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)

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

Settling Sediment Clouds

• Experiments– Effect of release height above water surface– Sediment-fluid separation– Waves– Currents

• Integral Modeling• Numerical Simulation

Lab Facilities

Cloud Number Scaling

PIV and LIF

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)

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.

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

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

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

Compared to observations

t = 1.3 s t = 3.3 s t = 6.6 s t = 13.3 s

prediction

observation

sediment

Large-Eddy Simulation of Sediment Cloud

Validated Particle-laden Large-Eddy Simulations offer 3-D high resolution data of sediment settlement process.

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

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

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.

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.