Computational Fluid Dynamic Study of Heaving-to David Allen Hickerson Thesis submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science In Ocean Engineering Leigh McCue-Weil Wayne Neu Chris Roy 24 July 2013 Blacksburg, Virginia Keywords: heaving-to, hove-to, storm tactics, ocean waves Computational Fluid Dynamic Study of Heaving-to David Hickerson ABSTRACT This study looks at the fluid interactions from the wake of a sail boat performing the heaving-to storm tactic in heavy weather seas with the waves. This interaction causes the wave height in the wake to be reduced. The fluid flow in the top layer of the wave is seen to move with the wake as the hull drifts with the wind. This movement of the top layer of the wave provides a vertical momentum cancelation affect with the portion of the wave that it moves over reducing the wave height. STAR-CCM+ CFD software is used to perform the simulations of the steep waves with wavelength of 25 meters, 55 meters, and 67 meters. In the simulation, a propulsive force is used to simulate the wind force on the boat. Acknowledgements I would like to express my gratitude to my graduate advisor, Dr. Leigh McCue-Weil, and my graduate committee, Dr. Wayne Neu and Dr. Chris Roy, who allowed me to explore this area of study in which I had a personal interest as a sailor. Their guidance and patience is most appreciated. To my wife, Katricia, thank you for the help reviewing this thesis and for all of your support during my education. You have been there each step of the way, not just once but twice. She has done so much to encourage me and to make my life better. I love you. Thanks also goes out to Lin and Larry Pardey who wrote the book on heaving-to that started me on this journey. They also allowed me to use some of the tables in their book within this thesis and I thank them for that. I want to thank Grant Headifen at NauticEd, who allowed me to use a picture from their website on the heaving-to procedure. Pictures are so important in communicating ideas, and this diagram made explaining this concept easier. iii Table of Contents Acknowledgements ............................................................................................................ iii Table of Contents ............................................................................................................... iv Figures................................................................................................................................ vi Tables .................................................................................................................................. x Terminology and Nomenclature ........................................................................................ xi 1. Introduction ................................................................................................................. 1 1.1 Motivation and Background ................................................................................. 1 1.1.1 1979 Fastnet Race ......................................................................................... 1 1.1.2 Previous Scientific Studies ........................................................................... 1 2. Purpose ........................................................................................................................ 2 3. Simulation Background .............................................................................................. 3 3.1 Heaving-to Procedure ........................................................................................... 3 3.2 Ocean Waves ........................................................................................................ 6 3.2.1 Ocean Wavelengths ...................................................................................... 9 3.2.2 Wave Heights .............................................................................................. 10 3.2.3 Wave Flow Behavior .................................................................................. 11 3.3 Waves and CFD ................................................................................................. 11 3.4 Physics ................................................................................................................ 11 3.4.1 Assumptions ................................................................................................ 11 3.4.2 Equations..................................................................................................... 12 4. Simulation ................................................................................................................. 17 4.1 Ideal Model ........................................................................................................ 17 4.2 Simulation Constraints ....................................................................................... 17 4.2.1 Hardware ..................................................................................................... 17 4.2.2 Software ...................................................................................................... 18 4.3 Simplified Model................................................................................................ 18 4.4 Mesh ................................................................................................................... 19 4.4.1 Cell Size Selection ...................................................................................... 19 4.4.2 Grid Size ..................................................................................................... 23 4.4.3 Meshes ........................................................................................................ 29 4.4.4 Hull Form .................................................................................................... 31 4.5 Time Step Refinement ........................................................................................ 33 4.6 Solvers ................................................................................................................ 36 4.7 Boundary Conditions.......................................................................................... 37 4.8 Initial Conditions ................................................................................................ 