A Shifted Double Wavelet Iteration Algorithm for Detecting the Gross Errors in Shipborne GravityWang, X.; Fan, J. Y.; Deng, K. L.; Chen, X.
doi: 10.1088/1742-6596/2486/1/012053pmid: N/A
Detecting the discrete gross error and regional gross error in shipborne gravity is a key step for improving the measurement quality. The traditional wavelet threshold shrinkage (WTS) method misidentifies discrete gross errors and cannot detect regional gross errors. Here we propose a shifted double wavelet iteration (SDWI) method. This method decomposes the measurement sequence by shifted double wavelet to obtain wavelet coefficients, and then apply threshold processing to the obtained coefficients to accurately detect gross errors. After that, we reconstruct the identified gross errors, and perform iterative processing to the regional gross errors. Finally, the difference of the gravity before and after gross error detection is used for gross error positioning. In the simulation experiment, we use the proposed SDWI method to detect the discrete gross error, the regional gross error and discrete-region gross error in the shipborne gravity, separately. The results show that the detection success rate is 100% and failure rate is 0 for all three kinds of gross errors, better than that of the traditional WTS method. The real data experiment also confirms that the proposed method is effective in detecting gross errors.
Summary of research on generator of offshore wind wave combined power generation systemZhao, Chenyin; Qian, Han; Gu, Jie; Zhu, Yingqian; Gao, Xiang
doi: 10.1088/1742-6596/2486/1/012048pmid: N/A
In recent years, multi energy complementary utilization has become a new trend of energy development. Offshore wind and wave energy have many advantages, such as no pollution, concentrated energy form, etc. a new wind wave combined power generation system based on two degree of freedom linear rotating generator came into being. The research status of offshore wind and wave power generation system is summarized, and the advantages and disadvantages of independently developed offshore wind and wave power generation system, traditional wind wave combined power generation system and new offshore wind wave combined power generation system are compared. The research status of rotating generator of two degree of freedom straight line as the core energy conversion device of a new offshore wind wave combined power generation system is summarized, and the feasibility of using two degree of freedom generator in the new offshore wind wave combined power generation system is preliminarily verified by finite element method. Then, the research hotspots and difficulties of this kind of generator are discussed. Finally, the main research directions of two degree of freedom generator for offshore wind wave combined power generation system in the future are prospected.
The analysis of the depth dependence of ambient noise in the South China SeaRen, C; Huang, Y W
doi: 10.1088/1742-6596/2486/1/012088pmid: N/A
A 64-element vertical array was deployed in the South China Sea for ocean ambient noise observation. A rainstorm passed over the area during the experiment, lasting a total of 35 minutes. The differences between the depth distribution and vertical coherence of wind-driven noise and rain noise are compared, and the influence of rainfall rates on them is analyzed. The wind-driven noise intensity decreases with increasing depth, and it is basically consistent with the theoretical results. The depth distribution of rain noise is different from that of wind-driven noise. When the rainfall rate exceeds 48mm/h, the rain noise intensity in the frequency band above 3200Hz increases with increasing depth. Compared with wind-driven noise, the vertical coherence function depth distribution of rain noise is more uniform. The vertical coherence function of rain noise is in good agreement with the simulation results when the noise source directivity index take a larger value.
Research on the Estimation Method of Target Motion Parameters Based on Ternary ArrayZhang, Yujie; Cui, Hongxu; Wang, Liang
doi: 10.1088/1742-6596/2486/1/012090pmid: N/A
The ternary array passive positioning technique performs the estimation of target distance and bearing by measuring the time delay difference between array elements. The estimates are limited by the geometric model and time delay measurement errors, and the positioning accuracy and reliability are poor. In this paper, we propose an orientation matching-based motion target localization model. By introducing the target motion model, and establish a matching objective function for the time delay difference obtained by calculating the predefined target motion trajectory and the actual received data of the ternary array separately. The matching objective function is optimally solved by using Burg algorithm in the AR spectrum estimation method, and a highly accurate and reliable target parameter estimation can be obtained in a short time. The results of computer simulation experiments verify the effectiveness of the method.
Inversion of Full-depth Temperature Profiles Based on Surface Temperature and AUV Measured DataXian, Yan; Qianqian, Li; Qian, Tong; Ziwen, Wang; Shoulian, Cao; Zhichuan, Ma
doi: 10.1088/1742-6596/2486/1/012011pmid: N/A
The sound speed profile has an important impact on sound propagation and underwater acoustic detection, and the water temperature has the most significant impact on the sound speed, so it is critical to obtain high-precision full-depth temperature profiles. With the rapid development of marine mobile platforms, it is possible to obtain depth-fixed temperature data using surface velocimeter or autonomous underwater vehicles (AUVs). This paper uses the measured thermistor chain data to carry out numerical simulation, and discusses the feasibility of reconstructed full-depth temperature profiles using measured temperature of few discrete depths. The back propagation (BP) neural network is used to generate the nonlinear mapping relationship between the temperature in a few discrete depths and the first two empirical orthogonal function (EOF) coefficients. The experimental results show that the temperature at two specially selected depths can reflect the full-depth temperature profiles to a certain extent. However, the information about the water temperature at different depths is diverse and the thermocline contains the most information. As the depth-fixed data measured by the AUV increases, the inversion accuracy of the full-depth temperature profiles increases accordingly. Results shows that, even in ocean regions that have solitary internal waves, when the depth of the depth-fixed data is selected the same as the depth of the surface layer and the two extreme points of the second EOF, the root mean square error (RMSE) of almost all reconstructed temperature profiles in the test set is less than 0.2°C, and the mean RMSE is about 0.12°C.
