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Numerical Modelling of Armour Layer Stability in Low-crested Breakwaters Using Smoothed Particle Hydrodynamics (SPH) and Discrete Element Method (DEM)

Sarfaraz, Mohammad | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51798 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Pak, Ali
  7. Abstract:
  8. Rubble mound low-crested breakwaters protect the structures and ships in the port against wave attacks. Due to the overtopping, these structures provide a more attractive landscape and helps preserve the port's environment. Stability of low-crested breakwaters relies on the stability of the armor layer against the wave action, requiring the choice of the appropriate diameter for the armour blocks. For cubic armours that are of interest to the designers, there is currently no design relationship, and they inevitably use formulae specified for high-crested breakwaters that may not be in the safe side. The conventional method for determining the required armour diameter for a breakwater is laboratory experiments. Compared to the laboratory methods that are costly and suffer from scale effects, a rational method is to calculate the forces applied to armour units using numerical models in their prototype scale which can be used to analyze the stability of the armour layer. In this study, Lagrangian meshfree method of smoothed particle hydrodynamics (SPH) and discrete element method (DEM) are utilized to calculate the applied wave forces to the armour blocks and to investigate their stability. Verification problems reveal that this numerical method is appropriate for studying the stability of the armour blocks against the sea waves action. In this research, stability of cubic armour units in high-crested breakwaters is investigated. Comparison of the numerical results with design formulae shows good agreement. Then the cubic armour layer stability is modelled numerically for low-crested breakwaters under different physical and geometrical conditions. The numerical modeling results indicate that the flow field around the low-crested structure is complicated due to wave breaking and passing. Armour layer behavior and its stability depend on the freeboard, wave period, and slope of the structure. In time history of applied forces and moments on armour units, frequencies other than the main frequency of the wave are observed. This phenomenon shows the complexity of the flow field, and affects the dynamical analysis of the armour layer’s stability. Wave attacks are concentrated mainly on the crest of the low-crested breakwaters. For this reason, the instability of the armor layer is mostly observed in this area. In this research, for the first time design relationships are presented for calculating the cube armor diameter required for low-crested breakwaters in terms of physical parameters of the wave and geometry of the structure. Although there are limitations in the current study, the proposed formulae can be applied with acceptable accuracy for the design of the armor layer in the low-crested breakwaters
  9. Keywords:
  10. Coastal Protection Structures ; Low-Crested Breakwaters ; Single Layer Armour Stability ; Numerical Modeling ; Meshless Method ; Smoothed Particle Hydrodynamics (SPH) ; Discrete Element Method

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