38 4.9 Simulation Sets ................................................................................................... 38 4.10 Convergence and Forward Simulation Progression ....................................... 38 5. Results ....................................................................................................................... 39 5.1 Results for Smooth Hull ..................................................................................... 39 5.1.1 Smooth Hull on 25 meters long and 3meters high wave drifting ............... 39 5.1.2 Smooth Hull on 25 meters long and 3 meters high wave moving at ~1 m/s 47 5.2 Results for Keeled Hull ...................................................................................... 62 5.2.1 H=3.0m, h=50m, and λ=25m ...................................................................... 62 5.2.2 H=6.5m, h=50m, and λ=50m ...................................................................... 72 iv 5.2.3 H=8.0m, h=50m, and λ=67m ...................................................................... 82 6. Analysis..................................................................................................................... 90 6.1 Wave Height Reduction ..................................................................................... 90 6.2 Bow Wave Stabilizing Factor ............................................................................ 92 7. Conclusions and Further Study ................................................................................. 94 References ......................................................................................................................... 95 v Figures Figure 1: Sailboat in a storm in a heave-to position (Nauticed.org, 2011). Courtesy of NauticEd. ............................................................................................................................ 4 Figure 2: Wave Notation ..................................................................................................... 9 Figure 3: Particle motion for H=3.56, h=50m and λ=25m. .............................................. 20 Figure 4: Particle velocity for H=3.56, h=50m and λ=25m. ............................................. 21 Figure 5: Particle motion for H=9.26, h=50m and λ=65m. .............................................. 22 Figure 6: Particle velocity for H=9.2, h=50m and λ=65m. ............................................... 23 Figure 7: Mesh refinement study mesh. ............................................................................ 24 Figure 8: Velocity profile at end of 7 time steps. ............................................................. 25 Figure 9: x and z velocity vs. iteration for cell size 0.125 meters. ................................... 26 Figure 10: x and z velocity vs. iteration for cell size 0.09 meters. ................................... 26 Figure 11: x and z velocity vs. iteration for cell size 0.075. ............................................. 27 Figure 12: Combined graph of velocities for meshes with cell size 0.075, 0.090, and 0.125 meters ...................................................................................................................... 27 Figure 13: Velocity differences between base mesh and finer meshes ............................ 28 Figure 14: Velocity along a probe line starting at 0, 0.25, -2 to -10, 0.25, -15 meters for cell sizes 0.075, 0.090, and 0.125 meters after 7 time steps over 350 iterations. ............. 28 Figure 15: Pressure along a probe line starting at 0, 0.25, -2 to -10, 0.25, -15 meters for cell sizes 0.075, 0.090, and 0.125 meters after 7 time steps over 350 iterations. ............. 29 Figure 16: Mesh used in 25 m through 50 m wavelength wave simulations. ................... 30 Figure 17: Close up of overset mesh at the end of a simulation. ...................................... 30 Figure 18: Hull CAD model and overset mesh. ................................................................ 31 Figure 19: Time step refinement using velocity along the line from [0, 0.25, -2] to [-10, 0.25, -15]. .......................................................................................................................... 34 Figure 20: Time step refinement using pressure along the line from [0, 0.25, -2] to [-10, 0.25, -15] ........................................................................................................................... 35 Figure 21: Time step refinement using velocity at the point [0, 0.251, -5]. ..................... 36 Figure 22: Velocity profile close-up on centerline for H=3.0m, h=50m, and λ=25m with smooth hull at time 3.45s. ................................................................................................. 40 Figure 23: Velocity profile on centerline for H=3.0m, h=50m, and λ=25m with smooth hull at time 3.45s. .............................................................................................................. 41 Figure 24: Velocity profile at the wall for H=3.0m, h=50m, and λ=25m with smooth hull at time 3.45s. ..................................................................................................................... 42 Figure 25: View of wave surface deformation for H=3.0m, h=50m, λ=25m with smooth hull at time 3.45s. .............................................................................................................. 43 Figure 26: Wave deformation amount showing about 2.0 meter height on the unaffected area and 1.8 meters on the affected area for H=3.0m, h=50m, and λ=25m with smooth hull at time 2.70s. All heights are in meters from still water level. .................................. 44 Figure 27: Hull cresting wave at time 3.45s for H=3.0m, h=50m, and λ=25m. All heights are in meters from still water level. .................................................................................. 45 Figure 28: X velocity and translation plot for H=3.0m, h=50m, and λ=25m with smooth hull at time 3.45s. .............................................................................................................. 46 Figure 29: Velocity profile for smooth hull on H=3.0 m, h = 50m, and λ = 25m at 2.71s. ........................................................................................................................................... 