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This paper focuses on the research of the radiation noise of underwater unmanned vehicle (UUV), which is one of the most important indicators for evaluating the performance of underwater unmanned equipment. Integrating experimental study and numerical calculations, this paper investigates the underwater radiated noise characteristics and hydrodynamic properties of the propeller of UUV. Firstly, an open-water radiated noise experiment is conducted. To ensure the accuracy of acoustic test, the UUV are held stationary during the experiment. Then, the hydrodynamic performance of a propeller in a steady flow field is calculated using Computational Fluid Dynamics (CFD). Finally, the noise in the unsteady flow field is calculated using the Ffowcs Williams-Hawkings (FW-H) equation. The results show that the propeller, as the main noise source when the UUV is working, exhibits distinct characteristic line spectra in the frequency response curve. By comparing the numerical and experimental results, it was found that the overall trend of the sound pressure level is similar. But the line spectrum characteristics of the numerical results between 100 and 400 Hz are more obvious, mainly because the simulation model is more idealized compared to the experimental tests. The study further examines the hydrodynamic characteristics, propeller noise, and directional characteristics of UUV under different operating conditions.

In this paper, in view of the characteristic that UUV radiation noise is low and easily interfered by strong noise, the complementary Ensemble Empirical Mode Decomposition (CEEMD) combined with symmetric correlation processing is proposed, which can improve the extraction performance of UUV’s propeller features. First, the CEEMD decomposition combined with symmetric correlation processing was used to reduce the radiated noise of the target, then the signals after the noise reduction were demodulated and computed to obtain the DEMON spectrum, and finally features such as the rotational speed of the UUV’s propeller were extracted from the DEMON spectrum. The Sea trials signal processing results prove that the method has better noise suppression performance under low SNR conditions, and can clearly and comprehensively extract the DEMON information of the radiated noise, and then accurately extract the propeller features of the UUV. Compared to conventional demodulation techniques, this technique has a greater ability to suppress noise and does not require manual selection of the modulated frequency band.

To address the problem that acoustic transfer functions with underwater platforms cannot be measured accurately, this paper presents a method based on phase compensation to improve the accuracy of acoustic transfer function measurements on underwater platforms. The time-domain impulse response signals with multiple cycles are first collected and intercepted, and then their phase differences are estimated using the least-squares method, and phase compensation is used to align the phases of all the signals, and then the impulse response signals are weighted and averaged over all the impulse response signals to cancel out the random noise. The water pool test proves that this method reduces the measurement random noise while obtaining a high-fidelity time domain transfer function, which effectively improves the signal-to-noise ratio of the measurement. The method adopts only one measurement signal, and without changing the measurement system, the random noise is cancelled out by the in-phase superposition of the multi-cycle impulse response signals to avoid the nonlinear distortion of the measurement results.