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Content: Background for and aim of model test Model and instrumentation Environmental conditions

HEIDRUN TLP MODEL TESTS Summary of results (Pictures and figures are partly prepared by Marintek personel) Sverre Haver, Statoil, December 2003. Content: Background for and aim of model test Model and instrumentation Environmental conditions Phase 1 – Examples, results and conclusions

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Content: Background for and aim of model test Model and instrumentation Environmental conditions

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  1. HEIDRUN TLP MODEL TESTSSummary of results(Pictures and figures are partly prepared by Marintek personel)Sverre Haver, Statoil, December 2003 Content: Background for and aim of model test Model and instrumentation Environmental conditions Phase 1 – Examples, results and conclusions Phase 2 – Examples, results and conclusionsComparison with original design values Heidrun TLP Model Tests - Summary

  2. Background and Aim • More severe accidental wave conditions (i.e. wave conditions corresponding to an annual probability of 10-4) are predicted. Significant wave height increased from 18.6m to 20m.(ULS sea state conditions (10-2) are more or less as before, increased from15.5m to 16m.) • With updated accidental wave conditions, the topside structure (in particular the MSBs) is much more exposed to wave impacts than accounted for in original design. • Due to these impacts, increased structural response is expected in lower hull, in main support beams (MSBs), in tethers, and in tether connections to hull and bottom foundation. Life boats may also be exposed to wave impacts. • The aim of the model test is to establish the background for predicting reliable estimates for the 10-4 response in all structural elements mentioned above. • Phase 1 should identify the critical 10-4 environmental condition and ensure that a proper instrumentation was carried out. Phase 2 should ensure that the inherent randomness of the extremes was accounted for by executing a large number of realizations for the critical environmental condition. Heidrun TLP Model Tests - Summary

  3. Heidrun TLP Heidrun TLP Model Tests - Summary

  4. Test Model Heidrun TLP Model Tests - Summary

  5. LOCATION OF AIRGAP AND FORCE SENSORS In Phase 2, the lifeboat force sensor was moved to a lifeboat closer to centerline. Some airgap sensors were also moved Heidrun TLP Model Tests - Summary

  6. SENSORS FOR MEASURING DECK IMPACTS Heidrun TLP Model Tests - Summary

  7. ENVIRONMENTAL CONTOUR LINES FOR SEA STATE CHARACTERISTICS Hs and TpHEIDRUN SITE Heidrun TLP Model Tests - Summary

  8. Contour lines for individual wave parameters, H and T Heidrun TLP Model Tests - Summary

  9. Example from Test 2111Regular waves with height 20m and period 11s Heidrun TLP Model Tests - Summary

  10. Example from Test 2750Regular waves with height 35m and period 16.5s Heidrun TLP Model Tests - Summary

  11. MAX TETHER LOAD FOR REGULAR WAVESNote: Given height and period are target values, actual values may differ somewhat, especially for the height. Heidrun TLP Model Tests - Summary

  12. OBSERVATIONS FROM REGULAR WAVE TESTS • The most critical individual waves are steep waves with a rather large crest height. • Too much weight should not be given to the total tether forces shown in table on previous page – in particularly not for the highest waves. When repeating such extreme waves, the offset and therefore the set-down will be very much amplified. The mean tension will be significantly overestimated (25-30%) as compared to the mean tension in a severe storm. Focus should be on the dynamic tension. However, this quantity is also somewhat conservative since an overestimation of the set-down will make topside more exposed to wave impacts. • The criticality of steep waves may seem to be in conflict with the selected extreme sea state, hs = 20m and tp = 20s (irregular sea state). However, this sea state is likely to be of a combined nature, i.e. a considerable amount of the energy is concentrated around a period band much shorter than 20s, see figure next page. Heidrun TLP Model Tests - Summary

  13. WAVE SPECTRUM OF CRITICAL ALS SEA STATENote combined nature of sea state (swell + wind sea) Heidrun TLP Model Tests - Summary

