ADVANCE IN BIOMECHANICS OF HUMAN EAR AS HEARING SYSTEM

耳是人体重要的听觉器官. 人耳是一个典型的在声波激励下的传导振动,继而将振动转变成听神经纤维的脉冲发放结构. 建立完整有效的人耳结构生物力学模型,研究它的生物动力学行为,有助于我们认识和分析人耳的传音及感音机理,研究人耳病理状态下和手术后的传声及感音机制的变化,进一步为研究相关临床疾病的生物力学机制提供理论依据. 本文总结了人耳听力系统生物力学模型及临床应用的研究进展,并展望了今后的研究工作.     

检验人工听骨力学性质的解析方法

传导性耳聋多由鼓膜或听骨链病变所致,人工中耳已在临床上广泛应用于传导性耳聋治疗.根据人工中耳结构试验和力学假设,用变分原理建立在任意时刻$t$点,人工鼓膜受迫振动位移与激发声压的关系,推导控制方程. 采用分离变量法及贝塞尔函数对方程求解,得到鼓膜和听骨位移的解析解. 通过与文献试验数据比较,感觉曲线形状与走势基本一致,证明了该方程是正确的,能够反映声音的传导机制. 利用方程计算得到:质量小的材料传音效果好于质量大的;顶盘面积一定时,质量为某一特定值时传音效果更佳; 该结果与相关文献的试验结果相符合. 研究表明: 该方程对于人工中耳数据的获得非常方便,并且能够优化人工听骨材料,特别是对质量的控制能达到科学的效果,避免测量因素及其他因素的干扰.该方法为耳生物力学的研究及应用提供了新的视点.      

内皮抑素抑制肿瘤血管生成的数值模拟

数值模拟抗血管生成药物内皮抑素对肿瘤血管生成的抑制效应. 建立内皮抑素作用下肿瘤内外血管生成的二维、三维离散数学模型,模型中考虑内皮抑素的抑制作用、内皮细胞自身的增殖、促血管生成因子TAF和Fibronectin对内皮细胞产生的趋化性和趋触性以及内皮细胞自身扩散引起的随机性运动,数值模拟肿瘤内外微血管网的生成过程. 模拟结果表明,抗血管生成药物内皮抑素对肿瘤内外血管生成的速度、成熟度以及血管分支数量均有明显的抑制作用,从而有效地抑制肿瘤新生血管的形成. 该模型能够较好地模拟内皮抑素对肿瘤血管内皮细胞迁移与增殖的抑制效应,为临床抗血管生成治疗肿瘤提供有益的信息.      

平整冰和碎冰区单桩锥体风电基础结构冰载荷离散元分析

在渤海和北黄海海域,冰载荷是影响风电基础结构振动响应及疲劳寿命的关键因素.对于单桩风电柔性结构而言,在水线处安装抗冰锥可有效降低冰载荷,保障海上风电安全运行.为分析海冰对锥体风电结构的冰载荷,基于扩展多面体离散元方法模拟了平整冰和碎冰对锥体风电结构的作用过程,分析了不同锥径和海冰密集度下的锥体风电结构冰载荷及冰激结构振...     

具有强SORET效应的充分发展的混合流体行进波对流

混合流体Rayleigh-Benard对流是研究对流稳定性,时空结构和非线性特性的典型模型之一。本文利用流体力学扰动方程组的数值模拟,讨论了偏离传导状态具有强SORET效应的混合流体行进波对流的温度场和浓度场的成长过程,分析了充分发展对流情况下的对流振幅,Nusselt数及混合参数与相对瑞利数的关系。并给出了行进波相速度对相对瑞利数的依赖关系。结果说明混合参数的曲线与行进波相速度的分布曲线是类似的。文末,给出了垂直速度,温度和浓度场的分布并讨论了相对瑞利数对场的分布及不同场之间的相位差的影响。     

结构可靠性仿真方法研究

可靠性仿真是对复杂结构系统进行可靠性分析计算最为有效的方法,引起了研究者越来越广泛的关注.综合目前结构可靠性仿真方法研究现状,介绍了蒙特卡罗(Monte-Carlo,MC)法、极限状态方程重构法、随机有限元法(stochastic finite element method,SFEM)进行结构可靠性仿真计算的特点及发展现状,归纳了固体火箭发动机(solid rocket motor,SRM)结构可靠性的特点及当前进行仿真的方法;并在此基础上分析了目前结构可靠性仿真方法及对SRM结构可靠性进行仿真分析计算时存在的不足及需要进一步研究的内容.     

