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Decrop numerical and experimental modelling of near field overflow dredging plumes

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Boudewijn Decrop van IMDC stelde zijn doktoraatswerk aan UGent en KUL voor rond het modelleren van baggerpluimen, zowel in detail als bronterm voor grotere modellen.

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Decrop numerical and experimental modelling of near field overflow dredging plumes

  1. 1. Numerical and Experimental Modelling of Near-Field Overflow Dredging Plumes Boudewijn Decrop Belgian Hydraulics Day Flanders Hydraulic Research 5/10/2015
  2. 2. 7-Oct-15 / Belgian Hydraulics Day/ slide 2 Introduction Numerical and Experimental Modelling of Near-Field Overflow Dredging Plumes
  3. 3. 7-Oct-15 / Belgian Hydraulics Day/ slide 3 TSHD Research Hypothesis Introduction
  4. 4. 7-Oct-15 / Belgian Hydraulics Day/ slide 4 Introduction General objective: To develop a 3D near-field plume model of which the output is used as sediment source for far-field plume models, which renders far-field plume predictions more accurate. This leads to improved forecasting of the plume behaviour and therefore to a reduced environmental impact WHY?
  5. 5. 7-Oct-15 / Belgian Hydraulics Day/ slide 5 Introduction  Plume prediction modelling: far-field + near-field models Large-scale far field models at IMDC (unstructured) Persian Gulf Gulf of Oman Gulf of Aden Red Sea Indian Ocean iCSM Tethys model
  6. 6. 7-Oct-15 / Belgian Hydraulics Day/ slide 6 Introduction Plume predictions Environmental management Sea current (from model)
  7. 7. 7-Oct-15 / Belgian Hydraulics Day/ slide 7 Introduction Plume predictions Environmental management Sea current (from model)
  8. 8. 7-Oct-15 / Belgian Hydraulics Day/ slide 8 Introduction Plume predictions Environmental management Sea current (from model)
  9. 9. 7-Oct-15 / Belgian Hydraulics Day/ slide 9 Introduction Plume predictions Environmental management Sea current (from model)
  10. 10. 7-Oct-15 / Belgian Hydraulics Day/ slide 10 Introduction Plume predictions Environmental management Sea current (from model) MAIN RESEARCH QUESTION: How much sediment to put in the far-field model and how is it distributed??
  11. 11. 7-Oct-15 / Belgian Hydraulics Day/ slide 11 Introduction Plume predictions Environmental management Sea current (from model) TODAY: * Assumptions with weak justification * ‘Best guess’ sediment distribution
  12. 12. 7-Oct-15 / Belgian Hydraulics Day/ slide 12 Introduction Plume predictions Environmental management Sea current (from model) SOLUTION: Develop a new near-field model to simulate detailed flow near ship!
  13. 13. 7-Oct-15 / Belgian Hydraulics Day/ slide 13 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  14. 14. 7-Oct-15 / Belgian Hydraulics Day/ slide 14 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENTLab EXPERIMENTS
  15. 15. 7-Oct-15 / Belgian Hydraulics Day/ slide 15 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Lab-scale MODEL
  16. 16. 7-Oct-15 / Belgian Hydraulics Day/ slide 16 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Model matches Experiment ?
  17. 17. 7-Oct-15 / Belgian Hydraulics Day/ slide 17 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Next step: validate upscaling to real-life scale
  18. 18. 7-Oct-15 / Belgian Hydraulics Day/ slide 18 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Real-scale MODEL
  19. 19. 7-Oct-15 / Belgian Hydraulics Day/ slide 19 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Real-scale MEASUREMENT
  20. 20. 7-Oct-15 / Belgian Hydraulics Day/ slide 20 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Model matches Field Measurements ?
