Staad Offshore [PDF]

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OFFSHORE LOADING MODULE FOR STAAD.Pro



TYPES OF OFFSHORE STRUCTURES



MARINE AND OFFSHORE STRUCTURES FIXED



FLOATING



FLEXIBLE



Drilling Jackets Production Platform Caissons



FPSO, FSO Semisub TLP Articulated Towers



CALM, SALM Risers TLP Tendons



PHOTOS:



Jacket



Courtsey: Respective Websites



PHOTOS:



Jackup Rig



Courtsey: Respective Websites



FPSO



FSO



Courtsey: Respective Websites



PHOTOS:



Semi−submersible



Courtsey: Respective Websites



PHOTOS:



TLP



Courtsey: Respective Websites



OFFSHORE STRUCTURES IN OIL FIELD



Courtsey: Respective Websites



LOADINGS:



• • • • • • •



General Dead Loads Live Loads Environmental Loads Transportation Loads Impact Loads Others



Offshore Load Generator Module



ANALYSIS:



• • • •



Static Dynamic Random Response Fatigue



Offshore Load Generator Module



DESIGN STANDARDS:



• Rules/Regulations from various Classification Societies such as ABS, DnV, Lloyds, BV, etc. • Classification Notes/Design Guidelines/Recommended Practices from Class (DnV’s CN-30.5, RP-C203) • API RP-2A-WSD/API RP-2A-LRFD Most popular and used standards



ENVIRONMENTAL LOADS: Due to natural phenomena of general importance:



• Wave • Current • Wind



Wave Load Module



Due to natural phenomena of specific importance:



• Earthquake • Snow, Ice • Temperature



TRANSPORTATION LOADS: • The inertial forces beside gravity are generated due to motion of the vessel on which the structure is mounted due to combined random effects of wave, wind, current, etc. during transportation. • The inertial forces are generally to be computed using the appropriate period and amplitude by combining roll with heave and pitch with heave



Transport Load Module



Offshore Structure Design



Fatigue Module of OLP



• Check with API/AISC • Check Fatigue Life • Redesign • Report for Approval



OVERVIEW:



Offshore Loading Program



Wave Load Module



Transport Load Module



Computes Loads/Load Cases to be used with STAAD.Pro



Fatigue Module



Use STAAD.Pro Results due to wave loads to compute Fatigue Damage of Joints



WAVE LOAD MODULE: • Computes particle velocities and accelerations • Computes design wave forces (drag & inertia) on 3D structures in the global X, Y and Z-directions • Sections include pipe, tubes and open sections such as Ibeams, etc. • Comply API RP 2A-WSD • Total Base Shear and Overturning Moment are calculated



• Calculate weight & submerged buoyancy of structure • Calculates COG & COB • Generates wave load cases, a single buoyancy load case in a new STAAD.Pro input file, filename_wave.std • Additional user supplied loads and analysis commands can be added to this STAAD.Pro file



Theoretical Background: Steps to Compute Environmental Forces



Sheet 1



Sheet 2



Theoretical Background: Wave Theory • Appropriate order of Stream Function • Stokes V • Airy Linear • User defined grid of Velocities and Accelerations H Applicability Function of H, Tapp and d



Stokes V/ Stream 3



2 gTapp



Airy/ Stream 3



Stream Function



d 2 gTapp



Sheet 3



Theoretical Background: Other Factors • Combined Wave/Current Kinematics • Marine Growth • Drag/Inertia Coefficients • Conductor Shielding Factor Hard Growth



t



Dc



D



Pipe e = k/D k



D = Dc + 2t



Marine Growth



With no Wave



Current Profile Stretching



Current Profile



Sheet 4



Theoretical Background: Drag/Inertia Coefficients, CD, Cm Reynold’s number, Re Keulegan-Carpenter number, Kc Relative Surface Roughness, k/D Current/Wave Velocity Ratio, r Gap Ratio between Cylinder and fixed boundary, H/D



CD



• • • • •



k/D



Re Drag Coefficients for Circular Cylinders



Note: 1) Refer to DnV’s CN No. 30.5 and API RP 2A



3) APPURTENANCES should be defined as INACTIVE members in STAAD.Pro basic input file



−1



Cm



2) ALPHA values should be used in STAAD.Pro basic input file to define whether members are flooded or buoyant



Cm



H   = 1 +  10 + 1 D  



Gap Ratio, H/D Inertia Coefficients Variation



Theoretical Background:



Sheet 5



Hydrodynamic Force Computation Morison’s Equation on Slender (λ/D > 5) member



F(y,t) = FD + FI =



1 δV C D ρ A V V + (Cm ρ Vr + ρVd ) 2 δt



Where, FD = Drag force vector/unit length; FI = Inertia force vector/unit length CD = Drag Coefficient; Cm = Inertia/added mass Coefficient ρ = Water mass density; Vr = Reference volume/unit length Vd = Displaced volume/unit length V = Velocity vector (combined wave and current) normal to axis A = Projected area normal to axis/unit length (=D, for circular cylinder)



