Waterloo CFD Engineering Consulting

The aim of this study was to compare classical friction (FR) in passive self-ligating brackets (P-SLBs), active self-ligating brackets (A-SLBs) and atraditional twin bracket, in vitro, and to identify the point of initiation of bracket-archwire engagement. Nine bracket systems of 0.022 in slot size were FR tested: 5 P‑SLB systems; 4 A‑SLB systems; and a control group of twin brackets with elastomeric ligatures. Single upper right central incisor brackets were mounted on acustom metal fixture for testing. Straight sections of various round and rectangular nickel-titanium (NiTi) archwires (0.016, 0.018, 0.018 × 0.018, 0.020 × 0.020, 0.016 × 0.022, 0.017 × 0.025, 0.019 × 0.025, and 0.021 × 0.025 in) were ligated to the bracket and peak static FR (cN) was measured with an Instron Universal Testing Machine. Ten unique tests each utilizing anew bracket and new archwire were conducted for each group in the dry state. FR was significantly different between control, P‑SLB and A‑SLB systems (P < 0.001). P‑SLB groups displayed no significant differences in FR between each other, regardless of archwire size. A‑SLB groups did exhibit significant differences in FR between each other depending on both the bracket system and archwire size. Each A‑SLB system tested possessed adistinctly different pattern of initiation of bracket-archwire engagement. FR between the archwire and bracket slot differs between P‑SLB and A‑SLB systems, with adistinct pattern of FR and bracket-archwire engagement for each A‑SLB system. Understanding the different bracket-wire interactions of SLB systems should help orthodontic clinicians to plan effective and efficient biomechanics with the bracket system of their choice.

A dense, solid particle flow is numerically studied at a mesoscale level for a cylindrical shock tube problem. The shock tube consists of a central high pressure gas driver section and an annular solid powder bed with air in void regions as a driven section with its far end adjacent to ambient air. Simulations are conducted to explore the fundamental phenomena, causing clustering of particles and formation of coherent particle jet structures in such a dense solid flow. The influence of a range of parameters is investigated, including driver pressure, particle morphology, particle distribution and powder bed configuration. The results indicate that the physical mechanism responsible for this phenomenon is twofold: the driver gas jet flow induced by the shock wave as it passes through the initial gaps between the particles in the innermost layer of the powder bed, and the chaining of solid particles by inelastic collision. The particle jet forming time is determined as the time when the motion of the outermost particle layer of the powder bed is first detected. The maximum number of particle jets is bounded by the total number of particles in the innermost layer of the powder bed. The number of particle jets is mainly a function of the number of particles in the innermost layer and the mass ratio of the powder bed to the gas in the driver section, or the ratio of powder bed mass (in dimensionless form) to the pressure ratio between the driver and driven sections.

Four different formation processes of spinning detonation in a narrow square tube are investigated by three-dimensional parallel simulations. High-resolution simulations are performed with a Riemann solver of the HLLC-type, high-order, parallel AMR reactive flow code. The simulations clearly show that the detonation structure transforms from rectangular and diagonal modes into spinning mode respectively during the propagation processes. Transverse wave dynamic and periodic oscillation of the front plays a significant role in the spinning detonations' formation.

Abstract A pilot-scale anaerobic/aerobic ultrafiltration system and a bench-scale anaerobic/aerobic system were tested to treat high-strength tomato-processing wastewater and bean-processing wastewater. The anaerobic/aerobic pilot-scale system achieved 99.4% SBOD removal, 91.9% NH3-N removal, and 100% phosphorus removal at an overall hydraulic retention time (HRT) of 1.5 days and solids retention time (SRT) of 5 days during the tomato canning season. The bench-scale anaerobic/aerobic system was used to confirm the pilot-scale anaerobic/aerobic system performance. Wastewater fractionation and kinetic coefficients were studied using respirometric methods.KeywordsChemical Oxygen DemandChemical Oxygen Demand RemovalOrganic Loading RateAeration TankUpflow Anaerobic Sludge BlanketThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The conventional volume-of-fluid method has the potential to deal with large free surface deformation on a fixed Cartesian grid. However, when free-surface flows are within or over complex geometries of industrial relevance, such as free-surface flows over offshore oil platforms, it is advantageous to extend the method originally written in Cartesian forms into non-Cartesian forms. In the present study, an algorithm similar to the algorithm described by Rudman in 1997 is proposed for use with curvilinear co-ordinates. This extension results in the ability to model complex geometries which could not be modelled using the original algorithm. Excellent agreement between the solutions obtained on both orthogonal and non-orthogonal meshes is achieved, although in general the L 1 error, based on the exact solution, on the non-orthogonal mesh is slightly higher than that on the orthogonal mesh. The extended fluid flow solving capacity of the present method is demonstrated through its application to a non-orthogonal Rayleigh–Taylor instability problem.