二维矩形腔体中混合流体行进波对流

Rayleigh-Benard模型是研究对流稳定性,时空结构和非线性特性的典型模型之一。本文的兴趣集中在二维矩形腔体中混合流体对流场的结构方面。利用SIMPLE算法数值求解流体力学方程组,模拟了充分发展的二维矩形腔体中混合流体对流。结果说明偏离传导失去稳定的系统经过亚临界分叉产生了振动对流。进一步,我们给出了分叉曲线及其沿分叉曲线的上部分支三个Rayleigh数对应的对流图案的垂直速度场,流线,温度场,浓度场和Shadowgraph强度的等值线图。所有场的结构分析表明浓度场及Shadowgraph强度的等值线图可以很好的特征行进波的运动特性。     

冷热组合凹模的最优化设计理论

通常组合凹模的设计是根据经验公式确定直径及过盈量,往往不是最优值.本文根据工作状态的内压力及模具的材料屈服强度,用弹塑性理论及热的传导理论及多元函数偏微分求极值的方法得出组合凹模各直径及过盈量的最优设计值,最大地增加模具承受的内压力,从而提高模具寿命.用此方法进行设计,已在我厂生产实践中收到良好效果.     

一种骨小管中液体流动产生的流量及切应力模型

骨组织受力变形后其内部液体就会流动,同时在其微观结构——骨单元壁中扩散,并进一步产生一系列与骨液流动相关的物理效应,如流体剪切应力、流动电位等,这些物理效应被细胞感知并做出破骨或成骨等反应,来使骨适应外部载荷环境.鉴于骨组织产生的内部液体流动很难实验测定,理论模拟是目前的主要研究手段.基于骨单元的多孔弹性性质建立了骨小管内部液体的流动模型,该模型将骨单元所受的外部载荷与骨小管内部液体的压力、流速、流量和切应力联系起来,并进一步可以研究其力传导与力电传导机制.骨小管模型的建立分别基于中空和考虑哈弗液体的骨单元模型,并考虑了骨单元外壁的弹性约束和刚性位移约束两种边界条件.最终得到骨单元在外部轴向载荷作用下,骨小管内部液体的流量及流体切应力的解析解.结果表明:骨小管中的液体流量与流体切应力都正比于应变载荷幅值和频率,并由载荷的应变率决定.因此应变率可以作为控制流量和流体切应力的一种生理载荷因素.流量随着骨小管半径的增大而非线性增大,而流体切应力则随着骨小管半径的增大而线性增大.此外,在相同的载荷下,含哈弗液体的骨单元的模型中,骨小管中液体的流量和切应力均大于中空骨单元模型.     

口腔种植体中的生物力学

 介绍了口腔种植体的发展历史及基于骨结合理论基 础上的现代口腔种植体所取得的巨大成绩. 概述了种植体设计及临床应用中所遇 到的生物力学问题, 包括种植体的载荷传导特点、种植体/颌骨系统的力学建模、 种植体所引起的骨吸收等等. 指出了我国研发具有自主知识产权的种植体体系的 重要性.     

Blood flow and microgravity

The absence of gravity during space flight can alter cardio-vascular functions partially due to reduced physical activity. This affects the overall hemodynamics, and in particular the level of shear stresses to which blood vessels are submitted. Long-term exposure to space environment is thus susceptible to induce vascular remodeling through a mechanotransduction cascade that couples vessel shape and function with the mechanical cues exerted by the circulating cells on the vessel walls. Central to such processes, the glycocalyx – i.e. the micron-thick layer of biomacromolecules that lines the lumen of blood vessels and is directly exposed to blood flow – is a major actor in the regulation of biochemical and mechanical interactions. We discuss in this article several experiments performed under microgravity, such as the determination of lift force and collective motion in blood flow, and some preliminary results obtained in artificial microfluidic circuits functionalized with endothelium that offer interesting perspectives for the study of the interactions between blood and endothelium in healthy condition as well as by mimicking the degradation of glycocalyx caused by long space missions. A direct comparison between experiments and simulations is discussed.     

