Schulich School of Engineering Research & Publications
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- ItemOpen AccessDirect simulation of stably stratified wall-bounded turbulence using the lattice Boltzmann method(2023-04-27) Guo, Junwei; Zhou, Qi; Wong, Ron Chik-KwongThe lattice Boltzmann method (LBM) is employed to simulate stratified plane Couette (SPC) flows in their statistically stationary turbulent state. The aim is to assess the suitability of the LBM for direct simulation of wall-bounded, sheared turbulence under the influence of stable stratification. The SPC flow is generated by two parallel plates moving in opposite directions with velocities ± U w, and the buoyancy is fixed at ± b w at the upper and lower plates, respectively. The Reynolds number Re = U w h / ν, where h is the half-gap height, and ν is the kinematic viscosity, varies from 1000 to 3000. The Richardson number Ri = b w h / U w 2 is set to 0 or 0.01. The LBM results are compared to direct numerical simulations using the conventional pseudo-spectral method, and good agreement is found in various turbulence statistics, such as mean and fluctuation velocity and buoyancy, Reynolds stress, turbulent heat flux, dissipation rate, wall fluxes of momentum and heat, and longitudinal and transverse turbulence spectra. The results from grid-sensitivity tests indicate that the uniform isotropic grid spacing Δ x in LBM needs to be no greater than approximately the near-wall viscous length scale δ ν to achieve adequate resolution of stratified wall-bounded turbulence.
- ItemEmbargoExtended-FEM analysis of injection-induced slip on a fault with rate-and-state friction: Insights into parameters that control induced seismicity(Springer, 2023-03-09) Hosseini, Navid; Priest, Jeffrey; Eaton, DavidThe extended finite element method (X-FEM) is utilised to simulate the behavior of a heterogeneous fault characterized by rate-state frictional rheology, embedded within a poroelastic medium. The displacement and pore-pressure fields that are discontinuous across the fault are computed using X-FEM, by enriching the standard finite element approximation with additional degrees of freedom for elements intersected by the fault. We investigate a Mw 4.1 injection-induced earthquake in western Canada; this model incorporates depth-varying rate-slip behavior wherein a high-pressure zone due to hydraulic fracturing stimulation intersects the fault within a stable layer, producing aseismic slip that progressively loads an unstable fault region, thereby triggering dynamic rupture. Parametric studies using our numerical approach provide insights into the influence of rate-state parameters on fault activation, as well as hydraulic properties of a damage zone that surrounds the fault. Results confirm that aseismic slip near the injection zone propagates outwards to seismogenic unstable regions of the fault. The coseismic slip profile, seismic moment, and slip latency are determined by the difference a − b for rate-state parameters of the unstable fault regions. Hydraulic diffusivity in the damage zone controls the rate of pore-pressure diffusion along the fault, which affects timing of the initial seismic event and aftershock productivity.
- ItemOpen AccessTibial-fibular geometry and density variations associated with elevated bone strain and sex disparities in young active adults(Elsevier, 2022-05-20) Bruce, Olivia L; Baggaley, Michael; Khassetarash, Arash; Haider, Ifaz T; Edwards, W BrentTibial stress fracture is a common injury in runners and military personnel. Elevated bone strain is believed to be associated with the development of stress fractures and is influenced by bone geometry and density. The purpose of this study was to characterize tibial-fibular geometry and density variations in young active adults, and to quantify the influence of these variations on finite element-predicted bone strain. A statistical appearance model characterising tibial-fibular geometry and density was developed from computed tomography scans of 48 young physically active adults. The model was perturbed ±1 and 2 standard deviations along each of the first five principal components to create finite element models. Average male and female finite element models, controlled for scale, were also generated. Muscle and joint forces in running, calculated using inverse dynamics-based static optimization, were applied to the finite element models. The resulting 95th percentile pressure-modified von Mises strain (peak strain) and strained volume (volume of elements above 4000 με) were quantified. Geometry and density variations described by principal components resulted in up to 12.0% differences in peak strain and 95.4% differences in strained volume when compared to the average tibia-fibula model. The average female illustrated 5.5% and 41.3% larger peak strain and strained volume, respectively, when compared to the average male, suggesting that sexual dimorphism in bone geometry may indeed contribute to greater stress fracture risk in females. Our findings identified important features in subject-specific geometry and density associated with elevated bone strain that may have implications for stress fracture risk.
- ItemOpen AccessA statistical shape model of the tibia-fibula complex: sexual dimorphism and effects of age on reconstruction accuracy from anatomical landmarks(2021-11-03) Bruce, Olivia L; Baggaley, Michael; Welte, Lauren; Rainbow, Michael J; Edwards, W BrentA statistical shape model was created for a young adult population and used to predict tibia and fibula geometries from bony landmarks. Reconstruction errors with respect to CT data were quantified and compared to isometric scaling. Shape differences existed between sexes. The statistical shape model estimated tibia-fibula geometries from landmarks with high accuracy (RMSE = 1.51-1.62 mm), improving upon isometric scaling (RMSE = 1.78 mm). Reconstruction errors increased when the model was applied to older adults (RMSE = 2.11-2.17 mm). Improvements in geometric accuracy with shape model reconstruction changed hamstring moment arms 25-35% (1.0-1.3 mm) in young adults.
- ItemEmbargoThreshold behavior of local gradient Richardson number in strongly stratified nonequilibrium turbulence(American Physical Society, 2022-10-20) Zhou, QiIn this paper we examine the possible self-organization of strongly stratified turbulence around a local critical state by analyzing a data set of a numerically simulated stratified turbulent wake. To facilitate the analysis, the turbulent flow field is decomposed into a“large-scale” flow of horizontal scales greater than the Ozmidov scale, and a “small-scale” flow of scales below O. A local gradient Richardson number, Ri, characterizing the large-scale flow is calculated and then utilized to produce conditional sampling of various turbulence statistics relevant to the local dynamics. While the bulk turbulence is observed to decay by approximately one order of magnitude in terms of the dissipation rate, the median Ri has remained nearly constant due to the self-organization of flow structures under strong stratification; the subsampled Ri distribution peaks around 1/4 for regions in the upper quartile of local dissipation. Regions of small Ri are found to be associated with large dissipation and large net transfer of energy to the small scales. Regions of “back-scatter”of kinetic energy to large scales, where the local eddy viscosity,νe, takes a negative value,are also observed. Occurrence of a large magnitude of both positive and negative νe appears to be most frequent around the critical value of Ri∼1/4, indicating an intense two-way exchange of kinetic energy between the large and small scales around the local critical state. The threshold behavior of Ri underscores the dynamical significance of the critical Ri of 1/4 for locally self-sustained turbulence in a strongly stratified configuration and bears some resemblance to the celebrated self-organized criticality dynamics [Baket al.,Phys.Rev.Lett.59, 381 (1987)].