  14. Example from Test 3010Irregular sea states with hs=12.3m and tp=11s Heidrun TLP Model Tests - Summary

  15. Example from Test 3060Irregular sea state with hs=17.5m and tp=15.5s Heidrun TLP Model Tests - Summary

  16. RESULTS OF IRREGULAR SEA STATE TESTS PHASE 1 • The next figures show: The 3-hour maximum tether tensions for the most exposed corner are shown for all tests. The minimum air gap are given for a number of positions. (Zero air gap is defined as the airgap when the wave crest reach cellar deck level.) • Test numbers, wind/current offset = 15m (3xxx = 270deg. and 4xxx = 315deg.):hs=12.3m, tp=11s: 3001,3002,3020, 4000,4011 hs=14.5m, tp=13s: 3020,3030,3040,3051, 4022,4030,4040,4050hs=17.5m, tp=15.5s: 3060,3070,3080,3090, 4060,4070,4080,4090hs=18.8m, tp=17s: 3110,3120,3130,3140, 4110,4120,4130,4140hs=19.8m, tp=18.5s: 3150,3160,3170,3180, 4150,4160,4170,4180hs=20m, tp=20s: 3210,3220,3231,3240, 4210,4221,4231,4240hs=19m, tp=22s: 3250,3260, 4250,42603241, 3242: Repeating 3240 to check repeatability.3310, 3320,3330: Repeating 3240 with wind/current induced offset: 10m, 22.5m, 30m3340: Repeating 3140 with offset 30m, 3510: Repeating 3010 with offset 0m3410: Repeating 3240 with no deck.4310, 4324,4333: Repeating 4240 with offset: 10m, 22.5m, 30m4341: Repeating 4140 with offset 30m. Heidrun TLP Model Tests - Summary

  17. MAX TETHER TENSION PHASE 1 TESTS – 270deg. Heidrun TLP Model Tests - Summary

  18. MAX TETHER TENSION PHASE 1 TESTS – 315deg. Heidrun TLP Model Tests - Summary

  19. AIRGAP AT FRONT OF MSB_WEST – 270deg.Wave crest reaches MSB for an airgap less than 8.5m Heidrun TLP Model Tests - Summary

  20. AIRGAP IN FRONT OF MSB_EAST – 270 deg.Wave crest reaches MSB for an airgap less than 8.5m Heidrun TLP Model Tests - Summary

  21. AIRGAP AT TWO LIFE BOAT POSITION-270 deg.Wave crest reaches life boat if airgap less than about 8m NORTH WEST CORNER NORTH BETWEEN MSBs Heidrun TLP Model Tests - Summary

  22. AIRGAP AT TWO LIFE BOAT POSITIONS – 315 deg. NORTH WEST CORNER NORTH BETWEEN MSBs Heidrun TLP Model Tests - Summary

  23. AIRGAP AT FRONT OF MSB-WEST – 315 deg.Wave crest reaches MSB for an airgap of less than 8.5m Heidrun TLP Model Tests - Summary

  24. CONCLUSIONS OF PHASE 1 • The most critical ”10-4 sea state” is the sea state defined by hs=20m and tp=20s. Large tether loads are also observed for a sea state defined by hs=18.8m and tp=17s. • The largest deck impact loads are observed for beam sea direction. A comparable tether load level is observed for both the diagonal and the beam sea direction. This because fewer tethers (4) have to carry the most of the dynamic load for the diagonal direction. (In original design the diagonal direction was found to be the most critical direction because deck impacts were less pronounced.) • In Phase 2 a large number (20) of runs with different random seeds of the critical sea state are carried out for both beam sea and diagonal sea. For the most extreme events, the tests are repeated without the deck structure in order to isolate deck impact induced ringing from classical ringing. Heidrun TLP Model Tests - Summary

  25. HORISONTAL DECK IMPACT VERSUS UNDISTURBED CREST HEIGHTPhase 1 and Phase 2 results 270deg. Wave4_Cal: Undisturbed incoming crest height at nominal position of MSB_west Heidrun TLP Model Tests - Summary

  26. VERTICAL VERSUS HORISONTAL IMPACT LOADPhase 1 and Phase 2 results, 270 deg. Heidrun TLP Model Tests - Summary

  27. HISTOGRAM DECK IMPACT LOADS3-hour maximum of each test with hs=20m and tp = 20s, 24 obs. FIGURES CLEARLY DEMONSTRATE THE VERY LARGE SCATTER FROM REALIZATION TO REALIZATION. THIS IS THE REASON FOR THE NEEDOF A RATHER LARGE NUMBER OF 3-HOUR REALIZATIONS OF THE CRITICAL SEA STATE, HERE 24 REALIZATIONS ARE SELECTED. IF THERE HAD BE ”NO” SCATTER FROM REALIZATION TO REALIZATION, WE COULD HAVE ADOPTED THE MEAN 3-HOUR MAX OF THE 10-4 SEA STATE AS AN ADEQUATE ESTIMATE OF THE 10-4 IMPACT LOAD. DUE TO THE SCATTER, LOADS LARGER THAN THE MEAN MAY BE OBSERVED FOR LOWER SEA STATES. IN ORDER TO ACCOUNT FOR THIS, A HIGHER FRACTILE HAS TO BE SELECTED. HERE THE 90% FRACTILE IS SELECTED. Heidrun TLP Model Tests - Summary

