Pet.Sci.(1)7:547-554 DOI 1.17/s118-1-17-8 547 Model test investigation on an innovative lifting syste for deepwater riser installation Mao Dongfeng 1,, Duan Menglan, Wang Yi, He Ning 4, Chen Bangin and Zhang Yingjie 1 School of Mechanical Engineering, Yangtze University, Jinzhou Hubei 44, China Offshore Oil/Gas Research Center, China University of Petroleu, Beijing 149, China Departent of Naval Architecture & Ocean Engineering, Dalian University of Technology, Dalian, Liaoning 116, China 4 Offshore Oil Engineering Co., Ltd., Tanggu, Tianjin 45, China China University of Petroleu (Beijing) and Springer-Verlag Berlin Heidelberg 1 Abstract: An S-lay crane barge, naed CNOOC 1, has been built for pipe laying in deepwater oil/ gas fields in the South China Sea. It is due to be coissioned by the end of the year 1. A special lifting syste is developed to eet the challenge that installing deepwater risers fro an S-lay barge is difficult and has not been achieved. The purpose of this paper was to investigate the odel test on such an innovative syste, which has to be done before field application. By applying the siilarity theory, the oveent of the S-lay barge is siulated through a six degrees-of-freedo otion platfor, and a truncated odel riser is utilized for the odel testing. The displaceent and force boundary conditions at the truncated position of the riser are obtained fro the catenary governing equation and becoe realized by a slideway cart and a loading syste designed to control the configuration of the odel riser, which presents a siilar configuration to a real riser in deepwater. The test results are in very good agreeent with theoretical calculations, showing that the active truncated test is applicable for controlling the configuration of the deepwater riser in odel testing investigation. Key words: Deepwater riser, lifting syste, odel test, six degrees-of-freedo, otion platfor, active truncation 1 Introduction The field LW-1 is the first giant gas field to be discovered in deep water in China. An S-lay crane barge, naed CNOOC 1, has been built for pipe laying in deepwater (, ) in South China Sea and will be in operation in the end of the year 1 (Zhen, 8). It will play a very iportant role in the developent of the gas field LW-1. Copared with horizontal operations of pipe laying in an S-lay barge, vertical operations in a J-lay barge are uch ore practical for deepwater riser installation. In addition, it is difficult to transit the tension fro an S-lay barge to a production platfor in riser installation because of the big stinger syste at the barge rear (Bouwan, 7). A J-lay tower was taken into consideration in conceptual design of the CNOOC 1, but not accepted in detailed design. The J-lay tower design akes uch easier to perfor the installation of deepwater risers, while the S-lay design has never been used for such an operation. It has been well recognized that a ulti-functional barge is required to fulfill all operations in the developent of *Corresponding author. eail address: lduan@cup.edu.cn Received March 1, 1 offshore oil fields including pipeline/riser laying, installation of various kinds of subsea production hardware in order to save tie in offshore operations, and to reduce operational and capital expenses (OPEX and CAPEX). In such a case, a special lifting syste for deepwater riser installation for the CNOOC 1 was designed in reference to the technology of a J-lay syste (Jiang et al, 9; Duan et al, 1). The overall diension of the lifting syste is 5.6 4. 1.5 with a lifting capacity of up to 4 tonnes. The syste is to be positioned on the port side of the vessel and connected with the deck girder of the barge, as shown in Fig. 1. The success of such an innovative design not only satisfies the installation of risers but also eets the requireent of the subsea hardware such as pipeline end terination (PLET), pipeline end anifold (PLEM), subsea anifolds, jupers and spools (Duan, 1). The special lifting syste for deep water riser installation is large and coplex, withstanding loads not only fro lifting operation of the riser but also fro dynaics of the barge besides environental loads fro waves, currents and wind. The theoretical and nuerical calculations for the design of the syste are not sufficient for its developent, and odel testing has to be conducted to verify the perforance both in
