ANALYSIS OF DYNAMIC STABILITY OF SUBMERGED STRUCTURE

The submerged structure is basically a large three-dimensional structure of few statically redundant members. The structure is subjected to vertical dead and live loads in addition to the wave forces. An analysis of dynamic stability of the submerged structure without damping has been made by J. Thomas and Abbas (1980). In this paper the analyses of dynamic stability of the sumberged structure with damping are conducted. The case structure with damping is more complicated 'than the case without it. According to the principle of perturbation, a new model for dynamic stability calculation in consideration of damping effect is developed. In this paper, the formulas are deduced, the computational program is compiled, the practical examples are analysed, and this problem is solved very satisfactorily. The computational results show that the shape and value of the regions of dynamic instability can be changed significantly by damping. So only by considering damping can the property of dynamic stability of the submerged structure be reflected correctly.

Time-domain analysis for vibration and sound radiation of submerged spherical shell excited by force

The vibration and sound radiation of a submerged spherical shell are studied in the time-domain by Laplace transform method, where a CW pulse force acts at the apex of the shell. The numerical results for the case of long pulse show that the different vibrational modes and the resonant or beat radiated sound are excited for different carrier-frequencies, but litle sound is radiated for some vibrational modes. For the case of short pulse the waveforms of the pulse become widened and deformed, when the pulse propagates between apexes of the shell. Then, the Doubly Asymptotic Approximations (DAA2) and Kirchhoff's Retarded Potential Formulate (KRPF)are used to solve the same problem. It is shown that the results of DAA2 and KRPF method have a good agreement with the results of Laplace transform method.

Computation and analysis of the Bessel beam scattering by a submerged elastic sphere

Taking an elastic sphere for example, the acoustic scattering of a submerged object illuminated by a Bessel beam is studied. The partial wave series representation for an elastic sphere has been extended to the case of Bessel beam scattering. Referring to the scattering of a plane wave, the peak to peak intervals in backscattering form function caused by the interference of the specular wave and the Franz wave have been analyzed in geometry. The influence of the characteristic parameterβ of a Bessel beam on the peak to peak intervals has been indicated, and a predictive formula of the the first time. Meanwhile the elastic scattering peak to peak intervals has been established for of each partial wave has been separated based on the Resonance Scattering Theory. The influence of β on the pure elastic resonance has been studied further. The results show that selecting specific β can reduce the contribution of a certain partial wave. Therefore the resonance at the corresponding frequency and the nearby region in the backscattering is remarkably suppressed. The work of this paper could be helpful to the applications of Bessel beams on the acoustic detection of submerged objects.