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OFFSHORE LOADING MODULE
FORSTAAD.Pro
TYPES OF OFFSHORE STRUCTURES
Drilling JacketsProduction Platform
Caissons
FIXED
FPSO, FSOSemisub
TLPArticulated Towers
FLOATING
CALM, SALMRisers
TLP Tendons
FLEXIBLE
MARINE AND OFFSHORESTRUCTURES
PHOTOS:
Courtsey: Respective Websites
Jacket
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 LoadGeneratorModule
ANALYSIS:
• Static• Dynamic• Random Response• Fatigue
Offshore LoadGeneratorModule
DESIGN STANDARDS:• Rules/Regulations from various
Classification Societies such as ABS, DnV,Lloyds, BV, etc.
• Classification Notes/DesignGuidelines/Recommended Practices fromClass (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 LoadModule
Due to natural phenomena of specific importance:
• Earthquake• Snow, Ice• Temperature
TRANSPORTATION LOADS:
• The inertial forces beside gravityare generated due to motion of thevessel on which the structure ismounted due to combined randomeffects of wave, wind, current, etc.during transportation.
• The inertial forces are generally tobe computed using the appropriateperiod and amplitude by combiningroll with heave and pitch withheave
TransportLoad Module
Offshore Structure Design
Fatigue Module of
OLP
• CheckwithAPI/AISC
• CheckFatigueLife
• Redesign• Report for
Approval
Offshore Loading Program
OVERVIEW:
Wave Load Module
Fatigue Module
Transport Load
Module
Computes Loads/Load Cases tobe used with STAAD.Pro
Use STAAD.Pro Results dueto wave loads to computeFatigue Damage of Joints
WAVE LOAD MODULE:
• Computes particle velocitiesand accelerations
• Computes design waveforces (drag & inertia) on 3-D structures in the global X,Y and Z-directions
• Sections include pipe, tubesand open sections such as I-beams, etc.
• Comply API RP 2A-WSD• Total Base Shear and
Overturning Moment arecalculated
• Calculate weight & submergedbuoyancy of structure
• Calculates COG & COB• Generates wave load cases, a
single buoyancy load case in anew STAAD.Pro input file,filename_wave.std
• Additional user supplied loadsand analysis commands can beadded to this STAAD.Pro file
Theoretical Background: Sheet 1
Steps to Compute Environmental Forces
Theoretical Background:Wave Theory
• Appropriate order of Stream Function• Stokes V• Airy Linear• User defined grid of Velocities and Accelerations
Applicability
Function of H, Tappand d
Sheet 2
2appgT
H
2appgT
d
Stokes V/Stream 3
Airy/Stream 3Stream
Function
Other Factors• Combined Wave/Current Kinematics• Marine Growth• Drag/Inertia Coefficients• Conductor Shielding Factor
Pipe
Hard Growth
t
e = k/D
D = Dc + 2t
DDc
k
Marine Growth Current Profile
With no Wave
Current Profile Stretching
Theoretical Background: Sheet 3
Drag/Inertia Coefficients,CD, Cm
Drag Coefficients for Circular Cylinders
Theoretical Background: Sheet 4
k/D
Re
CD• 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
Gap Ratio, H/D
Cm
1
1101−
++=
DHC m
Note: 1) Refer to DnV’s CN No. 30.5 and API RP 2A
2) ALPHA values should be used in STAAD.Pro basic input file to define whether members are flooded or buoyant
3) APPURTENANCES should be defined as INACTIVE members in STAAD.Pro basic input file
Inertia Coefficients Variation
Hydrodynamic Force Computation
Theoretical Background: Sheet 5
Morison’s Equation on Slender (λ/D > 5) member
F(y,t) = FD + FI = ( )tVVVCVVAC drmD δδ
ρρρ ++21
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;
A = Projected area normal to axis/unit length (=D, forcircular cylinder)
V = Velocity vector (combined wave and current) normalto axis
Vr = Reference volume/unit length
Vd = Displaced volume/unit length
Theoretical Background: Sheet 6
Morison’s Equation to Inclined Members• The drag and inertia pressure resultants are
assumed to act on the projected area of themember and resulting forces are then resolvedinto normal and tangential components.
• Resolution of the resultant drag and inertiapressures into normal and tangential components,the tangential components are ignored.
• Resolution of the resultant velocity andacceleration into normal and tangentialcomponents, the tangential kinematics aregenerally ignored.
