87 research outputs found
股骨髁上简单骨折随愈合时期变化的负重能力研究
股骨远端骨折稳定性差、并发症多,目前多主张进行积极的手术治疗。术后的早期康复训练有助于促进骨折愈合,但大多基于临床医生经验,缺乏客观指导。本文通过影像学数据获得了股骨的三维几何模型,建立了使用锁定板固定的股骨髁上简单骨折模型,研究了股骨在单腿站立姿态下,不同愈合时期骨折固定模型的应力分布和传递机制。结果表明:骨折固定模型的应力分布状态受骨折方向和愈合时期的影响,例如锁定板的最大Mises应力在相邻两个愈合期最高相差70%。文章以锁定板系统失效为标准,给出了股骨髁上简单骨折早期承载能力的半定量指标,表明了患者需要针对骨折方向和愈合时期及时调整术后负重大小,对临床康复训练有指导意义
遥感-岩石力学(III)——交汇断层粘滑的热红外辐射与声发射规律及其构造地震前兆意义
以构造地震孕震机制之三即交汇断层粘滑发震为模拟对象,利用双轴加载实验系统和红外热像仪对自然界经常出现的断层组合模式——不同交汇角度的组合断层的物理模型进行了室内加载实验,利用红外热像仪和声发射仪分别测定了加载过程中试样表面的红外辐射及断层活动的声发射时间序列。结果表明:(1) 声发射及红外辐射的时间序列特征受加载过程中试样的力学行为所控制,并表现出阶段性变化特点;(2) 声发射与红外辐射特征与断层几何结构有密切关系,当主应力与主断层成45°角时,红外辐射异常区主要沿主断层发育;(3) 垂直交汇的断层与斜交断层的声发射及红外辐射特征有明显差异,交汇角度(1°~90°)越大,交汇点处的红外辐射异常越明显
Selectivity of biopolymer membranes using HepG2 cells
Bioartificial liver (BAL) system has emerged as an alternative treatment to bridge acute liver failure to either liver transplantation or liver regeneration. One of the main reasons that the efficacy of the current BAL systems was not convincing in clinical trials is attributed to the lack of friendly interface between the membrane and the hepatocytes in liver bioreactor, the core unit of BAL system. Here, we systematically compared the biological responses of hepatosarcoma HepG2 cells seeded on eight, commercially available biocompatible membranes made of acetyl cellulose–nitrocellulose mixed cellulose (CA–NC), acetyl cellulose (CA), nylon (JN), polypropylene (PP), nitrocellulose (NC), polyvinylidene fluoride (PVDF), polycarbonate (PC) and polytetrafluoroethylene (PTFE). Physicochemical analysis and mechanical tests indicated that CA, JN and PP membranes yield high adhesivity and reasonable compressive and/or tensile features with friendly surface topography for cell seeding. Cells prefer to adhere on CA, JN, PP or PTFE membranes with high proliferation rate in spheriod-like shape. Actin, albumin and cytokeratin 18 expressions are favorable for cells on CA or PP membrane, whereas protein filtration is consistent among all the eight membranes. These results further the understandings of cell growth, morphology and spreading, as well as protein filtration on distinct membranes in designing a liver bioreactor.</p
Dynamic Parameter Optimization of High-Speed Pantograph Based on Swarm Intelligence and Machine Learning
Good pantograph-catenary interaction quality is a fundamental premise for ensuring stable and reliable current collection of high-speed trains, and the optimization of dynamic parameters of high-speed pantographs provides an effective approach to improve the current collection quality of the pantograph-catenary system. In this paper, with the objective of minimizing the standard deviation of the pantograph-catenary contact force, the multi-parameter joint optimization for pantograph at different filtering frequencies and running speeds was carried out by using swarm intelligence optimization algorithm and artificial neural network method. First, the selection operator in genetic algorithm (GA) was introduced into crow search algorithm (CSA), and the selective CSA was proposed, which can effectively improve the solution accuracy and convergence rate of multi-parameter optimization. Second, a radial basis function (RBF) neural network was used to construct a surrogate model of the standard deviation of contact force with respect to the running speed and pantograph dynamic parameters, and a method for optimizing the upper limit of mapping interval of the decision variables by the selective crow search algorithm (SCSA) was proposed, which effectively improves the generalization ability of the surrogate model. Finally, by combining the surrogate model and SCSA, optimization iterations for a total of 630 combined conditions such as cut-off frequency, running speed and pantograph dynamic parameters were conducted, and an optimization method for high-speed pantograph dynamic parameters with universal applicability was proposed
Mechanical behavior and mechanism investigation on the optimized and novel bio-inspired nonpneumatic composite tires
Two novel nonpneumatic tires named Tweel-2, designed based on the commercial Tweel model, and Saddle with hyperbolic paraboloid spokes are proposed in this study. Four nonpneumatic tire samples were successfully prepared with the 3D printing technology to measure and analyze and compare their properties. The results of quasi-static compression experiments showed that with the same relative density, the vertical bearing capacity of Tweel-2 tire was 1.4 times that of Tweel tire, while the vertical bearing capacity of the saddle tire was 4 times and 2.4 times that of Tweel and honeycomb tires, respectively. The finite element simulation method was used to explore the mechanism of improvement in vertical bearing capacity and energy absorption of the Tweel-2 and saddle design. The so-called circumferential unit in Tweel-2 and honeycomb tires enhances the deformation coordination between the spokes of Tweel-2 and increases the critical bearing capacity of the spokes by shortening the length of the deformation zone, so that more external work can be consumed under the same vertical deformation. The spatial configuration of the hyperbolic paraboloid can optimize the spatial stress distribution of the saddle tire and makes sure that a bigger amount of material deforms and participates in energy absorption, thus improving the overall strain energy level of the spokes
Experimental and numerical study on crashworthiness of bionic hedgehog spine thin-walled structures
Natural impact-resistant biomaterials, with ingenious and exquisite geometric configurations, have resistance to external impact, and thus provide a perfect bionic example for the optimization design and crashworthiness improvement of new thin-walled structures. Based on the configuration characteristics of hedgehog spine, this paper designed the bulkheaded hedgehog spine thin-walled structure and studied the dynamic behavior of thin-walled structures under axial and oblique impact compression by combining 3D metal printing, quasi static compression test and finite element simulation. The results show that the combined effect of the ribs, inner walls and bulkheads of the bulkheaded hedgehog spine thin-walled structure effectively improves its deformation coordination ability and crashworthiness. The specific energy absorption of the bulkheaded hedgehog spine thin-walled structure under axial or oblique impact is about 4.1, 2.1 and 1.4 times that of the single-wall cylinder, spider web and simplified hedgehog spine thin-walled structures, respectively
非均质多孔结构的冲击响应和能量吸收特征
金属多孔材料具有出色的缓冲吸能效果,为了从机理上阐述多孔材料的冲击响应特性,基于一维激波[2]传播理论的刚塑性完全锁定(RPPL)模型最先被提出。该模型可以较好预测在单轴冲击载荷作用下,密度均匀分布的多孔材料其平台应力以及塑性耗能的变化情况。然而,目前的研究很少涉及密度分布不均匀的非均质多孔材料,为了能够从理论上对这类结构的力学性能进行分析和预测,本文在RPPL模型的基础上,提出了全新的理论模型,同时通过与有限元模拟结果进行对比验证。结果表明:本文中的理论可以准确的预测非均质多孔材料其冲击端平台应力和整体塑性耗能,此外,在整体相对密度保持一致的前提下,非均质多孔材料有着比密度均匀分布结构更出色的能量吸收效率
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