Deformation effects
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The deformation of a vessel by its load, and that of positioning piles by temperature have consequences for the accuracy of the survey. This presentation by Erich Gaickhorst (GeoVisie) shows how.

The deformation of a vessel by its load, and that of positioning piles by temperature have consequences for the accuracy of the survey. This presentation by Erich Gaickhorst (GeoVisie) shows how.

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  • It is very difficult subject bacause it is not easy to determine the errors related to the flexibillity of a vessel. This because the effects manifest mainly in realtime enviroment making it difficult time consumming and expensif to measure.Flexibillity will influence the relations and calibrations offsets of the various sensors over a time periode. Long term or may be in day and night cyclusI selected two examples of errors induced due to flexebility of the vessel. One with changing loads and one with changing ambiant temperature or due to solar radiation (or insolation - the sun shines on the surface).
  • Remaining error after calibration= Offset survey +Sensor noise + Sensor Drift + Calibration Noise + vessel deformationsWhat is influencing the vessel? Load (empty or full), seastate, temperature
  • In this case the client had installed Octans and MRU motion sensors. The offsets where surveyed. Angels calibrated. Hipap system fully calibrated but still avariable shift in the position of the ROV when shifting between the two systems. These shifts caused unwanted results in the survey results.Our scope was to determine if the vessel was flexing over the longtidunal axis.
  • Typicall fallpipe vessel Hopper in the frontMoonpoolreducing the hull strenghtPipe rackHopper on the aft
  • Two acoustic positioning systems, Hipap 350 installed on the stern and Hipap 500 forwardDifference in position of the ROV when changing positioning system. There were assumptions that the vessel was flexing along the longtidunal axis, but needed prove.
  • Geometrie survey when the vessel was in dry dock. This survey was the starting point as the straightness of the keel plane could be accurate determinedRepeat the same survey with different loads. Empty and loaded.
  • Profile points on the PS and SB site.
  • Shape fitting and calculate the error in the pitch.The found angle between the two perpendiculars extrapolated to the working dept of the ROV and the position shifts where in the same magnitude. The problem was not solved with this survey but it was a good step forward of finding a practical solution to deal with this phenomenon.
  • For this project I was the surveyor onside and tell in more detail. To meet the clients accuracies take the temperature influences in to accound.Different tolerances placing of the gravel within +/- 35mm.What is the lenght of the fallpipe? Or by which temperature
  • Lenght of the fallpipe 65mPlacing accuracy gravel +/-35mm Error budget (including RTK height error 11mm /montion sensor 5mm /lenght hydraulic cilinders 2mm/offset..etc..). The error introduced by the linear expansion of steel by temperature became very important.
  • Fallpipe assambled in December in the Netherlands. This was also the moment to survey of the pipe geometrie (sensor location and lenght).Temperature during this survey +5 C after this mobilisation the unit was shiped to site in Mexico.Calibration onsite Mexico. High ambiend temperature and very high steel temperature due solar radiation.
  • When placing gravel a part of the pipe is under water and a part is still above water. An average temperatur is calculated based on the lenght of the pipe under and above water. This value is giving us a temperature offset to apply.
  • From the first survey at 5deg to the calibration on a sunny day with a steel temperature of 60deg is 40mm. More than the total error budget.Each individual calibration is good but due to the changing enviroment the offsets will change.Finaly all the tunnel elements where put on top of the gravel bed with an averge hight error of 18mm on water depts up to 34m.

