Structural optimization was not prioritized in offshore structural design for various reasons. The environmental conditions have many uncertainties. The large-scale offshore structures have complicated systems and shapes. The design process is multidisciplinary. The structural design often only converges towards the end of the project thus very little adjustment will be possible. As a result, the objectives of structural optimization, reducing the cost and enhancing the performance by minimizing structural weight, are often not strong enough to motivate optimization in offshore structures design process. Despite all these factors, there were applications of structural optimization at local level and early design stage where the design space is relatively simple. In recent time, there are growing concerns about the cost and environmental impact of offshore structures. The optimization techniques in computer-aided engineering designs have been proven effective and robust by numerous applications in many industries. Under these circumstances, offshore structures are expected to implement more optimization process in the design. This paper presents a multi-level structural optimization approach in the topsides deck truss design of a floating offshore platform. First, in the concept study phase, fundamental design parameters including the numbers of decks and major truss rows are determined by parametric study. Next, the preliminary design uses topology optimization technique to find optimal material distribution under simplified load conditions and generate basic truss structure configurations. After the initial deck truss structural layout is set up, the individual member sizes are optimized based on Finite Element Analysis and code check results. Last, in the local deck joint detailed analysis, optimal shapes and sizes are selected for local reinforcement structures. The optimized offshore platform topsides deck truss structure demonstrates advantages of lower structural weight, lower manufacturing cost, higher performance, and quantifiable environmental benefits. The practical multi-level structural optimization approach presented in this study utilizes mathematical optimization algorithms, first principle design analysis, and design experiences. The design optimization approach has been effectively applied to the complex offshore platform deck truss system which takes a multi-year project to complete and often requires assumptions and approximated design data at early phase. The optimization approach can be applied to other marine and offshore systems like the floating offshore wind turbine concept development.

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