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design guidlines of offshore structures.

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design guidlines of offshore structures

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Oleh: Oleh: Ir. Murdjito, MSc.Eng Ir. Murdjito, MSc.Eng Dosen Jurusan Teknik Kelautan Fakultas Teknologi Kelautan Institut Teknologi Sepuluh Nopember (ITS) Surabaya Agustus 2014 Agustus 2014 DESIGN GUIDELINES DESIGN GUIDELINES BANGUNAN LEPAS PANTAI BANGUNAN LEPAS PANTAI
Outline Outline  ASPEK DESAIN  DATA LINGKUNGAN DAN TANAH  TAHAPAN DESAIN  BEBAN
PERTIMBANGAN UMUM PERENCANAAN PERTIMBANGAN UMUM PERENCANAAN Platform dirancang untuk memenuhi kriteria keselamatan, keandalan, biaya dan flexibility Perancangan harus memenuhi kriteria serviceability Perancangan harus memenuhi Codes and Standards yang berlaku
CIRI POKOK CIRI POKOK anjungan lepas pantai adalah bahwa struktur tersebut dibuat dan dirakit di tempat lain. BBERARTI BBERARTI proses perancangan tidak hanya harus memperhatikan keadaan di lokasi (as installed as it’s intended location), namun juga harus memperhatikan bagaimana struktur dibuat, dan diangkut ke lokasi. Offshore Structure Offshore Structure   Land-Base Structure Land-Base Structure
TAHAPAN PERENCANAAN TAHAPAN PERENCANAAN TAHAPAN DESAIN STRUKTUR FIXED OFFSHORE PLATFORM DESAIN KONSEPTUAL PEMERIKSAAN PIHAK KETIGA DOKUMENTASI DESAIN DETAIL DESAIN KRITERIA Tersedia atau tidaknya Derrick dan Cargo barge Studi Peralatan Produksi Perhitungan ukuran-ukuran utama struktur Analisa awal pembebanan Orientasi dan lokasi platform Rute dan ukuran pipeline Penyelidikan oceanografi, hidrografi, dan meteorologi Penyelidikan geofisik dan geoteknik Penelitian beban-beban Analisa Dinamik (Gempa) Analisa Inplace (Operating, Storm) Analisa Lelah (Fatique) Analisa Transportasi Analisa Instalasi Analisa Pipeline Riser Detail Struktur Analisa Tiang Pancang Spesifikasi Teknis Dokumen Tender Laporan Desain Spesifikasi Teknis Laporan Desain
Tahapan Pembangunan Tahapan Pembangunan Rancangan awal ( Rancangan awal (Pre-conceptual design Pre-conceptual design) ) Rancangan konsep ( Rancangan konsep (Conceptual design Conceptual design) ) Rancangan rinci ( Rancangan rinci (Detailed design Detailed design) ) Fabrikasi/Pembangunan ( Fabrikasi/Pembangunan (Fabrication Fabrication) ) Loadout Loadout Seafastening Seafastening Instalasi ( Instalasi (Installation & hook-up Installation & hook-up) ) Testing Testing
Fungsi Geografis Operasi Lingkungan Ekonomi Beban Mati Beban Hidup Beban Lingkungan Beban Kecelakaan Beban Khusus Keandalan ( Keandalan (Reliability Reliability) ) Struktur Struktur Pertimbangan Perancangan Pertimbangan Perancangan
Static In-place Analysis Static In-place Analysis Pile Analysis Pile Analysis Fatigue Analysis Fatigue Analysis Seismic Analysis Seismic Analysis Load-out Analysis Load-out Analysis Transportation Analysis Transportation Analysis Installation/On-Bottom Stability Installation/On-Bottom Stability Analysis Analysis Pile Driven Analysis Pile Driven Analysis Metoda Analysis Metoda Analysis
Kendala-Kendala Kendala-Kendala Kendala Fabrikasi Kendala Berat, Panjang dan Ukuran Kendala Instalasi
Outline Outline  ASPEK DESAIN  DATA LINGKUNGAN DAN TANAH  TAHAPAN DESAIN  BEBAN
ASPEK DESAIN ASPEK DESAIN KRITERIA PERENCANAAN KONSTRUKSI FIXED OFFSHORE PLATFORM KRITERIA OPERASIONAL KRITERIA LINGKUNGAN KRITERIA INSTALASI KRITERIA FABRIKASI Fungsi Anjungan Cara Pengeboran Pola Transportasi Personil Pola Transportasi Minyak Kedalaman Laut Kondisi Tanah Dasar Laut Angin, Gelombang Laut, Arus, Pasang Surut (Tide), Korosi Pola Komponen Struktur Roll-Up Pola Transportasi J aket, Dek, dan Peralatan Pola Instalasi J aket, Dek, Peralatan
