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Dynamics of sand ripples in heteroge...

Arizona State University.

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Dynamics of sand ripples in heterogeneous sediment beds.

Record Type:	Language materials, printed : Monograph/item
Title/Author:	Dynamics of sand ripples in heterogeneous sediment beds./
Author:	Balasubramanian, Sridhar.
Description:	115 p.
Notes:	Source: Dissertation Abstracts International, Volume: 69-12, Section: B, page: 7758.
Contained By:	Dissertation Abstracts International69-12B.
Subject:	Engineering, Mechanical. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3339562
ISBN:	9780549934813

Dynamics of sand ripples in heterogeneous sediment beds.
Balasubramanian, Sridhar.

Dynamics of sand ripples in heterogeneous sediment beds. - 115 p.

Source: Dissertation Abstracts International, Volume: 69-12, Section: B, page: 7758.

Thesis (Ph.D.)--Arizona State University, 2008.

Sediment ripples that form as a result of wave forcing in oceanic coastal zones are of great consequence in acoustic sensing of seafloor (e.g. mine sweeping operations), local wave attenuation/dissipation by bottom roughness, coastal circulation and along/cross shore sediment transport. An understanding of these coastal processes requires an in-depth knowledge of the evolution, dynamics and the decay of ripples as well as inhomogeneities resulting from sediment sorting in the presence of heterogeneous sediments. This dissertation concerns a laboratory experimental and theoretical modeling program conducted to investigate the aforementioned topics when the background flow is oscillatory and/or turbulent. The experiments were conducted in a water channel with an oscillatory tray filled with a heterogeneous sediment mixture. Particle image velocimetry and a laser displacement sensor were employed to collect data on flow/ripple characteristics. First, the ripple formation and their dynamics under variable oscillatory flow conditions were studied in heterogeneous mixture. The results show that sediment heterogeneity has a stabilizing effect, and consequently modifies the ripple characteristics and dynamics when compared to homogeneous sediment of equivalent size. A previous model for homogeneous sediments developed at Arizona State University (ASU) was modified to account for the heterogeneity based on the use of an effective grain size, which explained the laboratory observations reasonably well. It was demonstrated that selective transport leads to sediment sorting, with coarse grains accumulating at ripple crests and fine grains on the troughs. Second, the ripple decay under variable oscillatory flow conditions and background turbulence was studied for both homogeneous and heterogeneous sediments. In these experiments, established ripples were subjected to either weak transport conditions (below the ripple-formation threshold) or random shear-free turbulence. A decrease of ripple height was documented in both cases and explained using a 1-D ripple diffusion model. The effective ripple diffusivities inferred were in reasonable agreement with available field measurements.

ISBN: 9780549934813Subjects--Topical Terms:

783786
Engineering, Mechanical.

Dynamics of sand ripples in heterogeneous sediment beds.
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020 $a 9780549934813
035 $a (UMI)AAI3339562
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100 1 $a Balasubramanian, Sridhar. $3 1028941
245 1 0 $a Dynamics of sand ripples in heterogeneous sediment beds.
300 $a 115 p.
500 $a Source: Dissertation Abstracts International, Volume: 69-12, Section: B, page: 7758.
502 $a Thesis (Ph.D.)--Arizona State University, 2008.
520 $a Sediment ripples that form as a result of wave forcing in oceanic coastal zones are of great consequence in acoustic sensing of seafloor (e.g. mine sweeping operations), local wave attenuation/dissipation by bottom roughness, coastal circulation and along/cross shore sediment transport. An understanding of these coastal processes requires an in-depth knowledge of the evolution, dynamics and the decay of ripples as well as inhomogeneities resulting from sediment sorting in the presence of heterogeneous sediments. This dissertation concerns a laboratory experimental and theoretical modeling program conducted to investigate the aforementioned topics when the background flow is oscillatory and/or turbulent. The experiments were conducted in a water channel with an oscillatory tray filled with a heterogeneous sediment mixture. Particle image velocimetry and a laser displacement sensor were employed to collect data on flow/ripple characteristics. First, the ripple formation and their dynamics under variable oscillatory flow conditions were studied in heterogeneous mixture. The results show that sediment heterogeneity has a stabilizing effect, and consequently modifies the ripple characteristics and dynamics when compared to homogeneous sediment of equivalent size. A previous model for homogeneous sediments developed at Arizona State University (ASU) was modified to account for the heterogeneity based on the use of an effective grain size, which explained the laboratory observations reasonably well. It was demonstrated that selective transport leads to sediment sorting, with coarse grains accumulating at ripple crests and fine grains on the troughs. Second, the ripple decay under variable oscillatory flow conditions and background turbulence was studied for both homogeneous and heterogeneous sediments. In these experiments, established ripples were subjected to either weak transport conditions (below the ripple-formation threshold) or random shear-free turbulence. A decrease of ripple height was documented in both cases and explained using a 1-D ripple diffusion model. The effective ripple diffusivities inferred were in reasonable agreement with available field measurements.
590 $a School code: 0010.
650 4 $a Engineering, Mechanical. $3 783786
650 4 $a Geophysics. $3 535228
690 $a 0373
690 $a 0548
710 2 $a Arizona State University. $3 1017445
773 0 $t Dissertation Abstracts International $g 69-12B.
790 $a 0010
791 $a Ph.D.
792 $a 2008
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3339562