Abstract:

Abstract:In order to solve the parameter adjustment problems of adaptive stochastic resonance system in the areas of weak signal detection, this article presents a new method to enhance the detection efficiency and availability in the system of two-dimensional Duffing based on particle swarm optimization. First, the influence of different parameters on the detection performance is analyzed respectively. The correlation between parameter adjustment and stochastic resonance effect is also discussed and converted to the problem of multi-parameter optimization. Second, the experiments including typical system and sea clutter data are conducted to verify the effect of the proposed method. Results show that the proposed method is highly effective to detect weak signal from chaotic background, and enhance the output SNR greatly.

Abstract:To calibrate the phase retardance of a Liquid crystal variable retarder (LCVR) , its birefringence dispersion characteristic was analyzed, and the Support vector machines (SVM) algorithm was adopted to establish the prediction model. The obtained SVM decision function was used as a part of LCVR phase retardance, which was generated by the driving voltage. The experimental verification was carried out with a 568 nm laser. The results show that the deviation of the experimental value and the theoretical value is about 0.0061λ. SVM method could be used as an effective method for LCVR phase retardance characteristic calibration.

Abstract:This paper analysis the developing of expendable conductivity temperature depth measuring system (XCTD) and introduce its principle of measuring about temperature, salinity and depth of ocean. Some key techniques are put forward. According to the real needs of XCTD, conductivity sensor with high sensitivity is designed by principle of electromagnetic induce, the ocean conductivity from induced electromotive force has been calculated. Adding temperature correction circuit would help to reduce error of conductivity measurement because of sharply changing temperature. Advanced temperature measuring circuit of high precision and the constant current source is used to weaken effect of self-heating of resistance and fluctuation of the source. On respect of remote data transmission, LVDS is a good choice for the purpose of guarantee the quality of data transmitted and the transmission distance is reaching to thousand meters in the seawater. Modular programming method is also brought into this research aimed at improve the stability, reliability and maintainability of the whole measuring system. In February, 2015, the trials in South China Sea demonstrate that the developed XCTD realize effective measurement at a speed of 6 knots and detection depth at 800 m. The consistency coefficient of the acquired data is greater than 0.99 and the success rate of probe launching is above 90%.

Abstract:Recently ocean wave energy draw much more attention for its widespread, abundant and highly energy flux density properties. Extracting energy from incident wave however, is limited for the random and unstable power input. Motion control for WEC is a promising method to improve the energy absorption and some practical applications are also verified such as latching control. In this paper, an active control strategy is proposed to achieve maximum energy capture. The mathematical description shows that the active control has the characteristic of anti-causal and the wave premonition is necessary for controller design. But the fact of premonition time horizon is still unclear. In this paper, the premonition nature is described mathematically based on hydrodynamic theory. Furthermore, a simulation is also performed to study the impacting of premonition time horizon on WEC’s properties and give a more insightful understanding of WEC active control.

Abstract:As the traditional methods can not meet the requirements of marine radioactivity monitoring, a radioactivity monitoring sensor used in marine field has been proposed. This sensor is based on Nal(TI) scintillation crystal and employs the special shielding method, the anticoincidence design, the spectrum stabilization algorithm of characteristic peaks and the Monte Carlo simulation fitting calibration formula. Through the continuous tests of terminals and the activity test for target nuclide 40K, it is found that the sensor is stable and the error is less than 10%.

Abstract:In order to research the underwater echo characteristics of elastic shell, the numerical expressions of surface sound pressure and particle vibration velocity are derived based on finite element and boundary element theories. The echo characteristics of hollow coaxial cylinder-cone assembled elastic shell are calculated with simulation and experiment methods to obtained the azimuth angle and frequency characteristics. It's shown in the results that the more quantity of mesh point, the higher precision of calculation. Meanwhile, the magnitude of mirror reflection wave is largest in the echo wave between 20 and 40 kHz, and increases as the scattering cross-section. The backscatter sound pressure of elastic shell has the obvious frequency characteristic.

Abstract:RLS and LMS blind adaptive multi-user detection algorithm and multi-user detector was proposed to solve the problem of multi-user signal detection problem encountered in underwater acoustic communication networks. In simulation analysis, RLS and the LMS blind adaptive multi-user detector were designed and tested for synchronous and asynchronous multi-user communication process. The results of SIR comparison and MMSE comparison show that, both of the two methods can realize blind adaptive detection when any user change in multi-user communication, during this process, the training communication sequences are not needed. The RLS algorithm has about 5dB higher in SIR compared with LMS algorithm, and the convergence velocity of RLS algorithm is also higher than LMS algorithm when the communication users change. RLS algorithm has better ability in multi-user detection than that of LMS algorithm, and it has great attraction and guiding significance for solving the problem of multiple access interference (MAI) in multi-user communication.