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

对高速船舶喷水推进的振动与损伤进行了研究。水流湍急的风管可以降低矩形截面管结构即箱梁的固有频率。本文通过建立力学模型和本征系统的计算，阐明了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部流动的边界元。该公式证明了流动降低了流固耦合系统的刚度，并且还原矩阵与密度和流体速度的平方成正比，但加入的水质量与速度无关。此外，通过数值分析还可以得到由于内部流体作用而引起的相邻板间或相对板间的耦合振动特征。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.