Precise positioning of underwater vehicles using only a single beacon for range measurement is one of the toughest challenges for underwater navigation, especially when the underwater vehicle travels along a straight path resulting in the system unobservable. In this paper, acoustic range measurements are combined with inertial navigation to determine the position of an underwater vehicle using two consecutive measurement points. The contributions of the work presented here are twofold: First, the underwater single beacon localization algorithm proposed in this paper is able to operate under a linear track, and give the solution of the method to reject multi-valuedness. Second, considering the actual work of underwater carriers, extending the strategy to any trajectory can be used. The results obtained by the algorithm are fed back to the inertial navigation system, which can suppress the continued dispersion of inertial navigation errors. The experimental results show that the proposed “Linear track underwater carrier Strapdown Inertial Navigation System (SINS) correction method based on hydroacoustic single beacon” can solve the positioning problem of underwater long-range carriers and suppress further dispersion of their inertial navigation system errors.

This study experimentally and theoretically investigates the effects of surface microstructures on cavity dynamics during vertical water entry of cylindrical bodies. Experimental results indicate that surface microstructures enable rapid cavity expansion during the initial phase of water entry and overcome original characteristic length constraints. Furthermore, the Froude number (Fr) is a critical parameter influencing cavity morphology. Over the tested range, the pinch-off depth of the cavity formed by the cylinders with microstructures still obeys the Fr13scaling law, the microstructured surfaces mainly accelerate the formation of larger cavities. Consistently, as Fr increases, the pinch-off depth, pinch-off time, and cavity growth rate significantly increase, facilitating the formation of a complete cavity envelope in water. This cavity evolution, resulting from the enhanced slip effect identified in our theoretical analysis, transforms the no-slip boundary condition at the solid–liquid interface into a slip condition at the gas–liquid interface, thereby enhancing cavity-liquid coupling dynamics and enriching subsequent water entry behavior. Overall, these findings indicate the role of microstructured surfaces in modulating hydrodynamic interactions, offering insights for designing advanced microstructured surfaces to optimize drag reduction, enhance stability, and improve performance in trans-media vehicles.

The distribution of the geometric positions of the ground navigation stations determines the Geometric Dilution of Precision (GDOP), which is also one of the important factors determining the positioning accuracy of the system. This paper develops a GDOP simulation study of the traditional hyperbolic positioning mode for the Chinese loran C positioning system, constructs the geographical distribution map of the system's GDOP in China, and analyzes the system's high-precision positioning area, common working area, and The distribution of the sea areas and inland areas corresponding to the positioning area provides an important reference for maritime and inland users to maximize the use of the Loran C system positioning service, ensuring user navigation safety.

The development of underwater high-precision navigation technology is of great significance for the application of autonomous underwater vehicles (AUVs). Traditional long baseline (LBL) positioning systems require pre-deployment and the calibration of multiple beacons, which consumes valuable time and manpower. In contrast, the range-only single-beacon (ROSB) positioning technology can help autonomous underwater vehicles (AUVs) obtain accurate position information by deploying only one beacon. This method greatly reduces the time and workload of deploying beacons, showing high application potential and cost ratio. Given the operational constraints of AUV open-ocean navigation with single-beacon weak observations and absence of valid a priori positioning data in calibration zones, a multi-sensor underwater virtual beacon localization framework was established, proposing a differential Chan–Gauss–Newton (DCGN) methodology for submerged vehicles. Based on inertial navigation, the method uses the distance measurement information from a single beacon and observations from multiple sensors, such as the Doppler velocity log (DVL) and pressure sensor, to obtain accurate position estimates by discriminating the initial position of multiple hypotheses. A simulation experiment and lake test show that the proposed method not only significantly improves the positioning accuracy and convergence speed, but also shows high reliability.

Initial alignment is the pre-step of the SINS navigation solution. High-precision initial alignment technology is an important guarantee for SINS's long-time, long-distance, and high-precision navigation and positioning. Kalman filter, as an important method of the initial fine alignment process, has been widely used in engineering practice. This paper is based on the indirect Kalman filter closed-loop algorithm, in order to make full use of the observation information, multiple iterative operation is performed on the state vector obtained from the Kalman filter feedback correction, and a more accurate state vector prediction result is obtained to reduce the linearization error and then the filter accuracy is improved. The final simulation results show that the proposed method can significantly improve the yaw alignment accuracy under the condition of different small initial yaw misalignment angles, which prove the effectiveness of the proposed algorithm.