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Rule Based Design Application to Offshore Jacket Structures


 Rule based system design has been developed in two stages - first for weight estimates and second for jacket design automation using a standardized jacket concept. A simple fixed offshore jacket design involves many governing parameters such as environmental criteria, deck size and weight, site specific parameters, construction and installation variables. A domain-based approach has been used to minimize the governing parameters in the design, so that rule-based system can be developed. The paper presents the rule-based system developed for fixed well head platform jacket with 4 legs, leg through pile, lift installed jacket in a water depth up to 60m.
 McDermott has constructed and installed more than 300 jackets in the above domain. A database has been developed from these jackets installed in middle east, which included the key design variables required for the jacket design. Empirical formulae along with the information from this database, were used to develop rules to generate the gravity loads, environmental loads and installation loads required for the jacket design. A range of soil capacity curves were used to simulate the soil capacity variation in the selected jacket domain. Rules for developing the pile diameter, pile penetration and possible hammer required to drive the piles were developed. These rules formed the basis for the knowledge base required for the rule-based system. This rule-based system has been used in the first stage for weight estimation with accuracy of +/−20%, so that this can form a good input for the cost estimate with a quick turnaround.
 In the second stage, a screening analysis was performed using the rules developed to select the design parameters and site-specific data to be used for jacket design without compromising the optimization of the jacket. Similarly, the appurtenances viz. conductors, risers, boat landing, etc. on the jacket were grouped into a range to minimize the parameters to be considered for the jacket design. Using this approach, few thousand possible design parameters were reduced to less than hundred governing parameters for possible range of water depth, specific to site. Standard jacket configuration developed for the selected domain has been analyzed and compared with the jacket weights derived from the rules. Rules were finetuned based on this standard jacket analysis to aid automation of the jacket for a specific location with predefined design parameters. Construction, installation and build methods were confirmed along with the jacket configuration development.
 Rule based system which is a part of the Artificial Intelligence development tool, has been historically used in disease diagnosis, automobile production industry, select tactical moves to play a game, graphic interface development. This paper presents a McDermott's initiative to arrive at jacket configuration by using rule based system which can help to automate the jacket design.