藏东南波密地区岩石风化速率及其影响因素分析

根据解剖学发现的人体小腿骨间膜血管和胶原纤维有序排列的特点,建立三维组织间隙液渗 流模型,控制方程用Brinkman方程和连续性方程,使用Fluent软件进行数值模拟. 计算结 果显示,组织液在组织间隙中流动的方向总体是与平行毛细血管的方向相一致的;组织间隙 多孔率会影响速度的分布,当多孔率增加时,空间的速度趋于均匀,从而使得最大速度变小, 正常生理范围内多孔率的改变对于组织液流动的影响较小. 但当多孔率很小时(组织纤维化), 会大大影响组织液流动的均匀性;组织间隙平行胶原的存在,会使得组织间隙速度在空间上 的分布趋于均匀;另外,间隙流场随血压的增加而增加,随组织压的增加而降低,这与临床 和经络研究的发现相一致.     

多层平行裂隙型多孔介质通道内流体流动传热特性

基于Brinkman-extended Darcy模型和局部热平衡模型, 对多层平行裂隙型多孔介质通道内的流动传热特性进行研究. 获得了多层平行裂隙型多孔介质通道内各区域的速度场、温度场、摩擦系数及努塞尔数解析解, 并分析了裂隙层数、达西数、空心率、有效热导率之比等对通道内流动传热特性的影响. 结果表明: 达西数较小时, 通道多孔介质层内会出现不随高度变化的达西速度, 此达西速度会随裂隙层数的增加而增大, 但却不受各裂隙层下多孔介质层位置变化的影响. 增加裂隙层数会减弱空心率对压降的影响, 会使通道内流体压降升高, 但升高程度会逐渐降低. 增大热导率之比或减小空心率会使多裂隙通道内出现阶梯式温度分布, 而在较小热导率之比或较大空心率时多裂隙情况下的温度分布曲线会趋于一致. 此外, 当热导率之比较小时, 多层裂隙通道内的传热效果在任何空心率下都要优于单裂隙情况, 当热导率之比较大时, 存在临界空心率使各裂隙层数通道内的传热效果相同, 且多裂隙通道内继续增加裂隙层数对传热强度影响不大.      

基于Starling假设新发现的组织流场模拟

根据微血管壁渗流的Starling假设新发现,对人体骨间膜的组织液流动进行数值模拟,讨论 了组织间隙蛋白质非均匀分布对流动的影响. 结果发现血管壁中对蛋白质有渗透屏障作用的 纤维基质层, 导致了组织空间蛋白质非均匀分布. 靠近动脉端,高静水压引起毛细血管内液体 的净流出,使组织蛋白无法扩散到血管壁附近;在静脉端,由于毛细血管内静水压较低,蛋 白质可以扩散到血管壁附近. 将组织空间蛋白质非均匀分布与传统的Starling模型假设的蛋 白质浓度定常的数值模拟结果对比发现,两者组织液流动的速度有较大的差异,前者的最大 速度是后者的一半,非均匀分布模型的模拟结果更符合实验观察的现象,说明组织间隙蛋白 质的非均匀分布对组织液的流动很重要.     

膨胀性非牛顿流体多孔介质流动的模拟分析

在表征体元尺度采用格子Boltzmann方法分析膨胀性非牛顿流体在多孔介质中的流动,基于二阶矩模型在演化方程中引入表征介质阻力的作用力项,求解描述渗流模型的广义Navier-Stokes方程．采用局部法计算形变速率张量,通过循环迭代得到非牛顿粘度和松弛时间．对多孔介质的Poiseuille流动进行分析,通过比较发现结果与孔隙尺度的解析解十分吻合,并且收敛较快,表明方法合理有效．分析了渗透率和幂律指数对速度和压力降的影响,研究结果表明,膨胀性流体的多孔介质流动不符合达西规律,压力降的增加幅度小于渗透率的减小幅度．当无量纲渗透率Da小于10-5时,流道中的速度呈现均匀分布,并且速度分布随着幂律指数的减小趋于平滑．压力降随着幂律指数的增加而增加,Da越大幂律指数对压力降的影响越明显．     

不同润湿性纳米通道内库埃特流动的模拟

利用非平衡分子动力学模拟方法, 模拟了两无限大平行平板组成的纳米通道内的库埃特流动, 并给出了壁面润湿性和速度对流场密度、速度分布及壁面滑移的影响规律.数值模拟中, 统计系综采用微正则系综, 势能函数选用LJ/126模型, 壁面设为刚性原子壁面, 温度校正使用速度定标法, 牛顿运动方程的求解则采用文莱特算法.结果表明, 纳米通道内流体密度呈对称的衰减振荡分布, 且随壁面润湿性的降低, 振荡幅度减小, 振荡周期保持不变;滑移量随壁面润湿性的提高而降低, 甚至在亲水壁面时出现负滑移现象;随壁面速度的增加滑移速度逐渐增大, 且在流体呈现非线性流动阶段其增幅显著加大.另外, 还发现当壁面设置为超疏水性时, 壁面滑移呈现出随润湿性降低而减小的反常现象, 并基于杨氏方程对其进行了解释.     