Gelombang Arus Angin Gempa Beban Lingkungan pada Anjungan Lepas Pantai
Kriteria Desain dari Aspek Teknis Kriteria Desain dari Aspek Teknis Kedalaman Laut. Gelombang (tinggi, periode, distribusinya). Seismik. Kondisi Tanah. Angin Arus Marine Growth Kapasitas desain dari deck
PERTIMBANGAN KONDISI PERTIMBANGAN KONDISI OPERASIONAL OPERASIONAL  FUNGSI  LOKASI OPERASI  ORIENTASI PLATFORM  KEDALAMAN AIR  ACESS SYSTEM  FIRE PROTECTION  ELEVASI DECK  JUMLAH SUMUR/ WELS  EQUIPMENTS & MATERIAL LAYOUT  PERSONNEL & MATERIAL HANDLING  SPILLAGE & CONTAMINATION  EXPOSURE
PERTIMBANGAN LINGKUNGAN PERTIMBANGAN LINGKUNGAN  water depth at location  soil, at seabottom and in-depth, scour, seafloor instability  wind speed, air temperature  waves, tide and storm surge, current  ice (fixed, floes, icebergs)  earthquakes (if necessary)  Marine growth  Normal Environmental Condition – Occur frequently during life of structure – Important For construction & service life  Extreme Environmental Condition – Occur quite rarely during life of structure – Important in formulating platform design loadings
Design Acceptance Criteria Design Acceptance Criteria Vertical Deflections Allowable Stress Slenderness ratio Diameter to thickness ratio Thickness limit Platform natural period Joint fatigue life Corrosion protection
Vertical Deflections Vertical Deflections
Allowable Stresses Allowable Stresses
Outline Outline  ASPEK DESAIN  DATA LINGKUNGAN DAN TANAH  TAHAPAN DESAIN  BEBAN
ASPEK LINGKUNGAN ASPEK LINGKUNGAN  Platform Location & Orientation  Water Depth  Tide  Storm surge  Wind speed  Waves and Wave occurences  Current  Marine growth  Corrotion allowances  Soil data  Seismic data  Air Gap  Seafloor movement
Platform Location Platform Location Platform coordinate  Latitude 050 53’ 45" S  Longitude 107o 29’ 34,00” E Platform Orientation
Water Depth, Tide & storm surge Water Depth, Tide & storm surge Description Return Periods 1 Yr 100 Yr Chart datum (ft) -2.46 -2.46 Highest Astronomical Tide (HAT) (ft) 2.62 2.62 Storm Surge (ft) 0.59 1.02 Mean Sea Level (ft) 103.57 103.57 Maximum Water Depth (ft) 106.78 107.21
Wind Wind  combination with wave loads: – DNV and DOE-OG rules recommend the most unfavorable of the following two loadings:  1-minute sustained wind speeds combined with extreme waves.  3-second gusts.  API-RP2A distinguishes between global and local wind load effects. – first case: it gives guideline values of mean 1-hour average wind speeds to be combined with extreme waves and current. – second case: it gives values of extreme wind speeds to be used without regard to waves.  Wind loads are generally taken as static. When the ratio of height to the least horizontal dimension of the wind exposed object (or structure) > 5, then this object (or structure) could be wind sensitive.  API-RP2A requires the dynamic effects of the wind to be taken into account in this case and the flow induced cyclic wind loads due to vortex shedding must be investigated.
Wind Speed Parameter Wind Speed Parameter act on the portion of a platform above the water level The wind velocity profile (API-RP2A ) – Vh/VH = (h/H)1/n  1/n=1/13 to 1/7, – depending on the sea state, the distance from land and the averaging time interval. – approximately = 1/13 for gusts and 1/8 for sustained winds in the open ocean.
