Spar Configuration

7/31/2019 Spar Configuration

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Design o f Float ing St ruc t ures

CE 5710

Lecture 6BSpar Design

Sept. 19, 2006Dr. John Halkyard

E1A-07-15Tel 6516 2153

[email protected]


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1

SPAR SIZING

Oryx Neptune


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2SPAR PROGRESSIONSPAR PROGRESSION

Classic

Spars

Also FDPSO

TrussSpars

Cell Spar


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3

290'-0"

TOP TENSIONEDRISER

25'-0"

STEELCATENARYRISER (SCR)

EL (-) 505'-0"

HEAVE

KEEL TANKFOR FLOATOUT& FIXED BALLAST

PLATE

STEMLOWER

EL (+) 50'-0"

TANK

VARIABLEBALLAST

STRAKE

BULKHEADCONTROLDAMAGE

MWL

CHAINJACK

DRYTREE

EXTENSIONSTEMUPPER

RISERBUOYANCYCAN

BUOYANCYCANGUIDELEVEL

MOORINGCHAIN

FAIRLEAD

EXTENSION

GUIDESTEM

(TYP.)

240'-0"

VOID

VOIDVOID

VOID

VOIDVOID

SCR

275'-0"

TANKBALLASTFIXED

CHAINMOORING

RISERTENSIONED

FAIRLEAD

CANSBUOYANCY

BULKHEAD

275'-0"

CONTROLDAMAGE

TANK

STRAKE

BALLASTVARIABLE

MWL

RISERTOP TENSIONED

DRYTREE

EL (-)530'-0"

EL (+)50'-0"

TOP

VOID

VOID

VOID

VOID

35'-0"

VOID

VOID

VOID

VOID

Hard Tank

Midsection

Soft Tank

(fixed ballast)Keel

Freeboard

Basic Arrangements and Terms

Classic Truss


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4

SCR

275'-0"

TANKBALLASTFIXED

CHAINMOORING

RISERTENSIONED

FAIRLEAD

CANSBUOYANCY

BULKHEAD

275'-0"

CONTROLDAMAGE

TANK

STRAKE

BALLASTVARIABLE

MWL

RISERTOP TENSIONED

DRYTREE

EL (-)530'-0"

EL (+)50'-0"

TOP

VOID

VOID

VOID

VOID

35'-0"

VOID

VOID

VOID

VOID

Dk 1Dk 3

Dk 4

Dk 5

Dk 6

Dk 7

Dk 8

Dk 9Dk 10

CHAIN

MOORING

TENSIONED

FAIRLEAD

CANSBUOYANCY

BULKHEAD

275'-0"

CONTROLDAMAGE

TANK

STRAKE

BALLASTVARIABLE

MWL

TOP

VOID

VOID

VOID

VOID

VOID

VOID

VOID

VOID

ChainLocker


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5Setting the Spar Configuration

Start with the Risers

Size the Centerwell

Provide Buoyancy to Support all the vertical loads: TopsidesOutfitted Hull Weight SCR Vertical LoadsMooring Vertical Loads

Variable Ballast Fixed Ballast Risers that are not supported on buoyancy cans

Provide adequate stability


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6Main Spar Input Parameters

WT Topsides Weight (Fixed +Variable)

ZT Topsides VCG (above spar deck) AT Wind Area for Topsides Zw Centroid of Wind Area (from

Waterline)

Topsides Eccentricity

Depth (for mooring and risers) Number of Risers & Slots Spacing of Risers

Allowances for future risers.

Fmoor Vertical Mooring Load KF Fairlead Elevation above keel*

Friser Riser Vertical Load

KR Riser Elevation above keel

Environment Survival Wave, Wind &Current

ZT

Fmoor

Friser

Water

Depth

KF

ZW

* - Actually design variable


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7Main Spar Constraints

Max Diameter for Construction Largest spar D=45 m

Typical D = 33 m Max length and hull weight for dry

transport (150 m and 25,000 t) Check Heavy Lift Vessels

Max Draft in Horizontal for float-off (10m)

Minimum deck clearance (air gap)

Can use two piece transport for large

spars.

Air Gap >= 1.15*Hs (1st cut) Hmax = 1.86*Hs Amax = 0.93*Hs

ZT

Fmoor

Friser

Water

Depth

KF

Air Gap

4.5 m forequipment


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8Main Spar Design Parameters

CW Centerwell Width HHT Hard Tank Depth FB Free Board T Draft D Diameter Compartment Sizes

Variable Ballast

Fixed Ballast

T

HHT (Hard Tank Depth)

D

CW

FB

Fixed

Ballast

VariableBallast


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9Sizing the Wellbay

Number of riser slots?

