| Turbulence observation has become important measures to research the ocean turbulence. The achievementsof turbulence observation help us to improve understanding of the turbulence and ocean mixing process on circulation dynamics. However, the technologies of ocean turbulence observationhave always been the major problems in the field of marine research turbulence all overthe world. Shear sensorsarethe main tools in the application of ocean turbulenceobservation, ithas many advantages:high flexibility, high spatial response capability and high resolution, etc. Turbulence observation data are obtained by shear sensors hashigh reliability and versatility. Therefore, shear sensorsarethe necessary sensors in turbulenceobservation platform. After shear sensors are used in different observation platforms to measure turbulence signals, observation platform which is equipped with shear probes has special requirements because of the detection principles of sensors.To study the characteristics of ocean turbulence, OUC(Ocean University of China)has newly designed an observing systems based on mooring platform andequipped with shear sensors. The mooring system can provide turbulence measurements for long-term periods. To detectthe reliability and applicability of the system, we analyze andprocess the data obtained from mooring system. In this paper, the object of study is the data obtainedfrom the experiment of the turbulence observation system in the South China Sea. We firstly analyzedthe motion state of the mooring platform and the results show that the mooring system can meet the requirements of the turbulence observation. Then, we mainly focused on the impact of the vibration signal obtained in measurement processon turbulence signals and discussed the method to build complex networksby usingthetimeseries of TKE(Turbulent Kinetic Energy).Finally,apreliminary study of the characteristics of dissipation rate of TKE is given.First of all, the characteristics of the instrument to track flow direction, characteristics of anglepitch and the characteristics of vibration for mooring platformwere were analyzed from a comprehensive perspective of the turbulence measurement principle and observation requirements by using a graphical comparison and correlation coefficient. Then,we described and summarized the causes of the noises which are generated in the process of measuring turbulence signals.For mechanical vibration, the damping materials were used to increase damping,and for vortex-induced vibration and noise, the denoising algorithm of cross spectrum was improved.Finally, according to the basic characteristics of the turbulence data of TKE, the method to build complex networks was proposed by using dissipation rate of TKE time series. By studying the data based on mooring platform of the turbulence observation system, wehad verifiedthe reliability and validity of the system. The main contribution of the paper is as follows:(1) Research on the motion state of the mooring platformUsing a graphical comparison to compare the data obtained byattitude sensor with the data obtained by RCM (Record Current Meter),we did a comprehensive analysis for the characteristicsof flow tracking, angle pitch and vibrationof the platform by correlation coefficient. The results suggested that the heading of moored platform could always keep 180°With flow direction, so we could say that the platform had a good ability of tracking flow direction. In addition, the angle pitch of platform ranged between -10°and 10°which had also met the requirements of turbulence detection. Due to affecting by various ocean environments, the mooring system was vibrated strongly in the Y-axis and Z-axis. The results above all had validated that the turbulence observation system based on mooring platform had reached to the design requirements and had met the long-term ocean turbulence observation conditions.(2) Research on the mechanical vibration of the mooring platform and the de-noise methodIn the marine environment, the mooring platform can produce noises which can contaminate the turbulence measurement signals. We had analyzed the sources of noise and summarized that vibration transmission is a major factor.For the noiseof mechanical vibration, we proposed the method of using water-based vibration damping materials to reduce noises and improved the installation of the mooring system. The verification test was carried in the laboratory, by analyzing the vibration signals in the time domain and frequency domain, the results suggested that the vibration energy can be significantly reduced by usingthe new method.(3) Research on the de-noising algorithm based on cross-spectral theoryAccording to the mathematical model and cross spectrum theory of turbulence measurement signals, we had improved the original cross spectrum de-noising algorithm in this paper. Reference to the results concluded in the analysis of vibration of mooring platform, we used the dual vibration signal of Y-axis and Z-axis to reduce noises, the effects is significantly improved and the magnitudeof TKE can reduce 1-2 orders. The new algorithm improved the accuracy of turbulence measurements, which has very important implications for the study of turbulence.(4)Research on the time seriesof the dissipation rate of TKEWe use the statistical averaged methods to process the dissipation rate of TKE, and the results show that the dissipation rate of TKEhas some certain regularity:the peak appears twice a monthand once a troughin the chart and has a peak corresponding to the 18th in the lunar calendar.(5) Research on thedissipation rateof TKE based on the complex networksBased on the approach to build complex networks and the characteristics of dissipation rate of TKE, we set up the network nodes, and improved visual principles and a new approach to the complex networks is proposed. Then, the node degree distribution of the complex networks is analyzed preliminarily. The result shows that the exponent is estimated to be α≈3.5 and the networks is scale-free networks. |
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