A set of calibration system for multi-beam sonar is designed by the principle and method of underwater acoustic metrology. Using the multi-dimensional operation control device, the calibration for acoustical index is completed in the anechoic pool, including the sound source level and beam width. The calibration for geometrical index is carried out in the large scale and deep-water prototype pool, including the bathymetric accuracy. Components and method of the calibration system are introduced, as well as the expanded uncertainty of the calibration system is presented. By comparing the calibrating value and the indicating or nominal value of the detected multi-beam sonar, test results show that the sound source level error is less than 0.7dB, the beam width indication error is less than 10% and the bathymetry value error is less than 0.2%. © 2021 Institute of Physics Publishing. All rights reserved.

During petroleum exploration and exploitation, the oil well-testing data collected by pressure gauges are used for monitoring the well condition and recording the reservoir performance. However, due to the large number of the collected data, the classification of this large volume of data requires a previous processing for the removal of noise and outliers. It is impractical to partition and process these data manually. Vibration-based features reflect geological properties and offer a promising option to fulfil such requirements. Based on the 75 on-site measured samples, the time-frequency-domain features are extracted and the classification performance of three classical classifiers are investigated. Then the downhole data processing and classification method is present by analysing the cross interaction of different types of data features and different classification mechanism. Several feature combinations are tested to establish a processing flow that can efficiently remove the noise and preserve the shape of curves, high signal to noise ratio rates, with minimum absolute errors. The results show that optimal multi-feature combination can achieve the highest working stage identification rate of 72%, the parameters optimized support vector machine can achieve the better classification performance than other listed classifiers. This paper provides a theoretical study for the data denoising and processing to enhance the working stage classification accuracy.

Time delay is a very significant measurement in the field of detection and positioning. The accuracy of time delay estimation directly influences the precision and reliability of the positioning. Aiming at improving the accuracy of time delay estimation in positioning, a new method of high precision time delay estimation is proposed in this paper. Assuming the background noise as Gaussian distribution and Laplace distribution, the new method firstly performs auto-correlation and cross-correlation operation on the received signal to suppress noise initially, and then performs fourth order cumulant operation to further suppress noise and finally extract time delay information by cross correlation method. Comparing with generalized cross-correlation method, second-correlation method and high-order cumulant method, the new method can effectively suppress Gaussian noise and Laplace noise interference. The new method can achieve higher precision and obtain high precise detection and positioning. At last the simulation results verify the effectiveness of the new method. © 2019 IEEE.

Chongqing city is the important node of golden waterway of Yangtze River. As the promotion of the Yangtze River economic belt strategy and normal operation of Three Gorges Reservoir (TGR), more and more attention has been paid to the sediment problem of Chongqing reach. After the experimental storage of 175m in the TGR, Chongqing reach is located in the fluctuating backwater area, with export boundary conditions and river-bed erosion and deposition changed. In recent years, with the water storage of cascade reservoirs in the lower reaches of Jinsha River, the condition of water inflow and sediment in this section has changed and the river-bed is adjusted accordingly. According to prototype observation data from 2003 to 2017, the flow-sediment conditions and river-bed erosion and deposition of Chongqing reach after the impoundment of TGR at different stages were comarred and analyzed. Results showed that during the initial storage period of TGR, from June 2003 to May 2008, sediment erosion and sediment was mainly related to water and sediment of upstream, with whole reach in a state of erosion and intensity was about 140.8 million m3 every year. After the impoundment of TGR, from September 2008 to October 2012, the condition of incoming water and sediment in Chongqing reach maintained original change trend and sediment erosion was mainly related to impoundment of TGR, with whole reach in a state of erosion, but intensity was small. From October 2012 to December 2017, sand from upstream of Chongqing reach reduced greatly, so river bed was drastically adjusted and scour intensity increased significantly, was about 312.2 million m3 every year. It concluded that decrease of upstream sediment is one of the important reasons for increased scour intensity in Chongqing reach. © Published under licence by IOP Publishing Ltd.

As traditional linear Lamb wave technique is insensitive to early stage damage such as micro-cracks and the existing nonlinear Lamb wave methods have difficulty in locating the damage, this paper proposes a novel Lamb wave-mixing method to detect and locate micro-cracks in plate, which extends the wave-mixing method in bulk wave to Lamb wave. Taking advantage of the characteristics of different modes of Lamb wave with different velocities, the meeting problem in hulk wave is changed into a pursuit problem to realize the location of the micro-crack. The pursuit process of S0 mode and A0 mode Lamb wave in a plate with micro-crack was simulated in the finite element method. The results show that when S0 mode Lamb wave catches up with A0 mode in the crack region, there will be obvious wave mixing effect. The closer the meeting location is to the micro-crack, the larger the amplitude of difference frequency signal will be. The feasibility of Lamb wave-mixing method to locate the micro-crack is verified by an experiment.