Comparative research on 3D visualization of underwater acoustic fields using near real-time databaseChen, Jiandong; Tian, He
doi: 10.1088/1742-6596/2486/1/012074pmid: N/A
In order to realize the near real-time prediction of the ocean acoustic field, this paper conducted a comparative study of HYCOM data and NMDC data for the application of hydrographic datasets, and drew pseudo-color maps of ocean surface temperature distribution and sound velocity distribution characteristics in the area of 4°N~26°N and 105°E~1236°E respectively. Moreover, the 3D visual distribution of sound velocity in the ocean acoustic field in a 1° grid region of 114°E~115°E, 18°N~19°N is also conducted. Comparisons of the results with the two datasets shown that the acoustic velocity distribution characteristics generated by these two datasets remain consistent overall, and the data generated by HYCOM has more detailed features than the NMDC, however, NMDC data has smaller size and advantageous data type of acoustic velocity, which reduces the requirements for computer hardware and offers a faster processing speed.
Track Detection of Underwater Moving Targets Based on CFARZhang, Haoting; Tian, Mei; Ouyang, Qicheng; Liu, Jingjing; Shao, Gaoping; Cheng, Juan
doi: 10.1088/1742-6596/2486/1/012076pmid: N/A
In this paper, we propose a 2D-Weibull-Constant False Alarm Rate (2D-Weibull-CFAR) detection algorithm to solve the problem that detecting current underwater targets is difficult due to the influence of reverberation noise. Specifically, referring to the idea that CFAR uses the probability distribution of reference units to detect objects, this paper introduces the pixel distribution of reverberation noise into the CFAR detector. After that, the probability distribution of the extracted reference units is estimated, and then the adaptive detection threshold is obtained to achieve reliable detection of underwater targets. Finally, the Hough transform extracts the trajectory of the detection results. The experimental test shows that the algorithm in this paper can solve the problem of false alarms and missed alarms in detecting targets hidden in the reverberation noise. The algorithm in this paper can effectively detect the target in the reverberation noise. The detection results show that the algorithm in this paper has higher accuracy and lower false alarm rate than the comparison algorithm.
Research on magnetic anomaly detection method assisted by geomagnetic mapYu, Ziqiang; Pan, Mengchun; Liu, Zhongyan; Xu, Yujing; You, Guanjie; Zhang, Qi
doi: 10.1088/1742-6596/2486/1/012062pmid: N/A
Magnetic anomaly detection is a detection technology for underwater/underground ferromagnetic targets. In the geomagnetic anomaly area, the change of magnetic feld is very complicated, and the detection ability of traditional detection methods will decline sharply. To solve this problem, we construct a high-precision local geomagnetic map, which turns geomagnetic anomalies into known prior information to assist detection. Firstly, the accuracy of local geomagnetic map is improved by the optimized variation function of interpolation algorithm and an efficient mapping strategy. Secondly, the magnetic target detector assisted by geomagnetic map is designed on basis of BP neural network and its internal structure is optimized. Finally, simulation and experiment were carried out. The results show that the method improves the detection performance in the geomagnetic anomaly area by 75%–80%, and well-adapted to low SNR situations. This proposed method makes the detection of geomagnetic anomaly are effective.
Scaled model testing for the helical strakes in reducing the vortex-induced vibrationsSun, Jiayao; Mo, Shiqi; Ye, Renchuan; Liu, Hu
doi: 10.1088/1742-6596/2486/1/012007pmid: N/A
The accuracy of the prediction of the suppression efficiency of the triplex helical strakes for vortex-induced vibrations (VIV) is important in the offshore industry for the risers. Towing tank tests of the 1:1 section model have been used in the study of one degree of freedom; however, this method requires a long time for both the preparation and the testing. In this study, a scaled model testing method based on the flume and the oscillating frame is proposed, which measured the oscillating amplitude and the forces for both the bare pipe and the triplex helical strakes. The scaled tests were carried out in the TU Delft, with the range of Reynolds number between 6000 and 20000. The results were compared with the real model test applied in the towing tank to evaluate the accuracy. The measured strake efficiency of the scale model test agrees with the full-scale model test, providing support for the scaled model test in reducing the vortex-induced vibrations.
Comparative Analysis of Marine Atmospheric Boundary Layer Height Changes in the East China Sea Based on FNL and ERA5 DataChang, Shujie; Zhang, Yisan; Li, Yongchi
doi: 10.1088/1742-6596/2486/1/012002pmid: N/A
This study compiled the NCEP FNL and ERA5 data from 2010 to 2019 to study the characteristics of the height changes of the marine atmospheric boundary layer (MABL) in the East China Sea and selected coastal (region A), offshore (region B), and Kuroshio areas (region C) for comparative analysis. The results show that, in general, the MABL heights of both datasets show a decreasing trend year by year, and the FNL decreasing trend is more significant. The two datasets show the largest difference in the eastern regions, while they are more consistent in the Taiwan Strait, suggesting substantial regional variations. The FNL decreasing trend is more significant than the ERA5 decreasing trend in regions A, B and C from 2014 to 2017. The root mean square (RMS) of the difference between FNL and ERA5 MABL is the largest in winter, followed by summer, showing significant seasonal variations. Regional MABL variations in the ERA5 dataset were more pronounced in summer and the areas with greater regional variations coincided with the areas with mean absolute differences and the RMS large value area of the MABL variation. Both datasets show region A had the largest differences in fall while regions B and C had the largest differences in winter. In terms of daily variation, both MABL reached their highest at 14:00, with the largest differences at 14:00 in regions A and C and at 20:00 and 02:00 in region B. Region A had the largest daily variations as reflected by its largest mean absolute difference and RMS of the 14:00 MABL differences. The effect of seasonal and daily variations in different regions must be considered to study the variation of MABL height in the East China Sea.