Three-Dimensional Numerical Modeling of Wave-Induced Scour Around Caisson Breakwater Suspended on Piles

Abstract

Scouring around vertical piles in ocean environments, especially under wave action, can significantly affect the stability of structures. Therefore, accurately predicting scour depth is essential for proper pile design. While empirical methods are commonly used, they often lack the accuracy required to model such complex processes, whereas data mining techniques provide more reliable predictions. This study evaluates the predictive performance of a morphological model for caisson breakwaters supported by piles under clear-water conditions, using the Flow-3D HYDRO mathematical modeling tool, addressing a gap in its application. In this study, a series of three-dimensional numerical models were developed to investigate the mechanisms of local scour around semi-immersed caisson breakwaters supported by piles. The investigation focused on key parameters such as the spacing between the piles and the gradual increase in the draft of the caisson barrier, subjected to different wave actions. The Reynolds-averaged Navier-Stokes (RANS) equations, along with the renormalization group (RNG) turbulence model and the Van Rijn sediment transport model, were used to simulate the morphological changes around the caisson breakwater. A numerical contour map was generated to assess the scour topography and sediment deposition beneath the breakwater and around the piles. A three-dimensional numerical model is developed to investigate modifying the caisson’s cross section for different two scenarios on controlling the scour progress around a semi-immersed caisson suspended on piles under wave action. The simulation results were compared to previous experimental data, showing a high level of agreement. The effects of pile spacing on the flow field, bed elevation contours, deposition height, scour length, and scour depth were examined in two different scenarios with varying breakwater drafts. The findings reveal that pile spacing significantly affects the flow dynamics, local scour around the piles, and beneath the breakwater. This influence leads to distinctly different patterns of scour holes and variations in scour depth under the barrier. Detailed discussions are provided on the relationships between these effects and the dimensionless wave number. The attempt to increase the overall width of the breakwater by 0.25 W successfully moved scour away from the breakwater and the piles while maintaining its constant value

Keywords

Breakwater / Caisson / Deposition / Piles / Scour

References

[1] Ahmad N, Bihs H, Myrhaug D, Kamath A, Arntsen A. Numerical modeling of breaking wave-induced seawall scour. Coastal Engineering, 2019, 150: 108-120.

[2] Baykal C, Sumer BM, Fuhrman DR, Jacobsen NG, Fredsoe J. Numerical investigation of flow and scour around a vertical circular cylinder. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2015, 373: 20140104.

[3] Baykal C, Sumer BM, Fuhrman DR, Jacobsen NG, Fredsoe J. Numerical simulation of scour and backfilling processes around a circular pile in waves. Coastal Engineering, 2017, 122: 87-107.

[4] Dean RG. Coastal armoring: Effects, principles and mitigation. Proceedings of the Coastal Engineering Conference, 1987, 3: 1843-1857

[5] Gíslason K, Fredsoe J, Deigaard R, Sumer BM. Flow understanding wave. Part 1. Shear stress distribution, energy flux, and steady streaming. Coastal Engineering, 2009, 56: 341-362.

[6] Heikal EM, Koraim AS, Elsebaie ME, Elbagory IA. Seabed changes and hydrodynamic characteristics of the caisson breakwater supported on piles. NeuroQuantology, 2022, 20: 10711-10726

[7] Kamphuis JW, Rakha KA, Jui J. Hydraulic model experiments on seawalls. Coastal Engineering, 1992, 1992: 1272-1284

[8] Koraim A. Effect of pile system characteristics on the caisson breakwater efficiency and seabed changes. Mansoura Engineering Journal, 2005, 31: 53-68

[9] Kraus NC, McDougal WG. The effects of seawalls on the beach: Part I, an updated literature review. Journal of Coastal Research, 1996, 123691701

[10] Lin IF, Tseng IF, Lee CP. A three-dimensional numerical model for evaluation of seabed scour potential around a breakwater in Mailiao. Oceans 2014-Taipei, 201415

[11] McDougal WG, Kraus NC, Ajiwibowo H. The effects of seawalls on the beach: Part II, numerical modeling of super tank seawall tests. Oceanographic Literature Review, 1997, 344283

[12] Myrhaug D, Ong MC. Random wave-induced scour at the trunk section of a breakwater. Coastal Engineering, 2009, 56: 688-692.

[13] Roelvink JA, Stive MJF. Bar-generating cross-shore flow mechanisms on a beach. Journal of Geophysical Research: Oceans, 1989, 94: 4785-4800.

[14] Sumer BM, Fredsoe J. Experimental study of 2D scour and its protection at a rubble-mound breakwater. Coastal Engineering, 2000, 40: 59-87.

[15] Sutherland J, Obhrai C, Whitehouse RJS, Pearce A. Laboratory tests of scour at a seawall. Proceedings 3rd International Conference on Scour and Erosion, CURNET, 2006

[16] Tsai CP, Chen HB, You SS. Toe scour of seawall on a steep seabed by breaking waves. Journal of Waterway, Port, Coastal, and Ocean Engineering, 2009, 135: 61-68.

[17] Vitousek S, Barnard PL, Fletcher CH, Frazer N, Erikson L, Storlazzi CD. Doubling of coastal flooding frequency within decades due to sea-level rise. Scientific Reports, 2017, 7: 1-9.

[18] Wang C, Liang F, Yu X. Experimental and numerical investigations on the performance of sacrificial piles in reducing local scour around pile groups. Natural Hazards, 2017, 85: 1417-1435.

[19] Wei G, Brethour J, Grünzner M, Burnham J. The sedimentation scours model in FLOW-3D, 2014126

[20] Xie Z. Scouring patterns in front of vertical breakwaters and their influences on the stability of the foundations of the breakwaters, 1981, Delft, The Netherlands: Department of Civil Engineering. Delft University of Technology, 66

[21] Yang M, Tang Y, Zhao F, Xu S, Fang G. Numerical simulation of local scour around a square artificial reef. Journal of Offshore Mechanics and Arctic Engineering, 2024, 146: 021202.

Rights & permissions

Harbin Engineering University and Springer-Verlag GmbH Germany, part of Springer Nature