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Despre platforme petroliere

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Prezentare Oil Rigs
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١٠/١٢/١٤٣٣ ١ Supervised by: Prof Prof Prof Prof. Dr Dr Dr Dr. Aly Aly Aly Aly G. A. Abdel Abdel Abdel Abdel-Shafy Shafy Shafy Shafy Prof Prof Prof Prof. Dr Dr Dr Dr. Fayez Fayez Fayez Fayez Kaiser Kaiser Kaiser Kaiser Abdel Abdel Abdel Abdel-Seed Seed Seed Seed Assoc Assoc Assoc Assoc Prof Prof Prof Prof. Shehata Shehata Shehata Shehata E. Abdel Abdel Abdel Abdel Raheem Raheem Raheem Raheem Examined by: Prof Prof Prof Prof. Dr Dr Dr Dr. Ahmed Ahmed Ahmed Ahmed El El El El-Badawey Badawey Badawey Badawey Sayed Sayed Sayed Sayed Prof Prof Prof Prof. Dr Dr Dr Dr. Mahmoud Mahmoud Mahmoud Mahmoud H. Ahmed Ahmed Ahmed Ahmed Prof Prof Prof Prof. Dr Dr Dr Dr. Aly Aly Aly Aly G. A. Abdel Abdel Abdel Abdel-Shafy Shafy Shafy Shafy Prof Prof Prof Prof. Dr Dr Dr Dr. Fayez Fayez Fayez Fayez Kaiser Kaiser Kaiser Kaiser Abdel Abdel Abdel Abdel-Seed Seed Seed Seed Assoc Assoc Assoc Assoc. Prof Prof Prof Prof. Shehata Shehata Shehata Shehata E. Abdel Abdel Abdel Abdel Raheem Raheem Raheem Raheem Nonlinear Nonlinear Nonlinear Nonlinear Analysis of Offshore Structures Analysis of Offshore Structures Analysis of Offshore Structures Analysis of Offshore Structures Master of Science By Elsayed Mahmoud Aly Abdel-Aal B.Sc. 2004, Senior Engineer in Egypt Gas Company Exploration and production of oil and gas, Harnessing power from sea, Navigational lighting, Radar surveillance, Space operations, Oceanographic research. In this study We focus on the structures used for the exploration and production of oil and gas industry. The offshore structures is very important structures as install in the sea for many purpose; There are about more than 9000 fixed offshore platforms around the world related to hydrocarbon/oil production. In Egypt there are platforms in Gulf of Suez and Mediterranean Sea.
Transcript
Page 1: Despre platforme petroliere

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Supervised by:

ProfProfProfProf.... DrDrDrDr.... AlyAlyAlyAly GGGG.... AAAA.... AbdelAbdelAbdelAbdel----ShafyShafyShafyShafy

ProfProfProfProf.... DrDrDrDr.... FayezFayezFayezFayez KaiserKaiserKaiserKaiser AbdelAbdelAbdelAbdel----SeedSeedSeedSeed

AssocAssocAssocAssoc ProfProfProfProf.... ShehataShehataShehataShehata EEEE.... AbdelAbdelAbdelAbdel RaheemRaheemRaheemRaheem

Examined by:

ProfProfProfProf.... DrDrDrDr.... AhmedAhmedAhmedAhmed ElElElEl----BadaweyBadaweyBadaweyBadawey SayedSayedSayedSayed

ProfProfProfProf.... DrDrDrDr.... MahmoudMahmoudMahmoudMahmoud HHHH.... AhmedAhmedAhmedAhmed

ProfProfProfProf.... DrDrDrDr.... AlyAlyAlyAly GGGG.... AAAA.... AbdelAbdelAbdelAbdel----ShafyShafyShafyShafy

ProfProfProfProf.... DrDrDrDr.... FayezFayezFayezFayez KaiserKaiserKaiserKaiser AbdelAbdelAbdelAbdel----SeedSeedSeedSeed

AssocAssocAssocAssoc.... ProfProfProfProf.... ShehataShehataShehataShehata EEEE.... AbdelAbdelAbdelAbdel RaheemRaheemRaheemRaheem

NonlinearNonlinearNonlinearNonlinear Analysis of Offshore StructuresAnalysis of Offshore StructuresAnalysis of Offshore StructuresAnalysis of Offshore Structures

Master of ScienceBy

Elsayed Mahmoud Aly Abdel-AalB.Sc. 2004, Senior Engineer in Egypt Gas Company

� Exploration and production

of oil and gas,

� Harnessing power from sea,

� Navigational lighting,

� Radar surveillance,

� Space operations,

� Oceanographic research.

� In this study We focus on

the structures used for the

exploration and production of

oil and gas industry.

� The offshore structures is very important structures as install in the sea

for many purpose;

� There are about more than 9000 fixed offshore platforms around the

world related to hydrocarbon/oil production.

� In Egypt there are platforms in Gulf of

Suez and Mediterranean Sea.

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� General Introduction on offshore structures

(classification, objective, methods of installation,

challenges that faced )

� Forces affect on offshore structures

� Finite Element Procedures and Mathematical modeling

� Numerical study and Results discussions

� Conclusions and recommend future extension of

present research

General Introduction on General Introduction on General Introduction on General Introduction on offshore structuresoffshore structuresoffshore structuresoffshore structures

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An offshore structure has no fixed access to dry land and may be

required to stay in position in all weather conditions. The going to it

only by boat or helicopter.

