A compliant connector concept for the mobile offshore base

Abstract

In order to reduce the large loads that are developed in connecting semi-submersible platforms on a 5000 ft long mobile offshore base (MOB), a compliant connector concept was developed. This concept employs the cable compliant technology developed by NASA-Goddard and is based upon the use of 3-D Through-the-Thickness ® braid reinforced elastomeric tubes as the compliant element in the connector. By selectively placing and orienting the composite tubes, the connector can be designed to provide stiffness in degrees of freedom critical to maintaining runway smoothness (such as relative heave or roll) while permitting larger displacements in other degrees of freedom (such as relative pitch or surge). Two different connectors were designed: a four-degree-of-freedom (4 DOF) connector for the deck attachment and a 6 DOF connector for connecting at the pontoon level. The work presented includes material characterization testing, including some fatigue studies, and constitutive model development to fully understand the material behavior. The constitutive model for the material included both the material nonlinearity of the urethane elastomer matrix and geometric nonlinearities to include the fiber reorientation during loading. Tests were performed on a subscale connector design validate the analytical technique used to predict the connector performance. Six different tests configurations were performed with different loading conditions and connector configurations, and good correlation was found between the experimental and analytical results. The performance of full-scale connectors were determined through analysis and incorporated into a finite element model of a scaled MOB design. The connector loads of the compliant connector are compared with the rigid or hinge-type connector for two different hull configurations and various sea conditions and headings and is shown to reduce the loads over the conventional design.