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INS (+DVL) AIDED SUBSURFACE POSITIONING FOR ROV SURVEYS

INS (+DVL) AIDED SUBSURFACE POSITIONING FOR ROV SURVEYS. Allseas’ identity. Privately owned Providing technically advanced solutions Daring to take on challenges No-nonsense approach Safe working environment. Installation Contractor. In house ROV & Survey Services. Allseas’ vessels.

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INS (+DVL) AIDED SUBSURFACE POSITIONING FOR ROV SURVEYS

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  1. INS (+DVL) AIDED SUBSURFACE POSITIONING FOR ROV SURVEYS

  2. Allseas’ identity • Privately owned • Providing technically advanced solutions • Daring to take on challenges • No-nonsense approach • Safe working environment Installation Contractor In house ROV & Survey Services

  3. Allseas’ vessels 382 m Pieter Schelte 1253 ft 300 m Solitaire 984 ft 225 m Audacia 738 ft 183 m Lorelay 600 ft 151 m Calamity Jane 495 ft 111 m Tog Mor 364 ft +3 sub-contracted SVs

  4. ALLSEAS ROV & SURVEY SERVICES • Since 2007 • Implemented 2007-2009 • 7x Shilling UHDs • Installed on: • Solitaire • Lorelay • Calamity Jane • Highland Navigator (2x) • Highland Rover • Highland Fortress

  5. ROV Fitted on the ROV • Standard Equipment: • USBL/LBL • DVL • Octans • DQ • Multi-beam • TSS-350 • SVX • Optional Equipment: • LodestarINS

  6. “Solving” a design issue and Coping with the “SD” fetish Out of Straightness (OOS)

  7. What is OOS • Maximum allowed deviation over specified length e.g. 0.3m/100m in both vertical/horizontal plains. • Criteria: • Expansion restrained by: • Pipe Material • Soil Strength • >> Uncontrolled Buckling << • >> Controlled Buckling << • Measures: • -Design (wall thickness/weight coat) • -Trenching/Backfilling • -Rock-dumping • -Buckle Initiators (buoyancy/supports) Restrain or Control Problematic @ larger depths www.linxs.net Collapse when strength is exceeded

  8. Vertical OOS • Vertical = Straight Forward: • -Based on DQ (HP/HR) • -Pipe defines low pass filter settings • Problems: • -Swell in water depth <200m • -SD fetish design Houses • -Relative versus absolute requirements • Solution: • -FFT based low pass filtering (1997/98) • -INS embedded (Kalman) filtering (2012) 1 Dimension

  9. Horizontal OOS 2 Dimensions • Horizontal = Complicated: • -Sensors (USBL/DVL) lack HP/HR • -Low pass filter may/may not work. • Problems: • -Accuracy DVL aided USBL • -Repeatability • -User/Data Interaction • Solution: • -INS embedded (Kalman) filtering (2010) • Trials based on: • Phins & HAIN & Lodestar

  10. Trials with a Lodestar performed o/b Highland Fortress (2012) Reviewed against earlier trials/work with Phins & HAIN INS aiding to meetOut of Straightness (OOS)requirements

  11. INS Trials • Earlier work: • Phins in Australia performed unsatisfactorily • Partially caused by interfacing issues and human error • Performance still not convincing • HAIN substituted Phins with satisfactory results • Major disadvantage >Only works with HiPAP< • Challenge: • How to prove “relative” repeatability (3D shape) • Solution: • Trials against existing pipeline (4x in opposite directions) • Built DTM • Assess relative repeatability (shape) though “moving deviation”

  12. INS for OOS surveys • Question: • Can we detect a 0.20m deflection over 50m of pipe? • Trial Concept: • Compare TOP’s derived objectively from independent free flying ROV surveys on an exposed pipeline. • Prove Significance . . . . . .

  13. INS/DVL versus DVL based ROV track and DTM Movie #1 What’s real?

  14. USBL-DVL based TOP Movie #2 Remaining artefacts Not a detection problem!

  15. INS based TOP (including XYZ and Kp, DOT) Movie #3 “No” artefacts Significance?

  16. Compare results DOT against Kp 4 passes

  17. DOT analysis • When is an event significant? • Analysis length 50m • Differences < 0.20m • If so, relative accuracy is within 0.2m and deflection > 0.2m can be detected • Moving Window • Assess the spread relative to normalised start position for each line

  18. Single segment analysis • An arbitrary piece of 100m was taken from the INS based data and the first sample of each line was referenced to zero When perfect these will tie-in > spread = significance/repeatability

  19. Single segment analysis • The max relative difference in shape (dDOT) between any pair of lines is less than 0.20m

  20. Multiple segment analysis • A 50m window is passed through the data with steps of 1m • For all position solutions (USBL-DVL, Online INS, DIRK filtered USBL, INS post processed) 4 filters > relative difference in shape!

  21. Multiple segment analysis • Statistics on the results gives the 95% confidence level of the delta DOT for each meter distance from the reference point Combined Drift

  22. Conclusion & Questions • The maximum difference is less than 0.20m over a distance of 50m thus it is possible to detect a 0.20m deflection over 50m of pipe • Thanks go out to MIWB student Karel Epke, the writer of the thesis called “performance & implementation of an INS for Pipeline Surveys”, 2012

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