ObjectiveObjectiveObjectiveObjective:::: The majority of offshore structures support the exploration

and production of oil and gas industry

Offshore Structure Definition Offshore Structure Definition Offshore Structure Definition Offshore Structure Definition

� Platform classification (Function and Types)

Steel jacketSteel jacketSteel jacketSteel jacketSteel towerSteel towerSteel towerSteel towerSteel gravitySteel gravitySteel gravitySteel gravity

Concrete gravityConcrete gravityConcrete gravityConcrete gravity

RigidRigidRigidRigid

Fixed Fixed Fixed Fixed offshoreoffshoreoffshoreoffshoreplatformsplatformsplatformsplatforms

Free standing towerGuyed towerSpar towerTension Leg Platform (TLP)

Compliant

The variety of platform types

is due to different factors:

technological and scientific

progress, economical factors,

deeper natural reservoirs,

ecological constraints.

jacketjacketjacketjacket

General scheme of offshore platforms in relation with water depth

jacketjacketjacketjacket

jackjackjackjack----upupupup

SemiSemiSemiSemi----submersiblesubmersiblesubmersiblesubmersible

Drilling shipDrilling shipDrilling shipDrilling ship

TLPTLPTLPTLP

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The most classical and widely

used offshore platform. ThisThisThisThis typetypetypetype

isisisis thethethethe casecasecasecase studystudystudystudy inininin thisthisthisthis thesisthesisthesisthesis....

It is composed of three principal parts: the

deck, carrying the topsides (living quarters,

drilling derrick consumables, facilities,

helideck, flare etc.), the jacket itself and the

foundation piles.

Steel jackets are normally used in shallow to

moderate deep waters (from(from(from(from 20202020 totototo100100100100 m)m)m)m)....

Rigid platforms: Rigid platforms: Rigid platforms: Rigid platforms: Steel JacketSteel JacketSteel JacketSteel Jacket

StepStepStepStep1111: Barge install the jacket: Barge install the jacket: Barge install the jacket: Barge install the jacket

StepStepStepStep2222: Barge install the platform deck : Barge install the platform deck : Barge install the platform deck : Barge install the platform deck

StepStepStepStep3333: Mating of platform deck with jacket: Mating of platform deck with jacket: Mating of platform deck with jacket: Mating of platform deck with jacket

Methods of InstallationMethods of InstallationMethods of InstallationMethods of Installation

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1: Construction in a coast yard;

2: Transportation by barge on theoil field;

3:::: Launching of the jacket.

The construction phases of a jacketThe construction phases of a jacketThe construction phases of a jacketThe construction phases of a jacket

Light /Shallow waterLight /Shallow waterLight /Shallow waterLight /Shallow water Jacket: Jacket: Jacket: Jacket: (Steel jacket) Piles are inserted in the legs

Heavy /Deep Water Jacket:Heavy /Deep Water Jacket:Heavy /Deep Water Jacket:Heavy /Deep Water Jacket:. (Steel tower ) Piles are inserted in Skirt piles around the outside of the legs.

Platform Jacket FoundationPlatform Jacket FoundationPlatform Jacket FoundationPlatform Jacket Foundation

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Rarely used, uses its own weight to counter the lateral actions due to wind and waves: the weight is used as a stabilizing force.

Nevertheless, the real reason for using gravity platforms is the nature of the soil, when it is of solid rock, it is impossible to drive piles into it.

An important feature of all the gravity platforms is that they can be removed for demobilization or re-use.

Normally, the structure has a certain number of large tanks, flooded by water or by crude oil, to ballast the platform and provide the necessary weight to counter overturning lateral forces.

These tanks, in the transportation phase, provide the necessary buoyancy.

Rigid Gravity Platforms (Steel or Concrete)Rigid Gravity Platforms (Steel or Concrete)Rigid Gravity Platforms (Steel or Concrete)Rigid Gravity Platforms (Steel or Concrete)

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ConcreteConcreteConcreteConcrete gravitygravitygravitygravity platformsplatformsplatformsplatforms:::: MalampayaMalampayaMalampayaMalampaya is a concrete gravityplatform (Philippines).

1111. construction in a dock under the sea level. construction in a dock under the sea level. construction in a dock under the sea level. construction in a dock under the sea level

2222. construction of the towers. construction of the towers. construction of the towers. construction of the towers3333. flooding of the dock: the platforms is ready to . flooding of the dock: the platforms is ready to . flooding of the dock: the platforms is ready to . flooding of the dock: the platforms is ready to be towedbe towedbe towedbe towed

4444. towing of the concrete substructure. towing of the concrete substructure. towing of the concrete substructure. towing of the concrete substructure 5555. ballasting of the concrete substructure. ballasting of the concrete substructure. ballasting of the concrete substructure. ballasting of the concrete substructure

6666. mating. mating. mating. mating 7777. the final platform. the final platform. the final platform. the final platform

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CompliantCompliantCompliantCompliant PlatformsPlatformsPlatformsPlatforms:::: FreeFreeFreeFree StandingStandingStandingStanding TowersTowersTowersTowers

� classical towers but so slender that their structural behavior is that of acompliant structure: large sway displacements and high oscillating period.system is strong enough to with stand hurricane conditions.

� Baldpate:Baldpate:Baldpate:Baldpate: is one of the highest, freestanding compliant structure in the world.

