Research On Hydrodynamic Performance Of Caisson-pile-deck Composite Structure

As deepwater open sea pier developed and the depth of water is more and more deep in front of the wharf, pure gravity pier appears many disadvantages (such as high cost, large wave force, high foundation, etc.). A new offshore-type composite structure is proposed. The composite structure, combined bottom caisson with middle piles and upper structures, make full use of wave energy concentrating on the surface of sea water to reduce the wave impacts on structures as well as structural responses to wave attacks. It contain stable by using its own weight. It can be predicted that the offshore composite structure would be used as a more suitable structure for deepwater open sea pier building and has its own particular practical value. As author's known, there is seldom corresponding research works focused on the wave load calculation method and dynamics of the composite structure in the literature. For the purpose of using this structure efficiently, the accurate prediction model of considering the three dimensional (3-D) interaction between wave and the structure should been developed. Therefore, performing the research works on hydrodynamic characteristics of the composite structure have an important meaning both from scientific research and practical engineering point of view.This paper presents the experiment investigation and numerical simulation of the wave forces on the caisson-pile-deck composite structure.Firstly, an experimental investigation of the regular wave forces and irregular wave forces 'on the composite structure is conducted. The statistical distribution characteristics of the perpendicular wave pressure on the surface of the composite structure is discussed. The relation between wave pressure and the relative wave height (H/S1)is also discussed. Secondly, systematically study was carried out for wave forces acting on the composite structure. The total horizontal force and the total vertical force of regular waves and irregular waves acting on composite structure are systematically investigated by experiments in this study. Empirical relationship between the total wave force and the influencing factors is given. Furthermore, the correlation equations for the calculation of total horizontal wave forces and total vertical wave forces are obtained based on the Least Square Method, which may be useful for the practical engineering application.Then, Based on the Reynolds Averaged Navier-Stokes (RANS) equations in conjunction with pore media theory and the volume of fluid (VOF) method, a three-dimensional numerical model is established to simulate surface wave interaction with the composite structure. The numerical results agree very well with experimental data on total force and the estimation of vertical wave force is more accurate by considering uplift force on the lower surface of caisson. The comparison of wave forces on each compoment with and without the influence of composite structure are carried out. A simplied calcuted method of wave force on each compoment is proposed. The spatial distributions of non-dimensional wave height and the maximum of wave pressure on surface of composite structure are presented and discussed. The velocity fields around the composite structure are computed. The effects of relative caisson length, relative wave height and relative caisson height on horizontal wave force are given. The result indicated that horizontal wave force get maximum value when A1/L=0.19and horizontal wave force linearly increase with relative caisson height and relative wave height increase. It is proved that the model is an accurate and efficient numerical tool to investigate different wave-structure interactions problems.Finally, based on the numerical simulation, the composite structure size is improved. The calculated method of the wave force and the determinations of top elevation of the new open sea terminal are proposed.