Wave Attenuation Capacity of Suspended Aquaculture Structures with Sugar Kelp and Mussels

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Wave Attenuation Capacity of Suspended Aquaculture Structures
with Sugar Kelp and Mussels, Is A Well-Researched Topic, It Is To Be Used As A Guide Or Framework For Your Research.

ABSTRACT

Large aquaculture systems may have the potential to damp wave energy for coastal protection. The performance of these systems are influenced by the dynamics of components such as flexible kelp blades and mussel droppers. In this thesis, the dynamics of kelp blades and mussel droppers were investigated with a consistent-mass cable model with focus on understanding the asymmetric motion of kelp blades. The results showed the asymmetric blade motion in symmetric waves is caused by the spatial asymmetry of the encountered wave orbital velocities due to blade displacements and the asymmetric action on the blade by vertical wave orbital velocities. For the kelp grown from the bottom, the asymmetry of blade motion provides ‘shelter’ that could inhibit sediment suspension and coastal erosion. For suspended kelp attached to a longline, the asymmetric motion would induce the kelp to roll over the attachment in large wave conditions. With understanding the blade dynamics, physical model experiments using the morphological and mechanical properties of the cultivated Saccharina latissima at Saco Bay, Maine in the USA were conducted to investigate the wave attenuation characteristics of suspended kelp farms. The results indicated that 20 longlines with 100 plants/m could reduce up to 23% energy of 6.3 s waves. To predict wave attenuation under wider conditions, numerical and analytical wave attenuation models coupled with blade motion were developed for regular and irregular waves. With the analytical model, a case study at a site in Northeastern US showed the potential of suspended aquaculture farms to dissipate wave energy in a storm event. Compared to naturally occurring submerged aquatic vegetation (SAV), suspended aquaculture farms were found to perform better at attenuating shorter waves and less impacted by water level changes due to tides, surge and sea level rise. Implementing offshore aquaculture structures in conjunction with SAV-based living shorelines that can enhance the coastal defense of SAV-based living shorelines. This research is useful for the design of suspended aquaculture structures for nature-based coastal protection. The analytical wave attenuation models are also convenient to implement in large-scale models to analyze the influences of wave attenuation on coastal morphology.

TABLE OF CONTENTS

DEDICATION …………………………………………………………………………………………………………………………… iii
ACKNOWLEDGEMENTS …………………………………………………………………………………………………………. iv
LIST OF TABLES ………………………………………………………………………………………………………………………. x
LIST OF FIGURES ……………………………………………………………………………………………………………………. xi
Chapter
1. INTRODUCTION ……………………………………………………………………………………………………………….. 1
1.1 Asymmetric motion of flexible blades in waves ……………………………………………………………… 2
1.2 Physical model experiments for wave attenuation by suspended kelp canopies ………………….. 3
1.3 Analytical wave attenuation model for flexible canopies …………………………………………………. 4
1.4 Frequency dependent random wave attenuation by flexible canopies ………………………………… 6
1.5 Outline…………………………………………………………………………………………..7
2. MECHANISMS FOR THE ASYMMETRIC MOTION OF SUBMERGED AQUATIC VEGETATION IN WAVES: A CONSISTENT-MASS CABLE MODEL ………………………………….. 9
2.1. Background ………………………………………………………………………………………………………………. 9
2.2. Methodology …………………………………………………………………………………………………………… 11
2.2.1. 2D Cable model ………………………………………………………………………………………… 12
2.2.2. Hydrodynamic force coefficients …………………………………………………………………. 14
2.3. Model-data comparison ……………………………………………………………………………………………. 15
2.3.1. Blade motion in combined waves and currents ……………………………………………… 15
2.3.2. Blade motion in waves ……………………………………………………………………………….. 17
2.4. Symmetric and asymmetric blade motions ………………………………………………………………….. 25
2.4.1. Definition …………………………………………………………………………………………………. 25
2.4.2. Theory ……………………………………………………………………………………………………… 26
2.4.3. Case study ………………………………………………………………………………………………… 32

