Design And Optimization Of Mega-Frame Offshore Platform

The fixed jacket platform is the common offshore structure widely used in oil exploration and production. With the development of oil exploration and exploitation going into deep water, the fixed jacket platforms are facing many technical challenges. In the first place, along with the water depth and the structures'sizes increase, the bending stiffness of the platform decreases. Under the action of severe loads in the sea, the fixed offshore platforms vibrate much more obviously and severely and may be integrally damaged. Second, with the enlargement of the structures, the wave loading on the platform will also increases and will cause the platforms'overall vibration response. In addition, the enlargement of the structure will make the construction cost of the platform increase sharply, the time of marine transportation and operations be longer, effect of the environment be larger. In order to solve the bottleneck problems which hinder the development of the fixed offshore platform into deep water, a new platform named mega-frame offshore platform (abbreviated to MFP) is designed base on both the design theory of the traditional platform and the modern mega-structure. The optimal parameters of the MFP are determined on the study of the performance and its affecting factors for the new offshore structure.Firstly, the mega-frame structure is applied in the design of the mega-frame offshore platform. Based on the use of giant frame and its theory maturely applied on high-rise building on land, the model of the offshore platforms is constructed on which horizontal wave loadings and vertical gravity loadings are imposed for topology optimization. The mega-frame platform is constructed based on both the results of the topology optimization analysis and the design criteria of the offshore platforms.Secondly, the MFP's performance and its affecting factors are studied in the article. Model analyses, which can show the MFP's dynamic performance, are executed using the finite element analysis software. The effect of structural parameters on the platform vibration characteristics is also analyzed by the simulation analyses. The dynamic response and load-bearing characteristics of the MFP are studied under the wave loading in the different given environment.Thirdly, the wave loading calculation method and its influencing factors of MFP are studied in detail. The parameters of the MFP include both the mega columns and mega beams'structural parameters. In consideration of the platform's performance, structural parameters are optimized to reduce wave loading for the platform. According to the structural characteristics of MFP, a simplified theoretical model is obtained in order to theoretical wave loading calculation, which can construct a theory for the engineering application of MFP.Fourthly, the dynamic optimization of MFP is carried by orthogonal experimental design method. The influence of four factors which include the pipe's diameters of major beam, leg batter, the pipe diameters of the major columns and the height of the major beam is studied under the sine loadings. By the shape optimization, a desirable MFP is found out. And the MFP's load-bearing characteristics under the worse working conditions are studied by the simulation analyses.Fifthly, a general design method for the mega-frame offshore platform is established. The instructional constructing principles of MFP are found out based on the summarizing and analyzing the mechanical properties, load-bearing characteristics, wave loadings calculation method and the law of structural parameters significance. This design method will give the guide theoretically for the mega-frame offshore platform's engineering application.