Wind Speed (ex.) Wind Speed (ex.) Wind Speed (m/s) Return Periods 1 Yr 100 Yr 60-minute mean 10.7 19.8 1-minute mean 13.3 24.6 3-second gust 16.1 29.9
WAVE CONCEPTS WAVE CONCEPTS  Design/ regular wave concept: – a regular wave of given height and period is defined and the forces due to this wave are calculated using a high-order wave theory. – Usually the 100-year wave for storm condition and 1-year for opearting condition – No dynamic behavior of the structure is considered. This static analysis is appropriate when the dominant wave periods are well above the period of the structure. – This is the case of extreme storm waves acting on shallow water structures.  Statistical analysis: – on the basis of a wave scatter diagram for the location of the structure. – Appropriate wave spectra are defined to perform the analysis in the frequency domain and to generate random waves, if dynamic analyses for extreme wave loadings are required for deepwater structures. – With statistical methods, the most probable maximum force during the lifetime of the structure is calculated using linear wave theory. – The statistical approach has to be chosen to analyze the fatigue strength and the dynamic behavior of the structure.
Wave Theories Wave Theories •linear Airy theory, •Stokes fifth-order theory •solitary wave theory, •cnoidal theory, •Dean's stream function theory •numerical theory by Chappelear.
REGION WAVE THEORY REGION WAVE THEORY APPLICABLITY APPLICABLITY
Wave Spectrum Wave Spectrum  JONSWAP Spectrum  Pierson-Moskowitz Spectrum  Bretsneider  ISSC Spectrum
Wave Data Wave Data Wave Return Periods 1 Yr 100 Yr Siginificant Wave height (Hs) - m 3.4 6.2 Significant wave period (Tz) - s 6.9 8.9 Max. Idividual Wave height (Hm) - m 6.1 11.2 Max. Indvidual wave period (Tas) - s 8.9 11.6
Wave Statistics Data Wave Statistics Data Wave Significant Total Height (ft) N & S NW & SE E & W SW & NE No.Waves (N 0.0-3.9 2 4.6 9,484,800 13,447,600 28,194,300 13,837,300 64,964,000 4.0-7.9 6 6.4 358,335 507,625 1.059,000 520,470 2,445,430 8.0-11.9 10 6.8 11,409 16,737 38,129 18,985 85,260 12-15.9 14 7.3 440 521 1,502 720 3,183 16-19.9 18 7.7 15 16 48 24 103 20-23.9 22 7.9 1 1 1 1 4 9,855,000 13,972,500 28,233,980 14,377,500 67,497,980 TOTAL Hs rata-2 (ft) Period (sec) Wave Occurrences
Current Current  Currents affect: – location and orientation of boat landings and barge bumpers, – forces on the platform  Design current speed for 1 year and 100 year period  For combination with wave load, current speed is assumed to be acting concurently with wave in same direction  Assumed an omni-directional current profile  Current speed is measured in the whole water columns from surface till seabed
Current Speed Data Current Speed Data Percentage Water Depth above mud- line 1-Year Return Storm Current Velocity (Ft/Sec) 100-Year Return Storm Current Velocity (Ft/Sec) 0 2.59 (0.75 m/s) 4.00 (1.22 m/s) 10 2.26 (0.69 m/s) 3.28 (1.00 m/s) 20 2 (0.61 m/s) 2.76 (0.84 m/s) 30 1.8 (0.55 m/s) 2.36 (0.72 m/s) 40 1.67 (0.51 m/s) 2.07 (0.63 m/s) 50 1.57 (0.48 m/s) 1.87 (0.57 m/s) 60 1.51 (0.46 m/s) 1.71 (0.52 m/s) 70 1.44 (0.44 m/s) 1.61 (0.49 m/s) 80 1.41 (0.43 m/s) 1.51 (0.46 m/s) 90 1.38 (0.42 m/s) 1.48 (0.45 m/s) 100 1.38 (0.42 m/s) 1.41 (0.43 m/s)
Marine Growth Marine Growth  Marine growth is accumulated on submerged members.  Its main effect is to increase the wave forces on the members by increasing not only exposed areas and volumes, but also the drag coefficient due to higher surface roughness.  It increases the unit mass of the member, resulting in higher gravity loads and in lower member frequencies.  Depending upon geographic location, the thickness of marine growth can reach 0,3m or more.  It is accounted for in design through appropriate increases in the diameters and masses of the submerged members.
