半悬臂式燃料元件在间隙限制约束下非线性振动的等效方法研究

Equivalent Method Research on Nonlinear Vibration of Semi-cantilever Fuel Pin Under Gap-limited Constraints

半悬臂式燃料元件为上端固定、下端间隙限制的结构形式,该结构可节省使用和安装空间,具有在小型反应堆应用的潜力。相较于传统的两端固定结构,半悬臂式燃料元件下端呈现弱约束特性,在振动工况下存在碰撞接触非线性行为。针对间隙引起的非线性问题,采用弹支梁等效方法,将底端间隙配合等效为弹簧结构。本文将半悬臂式燃料元件的非线性振动过程通过单摆—悬臂梁模型进行等效,推导出半悬臂式燃料元件振动周期公式,结合弹支梁振动方程,可快速准确得到等效弹簧刚度,从而建立半悬臂式燃料元件在间隙限制约束下非线性振动的等效方法。通过半悬臂式燃料元件抗震分析,对本文方法与传统有限元方法进行对比,结果显示:该案例计算时间大幅度减少,本文计算方法所用时间仅为传统有限元方法的1/74;两种方法的结果表明:在关键部位的振动响应基本一致,初步验证了本方法可快速有效求解具有间隙约束的半悬臂式燃料元件振动问题,为小型反应堆提供了快速设计工具。

The semi-cantilever fuel pin is a structure with fixed at upper end and weak constraint at lower end,that can much reduce size for utilization and installation,and has the potential to be employed in small reactors.Compared with the traditional fuel pin fixed at both ends,semi-cantilever fuel pin with weak constraint at lower end,explored nonlinear behavior of collision and contact under vibration conditions.Aiming at the abovementioned nonlinear problem,an elastic beam with an artificial spring at the lower end is equivalently adopted.In this paper,the nonlinear vibration process of the semi-cantilever fuel pin is equivalent by the single pendulum-cantilever beam model,and the equivalent stiffness of artificial spring is determined from the preliminary vibration in collision condition.Through the seismic analysis of the semi-cantilever fuel pin,the method proposed in this paper is compared with traditional nonlinear FEM.The calculation time of the new method is greatly reduced,which is 1/74 of the traditional nonlinear FEM,and the vibration of key components is much agreed with each other.It is preliminarily verified that the proposed method can quickly and effectively solve the vibration problem of the semi-cantilever fuel pin with weak constraints,and provides a rapid design tool for small reactors.