The chaotic behavior of underwater ray system is studied. Because the parabolic equation is an approximation under small ray angle with respect to horizontal, the elliptic equation system is considered here besides the parabolic system. We pay main attention to the interval of large ray angle. A comparison between these two forms of system is performed. We find that when the ray angle is not large (θ_0=0° - 18°), the two systems show the same qualitative behavior. However, in interval of large ray angle (θ_0 ≥ 19°), if the perturbation strength is not very small, e.g. δ=0.05, the parabolic system shows regular motion, while the elliptic system exhibits chaotic behavior in most of this interval except a few quasiperiodic islands studded in the chaotic ocean. Dynamical behaviors of the two systems show surprising difference.
An ocean sparker with a stored energy of 20 kJ was developed for high resolution ocean seismic survey. The sparker is mainly composed of a high voltage high frequency charging supply, energy storage capacitors, a discharging switch and discharging electrodes. The H-bridge inverter and series resonant mode were adopted in the charging supply, and a dry high voltage transformer was used to improve the safety and maintenance, the average charging rate exceeded 4 kJ/s. An optical fiber connected between the high voltage system and the control system was used to isolate high voltage and transmit the high voltage signal. The high voltage electrodes of the discharging electrodes consisted of several hundreds of electrodes. The experimental results show that the sparker can be operated at repetition rates of 12 shots/min, and can meet the expected design requirements. Further field tests will be done in the near future.
In the present paper, a comparison of analytical calculations, FEM harmonic analysis, and real data from laboratory stand of fluid-loaded structure were taken under consideration. Resonant frequencies of the investigated structure were measured using swept sine technique on laboratory stand. Analytical calculations of the first twelve modes were made and the numerical model was build using the finite element method. Results from real data, analytical calculations, and numerical calculations are comparable.
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