Motion control of unmanned surface vehicles (USVs) is a crucial issue in sailing performance and navigation costs. The actuators of USVs currently available are mostly a combination of thrusters and rudders. The modeling for USVs with rudderless double thrusters is rarely studied. In this paper, the three degrees of freedom (DOFs) dynamic model and propeller thrust model of this kind of USV were derived and combined. The unknown parameters of the propeller thrust model were reduced from six to two. In the three-DOF model, the propulsion of the USV was completely provided by the resultant force generated by double thrusters and the rotational moment was related to the differential thrust. It combined the propeller thrust model to represent the thrust in more detail. We performed a series of tests for a 1.5 m long, 50 kg USV, in order to obtain the model parameters through system identification. Then, the accuracy of the modeling and identification results was verified by experimental testing. Finally, based on the established model and the proportional derivative+line of sight (PD+LOS) control algorithm, the path-following control of the USV was achieved through simulations and experiments. All these demonstrated the validity and practical value of the established model.

Many marine mammal species, such as different kinds of whales and dolphins, live together in groups. Although having no nice eyesight, they can accomplish cooperative foraging, intercommunication and group sailing very efficiently and accurately only depending on their sound. Generally, present interception systems almost always classify biological signals as ocean noise and try to filter them out. In addition, the covertness and security are very important for many military underwater platforms (MUPs) and their formations. Based on above classification fact and covert communication demand, this article designs a basic bio-inspired camouflage communication frame (BBICCF) for secure underwater communication among military underwater platforms based on the killer whale sound. According to characteristics of the killer whales’ original call pulse trains, the original long duration call pulses (whistles and pulsed calls) are utilized as communication address codes for each MUP so as to provide disguised communication addressing support for interconnection among multiple MUPs in the same formation, and the original short duration call pulses (clicks) are used as other communication codes, so as to construct BBICCF for highly camouflaged conveying communication information. A simple and effective timefrequency (TF) contour extraction method is proposed to achieve the accurate extraction of the TF contour of the fundamental frequency of whistles and pulsed calls of killer whales for efficient classification and decoding of address codes. Next, this article provides some extensions and applications about how to let the BBICCF to be applied in conventional communication networks for MUP formation. Finally, simulation results show the effectiveness and concealment ability of designed BBICCF.

The covertness of an active sonar is a very important issue and the sonar signal waveform design was studied to improve covertness of the system. Click is one of the most common cetacean sounds, and has excellent detection performance. Meanwhile, existing interception systems normally classify cetacean sounds as ocean noise and filter them out. Based on this, a bio-inspired covert active sonar detection method is proposed by encoding the clicks produced by sperm whales. First, based on the frequency distribution characteristic of sperm whale clicks and frequency-hopping sequence, a set of bionic sub-pulses are constructed by encoding the centroid frequency of the real clicks. Based on the inter-click interval characteristic of the clicks and time-hopping sequence, the bionic sonar signal is constructed by combining the constructed bionic sub-pulses and encoding the inter-pulse interval between two adjacent pulses. Then, a single bionic sonar signal is utilized to estimate the speed and range of the target. Based on the characteristics of sperm whale click trains, a camouflage application method is designed to improve the camouflage ability of the bionic sonar signal. Finally, experiment results show that when the target speed is 5m/s and 10m/s and the signal to noise ratio varies from −20dB to 20dB, the root-mean-square error of estimated speed and range are lower than 0.1m/s and 0.1m, respectively. In addition, the constructed bionic sub-pulses have a 99% probability of being classified into sperm whale clicks. Experimental results demonstrate the effectiveness and covertness of the proposed method.

For most conventional bionic signal design methods, they cannot construct high-similarity bionic signals to match those complex cetacean sounds because they are only based on relatively simple bionic signal models. Besides, although very few methods based on the weighted signal superposition technology can construct high-similarity bionic signals, it’s very difficult to adjust relevant parameters to match different cetacean sounds or synthesize other desired bionic signals. To solve these problems, firstly, two bionic signal models are proposed individually to mimic cetacean sounds with a simple time-frequency (TF) structure, and then they are combined to mimic cetacean sounds with complex TF structures based on a designed piecewise construction strategy. Based on the two models, the parameters of the synthesized bionic signals can be adjusted to improve detection and communication performance of the bionic signals. The experimental results show that the Pearson correlation coefficient (PCC) results between 13 true cetacean sounds and their corresponding bionic signals are higher than 0.97, and 11 results of them are no less than 0.99. Four key performance indicators of a bionic signal are improved by more than 40% when bandwidth increases by 1kHz. Experimental results demonstrate that the proposed method cannot only efficiently imitate all kinds of simple and complex cetacean tonal sounds with high similarity, but also construct a variety of the same type of bionic signals by simply adjusting model parameters. In addition, the proposed method can also be applied to other areas, such as constructing a new cetacean sound database and so on.

The covertness of the active sonar is a very important issue and the sonar signal waveform design problem was studied to improve covertness of the system. Many marine mammals produce call pulses for communication and echolocation, and existing interception systems normally classify these biological signals as ocean noise and filter them out. Based on this, a bio-inspired covert active sonar strategy was proposed. The true, rather than man-made sperm whale, call pulses were used to serve as sonar waveforms so as to ensure the camouflage ability of sonar waveforms. A range and velocity measurement combination (RVMC) was designed by using two true sperm whale call pulses which had excellent range resolution (RR) and large Doppler tolerance (DT). The range and velocity estimation methods were developed based on the RVMC. In the sonar receiver, the correlation technology was used to confirm the start and end time of sonar signals and their echoes, and then based on the developed range and velocity estimation method, the range and velocity of the underwater target were obtained. Then, the RVMC was embedded into the true sperm whale call-train to improve the camouflage ability of the sonar signal-train. Finally, experiment results were provided to verify the performance of the proposed method.