Research on vibration and damages with water-jet propulsion in high speed ships

研究了高速船舶喷水推进系统的振动和损伤。水流湍急的输水管道会降低管道结构的固有频率，而管道结构是矩形截面的管结构，即箱形梁。本文通过建立力学模型和特征系统的计算，阐明了其固有频率降低的机理。在公式中采用了管道结构的有限元和水内流的边界元，已经证明，流动降低了流体的刚度-结构耦合系统的阻尼矩阵与密度和流速的平方成正比，而附加水质量与流速无关或相对的面板由于内部流体可以通过开发的数值分析获得。数值结果得到了实验的验证。

Vibration and damages in water-jet propulsion in high speed ships are investigated. Water duct in which water flows fast may reduce the natural frequencies of the duct structures which are pipe structures with rectangular cross section, that is, box girder. In the present study the mechanism of the reduction of natural frequencies are clarified by constructing mechanical models arid calculation of eigen systems. In the formulation finite elements for duct structures and boundary elements for inner flow of water are used.As the result of the formulation, It has been proved that the flow reduces thestiffness of the fluid-structure coupled system and the reduction matrix is propotional to dencity and the square of the fluid velocity but added mass of water does not depend on the velocity.Furthermore the features of coupling vibration between adjacent panels or opposite panels due to the internal fluid could be obtained by the developed numerical analysis. The numerical results have been verified by the experiments.