determined by the tail fin deflection angle and is largely unaffected by the propeller speed. The turning radius decreases with increasing tail fin deflection angle (from 3.35 times the submersible's body length to 0.75 times), though the rate of decrease diminishes. In contrast, the turning speed is affected by both the propeller speed and the tail fin deflection angle. The thrust generated by both propellers increases with higher propeller speeds and larger tail fin deflection angles. During turning, the thrust of the outer propeller consistently exceeds that of the inner propeller, and the thrust difference increases with greater tail fin deflection. Furthermore, tail fin deflection during turning leads to a significantly asymmetric surface pressure distribution on the submersible. This asymmetry becomes more pronounced with increasing tail fin deflection and is closely associated with the asymmetric flow characteristics of the surrounding flow field.

This study provides a reference for the design and performance analysis of trans-medium submersible configurations.

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 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.