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Published byMaci Hadfield Modified over 2 years ago

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INS (+DVL) AIDED SUBSURFACE POSITIONING FOR ROV SURVEYS

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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

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

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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

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ROV Fitted on the ROV Standard Equipment: USBL/LBL DVL Octans DQ Multi-beam TSS-350 SVX Optional Equipment: Lodestar INS

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OUT OF STRAIGHTNESS (OOS) “Solving” a design issue and Coping with the “SD” fetish

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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) www.linxs.net Collapse when strength is exceeded Restrain or Control Problematic @ larger depths

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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

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Horizontal OOS 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 2 Dimensions

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INS AIDING TO MEET OUT OF STRAIGHTNESS (OOS) REQUIREMENTS Trials with a Lodestar performed o/b Highland Fortress (2012) Reviewed against earlier trials/work with Phins & HAIN

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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”

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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......

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

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

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

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Compare results DOT against Kp 4 passes

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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

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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

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

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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!

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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

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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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