Impact of MG Impact of MG Mass: Submerged Weight CD:
MG Design Criteria MG Design Criteria Marine Growth Profile Marine dry density ~ 1400 kg/m^3
Corrotion Allowances Corrotion Allowances Considered mostly in splash zone Corrotion allowance shall be included in the in-place analysis as well as in fatigue analysis In general ¼” for in-place analysis and 1/8” for fatigue analysis
Seafloor Movements Seafloor Movements  Scour: – Removal of seafloor soil caused by currents and waves  Settlements – Ground motion due to overstressing of foundation elements  Subsidence
Scour Scour  Scour is removal of seafloor soils caused by currents and waves. Such erosion can be a natural geologic process or can be caused by structural elements interrupting the natural flow regime near the seafloor.  Scour can result in removal of vertical and lateral support for foundations, causing undesirable settlements of mat foundationsand overstressing of foundation elements  An example impact of scour to pile axial capacity Condition Pile Ultimate Capacity (MN) Reduction (%) As Design 10.37 0.00 Scouring 2.6 m 9.30 10.32 Scouring 4.0 m 8.79 15.34 Scouring 5.0 m 8.42 18.80
Ground Subsidence Ground Subsidence  Ground motion due to failure of seafloor slope  Can be defined as the vertical downwards-small movements of the ground.  Several physical causes (like earthquakes, tectonic movements, underground acvitiesetc.) and human activities  Impacts of ground subsidence – Decrease platform structual integrity – Operational problem  Subsidence scenario of Lima Field Subsidence As Built (1975) Measured Jun-2010 Prediction 2015 Prediction 2020 0.0 m 2.36 m 2.86 m 3.36 m
Air Gap Air Gap Distance between the underside of the lowest part of the topside (sub cellar deck) and the maximum wave crest elevation of the extreme 100-year wave return period Mnimum air gap: 1.50 m or 5 feet
Soil Data Soil Data  Soil data is taken from the soil and foundation / geotechnical investigation reports  Available on- or near-site soil borings and geophysical data should be reviewed  Foundation investigation for pile-supported structures should provide the soil engineering property data needed to determine the following parameters: – axial capacity of piles in tension and compression, – load-deflection characteristics of axially and laterally loaded piles, – pile driveability characteristics, – Mudmat bearing capacity.  Soil data required for jacket structural integrity analysis: P- Y Data, T-Z Data, Q-Z data
Seismic Data Seismic Data  Site-specific studies should be considered as a basis for developing the ground motion specification of the design criteria, particularly for sites in areas of high seismicity (Zones 3–5) or in any location where earthquake loading is anticipated to significantly influence structural design.  Design Basis  Peak Ground Acceleration (G) design basis – 200 yr return period (SLE) – 1000 yr return period (DLE)
Outline Outline  ASPEK DESAIN  DATA LINGKUNGAN DAN TANAH  TAHAPAN DESAIN  BEBAN
DESIGN LOADS CLASSIFICATION DESIGN LOADS CLASSIFICATION  Dead Loads: – Weight of the platform structure in air incl:weight of piles, grout, & ballast – Weight of appurtenant structures permanently mounted on the platform – Hydrostatic forces acting on the structure below the water line incl: external pressure & bouyancy  Functional loads: – Operating Loads: Fluid, contents in piping and equipment – Live Loads: the loads imposed during its use and may change during a mode of operation: static or dynamic functional loads arising form personnel, helicopter, maintenance loads, etc.  Environmental Loads: arise from the action of wave, currents and winds on the structure  Seismic loads: arise as result of the ground motion  Accidental Loads: arise as result of accident or abuse or exceptional conditions: boat impact, dropped objects, deformation, etc  Consctructions Loads: resulting from fabrication, load out, transportation & installation  Dynamic Loads: loads imposed due to response to an excitation of a cyclic nature as wave, wind, earthquake, etc.
