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Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
Structural Design of Drill Ships
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Structural Design of Drill Ships

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Set of presentations delivered by Torbjorn Lindemark at the seminar "Structural Design of Drill Ships", in Rio de Janeiro, July 3 2012

Set of presentations delivered by Torbjorn Lindemark at the seminar "Structural Design of Drill Ships", in Rio de Janeiro, July 3 2012

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  • 1. Structural design of drill shipsChallenges and requirements
  • 2. AGENDA  09:00 Welcome and introduction  09:30 Sesam for offshore floaters  10:00 Challenges and requirements  10:30 Coffee break  10:45 Hydrodynamic analysis  11:15 Finite element modelling and analysis  12:15 Lunch  13:30 Yield and buckling strength checks  14:00 Fatigue analysis methods  14:30 Coffee break  14:45 Simplified fatigue analysis  15:15 Spectral fatigue analysis  16:00 Closing remarksStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 2
  • 3. Typical arrangement Derrick Heli-deck Gantry cranes Drill floor Riser stack Moonpool ThrustersStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 4
  • 4. Hull strength requirements Derrick Heli-deck Cranes Drill floor Riser stack Moonpool ThrustersStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 5
  • 5. Challenges and high focus areas Drill floor support Crane foundation Structural discontinuities Moonpool cornersStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 6
  • 6. Hull and derrick interface Effect of hull deformationsStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 7
  • 7. Rules and regulations for structural design of drill ships  IMO MODU code  DNV-OS-C102 Structural design of offshore ships  ABS: Guide for Building and Classing of Drillships – Hull Structural Design and Analysis Required analysis Optional approach • Wave load analysis • Global FE analysis • Cargo hold FE analysis • Direct load application from • Local FE analysis for ultimate wave load analysis strength and fatigue • Spectral fatigue calculations • Simplified fatigue calculationsStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 8
  • 8. Analysis options and related software from DNV Software Analysis type DNV ship rules and Other class offshore standards (ABS, LR, …) Rule based calculations Nauticus Hull not supported Direct load calculations Sesam HydroD Direct strength calculations, FEA Sesam GeniE Plate code check Sesam GeniE Spectral fatigue calculations Sesam HydroD + GeniEStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 9
  • 9. Design conditions and loads – DNV-OS-C102 Design Wave data Load cases Load basis Load probability condition Heading profile Ship rules IACS North Atlantic Rule pressures 10-4 Transit Ship rules Direct for topside acc. All headings Accelerations 20 years Max draught Max Hs for drilling Drilling Direct calculations 3 hrs short term Min draught Specified heading profile Max draught North Atlantic or design limit Survival Direct calculations 100 years Min draught Specified heading profile  Fatigue design criteria - Minimum 20 years - World wide scatter diagram for transit condition - Site specific scatter diagram for operation (world wide for unrestricted service) - Load probability 10-4 - 80 % operation (unless specified) - 20 % transit (unless specified)Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 10
  • 10. Scope of direct strength calculations – ultimate strength  Hull strength - Cargo hold analysis - Optional: Full ship analysis  Local analysis - Toe of girder bracket at typical transverse web frame - Toe and heel of horizontal stringer in way of transverse bulkhead - Opening on main deck, bottom and inner bottom, e.g. moonpool corner. - Drill floor and support structure - Topside support structure - Crane pedestal foundation and support structure - Foundations for heavy equipment such as BOP, XMAS, mud pumps, etc - …Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 11
  • 11. Scope of direct strength calculations – fatigue strength  Hull - Openings on main deck, bottom and inner bottom structure including deck penetrations - Longitudinal stiffener end connections to transverse web frame and bulkhead - Shell plate connection to longitudinal stiffener and transverse frames with special consideration in the splash zone. - Hopper knuckles and other relevant discontinuities - Attachments, foundations, supports etc. to main deck and bottom structure openings and penetrations in longitudinal members.  Topside supporting structure - Attachments, foundations, supports etc. to main deck and hull - Hull connections including substructure for drill floor - Topside stool and supporting structures - Crane pedestal foundation and supporting structures.Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 12
  • 12. My drillshipStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 13