  21. 21. 7-Oct-15 / Belgian Hydraulics Day/ slide 21 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Applications: *Simplified Model *Influence factors * Ship Design
  22. 22. 7-Oct-15 / Belgian Hydraulics Day/ slide 22 Experiments Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  23. 23. 7-Oct-15 / Belgian Hydraulics Day/ slide 23 Results Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  24. 24. 7-Oct-15 / Belgian Hydraulics Day/ slide 24 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  25. 25. 7-Oct-15 / Belgian Hydraulics Day/ slide 25 Lab-scale Model • Navier-Stokes eq’s for the mixture • Large-Eddy Simulation (LES) • Dynamic Smagorinsky SGS model • Inflow: • water+sediment in pipe • flume crossflow • Solution • ∆t = 0.02 s • CFL = max. 1 • Variables: • pressure • velocity components • sediment fraction • sub-grid scale variables Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Water + sediment mixture (pipe) Background water flow (crossflow)
  26. 26. 7-Oct-15 / Belgian Hydraulics Day/ slide 26 Results • Mesh, initial: Schematised hull Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  27. 27. 7-Oct-15 / Belgian Hydraulics Day/ slide 27 Results • Mesh adaptation • Based on |S| and C (from RANS run) • Optimised number of cells (~106) Based on C Based on strain rate |S| Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  28. 28. 7-Oct-15 / Belgian Hydraulics Day/ slide 28 Results • Impression of the sediment plume Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  29. 29. 7-Oct-15 / Belgian Hydraulics Day/ slide 29 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Model matches Experiment ?
  30. 30. 7-Oct-15 / Belgian Hydraulics Day/ slide 30 Results • Qualitatively: Visually : Lab vs CFD Stable stratification Unstable stratification Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  31. 31. 7-Oct-15 / Belgian Hydraulics Day/ slide 31 Results Quantitatively: 1. Trajectory : Laboratory vs CFD • Centerline • Upper/lower edge • Plume entrainment due to vessel hull Decrop, B. et al. (2015). Large-Eddy Simulations of turbidity plumes in crossflow. European Journal of Mechanics - B/Fluids (53), p68-84, Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  32. 32. 7-Oct-15 / Belgian Hydraulics Day/ slide 32 Results Quantitatively: 2. SSC & Turbulence • RMS ui’ • RMS c’ Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  33. 33. 7-Oct-15 / Belgian Hydraulics Day/ slide 33 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Model matches Experiment ? YES!
  34. 34. 7-Oct-15 / Belgian Hydraulics Day/ slide 34 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  35. 35. 7-Oct-15 / Belgian Hydraulics Day/ slide 35 Real-scale model • Full-size TSHD • Propellers included (actuator disk) • Dynamic air bubble transport model: • Lagrangian, • Forces: drag, virtual mass, grad(p), g • Coalescence Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  36. 36. 7-Oct-15 / Belgian Hydraulics Day/ slide 36 Real-scale model • Mesh details Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  37. 37. 7-Oct-15 / Belgian Hydraulics Day/ slide 37 Real-scale model ! Validation needed  Monitoring campaigns Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Deep water, light mixture Shallow water Air bubble concentration Deep water, heavy mixture
  38. 38. 7-Oct-15 / Belgian Hydraulics Day/ slide 38 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  39. 39. 7-Oct-15 / Belgian Hydraulics Day/ slide 39 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Model matches Field Measurements ?
  40. 40. 7-Oct-15 / Belgian Hydraulics Day/ slide 40 Results Validation CFD Validation Case 1: • H=16m ; D=2m; W0=1.9 m/s; U∞=1.5 m/s, C0=55 g/l • CPU time: 25 hours at 32 CPU’s
  41. 41. 7-Oct-15 / Belgian Hydraulics Day/ slide 41 Results Validation CFD Validation Case1: Vertical profiles • Measurement carried out at < 200 m for near-field validation • Compared with time-averaged model results Measured CFD Model
  42. 42. 7-Oct-15 / Belgian Hydraulics Day/ slide 42 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Model matches Field Measurements ? YES!
