טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMoltchanov Sharon
SubjectQuantitative Analysis of Resuspension Phenomena Using PIV
Measurements
DepartmentDepartment of Agricultural Engineering
Supervisors Professor Uri Shavit
Professor Yehuda Agnon


Abstract

This research focuses on resuspension and transport of sediments in a partially standing water wave. The flow regime was generated using a pneumatic piston wavemaker in a small-scale laboratory glass flume. Particle Image Velocimetry (PIV) was used for simultaneous visualization and velocity measurements. Observations reveal that sediment particles resuspend intermittently at a location, which changes dynamically within a small limited range, and form coherent well-defined narrow streaks of sediments. Velocity vector fields across vertical cross sections along the flume centerline for both sediment and neutrally buoyant particles were obtained. The measured velocities were used to calculate the periodic velocity, drift velocity, shear stresses, vorticity, Lagrangian velocity, particle trajectories and turbulent field. A good correlation was found between the resuspension location and the location of maximum velocity gradient, ðuy . A topological similarity was identified when comparing the pattern of suspended matter and velocity related properties such as time average velocity field, Lagrangian velocity field, vorticity and particle trajectories. The velocity fields of the neutrally buoyant and of the sediment particles were almost identical. This indicates that flow modulation by the sediment particles is minimal and the convective flow field plays a major role in the transport of the sediments. The existence of a narrow particle streak and the particular shape it forms may indicate that a phase correlation exists between the resuspension of particles, the periodic field, maximum shear, and the instantaneous location of the particles streak. It is not clear yet what causes the resuspension intermittency. An analysis of the turbulent velocity field shows that it consists of long-lived vortex-like structures, which maintain their coherence for many wave periods. It is not clear what is the exact time history of these structures within the wave period. To answer this question, measurements at higher frequency are required.