  28. 3-HOUR EXTREME VALUE DISTRIBUTION FOR DECK IMPACTS 90% FRACTILE: 2.25 NB! NB!When selecting design impacts, more weight is given to upper tail than what standard fitting suggests, i.e. the design values given below are based on an ”eye fit” to upper tail. ALS DESIGN IMPACTS: FY_MAX = 150MN FZ_MAX = 130MN Both MSBs has to be checked for the horizonal impact load. The vertical impact load is mainly caused by wave-deck (not MSB) and has to be implemented in a conservative way. Heidrun TLP Model Tests - Summary

  29. DECK IMPACT AND TETHER RESPONSEExample 2 Heidrun TLP Model Tests - Summary

  30. TETHER TENSION VERSUS DECK IMPACTSWAVE DIRECTION: 270 DEG. Estimated ALS impact For a horisontal impact load of 150MN (ALS-impact), the corresponding tether force is likely to be between 225 and 250MN. Estimated ALS impact For a vertical impact load of 130MN (ALS-impact), the corresponding tether force is expected to be between 210 and 250MN. Heidrun TLP Model Tests - Summary

  31. HISTOGRAM 3-HOUR MAX TETHER LOAD Large scatter is observed, Consequently a higher fractile has to be selected as the proper estimate of 10-4 tether load. (See comments on slide no. 27.) Heidrun TLP Model Tests - Summary

  32. HISTOGRAM 3-HOUR MIN. TETHER LOAD Heidrun TLP Model Tests - Summary

  33. 3-HOUR EXTREME VALUE DISTRIBUTION TETHER LOAD (4 TETHERS) NB!NB! MORE WEIGHT IS GIVEN TO UPPER TAIL WHEN CHARACTERISTIC VALUES ARE SELECTED, SEE ALSO SLIDE No 27.90% FRACTILE ASSUMED TO ACCOUNT PROPERLYFOR SCATTER AROUND THE MEAN. (See slide no.27) 90% FRACTILE: 2.25 ALS TETHER LOAD, AUTUMN 2003: 4 TETHERS: 250MN PR. TETHER: 62.5MN ALS ORIGINAL DESIGN: PR. TETHER: 52.2MN Heidrun TLP Model Tests - Summary

  34. EXAMPLE 1: EFFECT OF DECK IMPACT ON TETHER LOADING Heidrun TLP Model Tests - Summary

  35. BUDGET ALS MAX TETHER LOAD(The last column will be updated as the results from Phase 2 is properly analysed.) (*) Based on tests with and without deck, at present no reason to change original ringing estimate. Further data analysis will be carried out. A CONSIDERABLE INCREASE IN THE DYNAMIC LOAD IS ESTIMATED Heidrun TLP Model Tests - Summary

  36. CONCLUSIONS OF TESTS • 10-4 TOPSIDE IMPACT LOADS ARE ESTIMATED TO BE: 150MN HORISONTAL AND 130MN VERTICAL. • ALS DYNAMIC TETHER LOAD (NON-YIELDING FULL SCALE MODEL ) FROM IRREGULAR WAVE TESTS (HS=20m and TP=20s): 36MN • DYNAMIC TETHER LOAD (NON-YIELDING FULL SCALE MODEL) FROM REGULAR WAVE TEST (ALS WAVE H=32m and T=13s): 42MN (THIS LOAD IS RATHER CONSERVATIVE SINCE THE REGULAR WAVE TEST CAUSE A VERY LARGE MEAN OFFSET AND, CONSEQUENTLY, A LARGE MEAN SET-DOWN.) • SUGGESTED ALS ROBUSTNESS CRITERIUM: THE NUMERICAL PLATFORM RESPONSE ANALYSES – ACCOUNTING FOR YIELDING AND SLACK TETHERS OF REAL FULL SCALE MODEL - SHALL ENSURE THAT THE HEIDRUN TLP WILL- WITH A REASONABLE MARGIN - WITHSTAND THE EXTERNAL FORCES CAUSING A DYNAMIC TETHER LOAD OF 36MN WHEN NO YIELDING IS ACCOUNTED FOR. AS A MEASURE OF A REASONABLE MARGIN 40MN DYNAMIC TETHER LOAD IS SUGGESTED. Heidrun TLP Model Tests - Summary

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