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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 specialconsideration in the splash zone. Hopper knuckles and other relevant discontinuities Attachments, foundations, supports etc. to main deck and bottom structure openings andpenetrations 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 Challenges and requirements 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 remarks Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Typical arrangement Derrick Heli-deck Gantry cranes Drill floor Riser stack Moonpool Thrusters Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Hull strength requirements Derrick Heli-deck Cranes Drill floor Riser stack Moonpool Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Thrusters Challenges and high focus areas Drill floor support Crane foundation Structural discontinuities Moonpool corners Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Hull and derrick interface Effect of hull deformations Structural design of drill ships © Det Norske Veritas AS. All rights reserved. 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 • Cargo hold FE analysis • Local FE analysis for ultimate strength and fatigue • Simplified fatigue calculations • Global FE analysis • Direct load application from wave load analysis • Spectral fatigue calculations Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Analysis options and related software from DNV Software Analysis type Rule based calculations DNV ship rules and offshore standards Other class (ABS, LR, …) 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 + GeniE Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Design conditions and loads – DNV-OS-C102 Design condition Load cases Load basis Wave data Heading profile Load probability Transit Ship rules Ship rules Direct for topside acc. IACS North Atlantic All headings Rule pressures 10-4 Accelerations 20 years Drilling Max draught Min draught Direct calculations Max Hs for drilling Specified heading profile hrs short term Survival Max draught Min draught Direct calculations North Atlantic or design limit Specified heading profile 100 years 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 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 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 remarks Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Simplified fatigue analysis in Nauticus Hull Stress calculation Fatigue loads or Fatigue damage calculation D= ν Td a Rule formulation of long term stress distribution ∆σ g + b ⋅ ∆σ l ∆σ = f m f e max a ⋅ ∆σ g + ∆σ l N load m pn q Γ(1 + ) ≤ η ∑ hn n =1 m n Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Combination of global and local stresses 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 standards Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Safeguarding life, property and the environment www.dnv.com Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Structural design of drill ships Spectral fatigue analysis 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 remarks Structural design of drill ships © Det Norske Veritas AS. All rights reserved. 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 remarks Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Why direct load and strength calculations Rule loads are not always the truth Modern calculation tools give more accurate loads 2000000 - Ultimate strength loads - Fatigue loads - Phasing and simultaneity of different load effects [kNm ] 1500000 1000000 500000 0 Design and strength optimizations based on analysis closer to actual operating conditions 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 VBM (linear) 150000 Improved decision basis for [kN] 100000 - In-service structural integrity management - Life extension evaluation 50000 0 Vertical Bending Moment Sea Pressure VSF (linear) Double Hull Bending Stress Total Stress Pressure Time Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Rule Direct Direct calculated loads vs. rule loads Fatigue loads: 1.20 1.00 0.80 Direct DNV Rule CSR 0.60 0.40 0.20 0.00 Vertical Bending Horizontal Bending Pressure WL Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Vert. Acc. 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. DNV Rule CSR 0.60 0.40 0.20 0.00 Bottom at B/4 Side at T/2 Side at T Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Trunk Deck Expected Fatigue Crack Frequency Simplified Stochastic (Spectral) Simulated Crack Frequency after 20 Years [%] 60.0 50.0 40.0 30.0 20.0 10.0 0.0 20 40 60 80 Calculated Average Fatigue Life [Years] Structural design of drill ships © Det Norske Veritas AS. All rights reserved. 100 Overview of fatigue methods Environment Simplified Spectral fatigue Long term rule Weibull distribution Wave loads Stress calculations: Fatigue damage calculation: Rule formulations for accelerations, pressure and moments on 10-4 probability level Direct calculated loads 3D potential theory Rule formulations for stresses. Load transfer to FE model. Complete stress transfer function. Rule correlations. Hotspot stress models for SCF Based on expected largest stress among 10^4 cycles of a rule long term Weibull distribution Based on summation of part damage from each Rayleigh distributed sea state in scatter diagram. Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Actual wave scatter diagram and energy spectrum Spectral fatigue analysis Hydrodynamic analysis Hydrodynamic model RAO’s •External pressure •Rel. wave elevation •Accelerations •Full load / intermediate/ ballast • ->800 complex lc Global FE-model Global + local FE-model Global stress/deflection Global structural analysis RAO’s •Global stress/deflections •Entire global model Deflection transfer to local model Local model boundary conditions Structural design of drill ships © Det Norske Veritas AS. All rights reserved. Load transfer RAO’s •External pressure •Internal pressure •Accelerations •Adjusted pressure for intermittent wetted areas Global deflections as boundary conditions on local model Spectral fatigue analysis Local stress/deflections Local structural analysis Principal stress Stress distribution for each load case RAO’s •Local stress/deflections 5.E+07 4.E+07 3.E+07 45 2.E+07 90 135 1.E+07 Local stress transfer functions 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 Geometric stress at hot spot (Hot spot stress) Stress Geometric stress Nominal stress Stress extrapolation Principal hotspot stress Hot spot Fatigue calculations Scatter diagram Input •Hot spot location Result •RAO •Principal hot spot stress Input •Wave scatter diagram •Wave spectrum •SN-curve •Stress RAO •=> Fatigue damage SN data Structural design of drill ships © Det Norske Veritas AS. All rights reserved. 10 Fatigue Calculation Program - Stofat Performs stochastic (spectral) fatigue calculation with loads from a hydrodynamic analysis using a frequency domain approach Assess whether structure is likely to suffer failure due to the action of repeated loading Assessment made by SN-curve based fatigue approach Accumulates partial damages weighed over sea states and wave directions Structural design of drill ships © Det Norske Veritas AS. All rights reserved. 11 RESULTS INTERFACE FILE Structures modelled by 3D shell and solid elements STRUCTURAL RESULTS INTERFACE FILE POSTPROCESSING Stofat Shell/plate fatigue Stofat database Safeguarding life, property and the environment www.dnv.com Structural design of drill ships © Det Norske Veritas AS. All rights reserved. 12 [...]... My tools – Sesam HydroD for wave load analysis Structural design of drill ships © Det Norske Veritas AS All rights reserved 15 My tools – Nauticus Hull for rule strength calculations Structural design of drill ships © Det Norske Veritas AS All rights reserved 16 My tools – Sesam GeniE for direct strength calculations Structural design of drill ships © Det Norske Veritas AS All rights reserved 17 Safeguarding... Longitudinal mass distribution Structural design of drill ship © Det Norske Veritas AS All rights reserved 16 Vertical and transverse centre of gravity Transverse centre of gravity Roll radius of gyration and inertia Pitch radius of gyration and inertia Example of mass models Direct input Beams with varying density Structural model and compartments Structural design of drill ship © Det Norske Veritas... 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 My drillship Structural design of drill ships © Det Norske Veritas AS All rights reserved 13 Main dimensions and design conditions Main dimensions - Unrestricted... rights reserved 17 Safeguarding life, property and the environment www.dnv.com Structural design of drill ships © Det Norske Veritas AS All rights reserved 18 Structural design of drill ship Hydrodynamic analysis 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... Accelerations 20 years Drilling Max draught Min draught Direct calculations Max Hs for drilling Specified heading profile 3 hours short term Survival Max draught Min draught Direct calculations North Atlantic or design limit Specified heading profile 100 years Fatigue - World wide scatter diagram (for unrestricted service) Load probability 10-4 80 % operation 20 % transit Structural design of drill ship ©... term Fatigue: 10-4 100 years Fatigue: 10-4 Structural design of drill ship © Det Norske Veritas AS All rights reserved 5 Hydrodynamic analysis Sesam HydroD Structural design of drill ship © Det Norske Veritas AS All rights reserved 6 HydroD Key features - Hydrostatics and stability calculations - Linear and non linear hydrodynamics Benefits - Handling of multiple loading conditions and models through... Wave directions Wave frequencies Hull geometry - Panel model - Morrison model Mass distribution - Compartments - Mass model Structural model - For load transfer Structural design of drill ship © Det Norske Veritas AS All rights reserved 9 Panel model Structural design of drill ship © Det Norske Veritas AS All rights reserved 10 Panel model guidelines Mesh size - In general depending on wave length... state for drilling operation - Hs = t m Load conditions Heading profile - Transit T=10 m - Drilling and survival T=12m - 60 % head sea - 30 % ± 15 degrees - 10 % ± 30 degrees Hull girder limits - Stillwater sagging Ms -2330500 kNm - Stillwater hogging Ms 1923560 kNm Structural design of drill ships © Det Norske Veritas AS All rights reserved 14 My tools – Sesam HydroD for wave load analysis Structural. .. strength checks 14:00 Fatigue analysis methods 14:30 Coffee break 14:45 Simplified fatigue analysis 15:15 Spectral fatigue analysis 16:00 Closing remarks Structural design of drill ship © Det Norske Veritas AS All rights reserved 2 Design conditions and loads – DNV-OS-C102 Design condition Load cases Load basis Wave data Heading profile Load probability Transit Ship rules Ship rules Direct... 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 Hull modelling in GeniE Model from scratch Import DXF Import from Rhino – plug-in available with GeniE 6.3 Structural design of drill ship © Det Norske Veritas AS All rights reserved 12 Import DXF – a typical tanker Convert . rights reserved. Structural design of drill ships Rules and regulations for structural design of drill ships IMO MODU code DNV-OS-C102 Structural design of offshore ships ABS: Guide. Structural design of drill ships Challenges and requirements © Det Norske Veritas AS. All rights reserved. Structural design of drill ships AGENDA 09:00 Welcome. reserved. Structural design of drill ships My tools – Sesam GeniE for direct strength calculations 17 © Det Norske Veritas AS. All rights reserved. Structural design of drill ships Safeguarding