Offshore support structure design

Abstract

The load and response analysis discussed in this chapter largely focuses on the assessment of structural responses of installed ORE devices. There are also important design considerations which are related to marine operations (such as installation and maintenance) and to the calculation of the structural resistance. Installation methods and costs can have significant consequences on the design of ORE substructures. For example, optimization of the weight of components and how high they need to be lifted needed storage area in a shipyard, ability to fit within available dry docks, and possibility of using available vessels for installation work may be more important than substructure optimization with respect to steel weight. Over the lifetime of a substructure, the costs of access and maintenance may be significant, and designs which allow for easier inspection or require less maintenance may be favored over designs which are less expensive to construct but more difficult to maintain. With respect to structural resistance, it is important to note the particular challenges related to corrosion in the marine environment. Designers must account for possible reductions in steel thickness due to corrosion through structural design (cathodic protection or coatings). ORE devices with significant dynamic motions near the free surface-implying surfaces which are at times submerged, at times dry, and also subjected to sea spray-may experience different corrosion rates compared to more static offshore structures.