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摘要:
大型直升机着陆过程中会对着陆场地施加较大的冲击荷载，两者之间的动力相互作用与着陆场地的类型密切相关。基于大型直升机的设计着陆工况，设计双锤冲击试验装置，对大型直升机双轮式起落架的双轮同时冲击黄土场地的工况进行小比尺的模型试验，分析双锤冲击下黄土场地不同深度的沉降特性和动应力分布规律，并在此基础上探讨落锤间距对场地变形及动力响应的影响。在双锤冲击荷载作用下，黄土场地浅层区域的沉降曲线呈典型的W型，不同位置处的竖向动应力时程发展曲线相似，呈单峰脉冲特征。沿落锤中心线下的沉降量和动应力幅值随深度增加而递减，但递减速率与深度有关，浅层区域的递减速率最大。不同落锤间距下黄土场地的沉降特性和动应力时程变化规律类似，落锤间距主要影响场地沉降和动应力量值的大小。
Abstract:Strong impact loading is applied to the site during the landing process of large helicopter. The dynamic interaction between a large helicopter and the landing site is significantly dependent on the property of the landing site. The small-scale model test was carried out by modeling the impact loadings of two wheels belonging to one dual-wheel landing gear on the loess site using the new double hammer impact testing equipment, which was based on the fixed landing situation of a big helicopter. The settlement and dynamic vertical stress produced in the loess site are analyzed together with the effects of hammer spacing. It is found that the settlement in the shallow layer of the loess site shows the typical W type under the impact of double hammers. Single pulse characteristics can be observed in the time history curve of dynamic vertical stress, which is comparable in different positions. The magnitude of the settlement and peak vertical stress along the centerline of the drop hammer decreases with increasing depth. However, their decreasing rate is related to the depth and the largest decreasing rate is produced in the shallow layer of the loess site. The hammer spacing mainly affects the magnitude of the settlement and dynamic vertical stress, which has minor effects on the variation pattern of the settlement and dynamic vertical stress.
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Key words:
- impact loading /
- loess /
- dynamic response /
- settlement /
- model tests
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图 3 土压力传感器及白砂标志线布置
Figure 3. Arrangement of earth pressure sensors and white sand marking lines
图 8 不同落锤间距下黄土场地沉降特征
Figure 8. Settlement characteristics of loess sites at different tamper spacings
图 9 冲击坑深度随落锤间距的变化关系
Figure 9. Relationship between impact crater depth and tamper spacing
图 10 不同落锤间距下沿落锤中心线的沉降
Figure 10. Settlement along centerline of hammer at different tamper spacings
图 11 不同落锤间距下竖直动应力时程曲线
Figure 11. Vertical dynamic stress curvies for different tamper spacings
表 1 落锤冲击模型试验各物理量相似比
Table 1. Similarity ratio of physical parameters in tamper impact model test
尺寸相似比 $ {C}_{\rho } $ $ {C}_{g} $ $ {C}_{W} $ $ {C}_{A} $ $ {C}_{E} $ $ {C}_{S} $ n 1 1 $ {n}^{2} $ $ {n}^{2} $ $ {n}^{4} $ $ n $ 
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表 2 大型直升机某真实着陆工况
Table 2. Real landing condition of heavy helicopter
工况 双轮轮距/
mm单轮载荷/
kN单轮接地
面积/cm2单轮冲击
动能/kJ直升机 520 120 517 35.7
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表 3 大型直升机某真实着陆工况的模拟工况
Table 3. Model condition of real landing of heavy helicopter
模拟工况 落锤间距/
mm单锤质量/
kg落锤半径/
mm单锤动能/J 双锤 104 9 29.5 57.15
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表 4 黄土的物理力学性质参数
Table 4. Physical and mechanical property parameters of loess
比重 天然
干密度/
$ (\mathrm{g}\cdot{{\mathrm{cm}}}^{-3}) $天然
含水率/
%最优
含水率/
%塑限
含水率/
%液限
含水率/
%塑性
指数2.71 1.44 18.4 22.4 19.3 36.1 16.8
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表 5 不同落锤间距条件下的荷载作用时间
Table 5. Load action times for different tamper spacing conditions
S/mm $ {T}_{{\mathrm{L}}}$/ms 59 24.4 104 21.9 156 20.9 208 20.0
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