Numerical Modeling of Wave- and Current-supported Turbidity Currents over Erodible Bed

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Numerical Modeling of Wave- and Current-supported Turbidity Currents over Erodible Bed, Is A Well-Researched Topic, It Is To Be Used As A Guide Or Framework For Your Research.

ABSTRACT

The physical processes that route sediments from nearshore to the continental margin provide vital information to the global assessment of the geochemically important matter and the life in the ocean. Therefore, understanding these processes at the fundamental level will help develop accurate models that can be integrated into operational ocean models. Wave- and current-supported turbidity currents (WCSTCs) are one of the mechanisms that deliver sediments to the continental margin. WCSTCs are slow-moving turbidity currents where near-bed turbulence driven by strong surface waves and/or currents, tide- and/or wind-driven, maintain the turbidity current in motion. This study investigates the along-shelf current-supported turbidity currents (ACSTCs) over an erodible bed, where only the along-shelf current drives the flow, and sediment suspension is sourced from the ephemeral fine sediment deposits. To mimic ACSTCs, direct numerical simulations of a flow in a steady, turbulent, sediment-laden channel with a mild spanwise slope were conducted over an erodible bed. The primary focus of this study is to determine the effect of various sediment settling velocity, erosion parameters, and associated sediment-induced density stratification on total suspended sediment concentration, velocity structure, and turbulent characteristics of the ACSTCs. Specifically, this study aims to analytically and numerically investigates the transition of alongshore current-supported turbidity currents to self-sustaining turbidity currents over erodible seabed composed of fine sediment. Thus, a simplified depth-integrated dynamic equation is developed for suspended sediment concentration. The stability of the developed equation is analyzed both in itself and through temporal linear stability analysis. The analyses find two criteria for the inception of the aforementioned transition. Both criteria indicate that transition is found to reflect the competition between erosion flux, enhanced by the cross-shelf motion of alongshore current-supported turbidity currents, and the deposition flux. In addition, drag coefficient associated with cross-shelf motion of ACSTCs is formulated as a function of the Reynolds number, sediment concentration, sediment settling velocity, and the bed slope.

TABLE OF CONTENTS

ACKNOWLEDGMENTS ……………………………………………………………………………………………….. ii
1. INTRODUCTION ………………………………………………………………………………………………………. 1
1.1. OVERVIEW…………………………………………………………………………………………………………. 1
1.2. MOTIVATION …………………………………………………………………………………………………….. 3
1.3. OVERALL GOALS AND OBJECTIVES ………………………………………………………………… 9
1.4. SIGNIFICANCE TO PRACTICAL IMPLICATIONS …………………………………………….. 12
1.5. THE SCOPE OF THE STUDY …………………………………………………………………………….. 12
2. NUMERICAL METHODOLOGY ………………………………………………………………………………. 14
2.1. GOVERNING EQUATIONS ……………………………………………………………………………….. 14
2.2. DISCRETIZATION …………………………………………………………………………………………….. 16
2.3. BOUNDARY CONDITIONS ……………………………………………………………………………….. 17
2.4. EVALUATION OF FIRST- AND SECOND-ORDER PARTIAL DERIVATIVES …….. 18
2.5. NON-LINEAR TERMS ……………………………………………………………………………………….. 22
2.6. TIME INTEGRATION ………………………………………………………………………………………… 24
2.7. SOLUTION OF THE GENERAL METHODOLOGY …………………………………………….. 27
3. ROLE OF SEDIMENT SETTLING VELOCITY ON ALONG-SHELF CURRENT-SUPPORTED TURBIDITY CURRENTS OVER ERODIBLE BED ………………………………. 29
3.1. INTRODUCTION ……………………………………………………………………………………………….. 29
3.2. METHODS…………………………………………………………………………………………………………. 35
3.3. RESULTS…………………………………………………………………………………………………………… 46
3.4. DISCUSSION …………………………………………………………………………………………………….. 61
3.5. SUMMARY AND CONCLUSIONS …………………………………………………………………….. 68
4. DIRECT NUMERICAL SIMULATIONS OF MINIATURE ALONG-SHELF CURRENT-SUPPORTED TURBIDITY CURRENTS: IMPLICATIONS TO PARAMETERIZATION AT THE FIELD SCALE ……………………………………………………………………………………………. 73
4.1. INTRODUCTION ……………………………………………………………………………………………….. 73
4.2. METHODS…………………………………………………………………………………………………………. 78
4.3. RESULTS AND DISCUSSIONS ………………………………………………………………………….. 86
4.4. SUMMARY AND CONCLUSIONS …………………………………………………………………… 107

170
BIBLIOGRAPHY……………………………………………………………………………………………………….. 163
APPENDIX D. SUPPLEMENTARY MATERIAL TO CHAPTER 5 ……………………………….. 162
APPENDIX C. SUPPLEMENTARY MATERIAL TO CHAPTER 4………………………………… 159
APPENDIX B. SUPPLEMENTARY MATERIAL TO CHAPTER 3………………………………… 156
APPENDIX A. SUPPLEMENTARY MATERIAL TO CHAPTER 2 ……………………………….. 149
6. SUMMARY AND CONCLUSIONS …………………………………………………………………………. 140
5.5. DISCUSSIONS AND CONCLUDING REMARKS………………………………………………. 137
5.4. TRANSITION OF ACSTCS TO SELF-SUSTAINING TURBIDITY CURRENTS ….. 129
5.3. SIMULATION RESULTS………………………………………………………………………………….. 116
5.2. METHODS……………………………………………………………………………………………………….. 112
5.1.

VITA…………………………………………………………………………………………………………………………. 170
BIBLIOGRAPHY……………………………………………………………………………………………………….. 163
APPENDIX D. SUPPLEMENTARY MATERIAL TO CHAPTER 5 ……………………………….. 162
APPENDIX C. SUPPLEMENTARY MATERIAL TO CHAPTER 4………………………………… 159
APPENDIX B. SUPPLEMENTARY MATERIAL TO CHAPTER 3………………………………… 156
APPENDIX A. SUPPLEMENTARY MATERIAL TO CHAPTER 2 ……………………………….. 149
6. SUMMARY AND CONCLUSIONS …………………………………………………………………………. 140
5.5. DISCUSSIONS AND CONCLUDING REMARKS………………………………………………. 137
5.4. TRANSITION OF ACSTCS TO SELF-SUSTAINING TURBIDITY CURRENTS ….. 129

Additional information

Author

Sahar Haddadian

No of Chapters

6

No of Pages

177

Reference

YES

Format

PDF

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