Dynamic Response of TLPs During Tether Installation

Abstract

A research study has been conducted into the dynamic response of TLPs during tether installation. The aims of this research study were to investigate tether dynamics due to coupled tether/TLP system response. In particular, to focus on low pretension conditions to include tether system behaviour during slacking (Ref Chapter 1). To facilitate this research study numerical prediction tools were developed and validated by means of comparison with experimental measurements. The prediction tools developed to predict the dynamic response of the coupled tether/TLP systems during installation utilise the time-domain simulation technique. 2No. forms of coupled tether/TLP model were developed: a Phase 1 model where the tether system was represented by a rotating axial spring system, a Phase 2 model where the tether system was represented by an assembly of 3D beam-column finite-elements (Ref Chapter 4). In addition to this software, a closed-form solution to the diffraction solution for an array of circular cylinders was also implemented into software (Ref Chapter 2). Software validation consisted of comparisons with experimental work conducted at the Universities of Glasgow and Newcastle on a case study TLP geometry (Heidrun TLP). The experiments at Glasgow University consisted of measurements of wave excitation and hydrodynamic reaction force components (Ref Chapter 3). The Newcastle experiments consisted of measurements of TLP system motion and tether tension dynamic response (Ref Chapter 5). A Case Study result data base was generated for 3No. TLP systems representative of a spectrum of TLP systems (Ref Chapter 6 and Appendix A). Comparisons were made between the Phase 1 and Phase 2 simulation models and the experimental data. Following these comparisons, and with reference to simulation and experimental data, conclusions were drawn regarding the response mechanisms governing the TLP/tether system response at low pretensions (Ref. Chapter 7). The research study undertaken is represented in the following flowchart: [diagram] A primary conclusion drawn from this study is the significance of the coupled TLP/tether system dynamics on the tether system motion and tension dynamic response during low pretension conditions