The three-dimensional nonlinear dynamics of a hanging chain, driven by harmonic excitation at the top, are studied first analytically and numerically, and then experimentally. Asymptotic results demonstrate a sensitive dependence on excitation frequency and amplitude. For moderately large excitation amplitudes there are distinct regions of stable two-dimensional and stable three-dimensional response as function of frequency, as well as a distinct region in which all steady-state solutions are unstable. Numerical results were obtained to verify the asymptotic solutions and investigate the dynamics within the irregular response region. Numerical results for even larger excitation amplitudes showed that large impulse-like tension forces cause the chain to lose tension over a region adjacent to its freely hanging end, and then collapse. Following the collapse, the chain configuration intersects itself. Experimental results confirm qualitatively and quantitatively the theoretical predictions. The experimental results also demonstrate the loss of tension and subsequent collapse of the chain at the predicted excitation amplitudes, as well as the intersection of the chain with itself.
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AbstractThe Mars riser systems are a major departure from those previously used on TLPs. All risers are operated with top tensions only 20% above their wet weight; the high-pressure, light-weight drilling riser has a secondary pressure barrier wllile drilling the majority of the well; a platform-style rig is used and all risers incorporate vortex suppression devices. These advances reduce TLP payload, reduce the risks associated with simultaneous dnlling and production and minimize fatigue damage and riser interference in an area exposed to frequent Loop Current events. The design and analysis of the systems required the development and improvement of analysis tools, the performance of a multitude of hydrodynamic tests and the development of a scheme for careful tension-sharing among the three tubulars.
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