  43. 43. 7-Oct-15 / Belgian Hydraulics Day/ slide 43 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Applications: *Simplified Model *Influence factors * Ship Design
  44. 44. 7-Oct-15 / Belgian Hydraulics Day/ slide 44 Overview Model development Applications: *Simplified Model *Influence factors * Ship Design
  45. 45. 7-Oct-15 / Belgian Hydraulics Day/ slide 45 Application to turbidity forecasting • Fast parameter model (< 1 sec.) • Programmed inside far-field modelling software  real-time evolution of overflow flux • Source terms: function of • Current velocity and direction • Sailing speed • Sediment Concentration, % fines • Overflow diameter and position Far field model Near-field Parameter model Current Source terms Parameters from CFD data fits Applications: *Simplified Model *Influence factors * Ship Design
  46. 46. 7-Oct-15 / Belgian Hydraulics Day/ slide 46 General Conclusions • 3D, multiphase CFD model • Validated in the laboratory + the field • Applied for: • Parameterisation • Overflow design • Influence factors
  47. 47. THE END
  48. 48. 7-Oct-15 / Belgian Hydraulics Day/ slide 48 Setup: Test case ‘Vertical plume’ • Geometry: • Vertical plume as a first test case for the CFD model • Mesh: • Unstructured tet mesh • ‘Inflation layers’ near walls (pipe) • Mesh ‘Adaptation’: 1. RANS simulation on relatively coarse mesh 2. Refinement where gradients / SSC significant 3. RANS on refined mesh 4. LES w u z r
  49. 49. 7-Oct-15 / Belgian Hydraulics Day/ slide 49 Setup: Test case ‘Vertical plume’ • Results • Self-similarity for z/D > 8 • Comparison with experiments • Good accuracy time-averaged W(r) and C(r) Decrop, B. et al. (2015). New methods for ADV measurements of turbulent sediment fluxes – Application to a fine sediment plume. Journal of Hydraulic Research 53 (3), p 317-331,
  50. 50. 7-Oct-15 / Belgian Hydraulics Day/ slide 50 Setup: Test case ‘Vertical plume’ • Results • Reynolds stresses accurate: peak value, peak location • Turbulent fluctuations C: radial profile correct Decrop, B. et al. (2015). New methods for ADV measurements of turbulent sediment fluxes – Application to a fine sediment plume. Journal of Hydraulic Research 53 (3), p 317-331,
  51. 51. 7-Oct-15 / Belgian Hydraulics Day/ slide 51 Experiments Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Goal of the experiments: • Insights in sediment plume behaviour • Produce data set to compare with model results • Preliminary estimate of influence factors: • Air bubbles • Ship hull
  52. 52. 7-Oct-15 / Belgian Hydraulics Day/ slide 52 • 34 different plumes at scale 1/50 • Flume: length = 15m, width = 0.8 m, depth = 0.6 m • W0 = 4 – 30 cm/s; C0 = 5 – 50 g/l; D = 3.4 – 6.5 cm • Sediment: kaolin, d50=4 μm • Dynamically scaled: • Densimetric Froude number FΔ • velocity ratio λ Experiments Upstream reservoir Downstream reservoir ASM 2 ASM 1 ADV’s Valve Honeycomb Ship ‘hull’ x z y U0 ρ∞ Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  53. 53. 7-Oct-15 / Belgian Hydraulics Day/ slide 53 Results 1. Plume trajectory Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT 2. Profiles of: • Sed. concentration • Velocity components • Turbulent properties 3. Influence factors Air bubbles Ship hull
  54. 54. 7-Oct-15 / Belgian Hydraulics Day/ slide 54 Lab-scale Model • Navier-Stokes eq’s for the mixture • Models: • Multiphase: mixture model (with drift flux term, slip velocity, drag) • Turbulence: Large-Eddy Simulation (LES) • SGS model: Dynamic Smagorinsky  each (x,y,z,t): t, Dt and Sct • Phases mixture model: • Liquid phase: fresh water • Sediment: spherical, d=4 µm • Stokes number << 1 • Volume concentration 0.2 to 4% • Inflow boundary: spectral synthesizer (vortex mimicking) • Water surface: rigid lid Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  55. 55. 7-Oct-15 / Belgian Hydraulics Day/ slide 55 Setup : Plume in crossflow • Mesh, initial: Schematised hull
  56. 56. 7-Oct-15 / Belgian Hydraulics Day/ slide 56 Setup : Plume in crossflow • Mesh, refined • Optimised number of cells (~106) Based on C (from RANS run) Based on strain rate
