Effect of Formation Hydrodynamics on Mechanical Properties of Container Materials

The objectives of this study were to compare the mechanical and physical properties of the sheets made using the Vortigen technology (a non-conventional technique that creates very high number vortices in a fluid flow mixture of water, fibers, and chemical additives) with those produced from a conventional method of papermaking and to provide insight into the impact of formation hydrodynamics on sheet properties. The results of formation, ultrasonic stiffness, and creep/accelerated creep measurements of the Vortigen sheets as compared with the standard sheets are presented. Samples of Vortigen (V) and standard (S) sheets (4 samples from each group) were obtained from papers produced on a pilot machine. Formation measurements (that provides a measure of density distribution in a sheet) were performed using a formation tester which is based on beta particle absorption. Measurements of creep and accelerated creep were made at a constant relative humidity (RH) of 80% and a cyclic RH between 30% and 80% for strips cut along the machine direction (MD) and cross machine direction (CD, which is perpendicular to MD) directions. There was a significant difference between the distributions of basis weights for the two types of papers. The mean coefficient of variation in grammage for the V samples was 8.97 while that for the S samples was 12.60. The mean MD/CD stiffness ratios for the V and S samples were 1.1 and 1.6, respectively. The mean Z-direction longitudinal specific stiffness corresponding to the V samples were 18% greater than the corresponding value for the S samples. The MD strips from the S samples exhibited the smallest creep while the CD strips from the S samples exhibited the largest creep. Creep values corresponding to the Vortigen sheets were between the extreme values of the standard samples. The results of this study indicated that because of the influence of formation hydrodynamics on fiber orientation and formation, in general, the stiffness properties (and specifically the CD stiffness) of the Vortigen samples were greater than those of the standard samples

Coaxial Jets with Disparate Viscosity: Mixing and Laminarization Characteristics

Mixing of fluids in a coaxial jet is studied under four distinct viscosity ratios, m = 1, 10, 20 and 40, using highly resolved large-eddy simulations (LES), particle image velocimetry and planar laser-induced fluorescence. The accuracy of predictions is tested against data obtained by the simultaneous experimental measurements of velocity and concentration fields. For the highest and lowest viscosity ratios, standard RANS models with unclosed terms pertaining to viscosity variations are employed. We show that the standard Reynolds-averaged Navier-Stokes (RANS) approach with no explicit modelling for variable-viscosity terms is not applicable whereas dynamic LES models provide high-quality agreement with the measurements. To identify the underlying mixing physics and sources of discrepancy in RANS predictions, two distinct mixing modes are defined based on the viscosity ratio. Then, for each mode, the evolution of mixing structures, momentum budget analysis with emphasis on variable-viscosity terms, analysis of the turbulent activity and decay of turbulence are investigated using highly resolved LES data. The mixing dynamics is found to be quite distinct in each mixing mode. Variable viscosity manifests multiple effects that are working against each other. Viscosity gradients induce additional instabilities while increasing overall viscosity decreases the effective Reynolds number leading to laminarization of the turbulent jet, explaining the lack of dispersion and turbulent diffusion. Momentum budget analysis reveals that variable-viscosity terms are significant to be neglected. The scaling of the energy spectrum cascade suggests that in the TLL mode the unsteady laminar shedding is responsible for the eddies observed

Numerical Simulation of the Effect of Gravity on Weld Pool Shape A high gravitational field strongly affects the outward flow of the weld pool

ABSTRACT. Understanding the physical phenomena involved in the welding process is of substantial value to improving the weldability of materials. The intense heat and the arc inherent in fusion welding make direct experimental observation of the weld pool behavior rather difficult. Thus, numerical models that can predict the processes involved have become an invaluable tool for studying welding. One of the major factors affecting the motion within the molten weld pool is the gravity-driven buoyancy force. This force can act to oppose or enhance the Marangoni and/or electromagnetic driven convective flow within the weld pool. To study the effect of gravity on weld pool processes, a series of numerical simulations was performed. It was found that higher gravitational fields tend to enhance the convective flow within the weld pool and thus affect the heat transfer, the depth and width of the two phase region, and the pool depth-towidth ratio

