December 2003Heidrun TLP Model Tests - Summary1 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 Phase 2 – Examples, results and conclusions Comparison with original design values

December 2003Heidrun TLP Model Tests - Summary2 Background and Aim More severe accidental wave conditions (i.e. wave conditions corresponding to an annual probability of ) are predicted. Significant wave height increased from 18.6m to 20m. (ULS sea state conditions (10 -2 ) are more or less as before, increased from 15.5m 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 response in all structural elements mentioned above. Phase 1 should identify the critical 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.

December 2003Heidrun TLP Model Tests - Summary3 Heidrun TLP

December 2003Heidrun TLP Model Tests - Summary4 Test Model

December 2003Heidrun TLP Model Tests - Summary5 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

December 2003Heidrun TLP Model Tests - Summary6 SENSORS FOR MEASURING DECK IMPACTS

December 2003Heidrun TLP Model Tests - Summary7 ENVIRONMENTAL CONTOUR LINES FOR SEA STATE CHARACTERISTICS H s and T p HEIDRUN SITE

December 2003Heidrun TLP Model Tests - Summary8 Contour lines for individual wave parameters, H and T

December 2003Heidrun TLP Model Tests - Summary9 Example from Test 2111 Regular waves with height 20m and period 11s

December 2003Heidrun TLP Model Tests - Summary10 Example from Test 2750 Regular waves with height 35m and period 16.5s

December 2003Heidrun TLP Model Tests - Summary11 MAX TETHER LOAD FOR REGULAR WAVES Note: Given height and period are target values, actual values may differ somewhat, especially for the height.

December 2003Heidrun TLP Model Tests - Summary12 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, h s = 20m and t p = 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.

December 2003Heidrun TLP Model Tests - Summary13 WAVE SPECTRUM OF CRITICAL ALS SEA STATE Note combined nature of sea state (swell + wind sea)

December 2003Heidrun TLP Model Tests - Summary14 Example from Test 3010 Irregular sea states with h s =12.3m and t p =11s

December 2003Heidrun TLP Model Tests - Summary15 Example from Test 3060 Irregular sea state with h s =17.5m and t p =15.5s

December 2003Heidrun TLP Model Tests - Summary16 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, 4022,4030,4040,4050 hs=17.5m, tp=15.5s: 3060,3070,3080,3090, 4060,4070,4080,4090 hs=18.8m, tp=17s: 3110,3120,3130,3140, 4110,4120,4130,4140 hs=19.8m, tp=18.5s: 3150,3160,3170,3180, 4150,4160,4170,4180 hs=20m, tp=20s: 3210,3220,3231,3240, 4210,4221,4231,4240 hs=19m, tp=22s: 3250,3260, 4250, , 3242: Repeating 3240 to check repeatability. 3310, 3320,3330: Repeating 3240 with wind/current induced offset: 10m, 22.5m, 30m 3340: Repeating 3140 with offset 30m, 3510: Repeating 3010 with offset 0m 3410: Repeating 3240 with no deck. 4310, 4324,4333: Repeating 4240 with offset: 10m, 22.5m, 30m 4341: Repeating 4140 with offset 30m.

December 2003Heidrun TLP Model Tests - Summary17 MAX TETHER TENSION PHASE 1 TESTS – 270deg.

December 2003Heidrun TLP Model Tests - Summary18 MAX TETHER TENSION PHASE 1 TESTS – 315deg.

December 2003Heidrun TLP Model Tests - Summary19 AIRGAP AT FRONT OF MSB_WEST – 270deg. Wave crest reaches MSB for an airgap less than 8.5m

December 2003Heidrun TLP Model Tests - Summary20 AIRGAP IN FRONT OF MSB_EAST – 270 deg. Wave crest reaches MSB for an airgap less than 8.5m

December 2003Heidrun TLP Model Tests - Summary21 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

December 2003Heidrun TLP Model Tests - Summary22 AIRGAP AT TWO LIFE BOAT POSITIONS – 315 deg. NORTH WEST CORNER NORTH BETWEEN MSBs

December 2003Heidrun TLP Model Tests - Summary23 AIRGAP AT FRONT OF MSB-WEST – 315 deg. Wave crest reaches MSB for an airgap of less than 8.5m

December 2003Heidrun TLP Model Tests - Summary24 CONCLUSIONS OF PHASE 1 The most critical ”10 -4 sea state” is the sea state defined by h s =20m and t p =20s. Large tether loads are also observed for a sea state defined by h s =18.8m and t p =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.