浅谈动脉流体动力学分析

就我们所熟知,绝大部分正常动脉流,其血液的流动特性是属于层流范围,但随着弯曲和分 支部分会产生血液流之二次回流区,进而形成所谓近似非稳态流及紊流. 因此动脉流体的特 性会随动脉外形及条件的改变而改变. 在某些情形下,异常动脉的血液动力特性会造成动脉 的病变. 因此,近年来动脉血液流体的特性的研究,常着重于异常动脉的血液动力特性所形 成剪应力和病变部位动脉粥状硬化关系的探讨. 动脉血液流动经常包含分离流或二次回流运动,而这是流体力学的分析或数值模拟最困难的 部分. 有关分离流或二次回流的研究包括正常血管流和异常血管流,藉由二次回流的模拟与 测量可以观察血管病变的形成与演变,其中最受注目探讨题目是窄化血管如粥状斑块相关的 血液流动分析. 将回顾二维和三维、稳态、非稳态之动脉血流与窄化血管相关的几何外形作模拟研究和 实验. 并提供对血液动力学的研究方向,以作为未来医疗诊断与发展相关器材之参考.     

3D numerical study of tumor blood perfusion and oxygen transport during vascular normalization

The changes of blood perfusion and oxygen transport in tumors during tumor vascular normalization are studied with 3-dimensional mathematical modeling and numerical simulation. The models of tumor angiogenesis and vascular-disrupting are used to simulate "un-normalized" and "normalized" vasculatures. A new model combining tumor hemodynamics and oxygen transport is developed. In this model, the intravasculartransvascular-interstitial flow with red blood cell(RBC) delivery is tightly coupled, and the oxygen resource is produced by heterogeneous distribution of hematocrit from the flow simulation. The results show that both tumor blood perfusion and hematocrit in the vessels increase, and the hypoxia microenvironment in the tumor center is greatly improved during vascular normalization. The total oxygen content inside the tumor tissue increases by about 67%, 51%, and 95% for the three approaches of vascular normalization,respectively. The elevation of oxygen concentration in tumors can improve its metabolic environment, and consequently reduce malignancy of tumor cells. It can also enhance radiation and chemotherapeutics to tumors.     

脉动流条件下动脉狭窄血管内脂质浓度极化现象的计算机数值模拟

在脉动流条件下,用计算机数值模拟的方法对低密度脂蛋白(LDL)在动脉狭窄血管段内的质量传输进行了研究。计算结果表明．无论是在定常流还是在脉动流条件下．LDL都将聚积于血管狭窄处峰口附近的流动分离点,LDL壁面浓度在此处最高。在脉动流条件下,LDL在血流受扰动区的聚积高于定常流的值;而且．流动分离点处LDL壁面浓度峰值覆盖的区域也宽于定常流。本文所揭示出的LDL在血管狭窄处的质量传输现象可能在动脉粥样硬化的局部性和动脉狭窄的形成中起着很重要的作用。     

Wave motions of a liquid in tubes of viscoelastic material. Waves of small amplitude

The pliability of the walls of blood vessels is one of the essential factors determining the movement of the blood. Although there is an extensive literature devoted to this problem (see, for example, the collection [1] and the bibliography it contains), little attention has been devoted to the physiologically important specific effects related to the presence of muscular layers in the vascular wall. These effects may be roughly characterized as a significant variation in the rheological properties of the wall resulting from the activity of the vascular musculature. The latter, in turn, is controlled not only by external, nonmechanical factors but also by the stressed state of the wall itself (see, for example, [2]). Experiments indicate that in the vascular walls there are time-dependent effects characteristic of viscoelastic bodies [1] and a complex static “pressure-radius” characteristic, which may have a decreasing segment [3, 4]. Both of these facts can be reasonably interpreted within the framework of the general continual model for muscle tissue presented in [5]. In what follows, we shall study in a quasi-one-dimensional approximation the combined effect of the above-mentioned properties of the wall material on the behavior of small disturbances imposed on the stationary flow in the tube. We consider the possible types of instabilities. It is assumed that the inertial effects are insignificant and that the rheological law applicable to the wall is a nonlinear generalization of the Poynting model.     