Single or Dual Casing Risers?

Required Top Tension Factor?

Workover Strategy?

Buoyancy can capacity and allowancefor damage?

Arrive at can diameter and length?

Minimum well spacing = can diameter+ allowance for grillage (.3 to .4 m)

Space allocation for drilling, SCRs

and moonpool for ROV launching

Arrive at a centerwell size

0

0.5

1

1.5

22.5

3

3.5

4

4.5

5

0 500 1000 1500 2000

Water Depth, m

WellbayRiser

Spacing,m

Well Spacing

Suggestion: Use 3.6 m for depth 1500 m


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10Spar Weight Categories

Topsides (Fixed and Variable) Hull Hull Outfitting Ballast Variable Ballast - Fixed

External Loads Mooring Risers (initial and future)

Buoyancy Must Balance the Weights andthe Hull Must Be Stable!


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Topsides (Fixed and Variable) Hull Hull Outfitting Ballast Variable

Ballast - Fixed




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12Topsides Parameters

Units here are English. Weight in

kips (1000 lb, .454 tonne)

1951 m2

5448 tonnes

35 m


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13

45 deg

Block Desc z center Ch (ABS) Length Height Area Area CorreAdj Area Cs CsChArea Force/Ur**2

1 Lower Decks 21.8 1.1 100 3.6 360 1 360 1 396 242

2 Rig 27 1.1 30 7 210 1 210 1 231 141

3 Quarters 30 1.1 20 10 200 1 200 1 220 134

4 Process 28 1.1 20 8 160 1 160 1 176 108

5 Derrick 55 1.3 15 40 600 0.6 360 1.25 585 357

6 Hull 7.6 1 21.9 15.2 334 1 334 1 334 204

7 Deck Supports 17.5 1.1 21.9 15.2 333 0.6 200 1 220 134

Force at 0 deg Total Force/Ur2 1187 N/(m/s)2

Equivalent Area = Force/(wgUr2) 1942 m

Centroid of Force 30.2

Force at 45 deg ~ 1.2* Force at 0 deg Total Force/Ur2

1424 N/(m/s)2

Use this in sizing of the hull >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Equivalent Area = Force/( wgUr2) 2331 m

2

Wind Force

1

2

3

4

5

Selectdifferent blockareas basedon elevation,shape

z2

z1

z4

z5

z3

6z6

0 deg

Wind Force


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15Hull Weight Estimating

Design Spiral Start with Guess for Hull Size, Compartments, etc. Make approximate weight estimate based on Area of plate, or

Volumetric Weights

Perform buoyancy and stability check (initial GM Target 4 6 m forspar; Natural Period in Pitch 40 75 sec)

Update size and approximate weight Once size is OK determine scantlings and actual weight including

margins based on local strength (check against previous designs)

Redo buoyancy and stability check until successful

Check global strength and fatigue later in design!

Hull Weight is based onlocal strength (pressure).

See MODU Rules, Course

Notes!


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16INTERNAL STRUCTURE - EXAMPLE


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17

AA

BB

A-A

B-B

Section atWaterline

TypicalSection

Hull Compartments

9

8

7

65

4

3

2

1

Section

Waterline


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18Design Head (Local Pressure)

Waterline

Design head is Static +

Dynamic (foroperational waves)


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19Structural Design

Struts reduce

girder span

Outer shell treatedas flat plate

Idealization ofOuter Shell as

Flat Panels


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20Weight Summary from Scantling Design Program (example)

Sect. Length, m Outer Shell Inner Shell Decks Primary B Centerwell Secondary Struts Totals

9 9.1 120.8 0.0 53.4 16.0 45.1 0.0 10.7 245.9

8 15.2 191.3 271.1 38.0 52.5 132.8 0.0 13.7 699.5

7 14.9 318.3 0.0 63.8 55.1 168.2 0.0 30.0 635.5

6 14.9 376.7 0.0 79.9 67.2 200.3 0.0 45.4 769.5

5 14.9 438.6 0.0 92.9 73.9 235.2 0.0 57.4 898.0

4 14.9 500.2 0.0 233.6 79.9 266.8 0.0 77.0 1157.5

3 118.9 2084.9 0.0 0.0 0.0 0.0 0.0 0.0 2084.9

2 11.0 310.3 0.0 172.1 176.0 91.8 0.0 24.9 775.0

1 1.2 20.8 0.0 367.0 13.7 5.7 0.0 0.0 407.1

Totals: 0.0 4361.9 271.1 1100.8 534.1 1145.9 0.0 259.0 7672.8

Weight, tonne


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21Weights - By Area

0

100

200

300

400

500

600

0 10 20 30 40 50 60 70 80

Design Head, m

Weight,kgf/sqm

Outer Shell

Deck

Primary BHD

Centerwell

Add all panel weights and add struts and

non-watertight bulkheads if applicable.

