Research On The Static And Dynamic Behavior Of The Structure Of Offshore Bucket Foundation Platform

Based on the patterns of innovation in the offshore oil platform foundation structure, the foundation of the jacket platform structure is developed to negative pressure bucket structure, thus, the new form of the platform-the bucket foundation platform is created. Because of its high efficiency, as well as its convenience in installation, moving and reusing, the bucket foundation platform has a broad application prospect in the offshore oilfield development. But due to its short developing time and complex stress, there still exists many problems.This paper mainly does the static and dynamic analysis on a certain type of structure under varieties of circumstances by using ANSYS, a large-scale finite element software, and as a result, some design suggestions are given. The main content of the research and analysis are as follows:(1) Taking fixed load, live load, extreme wind load, extreme ice and extreme wave flow into consideration, the nonlinear static calculation and the analysis of the bucket foundation platform structure is done under eight kinds of working condition by using p-y curve method. The result is compared with the results of m method. Research shows that m method is conservative in the simulation of bucket foundation and soil, while p-y curve method can truly simulate the interaction of pile displacement and soil counterforce relationships, which is more compatible for the static nonlinear characteristics of bucket foundation and the soil.(2) Analysis of transient dynamic of the platform structure under the wave load is done by using ANSYS, after which the characteristics of displacement and stress variation are decided. Research is done on the influence of different categories of soil and deck load. As a result, with the increase of level of soil resistance the displacement decreases while the stress is constant. On the other side, with the increase of deck weight, the natural frequency of the structure is decreased, as well as the column top displacement, while the vertical displacement is increasing. The results show that the adaptability of the large-diameter bucket foundation structure is adaptability to the offshore geological conditions, and it can resist to the wave force sufficiently.(3) By using spectrum analysis method the seismic dynamic response of the structure is calculated, then the vibration mode and frequency which have grate influence on the structure are analyzed. As a result, the order1,4,6and9of the mode shapes have greater influence on the platform structure. In addition, the influence of seismic action on the structural response is researched on different pillar scales, soil categories, site types and deck loads. Firstly, with the increase of column height and deck loads the displacement and stress increases, until the structural is instable. Secondly, the range of the dynamic response of the platform structure is10.1%in respond to different foundation soil, which indicates the structure to be adaptable. Last but not least, the site type of platform structure can influence the structure regularly. Specifically, the stress and displacement of the structure in hard and deep alluvium are larger than in shallow and hard alluvium, while in the rock the stress and displacement are the minimal. Besides the critical frequency of the basal sliding in hard and deep alluvium is smaller than in shallow and hard alluvium, while in the rock the critical frequency of the basal sliding is the maximal.