To address the inherent trade-off between large-scale exploration and high-precision manipulation in existing underwater vehicles, a novel morphable underwater intervention robot is developed. Designed for operations at depths of up to 1000 m, the robot integrates low-drag cruising with dual-arm collaborative capabilities, meeting the stringent inspection and maintenance requirements of offshore wind farms and subsea oil and gas platforms.

The overall design specifications were first established, followed by the optimization of the integrated design workflow. The configuration of the robot's pressure-resistant hulls and equipment layout were finalized, with the development of key components, including the morphing mechanism (lead screw lifting mechanism) and pressure-resistant hulls. Strength verification of key components was performed using finite element analysis (FEA) under a 12 MPa hydrostatic load, simulating a depth of 1000 m. Subsequently, the endurance and maneuverability during cruising mode, as well as the manipulator workspace and stability during manipulating mode, were systematically evaluated. Finally, hydrodynamic drag characteristics were verified through CFD simulations, and a coupled vehicle-manipulator dynamic model was developed in Matlab to validate the robot's self-recovery, disturbance rejection, and coupling suppression performance.

The results indicate that the internal layout is rational, with critical components meeting the operational requirements for 1000 m deep-sea environments. The maximum stress within the pressure hulls remains below the yield strength of the selected materials. In cruising mode, the robot achieves a maximum endurance of 7 h, and the configured propulsion system ensures high underwater maneuverability. At a cruise speed of 6 kn, the longitudinal drag is recorded at only 725.06 N, significantly lower than that in manipulating mode, demonstrating superior low-drag characteristics. In manipulating mode, the central buoyancy module is raised by 270 mm, increasing the vertical distance between the center of gravity and the center of buoyancy by 0.054 m. As a result, the maximum restoring moment increases by 202.1% compared to cruising mode, significantly enhancing operational stability. The heeling self-recovery time is reduced from 180 s to 60 s, alongside improved anti-disturbance capabilities. Furthermore, the dual-arm workspace effectively covers the lateral, forward, and downward regions of the vehicle, ensuring an efficient and collaborative operational envelope.

By utilizing autonomous configuration switching, an overall design scheme for a morphable underwater intervention robot with multi-task execution capability was proposed. This design effectively combines low-resistance detection in cruising mode with high-stability operation in manipulating mode, offering an innovative solution for underwater operations in complex deep-sea scenarios.

Education in the field of intelligent ships falls under higher maritime engineering education, characterized by a broad knowledge base and high practical requirements. The development and application of intelligent ships have a significant impact on higher maritime education and talent cultivation in ship and ocean engineering. A common issue exists in intelligent ship education, where theory learning is emphasized at the cost of design education and practice application, making it difficult for students to apply theoretical knowledge to solve complex problems in the research and development of unmanned surface vehicles (USVs). To address this challenge, this paper proposes an integrated and continuous experimental teaching platform for the development and verification of USV motion control systems, with the goal of enhancing students’ hands-on capabilities in this field.

This paper applies a model-based design and development paradigm to the practical teaching of USV navigation control systems. This paradigm has become an advanced and practical design and development model for such systems. Centered on the progression from basic navigation control principles to practice implementation, the model-based paradigm is integrated throughout the entire experimental teaching process, from development to verification. Experimental teaching cases are designed based on the typical three-degree-of-freedom planar motion equations of USVs and the classic “guidance-navigation-control” architecture. These cases involve constructing a digital USV controlled object model and an autonomous navigation control system. Through model-in-the-loop (MIL), software-in-the-loop, and hardware-in-the-loop (HIL) simulations, algorithms and key software and hardware are tested and verified in a serialized and phased manner. This approach mitigates the high cost and risk associated with real-vehicle testing while guiding students through experimental tasks, such as motion modeling, multiwaypoint tracking control, remote operation, and state machine design for autonomous mission switching. Finally, the key software and hardware verified through multiple simulation tests are deployed to a consumer-grade USV platform for field testing.

This paper presents a comprehensive experimental teaching platform for USV motion control systems, constructed based on a model-based design approach using MATLAB simulation tools, projected-based case studies, Raytheon V5 Nano controller, 0.68-meter consumer-grade USVs, and other software and hardware. Students engage in a full development cycle, from theoretical design and MIL simulation, to HIL simulation involving real vehicles and controllers, and finally to real-vehicle testing for the verification of autonomous navigation tasks. Through this integrated process design and innovative training approach, the platform successfully achieves the goal of unifying teaching and practice in the design and development of USV motion control systems.