Y=6.2*h+90

Y=9.6*h+75.4


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22Weights By Volume

y = 96.547e0.0157x

0

50

100

150

200

250

300

0 10 20 30 40 50 60 70 80

Design Head, m

Weight,kgf/m

3

Using volumetric factors is easier butless accurate that using area factors.


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23Weights of Midsection & Truss

Midsection in classic spar designed from minimum head (6.1 m) Control of ring frames is allowable deflection during construction, usually

less than about 50 mm!

Truss design is controlled by global bending at maximum pitch angle.

Assume static loads at 10 deg angle Select truss members for lateral gravity loads


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25Minimum Variable Ballast

Deck Eccentricity Future Risers Compensating a Flooded Compartment Overcoming buoyancy of stored oil over water (if any)


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26Minimum Variable Ballast Deck Eccentricity

Balance Deck Eccentricity

T

D

FB

Fixed

Ballast

VariableBallast

Deck

Eccentricity,

Centroid of Ballast,

topsidesWBallast =


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27Minimum Variable Ballast Damaged Compartment

If a single compartment is flooded, MODU Rules Require the ability torestore original draft and trim in order to initiate repairs.

Typically a damageddepth of 25 50 ft is assumed, include the equivalentamount of ballast from asingle flooded compartment (one quadrant of thebuoyanct hull).


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29Outfitting Weight

1st Cut Outfittingweights are about

20% of the hull

structural steel!


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30Parametric Model for Sizing

Desired Outcome(s) = Function of (size, weight, environment, etc.)

Keep iterating until the desired outcome is reached!!

S D i P


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31Spar Design Process

Select Input Parameters and Centerwell Size for Risers

Select Mooring Fairlead Elevation

Select A Trial Hull Size (draft, diameter, hardt tank depth)

Estimate hull weight by approximate method

Calculate Imbalance of Weight and Buoyancy. If excess weight, increase diameter or hard tank depth

If excess buoyancy, add fixed ballast

Calculate heel angle for 100 year storm If less than target (5) reduce diameter or hard tank length

If greater than target increase diameter or hard tank length

If target ismet perform detailed weight estimate and check

Iterate on this procedure for optimum design

SPAR SIZING


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32

WSoftTank

F

FixedBallast

W

SCR

WTruss

TrussB

MooringF

CurrentF

FWind

VariableBallast

W

W

Outfitting

BHardTank

HardTank

W

MooringF

MWL

WTopsides

SPAR SIZING

WIND LOAD

(100 YrStorm)

MOORING LOAD

THE CENTRAL CRITERIA INSPAR SIZING IS TOBALANCE THE

OVERTURNING MOMENTDUE TO WIND WITH THERESTORING MOMENT DUE

TO BGG

B

MaxHeel

Angle ~

5

Topsides

Hull

Var Ballast

Fixed Ballast

SPAR SIZING


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33SPAR SIZING

WSoft Tank

F

Fixed BallastW

SCR

WTruss

TrussB

MooringF

CurrentF

FWind

Variable Ballast

WW

Outfitting

BHard Tank

Hard Tank

W

MooringF

MWL

WTopsides

+=

=

IKGKBGM

GMKPitch

G

B

BG is the dominant restoring moment

The waterplane effect (BM) is not significant

The spar is unconditionally stable The center of gravity is always below the

center of buoyaancy

Flooding will not cause instability Broken mooring will not cause instability

Broken riser will not cause instability

BG ~ 5 8m BM < 1m

Hull Geometry Example ISAP


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34Hull Geometry Example ISAP

Draft = 198 m (650 ft)

Diameter = 21.9 m (72 ft)

Freeboard = 16.8 m (55 ft)

Centerwell = 9.8 m x 9.8 m (32 ft)

Hard Tank Depth = 67 m (220 ft)

