有限元法分析车辆低频振动时不同退变程度人体腰椎的力学响应

背景:长期处于车辆低频振动环境中不利于人体腰椎健康,且部分驾驶员腰椎已发生了一定程度的退变,然而车辆低频振动对不同退变程度腰椎的损伤机制尚无定论。目的:通过对比同一腰椎在不同振动环境以及不同腰椎在同一振动环境中的力学响应,确定不同振动频率对不同退变程度腰椎力学性能的影响。方法:建立4种不同退变程度人体腰椎有限元模型,施加车辆正常行驶时可能产生的低频振动,模拟腰椎在低频振动作用下的力学响应。结果与结论:①短时间低频振动时,4种腰椎的阻尼减振效果较好,而一旦振动时间过长,中度与重度退变腰椎的力学性能显著下降,因此建议已患有中、重度腰椎退变的驾驶员驾车时间不易过长;②随着退变程度加重,腰椎固有频率有逐渐降低的趋势;③排除共振频率,同一腰椎在不同振动频率作用下力学性能变化不显著,也就是说,驾驶同一辆车在不同良好铺装路面行驶对驾驶员腰椎力学性能的影响并无明显差异。

Recovery of coupled networks after cascading failures

With society＇s increasing dependence on critical infrastructure such as power grids and communications systems, the robustness of these systems has attracted significant attention.Failure of some nodes can trigger a cascading failure, which completely fragments the network, necessitating recovery efforts to improve robustness of complex systems. Inspired by real-world scenarios, this paper proposes repair models after two kinds of network failures, namely complete and incomplete collapse. In both models, three kinds of repair strategies are possible, including random selection（RS）, node selection based on single network node degree（SD）, and node selection based on double network node degree（DD）. We find that the node correlation in each of the two coupled networks affects repair efficiency. Numerical simulation and analysis results suggest that the repair node ratio and repair strategies may have a significant impact on the economics of the repair process. The results of this study thus provide insight into ways to improve the robustness of coupled networks after cascading failures.

基于三周期极小曲面的新型梯度支架设计及其力学、渗透、组织分化特性研究

为建立具有良好生物学性能的骨支架结构,本文基于螺旋(G)型、菱形(D)型三周期极小曲面(TPMS),设计了两种新型梯度TPMS支架:双向线性渐变G型(L-G型)支架、D型/G型融合(N-G型)支架,并通过压缩仿真获得了两种支架的结构力学性能参数。然后,本文通过计算流体动力学(CFD)仿真获得了支架内流体的流动性能参数,并由达西定律计算出两种支架的渗透率。基于组织分化理论,本研究预测了两种支架的组织分化面积。研究结果显示,L-G型支架较N-G型支架的承载能力更强,而N-G型支架在渗透率及软骨组织分化面积等生物学性能方面更优。L-G型和N-G型支架的建模过程为骨支架的设计提供了一种新思路,文中的仿真分析也可为支架植入人体后的骨整合预测提供参考。