1 / 22

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.

long
Download Presentation

INS (+DVL) AIDED SUBSURFACE POSITIONING FOR ROV SURVEYS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related