  • 13. Main dimensions and design conditions  Main dimensions  Unrestricted service - Rule length 240 m - Fatigue world wide - Breadth 43 m - Survival North Atlantic - Scantling draught 15 m  Max sea state for drilling operation - Block coefficient 0.89 - Hs = t m  Load conditions  Heading profile - Transit T=10 m - 60 % head sea - Drilling and survival T=12m - 30 % ± 15 degrees  Hull girder limits - 10 % ± 30 degrees - Stillwater sagging Ms -2330500 kNm - Stillwater hogging Ms 1923560 kNmStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 14
  • 14. My tools – Sesam HydroD for wave load analysisStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 15
  • 15. My tools – Nauticus Hull for rule strength calculationsStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 16
  • 16. My tools – Sesam GeniE for direct strength calculationsStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 17
  • 17. Safeguarding life, property and the environment www.dnv.comStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 18
  • 18. Structural design of drill shipHydrodynamic analysis
  • 19. AGENDA  09:00 Welcome and introduction  09:30 Sesam for offshore floaters  10:00 Challenges and requirements  10:30 Coffee break  10:45 Hydrodynamic analysis  11:30 Finite element modelling and analysis  12:15 Lunch  13:30 Yield and buckling strength checks  14:00 Fatigue analysis methods  14:30 Coffee break  14:45 Simplified fatigue analysis  15:15 Spectral fatigue analysis  16:00 Closing remarksStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 2
  • 20. Design conditions and loads – DNV-OS-C102 Design Wave data Load cases Load basis Load probability condition Heading profile Ship rules IACS North Atlantic Rule pressures 10-4 Transit Ship rules Direct for topside acc. All headings Accelerations 20 years Max draught Max Hs for drilling Drilling Direct calculations 3 hours short term Min draught Specified heading profile Max draught North Atlantic or design limit Survival Direct calculations 100 years Min draught Specified heading profile  Fatigue - World wide scatter diagram (for unrestricted service) - Load probability 10-4 - 80 % operation - 20 % transitStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 4
  • 21. Scope of hydrodynamic analysis Transit Drilling Survival Scatter diagram ULS: North Atlantic Max specified Hs Site specific Fatigue: World wide Unrestricted: North Atlantic Wave spreading Short-crested cos2 Short-crested cos2 Long-crested Heading profile All headings 60 % head sea 60 % head sea 30 % ± 15 degrees 30 % ± 15 degrees 10 % ± 30 degrees 10 % ± 30 degrees Calculation scope Topside accelerations Topside accelerations Topside accelerations Wave bending moment Bending moment Pressures Probability level ULS: 20 years 3 hrs short term 100 years Fatigue: 10-4 Fatigue: 10-4 Fatigue: 10-4Structural design of drill ship© Det Norske Veritas AS. All rights reserved. 5
  • 22. Hydrodynamic analysis Sesam HydroDStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 6
  • 23. HydroD  Key features - Hydrostatics and stability calculations - Linear and non linear hydrodynamics  Benefits - Handling of multiple loading conditions and models through one user interface and database - Sharing models with structural analysis - Direct transfer of static and dynamic loads to structural modelStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 7
  • 24. Hydrodynamic Analysis Model requirements Challenges  Hull shape as real ship  Obtain correct weight and mass distribution  Correct draft and trim  Balance of loading conditions  Weight and buoyancy distribution according to loading manual  Mass and buoyancy in balanceFPSO Full Ship Analysis© Det Norske Veritas AS. All rights reserved. 8
  • 25. HydroD models  Environment - Air and water properties - Water depth - Wave directions - Wave frequencies  Hull geometry - Panel model - Morrison model  Mass distribution - Compartments - Mass model  Structural model - For load transferStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 9
  • 26. Panel modelStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 10
  • 27. Panel model guidelines  Mesh size - In general depending on wave length (length < L/5) - At least 30-40 panels along the ship length - Wave period = 4s  wave length = 25m  panel length = 5m - Mesh size finer - Towards still water level - Towards large transitions in shape - Not too coarse in curved areas, in order to compute correct volume  If shallow water - Use ½ or even ¼ panel length. Test convergence!Structural design of drill ship© Det Norske Veritas AS. All rights reserved. 11
  • 28. Hull modelling in GeniE  Model from scratch  Import DXF  Import from Rhino – plug-in available with GeniE 6.3Structural design of drill ship© Det Norske Veritas AS. All rights reserved. 12
  • 29. Import DXF – a typical tankerConvert model to GeniE format6 June 2012© Det Norske Veritas AS. All rights reserved. 13