Characteristics:

water depth: 501 m;sway response cycle: 30 s;lateral displacement: 3 m;

cross section: 42.6 x 42.6 m (bottom) ,

27.4 x 27.4 m (top);

weight of the tower:28900 t;

weight of deck and

topsides: 2700 t ;

Compliant Platforms: Compliant Platforms: Compliant Platforms: Compliant Platforms: Guyed TowerGuyed TowerGuyed TowerGuyed Tower

Compliant platforms are composed by a slender jacket, normally pin-joined at its base, whose vertical stable position is ensured by the buoyancy of the structure itself and by a series of mooring catenaries lines.

The structure can oscillate under the lateral actions, the restoring force being provided by the buoyancy and the mooring lines. The clump weights provide additional restraining forces in case of storm.

These platforms are used for water depth in the range 200-600 m, and they can be re-used.

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Compliant Platforms: Compliant Platforms: Compliant Platforms: Compliant Platforms: SPAR towersSPAR towersSPAR towersSPAR towers

These platforms are composed by a large steel tube as substructure

directly supporting the deck and topsides.

� The tube is ballasted so as its floating stable equilibrium position is vertical (including topsides), and moored by tensioned risers and by

mooring lines (catenaries).

� The first Spar platform in the Gulf of Mexico was installed in September of 1996. It's cylinder measured 770 feet long, and was 70 feet in diameter, and the platform operated in 1,930 feet of water depth.

TLPTLPTLPTLP (Tension(Tension(Tension(Tension LegLegLegLeg Platforms)Platforms)Platforms)Platforms)

They are floating structures anchored to the seafloor by a series ofvertical tendons (tethers) pre-tensioned by extra-buoyancy. The tethers

are made by steel pipes.

� A TLP is composed by 4 principal parts: the deck,

the hull, the tethers and foundation template.

�TLP are very large structures, able to host great payloads. So, they are used for great fields and can host some refining processes and have a good storage capacity.

� TLP can be used from 150 m of water depth on, and theoretically there is no limit of water depth .

� The restoring force is given by extra buoyancy; this is obtained de-ballasting the TLP hull once the tethers installed.

�TLPs can be re-used.

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MiniMiniMiniMini TLPTLPTLPTLP: These TLP have a less

payload capacity, and are normally used

for deep water small field.

Snorre platformSnorre platformSnorre platformSnorre platform:::: is an example of TLP

Characteristics::::Water depth: 395 m;Dimension : (100 x 100 )m;Colum diameter: 24.4 m;Topsides weight : 30000 t;

hull's weight : 43700 t.

snorresnorresnorresnorre

Mini TLPMini TLPMini TLPMini TLP

The design of an offshore platform is a very complex process, as several different aspects must be taken into account.

Preliminary Phase: Preliminary Phase: Preliminary Phase: Preliminary Phase: data concerning the industrial activity, the construction facilities, the environmental conditions must be collected.

ConstructionConstructionConstructionConstruction PhasePhasePhasePhase:::: Greater jackets are skidded onto barges and then launchedinto the sea, eventually with the aid of a crane or of floating units.

TransitoryTransitoryTransitoryTransitory PhasePhasePhasePhase ofofofof PilePilePilePile DrivingDrivingDrivingDriving:::: the jacket must not overturnunder the action of moderate waves.

The knowledge of the climatic and geographic data allowsto determine some fundamental dimensions of thestructure. once the LAT (Lowest Astronomical Tide) andthe design wave known, the height h of the jacket can bedetermined:

Here, aaaa is the wave amplitude, t max is the maximumtide and agagagag is the so-called air-gap.

APIAPIAPIAPI RPRPRPRP----2222AAAA specifies that the lowest deck must maintain aminimum of 1.5 m air gap between the bottom of the deckbeams and the wave crest during the maximum expectedlevel of water

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� PermanentPermanentPermanentPermanent (dead)(dead)(dead)(dead) loadsloadsloadsloads:::: structural loads, operational dead loads,deformation and hydrostatic permanent loads.

� VariablesVariablesVariablesVariables (live)(live)(live)(live) loadsloadsloadsloads:::: are composed of operational live loads, environmentalloads, accidental loads, variable hydrostatic and deformation loads.

StructuralStructuralStructuralStructural loadloadloadload: Self weight of the structure constituting the platform; hence, itis a result of the design process.

DeformationDeformationDeformationDeformation loadsloadsloadsloads:::: Loads produced by an imposed state of strain on thestructure. (temperature differences, ground settlements, pre-stressedstates).

HydrostaticHydrostaticHydrostaticHydrostatic loadsloadsloadsloads:::: buoyancy of some submerged members (depending upontides and waves).

AccidentalAccidentalAccidentalAccidental loadloadloadload:::: wrong operations or by events not considered in thenormal operations of the platforms (explosions, impacts, fires).

� EnvironmentalEnvironmentalEnvironmentalEnvironmental LoadsLoadsLoadsLoads:::: Environment gives different kinds of actions onoffshore platforms such as:

� WaveWaveWaveWave force,force,force,force, CurrentCurrentCurrentCurrent force,force,force,force, MarineMarineMarineMarine growth,growth,growth,growth, IceIceIceIce forces,forces,forces,forces, WindWindWindWind force,force,force,force, SnowSnowSnowSnowforcesforcesforcesforces andandandand EarthquakeEarthquakeEarthquakeEarthquake actionactionactionaction.

