Browsing by Subject "Fluid dynamics--Simulation methods"

Now showing 1 - 2 of 2

Relationships between structure and dynamics of attractive colloidal fluids
(2008-08) Krekelberg, William Paul; Truskett, Thomas Michael, 1973-; Ganesan, Venkat
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.
Simulation of non-Newtonian fluids on workstation clusters
(2004) Barth, William L.; Carey, Graham F.
The subject of this work is the three-dimensional, parallel, finite element simulation on workstation clusters of coupled fluid flow and heat transfer of shear-thinning fluids modeled by the Powell-Eyring and extended Williamson models. After giving a description of the equations of motion and the numerical and computational techniques used to approximate them, the results of phenomenological studies for several different flow problems are presented. Of particular interest are nonlinear effects, multi-physics coupling, nonlinear instabilities, and multi-scale layer effects. First two internal pipe flow problems are presented to study the behavior of the fluid without the influence of thermal effects. The simulation of Poiseuille flow in a straight cylindrical pipe highlights the shear-thinning aspects of these fluids under a range of fluid parameters. This is followed by pressure-driven flow in a branched pipe where shear thinning may be seen to effect the development of certain flow structures. The latter problem is of interest in traditional engineering pipe flows as well as biomedical engineering applications such as blood flow treatment. We examine the detailed flow behavior in a branching zone. These studies are followed by two problems which are driven by temperature differences. The first is buoyancy-driven convection in an cube that was motivated by a benchmark challenge at CHT ’01—the challenge was to provide definitive simulations and compare wit a prior experimental study. A detailed comparison of experimental and computational results for the Newtonian case was made and followed by an extension of the Newtonian problem to the non-Newtonian fluids considered here. The non-Newtonian fluids are shown to lead to higher heat fluxes across the domain with as the shear-thinning effect increases. This is followed by a surface-tension-driven convection problem in a fluid layer heated from below where experimental and computational results for the Newtonian case are compared with simulations of the Powell-Eyring and extended Williamson fluids. A dynamic matrix formation procedure based on a “dial-an-operator” approach is also presented. This method uses a LATEX-like input language for the specification of the governing equations to be solved. A parallel, structural incomplete LU factorization (SILU(0)) preconditioner which exploits the implicit structure of the zero-block in the matrices arising in incompressible flow problems is described. The preconditioner from one linear solution step is found to be “reusable” in subsequent linear solution steps arising in the non-linear iterative method and the time-stepping procedure. Finally, some performance analyses and scaling results are presented for the algorithms developed and implemented in the work on a broad range of workstation clusters. And the author’s experience with cluster design, construction, and maintenance is described.