  • 30. Import lines from Rhino Rhino model GeniE lines GeniE mesh GeniE surfaceConvert model to GeniE format6 June 2012© Det Norske Veritas AS. All rights reserved. 14
  • 31. Mass modelStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 15
  • 32. Mass model alternatives With sectional loads: No sectional loads:  Alternatives  Alternatives - FE model (beam/shell/solid) - Direct input of global mass data - Point mass model - Direct input of mass matrix - Structure model  Requirements  Requirements - Vertical and transverse centre of gravity - Vertical and transverse centre of gravity - Roll radius of gyration - Transverse centre of gravity - Longitudinal mass distribution - Roll radius of gyration and inertia - Pitch radius of gyration and inertiaStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 16
  • 33. Example of mass models Direct input Beams with varying density Mass points Structural model and compartmentsStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 17
  • 34. Verification of still water loads  The mass and buoyancy forces may be verified by computing the still water forces and moments - HydroD stability analysis (requires a license extension for stability)  When the environment, models and loading conditions are defined, a stability analysis may be run ?Structural design of drill ship© Det Norske Veritas AS. All rights reserved. 18
  • 35. EnvironmentStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 19
  • 36. Wave headings  Typically 15-30 degrees interval  Head sea = 180 degrees  Short crested sea requires main headings ±90 degrees - Transit 0-360 degrees - Operation and survival 180 ± 120 degrees (120=30+90)Structural design of drill ship© Det Norske Veritas AS. All rights reserved. 20
  • 37. Wave frequencies  Define 25-30 periods, say from 4 – 40 s  Ensure good representation of relevant responses, including peak valuesStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 21
  • 38. Roll dampingStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 22
  • 39. About roll damping  Roll damping is non-linear and must be linearized for a frequency domain analysis  Linearization according to probability level of design value - 20 years for transit - 100 years for survival - 10-4 for fatigue  Long and short term statistics sensitive to roll if eigenperiod if there is significant wave energy in the range of the eigen period 12,00 10,00 8,00 No damp 6,00 5% 10 % 4,00 2,00 0,00 0 5 10 15 20 25 30 35 40Structural design of drill ship© Det Norske Veritas AS. All rights reserved. 23
  • 40. Roll damping options  Use an external damping matrix - General or critical  Use the roll damping model in Wadam - Requires an iteration since maximum roll angle is a parameter - If maximum roll angle is from short term statistics, automatic iteration can be performed - If maximum roll angle is from long term statistics, manual iterations must be performed  Use the quadratic roll-damping coefficient - Typically obtained from model tests - Requires short term stochastic iteration  Use Morison elements - Tune drag coefficient to obtain correct damping Only option 4 allows for load transfer of the roll-damping forceStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 24
  • 41. Load cross sectionsStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 25
  • 42. Sectional loads  Calculating of global shear forces and bending moment distribution along vessel - Stillwater loads - Wave loads  Z-coordinate = Neutral axis of structure, not waterline (or any other position) - Sectional loads include horizontal pressure components  sensitive to location of z- coordinateStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 26
  • 43. PostprocessingStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 27
  • 44. Basic highlights – Postresp  Plotting of response variables – RAO (HW(ω))2  Combinations of response variables  Calculating short-term response  Calculating long-term statistics Hydrodynamic analysis Seastate Transfer function Short term Response Postresp short term Long term Response Scatter diagram Postresp long termStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 28
  • 45. Statistical computations  Short term statistics - For a given duration of a sea state - Compute most probable largest response - Compute probability of exceedance - No. of zero up-crossings - For a given response level - Compute probability of exceedance - For a given probability of exceedance - Compute corresponding response level - For a given duration and probability level - Compute response level - Compute probability of exceedance  Long term statistics - Assign probability to each direction - Select scatter diagram - Select spreading function - Create long-term responseStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 29
  • 46. Demo of HydroDStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 30
  • 47. Topics  Panel model  Mass model  Balancing  Hydrodynamic analysis  Post processingStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 31
