ABSTRACT :

Seawall is one of the most common structures in coastal engineering. The seawall of composite profile has been used in protection projects on soft foundation. Offshore submerged-dike, which can cause wave breaking and energy dissipation, weaken the wave impact, has been widely used in protection projects on soft foundation. The 2D numerical wave flume, based on the RANS equations and the VOF method, is developed to study the effect of offshore submerged-dike on overtopping over composite seawall. The distance between main seawall and submerged-dike was changed and several wave heights were adopted. The numerical results are validated by the experimental data in terms of the overtopping discharge. It turns out that the maximum overtopping discharge appears when the submerged dike locates near the anti-node of the nonlinear partial standing waves in the front of seawalls, while the small overtopping discharge appears when it is near the node.

INTRODUCTION

When coastal buildings or roads are threatened, the typical response is to harden the coast with a seawall. Seawalls run parallel to the beach and can be built of concrete, wood, steel, or boulders. When storms attack the coastal areas, waves break against seawalls throwing water and spray over the top. Violent overtopping events can be extremely dangerous with people, cars and facilities in coasts. Waves generated by storms, either locally or offshore, exacerbated by high tides and low air pressure lead to the disruption of road services, flooding, structural damage and occasionally loss of life. For the design and maintenance works of coastal structures, reliable predictions of wave overtopping are required. Empirical formulae exist for dikes, rubble mound breakwaters and vertical breakwaters, however, often there are no suitable theoretical or numerical methods available for structures that deviate from standard shapes in appearance.

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