Theoretical Background: Morison’s Equation to Inclined Members • The drag and inertia pressure resultants are assumed to act on the projected area of the member and resulting forces are then resolved into normal and tangential components. • Resolution of the resultant drag and inertia pressures into normal and tangential components, OTC 1976, Paper 2723 DnV Rules the tangential components are and ignored. • Resolution of the resultant velocity and acceleration into normal and tangential components, the tangential kinematics are generally ignored. • The drag and inertia pressures are assumed to act on the projected area of the member and the force is then applied normal to the member axis.



Sheet 6 Option PROJ



PRES



RESV Mostly used



PRJN



Typical Output: • • • • •



Wave Characteristics Member forces in Local and Global Co-ordinates Joint Loads due to Dead Weight and Buoyancy Joint Loads for Appurtenances Total Base Shear and Overturning Moments (Global Structural Forces) • Generation of STAAD.Pro Input file (filename_wave.std) consisting of all load cases including one for buoyancy load case with basic analysis commands



Sheet 1



Input Data Screens: Job Identification



STAAD.Pro Model



Sheet 2



Input Data Screens: Load Wave WaveLoad



Force Coefficients Table Marine Growth Current Profile Table Wave Parameters Table Table



Analysis and Output Data Screens:



TRANSPORT LOAD MODULE: • Need the basic STAAD.Pro Input File of the model • Specify the vessel motion and the global position of center of rotation • Calculates the inertia forces on the members and joints due to motion accelerations consisting of any combination of 3-translational and 3-rotational d.o.f • Generates a complete STAAD.Pro Input File (filename_trans.std) consisting of basic load cases for the inertia loadings and commands for basic analysis • Other load cases and commands can be added manually. • Total Base Shear and Overturning Moment are calculated



Sheet 1



Theoretical Background:



Center of Rotation



DY, Heave RY, Yaw



Y X



RX, Roll



Z



DX, Surge RZ, Pitch DZ, Sway



Vessel Motion w.r.t. Global Coordinates



Sheet 2



Theoretical Background: The translational accelerations of a point relative to the center of rotation are as follows:



Z X Y



α



γ



Y



Center of Rotation



Roll Motion



Pitch Motion



Input Data Screens: Transport Load



Motion Parameters Table Joint Lumped Weights Table



Output Data Screens:



FATIGUE MODULE: • Computes the Fatigue Lives at up to 16 points around tubular joints and creates an output file comprising of minimum life of chord, stub and brace. • It can consider up to 16 wave approach directions • Maximum number of wave positions within the wave length is ten to calculate stress range. • Includes DOE’s S-N curves B, C, D, E, F, F2, G, W & T and has option to define user-defined S-N curves (log-bilinear) • SCF’s at the crown and saddle locations of chord and stub can be computed be the program or can be entered manually • The fatigue damage calculation is based on Miners cumulative damage rule.



S-N curves:



Sheet 1



For tubular joints:



Hot Spot Cyclic Stress Range (ksi)



Thickness correction



X X



Reference: API RP-2A-WSD Permissible Cycles of Load N



/



S-N curves:



Sheet 2



For Non-tubular members and connections



Stress Range (N/mm2)



Reference: DnV’s CN-30.2



Number of Cycles



SCF’s for Tubular Joints:



Sheet 1



SCF’s can be calculated at the crown and saddle positions for axial load, in-plane and out-of-plane bending moments by this module using either of these options:



. Wordsworth-Smedley . Lloyds



SCF’s for Tubular Joints:



Sheet 2



Classification of Joints:



Geometric parameters of Tubular joint



Range of Validity Example of Joint Classification



SCF’s for Tubular Joints:



Sheet 3



SCF Equations :



Reference: DnV’s Classification Note-30.2/RP-C203



Sheet 1



Input Data Screens: Fatigue Module



Wave Height Exceedance Table



Sheet 2



Input Data Screens: Fatigue Module



Stress-Wave Height Table



Sheet 3



Input Data Screens: Fatigue Module



Joint Details Table



Sheet 4



Input Data Screens: Fatigue Module



Wordsworth-Smedley SCF Table



Sheet 5



Input Data Screens: Fatigue Module



Computed SCF T



Output Data Screens:



EXAMPLE 1: 4 PILE JACKET ANALYSIS (In-Place) Basic Data: Jacket Height = 44.2 m Water Depth = 30.48 m Member Sections: 40”, 36”, 16”, 14”, 10”, 8”, 6”, W-Shapes Wave Parameters: Wave Directions = 0 deg, 45 deg, etc. 1st: Wave Ht. = 3.048 m; Period = 7 secs. 2nd: Wave Ht. = 1.829 m; Period = 5.4 secs. Initial Pos. = 0 deg., Final Pos. = 360 deg., Wave step = 45 deg. Wave Theory = Airy Drag & Inertia Co-efficients: Cd = 0.7 and Cm = 1.1 (As per API RP-2A)



Basic Input Screens:



X



Output: Wave Simulation for Wave Ht. = 3.048 m & Period = 7 sec.