  • 48. Safeguarding life, property and the environment www.dnv.comStructural design of drill ship© Det Norske Veritas AS. All rights reserved. 32
  • 49. Structural design of drill shipsFinite element modelling and analysis
  • 50. AGENDA  09:00 Welcome and introduction  09:30 Sesam for offshore floaters  10:00 Challenges and requirements  10:30 Coffee break  10:45 Hydrodynamic analysis  11:30 Finite element modelling and analysis  12:15 Lunch  13:30 Yield and buckling strength checks  14:00 Fatigue analysis methods  14:30 Coffee break  14:45 Simplified fatigue analysis  15:15 Spectral fatigue analysis  16:00 Closing remarksStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 2
  • 51. Cargo hold analysis  Minimum extent = moonpool + one hold fwd and aft - Longer often needed due to non-regular structure  Mesh size: stiffener spacing Derrick Heli-deck Gantry cranes Drill floor Riser rack Moonpool ThrustersStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 4
  • 52. Local FE models  Mesh size - Local yield: 50x50, 100x100 or 200x200 - Fatigue: t x t Derrick Deck openings Drill floor foundation Crane foundation Moonpool cornersStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 5
  • 53. Hull and derrick interface Derrick design Fy Fx Fz Fy Fx FzStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 6
  • 54. Derrick loads and accelerations Hook load (drilling string) Inertia loads Riser tension Design Static loads [t] Topside acceleration condition Mass Hook load Riser tension av at al Transit 2000 1.70 4.42 2.70 Drilling 2100 1500 1250 0.64 0.77 1.11 Survival 2100 1.52 2.62 2.10Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 7
  • 55. Overview of load cases  Hull strength, transverse structure - Ship rules (transit conditions)  Hull girder longitudinal strength - Drilling: Longitudinal structure (head seas, direct) - Survival: Longitudinal structure (head seas, direct)  Topside and support structure in transit (all headings) - Head sea - Beam sea - Oblique sea  Topside and support structure in drilling and survival (heading profile) - Max longitudinal acceleration - Max transverse acceleration - Max vertical accelerationStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 8
  • 56. Load cases – hull strength Design Load basis Load case Global loads Pressure Derrick and topside condition Transit Rule Rules Rules Rules Vertical forces Max draught Max sagging Static - dynamic Drilling Direct, max Hs Vertical forces Min draught Max hogging Static + dynamic Direct Max draught Max sagging Static - dynamic Survival Vertical forces North Atlantic Min draught Max hogging Static + dynamic My drillship: Design Load basis Load case Global loads Pressure Derrick force condition (bilge) Drilling Sag: -6 780 383 180 Transit Rule Fz = 23 012 Transit Hog: 6 221 616 130 Max draught Sag: -4 539 500 90 Fz = 50 696 Drilling Direct, max Hs Min draught Hog: 4 132 560 160 (incl. hook and riser) Direct Max draught Sag: -8 342 000 60 Survival Fz = 23 787 North Atlantic Min draught Hog: 6 842 060 190Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 9
  • 57. Load cases for topsides – Transit Topside loads Load case Max response Hull girder loads av at al Wind Sagging Ms + Mw 0.5 0.0 -r 1Head sea Hull deflection Hogging Ms + Mw -0.5 0.0 +r 1 Hogging Ms + a * Mw 1.0 1.0 -c 1Beam sea Transverse acceleration Hogging Ms + a * Mw 1.0 -1.0 -c 1 Longitudinal acceleration Hogging Ms + h * Mw +j 0.4 1.0 1Oblique sea Sagging Ms + k * Mw +m 1.0 0.9 1 Transverse acceleration Sagging Ms + k * Mw +m -1.0 0.9 1 L < 100 100 < L < 200 L > 200 a 0.9 = -0.004 L + 1.3 0.5 h 0.7 = 0.002 L + 0 .5 0.9 k 0.4 = -0.003 L + 0.7 0.1 c 0.4 = -0.003 L + 0.7 0.1 j 0.2 = -0.002 L + 0.4 0 m 0.7 = -0.004 L + 1.1 0.3 r 1 = -0.004 L + 1.4 0.6Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 10
  • 58. Topside interface loads – Transit Topside loads Heading Max response Hull girder loads Fx Fy Fz Sagging -6 780 383 -3235 0 21316 Head sea Hull deflection Hogging 6 221 616 3235 0 17924 Hogging 4 072 588 -539 8840 23012 Beam sea Transverse acceleration Hogging 4 072 588 -539 -8840 23012 Longitudinal acceleration Hogging 5 791 810 5392 3536 19620 Oblique sea Sagging -2 775 488 4853 8840 20638 Transverse acceleration Sagging -2 775 488 4853 -8840 20638Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 11
  • 59. Load cases for topsides – Drilling and survival Topside loads Max response Hull girder loads av at al Wind Longitudinal acceleration Sagging Ms + Mw -b -c 1.0 1 Transverse acceleration Hogging Ms + Mw 0.8 1.0 -e 1 Vertical acceleration Hogging Ms + Mw 1.0 +f -g 1 L < 100 100 < L < 200 L > 200 b 0.5 = 0.003 L + 0.2 0.8 c 0.6 = -0.002 L + 0 .8 0.4 e 0.6 = 0.004 L + 0.2 1,0 f 0.8 = -0.005 L + 1.3 0.3 g 0.6 = 0.004 L + 0.2 1.0Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 12