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� the wave theory describes the properties of one cycle of the regular waves

and these properties are invariant from cycle to cycle.

� The assumptions made in formulating the wave models:

ideal fluid (i.e. inviscid incompressible fluid); irrotational motion;

bi-dimensional flow; horizontal plane sea bottom.

� The model scheme is in the figure:

L: L: L: L: the wave length;d: d: d: d: the water depth;η: η: η: η: the wave surface position

above the still water level(SWL);a: a: a: a: the wave amplitude;H=H=H=H=2222a: a: a: a: the wave height;ω=ω=ω=ω=2222π/π/π/π/T: T: T: T: the wave frequency;T: T: T: T: the wave period;k=k=k=k=2222π/L: π/L: π/L: π/L: the wave number.

Wave Theories

Small amplitude wave theories,

Finite amplitude wave theories.

Wave Forces

� In computing wave forces on a structure, the structure is considered fixedin its equilibrium position. A distinction is made regarding small vs. large

structures.� For small structures, The Morison equation is used for the wave force

computation.

� For large structures, The linear diffraction/radiation theory is used for the

wave force computation.

Morison's Equation� It is an empirical formula to compute inertia and drag forces on a small structural member.

� The forces depend on the inertia and the drag coefficients. These coefficients are determined experimentally either in the laboratory or from

the field measurements.

� The Archimedes' force (static);� The inertial force (dynamic), due to waves;� The drag force (dynamic), due to waves and currents.

� In offshore engineering,. So, only three

forces due to the water are considered:

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� It is the case of slender bodies, i.e. of cylinders of small diameter incomparison with the wave length (D/L< 0.2).

� The force is given by the Morison's equation as the sum of the inertialterm (Froude-Krylov force) and the drag term.

� The force per unit length acting upon a vertical cylinder is:

API norms suggest the values CCCCDDDD = 0.6 to 1.2 and CCCCMMMM = 1.3 to 2.0.

� The general form of the wind drag force (pressure drag) is:

F d = 1/2 Cd ρa AU 2

� ρ: fluid density (air: 1,225 kg/m3);� A: area of the projection of the body on a plane orthogonal to the flow;�U: wind speed;� Cd : drag coefficient.

� VelocityVelocityVelocityVelocity profileprofileprofileprofile:::: concerning the wind

speed U, depends upon place and time:

U= U(x, y, z, t)

Cd = 1.5 for beams and sides of buildings, Cd = 0.5 for cylindrical sections and Cd = 1 for total projected area of platform

Wind Force

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Current Forces� A typical vertical profile of the current speed is decreasing with

deepness.

� DNV rules give the following velocity profile V(z)for a current, sum of the astronomic tide current Vt

(z) and of the wind current Vw (z);

�Marine growth is accumulated on submerged members. increase thewave forces on the members by increasing exposed areas and volumes,and the drag coefficient due to higher surface roughness.

� Depending upon geographic location, the thickness of marine growthcan reach 0.3 m or more.

Marine Growth

� The thickness of marine growthmay be assumed to increase linearlyto the given values over a period of2 years after the structure has beenplaced in the sea.

�The specific weight of the marinegrowth in air may be set equal to 13

kN/ m3.

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Finite Element Procedures Finite Element Procedures Finite Element Procedures Finite Element Procedures

and Mathematical Modeling and Mathematical Modeling and Mathematical Modeling and Mathematical Modeling

The State of Problem

� InInInIn EgyptEgyptEgyptEgypt the last decade the climate change and the wave height andwind speed increase than old measurements especially in Red Sea andMediterranean Sea.

� The Gulf of Suez in Red Sea subjected to high wind speed and increasingwave height in April 2010, which play a vital role in stability of offshoreplatforms and many of platforms subjected to problems and cracks.

� In Alexandria on coastal of Mediterranean Sea the wave height increasesin December 2010 and covered many structure beside sea costal, highroads and closed the ports.

� For these changes the forces and loading acting on offshore structures inEgypt change and increase and all old offshore structures subject to overload which affected on life time of platforms. Which a lot of offshoreplatforms in Gulf of Suez installed from 20 to 50 years needing todevelopment and extension.

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� After the high weather that occurred in 2010 at Gulf of Suez the offshoreproduction platform "July-6" has subjected to hugehugehugehuge laterallaterallaterallateral loadingloadingloadingloading andandandandcausedcausedcausedcaused cuttingcuttingcuttingcutting inininin 2222 legslegslegslegs ofofofof thethethethe jacketjacketjacketjacket andandandand mademademademade collapsecollapsecollapsecollapse inininin thethethethe horizontalhorizontalhorizontalhorizontal

bracesbracesbracesbraces atatatat toptoptoptop ofofofof jacketjacketjacketjacket....

BeforeBeforeBeforeBefore AfterAfterAfterAfter

ThisThisThisThis studystudystudystudy focusfocusfocusfocus onononon responseresponseresponseresponse ofofofof fixedfixedfixedfixed jacketjacketjacketjacket subjectedsubjectedsubjectedsubjected totototo differentdifferentdifferentdifferent

weatherweatherweatherweather conditionsconditionsconditionsconditions totototo predictpredictpredictpredict thethethethe criticalcriticalcriticalcritical deflection,deflection,deflection,deflection, failurefailurefailurefailure modesmodesmodesmodesandandandand thethethethe maximummaximummaximummaximum forceforceforceforce demandsdemandsdemandsdemands inininin platformsplatformsplatformsplatforms andandandand howhowhowhow totototo preventpreventpreventpreventoffshoreoffshoreoffshoreoffshore platformplatformplatformplatform fromfromfromfrom collapsecollapsecollapsecollapse....

