top 10 travel destinations on airbnb • Tel Aviv’s White City is UNESCO World Heritage Site, contains 4,000 International Style buildings, many of which were built in the 1930s and 1940s • top 10 most vibrant cities in nightlife category, “Miami of Middle East” • one of the best cities to open a start-up . . . . . .
Israeli universities - No. 1 in citation impact among Israeli universities - No. 1 choice among Israeli students - 15 international study programs - Over 1,200 international students - 2,000,000 people served in TAU’s 17 afﬁliated hospitals - 130 research centers and institutes - 2 Oscar-nominated ﬁlms . . . . . .
:) - Established in 70’s by Prof. A. Tsinober - 2 Faculty members - 2 Senior Researchers, 1 Engineer - 3 Ph.Ds, 12 M.Sc., 6 undergraduate students 2XU´SKLORVRSK\µ² learn from the change 7 Turbulence Polymers Particles Forcing Lagrangian Eulerian . . . . . .
Borisenkov et al. (2011) tip size is 20 - 60 µm sensor thickness is 20 nm 3D Particle Tracking Velocimetry - originally from ETH Zurich - FPGA based real-time image processing Kreizer (2010,2011) - open source software: http://3dptv.github.com . . . . . .
motion condition constitutes one of the classical and central problems of sediment transport In rivers, coastal areas and atmospheric ﬂows” • Industry: • Silicon wafer cleaning • Pneumatic conveying • Fluidized beds • Biomedical applications (pulsating ﬂows) . . . . . .
a smooth wall under turbulent ﬂow conditions without mean shear • Incipient motion due to ﬂuid motion refers to the beginning of movement (not only disturbed) of bed particles that stayed at rest. • We focus on the lift-off events at the moment (though we have the full history). Lift-off occurs only when the instantaneous lift force acting on the particle exceeds its effective weight force. The lift-off (pick-up) probability is a fraction of time when the lift force is greater than the effective weight for a given time interval, or the percentage of the number of particles in motion on a ﬁxed area of bed surface (Einstein 1942, 1950) . . . . . .
τw = µ ∂U ∂y y=0 Shields (1936) Stochastic view: turbulence, probability −ρ⟨u′v′⟩ + ρ⟨u′2⟩ + ρ⟨v′2⟩ + . . . Einstein (1949) * However: particles are observed to move also under very weak turbulent ﬂow conditions (e.g. Paintal, 1971) * In all models, turbulence is assumed to have a major inﬂuence on the phenomenon . . . . . .
(1999): . . 1 unsteady ﬂow effects play a vital role in particle removal even in the steady methods due to the start-up transient as the ﬂow is initiated. In most steady-ﬂow experiments, a high entrainment rate is observed when the ﬂow is ﬁrst turned on; The transients during ﬂow start-up produce higher forces on the bound particles than the subsequent steady ﬂows. . . 2 In periodic unsteady ﬂows, such as a pulsed jet, the transients are generated repeatedly. Nelson (2001), Smart and Habersack (2007), Schmeeckle et al. (2007): • entrainment due to deceleration, high pressure ﬂuctuations, rare episodes of specially high lift force • two important quantities: the instantaneous ﬂuid acceleration/deceleration and vertical normal stress component . . . . . .
the zero-mean shear ﬂows under oscillating grids: θ∗ = TKE g(s − 1)d Redondo and co-workers (e.g. Cont. Shelf. Res. 2001) focused on the lift off of sediments in ocean benthic layers: • A turbulent r.m.s velocity u′ lower than the u∗ Shields critical velocity is required to start the sediment motion. • One is able to lift off sediments much more efﬁciently with the grid stirring experiments (zero-mean ﬂow) as compared to the shear-induced turbulence experiment. . . . . . .
settling and diffusion of particles in a water column (lakes, reservoirs) using oscillating grids: • measurements are 1D, forcing is assumed to be according to the grid function: u′ = CfS1.5M0.5z−1 with empirical coefﬁcients • the modiﬁed Shields is found to be close to the original Shields for open channel ﬂows “only if the TKE exceeds the critical value, will resuspension occur” . . . . . .
for measuring turbulent ﬂows, w/o additives such as particles, colloids, dilute polymers . . 2 To develop better understanding of the mechanics of turbulence-particle interactions, speciﬁcally for the particle-detachment from the surfaces • detailed measurements of particle and ﬂuid motion under well controlled (or well characterized) ﬂows: oscillating grids, driven shear ﬂows, separation points, stratiﬁcation . . . . . .
simultaneously quantify ﬂow properties and particle motion through the various phases of re-suspension. . . 2 Identiﬁcation of ﬂuid motion patterns during particle resuspension, linking them to turbulent ﬂow properties * The focus is on the pick-up or lift-off phase. . . . . . .
(Willneff, 2003). 2-6 ± Stereo-matching -matching is based on epipolar geometry (see 2.6 2.6 below 2.6). We measure directly the full gradient tensor along the particle trajectories: ∂ui/∂xj(x, t) 5.4. Object space based tracking techniques Est con nat tim Fig. 15: Main processing steps . . . . . .
sweeps/ejections vs acceleration/deceleration events: • Some works report that local velocity of the ﬂuid is higher than the velocity of the particles that leave the bed - it is explained as u′ < 0, v′ > 0 ejection events. Others (see above) referred to the sweep events. We will address this question directly. • It can be also due to large acceleration/deceleration, and not of the relative velocities, i.e. not related to the sweeps/ejections. . . 2 Probe directly the balance of forces on the particle at the initial motion on the bed: relative velocity, pressure gradients, added mass . . 3 Repeat the analysis on a rough bed, adhesive particles, coagulation of particles . . 4 Shear ﬂow cases, e.g. lid driven cavity . . . . . .