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Improved Column Design on a DP3 Semi-Submersible Unit

Hale Saglam ; Oscar Lindekrantz
Göteborg : Chalmers tekniska högskola, 2014. 106 s. Report. X - Department of Shipping and Marine Technology, Chalmers University of Technology, Göteborg, Sweden, 2014.
[Examensarbete på avancerad nivå]

In this thesis a column stabilized semi-submersible drilling platform is analyzed. The purpose is to improve the column design of a generic 4-column semi-submersible with regard to the outer shape, including the general arrangement and layout of the compartments. The aim of this thesis is to decrease the unit’s complexity, increase the draught flexibility and reduce the total weight of the column. The report takes into account the multiple functions and features of a column design including establishing of the governing design factors. Based on these criteria and together with the rules and regulations relating to offshore operations, a design concept is selected for further evaluation. During the work frequent interaction with the affected design disciplines is carried out involving structural analysis, stability, weight management and systems and arrangement. Through this it can be verified whether the concept design was complying with the criteria requirements. Compartment volumes, system capacities and stability calculations are carried out using excel spread sheets. Structural strength assessment is carried out by using DNV PULS and GVA in-house created spreadsheet and input to this assessment is obtained by using a FE-model created in Genie. The investigation led to the choice of a circular & flat sided column shell with benefits to the structural integrity and hydrodynamic properties. A new larger trunk was established containing staircase, lift, routings, reserve/storage tanks and all equipment. In addition, the new compartment arrangement enables the catering for two horizontal cross bracings, transverse between the columns. The amount of compartments in need of regular personnel access was decreased which resulted in less watertight closures and dedicated supply ducts, thus reducing the inner column complexity. The new column design indicated an improvement to the unit’s draught flexibility, however not all stability requirement were met. In order to verify this it is suggested that a more detailed analysis is carried out involving the use of commercial hydrostatic and stability software. The changes in general arrangement and structural design led to an estimated total weight reduction between 6.2% and 8.3% with regard to the reference design. The results from the structural analysis indicated that further investigation can lead to more weight reduction, with regard to the safety factors against buckling and yield. However some assumptions regarding the input data involving the global stresses may turn out to increase the structural weight, once more accurate data is obtained.

Nyckelord: access trunk, column, drilling unit, DP3, offshore, semi-submersible,



Publikationen registrerades 2014-09-15. Den ändrades senast 2015-01-15

CPL ID: 202769

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