Development of a Tool for Design of Jack-Up Units
Examensarbete för masterexamen
Hossian, Md Shanower
The structure of a jack-up unit is very flexible and sensitive to environmental factors such as wind, current and wave. The suitability of a jack-up unit for a chosen location is governed by these environmental factors. The loads due to these factors have three effects on the jack-up unit: a dynamic amplification load due to excitation of the structure by environmental loads, an overturning moment which tends to capsize the unit and P-Δ effects due to large displacement. Dynamic amplification load and P-Δ effect contribute to reduce structural strength and decrease the stabilizing moment. Hence, it is important to take into account wind, current and wave loads along with their effects for the assessment of the unit and adopt a proper jack-up analysis technique to accurately reflect the occurring physical processes. This thesis is concerned with the development of a methodology that takes into account all the environmental loads and their effects and makes the design process easy, quick and accurate. The objective was to develop a design tool following the methodology for assessing the structural strength of the legs and overturning stability of the whole unit in the elevated mode. The tool considers non-linearities in the structure by utilizing a large displacement method and can be used to assess the unit in accordance with the design criteria set by any classification society or industry group. The design tool consists of five different modules, and, together, these determine the centre of gravity and connect it to the hull, the maximum and minimum hydrodynamic loads, the dynamic amplification load, the overturning stability ratio and P-Δ ratio (structural strength ratio considering the P-Δ effect). Finally, the design tool has been implemented on four different types of jack-up units and has been tested. For verification, it was implemented on a commercial project and the results have been compared with the manual calculation done in an Excel sheet by D2M consultants. It was found that the results determined by the tool were conservative. For confidentiality, the results have not been presented in this report but the analysis results of the four jack-up units have been presented to show how the design tool works through the complete assessment process.
Transport , Farkostteknik , Transport , Vehicle Engineering