The accuracy of underwater sound source localization depends on the preprocessing effect of signal denoising and delay estimation performance. In order to meet the needs of high-precision underwater positioning, this article studies a time delay estimation method based on nonlocal mean-enforced mean empirical mode decomposition (NLM-EEMD) autocorrelation denoising preprocessing and fuzzy C-means clustering (FCM)-generalized quadratic for underwater sound source localization technology. The theories such as NLM, EEMD, FCM, and generalized quadratic correlation delay estimation are studied in detail, and the speech signal of the test library in the TIMIT standard library is selected for simulation analysis, which verifies the correctness of the delay estimation method. Experiments were carried out in a larger outdoor pool. The analysis results show that the NLM-EEMD adaptive denoising method effectively reduces noise interference and improves the quality of EEMD decomposition and the FCM-generalized quadratic correlation method increases the correlation between two signals. The time delay estimation accuracy is improved, and the positioning accuracy is 48.66% higher than that of the direct generalized cross-correlation method.

The extraction of typical features of underwater target signals and excellent recognition algorithms are the keys to achieving underwater acoustic target recognition of divers. This paper proposes a feature extraction method for diver signals: frequency−domain multi−sub−band energy (FMSE), aiming to achieve accurate recognition of diver underwater acoustic targets by passive sonar. The impact of the presence or absence of targets, different numbers of targets, different signal−to−noise ratios, and different detection distances on this method was studied based on experimental data under different conditions, such as water pools and lakes. It was found that the FMSE method has the best robustness and performance compared with two other signal feature extraction methods: mel frequency cepstral coefficient filtering and gammatone frequency cepstral coefficient filtering. Combined with the commonly used recognition algorithm of support vector machines, the FMSE method can achieve a comprehensive recognition accuracy of over 94% for frogman underwater acoustic targets. This indicates that the FMSE method is suitable for underwater acoustic recognition of diver targets.

Underwater unmanned vehicle cluster cooperative area target searching is an inexpensive and efficient effort for salvaging and vigilance at sea. In order to realize the autonomous area searching of the attacking underwater unmanned vehicle (AUUV) cluster, a multiple AUUV cooperative area target searching method is put forward and simulated in this paper. The proposed method combines the AUUV with an underwater environment to create an environmental model, an AUUV motion model, a target probability and update model, and an object optimization function. Moreover, the global-best difference-mutation brain storm optimization algorithm is adopted to test the multiple AUUV cooperative area target searching path planning. The results of the simulation experiment verify the effectiveness of the proposed method and models. Hence, a new scheme is advanced to realize multiple AUUV cooperative area target searching and expand multiple AUUV applications.

A piezoelectric flextensional transducer was designed using the finite element method (FEM) for the passive detection of underwater frogmen. By studying the main performance parameters of sonar transducers for the detection of frogmen around the world, this paper presents the advantages of active and passive sonar in this task and proposes a passive method for the detection of frogmen. Subsequently, a Cymbal transducer was selected considering the needs of the research. After introducing the principles and methods of the FEM analysis, the acoustic and electromechanical characteristics of the Cymbal transducer were verified under the influence of structural dimensions, e.g., resonance frequency, conductance, and susceptance. The electromechanical performance of the Cymbal transducer was simulated with a FEM to study how it is affected by static water pressure and processing errors and to demonstrate the feasible application of the Cymbal transducer in practical applications. In the end, a Cymbal prototype was tested to verify that the designed Cymbal transducer performs in compliance with the requirements and can be used for the passive detection of underwater frogmen with open-circuit breathing.

A multi-resonance Cymbal hydrophone for detection of the open-circuit self-contained underwater breathing apparatus (scuba) diver was designed and fabricated in this work, which has the advantages of multi-resonant frequency, high sensitivity, and narrow bandwidth. By using standard hydrophones, the underwater acoustic signal of the open-circuit scuba diver in the pool was collected and the characteristics of the signal were analyzed: the signal was mainly distributed in high frequency and low frequency. According to this characteristic, a Cymbal hydrophone with multi-resonance frequencies was designed in the finite element method, and the resonant frequency, receiving sensitivity, and bandwidth of the hydrophone were calculated. The accuracy of the calculation was verified with the performance test of the prototypes fabricated in this work. Finally, the underwater acoustic signal of an open-circuit scuba diver in the pool was tested by the prototype to demonstrate that the multi-resonance Cymbal hydrophone developed in this paper can be used for open-circuit scuba diver detection.

Ocean acoustics is an important research topic in ocean engineering. Among them, the location of the impact point at sea is an important method to evaluate the firing accuracy of naval guns. Most of the traditional methods for locating the impact point at sea use the optical positioning principle, which is expensive and has a high false alarm rate. It is easy to be affected by natural conditions, such as marine visibility. Based on this, this paper proposes an improved location method of the impact point at sea based on the Beidou differential and acoustic array, which improves positioning accuracy greatly. First, through the simulation analysis of single array positioning error, this paper gives the basis of the positioning method, then deduces the positioning principle of this method in detail, and simulates and analyzes the positioning error of the double array. Finally, the simulation experiment of the voice signal is carried out to verify the positioning performance of the dual cross-array. The results show that the direction finding of the dual cross-array is very accurate, and the ranging error is relatively large. Among the five positioning points selected in this paper, the maximum relative direction-finding error is 0.33%, and the maximum relative ranging error is only about 1%, which is much better than the ranging performance of a single array. It has certain engineering application values and provides a certain reference for the design of the impact point positioning scheme at sea.