| 摘要 |
<p>In a substructure (10) for a floating oil or gas production platform, an arrangement to tension a plurality of risers (16) extending from the sea bed up to the substructure, the arrangement comprising: a conventional hydraulic tensioner/heave compensator (17) for each riser, in which there is a soft spring formed by a piston cylinder combination acting against an accumulator , the heave compensators for the risers being disposed to compensate for vertical oscillations of relatively short period (e.g. from 1 second to abou t 5 minutes) between the risers and a vertically adjustable Xmas tree deck (18 ); and a vertical position adjustment system (21/22) capable of intermittent operation to adjust the vertical position of the Xmas tree deck (18) relativ e to the floating substructure (10) to compensate for longer term changes whic h would otherwise cause the individual riser's tension or stroke position to depart from its target value/range; the Xmas tree deck vertical position adjustment system being normally located in one particular position within i ts range of movement to compensate for the longer term changes.</p> |