December 2003Heidrun TLP Model Tests - Summary25 HORISONTAL DECK IMPACT VERSUS UNDISTURBED CREST HEIGHT Phase 1 and Phase 2 results 270deg. Wave4_Cal: Undisturbed incoming crest height at nominal position of MSB_west

December 2003Heidrun TLP Model Tests - Summary26 VERTICAL VERSUS HORISONTAL IMPACT LOAD Phase 1 and Phase 2 results, 270 deg.

December 2003Heidrun TLP Model Tests - Summary27 HISTOGRAM DECK IMPACT LOADS 3-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 NEED OF 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 SEA STATE AS AN ADEQUATE ESTIMATE OF THE 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.

December 2003Heidrun TLP Model Tests - Summary28 3-HOUR EXTREME VALUE DISTRIBUTION FOR DECK IMPACTS 90% FRACTILE: 2.25 ALS DESIGN IMPACTS: FY_MAX = 150MN FZ_MAX = 130MN 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. 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.

December 2003Heidrun TLP Model Tests - Summary29 DECK IMPACT AND TETHER RESPONSE Example 2

December 2003Heidrun TLP Model Tests - Summary30 TETHER TENSION VERSUS DECK IMPACTS WAVE DIRECTION: 270 DEG. For a horisontal impact load of 150MN (ALS-impact), the corresponding tether force is likely to be between 225 and 250MN. For a vertical impact load of 130MN (ALS-impact), the corresponding tether force is expected to be between 210 and 250MN. Estimated ALS impact

December 2003Heidrun TLP Model Tests - Summary31 HISTOGRAM 3-HOUR MAX TETHER LOAD Large scatter is observed, Consequently a higher fractile has to be selected as the proper estimate of tether load. (See comments on slide no. 27.)

December 2003Heidrun TLP Model Tests - Summary32 HISTOGRAM 3-HOUR MIN. TETHER LOAD

December 2003Heidrun TLP Model Tests - Summary33 3-HOUR EXTREME VALUE DISTRIBUTION TETHER LOAD (4 TETHERS) 90% FRACTILE: 2.25 ALS TETHER LOAD, AUTUMN 2003: 4 TETHERS: 250MN PR. TETHER: 62.5MN ALS ORIGINAL DESIGN: PR. TETHER: 52.2MN NB!NB! MORE WEIGHT IS GIVEN TO UPPER TAIL WHEN CHARACTERISTIC VALUES ARE SELECTED, SEE ALSO SLIDE No % FRACTILE ASSUMED TO ACCOUNT PROPERLY FOR SCATTER AROUND THE MEAN. (See slide no.27)

December 2003Heidrun TLP Model Tests - Summary34 EXAMPLE 1: EFFECT OF DECK IMPACT ON TETHER LOADING

December 2003Heidrun TLP Model Tests - Summary35 BUDGET ALS MAX TETHER LOAD (The last column will be updated as the results from Phase 2 is properly analysed.) SOURCEORIGINAL DESIGN MODEL TEST 2003 (PRELIMINARY APPROXIMATE NUMBERS EXCEPT THE SUM) WAVE SLAMMING INDUCED RINGING (INCL. AS STATIC LOAD IN ORIGINAL DESIGN) 0.6 MN20-30MN DYNAMIC LOAD, EXCL. RINGING7MN8MN CLASSICAL RINGING20MN20MN (*) SUM DYNAMIC27.5MN36MN SUM TOTAL52.5MN62MN (Preliminary) A CONSIDERABLE INCREASE IN THE DYNAMIC LOAD IS ESTIMATED (*) Based on tests with and without deck, at present no reason to change original ringing estimate. Further data analysis will be carried out.

December 2003Heidrun TLP Model Tests - Summary36 CONCLUSIONS OF TESTS 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 (H S =20m and T P =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.