548 Pet.Sci.(1)7:547-554 Fi lv v g Fr F gl gl Froude nuber for original prototype: v Fr gl Froude nuber for the odel: F * v ' r g ' l ' Froude nubers for original prototype and the odel should be the sae, i.e., (1) () () F r F * r (4) functional operations and in reliability of the whole syste. It is also iportant to get ore inforation and experience on how to operate such creative equipent for in-situ application. In this way, the siilarity theory is applied to siulate the oveent of the S-lay barge by using a six degrees-offreedo (6-DOF) otion platfor, and an active truncation test ethod is developed to odel the deepwater riser where the catenary governing equation is used for definition of the displaceent and force boundary conditions at the truncated position of the riser. To control the configuration of the odel riser, a slideway cart and a loading syste were designed. The results show that the active truncation test ethod is applicable for controlling the configuration of the deepwater riser in odel testing investigation. Model testing design The placeent of the lifting syste Fig. 1 The placeent of the lifting syste on the target vessel -CNOOC 1 To ake the odel size large enough to eet test requireents, a larger reduced scale of 1:1 is taken for a water depth of,. The following parts are detailed representation for the siilarity deduction, siulation of riser and boundary conditions at the truncated position, siulation of the vessel otion and of riser lifting, and schee of odel test..1 The siilarity deduction for the deepwater riser lifting syste The odel testing of the riser lifting syste is ainly concerned with the force due to gravity on the riser and the stresses in the lifting syste. Therefore, two π nubers are chosen in the test: one is the Froude nuber and the other the ratio of elastic force over inertia force (Л.И.СеДОВ, 198; Yang et al, 8). Gravity: F g = ρgl. Inertia force: F i = rl v. Elastic force: F s = Aσ. Froude nuber is defined as: Moreover, the force due to gravity is constant, i.e., g g '. Substituting this and Eqs. ()-() into Eq. (4) yields, v l (5) v' l' The ratio of elastic force to inertia force gives, * ' ' Fs A Fs A (6) * ' ' ' Fi l v Fi l v Thus, the ratio of the stresses in the odel to those of the initial prototype is, ' l ' (7) l Fro the siilarity criterion of gravity and inertia force, the reduced scale siilarity constants of tie, velocity and force can be derived. If the length siilarity constant between the odel syste and the prototype syste is 1:1, the other relative reduced scale siilarity constants in the test are shown in Table 1. Table 1 Reduced scale siilarity constants Paraeter Size Tie Velocity Force Mass Stress Siilarity constants.1...1.1.1. Siulation of deepwater riser by the active truncated test As well known, if the riser is odeled strictly in accordance with a reduced scale of 1:1, the odeled length of a, riser is still while the outer diaeter of 16 (46.4 ) and the wall thickness of. will be only 1.6 (4.64 ) and., respectively. This eans, it is ipossible to anufacture the odel riser with so sall a diaeter, and is not feasible to test so long a riser in the laboratory (Zhang et al, 9). Based on the hybrid odel test ethod (Watts, 1999; ; Chen et al, ), a truncated odel riser is taken for experiental siulation, i.e., the riser is cut off at a suitable height and the truncated riser is still scaled down with initial reduced scale. Although the odel riser is truncated, it shall take exactly the sae configuration of the real catenary riser.
Pet.Sci.(1)7:547-554 549 As presented in Fig., the riser is supposed to be cut off below the water surface. The truncated riser is scaled down strictly in a reduced scale 1:1, giving the values of the outer diaeter, thickness and the length of the truncated odel riser for a 16 riser respectively as 4.64,., and. The boundary conditions at the truncated position of the odel riser can be obtained fro the catenary forula as follows. T (x, y ) y θ y S S 1 T 1 θ 1 (x 1, y 1 ) Truncated position Eq. (1) shows that the dip angle of the riser top end in the new configuration can be deterined fro the lowering depth, and the coordinates (x, y), tip angle and axial tension force at an arbitrary position, can be obtained. Let the tip angle of a 16 riser at a water depth of, be 8, the riser be truncated at the position under water, and lowering depth be -, the lowering depth, horizontal coordinate x, axial tension and tip angle at the truncated position where y=97 can be solved fro Eqs. (8)-(1). In this way, the boundary conditions of the odel riser are obtained as shown in Table. Lowering depth h, Table Calculated boundary conditions of odel riser x-coordinate Axial tension T, kgf Tip angle at the truncated position T O x T 1 x 1 x x 15.5 16.5 79.916 5 15.58 15.616 8.7 Fig. Configuration of the catenary riser The initial configuration of the