37.74



33.97



30.20



26.42



22.65



18.87



15.10



11.32



7.55



3.77



2.25 1.5 0.75 0 -0.75 -1.5 -2.25



0.00



Wave Elevn., z



Wave Length Vs Elevation



Wave Length, x



WAVE LENGTH = 75.48679 WAVE CELERITY = 10.78383



Typical Output of Member Loads: MEMBER NO = 35 DISTANCE FROM MEM LOCAL-AXIS START 'x'-DIR 'y'-DIR



0.0000 0.0000 0.0000 0.0000



Typical Joint Loads: TOWER DEAD WEIGHT JOINT LOADS JOINT NO 'X'-DIR 'Y'-DIR 72 0.000 -2.416 76 0.000 -2.425 71 0.000 -23.286 73 0.000 -3.804 79 0.000 -2.425 75 0.000 -2.305 77 0.000 -2.066



'Z'-DIR 0.000 0.000 0.000 0.000 0.000 0.000 0.000



TOWER BUOYANCY JOINT LOADS JOINT NO 'X'-DIR 'Y'-DIR 16 0.000 0.301 27 0.000 0.301 13 0.000 8.695 24 0.000 8.695 7 0.000 38.847 12 0.000 10.473 23 0.000 10.473



'Z'-DIR 0.000 0.000 0.000 0.000 0.000 0.000 0.000



* Wave Loading : Non Structural Members JOINT LOAD 136 FX -0.14 FY -1.671 FZ -0.14 135 FX -0.268 FY -3.349 FZ -0.268 134 FX -0.08 FY -1.017 FZ -0.08 133 FX -0.015 FY -0.149 FZ -0.015



Typical Base Shear and Base Moments: FX 10. -34. -54. -40. -5. 32. 55. 47. 10.



XYZ BASE SHEARS FY -44. -32. 0. 28. 40. 31. 4. -28. -44.



FZ



XYZ BASE MOMENTS MY MZ -9. -268. -9. 737. -4. 1194. -1. 875. 3. 131. 6. -694. 5. -1214. 0. -1077. -9. -268.



MX 253. -753. -1198. -875. -128. 696. 1217. 1077. 253.



9. -35. -54. -39. -5. 33. 55. 46. 9.



Fx and Mz



Fz and Mx



80



1500



80



1500



60



1000



60



1000 500



20



0 360



315



270



225



180



135



-20



90



0 45



Mz



Fz



Fx



0



360



315



270



225



180



135



90



45



-500



Mz



0



0 -20



40



500



20 0



Fx



40



-40



-40



-1000



-60



-1500



-60



-1500 Wave Position



Wave Position



TOWER WT 4160.92



CGXW 0.04



Mx



-500



-1000



Weights and CG’s:



Fz



Mx



WAVE POSN 0 45 90 135 180 225 270 315 360



CGYW 19.54



CGZW 0.01



BUOY WT 778.81



CGXB -0.01



CGYB 14.94



CGZB 0.01



Graphical Plots of Typical Wave Loads:



Generation of STAAD.Pro Input File: Wave Load Module generates filename_wave.std Total No. of Load Cases, n = NW + NB = 2x(2x(360/45 + 1)) + 1 = 37 Note: Other Load cases, any load combinations and analysis commands can be added manually in this STAAD.Pro Input File



Basic Data for Transportation Module: Center of Rotation = 0, -34.0, 0 (in m.) Gravity/Tilt = Motion Parameters: Heave (DY) = 6 m and Period = 10.0 secs Roll (RX) = 20 deg. and Period = 12.0 secs Combinations: Heave + Roll Starboard (DY + RX) Heave + Roll Port (DY - RX) Joint Lumped Weights: Joint No.