  57. 57. 7-Oct-15 / Belgian Hydraulics Day/ slide 57 Results • Qualitatively : well-known turbulent structures are present: 2. Counter-rotating vortex pair + double C-peak PIV/PLIF measurements, Diez et al. (2005) CFD
  58. 58. 7-Oct-15 / Belgian Hydraulics Day/ slide 58 Validation case : Bubble plume in crossflow • Case of Zhang et al. (2013) • Upward bubbly jet (20 vol.% air) • Tracer in jet fluid • Centerline tracer plume • Centerline bubble plume • LES model with three phases: • Water • Sediment (tracer) • Air bubbles: • Initial diameter: 1.7 mm • Collision model Coalescence  bubble size distribution • Influence bubbles on sediment plume: ok • Separation bubble plume: ok Sediment plume Separating bubble plume
  59. 59. 7-Oct-15 / Belgian Hydraulics Day/ slide 59 Results Quantitatively: 3. Turbulent Kinetic Energy k Decrop, B. et al. (2015). Large-Eddy Simulations of turbidity plumes in crossflow. European Journal of Mechanics - B/Fluids (53), p68-84, Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  60. 60. 7-Oct-15 / Belgian Hydraulics Day/ slide 60 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Next step: validate upscaling to real-life size
  61. 61. 7-Oct-15 / Belgian Hydraulics Day/ slide 61 Upscaling to realistic scale: CFD model with lab geometry
  62. 62. 7-Oct-15 / Belgian Hydraulics Day/ slide 62 Upscaling LES model to prototype scale 1. Take CFD model lab scale 2. Scale grid to large scale (similarity laws buoyant jets) 3. CFD simulation 4. Validation, based on: • Trajectories in similarity coordinates must coincide with lab scale • TKE resolved > 80%, for LES completeness (Pope, 2004) CFD (large scale, Re=1.9 106) Physical model (small scale, Re=1.2 104)
  63. 63. 7-Oct-15 / Belgian Hydraulics Day/ slide 63 Results Validation CFD • Density current + Surface plume (air bubbles, propellers) • 5% of sediments released to ‘far-field’ plume • Hypothesis confirmed? near-bed density current surface plume
  64. 64. 7-Oct-15 / Belgian Hydraulics Day/ slide 64 Measurements Determination of sediment concentration: • Sampling inside the overflow (to impose in model runs) • Measurements and samples in the dredging plume Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  65. 65. 7-Oct-15 / Belgian Hydraulics Day/ slide 65 Measurements SiltProfiler: • High-res. vertical profiler (free-fall,100 Hz) • Wireless connection when above water (BlueTooth) • CTD • 3-step turbidity sensor (0 – 50,000 mg/l) • Design avoids seabed disturbance Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT
  66. 66. 7-Oct-15 / Belgian Hydraulics Day/ slide 66 Measurements SiltProfiler results Consistent profile type: 1. Diluted surface plume: 10-200 mg/l 2. Near-bed layer, 2-6m thick: 200-1500 mg/l
  67. 67. 7-Oct-15 / Belgian Hydraulics Day/ slide 67 Measurements Transect sailing (near-field, 100-500m from stern) Across the plume Along the plume
  68. 68. 7-Oct-15 / Belgian Hydraulics Day/ slide 68 Results Validation CFD (Site 2) • Validation Case 2: • Data from earlier campaign • H=39m ; D=1.1m ; W0=3.2 m/s; U∞=1.5 m/s, C0=10 g/l  In some cases: 100% of sediment released to far-field plume log(C/C0) CFD model : ADCP: Bottom of plume
  69. 69. 7-Oct-15 / Belgian Hydraulics Day/ slide 69 Validation prototype scale CFD (Case 2) Case 2: Surface plume (OBS measurements) • In situ measurements: lumped, crossing the plume • Model output: at centreline  Cmax,insitu should be = Ccentreline,model
  70. 70. 7-Oct-15 / Belgian Hydraulics Day/ slide 70 Results Validation CFD (Site nr 2) Validation Case 2: • H=39m ; D=1.1m ; Overflow near stern  In contradiction to hypothesis: 100% of sediment released to far-field plume log(C/C0) CFD model : Measured bottom of plume
  71. 71. 7-Oct-15 / Belgian Hydraulics Day/ slide 71 Environmental valve efficiency • 2x 26 cases, with/without valve • Valve efficiency = function of surface plume sediment flux with/without valve