2.5. Discussion ………………………………………………………………………………………………………………. 35
2.5.1. Mechanisms for asymmetric blade motion ……………………………………………………. 35
2.5.2. Conditions for symmetric blade motion………………………………………………………… 37
2.5.3. Properties and implications of asymmetric blade motion ………………………………… 38
2.6. Summary.. ………………………………………………………………………………………………………………. 39
2.7. Acknowledgments……………………………………………………………………………………………………. 40
3. WAVE ATTENUATION BY SUSPENDED CANOPIES WITH CULTIVATED KELP (SACCHARINA LATISSIMA) ………………………………………………………………………………………………. 41
3.1. Background …………………………………………………………………………………………………………….. 41
3.2. Materials and methods ……………………………………………………………………………………………… 44
3.2.1. Theory for blade dynamics and wave attenuation ………………………………………….. 44
3.2.2. Measurements for cultivated S. latissima ……………………………………………………… 49
3.2.3. Experimental design…………………………………………………………………………………… 51
3.2.4. Wave decay measurements …………………………………………………………………………. 53
3.3. Results….. ………………………………………………………………………………………………………………. 55
3.3.1. Morphological and mechanical properties of S. latissima compared with the model blade ………………………………………………………………………………………………………… 55
3.3.2. Wave-induced motion of suspended blades …………………………………………………… 58
3.3.3. Horizontal force and wave attenuation …………………………………………………………. 60
3.3.4. Bulk drag coefficient and effective blade length ……………………………………………. 63
3.4. Discussion ………………………………………………………………………………………………………………. 65
3.4.1. Roll-over of suspended flexible blades …………………………………………………………. 65
3.4.2. Methods to predict wave attenuation ……………………………………………………………. 68
3.4.3. Suspended kelp aquaculture farms as nature-based coastal protection ………………. 68
3.4.4. Limitations ……………………………………………………………………………………………….. 71
3.5. Summary.. ………………………………………………………………………………………………………………. 71

3.6. Acknowledgments……………………………………………………………………………………………………. 72
4. ANALYTICAL MODEL FOR WAVE ATTENUATION BY FLEXIBLE CANOPIES ……………… 73
4.1. Background …………………………………………………………………………………………………………….. 73
4.2. Methodology …………………………………………………………………………………………………………… 76
4.2.1. Model set-up …………………………………………………………………………………………….. 76
4.2.2. Blade motion …………………………………………………………………………………………….. 77
4.2.3. Wave attenuation ………………………………………………………………………………………. 80
4.2.4. Bulk drag coefficient and effective blade length ……………………………………………. 81
4.3. Results….. ………………………………………………………………………………………………………………. 83
4.3.1. Model-data comparison ……………………………………………………………………………… 83
4.3.2. Bulk drag coefficient and effective blade length ……………………………………………. 85
4.3.3. Case study for wave attenuation in different seasons ……………………………………… 88
4.4. Discussion ………………………………………………………………………………………………………………. 91
4.4.1. Blade motion and the nonlinear effects…………………………………………………………. 91
4.4.2. Evaluations of the methods to obtain bulk drag coefficient and effective blade length ………………………………………………………………………………………………………. 93
4.4.3. Nature-based coastal protection strategies …………………………………………………….. 93
4.5. Summary.. ………………………………………………………………………………………………………………. 94
4.6. Acknowledgments……………………………………………………………………………………………………. 95
5. AQUACULTURE FARMS AS NATURE-BASED COASTAL PROTECTION: RANDOM WAVE ATTENUATION BY SUSPENDED AND SUBMERGED CANOPIES …………………………………… 96
5.1. Background …………………………………………………………………………………………………………….. 96
5.2. Theory….. …………………………………………………………………………………………………………….. 100
5.2.1. Background on analytical wave attenuation models ……………………………………… 100
5.2.2. Model set-up …………………………………………………………………………………………… 103
5.2.3. Models for the motion of canopy components……………………………………………… 105