Weight (kN)



89



20



90



20



91



30



92



30



Basic Input Screens:



Output: LOADING 1 DOF LOADS = +DY +RX MEMBER LOADS * * INERTIA FORCES DUE TO MEMBER SELF WEIGHT * 1 TRAP GY -0.331 -0.343 0.000 2.439 1 UNI GZ 0.381 0.000 2.439 2 TRAP GY -0.343 -0.355 0.000 2.438 2 UNI GZ 0.381 0.000 2.438 *INERTIA FORCES DUE TO APPURTENANCE SELF WEIGHT * JOINT LOADS * 132 FX 0.000 FY -15.605 FZ 17.971 136 FX 0.000 FY -28.981 FZ 29.073 * INERTIA FORCES DUE TO JOINT CONCENTRATED WEIGHT * 89 FX 0.000 FY -13.251 FZ 16.150 90 FX 0.000 FY -13.251 FZ 16.150



Heave + Roll Starboard



LOADING 2 DOF LOADS = +DY -RX MEMBER LOADS * * INERTIA FORCES DUE TO MEMBER SELF WEIGHT * 1 TRAP GY -0.366 -0.355 0.000 2.439 1 UNI GZ -0.381 0.000 2.439 2 TRAP GY -0.355 -0.343 0.000 2.438 2 UNI GZ -0.381 0.000 2.438



Heave + Roll Port



*INERTIA FORCES DUE TO APPURTENANCE SELF WEIGHT * JOINT LOADS * 132 FX 0.000 FY -15.473 FZ -17.971 136 FX 0.000 FY -28.735 FZ -29.073 * INERTIA FORCES DUE TO JOINT CONCENTRATED WEIGHT * 89 FX 0.000 FY -14.678 FZ -16.150 90 FX 0.000 FY -14.678 FZ -16.150



Graphical Plots of Transportation Loads:



Generation of STAAD.Pro Input File: Wave Load Module generates filename_trans.std Total No. of Load Cases, n = Combination sets in Motion Parameters Note: Other Load cases such as wind loads, preloads and load combinations can be added manually in this STAAD.Pro Input File



Fatigue Analysis: A typical Flare Tower mounted on FPSO has been chosen.



Basic Data: Tower Height ≅ 55 m Member Sections: 30”, 24”, 18”, 12”, 10”, etc., Channels Wind Loads: TYPE



DIRECTIONS



MAXM CYCLES/YR



NORMAL



±X, ±Z



87600



25 YR RETURN



±X, ±Z



87600



STORM



±X, ±Z



52300



100 YR RETURN



±X, ±Z



35040



Vessel Motion: TYPE



DIRECTIONS



MAXM CYCLES/YR



EXTREME



±X, ±Z



13075



API RP-2A Code Check: • In-built API code of STAAD.Pro is used to carry out Steel Design • Pinpoint Critical Joints for which Fatigue Analysis has to be carried out



Critical Joints 5&6 Maxm. CFR



Punching Shear Check:



< 1.0



Joint Data to Calculate SCF’s: Wordsworth-Smedley Concept is used.



•



Joint 6, Chord 28, Brace 27 – – – – – –



•



Joint Type = K Angle, A1 = 0.6634 rad Angle, A2 = 0.0 rad Angle, A3 = 1.57 rad Gap = 0.050 m Brace SCF = 2.5



Joint 5, Chord 30, Brace 24 – – – – – –



Joint Type = K Angle, A1 = 0.6634 rad Angle, A2 = 0.0 rad Angle, A3 = 1.57 rad Gap = 0.050 m Brace SCF = 2.5



Basic Input Screens:



Fatigue Life Evaluation: MEMBER NO JOINT NO CHORD LIFE 24 27



5 6



20.096 26.168



STUB LIFE 63.825 83.853



BRACE LIFE 13257.769 20305.904



List of Offshore Load Generator Module Users: • • • • • • • • • • • • • • • •



ABS Europe Ltd Aker McNulty Ltd AMEC Birwelco Limited Amec Offshore Services Ltd. Andrew Palmer & Associates BDL Engineering Limited Brico (UK) Ltd Capita Infrastructure Consultancy Consafe Engineering Ltd Det Norske Veritas Classification DRECO Ltd Forsyths Global Maritime Grootint Halliburton Brown & Root Ltd. Harland & Wolff S.H.I.



• • • • • • • • • • • • • •



J P Kenny Caledonia Ltd John Brown Hydrocarbons Limited Kvaerner Heurtey France Kvaerner Paladon Ltd Kvaerner Process Netherlands bv Lewis Offshore Ltd Lloyds Register Lloyds Register of Shipping M A Carroll Marine Technology Consultants Merpro Ltd MOS Ltd MSW Noble Denton Europe Ltd.



List of Offshore Load Generator Module Users: (Contd.) • • • • • • • • • • • • •



Ocean Resource Limite Ove Arup & Partners (Aberdeen) Ove Arup and Partners (London) PGS Production Services Rig Design Services Limited Shell Stork Protech (UK) Ltd Sunderland Offshore Swanhunter (Tyneside) Limited Tebodin Middle East Ltd THC Fabricators UK Ltd Trada Technology Ltd WS Atkins Consultants