  72. 72. 7-Oct-15 / Belgian Hydraulics Day/ slide 72 Environmental valve efficiency • Valve efficiency turns out to be related to a combination of length scales and a Froude number
  73. 73. 7-Oct-15 / Belgian Hydraulics Day/ slide 73 Environmental valve efficiency • Decomposition in constructional and operational efficiency • Operation has more impact on efficiency than construction influence diameter and overflow position influence sailing speed and sediment concentration
  74. 74. 7-Oct-15 / Belgian Hydraulics Day/ slide 74 Influence on surface turbidity • Number of overflows
  75. 75. 7-Oct-15 / Belgian Hydraulics Day/ slide 75 Influence on surface turbidity • Sediment load  sediment fraction in surface plume much larger for low C0 C0=10 g/l C0=150 g/l log(C/C0) log(C/C0) Applications: *Simplified Model * Ship Design
  76. 76. 7-Oct-15 / Belgian Hydraulics Day/ slide 76 Parameter model • Motivation: CFD model has high CPU cost, not practical in some cases Find a simple model that is: 1. Much faster 2. Almost as accurate A model with output:  In suitable form for far-field models input  Vertical profile of sediment flux behind ship • Parameter model = combination of • Analytical plume solutions • Parameter fits on data of +/- 100 CFD model runs Applications: *Simplified Model *Influence factors * Ship Design
  77. 77. 7-Oct-15 / Belgian Hydraulics Day/ slide 77 Parameter model • O(100) CFD runs, with variation of: • Current velocity • Sailing speed • Sediment concentration • Overflow diameter, position • Air bubble concentration  For ‘Model Training’ • Model Validation: against extra dataset CFD results • 90% has R²>0.5 • Valid for standard cases, for specific cases still CFD needed CFD Par. Mod. Applications: *Simplified Model *Influence factors * Ship Design
  78. 78. 7-Oct-15 / Belgian Hydraulics Day/ slide 78 Overview Model development Applications: *Simplified Model *Influence factors * Ship Design
  79. 79. 7-Oct-15 / Belgian Hydraulics Day/ slide 79 Influence of air bubbles • Environmental valve: air bubbles -90% (Saremi, 2014) • Perform simulations with/without air flow rate reduction Surface plume No surface plume log(C/C0) Applications: *Simplified Model *Influence factors * Ship Design
  80. 80. 7-Oct-15 / Belgian Hydraulics Day/ slide 80 Influence of velocity Relative velocity sea water - ship  sediment in surface plume x 10 2 knots 6 knots log(C/C0) Applications: *Simplified Model *Influence factors * Ship Design
  81. 81. 7-Oct-15 / Belgian Hydraulics Day/ slide 81 Overview Model development Applications: *Simplified Model *Influence factors * Ship Design
  82. 82. 7-Oct-15 / Belgian Hydraulics Day/ slide 82 Overflow position • Overflow at stern: plume mixed by propellers • Overflow at aft: plume has more time to descend Ship Applications: *Simplified Model *Influence factors * Ship Design log(C/C0)
  83. 83. 7-Oct-15 / Belgian Hydraulics Day/ slide 83 Overflow shaft extension • Studied earlier by de Wit et al. (2015) • C at surface reduced with factor up to 10 • Still surface plume because of rising air bubbles dair Ship extension Applications: *Simplified Model *Influence factors * Ship Design log(C/C0)
  84. 84. 7-Oct-15 / Belgian Hydraulics Day/ slide 84 Rectangular overflow shaft  Potentially 50% reduction of sediment concentration Applications: *Simplified Model *Influence factors * Ship Design Aspect ratio 1:3
  85. 85. 7-Oct-15 / Belgian Hydraulics Day/ slide 85 Overview Model development Lab EXPERIMENTS Lab-scale MODEL Real-scale MODEL Real-scale MEASUREMENT Applications: *Simplified Model *Influence factors * Ship Design
  86. 86. 7-Oct-15 / Belgian Hydraulics Day/ slide 86 Future research and applications Overflow design (CFD model) • Detailed study efficiency of: • Shaft extension • Rectangular overflow • Influence of: • Lateral position overflow • Number of overflows • Inclined overflow exit? • Overflow via draghead jetting Parameter model • Real-time plume forecasting • Tender-phase dredging strategy

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