Abstract: In view of the shortcomings of the present positioning method of loose parts of nuclear power station when estimating the signal arrival time difference, such as difficult judging the starting point accurately, big error and poor anti-noise performance, a time difference estimation method based on Hilbert transform is proposed, thereby the positioning can be realized by estimating the location of loose parts on the basis of the time difference. The Hilbert transform can extract the signal envelope, and the arrival time of the first peak of envelope is taken as the time of the biggest energy bending wave arrival to the sensor. The propagation speed of bending wave can be calculated by analyzing the main frequency of signal. On the basis of the wave speed and the signal arrival time difference between different sensors, the triangle positioning method is adopted to realize the positioning analysis of loose parts. A flat-plate test bench is built, and comparison tests are carried out under different signal-to-noise ratio (SNR) conditions and between different methods. Test results show that the average estimated deviation of this method is 34.1 mm, and even when the SNR is 1 dB, it still can obtain an accurate result. This method features high positioning accuracy, good anti-noise performance and high operating speed.

Key words: Envelope extraction, Hilbert transform, Loose parts, Positioning, Crashworthiness, Hot Forming, Multi-objective optimization, Radial basis function, Tailored property