In this paper, the near-trapping phenomena associated with four-cylinder structures affected by the side-wall of wave flume are investigated. The linear potential flow and the viscous fluid flow models are adopted, by which the difference between two numerical results with and without side-wall effect is compared. Numerical simulation shows that the side-wall has significant effect on the near-trapping phenomenon, including the free surface distribution and wave forces on the boxes. The general variation of wave amplitude around the structure and wave force on the box can be obtained by the potential flow model. However, it over-predicts the peak value around the frequencies where near-trapping and side-wall resonance happens. The comparisons of maximal wave amplitude and wave force by two numerical models with and without side-wall effect are performed in this work. The influence of the sidewall is much greater than that of the fluid viscosity can be observed.
In recent years, the exploitation of offshore resources has gradually developed into deep sea areas. Traditional jacket and jack-up offshore platforms cannot meet the engineering needs of deep-sea resources development. Floating offshore platforms, including tension legs and semi-submersible platforms, has attracted more and more attention. These platforms are usually composed of four large-diameter columns that provide buoyancy and restoring torque through large displacement. Under some severe sea conditions, the wave run-up has an impact on the lower deck of the platform, generating a large acting force and overturning moment. However, in order to avoid the excessive wind area of the platform caused by the high center of gravity, the design of the air gap of the platform should not be too large. Therefore, it is the key to the design of floating offshore platforms to fully consider the force of the supporting column under the action of waves and the change of the nearby free water surface. For the cylinders arranged in an array, the front row of cylinders mainly has a shielding effect that reduces the force of the rear row of cylinders, while the cylinders located in the same row mainly have the interference effect of increasing wave force. However, for large-diameter floating platforms, due to the strong influence of wave diffraction, the traditional method of ignoring wave diffraction based on small-scale objects cannot meet the calculation needs of large-scale objects.