47 vi Figure 30: Velocity profile for smooth hull on H=3.0 m, h = 50m, and λ = 25m at 3.49s. ........................................................................................................................................... 48 Figure 31: Time 5.63s to 5.75s for a wave: H=3m, h=50m, and λ =25m and a smooth hull. ................................................................................................................................... 49 Figure 32: Time 5.81s to 5.93s for a wave: H=3m, h=50m, and λ =25m and a smooth hull. ................................................................................................................................... 50 Figure 33: Time 5.99s to 6.11s for a wave: H=3m, h=50m, and λ =25m and a smooth hull. ................................................................................................................................... 51 Figure 34: Time 6.17s to 6.29s for a wave: H=3m, h=50m, and λ =25m and a smooth hull. ................................................................................................................................... 52 Figure 35: Time 6.35s to 6.47s for a wave: H=3m, h=50m, and λ =25m and a smooth hull. ................................................................................................................................... 53 Figure 36: Time 6.53s to 6.65s for a wave: H=3m, h=50m, and λ =25m and a smooth hull. ................................................................................................................................... 54 Figure 37: Time 6.71s to 6.83s for a wave: H=3m, h=50m, and λ =25m and a smooth hull. ................................................................................................................................... 55 Figure 38: Hull on crest of wave with reduced wave heights on either side at time 6.89s. ........................................................................................................................................... 56 Figure 39: Time 6.89s for a wave: H=3m, h=50m, and λ =25m and a smooth hull. ........ 57 Figure 40: Velocity profile at the wall for H=3m, h=50m, and λ =25m with a smooth hull at time 6.89s. ..................................................................................................................... 58 Figure 41: Velocity profile on centerline for H=3m, h=50m, and λ =25m with a smooth hull at time 6.89s. .............................................................................................................. 59 Figure 42: Time 3.69s for a wave: H=3m, h=50m, and λ =25m and a smooth hull. ........ 59 Figure 43: Wave deformation amount showing about 1.8 meter height on the unaffected area and 1.4 meters on the affected area for H=3.0m, h=50m, and λ=25m with smooth hull at time 3.69s. All heights are in meters from still water level. .................................. 60 Figure 44: X velocity and translation plot for H=3.0m, h=50m, and λ=25m with smooth hull at time 3.64s showing 5m/s, which is about 0.8 relative to the flow. ........................ 61 Figure 45: Velocity profile on centerline for H=3.0m, h=50m, and λ=25m with keeled hull at time 3.64s. .............................................................................................................. 62 Figure 46: Velocity profile at wall for H=3.0m, h=50m, and λ=25m with keeled hull at time 3.64s. ......................................................................................................................... 63 Figure 47: Velocity profile on centerline of wake and wave flow changes for H=3.0m, h=50m, and λ=25m with keeled hull at time 1.71s. .......................................................... 64 Figure 48: Velocity profile on centerline of wake and wave flow changes for H=3.0m, h=50m, and λ=25m with keeled hull at time 3.10s. .......................................................... 64 Figure 49: Velocity profile on centerline of wake and wave flow changes for H=3.0m, h=50m, and λ=25m with keeled hull at time 3.22s. .......................................................... 65 Figure 50: Velocity profile on centerline of wake and wave flow changes for H=3.0m, h=50m, and λ=25m with keeled hull at time 3.64s. .......................................................... 65 Figure 51: View of wave surface deformation for H=3.0m, h=50m, and λ=25m with keeled hull at time 3.64s. .................................................................................................. 66 Figure 52: Wave deformation amount showing about 1.7 meter height on the unaffected area and 0.8 meters on the affected area for H=3.0m, h=50m, and λ=25m with keeled hull at time 3.64s. All heights are in meters from still water level. ......................................... 67 vii Figure 53: X velocity and translation plot for H=3.0m, h=50m, and λ=25m with keeled hull at time 3.64s. .............................................................................................................. 68 Figure 54: Top view of wave H=3.0m, h=50m, and λ=25m with keeled hull at time 5.64s. All values are in meters from [0, 0]. ................................................................................. 69 Figure 55: Velocity profile on centerline of wake and wave flow changes for H=3.0m, h=50m, and λ=25m with keeled hull at time 3.14s for expanded overset mesh with prism layer and finer mesh volume in the wake of the keel. ...................................................... 70 Figure 56: Absolute total pressure for wave H=3.0m, h=50m, and λ=25m with keeled hull at time 2.96s. .............................................................................................................. 71 Figure 57: Velocity profile on centerline for H=6.5m, h=50m, and λ=55m with keeled hull at time 4.49s. .............................................................................................................. 72 Figure 58: Velocity profile at wall for H=6.5m, h=50m, and λ=55m with keeled hull at time 4.49s. ......................................................................................................................... 73 Figure 59: Velocity profile on centerline for H=6.5m, h=50m, and λ=55m with keeled hull at time 6.02s. .............................................................................................................. 