LOADING CONDITIONS LOADING CONDITIONS  The environmental conditions combined with appropriate dead and live loads  Operational (Normal) Condition:  1-year return period environmental loads  Allowable stresses max 1.0  Storm Condition  100-year return period environmental loads  Allowable stresses: increased by 1/3  Seismic Condition  Consider the effects of all gravity loads in combinations with simulatanous and collinear of loads due to ground motion  Allowable stresses: increased by 70%  Accidental Loads  Consider the effects of collision loads and due to dropped objects  Allowable stresses: increased by 1/3  For local design of elements, a dynamic load factor of 2.0 shall be used
Wind loads Wind loads Fw = (1/2) ρ V2 Cs A ρ : the wind density (ρ ~ 1.225 Kg/m3) Cs : the shape coefficient – Cs = 1,5 for beams and sides of buildings, – = 0,5 for cylindrical sections – = 1,0 for total projected area of platform. Shielding and solidity effects can be accounted for
WAVE & CURRENT LOADS WAVE & CURRENT LOADS  Represented by their static equivalent using Morisson’s equation  For deep water: requires a load analysis involving the dynamic action of the structure  For global structure: ignored lift forces, slam forces, and axial Froude-Krylov forces  If D/L >0.2, use diffraction theory  Total base shear and overturning moment are calculated for global structure forces  Local member stresses: due to local hydrodynamic forces (incl. slam, lift, Froude-Krylov, buoyancy) and loads transferred due to global fluid-dynamic force and dynamic response of the structure
PROCEDURE FOR CALCULATION OF WAVE PLUS PROCEDURE FOR CALCULATION OF WAVE PLUS CURRENT FORCES CURRENT FORCES
WAVE DIRECTION WAVE DIRECTION
WAVE PARAMETER WAVE PARAMETER  Wave Kinematic factor: – Consider wave directional spreading or irregularity in wave profile shape – Tropical storm: 0.85 – 0.95 – Extra tropical storm: 0.95 – 1.0  Current Blockage Factor: – Reducing current speed due to the presence of the structure  Conductor shielding – Depending upon the configuation of the structure and the number of conductor  Marine Growth: Increased in cross sectional area  Drag and Inertia Coefficient, depend on: – Reynold Number : R = Um D/ν – K-C number : K = 2 Um T2/D – Roughness : e = k/D – Current/Wave velcity : r = V1/Vmo – Member Orientation
WAVE PARAMETER WAVE PARAMETER Members with marine growth Cd = 0.8 Cm = 2.0 Members without marine growth Cd = 0.5 Cm = 2.0 IN-PLACE ANALYSIS FATIGUE ANALYSIS
Wave lift and slamming Loads Wave lift and slamming Loads In addition to the forces given by Morison's equation, the lift forces FL and the slamming forces FS, typically neglected in global response computations, can be important for local member design. – FL = (1/2) ρ CL Dv2 – FS = (1/2) ρ Cs Dv2 CL ≈1,3 CD. Cs ≈ π  For tubular members
Seimic Loads Seimic Loads  Two levels of earthquake intensity: – strength level (SLE) – ductility level (DLE).  SLE: reasonable likelihood of not being exceeded during the platform's life (mean recurrence interval ~ 200 - 500 years), the structure is designed to respond elastically.  DLE: maximum credible earthquake at the site, the structure is designed for inelastic response and to have adequate reserve strength to avoid collapse.  API-RP2A recommends: X, Y, 0.5 Z  DNV rules: 0,7X, O,7 Y and 0,5 Z  The value of a max and often the spectral shapes are determined by site specific seismological studies.