Deformation effects Presentation Transcript

  • 1. Deformation effects on vessels The effects of flexibility on calibrations HSB Workshop Vessel Geometry and Calibrations 15 January 2014 Erich Gaikhorst The effects of flexibility on calibrations
  • 2. Index • Two examples • Fallpipe vessels – Flexibility – Temperature The effects of flexibility on calibrations
  • 3. Remaining error after calibration Offset Survey Noise (Quality offset survey) Sensor Noise (Quality sensor) Sensor Drift (Quality sensor) Calibration Noise (Quality calibration survey) Vessel Deformations(Load/Sea state/temperature/design) + Remaining error The effects of flexibility on calibrations
  • 4. Example 1: Flexibility • • • • High accurate sensors Offsets with mm accuracy Angles with 0.01° accuracy Correct calibrations • Position jumps (xy) of the ROV • Why The effects of flexibility on calibrations
  • 5. The effects of flexibility on calibrations
  • 6. The effects of flexibility on calibrations
  • 7. Loaded Empty The effects of flexibility on calibrations
  • 8. 60.000 Top view Surveyed Fwd 50.000 • Points SB and PS 40.000 30.000 20.000 PS Dock SB Dock 10.000 PS floating SB floating 0.000 -15.000 -10.000 -5.000 0.000 5.000 10.000 15.000 -10.000 -20.000 -30.000 Aft -40.000 The effects of flexibility on calibrations
  • 9. Difference between docked and floating 0.120 0.120 0.100 0.100 0.080 0.080 0.060 0.060 SB Series2 Best fit circle SB 0.040 0.020 0.040 Average angle (pitch err) between Sb and Ps: 0.13° 0.020 0.000 -40.000 -30.000 -20.000 -10.000 0.000 0.000 10.000 20.000 30.000 40.000 50.000 The effects of flexibility on calibrations 60.000 Best fit circle PS
  • 10. Example 2: Temperature • High accurate sensors • Offsets with mm accuracy • Angles with 0.01° accuracy • Placing tolerance gravel +/-35mm • Temperature a significant part of the error budget. • Height influenced by temperature The effects of flexibility on calibrations
  • 11. 65m The effects of flexibility on calibrations
  • 12. • Geometry December +5°C – Steel +5°C • First calibration May +23°C Steel +30°C;Water +25°C • Last calibration August +35°C Steel +60°C ;Water +27°C The effects of flexibility on calibrations
  • 13. 35m The effects of flexibility on calibrations
  • 14. coefficient of linear expansion Steel 1.20E-02 mm/°C Aluminium 2.30E-02 mm/°C temp [°] Steel Lenght [m] 0 5 10 15 20 25 30 35 40 45 50 55 60 65 5 10 15 20 25 30 35 40 45 50 55 60 65 70 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 3.3 3.6 3.9 4.2 0.6 1.2 1.8 2.4 3.0 3.6 4.2 4.8 5.4 6.0 6.6 7.2 7.8 8.4 0.9 1.8 2.7 3.6 4.5 5.4 6.3 7.2 8.1 9.0 9.9 10.8 11.7 12.6 1.2 2.4 3.6 4.8 6.0 7.2 8.4 9.6 10.8 12.0 13.2 14.4 15.6 16.8 1.5 3.0 4.5 6.0 7.5 9.0 10.5 12.0 13.5 15.0 16.5 18.0 19.5 21.0 1.8 3.6 5.4 7.2 9.0 10.8 12.6 14.4 16.2 18.0 19.8 21.6 23.4 25.2 2.1 4.2 6.3 8.4 10.5 12.6 14.7 16.8 18.9 21.0 23.1 25.2 27.3 29.4 2.4 4.8 7.2 9.6 12.0 14.4 16.8 19.2 21.6 24.0 26.4 28.8 31.2 33.6 2.7 5.4 8.1 10.8 13.5 16.2 18.9 21.6 24.3 27.0 29.7 32.4 35.1 37.8 3.0 6.0 9.0 12.0 15.0 18.0 21.0 24.0 27.0 30.0 33.0 36.0 39.0 42.0 3.3 6.6 9.9 13.2 16.5 19.8 23.1 26.4 29.7 33.0 36.3 39.6 42.9 46.2 3.6 7.2 10.8 14.4 18.0 21.6 25.2 28.8 32.4 36.0 39.6 43.2 46.8 50.4 3.9 7.8 11.7 15.6 19.5 23.4 27.3 31.2 35.1 39.0 42.9 46.8 50.7 54.6 The effects of flexibility on calibrations 5 10 15 20 25 30 35 40 45 50 55 60 65 65 m 3.9 7.8 11.7 15.6 19.5 23.4 27.3 31.2 35.1 39.0 42.9 46.8 50.7
  • 15. Thank you for your attention Questions? The effects of flexibility on calibrations