某科考船艉部舱段振动固有频率计算方法

Calculation method for natural vibration frequency of stern cabin in oceanographic research vessel

[目的]艉部振动是研究船舶振动的重要组成部分,为了提高艉部振动的计算精度和效率,[方法]研究局部舱段模型建模范围和混合模型中舱段模型的建模比例。运用有限元法,对某直叶桨科考船分别建立不同的模型方案:6个不同比例的混合模型方案用于讨论详细舱段模型建模的比例;5个不同范围的局部舱段模型方案用于研究不同建模范围对固有频率的影响。此外,对刘易斯法和虚拟质量法考虑附连水质量的影响进行讨论。[结果]研究表明,混合模型的舱段模型建模比例在1/5L(船长)以上时,各方案的频率计算结果接近;当建模范围在振动节点附近时,局部舱段计算结果与混合模型计算结果吻合较好;使用刘易斯法和虚拟质量法对局部舱段模型进行计算时,计算结果差异较大。[结论]因此,建议用建模范围为1/4L的局部舱段模型研究船舶艉部振动,并推荐使用虚拟质量法考虑附连水的影响。

Vibration prediction for stern cabins is an important part of research into the global vibration of ships.To address the need to improve precision and efficiency,a study is carried out on the proportion of a mixed model and the length of a3D stern cabin model to investigate the natural frequency of a ship.Using the FE method,different types of model are established for a research vessel,including six mixed models that are used for the basis of a detailed discussion on the different proportions of mixed models,and five stern cabin models that are used to analyze the impact of the modeling range on the natural frequency.Moreover,the Lewis method and virtual mass method are both used to consider the impact of outside water in the analysis of the wet mode.It is observed that the results of the calculated natural frequency of the mixed models are approximately the same when the proportion of the mixed models is over1/5the length of the ship,and in good agreement with the results of the calculations when the modeling range of the stern cabin models is exactly in the vicinity of the vibration node of the ship.For the local vibration calculation of ships using the Lewis method and virtual mass method,the results of various schemes differ greatly when applied to the stern cabin models.The results suggest that the proportion of local cabin models should be1/4the length of the ship in the natural frequency calculation,and the virtual mass method is recommended for considering the impact of local additional water mass.