  • 60. Topside interface loads – Drilling and survival Hull girder loads Topside loads Drilling Hogging Sagging Fx Fy Fz Longitudinal acceleration 2323 647 46499 Transverse acceleration 4 132 560 -4 539 500 2323 1619 48658 Vertical acceleration 2323 486 48928 Hull girder loads Topside loads Survival Hogging Sagging Fx Fy Fz Longitudinal acceleration 4406 2203 18052 Transverse acceleration 6 842 060 -8 342 000 4406 5508 23150 Vertical acceleration 4406 1652 23787Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 13
  • 61. Combination of topside loads – Drilling and survival Topside loads Hull girder loads Fx Fy Fz Local loads + + - + - - Hogging - + - - - - Tank pressure + + - Sea pressure + - - Sagging - + - - - -Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 14
  • 62. Final load cases for topside supports Topside loads Drilling Fx Fy Fz Local loads 2323 1619 2323 -1619 Hogging 4 132 560 -2323 1619 Tank -2323 -1619 -48928 pressure 2323 1619 Sea pressure 2323 -1619 Sagging -4 539 500 -2323 1619 -2323 -1619 Topside loads Survival Fx Fy Fz Local loads 4406 5508 4406 -5508 Hogging 6 842 060 -4406 5508 Tank -4406 -5508 -23287 pressure 4406 5508 Sea pressure 4406 -5508 Sagging -8 342 000 -4406 5508 -4406 -5508Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 15
  • 63. Application of loads and boundary conditions Hook load Inertia loads cog Riser tension Global bending Pressures Note! Target bending moment to be adjusted for applied VBM from other loads Applied VBM = Target VBM ÷ VBM pressures ÷ VBM forcesStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 16
  • 64. Cargo hold analysis Nauticus Hull Sesam GeniEStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 17
  • 65. Nauticus Hull  Hull strength calculations according to DNV rules and IACS common structural rules  Section Scantlings - Global and local strength rule check and scantling calculations - Fatigue calculations of longitudinals  Rule Check XL - Suite of Excel based analysis programs for various rule check calculations  FEA interface to Sesam GeniE - Transfer and extruding cross sections - Generation of rule loads, boundary conditions, sets and corrosion additions to cargo hold modelsStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 18
  • 66. Sesam GeniE  Finite element program purpose-made for ship and offshore structures - Modelling with beams and/or plates - Load application - Structural analysis - Eigenvalue analysis - Wave load analysis for slender structures - Pile and soil analysis - Code checksStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 19
  • 67. Cargo hold analysis workflow Cross section Rule loads Nauticus Hull: Extruded section Concept model GeniE:Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 20
  • 68. GeniE Concept Model Compartments Concept Model Corrosion Addition Structure TypeStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 21
  • 69. GeniE Concept Model GeniE Local pressure loads Hull Girder loads (Slicer) Concept ModelStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 22
  • 70. GeniE Concept Model GeniE Mesh Linear analysis Concept Model Capacity model for buckling analysisStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 23
  • 71. Local modelling Sesam GeniEStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 24
  • 72. Submodelling in GeniE  Define a sub-set  Add local details  Change mesh density  Apply prescribed displacement as boundary conditions  Run Submod  Run analysisStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 25
  • 73. Sub-modelling procedure  Do first the global analysis global model  Then create the sub-model analyse - With prescribed boundary conditions where geometry is cut  Submod module: - Reads the sub-model - Reads the global analysis results file Submod - Compares the two models and fetches displacements from global analysis prescribed b.c. - Imposes these as prescribed displacements on the sub-model boundaries with prescribed b.c. sub-model  Perform sub-model analysis analyse  Check resultsStructural design of drill ships Slide 27© Det Norske Veritas AS. All rights reserved. November 15, Submod
  • 74. Safeguarding life, property and the environment www.dnv.comStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 28
  • 75. Structural design of drill shipsYield and buckling strength checks
  • 76. AGENDA  09:00 Welcome and introduction  09:30 Sesam for offshore floaters  10:00 Challenges and requirements  10:30 Coffee break  10:45 Hydrodynamic analysis  11:30 Finite element modelling and analysis  12:15 Lunch  13:30 Yield and buckling strength checks  14:00 Fatigue analysis methods  14:30 Coffee break  14:45 Simplified fatigue analysis  15:15 Spectral fatigue analysis  16:00 Closing remarksStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 2
  • 77. Acceptance criteria Nominal stress: Normal Shear Yield Buckling stress (VonMises) Transit, hull transverse 90 f1 (one plate flange) 0.85 160 f1 180 f1 structure 100 f1 (two plate flanges) (linear buckling) Transit, topside support 0.8 Drilling 0.8 (ultimate capacity) Survival f1 = 1 for normal steel, 1.28 for NV-32 steel, 1.39 for NV-36 steel Peak stress: Mesh size Yield (VonMises) 50x50 1.53 Transit 100x100 1.33 200 x 200 1.13 50x50 1.70 Operation and survival 100x100 1.48 200 x 200 1.25Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 4