74 Figure 60: Velocity profile at wall for H=6.5m, h=50m, and λ=55m with keeled hull at time 6.02s. ......................................................................................................................... 75 Figure 61: Velocity profile on centerline of wake and wave flow changes for H=6.5m, h=50m, and λ=55m with keeled hull at time 4.86s. .......................................................... 75 Figure 62: Velocity profile on centerline of wake and wave flow changes for H=6.5m, h=50m, and λ=55m with keeled hull at time 5.25s. .......................................................... 76 Figure 63: Velocity profile on centerline of wake and wave flow changes for H=6.5m, h=50m, and λ=55m with keeled hull at time 6.02s. .......................................................... 76 Figure 64: Velocity profile on centerline of wake and wave flow changes for H=6.5m, h=50m, and λ=55m with keeled hull at time 6.75s. .......................................................... 77 Figure 65: View of wave surface deformation for H=6.5m, h=50m, λ =55m with keeled hull at time 6.02s. .............................................................................................................. 78 Figure 66: Wave deformation amount showing about 4.3 meter height on the unaffected area and 2.8 meters on the affected area for H=6.5m, h=50m, and λ=55m with keeled hull at time 6.02s. All heights are in meters from still water level. ......................................... 79 Figure 67: X velocity and translation plot for H=6.5m, h=50m, λ =55m with keeled hull at time 6.02s. ..................................................................................................................... 80 Figure 68: Top view of wave H=6.5m, h=50m, and λ=55m with keeled hull at time 6.02s. All values are in meters from [0,0]. .................................................................................. 81 Figure 69: Velocity profile on centerline for H=8.0m, h=50m, and λ=67m with keeled hull. ................................................................................................................................... 82 Figure 70: Velocity profile at wall for H=8.0m, h=50m, and λ=67m with keeled hull. ... 83 Figure 71: Velocity profile on centerline of wake and wave flow changes for H=8.0m, h=50m, and λ=67m with keeled hull at time 5.33s. .......................................................... 83 Figure 72: Velocity profile on centerline of wake and wave flow changes for H=8.0m, h=50m, and λ=67m with keeled hull at time: 5.69s. ......................................................... 84 Figure 73: Velocity profile on centerline of wake and wave flow changes for H=8.0m, h=50m, and λ=67m with keeled hull at time 6.12s. .......................................................... 84 Figure 74: Velocity profile on centerline of wake and wave flow changes for H=8.0m, h=50m, and λ=67m with keeled hull at time 6.19s. .......................................................... 85 viii Figure 75: Wave deformation amount showing about 5.3 meter height on the unaffected area and 3.8 meters on the affected area for H=8.0m, h=50m, and λ=67m with keeled hull at time 6.19s. All heights are in meters from still water level. ......................................... 86 Figure 76: X velocity and translation plot for H=8.0m, h=50m, and λ=67m with keeled hull at time 6.19s. .............................................................................................................. 87 Figure 77: Top view of wave H=8.0m, h=50m, and λ=67m with keeled hull at time 5.95s. All values are in meters from [0,0]. .................................................................................. 88 Figure 78: Top view of wave H=8.0m, h=50m, and λ=67m with keeled hull at time 6.19s. All values are in meters from [0,0]. .................................................................................. 89 Figure 79: Wake moving wave water layer. ..................................................................... 90 Figure 80: Simulation showing wake moving wave water layer. ..................................... 90 Figure 81: Forces capsizing a sailboat by Strohmeier (Originally printed in Marine Technology, Vol. 22 , No. 4, Oct 1985, pp. 373-381. Reprinted with the permission of the Society of Naval Architects and Marine Engineers (SNAME). Material originally appearing in SNAME publications cannot be reprinted without written permission from the Society, 601 Pavonia Ave., Jersey City, NJ 07306) ................................................... 92 Figure 82: Stabilization from the bow wave. .................................................................... 92 ix Tables Table 1: Drift rates of sail boats (Pardey, 2008) (Courtesy of Lin and Larry Pardey, from Storm Tactics Handbook 3rd ed. Modern Methods of Heaving-to for Survival in Extreme Conditions p. 116). .............................................................................................................. 5 Table 2: Sea Conditions 1 from Handling Storms at Sea, The 5 Secrets of Heavy Weather Sailing. ................................................................................................................................ 7 Table 3: Sea Conditions 2 from Handling Storms at Sea, The 5 Secrets of Heavy Weather Sailing. ................................................................................................................................ 8 Table 4: Wave characteristics collected from National Data Buoy Center on 3 June 2013. ........................................................................................................................................... 10 Table 5: Wave characteristics collected from National Data Buoy Center for Tropical Storm Andrea. ................................................................................................................... 10 Table 6: Dimensions of flume, water surface, and overset meshes. ................................. 29 Table 7: Simulation sets. ................................................................................................... 38 Table 8: Simulation with wave height reduction values ................................................... 91 x