Lattice Boltzmann simulations of soft matter systems

This article concerns numerical simulations of the dynamics of particles immersed in a continuum solvent. As prototypical systems, we consider colloidal dispersions of spherical particles and solutions of uncharged polymers. After a brief explanation of the concept of hydrodynamic interactions, we give a general overview over the various simulation methods that have been developed to cope with the resulting computational problems. We then focus on the approach we have developed, which couples a system of particles to a lattice Boltzmann model representing the solvent degrees of freedom. The standard D3Q19 lattice Boltzmann model is derived and explained in depth, followed by a detailed discussion of complementary methods for the coupling of solvent and solute. Colloidal dispersions are best described in terms of extended particles with appropriate boundary conditions at the surfaces, while particles with internal degrees of freedom are easier to simulate as an arrangement of mass points with frictional coupling to the solvent. In both cases, particular care has been taken to simulate thermal fluctuations in a consistent way. The usefulness of this methodology is illustrated by studies from our own research, where the dynamics of colloidal and polymeric systems has been investigated in both equilibrium and nonequilibrium situations.Comment: Review article, submitted to Advances in Polymer Science. 16 figures, 76 page

Numerical simulations of complex fluid-fluid interface dynamics

Interfaces between two fluids are ubiquitous and of special importance for industrial applications, e.g., stabilisation of emulsions. The dynamics of fluid-fluid interfaces is difficult to study because these interfaces are usually deformable and their shapes are not known a priori. Since experiments do not provide access to all observables of interest, computer simulations pose attractive alternatives to gain insight into the physics of interfaces. In the present article, we restrict ourselves to systems with dimensions comparable to the lateral interface extensions. We provide a critical discussion of three numerical schemes coupled to the lattice Boltzmann method as a solver for the hydrodynamics of the problem: (a) the immersed boundary method for the simulation of vesicles and capsules, the Shan-Chen pseudopotential approach for multi-component fluids in combination with (b) an additional advection-diffusion component for surfactant modelling and (c) a molecular dynamics algorithm for the simulation of nanoparticles acting as emulsifiers.Comment: 24 pages, 12 figure

Effect of tube diameter and capillary number on platelet margination and near-wall dynamics

The effect of tube diameter $D$ and capillary number $Ca$ on platelet margination in blood flow at $\approx 37\%$ tube haematocrit is investigated. The system is modelled as three-dimensional suspension of deformable red blood cells and nearly rigid platelets using a combination of the lattice-Boltzmann, immersed boundary and finite element methods. Results show that margination is facilitated by a non-diffusive radial platelet transport. This effect is important near the edge of the cell-free layer, but it is only observed for $Ca > 0.2$, when red blood cells are tank-treading rather than tumbling. It is also shown that platelet trapping in the cell-free layer is reversible for $Ca \leq 0.2$. Only for the smallest investigated tube ($D = 10 \mu\text{m}$) margination is essentially independent of $Ca$. Once platelets have reached the cell-free layer, they tend to slide rather than tumble. The tumbling rate is essentially independent of $Ca$ but increases with $D$. Tumbling is suppressed by the strong confinement due to the relatively small cell-free layer thickness at $\approx 37\%$ tube haematocrit.Comment: 16 pages, 10 figure

A parallel cellular automata Lattice Boltzmann Method for convection-driven solidification

This article presents a novel coupling of numerical techniques that enable three-dimensional convection-driven microstructure simulations to be con- ducted on practical time scales appropriate for small-size components or experiments. On the microstructure side, the cellular automata method is efficient for relatively large-scale simulations, while the lattice Boltzmann method provides one of the fastest transient computational fluid dynamics solvers. Both of these methods have been parallelized and coupled in a single code, allowing resolution of large-scale convection-driven solidification problems. The numerical model is validated against benchmark cases, extended to capture solute plumes in directional solidification and finally used to model alloy solidification of an entire differentially heated cavity capturing both microstructural and meso-/macroscale phenomena