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.)