**FLUID MUD GRAVITY CURRENTS THROUGH EMERGENT AQUATIC VEGETATION**

**Fluid mud gravity currents through emergent aquatic vegetation**

by

Nazli Aslican Yilmaz

April, 2014

by

Nazli Aslican Yilmaz

April, 2014

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

OUTLINE:

Introduction and Motivation

Experimental setup, methodology and measurement techniques

Viscous fluid-mud gravity currents over smooth surfaces

Anatomy of fluid-mud gravity currents propagating through emergent aquatic vegetation

Propagation modeling of fluid-mud gravity currents through emergent aquatic vegetation

Conclusion

MOTIVATION:

Coastal dredge disposal operations result in fluid mud bottom gravity currents.

Fluid-mud underflows overrun everything in its path; damage aquatic flora and fauna, and engineering installations.

Other examples for gravity currents in nature: underwater landslides,snow avalanches, dust storms, ash clouds, etc.

Several industrial applications, i.e. effluent transportation, slurry transportation, free surface flows (foodstuff, paints, concrete)

Gravity Currents:

Viscous-buoyancy phase gravity current

The driving force acting on gravity current per unit width:

The resisting force acting on gravity current per unit width:

**Middle East Technical University, Ankara**

RESEARCH OBJECTIVES:

To formulate the Fanning friction coefficient for viscous shear forces of the bottom surface for gravity currents propagating over smooth surfaces.

To propose a relationship between the Fanning friction coefficient and Reynolds number for constant-flux viscous gravity currents.

To investigate effect of vegetation on the viscous fluid-mud gravity current anatomy.

To determine the effect of emergent stiff aquatic vegetation on the gravity current propagation dynamics; and formulate f-Re relation.

f-Re relations for closed conduit:

f=16/Re (Moody 1944)

f-Re relations for open channel flows:

Newtonian

f = K/Re (Straub et al. 1958)

K is a function of duct opening (Sparrow 1962)

non-Newtonian

f = 16/Re(Kozicki et al. 1966)

f = 16/Re for rectangular channels (Haldenwang and

Slatter 2006)

K is a function of channel cross-section and fluid

rheology (Burger et al. 2010)

Flow through aquatic vegetation:

Aquatic vegetation

Closed conduit flow through packed columns (Ergun 1952)

f is a function flow and material properties

f - Re relation for closed-conduit

Open channel flow through emergent cylinders (Tanino and Nepf 2008)

f - Re relation for open channel

Gravity current through emergent cylinders (Tanino et al. 2005)

Front velocity formulation for constant-volume Newtonian Gravity currents

Triangular profile of constant-volume Newtonian gravity currents

From conservation of momentum the coefficient of friction:

Order of magnitude analysis of shear stress at position xf :

Reynolds number of gravity current:

Friction coefficient equals to:

Correction factor for shape assumption:

Dimensionless shape factor, K is constant thoughout the propagation.

K is a function of parameters that remain fixed over time in a given gravity current.

K as a function of dimensionless parameters

where

EXPERIMENTAL SETUP:

DENSITY AND RHEOLOGY MEASUREMENTS:

Kaolinite Clay (OM4 Ball Clay)

Experimental conditions:

Only the experimental data that corresponds to the viscous-buoyancy propagation phase is used.

Data is corrected to exclude the side-wall friction force.

Experimental shape factor, K is formulated with a coefficient of determination value of 0.86

Viscous Propagation Model:

Bed Erosion:

increased siltation and sediment transport

self-sustaining turbidity currents

Gravity Current Profile

gravity current profile formulation in terms of friction coefficient, f (Findikakis and Law 1998)

Turbulent-Laminar Transition

critical Reynolds number

Vegetation effect of fluid-mud gravity currents:

3 sets of experiments with different fluid-mud concentrations and vegetation densities.

Presence of the vegetation changes the gravity current profile from blunt head with an almost rectangular body to a smooth distinct triangular shape.

a preliminary parameterization is proposed to relate the current slope to the flow behavior index and the vegetation density

Vegetation effect of fluid-mud gravity currents:

THANK YOU!

? QUESTIONS ?

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

BACKGROUND INFORMATION:

BACKGROUND INFORMATION:

BACKGROUND INFORMATION:

THEORETICAL ANALYSIS:

THEORETICAL ANALYSIS:

THEORETICAL ANALYSIS:

EXPERIMENTAL METHODOLOGY AND MEASUREMENT TECHNIQUES:

RESULTS:

DISCUSSION:

ONGOING WORK:

ONGOING WORK:

Re - f Relation for Constant-Flux Underflows

Nazli A. Yilmaz

ONGOING WORK:

Vegetation effect of fluid-mud gravity currents:

Vegetation effect on gravity current anatomy will be qualitatively and quantitatively examined.

Fanning friction factor for aquatic vegetation will be formulated.

f-cylinder Re relation will be studied.

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