This paper proposes an improved method to accurately and expediently detect water columns at the shells’ impact point. The suggested method combines a lightweight depthwise convolutional neural network (MobileNet v3) with the You Only Look Once X (YOLO X) algorithm, namely, YOLO X-m (MobileNet v3) that aims to simplify the network’s structure. Specifically, we used a weighted average pooling network and a spatial pyramid pooling network comprising multiple convolutional layers to retain as many features as possible. Moreover, we improve the activation and loss functions to reduce network calculations and afford better precision as well as fast and accurate water column detection. The experimental results reveal that YOLO X-m (MobileNet v3) ensures a good detection performance and adaptability to various light intensities, distances, and multiple water columns. Compared with the original YOLO X-m model, the improved network model achieves a 75.76% frames per second improvement and a 71.11% capacity reduction, while its AP50decreases by only 1.29%. The proposed method is challenged against the single shot multibox detector and various YOLO variants, revealing its appealing accuracy, real-time detection performance, and suitability for practical applications and projects.
An adaptive channel estimation algorithm for the channel length is proposed to construct a channel estimation model suitable for orthogonal frequency division multiplexing (OFDM) underwater acoustic communication signals for the dependence of traditional channel estimation algorithms on channel length information. This algorithm can be adopted to evaluate channel estimation quality in real time and to adaptively adjust the channel length of the channel estimation algorithm according to the evaluation result, which satisfies the need of accurate estimation of unknown underwater acoustic channels and communication application; based on the study on the relationship between the OFDM communication bit error rate and the subcarrier signal to noise ratio, a self-adjusting optimization scheme for OFDM subcarrier transmitting power is proposed, which realizes underwater communication with the low bit error rate through higher energy efficiency. The validity of the research content is verified through simulation and field experiments.
In order to improve the firing efficiency of large-caliber naval gun, a new method of “Time-on-target (TOT)” for fixed-loading ammunition of large-caliber naval gun is proposed in this paper, and a model of TOT for fixed-loading ammunition of largecaliber naval gun is established, which verifies the feasibility of multiple simultaneous firing. Based on the naval gun attacking small and fast targets on the sea surface, combined with the naval gun tactical application, the TOT firing method of fixed ammunition of naval gun based on ladder firing is given, and the effectiveness of the method is verified by simulation.
This paper proposes a three-dimensional laser beam-riding guidance
(LBRG) scheme with finite distance convergence for the interception
guidance problem of laser beam-riding guided missiles (LBRGMs). First,
the motion relationship between the guidance station, missile, and
target is constructed, and a three-dimensional LBRG model based on
position deviation is designed. Considering the finite range of the
laser beam and convergence performance of the guidance system, a
finite-distance convergence performance function is proposed, and its
guidance law is designed by combining the prescribed performance and
sliding mode control methods. Then, considering the unknown maneuvering
information of the target, the acquired maneuvering information is
converted into an estimation of the line-of-sight angle and its rate,
estimated by designing the command filter. In addition, Lyapunov theory
is employed to prove the stability of the guidance scheme. The position
deviation converged to the steady-state value within the prescribed
flight distance, thereby satisfying the prescribed transient and
steady-state performance requirements and realizing the interception of
the maneuvering target. Finally, the effectiveness of the guidance
scheme is verified through simulations.
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