考虑热流固耦合作用的多孔介质孔隙尺度两相流动模拟

为了研究深层油气资源在岩石多孔介质内的运移过程, 使用一种基于Darcy-Brinkman-Biot的流固耦合数值方法, 结合传热模型, 完成了Duhamel-Neumann热弹性应力的计算, 实现了在孔隙模拟多孔介质内的考虑热流固耦合作用的两相流动过程. 模型通过求解Navier-Stokes方程完成对孔隙空间内多相流体的计算, 通过求解Darcy方程完成流体在岩石固体颗粒内的计算, 二者通过以动能方式耦合的形式, 计算出岩石固体颗粒质点的位移, 从而实现了流固耦合计算. 在此基础上, 加入传热模型考虑温度场对两相渗流过程的影响. 温度场通过以产生热弹性应力的形式作用于岩石固体颗粒, 总体上实现热流固耦合过程. 基于数值模型, 模拟油水两相流体在二维多孔介质模型内受热流固耦合作用的流动过程. 研究结果表明: 热应力与流固耦合作用产生的应力方向相反, 使得总应力比单独考虑流固耦合作用下的应力小; 温度的增加使得模型孔隙度增加, 但当注入温差达到150 K后, 孔隙度不再有明显增加; 温度的增加使得水相的相对渗流能力增加, 等渗点左移.      

固液双相作用下多孔自润滑表面渗流行为分析

以多孔自润滑材料为研究对象，分析载荷作用下多孔基体变形和润滑液在孔隙中的流动特性，探讨多孔表面渗流速度随加载时间变化，分析固-液双相作用下多孔表面渗流与润滑行为.结果表明，多孔基体变形后，孔隙内储存的润滑液受迫流动，在多孔表面发生渗入和析出的流动现象.润滑液在接触区向多孔基体渗入，在接触区入口向多孔表面析出.恒定载荷下，入口两侧润滑液不能保持稳定的渗流现象，而随加载时间呈现出扩散和波动的变化过程.在竖直方向上，多孔材料内的最大流体压力发生在上表面，最大固相应力发生在靠近上表面的次表面位置.随加载时间延长，磨擦界面的液相承载力先增大后降低，固相承载力先降低后增大，最终液相承载力降低为零，外载荷全部由固相材料承担.适当增加载荷能提高润滑液在多孔表面上的渗流速度，改善润滑状态，但也使得润滑液的渗流速度波动更为剧烈.     

微纳米结构壁面对流场及动压润滑的影响研究

固体边界具有的微纳米结构将影响流体在近壁面处的流动行为,进而由于尺度效应改变流体在整个微间隙的流动或润滑规律.将壁面可渗透微纳米结构等效为多孔介质薄膜,采用Brinkman方程来描述流体在近壁面边界渗透层内的流动,并将其与自由流动区域的不可压缩流体Navier-Stokes控制方程耦合,在界面处的连续边界条件下求解和分析了速度分布规律和压力变化规律.针对恒定法向承载力的油膜润滑条件,进一步讨论了静止表面或运动表面的微纳米结构对近壁面流动行为的影响;并揭示了考虑壁面微纳米结构的流体动压润滑的油膜厚度和摩擦系数的变化规律.论文结果为具有可渗透微结构表面的微间隙流动与润滑提供了理论参考.     

叶片转动对涡轮间隙内部流动影响的数值研究

机匣与叶片的相对转动是影响涡轮叶顶间隙流动的重要冈素之一.对LISA 1.5级轴流涡轮间隙内部流动的数值计算结果表明:叶片转动对涡轮间隙流动有阻塞作用.叶片静止时,由于阻塞作用消失,导致间隙入口速度增大,间隙流鼍增加,并且通过间隙的流体全部卷起形成间隙涡.同时在叶片顶部吸力面侧前缘、中部各形成一个间隙涡,使得间隙流动损失增加.而且转速下降会加剧动叶出口截面气流过偏/偏转不足现象.同时叶片静止时,间隙前部各个弦长截面内静压自间隙入口开始一直呈增加趋势,直到叶片尾缘附近截面,间隙截面内静压才逐渐稳定.     