Buoyancy and Internal Water


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35Buoyancy and Internal Water

T

D

CW

FB

Fixed

Ballast TDBUOYANCY w2

4

=

A

B

Weight Summary


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36Weight Summary

Hull Weight = 8424 t (18567 kips)

Outfitting Wt = 1993 t (4389 kips)

Topside Wt = 5448 t (12000 kips)Fixed Ballast = 1123 t (2474 kips)

Var ballast = 1486 t (4876 kips)

Internal Water = 56617 t (124708 kips)

Vertical Loads = 1072 t (2361 kips)

Total = 76896 t (169375 kips)

Including Internal Water makes no Difference to Hydrostatics!


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37Including Internal Water makes no Difference to Hydrostatics!

Wt KG Wt KgWeight w/o Water 42306 493.1 167014 314.9

Vertical Loads 2361 310.0 2361 310.0

44666 483.5 169375 314.8

B KB

Disp w/o Water 44666 522.1 169375 325

BM 1.5 0.4

KB+BM-KG 40.1 10.6

GM*DISP 1791014 1791014

Without Internal Water With Internal Water

Whether you include internalwater or not does not makeany difference to the

hydrostatics. It does matterfor the hydrodynamics,however.

Disp 44666 kips (20278 t) 169375 kips (76896 t)

38

Oil Storage Spar


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38

STORAGE SPAR INBOARD PROFILE

EL (-)615'-0"

EL (-)650'-0"

SCR

EL (-)292'-0"

EL (-)220'-0"

EL (-)170'-0"

EL (-)120'-0"

EL (-)70'-0"

EL (-)20'-0"

EL (+)50'-0"

VOID

VOID

VOID

VOID

395'-0"

TOP

35'-0"

TANKBALLASTFIXED

CHAINMOORING

RISERTENSIONED

FAIRLEAD

BOLTHOLES

CANSBUOYANCY

BULKHEAD

275'-0"

CONTROLDAMAGE

TANK

STRAKE

BALLASTVARIABLE

VOID

VOID

VOID

VOID

MWL

PULL-IN

HOUSING

BOTTOM

SCR

GUIDE

OF SPAR

SCR

SCRHOUSING STAB-IN

TIE BACK

RISERTOP TENSIONED

RINGFLANGE

STEMRISER

JOINTSLEEVE

KEEL

RISER

RISER

STIFFENERBAR

EMULSIONLAYER

EL (-)585'-0"

A A

OIL

A - A

OIL

~~

the centerwell is extended through themidsection,

the shell is strengthened to withstandthe differential pressures generated

when the storage compartments arefilled with oil,

the amount of fixed ballast is increasedto account for the lower center ofbuoyancy

Oil Storage Spar

39Distribution of Loads for Spars


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39Distribution of Loads for Spars

TYPE OF SPAR TRUSS TRUSS TRUSS CLASSIC TRUSS TRUSS TRUSS CLASSIC

DISPLACEMENT 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0%

TOPSIDES 24.7% 23.8% 30.6% 27.7% 26.2% 27.7% 26.4% 26.3%

STORAGE IN HULL 1.4% 0.7% 2.0% 1.2% 0.0% 0.0% 0.0% 0.0%

VARIABLE BALLAST 5.5% 10.1% 0.0% 4.6% 6.1% 6.9% 4.9% 7.2%

FIXED BALLAST 16.5% 18.6% 26.4% 15.5% 23.3% 21.2% 23.6% 0.0%

SCR LOAD 0.8% 3.1% 2.1% 0.0% 2.2% 3.7% 2.4% 1.4%

TTR LOAD 12.2% 0.0% 1.4% 0.5% 0.0% 0.0% 0.0% 0.0%MOORING LOAD 5.0% 6.2% 3.4% 3.6% 7.0% 6.2% 7.1% 2.4%

OUTFITTED HULL WEIGHT 33.9% 37.5% 34.2% 46.9% 35.2% 34.3% 35.5% 62.7%

40Excercise


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40ce c se

Consider example spar in this lecture 72 ft (21.9 m) dia 220 ft (67 m) hard tank depth Etc.

Add 1000 tonne to deck weight (same VCG and wind area) . Total 6448tonnes

Increase hard tank depth and/or diameter to achieve the same GM

What is new hull weight (approximately)

Hint: you mayhave to increase fixed ballast as well.

Hmax = 75 ft

Period = 13 sec.

Spar Configuration

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