O-Tube – Hydrodynamic Physical Model Testing of Subsea Assets

Background

Atteris’ engineers have a detailed understanding of physical model testing allowing them to develop detailed test programs for any subsea structures. In response to a worldwide review of testing facilities conducted in 2007, Atteris identified an inability to model hydrodynamic events that involved on‑bottom combined steady and oscillatory flow. Supported by an industry requirement, Atteris responded by developing a concept to close this gap. Between 2007 and 2010, Atteris worked in collaboration with academia and industry to design, fabricate and construct a facility based on this concept. The facility was called the O-Tube and was commissioned and established in 2011.

Consisting of a closed loop channel containing 60 tonnes of water within a 1 m wide by 1.4 m high test section, it is capable of combining steady and oscillatory flow to produce realistic scaled on-bottom current conditions. Regular and random wave sequences can be replicated allowing the simulation of high‑intensity storms such as tropical cyclones and hurricanes. The O-Tube can also be programed to simulate strong tides, and other predominant unidirectional flows, which is not possible in more common U-tube flumes.

O-Tube Modelling Specifications

  • Peak oscillatory flow velocities of 2.5 m/s
  • Steady water flow velocities of up to 3 m/s
  • Large diameter (~40-inch) pipelines at 1:5 scale
  • Small diameter (~8-inch) pipelines, umbilicals and cables at full scale (1:1)
  • Concrete mattress and rock berm stability
  • Pipeline-soil resistance for a variety of soils and embedment levels
  • Wave and current induced seabed scour and erosion
  • Site specific soils obtained using grab samples can be installed in the test section to ensure that fluid soil interaction is modelled accurately

Commercial Applications by Atteris

  • Woodside Energy’s 1TL Life Extension Project – Trunkline stability and seabed scour
  • Chevron’s Wheatstone Project – Concrete mattress stability, rock berm stability, seabed scour and Trunkline / Pluto Flowline crossing
  • BHP Billiton’s Macedon Project – Self-burial of umbilical.

Benefits

The benefit of physical model testing is to assure risk, which has been defined by computational and analytical modelling, with additional identification of opportunities to optimise a design. This can be achieved through the observed response of subsea structures to hydrodynamic flow.

As the first commercial user of the O-Tube facility; a test facility capable of generating combined steady and oscillatory flow, Atteris has assured and optimised designs for pipelines, umbilicals, cables, mattresses, rock berms, as well as performing seabed scour and erosion assessments and understanding the complexities of pipe-soil interaction under hydrodynamic load.