4,013 research outputs found
Packing Characteristics of Different Shaped Proppants for use with Hydrofracing - A Numerical Investigation using 3D FEMDEM
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Subdivision Shell Elements with Anisotropic Growth
A thin shell finite element approach based on Loop's subdivision surfaces is
proposed, capable of dealing with large deformations and anisotropic growth. To
this end, the Kirchhoff-Love theory of thin shells is derived and extended to
allow for arbitrary in-plane growth. The simplicity and computational
efficiency of the subdivision thin shell elements is outstanding, which is
demonstrated on a few standard loading benchmarks. With this powerful tool at
hand, we demonstrate the broad range of possible applications by numerical
solution of several growth scenarios, ranging from the uniform growth of a
sphere, to boundary instabilities induced by large anisotropic growth. Finally,
it is shown that the problem of a slowly and uniformly growing sheet confined
in a fixed hollow sphere is equivalent to the inverse process where a sheet of
fixed size is slowly crumpled in a shrinking hollow sphere in the frictionless,
quasi-static, elastic limit.Comment: 20 pages, 12 figures, 1 tabl
Permeability of mixed soft and hard granular material: hydrogels as drainage modifiers
We measure the flow of water through mixed packings of glass spheres and soft
swellable hydrogel grains, at constant sample volume. Permeability values are
obtained at constant sample volume and at porosities smaller than random close
packing, for different glass bead diameters and for variable gel grain
diameter , as controlled by the salinity of the water. The gel content is
also varied. We find that the permeability decays exponentially in
where is the gel to glass bead number ratio and is
approximately 3. Therefore, flow properties are determined by the volume
fraction of gel beads. A simple model based on the porosity of overlapping
spheres is used to account for these observations
Computational Fluid Dynamics Analysis of Two-Phase Flow in a Packed Bed Reactor
Multiphase catalytic reactions are prominent in chemical engineering; however it is difficult to achieve efficient reactions. Computational fluid dynamics (CFD) software simulates fluid flow so interactions between phases may be analyzed and improved. This project included use of CFD to simulate an experiment on multiphase flow to compare results on flow regime and pressure drop. Results include discussion of the program’s capabilities for conducting this analysis and comparison of simulated flow parameters against experimentally determined values
Model Simplification for Efficient Collision Detection in Robotics
Motion planning for industrial robots is a computationally intensive task due to the massive number of potential motions between any two configurations. Calculating all possibilities is generally not feasible. Instead, many motion planners sample a sub-set of the available space until a viable solution is found. Simplifying models to improve collision detection performance, a significant component of motion planning, results in faster and more capable motion planners.
Several approaches for simplifying models to improve collision detection performance have been presented in the literature. However, many of them are sub-optimal for an industrial robotics application due to input model limitations, accuracy sacrifices, or the probability of increasing false negatives during collision queries.
This thesis focuses on the development of model simplification approaches optimised for industrial robotics applications. Firstly, a new simplification approach, the Bounding Sphere Simplification (BSS), is presented that converts triangle-mesh inputs to a collection of spheres for efficient collision and distance queries. Additionally, BSS removes small features and generates an output model less prone to false negatives
Direct Numerical Simulation of Complex Multi-Fluid Flows Using a Combined Volume of Fluid and Immersed Boundary Method
In this paper a simulation model is presented for the Direct Numerical Simulation (DNS) of complex multi-fluid flows in which simultaneously (moving) deformable (drops or bubbles) and non-deformable (moving) elements (particles) are present, possibly with the additional presence of free surfaces. Our model combines the VOF model developed by van Sint Annaland et al. (2005) and the Immersed Boundary (IB) model developed by van der Hoef et al. (2006). The Volume of Fluid (VOF) part features i) an interface reconstruction technique based on piecewise linear interface representation ii) a three-dimensional version of the CSF model of Brackbill et al. (1992). The Immersed Boundary (IB) part incorporates both particle-fluid and particle-particle interaction via a Direct Forcing Method (DFM) and a hard sphere Discrete Particle (DP) approach. In our model a fixed (Eulerian) grid is utilized to solve the Navier-Stokes equations for the entire computational domain. The no-slip condition at the surface of the moving particles is enforced via a momentum source term which only acts in the vicinity of the particle surface. For the enforcement of the no-slip condition Lagrangian force points are used which are distributed evenly over the surface of the particle. Dissipative particle-particle and/or particle-wall collisions are accounted via a hard sphere DP approach (Hoomans et al., 1996) using a three-parameter particle-particle interaction model accounting for normal and tangential restitution and tangential friction. The capabilities of the hybrid VOF-IB model are demonstrated with a number of examples in which complex topological changes in the interface are encountered
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