Riser Support Structure for Support of Flexible Risers and Umbilicals

Rayappa, J. W.; Christensen, Leif

doi:10.4043/26718-ms

Cited by 2 publications

(2 citation statements)

References 4 publications

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“…Simplified stick models for the full RSS tower representing the behaviour in the X-Y and Y-Z planes were provided by McDermott (Rayappa, 2016). These stick models comprised a series of beams and lumped masses sufficient to capture most of the main modes of the RSS tower.…”

Section: Tower Modelmentioning

confidence: 99%

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Numerical Modelling of Seismically Induced Settlement for Ichthys Riser Support Structure

Erbrich

Wallbridge

Yamamoto

2016

Day 3 Thu, March 24, 2016

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The Ichthys Riser Support Structure (RSS) is a very large subsea structure for supporting up to 25 flexible risers and umbilicals as they transition from the seabed to a semi-submersible Central Processing Facility. The Ichthys field is in a region affected by both local shallow crustal earthquakes and major subduction earthquakes emanating from the Australian/Eurasian plate boundary. Large beds of uncemented carbonate silts and sands are present at Ichthys, which are highly prone to excess pore pressure accumulation and liquefaction under cyclic loads. Any structure placed on the seabed will suffer from both co-seismic and post seismic settlement after an energetic earthquake event.This paper presents dynamic non-linear numerical analyses (2D and 3D FEA) of the coupled soil and structure that were performed in order to estimate the seismically induced settlement and the potential extent of soil liquefaction beneath the RSS, which is founded on a large skirted raft foundation. Extensive site specific laboratory test data, defining the material behaviour during and after cycling, was collected to provide the necessary input to this analysis.Significant areas of liquefaction (in the form of cyclic mobility, not flow liquefaction) were found under DLE conditions and hence the combined co-seismic and post-seismic foundation settlements were predicted to be substantial although tilts were modest due to low eccentricity of the centre of gravity. The RSS was demonstrated to be tolerant to such large settlements and hence the results were shown to be acceptable in this case.

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Section: Tower Modelmentioning

confidence: 99%

“…The structural design of the RSS structure is discussed in a companion paper (Rayappa, 2016), whilst the geotechnical design challenges are presented in two papers. Lee et.…”

Section: Introductionmentioning

confidence: 99%

Numerical Modelling of Seismically Induced Settlement for Ichthys Riser Support Structure

Erbrich

Wallbridge

Yamamoto

2016

Day 3 Thu, March 24, 2016

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Mid Depth Buoys Design for Long Life Using Syntactic Foam Buoyancy, Redundant and Replaceable Tether Systems

Aberle

Christensen

2016

Day 1 Tue, March 22, 2016

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Riser systems utilize various configurations depending on water depth, size, quantity, environment etc. In the Ichthys development, three systems are utilized, Fixed-S, Lazy-S and Lazy-Wave system. The riser system design [1] and the riser support structure [2] in the Fixed-S configuration are the subject of other papers and the current paper is related to the mid depth buoys in the Lazy-S configurations. Two large MDBs each supporting five risers were designed for the initial phase of the development, one for each mooring sector of a Floating Production Storage and Offloading vessel (FPSO) which has a 3×7 mooring system. Each MDB is moored to a gravity base via primary chain and redundant, secondary polyester tether systems. Large syntactic foam modules supported in a latticed buoy structure space frame provide the buoyancy to support the riser system for a 40-year design life. This paper presents the evolution of the design, featuring: Securement of syntactic foam in the buoy structure, to accommodate dimensional change of foam. Dimensional control of the buoy structure and syntactic foam modules, during fabrication. Configuration of the structures to cater for efficient installation of large volumes of syntactic foam during fabrication. Tensioning system to manage the redundant secondary tether system. Contingency "Diverless Tether Replacement Procedure" to design features for future implementation if needed. Management of the system net buoyancy throughout the design, fabrication and installation processes. Syntactic foam buoyancy in long life, mid depth buoys avoids the need for the certification and maintenance of pressure vessels, as can be required of steel tanks. Testing verified that bulk syntactic foam exhibits minimal degradation from dropped object, impact damage. Coupled with an efficient structural containment, the sensitivity of the design to "damaged" state conditions was essentially eliminated. Chain tether systems are ideally suited to conventional mid depth buoy installation techniques. Fully redundant secondary tether systems, can be effectively incorporated into buoy system designs, to enhance greatly the system reliability over long operating lives. The manufacturing length tolerances of tether systems required a unique system for managing the ‘in place’ tension of secondary tethers to ensure their longevity.

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Riser Support Structure for Support of Flexible Risers and Umbilicals

Cited by 2 publications

References 4 publications

Numerical Modelling of Seismically Induced Settlement for Ichthys Riser Support Structure

Numerical Modelling of Seismically Induced Settlement for Ichthys Riser Support Structure

Mid Depth Buoys Design for Long Life Using Syntactic Foam Buoyancy, Redundant and Replaceable Tether Systems

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