Motivation of this Research Work

Objective and Methodology

MethodologyMethodologyMethodologyMethodology:::: A nonlinear response analysis of a fixed offshore platform

under wave loading is presented

� The structure is discretized using the finite element method, wave force

is determined according to linearized Morison equation.

� Hydrodynamic loading on horizontal and vertical tubular members and

the dynamic response of fixed offshore structure together with the

distribution of displacement, axial force and bending moment along the

leg are investigated for regular and extreme conditions.

� The structure should keep production capability in conditions of the one

year return period wave (regular conditions) and must be able to survive

the 100 year return period storm conditions (extreme conditions).

TheTheTheThe objectiveobjectiveobjectiveobjective ofofofof thisthisthisthis researchresearchresearchresearch:::: is to develop an effective procedure for theinvestigation of the hydrodynamic forces resulting from environmental andinteractions of fixed jacket type offshore platform subjected to operationand extreme storm wave loads.

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Case Study Model� The case study platform is a fixed Jacket-Type platform, currently installedin the Suez gulf, Red sea, 1988.

� The offshore structure is a four legs jacket platform, consists of a steeltubular space frame. There are diagonal brace members in both vertical andhorizontal plans. The platform installed in 110 feet (33.5 m) water depth andsupported by four piles.

�In the splash zone area that is assumed to extend from EL. (-6 ft) to EL. (+6 ft) LAT. (Lowest Astronomical Tide).

� The jacket legs are horizontally braced with tubular members; In the vertical direction, the jacket is X-braced with tubular members

� The platform divide into Top side structure consists of Helideck (50 ft x 50 ft) at EL. (+ 54 ft) & Production deck (50 ft x 50 ft) at EL. (+26 ft) and jacket which top of jacket at level (+12.5 ft).

Model Description Platform was originally designed as a 4 Leg platform installed in 110 feet

water depth (jacket levels by feet and sections dimension by inch);

� The platform is supported by 4 piles (30" O.D. X 1.25" W.T.).

� All structural steel shapes, plates and tubular are normal mild steel in accordance with ASTM -A36 with minimum yield stress of 36 ksi.

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� A 3D model has been generated for The Platform using SAP 2000 (Structural Analysis Programmer) computer package.

� Secondary members that are not expected to contribute much to the structure strength are not included in the model simulation (i.e. ladders, grating, etc.) but their loads were reflected to the model.

� The right hand Cartesian system is used with the Z-axis vertically upwards and the origin is located at the Main water Level (MWL).

Finite Element Analysis Model

Environmental Forces� The design water depth at platform location shall be taken as actual water depth (-110 ft).The highest astronomical tide shall be taken as:

� 3 feet for the 1 year return period & 5 feet for the 100 years return.

�The platform in concern shall be checked and evaluated for the both:

�100 year extreme storm design criteria &1 year operation storm design.

Wind Force

� The 100 and 1 year return period sustained wind at 30 feet above LAT (lowest astronomical tide) shall be 70, 60 mph (mile per hour) respectively and the wind may act in any direction.

� The wind loads on the topsides and exposed part of the jacket shall be calculated based on the topsides layout configurations to determine the shape coefficients for both the 100 year storm and the 1 year storm.

Wave Force� The Omni-directional wave shall be taken as:

� For 100 year the Wave height = 26 feet, Wave period = 8 sec.

� For 1 year the Wave height = 17 feet, Wave period = 6.5 sec.

�A wave spreading factor (kinematics factor) = 0.95.

�The increase in all members radius shall be taken as 2 inch for the highest 50 feet and 1 inch for the rest of water depth down to mud line elevation.

Marine Growth

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Load Data� Dead Load; Dead Load; Dead Load; Dead Load; It automatically generates by the module of “SAP-2000”

computer program for all modeled members.

� Live Load; Live Load; Live Load; Live Load; It is assumed as uniformly distributed live load intensity of

� 50 psf " 0.245 t/m2 " applied for Helideck area

� 200 psf "0.978 t/m2 " applied for production deck and cellar deck area.

� The current profile assumed to act with the wave shall be taken as:

� For 100 year 4, 0 feet/second in accordance with the surface and mud line profile respectively. � for 1 year 3, 0 feet/second in accordance with the surface and mud line profile respectively.

Current Force

�Current blockage factors may be used as recommended by API (American petroleum institute) for jacket structures with 4 legs are:

� 0.8 for orthogonal current;

� 0.85 for diagonal current.

�Wave kinematics factor (spreading factor) due to wave directional spreading of 0.95 was adopted.

Hydrodynamic Load Data

� Buoyancy was generated for all modeled jacket members. Buoyancy was generated by "sea state" module based on the marine method in which buoyancy is generated as the weight of the displaced fluid and acting vertically on the members.

Buoyancy Loading

� Hydrodynamic coefficients, CD and CM, for clean and rough members as per item "2.3.1-7 of the API RP-2A –WSD " which :

� CD is 0.65 and 1.05 for smooth and rough tubular members respectively;

� CM is 1.6 and 1.2 for smooth and rough tubular members respectively.

� Coefficients for rough case shall be applied in areas subjected to marine growth.