riser is deterined by the governing equation for the catenary (Pytel and Kiusalaas, 1994): S y y T T x ln ( y1) y1 1 T T y T 1 cos T y cos 1 cos (8) (9) (1) (11) where T is the axial tensile force, kgf; θ is the dip angle of the riser, degrees; T is the horizontal coponent force, kgf; S the length of the riser, ; and ω are the unit length weight of the riser, kgf/. Assuing that the riser is lowered fro state S to S 1, with a lowering depth of Δy, and keeping the length of the riser unchanged after lowering, i.e., x =Δx+Δx 1 +Δx and S =Δx+S 1, the catenary governing equation will yield a relation between the lowering depth and the top end dip angle of the riser after lowering as follows: 1 15.6 15.19 8.96 15 15.67 14.8 8.184 15.71 14.456 8.67 5 15.75 14.64 8.55 15.8 1.675 8.44. Siulation of the vessel otion Fig. shows the otion of a vessel in 6-DOF: three translations (surge, sway, heave) and three rotations (roll, pitch, yaw). A siulator was developed for the 6-DOF otion of any vessel (Zhang and Liu, 9; Yang et al, ; Furutani et al, 4; Greenberg et al, 4), and all data for the otion siulation of the CNOOC 1 barge were obtained as presented in Table fro hydrodynaic analysis of the S-lay barge in conditions of South China Sea (Gusto, 6): wind velocity of 16 /s, wave height H S of, wave period T of 6-9 s, current velocity of kn, wave spectru of Jonswap, and wave-to-course angle φ of -6. Assuing that the phase differences between different otions are all 9, all the paraeters for the odel testing can be obtained fro Table and are presented for all the 4 operating conditions in Table 4. y y cos x y y tan1 1 cos y cos y cos y y 1 1 1 1 1 1 1 1 1cos 1cos 1 cos1 1 cos 1 ln y1 1 y1 1 1 y1cos1 y1cos 1 (1) z Heave Yaw Cog Sway y Pitch Fig. The 6-DOF otion of the vessel Roll Surge x
55 Pet.Sci.(1)7:547-554 Condition No. Wave height H S, Table Barge otion references Heading Wave period T, s Heave aplitude Roll Pitch 1 9.46.75 45 9.47.9 1.14 9 9 1.69.7 4 9.4.77 5 45 9.47 1.1 1.7 6 9 9.8.7.4 Siulation of the riser lifting syste The overall diension of the odel lifting syste shown in Fig. 4 is.56.4 1.1 in 1:1 scale. During lifting operation, the tensile force in the Abandonent & Recovery (A&R) cable ay vary in a sall range because of the barge otion. It is necessary to easure the tensile force to deterine the variation range of the A&R cable in the absence of a constant tensioning syste. The easureent was perfored by using S-shape tension sensors equipped with an XSB5 digital onitor, as shown in Fig. 5. The riser will be held by its fixture as soon as it is lifted fro subsea to the syste. The barge oveent has Table 4 Test operational conditions Condition No. Wave height H S, Heading Wave period T, s Aplitude Heave Roll Pitch Phase Aplitude Phase Aplitude Phase 1.84.46.75.84.46 9.75.84.46 9.75 4.84.46.75 9 5 45.84.47.9 1.14 6 45.84.47 9.9 1.14 7 45.84.47.9 9 1.14 8 45.84.47.9 1.14 9 9 9.84.169.7 1 9.84.169 9.7 11 9.84.169.7 9 1 9.84.169.7 9 1 18.84.4.77 14 18.84.4 9.77 15 18.84.4 9.77 16 18.84.4.77 9 17 5.84.47 1.1 1.7 18 5.84.47 9 1.1 1.7 19 5.84.47 1.1 9 1.7 5.84.47 1.1 1.7 9 1 7.84.8.7 7.84.8 9.7 7.84.8.7 9 4 7.84.8.7 9
Pet.Sci.(1)7:547-554 551 A&R cable liiting device Riser fixture Main tower Hydraulic control syste Fig. 4 Riser lifting syste for odel testing A & R cable tension easuring position 5 Riser fixture Riser Fig. 5 A&R cable tension easuring position and S-shape tension sensor significant action on the riser especially when the riser has a dip angle, which will increase the stress state of the riser fixture requiring ore strain gauges to onitor the stress distribution of the fixture. Fig. 6 shows 5 strain gauge positions on the riser fixture..5 Overall design of the odel test syste The odel test syste is scheatically presented in Fig. 7. The odel of the special lifting syste for deepwater riser installation was set on the vessel siulator, a 6-DOF otion platfor. One end of A&R cable was connected to the odel riser and the other was reeled over large pulleys to be linked to the odel A&R winch. The functional testing such as riser lifting and lowering, tension converting and hanging up to the platfor, etc., was carried out, while forces and stress were recorded during the whole testing to verify the perforance of the developed innovative lifting syste. During the test, the configuration of the truncated odel riser was strictly controlled all the way to the end of testing. Recovering of the axial force at the botto of the riser was achieved by a balance weight hanging by a steel cable, and the truncated position was always kept by the electric cart on slideway.
