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Numerical study of wave and submerged breakwater interaction

Numerical study of wave and submerged breakwater interaction

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Numerical study of wave and submerged breakwater interaction

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  1. Numerical study of wave and submerged breakwater interaction (Data-driven and Physical-based Model for characterization of Hydrology, Hydraulics, Oceanography and Climate Change) IMS-NUS PHUNG Dang Hieu Vietnam Institute of Meteorology, Hydrology and Environment Email: phungdanghieu@vkttv.edu.vn

  2. Waves on coasts are beautiful

  3. They are violent too! Fig. 2: Heugh Breakwater, Hartlepool, UK (photo: George Motyka, HR Wallingford) Fig.1: Overtopping of seawall onto main railway - Saltcoats,Scotland (photo: Alan Brampton)

  4. To reduce wave energy Land Breakwater • Submerged • Seawall breaking Seawall supported by porous parts

  5. Example of Seawall atMabori, Yokosuka, Japan

  6. Structure design diagram Physical Experiments Design Wave Conditions Numerical Simulations Wave Reflection, Transmission Wave Run-up, Rundown, Overtopping Velocity field, Turbulence Wave pressures & Forces upon structures Information For Breakwater & Seawall designs

  7. Some problems of Experiments related to Waves • Physical experiment of Small scale: • Scale effects • Undesired Re-reflected waves • Lager Scale experiment - Costly • Numerical Experiment • Cheap • Avoid scale effects and Re-reflected waves Difficulties: Integrated problems related to the advanced knowledge on Fluid Dynamics, Numerical Methods and Programming Techniques.

  8. What do we want to do? • Develop a Numerical Wave Channel • Navier-Stokes Eq. • Simulation of wave breaking • Simulation of wave and structure interaction • Do Numerical experiments: • Deformation of water surface • Transformation of water waves; wave-porous structure interaction

  9. Concept of numerical wave channel Non-reflective wave maker boundary Open boundary Free surface boundary air Solid boundary water Wave absorber Porous structure

  10. Governing Equations • Continuity Eq. • 2D Modified Navier-Stokes Eqs. (Sakakiyama & Kajima, 1992) extended to porous media (1) (2) (3)

  11. where: (4) CD : the drag coefficient CM: the inertia coefficient gn:: the porosity x ,z: areal porosities in the x and z projections e: kinematic eddy viscosity =n+nt (5)

  12. Turbulence model • Smangorinski’s turbulent eddy viscosity for the contribution of sub-grid scale: (6)

  13. Free-surface modeling • Method of VOF (Volume of fluid) (Hirt & Nichols, 1981) is used: (4) Volume of water F = ; Cell Volume F = 1 means the cell is full of water F = 0 means the cell is air cell 0< F <1 means the cell contains the free surface qF : the source of F due to wave generation source method

  14. Free surface approximation Simple Line Interface Construction- SLIC approximation .1 .6 .5 .6 .4 0 1 1 1 1 .4 0 Hirt&Nichols (1981) .7 1 1 1 1 .2 .9 1 1 1 1 1 Natural free surface 1 1 1 1 1 1 air water .6 .5 .6 .4 .1 0 .4 1 1 1 1 0 present study .7 .2 1 1 1 1 .9 1 1 1 1 1 1 1 1 1 1 1 Piecewise Linear Interface Construction- PLIC approximation

  15. Interface reconstruction P1 P2 O

  16. Numerical flux approximation SLIC-VOF approximation (Hirt&Nichols, 1981) PLIC-VOF approximation (Present study)

  17. Non-reflective wave maker (none reflective wave boundary) Wave generating source Vertical wall Free surface elevation Damping zone Progressive wave area Standing wave area

  18. MODEL TEST • Deformation of water surface due to Gravity • TEST1: Dam-break problem (Martin & Moyce’s Expt., 1952) • TEST2: Unsteady Flow • TEST3: Flow separation • TEST4: Flying water (Koshizuka et al., 1995) • Standing waves • Non-reflective boundary • Wave overtopping of a vertical wall

  19. (Martin & Moyce , 1952) TEST1: Dam-break time=0.085s L time=0s 2L time=0.21s time=0.125s

  20. Time history of leading edge of the water

  21. TEST2 Initial water column

  22. TEST3 Initial water column

  23. TEST4 (Koshizuka et al’s Experiment (1995) Initial water column Solid obstacle

  24. TEST4 time=0.04s obstacle time=0.05s (Koshizuka et al., 1995) Simulated Results

  25. MODEL TEST WITH WAVES • Standing waves • Wave overtopping • Wave breaking

  26. Regular waves in front of a vertical wall Vertical wall

  27. wave overtopping of a vertical wall 11 x 17cm =187cm G2 G1 G12 Wave conditions: Hi= 8.8 & 10.3cm T = 1.6s Wave overtopping 17cm hc=8cm air SWL water h= 42.5cm Experimental conditions

  28. Time profile of water surface at the wave gauge G1 Effects of re-reflected waves

  29. Time profile of water surface at the wave gauge G5 Effects of re-reflected waves

  30. Wave height distribution Vertical wall L: the incident wave length

  31. Overtopping water Effects of re-reflected waves Wave condition: Hi=8.8cm, T=1.6s

  32. Wave breaking Breaking point (x=6.4m from the original point) Run-up Area Surf zone SWL Sloping bottom s=1/35 x=7.275m Experimental conditions by Ting & Kirby (1994) (Hi=12.5cm, T=2s)

  33. Comparison of wave height distribution Breaking point Wave crest curves 2004) Wave trough curves

  34. Velocity comparisons at x=7.275m At z =-4cm At z =-8cm Horizontal velocity Vertical velocity

  35. Interaction of Wave and Porous submerged break water • What is the influence of inertia and drag coefficients on • wave height distributions ? Wave absorber 38 capacitance wave gauges • What is the influence of the porosity of the breakwater on the wave reflection and transmission? G31 G34 G38 H=9.2cm T=1.6s G1 G12 G17 3. What is the effective height of the submerged breakwater? air SWL 29cm Porous break water h=37.6cm water 33cm Objective: to answer the above questions partly by numerical simulations 115cm x x=0

  36. Influence of inertia coefficient on the wave height distribution Breaking point Cd=3.5 1.0<Cm<1.5

  37. Influence of drag coefficient on the wave height distribution Breaking point Cm=1.2 The best combination: Cd=1.5, Cm=1.2

  38. water surface elevations at the off-shore side of the breakwater

  39. Water surface elevations at the rear side of the breakwater

  40. Variation of Reflection, Transmission and Dissipation Coefficients versus different Porosities Porosity of Structure

  41. Optimal Depth d Consideration: - top width of the breakwater is fixed, - slope of the breakwater is fixed - change the depth on the top of the breakwater Find: Variation of Reflection, Transmission Coefficients

  42. Results

  43. REMARKS • There are many practical problems related with computational fluid dynamics need to be simulated in which wave-structure interaction, shore erosion, tsunami force and run-up, casting process are few examples. • A Numerical Wave Channel could be very useful for initial experiments of practical problems before any serious consideration in a costly physical experiment later on (water wave-related problem only). • Investigations on effects of wind on wave overtopping processes could be a challenging topic for the present research. THANK YOU

  44. Calculation of Wave Energy and Coefficients