Using smooth particle hydrodynamics to investigate femoral cortical bone remodelling at the Haversian level.

In the neck of the femur, about 70% of the strength is contributed by the cortical bone, which is the most highly stressed part of the structure and is the site where failure is almost certainly initiated. A better understanding of cortical bone remodelling mechanisms can help discern changes at this anatomical site, which are essential if an understanding of the mechanisms by which hips weaken and become vulnerable to fracture is to be gained. The aims of this study were to (i) examine a hypothesis that low strain fields arise because of subject-specific Haversian canal distributions causing bone resorption and reduced bone integrity and (ii) introduce the use of a meshless particle-based computational modelling approach SPH to capture bone remodelling features at the level of the Haversian canals. We show that bone remodelling initiated by strain at the Haversian level is highly influenced by the subject-specific pore distribution, bone density, loading and osteocyte density. SPH is shown to be effective at capturing the intricate bone pore shapes that evolved over time.

Investigating the relationships between peristaltic contraction and fluid transport in the human colon using Smoothed Particle Hydrodynamics.

Complex relationships exist between gut contractility and the flow of digesta. We propose here a Smoothed Particle Hydrodynamics model coupling the flow of luminal content and wall flexure to help investigate these relationships. The model indicates that a zone of muscular relaxation preceding the contraction is an important element for transport. Low pressures in this zone generate positive thrust for low viscosity content. The viscosity of luminal content controls the localization of the flow and the magnitude of the radial pressure gradient and together with contraction amplitude they control the transport rate. For high viscosity content, high lumen occlusion is required for effective propulsion.

Granular flow during hopper discharge.

Granular material freely discharging from a hopper under gravity is one of the oldest and most widely studied problems in granular flow. Despite the apparent simplicity of the system, expressions relating the discharge rate of the hopper to the properties of the individual grains are difficult to determine and typically empirical in nature. A mathematical model for discharge from a hopper is derived based on the dynamics of individual particles just within the outlet. In contrast to previous models, this analysis derives a flow rate from granular dynamics, rather than dimensional arguments. The model, therefore, uses no assumptions about the form of the stress distribution within the hopper, or the addition of empirical factors or fitting parameters. Our model gives a flow rate identical in form to a well-known empirical expression, showing that an experimentally determined constant used in this expression is purely geometry-dependent. Our analysis is also extended to derive an expression for the flow rate incorporating gas drag, which becomes dominant at small grain sizes, significantly reducing the outflow rate. The resulting expression shows excellent agreement with a range of computational simulations using a coupled discrete element and Navier-Stokes method. These simulations also show that the gas flow is much more complex than previously assumed in this region, and simplified assumptions used in prior hopper flow models do not hold.