Design Spectra Design Spectra
Accidental Loads Accidental Loads Impact loads, incl dropped object and collision loads Unintended flooding Loads caused by extreme weather Heat loads Explosion loads
Dropped Object Dropped Object E = M.g0.h E : impact energy (kJ) M : mass of object (tonnes) go : gravity (9.81 m/s2) h : Drop height in air (m)
Collision Loads Collision Loads E = ½ (M+a).ν2 E: Collision energy (kJ) M: Displacement of vessel a : added mass of vessel – Sideway collision~ 0.4 M – Bow/ stern collision ~ 0.1 M V : impact speed (m/s)
DAFTAR PUSTAKA DAFTAR PUSTAKA  API RP 2A Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms, 1993.  Bramlette Mc. Cleland: Planning and Design of Fixed Offshore Structure, Van Nostrand Reinhold Co, New York, 1986  Wardenier. J: Offshore and Hydraulic Steel Structrures, Delfi University of Technology, Deift, Netherlands, 1998  Murdjito: Bangunan Lepas Pantai, Diktat Kuliah, FT Kelautan ITS 1998  Chakrabarti, S.K.: Hydrodynamics of Offshore Structures, Springer-Verlag, berlin, 1987  DET NORSKE VERITAS, Offshore standard: structural design of offshore units (wsd method), APRIL 2002, DNV-OS-C201  BS6235, "Code of Practice for Fixed Offshore Structures", British Standards Institution, London, 1982.  DOE-OG, "Offshore Installation: Guidance on Design and Construction", U.K., Dept. of Energy, London 1985.  Clauss, G. T. et al: "Offshore Structures, Vol 1 - Conceptual Design and Hydromechanics", Springer, London 1992.  Hsu, H.T., "Applied Offshore Structural Engineering", Gulf Publishing Co., Houston, 1981.  Graff, W.J., "Introduction to Offshore Structures", Gulf Publishing Co., Houston, 1981.

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design guidlines of offshore structures.

  • 1. Oleh: Oleh: Ir. Murdjito, MSc.Eng Ir. Murdjito, MSc.Eng Dosen Jurusan Teknik Kelautan Fakultas Teknologi Kelautan Institut Teknologi Sepuluh Nopember (ITS) Surabaya Agustus 2014 Agustus 2014 DESIGN GUIDELINES DESIGN GUIDELINES BANGUNAN LEPAS PANTAI BANGUNAN LEPAS PANTAI
  • 2. Outline Outline  ASPEK DESAIN  DATA LINGKUNGAN DAN TANAH  TAHAPAN DESAIN  BEBAN
  • 3. PERTIMBANGAN UMUM PERENCANAAN PERTIMBANGAN UMUM PERENCANAAN Platform dirancang untuk memenuhi kriteria keselamatan, keandalan, biaya dan flexibility Perancangan harus memenuhi kriteria serviceability Perancangan harus memenuhi Codes and Standards yang berlaku
  • 4. CIRI POKOK CIRI POKOK anjungan lepas pantai adalah bahwa struktur tersebut dibuat dan dirakit di tempat lain. BBERARTI BBERARTI proses perancangan tidak hanya harus memperhatikan keadaan di lokasi (as installed as it’s intended location), namun juga harus memperhatikan bagaimana struktur dibuat, dan diangkut ke lokasi. Offshore Structure Offshore Structure   Land-Base Structure Land-Base Structure
  • 5. TAHAPAN PERENCANAAN TAHAPAN PERENCANAAN TAHAPAN DESAIN STRUKTUR FIXED OFFSHORE PLATFORM DESAIN KONSEPTUAL PEMERIKSAAN PIHAK KETIGA DOKUMENTASI DESAIN DETAIL DESAIN KRITERIA Tersedia atau tidaknya Derrick dan Cargo barge Studi Peralatan Produksi Perhitungan ukuran-ukuran utama struktur Analisa awal pembebanan Orientasi dan lokasi platform Rute dan ukuran pipeline Penyelidikan oceanografi, hidrografi, dan meteorologi Penyelidikan geofisik dan geoteknik Penelitian beban-beban Analisa Dinamik (Gempa) Analisa Inplace (Operating, Storm) Analisa Lelah (Fatique) Analisa Transportasi Analisa Instalasi Analisa Pipeline Riser Detail Struktur Analisa Tiang Pancang Spesifikasi Teknis Dokumen Tender Laporan Desain Spesifikasi Teknis Laporan Desain
  • 6. Tahapan Pembangunan Tahapan Pembangunan Rancangan awal ( Rancangan awal (Pre-conceptual design Pre-conceptual design) ) Rancangan konsep ( Rancangan konsep (Conceptual design Conceptual design) ) Rancangan rinci ( Rancangan rinci (Detailed design Detailed design) ) Fabrikasi/Pembangunan ( Fabrikasi/Pembangunan (Fabrication Fabrication) ) Loadout Loadout Seafastening Seafastening Instalasi ( Instalasi (Installation & hook-up Installation & hook-up) ) Testing Testing
