Dynamic Power Cable Optimized Configurations for Lazy Wave Riser Systems

Abstract

The rapid development of floating offshore wind energy requires advanced solutions for power transmission, particularly in the context of dynamic environments such as array and export cables. This thesis investigates optimized configurations for dynamic power cables within lazy wave riser systems, with the aim of enhancing performance and reliability while reducing the length of the cable. The study begins with a comprehensive review of offshore wind energy, comparing offshore and onshore wind farms, and detailing the design standards and criteria relevant to cable design. A systematic method is used to examine and improve the configuration of dynamic power cables. This includes conducting static analyzes, dynamic evaluations, and fatigue studies taking into account the environmental conditions of the site. A quasi-static model is created to study the cable, focusing on the lazy wave design. The cable is segmented into three parts: the drag section, the buoyancy section, and the sagging section. Subsequently, a nonlinear equation system is resolved for predetermined locations of the hang-off point on the floater and the anchor point of the cable. Subsequently, various lazy wave configurations are examined in Orcaflex, and as the stress factors methods are used to evaluate stress, every configuration is analyzed for curvature and effective tension in order to reduce the stress; the first configuration places the top of the buoyancy section at around one-fourth of the water depth, the second configuration positions the top of the buoyancy section at about one-half of the water depth, and the third configuration locates the buoyancy section’s top at roughly three-fourths of the water depth. For every configuration, an optimization is carried out; the tension at the hang-off point is minimized, the curvature in the sagging section is decreased to a specific reference value necessary to reduce motion at the TDP, the curvature in the re mainder of the cable is also reduced, and the overall length of the cable is minimized as well. The environmental conditions of the site are represented by 20 short-term sea states, fatigue damage is determined by examining the cable response over a 30-minute dynamic simulation for each sea condition. The critical location of the lazy wave design is found in the HOP. A design that uses a shorter cable length and maintains a lifespan that exceeds 32 years at this location is considered as good candidate. This thesis ends with the proposal of a new configuration for the dynamic power cable, summarizing key findings that can improve performance. Upon a thorough understanding of the system, several topics are identified for future research.