Design of a Reusable Elevation System for Offshore Topsides Float-Over Installation

Abstract

This thesis presents the design and evaluation of a reusable elevation system for topsides float-over installations in the offshore industry, aimed at addressing inefficiencies and environmental impacts associated with the current Deck Support Frame (DSF) methodology. Through a structured design approach, the system is developed in four distinct phases: recognition of need, problem definition, concept design, and basic design.

The need for a reusable elevation system arises from the limitations of the DSF, which is a single-use structure fabricated for each project and disposed of afterward. The proposed system offers multiple advantages, including cost savings through the elimination of single-use components, reduced environmental impact by minimizing material waste, adaptability to varying topsides dimensions and weights, and simplified installation processes by integrating functions. Market research into offshore wind trends confirms the relevance and potential demand for a modular, reusable elevation system.

The concept design phase involved generating a wide range of potential solutions and narrowing them down to the most feasible concept. During brainstorm sessions, 126 ideas were generated by 23 participants, resulting in 41 distinct working principles grouped into 21 concept categories. These were refined using the COCD-box framework, which balances practicality and innovation. The skidding-on-a-slope concept emerged as the most viable solution due to its low driving force requirements, direct load transfer, alignment with established offshore methodologies, and streamlined installation sequence. By extending horizontal skidding into a sloped configuration, the concept eliminates the need for the DSF and jacking system while optimizing the overall installation process.

In the basic design phase, the skidding-on-a-slope concept was further refined into a functional system layout. This phase included two sub-phases: modeling the operation and developing the structural design. A shallow slope angle was chosen to minimize driving forces, while a wedge facilitated topsides elevation. Strength analyses revealed insufficient bending capacity under hogging configurations, but recalculations confirmed that bending moments remain within safe limits. Stability evaluations showed that the concept improved barge stability by lowering the center of gravity. The structural design effectively accommodates normal loads but requires further development to manage lateral forces during skidding and mating operations. Modularity was highlighted as a key factor for transport, storage, and reusability across projects.

The thesis concludes that the skidding-on-a-slope system offers clear advantages over the DSF methodology in terms of environmental impact and long-term cost efficiency, provided the system is used more than once. The more the system is reused, the greater the reduction in costs and carbon footprint, with a projected 70% reduction after five installations. This reduction stems from the reusable steel components in the skidding-on-a-slope system compared to the single-use DSF. The adaptability of the system to varying topsides configurations and its streamlined installation sequence further enhance its practicality and relevance. The reduced carbon footprint also strongly aligns with Heerema Marine Contractors’ net-zero goals. Future research and optimization efforts should focus on operational and structural refinements to fully realize the potential of this innovative elevation system.