The Development of a Methodology for Analysing a Modular Based Jack-up Concept using Superelements

Abstract

A modular jackup, constructed from container-sized modules, offers mobility and design flexibility. The thesis aims to develop a fast and valid methodology for analyzing conceptual designs, focusing on the crucial connections between barges and couplings. Initial success is achieved through super elements in Finite Element Analysis, providing accurate results in under a minute. Case studies explore influences on design factors and reveal insufficiencies in the current barge connection. Recommendations include further investigation into leg-hull interaction for improved structural flexibility and punch-through simulation enhancements:

A modular jackup is a platform built from container-sized modules that altogether form a deck structure. Benefits of modular building are mobility (e.g., transportable over land) and flexibility in the design. One of the critical aspects of the design is the connections between barges and couplings, which can experience significant tensional and shear loading. The objective of the thesis is to develop a methodology for the analysis of conceptual designs in the early design phase. Following the requirements, the methodology must be capable of analyzing the endured loading by couplings. It must be able to consider different configurations and load cases. And lastly, it must provide fast and valid results. The starting point of the methodology is to create an environment in which configurations and load cases are generated using super elements for the barges and couplings. In Finite Element Analysis, a super element is a grouping of finite elements which, upon assembly, may be regarded as an individual element for computational purposes. From load cases, containing gravitational loading, payload, and environmental loading, the displacements in the structure are analyzed using the stiffness relations. Using these displacements, the loads between barges and couplings are determined. The first objective of the development of a methodology is achieved and put into practice in a model providing valid and accurate results in less than a minute. The second part of the thesis consists of case studies on a predetermined concept design (see figure). This study investigates the influences of the amount of couplings used, the location of payload on the deck, environmental loading, and a punch-through. Also, research is performed on the modeling of the leg-hull interaction. The model performs properly and provides valid results. In load cases considering horizontal loading (e.g., environmental conditions), it must be noted that the P-¢ effect is significant, affecting the accuracy of the results. From the findings of the studies, it is concluded that the current connection between barges is insufficient for these jackup designs even when using the maximum amount of couplings. During the studies, it is uncovered that the distribution of loads on the couplings is highly dependent on coupling location. With respect to shear loading, critical locations are found at the couplings close to the legs. For tension, these are at the outer edges halfway between the legs. A punch-through simulation is carried out with the use of this linear model. The soil constraints of the structure are modified, replacing simple supports with the use of springs. The results from the simulation are within reasonable boundaries, indicating that this model approximates the results of a punch-through. Investigations of the overall results show that large loading is introduced into the structure at the leg-hull interfaces influencing the coupling results. From research on the leg-hull interaction, it is found that making the connection more flexible in the transverse direction can significantly reduce the maximum shear load in the couplings. Recommendations are to investigate further on the leg-hull interaction, accounting for the effects on the structure’s stiffness considering the gap between leg and guide as well as P-Δ and leg inclination effects. Regarding the simulation of a punch-through, combining the current model with proper modeling of soil characteristics can improve the results."