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Numerical study andNumerical study andNumerical study andNumerical study andResults discussionsResults discussionsResults discussionsResults discussions

Analysis Procedure

� The natural frequencies and vibration mode shapes are computed byEigen value analysis.

� To provide a more accurate and effective design, a finite element modelis employed herein to determine the internal forces and displacements inan offshore leg under combined structural and wave loadings.

�The vertical structural load is essentially a static load, while the lateralwave loading fluctuates in time domain and is directly affected by theincident wave angle.

� The following table lists the properties of sea state in this studied.

DefinitionsWater depth

(MSL) ft

LAT

(MSL) ft

HAT

(MSL) ft

Tide

(ft)

H max.

(ft)

T

(sec)

1-year return period wave foroperating conditions

110' -6' 6'3' 17' 6.5

100 yearreturn period wave

for extreme conditions5' 26' 8

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� Different load combinations are applied to platform.

Load combination Description1 Dead Loads

2 Comb " Dead Load + Live load "

3 Comb+ ( Wind + wave ) 1 year+ currents hitting 00.0 deg.

4 Comb+ ( Wind + wave ) 1 year + currents hitting 45.0 deg.

5 Comb+ ( Wind + wave ) 1 year + currents hitting 90.0 deg.

6 Comb+ ( Wind + wave ) 1 year + currents hitting 135 deg.

7 Comb+ ( Wind + wave ) 1 year + currents hitting 180 deg.

8 Comb+ ( Wind + wave ) 1 year + currents hitting 225 deg.

9 Comb+ ( Wind + wave ) 1 year + currents hitting 270 deg.

10 Comb+ ( Wind + wave ) 1 year + currents hitting 315 deg.

11 Comb+ ( Wind + wave ) 100 year+ currents hitting 00.0 deg.

12 Comb+ ( Wind + wave ) 1 00year+ currents hitting 45.0 deg.

13 Comb+ ( Wind + wave ) 1 00year+ currents hitting 90.0 deg.

14 Comb+ ( Wind + wave ) 1 00year+ currents hitting 135 deg.

15 Comb+ ( Wind + wave ) 1 00year+ currents hitting 180 deg.

16 Comb+ ( Wind + wave ) 1 00year+ currents hitting 225 deg.

17 Comb+ ( Wind + wave ) 1 00year+ currents hitting 270 deg.

18 Comb+ ( Wind + wave ) 1 00year+ currents hitting 315 deg.

Numerical Results� Structural analysis has been performed to the platform under the platform status of configuration and loadings combination.

� In this study, the wave direction is taken as "positive X direction" and discusses the straining action on two legs in the wave direction.

� The computer analysis results which discuss Bending Moment "M3-3, M2-2" and Normal Force "N.F" and Displacement "U1, U2",for jacket "leg A, leg B" as in the following Figures.

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� To have a better understanding of the behavior over the entire height of the platform jacket, the analysis was conducted for a 110 ft water depth for the maximum wind and wave forces and hitting by current with different angles.

� It should be noted that the response considered are displacement in global X- direction; U1 and Y direction; U2; U1 dominated by the first sway mode of vibration in wave direction; while the deformation; U2 dominated by second sway mode of vibration.

� The displacement responses attain its peak values for the coincidence of the wave, current and wind directions, decrease as the current direction deviate from the wave incidence direction.

� Large inter-story drift of the jacket leg is not allowed for the jacket platform to satisfy the drilling and production requirements. Both the maximum deck acceleration and the maximum Deck to top of jacket displacement were important response parameters affecting the performance of equipment, vessels, and pipelines.

Displacement Response of the Structure

� Displacement U1 for leg A&B with respect to jacket levels for 1-year.

-120

-100

-80

-60

-40

-20

0

20

-20246810Displacement, mm

Lev

el, ft

U-1 A "DL"

U-1 A " DL+LL"

U-1 A"COMB+W1+0CUR"

U-1 A "COMB+W1+45CUR"

U-1 A " COMB+W1+90CUR"

U-1 A "COMB+W1+135CUR"

U-1 A"COMB+W1+180CUR"

U-1 A "COMB+W1+225 CUR"

U-1 A"COMB+W1+270 CUR"

U-1 A"COMB+W1+315 CUR"

-120

-100

-80

-60

-40

-20

0

20

-20246810Displacement, mm

Leve

l, ft

U-1 B " DL "

U-1 B " DL+LL"

U-1 B " COMB+W1+0CUR"

U-1 B "COMB+W1+45CUR"

U-1 B "COMB+W1+90CUR"

U-1 B"COMB+W1+135CUR"

U-1 B"COMB+W1+180CUR"

U-1 B "COMB+W1+225 CUR"

U-1 B "COMB+W1+270 CUR"

U-1 B "COMB+W1+315 CUR"

Leg ALeg ALeg ALeg A

Leg BLeg BLeg BLeg B

�The displacement response, U1 increases nonlinearly with the

height of the platform jacket.

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� Displacement U2 for leg A&B with respect to jacket levels for 1-year.