The integrated experimental teaching platform for USV motion control developed in this paper covers the entire process of “theory, design, and practice,” providing continuous and integrated experimental teaching from simulation to real-world application. Closely aligned with theoretical instruction, the platform supports comprehensive and challenging experimental tasks, such as motion modeling, algorithm design, motion control, and parameter tuning. This approach enhances students’ abilities in system-level experimental design, verification, and independent innovative practice. The development process is seamlessly linked and logically coherent, effectively fulfilling the training goal of integrated and continuous experimental teaching for USV navigation control. The platform enables students to master the core methodologies and workflows involved in the design and verification of control systems for intelligent marine equipment, laying a solid foundation for scientific research and engineering applications in the field of intelligent unmanned systems.

Aiming at the problem of accurate real-time pose acquisition in the autonomous recovery of an unmanned surface vehicle (USV), a STag marking visual guidance method for unmanned vehicle docking and recovery is proposed.

Due to the stable attitude characteristics of STag markers, they are selected as the fiducial markers in the visual guidance of this work. By detecting STag markers in the video stream obtained by the camera on the USV, combined with the camera's internal parameters and the size of the markers, EPnP and direct linear transformation (DLT) algorithms are fused to calculate the relative pose of the recovery device and USV. Amplitude limiting filtering and first-order low-pass filtering are then performed to obtain the required lateral offset and heading deviation for line-of-sight (LOS) docking guidance.

In the static performance test, the average angular error of target detection is 6.85° and the average distance error is 0.056 m. In the guided autonomous recovery lake test, the accuracy of static and dynamic docking is within plus or minus 0.5 m.

Compared to traditional USV docking and recovery methods, STag marking visual guidance can enhance the terminal accuracy of USV autonomous docking and improve the overall success rate of docking and recovery.

The paper aims to solves the limitations of the Goldstein body force method in a hydrodynamic simulation of a ducted propeller.

An analysis of the reason for the distortion of the duct hydrodynamic simulation is carried out based on the wing theory, and a correction method based on the mass flow and body force distribution model is proposed. The RANS method is then used to study the simulation accuracy of two kinds of improved body force method.

The results show that the average relative error of the total thrust coefficient of the two improved body force methods under open water conditions is about 5%. The average relative error of the resultant forward force of the two improved volume force methods behind the underwater vehicle are 1.8% and 11.6% respectively.

The simulation accuracy of a ducted propeller based on the improved body force method in open water and behind an underwater vehicle is greatly improved compared with the traditional method. The proposed method can accurately simulate the hydrodynamic performance of a ducted propeller, laying the foundation for the efficient dynamic maneuverability simulation of underwater vehicles.

This paper aims to propose a type of structural verification software for inland ships with embedded specifications, addressing the problem of low calculation efficiency and difficult model reuse in performing manual checking and calculation.

The software is constructted based on the model-view-controller (MVC) framework, with the hull model as the center and the development of core functional modules such as the structural database, section visualization and specification calculation. A hierarchical model of the structure is designed for parameter management and sharing; the model is abstracted to express special structures and decouple from the specifications; and derivation technology is integrated to facilitate software update and model reuse.

The calculation example shows that this verification software based on the abstraction of structural parameters can ensure the integrity and accuracy of specification calculation, and realize the complete compatibility and combination verification of various inland ship types and specifications, with an error rate of just 0.1% against the manual calculation results.

The proposed software breaks through the limitations of different ship types and specifications, realizes intelligent and dynamic structural verification, and reduces the dependence of users on complicated rules and regulations. As such, it can significantly improve the quality and efficiency of design and planning approval work. Compared with other standard structural checking software, this software has the advantages of accurate calculation and rapid modeling.

To deal with the external time-variance disturbances and possible failure of actuators during the dynamic positioning operation of an unmanned underwater vehicle (UUV), this paper proposes a nonlinear observer-based adaptive allocation strategy to achieve thruster fault tolerance.

The control scheme is first established by means of the power sliding mode control technique to obtain the dynamic position. Meanwhile, a nonlinear disturbance observer is designed to estimate external disturbances. Then, based on the estimated external disturbance and state deviation sequence under the failure mode, a quadratic programming problem is constructed and solved to obtain the efficiency factor of each thruster, and the thrust distribution matrix is modified to achieve adaptive control allocation under thruster fault tolerance.

The simulation results show that the UUV control system can effectively estimate external environmental disturbances and the efficiency factor of each thruster. Even if the actuator fails, the UUV can still accomplish its dynamic positioning mission.

The results of this study show that the proposed adaptive thruster allocation and sliding mode control algorithm is reasonable and can be effectively applied to UUVs under external environmental disturbances and actuator failure.