延安宝塔山景区滑坡地质灾害风险评估

机匣与叶片的相对转动是影响涡轮叶顶间隙流动的重要因素之一. 对LISA 1.5级轴流涡轮间隙内部流动的数值计算结果表明：叶片转动对涡轮间隙流动有阻塞作用. 叶片静止时,由于阻塞作用消失,导致间隙入口速度增大,间隙流量增加,并且通过间隙的 流体全部卷起形成间隙涡. 同时在叶片顶部吸力面侧前缘、中部各形成一个间隙涡,使得间 隙流动损失增加. 而且转速下降会加剧动叶出口截面气流过偏/偏转不足现象. 同时叶片静止 时,间隙前部各个弦长截面内静压自间隙入口开始一直呈增加趋势,直到叶片尾缘附近截面, 间隙截面内静压才逐渐稳定.     

Interstitial fluid flow: simulation of mechanical environment of cells in the interosseous membrane

In vitro experiments have shown that subtle fluid flow environment plays a significant role in living biological tissues,while there is no in vivo practical dynamical measurement of the interstitial fluid flow velocity.On the basis of a new finding that capillaries and collagen fibrils in the interosseous membrane form a parallel array,we set up a porous media model simulating the flow field with FLUENT software,studied the shear stress on interstitial cells’ surface due to the interstitial fluid flow,and analyzed the effect of flow on protein space distribution around the cells.The numerical simulation results show that the parallel nature of capillaries could lead to directional interstitial fluid flow in the direction of capillaries.Interstitial fluid flow would induce shear stress on the membrane of interstitial cells,up to 30 Pa or so,which reaches or exceeds the threshold values of cells’ biological response observed in vitro.Interstitial fluid flow would induce nonuniform spacial distribution of secretion protein of mast cells.Shear tress on cells could be affected by capillary parameters such as the distance between the adjacent capillaries,blood pressure and the permeability coefficient of capillary’s wall.The interstitial pressure and the interstitial porosity could also affect the shear stress on cells.In conclusion,numerical simulation provides an effective way for in vivo dynamic interstitial velocity research,helps to set up the vivid subtle interstitial flow environment of cells,and is beneficial to understanding the physiological functions of interstitial fluid flow.     

Numerical Investigation of Magnetic Nanoparticles Distribution Inside a Cylindrical Porous Tumor Considering the Influences of Interstitial Fluid Flow

A numerical simulation of interstitial fluid flow and blood flow and diffusion of magnetic nanoparticles (MNPs) are developed, based on the governing equations for the fluid flow, i.e., the continuity and momentum and mass diffusion equations, to a tissue containing two-dimensional cylindrical tumor. The tumor is assumed to be rigid porous media with a necrotic core, interstitial fluid and two capillaries with arterial pressure input and venous pressure output. Blood flow through the capillaries and interstitial fluid flow in tumor tissues are carried by extended Poiseuille’s law and Darcy’s law, respectively. Transvascular flows are also described using Starling’s law. MNPs diffuse by interstitial fluid flow in tumor. The finite difference method has been used to simulate interstitial fluid pressure and velocity, blood pressure and velocity and diffusion of MNPs injected inside a biological tissue during magnetic fluid hyperthermia (MFH). Results show that the interstitial pressure has a maximum value at the center of the tumor and decreases toward the first capillary. The reduction continues between two capillaries, and interstitial pressure finally decreases in direction of the tumor perimeter. This study also shows that decreasing in intercapillary distance may cause a decrease in interstitial pressure. Furthermore, multi-site injection of nanoparticles has better effect on MFH.     

含液颗粒材料液固耦合分析的离散颗粒模型及特征线SPH法

对含液颗粒材料流固耦合分析建议了一个基于离散颗粒模型与特征线SPH法的显式拉格朗日-欧拉无网格方案。在已有的用以模拟固体颗粒集合体的离散颗粒模型[1]基础上,将颗粒间间隙内的流体模型化为连续介质,对其提出并推导了基于特征线的SPH法。数值例题显示了所建议方案在模拟颗粒材料与间隙流相互作用的能力和性能以及间隙流体对颗粒结构承载能力及变形的影响。     

Numerical simulation of blood flow and interstitial fluid pressure in solid tumor microcirculation based on tumor-induced angiogenesis

A coupled intravascular–transvascular–interstitial fluid flow model is developed to study the distributions of blood flow and interstitial fluid pressure in solid tumor microcirculation based on a tumor-induced microvascular network. This is generated from a 2D nine-point discrete mathematical model of tumor angiogenesis and contains two parent vessels. Blood flow through the microvascular network and interstitial fluid flow in tumor tissues are performed by the extended Poiseuille’s law and Darcy’s law, respectively, transvascular flow is described by Starling’s law; effects of the vascular permeability and the interstitial hydraulic conductivity are also considered. The simulation results predict the heterogeneous blood supply, interstitial hypertension and low convection on the inside of the tumor, which are consistent with physiological observed facts. These results may provide beneficial information for anti-angiogenesis treatment of tumor and further clinical research. The project supported by the National Natural Science Foundation of China (10372026).     

