Slender structures Examples of slender structures such as risers, umbilicals and mooring lines. Case Description Tags Tool Simple flexible riser in lazy-wave configuration A flexible riser at 100 m water depth from a semi-submersible hang-off to a fixed seabed anchor, in three segments: bare lower section, buoyancy mid-section and bare upper section. The buoyancy gives a lazy-wave shape that decouples the touch-down region from vessel motions. Modelled with axisymmetric cross sections and driven by a SEMI vessel RAO. The regions to assess are the hang-off, the sag bend, the hog bend and the anchor. Full model description: Simple flexible riser flexible riser, lazy wave, buoyancy section, sag bend, hog bend, RAO Riflex Top-tensioned drilling riser A drilling riser in 600 m water depth, from a fixed connection at the BOP to the drilling vessel above the surface. Slick joints at the lower and upper ends, buoyancy joints in the mid-section, drilling mud as internal fluid, and a static load sequence covering vessel displacement, top tension, gravity and current. Used for VIV fatigue analysis with VIVANA. Full model description: VIVANA drilling riser drilling riser, top tension, buoyancy joints, internal fluid, BOP VIVANA, Riflex Catenary riser hung off an FPSO A free-hanging catenary riser connected to an FPSO at 300 m water depth, 680 m long over five segments and two pipe cross sections. Seabed contact in the touch-down zone is modelled with a spring formulation covering normal, axial and lateral stiffness and friction. Hang-off motion is prescribed by an FPSO RAO, and a local axis system on three short lines fixed to the vessel extracts the riser-to-vessel angle in the vessel’s moving frame. Scriptable variables and condition sets sweep riser length, element count and the hang-off rotational constraint. Full model description: Catenary riser catenary riser, touch-down zone, hang-off, FPSO, RAO, condition set Riflex Complex flexible riser over a mid-water arch A flexible riser in a steep-wave configuration at 90.5 m water depth, draped over a tethered mid-water arch. Combines several advanced features in one model: a tapered bending stiffener at the hang-off, the arch as a nodal body held by tethers and branch lines, elastic contact letting the riser slide over the curved arch, smeared buoyancy and clump-weight sections, and internal fluids with inlet pressure. Full model description: Complex flexible riser flexible riser, mid-water arch, steep wave, bending stiffener, elastic contact, smeared buoyancy Riflex Top-tensioned drilling riser with flex joints A realistic drilling-riser stack at 330 m water depth, about 341 m long, running from the wellhead through BOP and LMRP up to the drilling vessel. Includes a non-linear lower flex joint, slick, buoyancy and pup joints, a telescopic slip joint and a linear upper flex joint. Top tension is applied through a tension ring on six tensioner lines with static and dynamic friction. Irregular and regular wave environments are both defined, with condition sets for irregular-sea response and a top-tension sweep. Full model description: Drilling riser drilling riser, flex joint, slip joint, top tension, tensioner, BOP, condition set Riflex Riser through a guide tube (pipe-in-pipe) Pipe-in-pipe modelling of a riser passing through a guide tube and bellmouth at 315 m water depth. The guide tube hangs fixed from the vessel, its lower trumpet tapering from a 3.85 m flared mouth to a 1.0 m tube. Pipe-in-pipe contact elements distributed along the overlap give radial contact stiffness, friction and damping, so the riser slides axially while being constrained laterally. Driven by a severe JONSWAP sea state (Hs = 12.5 m, Tp = 14.5 s) through a vessel RAO. Full model description: Guide tube guide tube, bellmouth, pipe-in-pipe, contact, friction, RAO Riflex Clashing between two risers and a pontoon Two flexible risers suspended from the same vessel at 100 m water depth, geometrically identical but given different drag coefficients so they respond differently and move toward each other. A short horizontal line represents an adjacent pontoon. Hang-off motion combines a vessel RAO with low-frequency drift read from file. Displacements are stored for all nodes so the distances between lines can be reconstructed; clearance is assessed in the post processor. Note that distances are measured between line centres, so each line’s contact radius must be accounted for. Full model description: Riser clashing riser clashing, clearance, collision risk, drag coefficient, low-frequency motion, post processor Riflex Mooring line on a 3D seafloor read from file A single chain mooring line at 320 m water depth, from a fixed fairlead near the surface to an anchor on the seabed, with its lower part resting on the bottom. The 3D seafloor geometry is imported from an external file (ST_3D_bottom/bottom_3d3.dat) under Location > Regular 3D Bottom, and line-seafloor interaction is handled by a spring contact model applied to all segments. The chain uses an axisymmetric cross section. Full model description: 3D bottom mooring line mooring line, 3D seafloor, seabed contact, chain, friction Riflex Compare marine growth modelling Compare two ways of modelling marine growth on a top-tensioned riser (TTR), together with a case with no growth: line_a_bare: marine growth applied from a marine growth profile line_b_growth: marine growth accounted for in the cross sections as external coating. In the static analysis the scaling is set to zero for this line to avoid doubling of the marine growth line_c_bare: no marine growth (bare riser). In the static analysis the scaling is set to zero for this line so that no growth is added from the marine growth profile marine growth, bare,ttr ,cross section, external coating Riflex Catenary riser with a flat bottom modelled with user-defined elements A catenary riser where the flat sea floor is modelled with a user-defined element. Features in the model include: vessel with RAO sea floor contact local axis system to extract angles at hang-off a variable at the sea floor to increase the length of the line The Fortran source for the user-defined element is in the storage task ST_userdefined/flat/earth_example.f90 with the compiled earth_example.dll. The interface code is in ST_userdefined/template_code/earth_interface.f90. catenary riser, user defined element, sea floor contact, RAO, hang-off Riflex Floating production units Wind turbines