55 Pet.Sci.(1)7:547-554 5 4 1 Fig. 6 Sketch of strain gauge positions on the riser fixture 1 7 8 4 1 9 5 6 Fig. 7 Scheatic presentation of the odel test syste 1. Model,. A&R winch,. Vessel siulator, 4. Model riser, 5. Electric cart, 6. Slideway, 7. Target platfor, 8. Platfor A&R winch, 9. Support tower, 1. Balance weight Test results and discussion During the test, the odel riser was lifted, placed on the riser fixture and installed to the odel platfor successfully, and the riser and A&R cable did not touch the odel lifting syste at all. All these operations showed that the A&R cable liiting device was in effect, tension transition was successful and all functions of designed riser lifting syste for deepwater riser installation were achieved. The results on tensions in the A&R cable and stresses in the riser fixture under 4 operating conditions are listed in Table 4. The tensions in the A&R cable are shown in Fig. 7. Fig. 8 shows that the tension in the A&R cable was ainly controlled by the heave otion of the barge, and, the larger the heave aplitude, the bigger the variation range of the tension. Therefore, the stress variation range can be used to deterine the lifting capacity of the A&R winch and to check if the heave copensation could eet the requireents of all the operations. Fro Fig. 8, it can be seen that the axiu tension variation in the A&R cable reached 16 kgf, and the Tension, kgf 5 48 46 44 4 4 8 6 4 Max. tension Min. tension 4 6 8 1 1 14 16 18 4 Operating coditions Fig. 8 Tension in the A&R cable in different operating conditions total weight of the riser to be lifted is recoended to be less than tonnes. The ultiate bearing capacity of 4 tonnes of the A&R winch is enough for lifting risers of 16 inches in, deep water.
Pet.Sci.(1)7:547-554 55 The finite eleent nuerical siulation under operating condition 4, which is one of the ost severe conditions, was conducted, and the results for the riser fixture are shown in Table 5 and Fig. 9. The scaled down load was adopted in the siulation. Table 5 Nuerical siulation results of the riser fixture at easuring positions Measuring position 1 4 5 Stress, MPa 1. 4.9 1. 4.9 6.8 The recorded peak stresses at 5 positions obtained fro the tests under different operating conditions are shown in Figs. 1-1. It can be seen that ost of the stress peaks at different positions of the riser fixture are saller than calculated values except under several severe operating conditions. Many factors ay affect the test results, for exaple, adhesive effect of the strain gauges to the surface of the fixture or signal noise caused by electrical interference in the test field. However, the difference between the easured and calculated values is not large and the largest deviation does not exceed 5% of the calculated value. It is also proved that the input boundary conditions at the truncated position of the riser properly fit the initial configuration of the riser. S, Mises Multiple section points (Avg:75%) +.118e+7 +1.94e+7 +1.765e+7 +1.589e+7 +1.41e+7 +1.6e+7 +1.59e+7 +8.87e+6 +7.61e+6 +5.96e+6 +.51e+6 +1.766e+6 +5.785e+ ODBccc.odb Abaqus/Standard 6.9-1 Tue May 5 15 14 4 GMT+8 1 X Y Z Stepstep-1 Increent 1Step Tie=1. Priary VarS, Mises Defored VarU Deforation Scale Factor+1.e+ Fig. 9 Stress cloud chart of the riser fixture 11 1 Peak at position 1 Peak at position Calculated value at positions 1 and 6 5 Peak at position Peak at position 4 Calculated value at positions and 4 Stress, MPa 9 8 Stress, MPa 4 7 6 4 6 8 1 1 14 16 18 4 Operating conditions Fig.1 Measured and calculated values at positions 1 and 4 6 8 1 1 14 16 18 4 Operating conditions Fig.11 Measured and calculated values at positions and 4