  • 78. Plate code check Sesam GeniEStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 5
  • 79. Plate code check in GeniE  Fully integrated with the FE model and result  Automatic idealization of buckling panels Concept Model Capacity ModelStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 6
  • 80. Buckling results Colour code presentation of Utilization Factors (UF) Worse case – colour code presentation of the maximum UF from all load cases.Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 7
  • 81. Generate reportStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 8
  • 82. Safeguarding life, property and the environment www.dnv.comStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 9
  • 83. Structural design of drill shipsFatigue analysis methods
  • 84. AGENDA  09:00 Welcome and introduction  09:30 Sesam for offshore floaters  10:00 Challenges and requirements  10:30 Coffee break  10:45 Hydrodynamic analysis  11:15 Finite element modelling and analysis  12:15 Lunch  13:30 Yield and buckling strength checks  14:00 Fatigue analysis methods  14:30 Coffee break  14:45 Simplified fatigue analysis  15:15 Spectral fatigue analysis  16:00 Closing remarksStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 2
  • 85. Sources for fatigue calculation methods  DNV - OS-C102 “Structural Design of Offshore Ships” - RP-C102 “Structural Design of Offshore Ships” - RP-C203 “Fatigue Strength Analysis of Offshore Steel Structures” - RP-C206 “Fatigue Methodology of Offshore Ships” - CN 30.7 “Fatigue Assessment of Ship Structures”  ABS - “Guide for Building and Classing Floating Production Installations” - “Guide for Fatigue Assessment for Offshore Structures” - “Guide for Spectral-Based Fatigue Analysis for Floating Production, Storage and Offloading (FPSO) Installations” - “Guide for the Fatigue Assessment of Ship-type Installations”  LR - “Rules and Regulations for the Classification of Offshore Installation at a Fixed Location” - “Floating Offshore Installations Assessment of Structures” - “Fatigue Design Assessment Level 1” - “Fatigue Design Assessment Level 3”Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 4
  • 86. Fatigue calculation methods Simplified Deterministic Spectral Time domainStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 5
  • 87. Fatigue loads and stress components  Global wave bending moments  Hull girder stress  Stress in topside supports due to global hull deflections  Stress in turret and moonpool areas due to hull deflections  Wave pressure  Shell plate local bending stress  Local stiffener bending stress  Secondary stiffener bending due to deflection of main girder system  Local peak stresses in knuckles due to deflection of main girder system  Vessel motions (accelerations)  Liquid pressure in tanks  Stress in topside support from inertia forces  Mooring and riser fasteningsStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 6
  • 88. Simplified fatigue Weibull long term Load cycle at a given Stress by rule formulas Fatigue damage from load distribution probability level or FE analysis Weibull distribution  Pros  Cons - Computation demand - Handling of combined load effectsStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 7
  • 89. Deterministic fatigue calculations Fatigue damage by Selected Wave height FE analysis summation of part deterministic waves probability distribution damage from each load case H Hi log N Ni  Pros  Cons - Non-linear load effects can be included - Uncertainties selection of representative wavesStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 8
  • 90. Spectral fatigue calculations –full stochastic and component stochastic Unit waves for Fatigue damage by FE analysis Wave scatter “all” wave summation of part or stress diagram and headings and Stress RAOs damage from each cell component spectrum frequencies in the scatter diagram approach headings n  m  Nload seastates D = 0 Γ1 +  ∑ pn ∑ rijn (2 2m0ijn ) m a  2  n =1 i =1, j =1  Pros  Cons - “All” linear load effects and statistics - No non-linear effects preserved through the analysis - Computation demand - Assumes narrow banded processStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 9
  • 91. Time domain fatigue calculations Time series simulation of Wave FE analysis Fatigue damage by rainflow counting selected sea statistics states  Pros  Cons - Broad banded processes - Selection of sea states - Non-linear load effects - Computation demandStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 10
  • 92. DNV Software’s fatigue calculators Simplified Deterministic Spectral Time domain Nauticus Hull  Framework    Postresp   Stofat Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 11
  • 93. Critical details and calculation optionsStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 12