• The drag and inertia pressures are assumed to acton the projected area of the member and the forceis then applied normal to the member axis.
Option
PROJ
PRES
RESV
PRJN
Mostly used
OTC 1976, Paper 2723 and DnV Rules
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 buoyancyload case with basic analysis commands
Input Data Screens:
Job Identification
Sheet 1
STAAD.ProModel
Input Data Screens: Sheet 2
Marine Growth Table
Wave Load
Current Profile Table
Wave LoadWave Load
Force Coefficients Table
Wave Load
Wave Parameters 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 combinationof 3-translational and 3-rotational d.o.f
• Generates a complete STAAD.Pro Input File(filename_trans.std) consisting of basic load cases for theinertia loadings and commands for basic analysis
• Other load cases and commands can be added manually.• Total Base Shear and Overturning Moment are calculated
Theoretical Background: Sheet 1
DX, Surge
DZ, Sway
DY, Heave
RX, Roll
RY, Yaw
RZ, Pitch
Center ofRotation
X
Y
Z
Vessel Motion w.r.t. Global Coordinates
Z
Y
Center of Rotation
Roll Motion
α
Pitch Motion
γY
X
The translational accelerations of a point relative to the center ofrotation are as follows:
Theoretical Background: Sheet 2
Input Data Screens:
Transport Load
Joint Lumped Weights TableMotion Parameters Table
Transport Load
Output Data Screens:
FATIGUE MODULE:
• Computes the Fatigue Lives at up to 16 points aroundtubular joints and creates an output file comprising ofminimum 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-bi-linear)
• SCF’s at the crown and saddle locations of chord andstub can be computed be the program or can be enteredmanually
• The fatigue damage calculation is based on Minerscumulative damage rule.
S-N curves:
Permissible Cycles of Load N
Hot
Spo
t Cyc
lic S
tres
s Ran
ge (k
si)
X
X/
Thickness correction
For tubular joints:Sheet 1
Reference: API RP-2A-WSD
For Non-tubular members and connections
S-N curves: Sheet 2
Number of Cycles
Stre
ss R
ange
(N/m
m2 )
Reference: DnV’s CN-30.2
SCF’s can be calculated at the crown and saddle positions for axialload, in-plane and out-of-plane bending moments by this moduleusing either of these options:
SCF’s for Tubular Joints: Sheet 1
Wordsworth-Smedley Lloyds.
.
SCF’s for Tubular Joints: Sheet 2Classification of Joints:
Geometric parameters of Tubular joint
Example of Joint Classification
Range of Validity
SCF’s for Tubular Joints: Sheet 3SCF Equations :
Reference: DnV’s Classification Note-30.2/RP-C203
Input Data Screens:
Fatigue Module
Wave Height ExceedanceTable
Sheet 1
Fatigue Module
Stress-Wave Height Table
Input Data Screens: Sheet 2
Fatigue Module
Joint Details Table
Input Data Screens: Sheet 3
Fatigue Module
Wordsworth-SmedleySCF Table
Input Data Screens: Sheet 4
Input Data Screens: Sheet 5
Fatigue Module
ComputedSCF T
Output Data Screens:
EXAMPLE 1: 4 PILE JACKET ANALYSIS (In-Place)
Basic Data:Jacket Height = 44.2 m
Water Depth = 30.48 m
Wave Directions = 0 deg, 45 deg, etc.Wave Parameters:
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)
Member Sections:
40”, 36”, 16”, 14”, 10”, 8”, 6”, W-Shapes
Basic Input Screens:
Output: X Z0 -1.524
1.887 -1.5053.774 -1.4495.662 -1.3587.549 -1.2339.436 -1.078
11.323 -0.89613.21 -0.692
15.097 -0.47116.985 -0.23818.872 020.759 0.23822.646 0.47124.533 0.69226.42 0.896
28.308 1.07830.195 1.23332.082 1.35833.969 1.44935.856 1.50537.743 1.524
WAVE LENGTH = 75.48679WAVE CELERITY = 10.78383
Wave Simulation for Wave Ht. = 3.048 m & Period = 7 sec.
Wave Length Vs Elevation
-2.25-1.5
-0.750
0.751.5
2.25
0.00
3.77
7.55
11.3
2
15.1
0
18.8
7
22.6
5
26.4
2
30.2
0
33.9
7
37.7
4
Wave Length, x
Wav
e El
evn.
