Browsing by Author "Hemmati, Arman"
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- ItemOpen AccessEvolution of Large-Scale Structures in the Wake of Sharp-Edge Thin Flat Bodies(2016-01-29) Hemmati, Arman; Wood, David Howe; Smits, Alexander J.; Hu, Yaoping; Martinuzzi, Robert J.; Johansen, Craig T.This thesis describes computational fluid dynamic study of the wake behind thin flat plates at Reynolds numbers large enough for the formation of energetic structures and turbulence. The dynamically rich behavior of unsteady turbulent wake of bluff bodies consists of energetic and large-scale structures generated through flow instabilities, which have an anisotropic and geometry dependent topology. Large eddies are most important in characterizing the wake and provide the largest contribution to kinetic energy. The three-dimensional wake of thin flat plates positioned normal to a uniform flow is evaluated using Direct Numerical Simulations and Large Eddy Simulations. The flow around a 2D plate is examined at Re = 1200 and 2400 to characterize the wake and establish the dynamics of vortex formation and detachment processes. This is extended to the wake of finite aspect ratio (3D) thin flat plates at Re = 1200. The aspect ratios investigated are 3.2, 1.6 and 1.0. Flow topology eduction is carried out by examining the temporal evolution of aerodynamic forces and their phase-angles, as well as velocity and vorticity fields. Large-scale structures are investigated based on their topology, contributions to turbulent kinetic energy, and interaction with the surface pressure. The educed structures in the wake of 2D plates belong to three distinct regimes (H for high-, L for low-, and M for moderate-intensity vortex shedding) determined from periodicity of vortex shedding based on lift and drag fluctuations. The characteristics of previously identified H and L regimes were quantified, while introducing a new regime M. Formation and distortion of spanwise vortex rollers and streamwise vortex ribs coupled with Reynolds stress anisotropy and compression or stretching of the recirculation region characterize main differences among these regimes. The introduction of additional shear layers significantly alters the flow topology and vortex shedding process for 3D plates compared to 2D plates. Vortices are formed on longer edges of the plate, whereas shear layers on the shorter sides are carried away by the induced streamwise flow. This results in a single vortex shedding process. The vortex “peel-off” on shorter edges fixes the vortex detachment at sharp corners of the plate.
- ItemEmbargoPipeline Vibration Characterization and Monitoring System Development(2023-06) Chen, Haobin; Hugo, Ronald; Park, Simon; Wong, Ron Chik-Kwong; Tiamiyu, Ahmed Alade; Vyas, Rushi; Hemmati, ArmanPipeline systems are used for the transportation of energy over long distances. Pipeline systems play an important role both now and in the future, given that carbon-based energy products will slowly be replaced by carbon-neutral energy products. Structural Health Monitoring (SHM) utilizing operational vibroacoustic signals has become increasingly popular due to both its non-intrusive nature and its ability to provide continuous monitoring. To date, challenges have prevented widespread application to varying environments and flow conditions. The overall objective of this research is to experimentally and numerically investigate the operational vibration signal from pipelines under various boundary conditions (both above and below ground) and flow conditions (both single and multiphase) for the development of novel monitoring systems. In this thesis, several works have been performed: flow-induced vibration of a buried steel pipe structure due to internal flow turbulence; leak detection of small leaks in low-pressure pipelines; external disturbance detection and classification and flow pattern identification.