  • 94. Longitudinal bracket toe and heel Simplified • Loads: Nauticus Hull • Stress: Nauticus Hull, GeniE • Fatigue: Nauticus Hull Component stochastic • Loads RAOs: HydroD • Stress: CN 30.7, GeniE • Fatigue: Postresp Full stochastic • Loads RAOs: HydroD • Stress RAOs: GeniE • Fatigue: StofatStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 13
  • 95. Top stiffener and web frame Simplified • Loads: Nauticus Hull • Stress: Nauticus Hull, GeniE • Fatigue: Nauticus Hull Full stochastic • Loads RAOs: HydroD • Stress RAOs: GeniE • Fatigue: StofatStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 14
  • 96. Side shell plating Simplified • Loads: Nauticus Hull • Stress: CN 30.7 • Fatigue: Nauticus Hull Component stochastic • Loads RAOs: HydroD • Stress: CN 30.7 • Fatigue: Postresp Full stochastic • Loads RAOs: HydroD • Stress RAOs: GeniE • Fatigue: StofatStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 15
  • 97. Deck openings and penetrations Simplified • Loads: Nauticus Hull • Stress: CN 30.7 (Nauticus Hull) • Fatigue: Nauticus Hull Component stochastic • Loads RAOs: HydroD • Stress: CN 30.7 • Fatigue: Postresp Full stochastic • Loads RAOs: HydroD • Stress RAOs: GeniE • Fatigue: StofatStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 16
  • 98. Topside support Simplified • Loads: Nauticus Hull • Stress: CN 30.7 (Nauticus Hull) • Fatigue: Nauticus Hull Component stochastic • Loads RAOs: HydroD • Stress: CN 30.7 • Fatigue: Postresp Full stochastic • Loads RAOs: HydroD • Stress RAOs: GeniE • Fatigue: StofatStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 17
  • 99. Hopper knuckle Simplified • Loads: Nauticus Hull • Stress: GeniE • Fatigue: Nauticus Hull Full stochastic • Loads RAOs: HydroD • Stress RAOs: GeniE • Fatigue: StofatStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 18
  • 100. Wave statisticsStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 19
  • 101. Site specific conditions Scatter diagram Wave spectrum Heading profile Direction Probability Head sea 60% ±15 degrees 30% ±30 degrees 10%Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 20
  • 102. Site specific fe factor – draft DNV-RP-C102 Vessel length Zone no. 300m 200m 100m 1 0.79 0.88 0.92 2 0.64 0.73 0.78 3 0.95 1.00 1.00 … … … … 104 0.88 0.94 0.97 fe factor derived as the weighted average by sailing time in each zoneStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 22
  • 103. Trade specific scatter diagram  Combine scatter diagram by weighted summation of occurrence/probability of each sea state by sailing time: Scatter 1 Scatter 2 Combined scatter Tz Tz Tz Hs 5 6 Hs 5 6 Hs 5 6 5* 1 10 20 +2* 1 10 20 = 1 5*10+2*20=70 140 2 30 40 2 30 40 2 210 280  fe factor derived from wave load analysis as the ratio between the long term loads in trade specific and North Atlantic scatter diagramsStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 23
  • 104. Safeguarding life, property and the environment www.dnv.comStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 24
  • 105. Structural design of drill shipsSimplified fatigue analysis
  • 106. AGENDA  09:00 Welcome and introduction  09:30 Sesam for offshore floaters  10:00 Challenges and requirements  10:30 Coffee break  10:45 Hydrodynamic analysis  11:15 Finite element modelling and analysis  12:15 Lunch  13:30 Yield and buckling strength checks  14:00 Fatigue analysis methods  14:30 Coffee break  14:45 Simplified fatigue analysis  15:15 Spectral fatigue analysis  16:00 Closing remarksStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 2
  • 107. Simplified fatigue analysis in Nauticus Hull Stress calculation Fatigue loads or Fatigue damage Rule formulation of long Combination of global calculation term stress distribution and local stresses ∆σ g + b ⋅ ∆σ l ν 0 Td N load m ∆σ = f m f e max D= a ∑ pn q Γ(1 + h ) ≤ η n =1 m n a ⋅ ∆σ g + ∆σ l nStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 4
  • 108. Updates to fatigue calculations in Nauticus Hull Nov 2011  New features - Specification of past and future operation - User defined loading conditions - Partial filling of tanks - Sailing route and mean stress reduction factor assignment to loading conditions - Re-coated at conversion - Fatigue report module  Benefits - Quick and easy prediction of remaining fatigue life - Improved decision basis inspection and repairs - Document compliance with offshore standardsStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 5
  • 109. Safeguarding life, property and the environment www.dnv.comStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 6
  • 110. Structural design of drill shipsSpectral fatigue analysis
  • 111. AGENDA  09:00 Welcome and introduction  09:30 Sesam for offshore floaters  10:00 Challenges and requirements  10:30 Coffee break  10:45 Hydrodynamic analysis  11:15 Finite element modelling and analysis  12:15 Lunch  13:30 Yield and buckling strength checks  14:00 Fatigue analysis methods  14:30 Coffee break  14:45 Simplified fatigue analysis  15:15 Spectral fatigue analysis  16:00 Closing remarksStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 2