Pulsatile blood flow in a resistance vessel

The quasi-one-dimensional Newtonian fluid flow in an active vessel in which the inlet pressure oscillates about a mean value is considered. The vascular wall is assumed to display the Bayliss effect and a reaction to changes in blood flow. The first is characterized by the dependence of the contractility of the vascular smooth-muscle cells on the intravascular pressure and the second by the sensitivity of the endothelial cells to the wall shear stress. The dependence of the period-average radius and blood flow rate on the mean value and pulsation amplitude and frequency of the inlet pressure is investigated numerically. The characteristics are compared for the passive vessel, the vessel with the Bayliss effect, and the vessel with both reactions.     

Exploring the potential of blood flow network data

To gain a better understanding of the role of haemodynamic forces during the development of the cardiovascular system, a series of studies have been reported recently that describe flow fields in the vasculature of model systems. Such data sets, in particular those reporting networks at multiple stages, mark a transition in the focus from single blood vessels to large parts of vascular networks. It becomes possible to investigate the behaviour of a blood vessel in the context of its surroundings, rather than as an isolated entity. In this study, a framework is presented that facilitates the analysis of such data sets. The blood vessel data is represented as a graph, with each node connected by a vessel segment with known properties. Using this framework the pressure distribution and other parameters of interest can then be estimated. Two examples are given that make use of this scheme: (1) a method to detect and reduce measurement errors in the network and (2) a method that allows the testing of various haemorheological models. For both examples a proof-of-principle result is shown.     

Simulations of magnetic capturing of drug carriers in the brain vascular system

The present paper reports on numerical simulations of blood flow and magnetic drug carrier distributions in a complex brain vascular system. The blood is represented as a non-Newtonian fluid by the generalised power law. The Lagrangian tracking of the double-layer spherical particles is performed to estimate particle deposition under influence of imposed magnetic field gradients across arterial walls. Two situations are considered: neutral (magnetic field off) and active control (magnetic field on) case. The double-layer spherical particles that mimic a real medical drug are characterised by two characteristic diameters - the outer one and the inner one of the magnetic core. A numerical mesh of the brain vascular system consisting of multi-branching arteries is generated from raw MRI scan images of a patient. The blood is supplied through four main inlet arteries and the entire vascular system includes more than 30 outlets, which are modelled by Murray’s law. The no-slip boundary condition is applied for velocity components along the smooth and rigid arterial walls. Numerical simulations revealed detailed insights into blood flow patterns, wall-shear-stress and local particle deposition efficiency along arterial walls. It is demonstrated that magnetically targeted drug delivery significantly increased the particle capturing efficiency in the pre-defined regions. This feature can be potentially useful for localised, non-invasive treatment of brain tumours.     

A mathematical model for ATP-mediated calcium dynamics in vascular endothelial cells induced by fluid shear stress

In consideration of the mechanism for shear-stress-induced Ca^2＋ influx via ATP（adenosine triphosphate）-gated ion channel P2X4 in vascular endothelial cells, a modified model is proposed to describe the shear-stress-induced Ca^2＋ influx. It is affected both by the Ca^2＋ gradient across the cell membrane and extracellular ATP concentration on the cell surface. Meanwhile, a new static ATP release model is constructed by using published experimental data. Combining the modified intracellular calcium dynamics model with the new ATP release model, we establish a nonlinear Ca^2＋ dynamic system in vascular endothelial cells. The ATP-mediated calcium response in vascular endothelial cells subjected to shear stresses is analyzed by solving the governing equations of the integrated dynamic system. Numerical results show that the shear-stress-induced calcium response predicted by the proposed model is more consistent with the experimental observations than that predicted by existing models.     

夹层动脉瘤及覆膜支架模型的流固耦合分析

腹主动脉瘤腹主动脉瘤(Abdominal Aortic Aneurysm,AAA)是危及病人生命的严重疾病,若主动脉瘤不加以治疗,瘤腔将不断长大而有破裂的危险,尽管目前对主动脉瘤的研究较多,但对主动脉夹层动脉瘤(Aortic Dissecting Aneruysm,ADA)的研究较少,本文在周期性脉动速度和压力条件下,对DNA内部流场及植入覆膜支架进行了流固耦合的数值模拟.得到了夹层动脉瘤内部流场的速度矢量分布,瘤壁上的位移、应力分布.同时对夹层动脉瘤植入覆膜支架前后进行了对比分析,覆膜支架的植入使得瘤壁上的最大应力和最大位移均从瘤腔壁面转移到管状动脉壁上,且数值大大下降,说明植入覆膜支架能很好的防止夹层动脉瘤破裂.