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

研究了高速舰船喷水推进中的振动与损伤问题。水流湍急的输水管道可能会降低矩形截面管道结构，即箱梁的自振频率。本文通过建立力学模型和对本征系统进行计算，阐明了固有频率降低的机理。公式中采用了用于管道结构的有限元和用于水的内部流动的边界单元。作为公式的结果，证明了流动降低了流固耦合系统的刚度，简化矩阵与密度和流体速度的平方成正比，而附加水的质量与速度无关。此外，通过所建立的数值分析，可以得到由于内部流体引起的相邻平板或相对平板之间的耦合振动特性。数值计算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.