民机典型机身框段垂直入水冲击特性研究

Vertical water-entry impact characteristics of typical fuselage section of civil aircraft

为了研究民机典型机身框段垂直入水冲击特性,采用入水冲击试验系统开展不同高度下的圆柱体入水冲击试验,研究其入水冲击响应;基于LS-DYNA任意拉格朗日-欧拉(arbitrary Lagrange-Euler,ALE)方法建立流体域均匀网格及局部加密网格模型,通过对比圆柱体入水冲击试验结果验证网格收敛性及流体域模型;基于验证的流体域模型及机身框段模型,研究机身框段在6.02 m/s速度下的入水冲击特性,并分析与刚性地面冲击特性的差异性以及不同入水冲击速度下的机身框段冲击响应特性。结果表明:ALE方法在结构入水冲击方面具有较高的模拟精度,且采用局部加密网格时可以极大减少流体域模型网格数量和入水冲击计算时间。机身框段入水冲击时的失效模式与刚性地面冲击时的失效模式较为一致,但机身框段结构整体变形程度减小,客舱地板横梁变形程度增大;机身框仍是吸能最多的部件,但水也吸收了大量的冲击能量,使得地板导轨处的加速度始终小于刚性地面冲击时的加速度;随着机身框段入水冲击速度的增大,机身框发生弯折和上翘的程度加剧。

Here,to study vertical water-entry impact characteristics of typical fuselage section of civil aircraft,firstly,a water-entry impact test system was used to conduct water-entry impact tests for cylindrical bodies at different heights,study their water-entry impact responses.Secondly,based on LS-DYNA arbitrary Lagrange-Euler(ALE)method,a fluid domain uniform mesh model and a fluid domain locally refined mesh model were established.Mesh convergence and fluid domain models were verified by comparing the results of cylinder water-entry impact tests.Finally,based on the verified fluid domain models and fuselage section model,water-entry impact characteristics of fuselage section at a speed of 6.02 m/s were studied,and differences between the former and its impact characteristics against rigid ground were analyzed,impact response characteristics of fuselage section at different water-entry impact velocities also were studied.The results showed that ALE method has higher simulation accuracy in structural water-entry impact,using fluid domain locally refined mesh model can greatly reduce mesh number of fluid domain model and calculation time for water-entry impact;the failure mode of fuselage section during water-entry impact is more consistent with that of fuselage section impacting rigid ground,but the overall deformation degree of fuselage frame structure decreases,while the deformation degree of cabin floor crossbeam increases;fuselage frame is still the component with the highest energy absorption,but water also absorbs a large amount of impact energy to make acceleration at floor guide-rail be always less than that during section impacting rigid ground;with increase in water-entry impact speed of fuselage section,fuselage frame’s bending and upwarping degree increases.