SPREADER FRAMES AND PADEYES IN OFFSHORE HEAVY LIFT : DESIGN, ANALYSIS AND KNOWLEDGE REPRESENTATION

The rapid development of technology has revolutionized ideas beyond the imagination of our forefathers. The speed at which this is taking place is made possible with the aid of computers. The ever-improving sophistication of software and hardware has also brought about a computer revolution, facilitating research efforts to use it more effectively in aiding design. Current research efforts geared towards creating an environment enhancing man's decision-making capabilities relieve man of routine and tedious tasks while providing guidance and help, yet leaving crucial and critical decisions to the user. The offshore industry itself has very much been influenced in areas of design and modelling of offshore structures such as jackets and specific components including joints and lifting points. Knowledge processing is gaining ground against data processing. The industry itself has evolved through years of accumulated experience. Development of such tools as expert and knowledge-based engineering systems has proved to be one of the avenues for which research can be pursued. This thesis contains discussions on spreader frames and padeyes: design, analysis and development of an integrated design and decision tool. The work addresses some inherent design intricacies of a component in the spreader frame, specifically the padeye and the spreader frame itself. Due to the circumstantial variation of the spreader frame and padeye designs, the scope of investigation has been narrowed down. The chosen designs serve to emphasize the applicability of the adopted methodology. The padeyes are analysed using the finite element method and the results verified with work of other researchers. An attempt is made to define the role of the machine as man's design assistant by representing the knowledge and design codes using symbolic representation in a shell. Three spreader frame designs are looked into. These designs correspond to certain conditions favourable to their use, in terms of material and cost savings, centre of gravity positioning and other factors. For the padeyes, various parameters are investigated using strength as the main criterion for design. The efficiency of the design is also measured using the types of failure modes associated with geometry, edge distances and pin-hole tolerance. In the finite element analysis, a plane stress condition with zero friction is assumed and this is found to be acceptable. Results from the analyses show that geometry contributes insignificantly to the strength of the padeye. On the other hand, edge distance governs the mode of failure and large pin-hole tolerance causes early yielding at the point of contact due to high stress concentration. It is also demonstrated that interacting effects between pin-hole tolerance and edge distance exist. Within the range of parameters investigated, the linearization of the relationship between strength reduction and pin-hole clearance is reasonable. In the development of the Knowledge-Based Engineering System, the design codes from relevant authorities are used. The results from the parametric study of the padeye are also incorporated into the system. The system inquires the user for certain inputs which are required for the instantiation of the frame through a simple built-in user interface. The attributes of the object or frame are demand-driven. This means that computation or user input request is only performed on a when-needed basis. This saves time and computer resources. In prompting the user for inputs, the system provides defaults as well as a help. The inputs are translated into a graphical object which can be viewed on screen. Individual components of the spreader frame can also be extracted for information such as dimensions, on account of the object-oriented nature of modelling. The system was developed within the workstation UNIX X-windows environment using the ICAD platform by ICAD, providing both the expert system shell as well as the graphical interface. FORTRAN programming was also employed in areas which require detailed mathematical iteration and computation.

Author dc:creator

• CHOI KONG CHEONG