554 Stress, MPa 7.4 7. 7. 6.8 6.6 6.4 6. 6. 4 Conclusions The odel test of the special lifting syste for deepwater riser installation is one of the ost iportant parts in deepwater riser installation technologies. The active truncated test developed in this paper for the odel testing has proved to be an effective eans for solving the difficulties in odeling so long and thin walled risers in deepwater. By applying the theory of siilarity, the transferred control paraeters are input to the 6-DOF Stewart platfor and truncated position of the odel riser in a odel scale of 1:1 for the testing investigation. The ethod presented in this paper can accurately siulate lay barge oveent and aintain the configuration of riser during the whole tests. The odel test results provide very valuable inforation for application of the special lifting syste for deepwater riser installation. And in this way, large tanker testing is avoided which is tie-consuing and expensive. Acknowledgeents Peak at position 5 Calculated value at position 5 4 6 8 1 1 14 16 18 4 Operating conditions Fig.1 Measured and calculated values at position 5 The authors are grateful for the financial support fro the National Natural Science Foundation of China (granted nuber 597911), and the National 86 Progra of China (granted nuber 6AA9A15). Sincerely thanks go to the colleagues in the COOEC Ltd. (Offshore Oil Engineering Corporation Ltd.) and in the Offshore Oil/Gas Research Centre, China University of Petroleu, Beijing, who are involved in this wide range of research. References Pet.Sci.(1)7:547-554 Bou wan J. Installation challenges with lifting and pull-in of the SCR. Paper SPE 1961 presented at Offshore Technology Conference, April- May 7, Houston, Texas Che n X, Zhang J, Johnson P, et al. Studies of the dynaics of truncated ooring line. The 1th ISOPE Conference, Seattle, USA,. 94-11 Dua n M L. A lifting syste for installation of deeperwater risers and subsea hardware. The 1 SUT Technical Conference, Society for Underwater Technology, March -4, 1, Rio de Janeiro, RJ, Brazil Dua n M L, Wang Y and Estefen S. Soe recent advances in installation of deepwater risers. China Ocean Engineering. 1. 4(4): in press (in Chinese) Fur utani K, Suzuki M and Kudoh R. Nanoetre-cutting achine using a Stewart-platfor parallel echanis. Measureent Science and Technology. 4. 15: 467-477 Gre enberg J A and Park T J. The Ford driving siulator. SAE Technical Paper Series. 4. (94): 176 Gus to B V. Vessel DP and otion analysis calculation report. Deepwater Pipelay Crane Vessel DPV75C. 6. 46-51 Jia ng X Z, Li Z G, He N, et al. A new lifting syste for installation of risers in deeper water. Proceedings of ISOPE-IDOT 9, Beijing, China, June 8-July 1, 9 Pyt el A and Kiusalaas J. Engineering Mechanics: Statics and Dynaics. New York: Harper Collins College Publishers. 1994. 84- Wat ts S. Hybrid hydrodynaic odeling. Journal of Offshore Technology. 1999. 7(1): 1-14, 16-17 Wat ts S. Siulation of etocean dynaics: Extension of the hybrid odeling technique to include additional environental factors. The SUT Workshop: Deepwater and Open Oceans, the Design Basis for Floaters, Houston, TX, USA, Yan g J M, Xiao L F and Sheng Z B. Hydrodynaic experient investigation of ocean engineering. Shanghai: Shanghai Jiao Tong University Press. 8. 1 Yan g S X, Yang T and Xun Y T. The developent of the digital six-dof stewart platfor. Hydraulics & Pneuatics.. (8): 46-47 (in Chinese) Zha ng H M, Sun Z L, Yang J M, et al. Investigations into optiization design of equivalent water depth truncation. Science in China. 9. 9 (4): 5-56 (in Chinese) Zha ng Z and Liu S J. Research into a siulation experiental schee of heave copensation in deep sea ining. Modern Manufacturing Engineering. 9. (1): 116-1 (in Chinese) Zhen J W. CNOOC 1 begins to be built in the Rongsheng Heavy Industries Group Co. Ltd. Nantong Daily. Septeber 17, 8 (in Chinese) Л.И. СеДОВ. Siilitude Methodology and Theory of Diension in Mechanics. Beijing: Science Press. 198. 45-7 (in Chinese) (Edited by Sun Yanhua)