  • 7. Fungsi Geografis Operasi Lingkungan Ekonomi Beban Mati Beban Hidup Beban Lingkungan Beban Kecelakaan Beban Khusus Keandalan ( Keandalan (Reliability Reliability) ) Struktur Struktur Pertimbangan Perancangan Pertimbangan Perancangan
  • 8. Static In-place Analysis Static In-place Analysis Pile Analysis Pile Analysis Fatigue Analysis Fatigue Analysis Seismic Analysis Seismic Analysis Load-out Analysis Load-out Analysis Transportation Analysis Transportation Analysis Installation/On-Bottom Stability Installation/On-Bottom Stability Analysis Analysis Pile Driven Analysis Pile Driven Analysis Metoda Analysis Metoda Analysis
  • 10. Outline Outline  ASPEK DESAIN  DATA LINGKUNGAN DAN TANAH  TAHAPAN DESAIN  BEBAN
  • 11. ASPEK DESAIN ASPEK DESAIN KRITERIA PERENCANAAN KONSTRUKSI FIXED OFFSHORE PLATFORM KRITERIA OPERASIONAL KRITERIA LINGKUNGAN KRITERIA INSTALASI KRITERIA FABRIKASI Fungsi Anjungan Cara Pengeboran Pola Transportasi Personil Pola Transportasi Minyak Kedalaman Laut Kondisi Tanah Dasar Laut Angin, Gelombang Laut, Arus, Pasang Surut (Tide), Korosi Pola Komponen Struktur Roll-Up Pola Transportasi J aket, Dek, dan Peralatan Pola Instalasi J aket, Dek, Peralatan
  • 13. Kriteria Desain dari Aspek Teknis Kriteria Desain dari Aspek Teknis Kedalaman Laut. Gelombang (tinggi, periode, distribusinya). Seismik. Kondisi Tanah. Angin Arus Marine Growth Kapasitas desain dari deck
  • 14. PERTIMBANGAN KONDISI PERTIMBANGAN KONDISI OPERASIONAL OPERASIONAL  FUNGSI  LOKASI OPERASI  ORIENTASI PLATFORM  KEDALAMAN AIR  ACESS SYSTEM  FIRE PROTECTION  ELEVASI DECK  JUMLAH SUMUR/ WELS  EQUIPMENTS & MATERIAL LAYOUT  PERSONNEL & MATERIAL HANDLING  SPILLAGE & CONTAMINATION  EXPOSURE
  • 15. PERTIMBANGAN LINGKUNGAN PERTIMBANGAN LINGKUNGAN  water depth at location  soil, at seabottom and in-depth, scour, seafloor instability  wind speed, air temperature  waves, tide and storm surge, current  ice (fixed, floes, icebergs)  earthquakes (if necessary)  Marine growth  Normal Environmental Condition – Occur frequently during life of structure – Important For construction & service life  Extreme Environmental Condition – Occur quite rarely during life of structure – Important in formulating platform design loadings
  • 16. Design Acceptance Criteria Design Acceptance Criteria Vertical Deflections Allowable Stress Slenderness ratio Diameter to thickness ratio Thickness limit Platform natural period Joint fatigue life Corrosion protection
  • 19. Outline Outline  ASPEK DESAIN  DATA LINGKUNGAN DAN TANAH  TAHAPAN DESAIN  BEBAN
  • 20. ASPEK LINGKUNGAN ASPEK LINGKUNGAN  Platform Location & Orientation  Water Depth  Tide  Storm surge  Wind speed  Waves and Wave occurences  Current  Marine growth  Corrotion allowances  Soil data  Seismic data  Air Gap  Seafloor movement
  • 21. Platform Location Platform Location Platform coordinate  Latitude 050 53’ 45" S  Longitude 107o 29’ 34,00” E Platform Orientation
  • 22. Water Depth, Tide & storm surge Water Depth, Tide & storm surge Description Return Periods 1 Yr 100 Yr Chart datum (ft) -2.46 -2.46 Highest Astronomical Tide (HAT) (ft) 2.62 2.62 Storm Surge (ft) 0.59 1.02 Mean Sea Level (ft) 103.57 103.57 Maximum Water Depth (ft) 106.78 107.21
  • 23. Wind Wind  combination with wave loads: – DNV and DOE-OG rules recommend the most unfavorable of the following two loadings:  1-minute sustained wind speeds combined with extreme waves.  3-second gusts.  API-RP2A distinguishes between global and local wind load effects. – first case: it gives guideline values of mean 1-hour average wind speeds to be combined with extreme waves and current. – second case: it gives values of extreme wind speeds to be used without regard to waves.  Wind loads are generally taken as static. When the ratio of height to the least horizontal dimension of the wind exposed object (or structure) > 5, then this object (or structure) could be wind sensitive.  API-RP2A requires the dynamic effects of the wind to be taken into account in this case and the flow induced cyclic wind loads due to vortex shedding must be investigated.
