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Experimental and Analytical Studies of Settling Sediment Clouds
Speaker: Ruo-Qian Wang (MIT)
Co-Authors: Dr. E Eric Adams (MIT)
Dr. Adrian Wing-Keung Law, Bing Zhao,
Dr. Zhenhua Huang (NTU)
Dr. Chun Hin Adrian Lai (CENSAM)
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Motivation
Source: Great Lakes Dredge and Dock Company
Boston Harbor Navigation Projects
Source: Monitoring survey at the Boston harbor CAD cell site-August 2004 Source: USACE, 2002
Mystic River CAD cells Massachusetts Bay open disposal
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Settling Sediment Clouds
• Experiments– Effect of release height above water surface– Sediment-fluid separation– Waves– Currents
• Integral Modeling• Numerical Simulation
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Lab Facilities
Cloud Number Scaling
PIV and LIF
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Effect of release height above water surface
Zhao et al. (2012) J. Hydraulic Research.
Penetration rate decreases with increasing release height. Therefore, lower release is less prone to sediment loss.
Z c/L st
t/Tst
2 cm (1.1m)
10 cm (5.5m)
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one sediment size two sediment sizes
Sediment-fluid Phase Separation
Phase separation (size) occurs gradually and should be included in integral models of sediment clouds.
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Waves
Within practical range of wave height and period, sediment clouds are transported passively with waves.
Zhao et al. (2012) J, Water, Port, Coastal, and Ocean Engineering
H=4cm (2.2 m in field) T=1.2 s (8.9 s in field)
us
wt
uw
TheoryExperiment
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Currents
Gensheimer, et al., J. Hydraul. Eng. (2012)
Strong current destroys the particle cloud self-circulating pattern; the trailing stem under current deposits out of the targeted region.
W* = raws3/(rs-ra)gn)
u a/w
t = u
aro/
(Bo/
r a)
Strong current
Weak current
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Integral ModelingKoh and Chang (1973)
Ad hoc loss mechanism: Abdelrhman and Dettmann (1993) and Johnson and Fong (1995) STFATE
Gravity
Particle Cloud
Drag + Added Mass
Entrainment
Only particles retained in cloud contribute buoyancy
Solid phase Particle group is transported by idealized vortex ring in fluid phase
Fluid phase
An idealized expanding Hill’s spherical vortex ring
Uo(t1)
Uo(t2)
Uo(t3)
ro(t1)
ro(t2)
ro(t3)
Phase-Separation Model
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Compared to observations
t = 1.3 s t = 3.3 s t = 6.6 s t = 13.3 s
prediction
observation
sediment
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Large-Eddy Simulation of Sediment Cloud
Validated Particle-laden Large-Eddy Simulations offer 3-D high resolution data of sediment settlement process.
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Numerical Simulation of Trailing Stem
Gharib et al., 1998
L/D=3
L/D=5
D
L
Wang et al. (2009, 2010) ,Physics of Fluids
Smaller L/D and greater buoyancy promote less stem mass (reduced sediment residual).
Criti
cal L
/D
Gharib et al., 1998 Marugan-Cruz et al, 2009
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Developed tools
• Lab facilities: flumes and tanks– PIV and LIF allow accurate quantification of cloud
behavior
• New modeling software– New integral modeling offers more realistic phase-
separation prediction
• Open-source LES simulations– High resolution simulations offer full details of cloud
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Take Home Messages• Release height:
– Penetration rate decreases with increasing release height. Therefore, lower release is less prone to sediment loss.
• Solid-fluid phase separation:– Phase separation occurs gradually and should be included in integral models of
sediment clouds.
• Wave:– Within practical range of wave height and period, sediment clouds are transported
passively with waves.
• Current:– Strong current destroys the particle cloud self-circulating pattern; the trailing stem
under current deposits out of the targeted region.
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THANKS
AcknowledgementsDr. Dongdong Shao (Beijing Normal University)Dr. Dai Chin (Shanghai University)Mr. James Gensheimer (US Navy)Mr. Godine K.Y. Chan (MIT)
This research was supported by the National Research Foundation Singapore through the Singapore MIT Alliance for Research and Technology's CENSAM IRG research programme.