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仿真分析了磁场和剪切场作用下双分散、单分散磁流变液的微观结构演化,从4个方面考察了磁流变液悬浮性态:微观结构相变,链长分布,聚合结构各向异性和悬浮粒子运动涨落。结果表明,在磁场作用下,场强幅值越高,相态迁移的时间越短、簇-墙相越明显;在低磁场时,双分散悬浮较单分散悬浮容易形成长链,而在中、高磁场时,单分散悬浮却较双分散悬浮容易形成长链;磁极粒子具有智能特性,在无剪切场作用下总是寻找最易形成墙的方向排列成簇,而在稳态剪切作用下沿流场方向形成通长墙相以抑制流场的输运;外加磁场有助于减小悬浮粒子的运动涨落,但在剪切场的引导作用下,磁场强度的变化对悬浮粒子运动涨落无明显影响。

Performance of magnetorheological fluid suspensions including bidisperse and monodisperse suspensions under external magnetic fields with different magnitudes and steady shear fields is investigated using a molecular dynamical simulation technique.Numerical simulations are performed employing the large-scale atomic/molecular massive parallel simulator(LAMMPS).We investigate four kinds of typical characteristics of microstructural evolution of magnetorheological fluid,i.e.phase transition of structures,statistics of chain size,structural anisotropy of aggregates and fluctuation of suspensions.It is noted that the higher the magnitude of external magnetic fields,the shorter the time of phase transition comes through,and more obvious the cluster phase appears.Magnetic dipolar particles,moreover,have some structured behavior that they tend to cluster into sheets along particular directions,even under conditions of uniform initial configuration and steady external magnetic field.The investigation of statistics of chain size indicates that bidisperse suspensions have a higher tendency to form straight chains than monodisperse suspensions under lower magnetic field,while the reverse is true under medium and high magnetic fields.Besides,we observe that the suspensions with presence of shear flow submit to the flow field,and connect to form long sheets along flow direction towards restraining the transportation of the shear flow.

参考文献

[1] Martin JE.;Tigges CP.;Anderson RA. .Simulation of the athermal coarsening of composites structured by a biaxial field[J].The Journal of Chemical Physics,1998(18):7887-7900.
[2] Baxterdrayton Y.;Brady JF. .BROWNIAN ELECTRORHEOLOGICAL FLUIDS AS A MODEL FOR FLOCCULATED DISPERSIONS[J].Journal of Rheology,1996(6):1027-1056.
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