Pile-cap foundations are adopted in China-Maldives Friendship Bridge, and it faces great severe wave conditions. In this manuscript, a numerical wave tank (NWT) is developed based on commercial software package FLUENT. Mesh convergence has been conducted prior to the numerical studies. Validation computations on the numerical model are performed by comparing the wave forces on horizontal cylinder with other experimental and numerical results. Wave forces on pile structures are obtained and compared with the prediction of Morison equation, and the agreement is quite well which proves the numerical model is suitable to model wave-structure interaction. Wave forces on the fusiform cofferdam are numerically calculated under multiple regular waves and directions, and it is found that the maximum wave force is much smaller for long waves. During the construction of the Bridge, the wave statistic characteristics like significant wave height and peak wave periods are measured and numerically regenerated. 36 sets of pressure sensors are laid out on the surface of the cofferdam. Fast Fourier transform and filtering method are used to separate wave pressure components from the measured data. Through integration of wave pressure, wave forces on steel cofferdam are obtained and compared with CFD results. This research serves as a technical support for the construction of the Bridge.
Recently, sea-crossing bridges are moving from shallow water to deep open water, and they will face much more severe environmental conditions that will pose great damages on the bridges. Pile-cap foundations are widely used in sea-crossing bridges, offshore wind turbines, oil and gas platforms. Understanding the interaction of waves with these structures is important for the accurate prediction of the hydrodynamics loads on them.
For circular cylindrical structures, Morison et al. (1950) investigated the forces on piles systematically and proposed an empirical formula which is known as the Morison equation, and the total forces on pile are separated into drag and inertia components that CD and Cm are the coefficients for drag and inertial forces, respectively. Hogben et al. (1977) summarized the range of values for CD and CM used in Morison equation. The contribution of drag and inertia forces to the total forces is determined by the KC number and the diffraction parameter. As the KC number is smaller than 2 and the wave diffraction parameter (D/λ, D is the diameter and λ is the incident wave length) is greater than 0.2 (D/λ > 0.2), the inertia component plays the dominated role and wave diffraction effect can't be ignored (Isaacson, 1979). Linear solutions can be obtained with analytical equations based on potential theory by assuming the fluid is inviscid, irrotational and the wave amplitude is small compared with the diameter of the cylinder.