Relationships between structure and dynamics in fluids have a wide variety of applications. Because theories for fluid structure are now well developed, such relationships can be used to “predict” dynamic properties. Also, recasting dynamic properties in terms of structure may provide new insights. In this thesis, we explore whether some of the relationships between structure and dynamics that have proven useful for understanding simple atomic liquids can also be applied to complex fluid systems. In particular, we focus on model fluid systems with particles that interact with attractive forces that are shortranged (relative to the particle diameter), and display properties that are anomalous when compared to those of simple liquids. Examples of fluids with short-range attractive (SRA) interactions include colloidal suspensions and solutions of micelles or proteins. We show via simulations that common assumptions regarding free volume and dynamics do not apply for SRA fluids, and propose a revision to the traditional free volume perspective of dynamics. We also develop a model which can predict the free volume behavior for hard-sphere and SRA fluids. Next, we demonstrate that the dynamic properties of SRA fluids can be related to structural order. In terms of structural order, the properties of SRA fluids can be related to those of another anomalous fluid, liquid water. In both fluids, anomalous dynamics are closely related to anomalous structure, which can be traced to changes in second and higher coordination shells. We also find that a similar relationship between structural order and dynamics approximately holds for fluids under shear. Motivated by previous work, we explore via simulation how tuning the particle-wall interactions to flatten or enhance the particle layering in a confined fluid impacts its self-diffusivity, viscosity, and entropy. We find that the excess entropy explains the observed trends. Finally, we present preliminary simulation data regarding the relationship between heterogeneous dynamics and structure. We show that the mobility of particles is related in a simple way to the structure of the particles surrounding them. In particular, our results suggest that a critical amount of local disorder allows a particle to be mobile on intermediate time scales. / text

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We experimentally investigate the phenomena of large jet rebound, a mode of fluid transfer following oblique jet impacts on hydrophobic substrates. We initially seek to describe the jet rebound regimes in tests conducted in the weightless environment of a drop tower. A parametric study reveals the dependence of the flow structure on the relevant dimensionless groups such as Reynolds number and Weber number defined on the velocity component perpendicular to the substrate. We show that significantly larger diameter jets behave similarly as much smaller jets demonstrated during previous terrestrial investigations is some parameter ranges while the flow is fundamentally different in others. Level-set numerical predictions are provided for comparisons where practicable. Simple models are developed predicting landing geometry and the onset of instability that are found to yield good agreement with experiments and simulations. Improving our understanding of such jet rebound opens avenues for unique transport capabilities.

Thesis (Ph. D.)--Worcester Polytechnic Institute. / Keywords: fluid-structure interaction; low dimensional models; coupled map lattices; vortex shedding; cylinder wake patterns; flow control; multi-variable least squares algorithm; neural networks; adaptive estimation. Includes bibliographical references (p. 147-149).

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