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Effect of Aquatic Plants on Hydrodynamic and Dispersion in the Wave Motion

Tofighi, Mohammad Ali | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 45867 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Jamali, Mirmosadegh
  7. Abstract:
  8. Aquatic plants play an important role in water environment. Increasing drag force, distorting the velocity and turbulence structures and other related parameters, are the results of the presences of plants. These changes affect the dispersion and mass transport in the aquatic areas. This thesis presents laboratory visualizations and measurements of wave motion, and passive solute surface dispersion (longitudinal and lateral) in arrays of cylinders, a model for emergent, rigid aquatic plants. In the range of (where is Keulegan–Carpenter number, is the maximum oscillatory velocity perpendicular to the cylinder axis, is the period of oscillation, and is the diameter of the cylinder), and (where is the Reynolds number, and ν is the kinematic viscosity of fluid), flow patterns and vortex shedding around an isolated cylinder are in three predominant types. The double-shooting in , single-pair in , and double-pair in are the predominant flow regimes in the progressive wave motion around a single cylinder. With arraying the cylinders, the vortex shedding is more regulated and the predominant patterns are frequently observed.Because of the flow interactions, lag time of approaching wave, damping the wave height, and changing the velocity and shear in the wave motion through array, ranges are different along the array of cylinders. Up to , symmetric and asymmetric non-shedding, double-shooting, and single-pair are the predominant flow regimes in the progressive wave motion around the array of cylinders. The double-shooting and single-pair in , and double-pair in are the predominant regimes in other ranges. Therefore, we see the variety of flow patterns in the depth wise and longitudinal direction of the array of cylinders.For a certain , increasing the wave steepness, conducts the shedding to the wave direction. Reynolds number has no significant role in flow pattern in the ranges examined here. Using Lagrangian single-particle tracking technique, it is found that the array of cylinders increase the lateral dispersion. For all flow regimes, lateral displacement covariance is ascending. Lateral dispersion coefficient is positive and bounded, and longitudinal displacement covariance, and dispersion are oscillating in the wave frequency. Progressing the time, longitudinal dispersion coefficient decreases but its average increases slowly. In the wave motion around aquatic plants, the flow regime around stems, arrangements of the plants, and the geometric properties, affect the solute dispersion. In a certain stems’ density, if the distance between stems’ rows perpendicular to the wave direction is more than those in parallel to the wave direction, the longitudinal dispersion is bigger than the lateral dispersion and vice versa. Increasing the density and the length of plants in the direction of wave motion decreases the dispersion. However, increasing the , increases the longitudinal and lateral dispersion
  9. Keywords:
  10. Water Wave ; Flow Visualization ; Particle Image Velocimetery (PIV) ; Aquatic Plants ; Lagrangian Dispersion

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