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分子动力学与连续介质力学耦合模型的研究及应用
其他题名Study and application of hybrid computation scheme adjoining molecular dynamics and continuum mechanics
李玉秀
导师徐进良
2009-01-06
学位授予单位中国科学院广州能源研究所
学位授予地点广州能源研究所
学位名称博士
关键词分子动力学 跨尺度耦合 界面边界条件
摘要流固界面边界条件是制约能源动力系统能量转化、储存、及传递的关键科学问题之一,是一个古老而又没有彻底解决的问题,研究流固界面边界条件不仅具有重要的科学意义,又具有广义的工程应用背景。特别的,在广泛兴起的微纳高科技领域,通道尺度跨越纳米、微米、直到毫米的广阔区间。同时,流固材料、表面湿润性、粗糙度等诸因素均对边界条件有影响,使这个问题变得更加复杂。本文从以下四个相互关联的方面,开展了流固界面边界条件的深入研究。 建立了完整的界面边界条件问题的参数表征体系,揭示了影响流固界面边界条件诸因素及各参数之间的内在联系及因果关系。 在该表征体系的框架下,从流固原子相互作用的微观机制及短程力特点出发,提出了三原子模型,在理论上获得了制约界面边界条件的准则数,建立了该准则数与界面湿润性之间的内在联系。物理上,当该准则数等于0.757时,表示亲水性表面,对应无滑移或锁定边界条件。当该准则数偏离0.757时,表示疏水性表面,对应滑移边界条件。 研制了分子动力学计算程序MDARGON,可计算微库特流/泊肃叶流场,验证了所提出的三原子模型的正确性,复现了纳米尺度下固液界面滑移、无滑移、及锁定三类边界条件,并发现了高剪切率下的非牛顿流体特性。 研制了分子动力学与连续介质力学跨尺度耦合模型计算软件MDNSCOUP,可计算纳米、微米、直到毫米尺度下的速度场。提出了划分计算区域的方法,即与固体壁面相邻近的MD区,中间重叠区、及远离流固界面的NS区。对各计算区域,给出了严格的数学描述。在重叠区导出了保证在空间上连续,在时间序列上收敛的约束条件。 采用该模型,研究了从微纳米到宏观尺度下界面边界条件这一长期悬而未决的难题,发现了滑移长度守恒原则:即滑移长度相对于通道尺度来说是不变的,仅取决于流固材料匹配。滑移长度守恒原则表示边界条件问题的本质,也称为边界条件的绝对性。另一方面,随着通道尺度的增加,界面上的流体相对滑移速度无限趋近于零。该特性称为边界条件的相对性,反映边界条件问题的表面现象。本质上,对于边界条件问题来说,不存在宏观与微观之分。边界条件的绝对性与相对性是一个问题的两个方面,它的发现为正确模拟微纳流动提供了科学依据。
其他摘要Boundary condition on the solid-fluid interface is one of the key scientific issues relating to the energy conversion, storage, and transfer in energy systems. It is an old but not well-solved problem. Study of such a problem not only is important in science, but also has wide engineering applications. Specifically, in the fast developing micro/nano systems, the channel size covers nanometer, micron, and even millimeter scale. Meanwhile, the solid and fluid material, wettability, and surface roughness etc. all have important influences on the boundary conditions, making the problem very complicated. This thesis presented studies on the boundary conditions from the following four related aspects. A complete set of characteristic parameters governing the boundary conditions was established, identifying the internal relationship among these parameters. Within the developed parameter sets, a three-atom-model was proposed, from the interactions of the atomes and the short range interaction characteristic, physically. A criterion number controlling the boundary conditions was achieved, which is related to the surface wettability. Physically, the criterion number of 0.757 stands for the hydrophilic surface, corresponding to the non-slip or locking boundary conditions. Deviation from 0.757 of the criterion number represents the hydrophobic surface, corresponding to the slip boundary conditions. A molecular dynamics simulation code was developed, which could compute the flow field of the micro Couette and Poiseuille flow. The computation results verified the propsed three-atom-model. The computation also reproduces the three types of boundary conditions of slip, non-slip, and locking. The non-Newton flow behavior at high shear rates was found. A hybrid computation code adjoining the molecular dynamics and continuum fluid mechanics was developed, which could calculate the flow field with the channel size from nanometer, micron, to millimeter. The domain decomposition method was proposed. Three regions were subdivided: the MD region close to the solid-fluid surface, the coupling region, and the NS region far away from the surface. The strict mathematic formulation in each region was given. The constraint criterion was proposed in the coupling region, ensuring the parameter continuous in the space coordinate, and the convergence in the time series. The boundary conditions with the channel size from micro/nano meter to macroscale were studied using the developed code. The constant slip length principle was found, i.e., the slip lengths are not depended on the channel size, but only depended on the solid-fluid interactions. Such a principle stands for the real physical mechanism, which is also called as the absouleteness of the boundary conditions. On the other hand, the slip velocities at the solid-fluid surface approach zero when the channel size is continuously increased, which is named as the relativity of the boundary conditions, standing for the appearance. Physically, there is no transfer from micro to macro regarding the boundary condition issue. The absoluteness and relativity of the boundary conditions are the two aspects of the problem, providing the guideline for the design of the micro/nano systems.
页数128
语种中文
文献类型学位论文
条目标识符http://ir.giec.ac.cn/handle/344007/4059
专题中国科学院广州能源研究所
推荐引用方式
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李玉秀. 分子动力学与连续介质力学耦合模型的研究及应用[D]. 广州能源研究所. 中国科学院广州能源研究所,2009.
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