5.2.3.1. Cantilever-beam model ………………………………………………………………. 106
5.2.3.2. Buoy-on-rope model …………………………………………………………………… 108
5.2.4. Solutions for random wave attenuation ………………………………………………………. 109
5.3. Model-data comparison ………………………………………………………………………………………….. 110
5.3.1. Submerged canopy …………………………………………………………………………………… 110
5.3.2. Suspended canopy ……………………………………………………………………………………. 114
5.4. Case study at the field site ………………………………………………………………………………………. 116
5.4.1. Properties for the mussel farm and submerged aquatic vegetation ………………….. 117
5.4.2. Mussel farm and SAV at the same water depth ……………………………………………. 119
5.4.3. Mussel farm and SAV at different water depths …………………………………………… 123
5.5. Discussion …………………………………………………………………………………………………………….. 125
5.5.1. Wave attenuation characteristics of suspended aquaculture farms and SAV ……. 125
5.5.2. Simplified analytical solutions …………………………………………………………………… 126
5.6. Summary.. …………………………………………………………………………………………………………….. 128
5.7. Acknowledgments………………………………………………………………………………………………….. 129
6. CONCLUSIONS ………………………………………………………………………………………………………………. 130
6.1. Chapter summary …………………………………………………………………………………………………… 130
6.2. Findings and academic contributions ………………………………………………………………………… 130
6.2.1. Chapter 2: Asymmetric blade motion in waves ……………………………………………. 130
6.2.2. Chapter 3: Physical model experiments for wave attenuation by suspended kelp canopies …………………………………………………………………………………………………. 131
6.2.3. Chapter 4: Analytical wave attenuation model for flexible canopies ………………. 131
6.2.4. Chapter 5: Random wave attenuation by flexible canopies ……………………………. 132
6.3. Engineering implications for nature-based solutions …………………………………………………… 133
6.4. Suggestions for future research ………………………………………………………………………………… 134
BIBLIOGRAPHY ……………………………………………………………………………………………………………………. 137

APPENDIX A: CONDITIONS FOR SYMMETRIC BLADE MOTION IN SYMMETRIC WAVES ………………………………………………………………………………………………………….. 154
APPENDIX B: WAVE HEIGHT FITTING ALONG A CANOPY WITH REFLECTIVE WAVES ….. 156
APPENDIX C: PIECEWISE FUNCTION METHDOD REALTING KOBAYASHI AND DALRYMPLE WAVE ATTENUATION MODELS …………………………………………………………………… 157
Appendix C.1. Extension of the solution by Kobayashi et al. (1993) to suspended canopy ……. 157
Appendix C.2. Extension of the solution by Dalrymple et al. (1984) to suspended canopy ……. 158
Appendix C.3. Piecewise function method linking Kobayashi- and Dalrymple-based techniques ……………………………………………………………………………………………… 159
APPENDIX D: THE THREE-LAYER THEORETICAL SOLUTION FOR SUSPENDED AND SUBMERGED CANOPY BASED ON MOMENTUM AND CONTINUITY EQUATIONS…………………………………………………………………………………………………… 162
Appendix D.1. Governing equations ………………………………………………………………………………. 162
Appendix D.2. Linear solution ……………………………………………………………………………………….. 164
Appendix D.3. First-order approximation for the linear solution ………………………………………… 167
APPENDIX E: NORMAL MODE SOLUTIONS FOR BLADE DISPLACEMENTS IN RANDOM WAVES ………………………………………………………………………………………………………….. 171
BIOGRAPHY OF THE AUTHOR …………………………………………………………………………………………….. 173

Additional information

Author

Longhuan Zhu

No of Chapters

6

No of Pages

191

Reference

YES

Format

PDF

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