, z
MEMBER NO = 35 DISTANCE FROM MEM LOCAL-AXIS GLOBAL-AXIS START 'x'-DIR 'y'-DIR 'z'-DIR 'X'-DIR 'Y'-DIR 'Z'-DIR <-------- MEMBER LOADS --------> 0.00 -0.0111 -0.0089 0.0000 -0.0111 -0.0089 0.0000 2.33 -0.0077 -0.0098 0.0000 -0.0077 -0.0098 0.0000 4.66 -0.0039 -0.0103 0.0000 -0.0039 -0.0103 0.0000 7.00 0.0000 -0.0105 0.0000 0.0000 -0.0105 0.0000
Typical Output of Member Loads:
TOWER DEAD WEIGHT JOINT LOADS JOINT NO 'X'-DIR 'Y'-DIR 'Z'-DIR 72 0.000 -2.416 0.000 76 0.000 -2.425 0.000 71 0.000 -23.286 0.000 73 0.000 -3.804 0.000 79 0.000 -2.425 0.000 75 0.000 -2.305 0.000 77 0.000 -2.066 0.000
TOWER BUOYANCY JOINT LOADS JOINT NO 'X'-DIR 'Y'-DIR 'Z'-DIR 16 0.000 0.301 0.000 27 0.000 0.301 0.000 13 0.000 8.695 0.000 24 0.000 8.695 0.000 7 0.000 38.847 0.000 12 0.000 10.473 0.000 23 0.000 10.473 0.000
Typical Joint Loads:
* Wave Loading : Non Structural MembersJOINT LOAD136 FX -0.14 FY -1.671 FZ -0.14135 FX -0.268 FY -3.349 FZ -0.268134 FX -0.08 FY -1.017 FZ -0.08133 FX -0.015 FY -0.149 FZ -0.015
WAVE XYZ BASE SHEARS XYZ BASE MOMENTS POSN FX FY FZ MX MY MZ 0 10. -44. 9. 253. -9. -268. 45 -34. -32. -35. -753. -9. 737. 90 -54. 0. -54. -1198. -4. 1194. 135 -40. 28. -39. -875. -1. 875. 180 -5. 40. -5. -128. 3. 131. 225 32. 31. 33. 696. 6. -694. 270 55. 4. 55. 1217. 5. -1214. 315 47. -28. 46. 1077. 0. -1077. 360 10. -44. 9. 253. -9. -268.
Typical Base Shear and Base Moments:
Fx and Mz
-60-40-20
020406080
0 45 90 135
180
225
270
315
360
Wave Position
Fx
-1500
-1000
-500
0
500
1000
1500M
z FxMz
Fz and Mx
-60-40-20
020406080
0 45 90 135
180
225
270
315
360
Wave Position
Fz
-1500
-1000
-500
0
500
1000
1500
Mx Fz
Mx
TOWER WT CGXW CGYW CGZW BUOY WT CGXB CGYB CGZB 4160.92 0.04 19.54 0.01 778.81 -0.01 14.94 0.01
Weights and CG’s:
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 beadded manually in this STAAD.Pro Input File
Basic Data for Transportation Module:
Motion Parameters:
Center of Rotation = 0, -34.0, 0 (in m.)
Gravity/Tilt =
Heave (DY) = 6 m and Period = 10.0 secsRoll (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 CONCENTRATEDWEIGHT* 89 FX 0.000 FY -13.251 FZ 16.150 90 FX 0.000 FY -13.251 FZ 16.150
Heave + RollStarboard
LOADING 2 DOF LOADS = +DY -RXMEMBER 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
*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
Heave + RollPort
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 canbe 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 YRRETURN
±X, ±Z 35040
Vessel Motion:TYPE DIRECTIONS MAXM
CYCLES/YREXTREME ±X, ±Z 13075
API RP-2A Code Check:
• In-built API code ofSTAAD.Pro is used to carryout Steel Design
• Pinpoint Critical Joints forwhich Fatigue Analysis hasto be carried out
Critical Joints5 & 6
Maxm. CFR
Punching Shear Check:
< 1.0
• 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
• 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 Data to Calculate SCF’s:Wordsworth-Smedley Concept is used.
Basic Input Screens:
MEMBER NO JOINT NO CHORD LIFE STUB LIFE BRACE LIFE
24 5 20.096 63.825 13257.769 27 6 26.168 83.853 20305.904
Fatigue Life Evaluation:
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.
• 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
List of Offshore Load Generator Module Users: (Contd.)