-120

-100

-80

-60

-40

-20

0

20

-1.6-1.2-0.8-0.400.40.81.21.6Displacement, mm

Lev

el, ft

U-2 A" D.L"U-2 A" D.L+L.L"U-2 A"COMB+W1+0 CURR"

U-2 A"COMB+W1+45 CUR"U-2 A"COMB+W1+90 CUR"U-2 A"COMB+W1+135 CUR"U-2 A"COMB+W1+180 CUR"U-2 A"COM+W1+225 CUR"

U-2 A"COMB+W1+270 CUR"U-2 A"COMB+W1+315 CUR"

-120

-100

-80

-60

-40

-20

0

20

-2-1.6-1.2-0.8-0.400.40.81.21.6

Displacement, mm

Lev

el, ft

U-2 B" D.L"U-2 B" D.L+L.L"U-2 B"COMB+W1+0 CURR"U-2 B"COMB+W1+45 CUR"U-2 B"COMB+W1+90 CUR"U-2 B"COMB+W1+135 CUR"U-2 B"COMB+W1+180 CUR"U-2 B"COM+W1+225 CUR"U-2 B"COMB+W1+270 CUR"U-2 B"COMB+W1+315 CUR"

Leg ALeg ALeg ALeg A

Leg BLeg BLeg BLeg B

� Displacement U1 for leg A&B with respect to jacket levels for 100-year.

-120

-100

-80

-60

-40

-20

0

20

-2024681012141618

Displacement, mm

Lev

el, f t

U-1 A "DL"

U-1 A " DL+LL"

U-1 A "COMB+W100+0CUR"

U-1 A"COMB+W100+45CUR"

U-1 A"COMB+W100+90CUR"

U-I A"COMB+W100+135CUR"

U-1 A"COMB+W100+180CUR"

U-1 A"COMB+W100+225 CUR"

U-1 A"COMB+W100+270 CUR"

U-1 A"COMB+W100+315 CUR"

-120

-100

-80

-60

-40

-20

0

20

-2024681012141618

Dispalcement, mm

Leve

l, ft

U-1 B " DL "

U-1 B " DL+LL"

U-1 B"COMB+W100+0CUR"

U-1 B"COMB+W100+45CUR"

U-1 B "COMB+W100+90 CUR

U-1 B "COMB+W100+135CUR"

U-1 B"COMB+W100+180CUR"

U-1 B"COMB+W100+225CUR"

U-1 B"COMB+W100+270CUR"

U-1 B"COMB+W100+315 CUR"

Leg ALeg ALeg ALeg A

Leg BLeg BLeg BLeg B

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� Displacement U2 for leg A&B with respect to jacket levels for 100-year.

-120

-100

-80

-60

-40

-20

0

20

-3-2.5-2-1.5-1-0.500.511.522.53

Displacement, mm

Lev

el, ft

U-2 A" D.L"

U-2 A" D.L+L.L"

U-2 A"COMB+W100+0 CURR"

U-2 A"COMB+W100+45 CUR"

U-2 A"COMB+W100+90 CUR"

U-2 A"COMB+W100+135 CUR"

U-2 A"COMB+W100+180 CUR"

U-2 A"COM+W100+225 CUR"

U-2 A"COMB+W100+270 CUR"

U-2 A"COMB+W100+315 CUR"

-120

-100

-80

-60

-40

-20

0

20

-3-2.5-2-1.5-1-0.500.511.522.53

Displacement, mm

Lev

el, ft

U-2 B" D.L"

U-2 B" D.L+L.L"

U-2 B"COMB+W100+0 CURR"

U-2 B"COMB+W100+45 CUR"

U-2 B"COMB+W100+90 CUR"

U-2 B"COMB+W100+135 CUR"

U-2 B"COMB+W100+180 CUR"

U-2 BA"COM+W100+225 CUR"

U-2 B"COMB+W100+270 CUR"

U-2 B"COMB+W100+315 CUR"

Leg ALeg ALeg ALeg A

Leg BLeg BLeg BLeg B

� From analysis results, it can be observed that the critical nodes for displacement responses are at jacket - deck connection and at jacket level (+10 ft).

-0.012

-0.008

-0.004

0.000

0.004

0.008

0.012

0.016

0.020

123456789101112131415161718

Load comb.

Dis

pla

cem

ent,

m

U1-A1 U2-A1 U3-AI

-0.012

-0.008

-0.004

0.000

0.004

0.008

0.012

0.016

123456789101112131415161718

Load Comb.

Dis

pla

cem

ent,

mU1-B1 U2-B1 U3-BI

� The results indicate a significant effect of the current incidence direction.

Node BNode BNode BNode B1111Node ANode ANode ANode A1111

Node ENode ENode ENode E2222

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(c) Load Combination No. 13 (d) Load Combination No. 14

(f) Load Combination No. 16 (g) Load Combination No. 17 (h) Load Combination No. 18(e) Load Combination No. 15

(b) Load Combination No. 12(a) Load Combination No. 11

Deformation shape of top of jacket (plan at level +Deformation shape of top of jacket (plan at level +Deformation shape of top of jacket (plan at level +Deformation shape of top of jacket (plan at level +10101010 ft)ft)ft)ft)

� A comparison of the maximum bending moments (M3-3, M2-2) at critical nodal points.

� As the bending moment is generally concentrated at the connection points between the different structural systems.

� The biggest value can be expected to occur at the top of the structure.

� The bending moment at node A1 due to 100 year wave show an inverse pattern compared to those at node A2 (i.e., the maximum value decreases).

� This phenomenon can be explained because the node A1 locates at deck –jacket level at member span, while the node A2 locate at connection joint.

� the moment direction at both nodes has opposite direction, so the wave loading has inverse effect on the peak values response.