An analytical poroelastic model for laboratorial mechanical testing of the articular cartilage (AC)

The articular cartilage (AC) can be seen as a biphasic poroelastic material. The cartilage deformation under compression mainly leads to an interstitial fluid flow in the porous solid phase. In this paper, an analytical poroelastic model for the AC under laboratorial mechanical testing is developed. The solutions of interstitial fluid pressure and velocity are obtained. The results show the following facts. (i) Both the pressure and fluid velocity amplitudes are proportional to the strain loading amplitude. (ii) Both the amplitudes of pore fluid pressure and velocity in the AC depend more on the loading amplitude than on the frequency. Thus, in order to obtain the considerable fluid stimulus for the AC cell responses, the most effective way is to increase the loading amplitude rather than the frequency. (iii) Both the interstitial fluid pressure and velocity are strongly affected by permeability variations. This model can be used in experimental tests of the parameters of AC or other poroelastic materials, and in research of mechanotransduction and injury mechanism involved interstitial fluid flow.     

Finite-Difference Approximation for Fluid-Flow Simulation and Calculation of Permeability in Porous Media

We introduce a finite-difference method to simulate pore scale steady-state creeping fluid flow in porous media. First, a geometrical approximation is invoked to describe the interstitial space of grid-based images of porous media. Subsequently, a generalized Laplace equation is derived and solved to calculate fluid pressure and velocity distributions in the interstitial space domain. We use a previously validated lattice-Boltzmann method (LBM) as ground truth for modeling comparison purposes. Our method requires on average 17 % of the CPU time used by LBM to calculate permeability in the same pore-scale distributions. After grid refinement, calculations of permeability performed from velocity distributions converge with both methods, and our modeling results differ within 6 % from those yielded by LBM. However, without grid refinement, permeability calculations differ within 20 % from those yielded by LBM for the case of high-porosity rocks and by as much as 100 % in low-porosity and highly tortuous porous media. We confirm that grid refinement is essential to secure reliable results when modeling fluid flow in porous media. Without grid refinement, permeability results obtained with our modeling method are closer to converged results than those yielded by LBM in low-porosity and highly tortuous media. However, the accuracy of the presented model decreases in pores with elongated cross sections.     

骨陷窝-骨细胞形状和方向对骨单元内液体流动行为的影响

骨组织内的流体流动不仅为骨细胞的生存提供了充足营养供应及代谢物排放途径,也在骨重建过程中起到关键作用. 为了更精确地阐明骨内液体流动的具体形式,这项研究利用骨陷窝-骨细胞的密度,形态和方向等参数来计算骨单元内液体的流动行为. 首先,计算出不同形状和方向的骨陷窝周围骨小管的数量及分布情况,其次利用算出的参数以及骨组织其他微结构数据来估计骨组织的渗透率和孔隙率等参数,最后根据计算所得的参数建立骨单元的多孔弹性力学有限元模型,并分析了在轴向位移载荷作用下骨陷窝形状和方向对骨单元内液体渗流行为的影响. 结果表明,在所研究的参数范围内不同骨单元模型的相同区域上,骨陷窝形状影响下的骨单元最大压力和流速比最小的分别增加了86%和18%;骨陷窝方向影响下的最大压力和流速比最小的分别增加了125%和56%. 伸长形骨陷窝对单个骨单元局部压力的影响远大于扁平形和圆形骨陷窝. 骨陷窝从0°绕$x$轴旋转到90°过程中压力是逐渐降低的,且30°,45°和60°的模型对骨单元内局部流速有显著影响. 该模型表示骨陷窝的形状和方向以及骨小管的三维分布对骨单元内液体压力和流速幅值及沿不同方向的流动差异有显著的影响. 这项研究将有助于精确量化描述骨内液体的流体行为.      

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.     

MASS TRANSPORT IN SOLID TUMORS (Ⅰ)──FLUID DYNAMICS

A three-porous-medium model for transvascular exchange and extravascular transport of fluid and macromolecules in a spherical solid tumor is developed. The microvasculature, lymphatics, and tissue space are each treated as a porous medium with the flow of blood. lymph, and interstitial fluid obeying Darcy’s law and Starling’s assumption. In this part, the role of interstitial pressure and fluid convection are studited. The analytical soiutions are obtained for foe isolated tumor and the normal-tissue-surrounded tumor respectively. The calculated interstitial pressure profue are consistent with the experimental observation that the elevated interstitial pressure is a major barrier in the penetration of macromolecular drug into tumors. The factors which may reduce the interstitial pressure are analyzed in details.