  • 112. AGENDA  09:00 Welcome and introduction  09:30 Basic characteristics of drill ships  10:00 Sesam for offshore floaters  10:30 Coffee break  10:45 Challenges and requirements  11:15 Hydrodynamic analysis  12:15 Lunch  13:30 Finite element modelling and analysis  14:00 Yield and buckling strength checks  14:30 Coffee break  14:45 Fatigue analysis methods  15:15 Simplified fatigue analysis  15:45 Coffee break  16:00 Spectral fatigue analysis  16:30 Closing remarksStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 3
  • 113. Why direct load and strength calculations  Rule loads are not always the truth  Modern 2000000 calculation tools give more accurate loads 1500000 [kNm ] - Ultimate strength loads 1000000 - Fatigue loads 500000 - Phasing and simultaneity of different load effects 0 0 0.2 0.4 0.6 0.8 1  Design and strength optimizations based on analysis VBM (linear) closer to actual operating conditions 150000  Improved decision basis for 100000 [kN] - In-service structural integrity management 50000 - Life extension evaluation 0 0 0.2 0.4 0.6 0.8 1 Vertical Bending Moment VSF (linear) Sea Pressure Double Hull Bending Total Stress  Stress Rule Direct  Pressure TimeStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 4
  • 114. Direct calculated loads vs. rule loads  Fatigue loads: 1.20 1.00 0.80 Direct 0.60 DNV Rule CSR 0.40 0.20 0.00 Vertical Horizontal Pressure WL Vert. Acc. Bending BendingStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 5
  • 115. Spectral vs Simplified Fatigue Analysis  Comparison of fatigue damage by DNV rules and Common Scantling Rules relative to spectral fatigue calculations: 1.20 1.00 0.80 Comp. Stoch. 0.60 DNV Rule CSR 0.40 0.20 0.00 Bottom at Side at Side at T Trunk B/4 T/2 DeckStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 6
  • 116. Expected Fatigue Crack Frequency Simplified Stochastic (Spectral) 60.0 Simulated Crack Frequency 50.0 after 20 Years [%] 40.0 30.0 20.0 10.0 0.0 0 20 40 60 80 100 Calculated Average Fatigue Life [Years]Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 7
  • 117. Overview of fatigue methods Environment Simplified Spectral fatigue Actual wave scatter Long term rule Weibull diagram and energy distribution spectrum Wave loads Rule formulations for Direct calculated loads - accelerations, pressure 3D potential theory and moments on 10-4 probability level Stress calculations: Rule formulations for Load transfer to FE model. Complete stresses. stress transfer function. Rule correlations. Hotspot stress models for SCF Based on expected largest Based on summation of part Fatigue damage stress among 10^4 cycles damage from each Rayleigh calculation: of a rule long term distributed sea state in scatter Weibull distribution diagram.Structural design of drill ships© Det Norske Veritas AS. All rights reserved. 8
  • 118. Spectral fatigue analysis RAO’s •External pressure Hydrodynamic •Rel. wave elevation Hydrodynamic model •Accelerations analysis •Full load / intermediate/ ballast • ->800 complex lc Global FE-model RAO’s •External pressure •Internal pressure Global + Load transfer •Accelerations local FE-model •Adjusted pressure for intermittent wetted areas Global structural RAO’s Global stress/deflection •Global stress/deflections analysis •Entire global model Global deflections as Deflection transfer boundary conditions on Local model boundary conditions to local model local modelStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 9
  • 119. Spectral fatigue analysis Stress distribution for Local stress/deflections each load case Local structural analysis RAO’s Principal stress •Local stress/deflections 5.E+07 4.E+07 3.E+07 0 Local stress transfer 2.E+07 45 90 135 functions 1.E+07 180 0.E+00 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 Wave per iod [ s] Notch stress Input Stress Geometric stress at hot spot (Hot spot stress) •Hot spot location Geometric stress Stress Principal hotspot stress Result Hot spot Nominal stress extrapolation •RAO •Principal hot spot stress Input •Wave scatter diagram Fatigue •Wave spectrum Scatter diagram •SN-curve calculations •Stress RAO •=> Fatigue damage SN dataStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 10
  • 120. Fatigue Calculation Program - Stofat  Performs stochastic (spectral) fatigue POSTPROCESSING calculation with loads from a hydrodynamic analysis using a frequency domain approach STRUCTURAL RESULTS INTERFACE FILE  Structures modelled by 3D shell and solid elements Stofat Shell/plate  Assess whether structure is likely to suffer fatigue failure due to the action of repeated loading RESULTS INTERFACE FILE  Assessment made by SN-curve based fatigue approach  Accumulates partial damages weighed over Stofat sea states and wave directions databaseStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 11
  • 121. Safeguarding life, property and the environment www.dnv.comStructural design of drill ships© Det Norske Veritas AS. All rights reserved. 12

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