Bending Moment Response of the StructureBending Moment Response of the StructureBending Moment Response of the StructureBending Moment Response of the Structure

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M M M M 3333----3333

M M M M 2222----2222

� Bending moment response for leg A & B with respect to jacket levels for 100-year extreme for load combination (DL + LL + Wave 100 + 0o Current).

� It displays the shape of bending moment along jacket and the changes of its direction to able to fixed risers along it and if needing extension for the platform.

� It is important in the design of platform leg to determine the location of maximum bending moment because the jacket diameter wall thickness can be reduced below locations of maximum stresses.

�M 3-3 For 100 year

�M 2-2 For 100 year

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Axial Force Response of the Structure� In the following Figure shows a comparison of the maximum axial force at critical nodal points along jacket height with different load combination.

� It is important in the design of platform legs to determine the location of maximum normal force because the jacket diameter wall thickness can be reduced below locations of maximum stresses.

NormalNormalNormalNormal forceforceforceforce withwithwithwith respectrespectrespectrespect totototo jacketjacketjacketjacket levelslevelslevelslevels forforforfor 100100100100----yearyearyearyear safetysafetysafetysafety

�Leg A

�Leg B

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Conclusions Conclusions Conclusions Conclusions and and and and

recommend future extension of recommend future extension of recommend future extension of recommend future extension of present researchpresent researchpresent researchpresent research

� Safe and cost effective design of offshore platforms depends to a largeextent on the correct assessment of response demands which is expected tobe encountered by the structures during its life span.

� The structure as a whole needs to withstand extreme design conditions. Itis crucial to reduce the overall response of a jacket platform subjected toenvironment loads.

� In general, the reduction of dynamic stress amplitude of an offshorestructure by 15% can extend the service life over two times, and can result indecreasing the expenditure on the maintenance and inspection of thestructure.

� TheTheTheThe aimaimaimaim ofofofof thisthisthisthis studystudystudystudy isisisis totototo improveimproveimproveimprove thethethethe understandingunderstandingunderstandingunderstanding ofofofof thethethethe effectseffectseffectseffects ofofofofwavewavewavewave loadingsloadingsloadingsloadings withwithwithwith thethethethe currentcurrentcurrentcurrent incidenceincidenceincidenceincidence angleangleangleangle variationvariationvariationvariation onononon thethethethe responseresponseresponseresponse ofofofoffixedfixedfixedfixed jacketjacketjacketjacket platformsplatformsplatformsplatforms.... FiniteFiniteFiniteFinite elementelementelementelement analysesanalysesanalysesanalyses havehavehavehave beenbeenbeenbeen usedusedusedused totototo simulatesimulatesimulatesimulateresponseresponseresponseresponse seriesseriesseriesseries....

� A finite element formulation has been developed for the nonlinearresponse of a fixed offshore platform jacket. Where, three-dimensional beamelement incorporating large displacement, time dependent wave forces isconsidered.

�Offshore platform jacket displacement, axial forces, bending moments, andnatural modes and frequencies of free vibration are evaluated

Summary

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� The jacket-deck level (+12.5 ft) and the first horizontal brace level ofjacket (+10 ft) show maximum stresses and displacement demandsfrom wave action for working and construction stage.

� A comparison of the maximum displacement at all nodal points forvarious current incidence angles indicates a significant effect of thecurrent incidence direction. The maximum platform displacement inthe wave direction is 1.0 cm and 1.8 cm at jacket – deck level for 1year and 100 year return period wave and wind loadings, respectively.

� The displacement responses attain its peak values for the coincidenceof the wave, current and wind directions, decrease as the currentdirection deviate from the wave incidence direction.

� The displacement response, U1 increases nonlinearly with the heightof the platform jacket and display fundamental mode of deformation,but there is a significant curvature to the displacement response, U2

along the platform height and displays higher mode of deformation.

Conclusions

� The deformation shape for the horizontal plane of jacket (level +10 ft)changes in irregular movement with different current orientationangels from (0.00o to 360o) for wave extreme values.

� Both the maximum deck acceleration and the maximum Deck to top ofjacket displacement are important response parameters affecting theperformance of equipment, vessels, and pipelines.

o low maximum deck acceleration was desirable for the vessels andequipment,

o but, a small deck-to-top of shaft displacement was desirable forthe risers and caissons.

� The bending moment at nodes in jacket – deck level due to wave actionshow an inverse pattern compared to those at nodes in the firsthorizontal brace level of jacket (i.e., the maximum value decreases).

� The splash zone area between (0, +12.5ft) must be inspectedcontinuously and protect it from corrosion by rubber covering orprotective paints to prevent reduction of jacket legs thickness toextend platform service life time.

Conclusions

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Recommend Future Extension of Present ResearchRecommend Future Extension of Present ResearchRecommend Future Extension of Present ResearchRecommend Future Extension of Present Research

� For producing oil and gas in deep and ultra-deep waters reachingmore than 1000 m water depth, the use of floating-type offshorestructures is required. An extension of the present study to considerdifferent types of offshore structures.

� it is interesting to note that they commonly give rise to highlynonlinear structural consequences in terms of geometricnonlinearity associated with buckling and material nonlinearitytogether with various other parameters of influence such astemperature, strain rate, fabrication related initial imperfections and

age-related degradation.

� Earthquake Response of Offshore Structures With Soil‐StructuresInteraction

� Studying the straining action and the responses for compliantplatforms as the demand of these structures will be more in thefuture in Egypt and all over the world.


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