  • 24. Wind Speed Parameter Wind Speed Parameter act on the portion of a platform above the water level The wind velocity profile (API-RP2A ) – Vh/VH = (h/H)1/n  1/n=1/13 to 1/7, – depending on the sea state, the distance from land and the averaging time interval. – approximately = 1/13 for gusts and 1/8 for sustained winds in the open ocean.
  • 25. Wind Speed (ex.) Wind Speed (ex.) Wind Speed (m/s) Return Periods 1 Yr 100 Yr 60-minute mean 10.7 19.8 1-minute mean 13.3 24.6 3-second gust 16.1 29.9
  • 26. WAVE CONCEPTS WAVE CONCEPTS  Design/ regular wave concept: – a regular wave of given height and period is defined and the forces due to this wave are calculated using a high-order wave theory. – Usually the 100-year wave for storm condition and 1-year for opearting condition – No dynamic behavior of the structure is considered. This static analysis is appropriate when the dominant wave periods are well above the period of the structure. – This is the case of extreme storm waves acting on shallow water structures.  Statistical analysis: – on the basis of a wave scatter diagram for the location of the structure. – Appropriate wave spectra are defined to perform the analysis in the frequency domain and to generate random waves, if dynamic analyses for extreme wave loadings are required for deepwater structures. – With statistical methods, the most probable maximum force during the lifetime of the structure is calculated using linear wave theory. – The statistical approach has to be chosen to analyze the fatigue strength and the dynamic behavior of the structure.
  • 27. Wave Theories Wave Theories •linear Airy theory, •Stokes fifth-order theory •solitary wave theory, •cnoidal theory, •Dean's stream function theory •numerical theory by Chappelear.
  • 28. REGION WAVE THEORY REGION WAVE THEORY APPLICABLITY APPLICABLITY
  • 29. Wave Spectrum Wave Spectrum  JONSWAP Spectrum  Pierson-Moskowitz Spectrum  Bretsneider  ISSC Spectrum
  • 30. Wave Data Wave Data Wave Return Periods 1 Yr 100 Yr Siginificant Wave height (Hs) - m 3.4 6.2 Significant wave period (Tz) - s 6.9 8.9 Max. Idividual Wave height (Hm) - m 6.1 11.2 Max. Indvidual wave period (Tas) - s 8.9 11.6
  • 31. Wave Statistics Data Wave Statistics Data Wave Significant Total Height (ft) N & S NW & SE E & W SW & NE No.Waves (N 0.0-3.9 2 4.6 9,484,800 13,447,600 28,194,300 13,837,300 64,964,000 4.0-7.9 6 6.4 358,335 507,625 1.059,000 520,470 2,445,430 8.0-11.9 10 6.8 11,409 16,737 38,129 18,985 85,260 12-15.9 14 7.3 440 521 1,502 720 3,183 16-19.9 18 7.7 15 16 48 24 103 20-23.9 22 7.9 1 1 1 1 4 9,855,000 13,972,500 28,233,980 14,377,500 67,497,980 TOTAL Hs rata-2 (ft) Period (sec) Wave Occurrences
  • 32. Current Current  Currents affect: – location and orientation of boat landings and barge bumpers, – forces on the platform  Design current speed for 1 year and 100 year period  For combination with wave load, current speed is assumed to be acting concurently with wave in same direction  Assumed an omni-directional current profile  Current speed is measured in the whole water columns from surface till seabed
  • 33. Current Speed Data Current Speed Data Percentage Water Depth above mud- line 1-Year Return Storm Current Velocity (Ft/Sec) 100-Year Return Storm Current Velocity (Ft/Sec) 0 2.59 (0.75 m/s) 4.00 (1.22 m/s) 10 2.26 (0.69 m/s) 3.28 (1.00 m/s) 20 2 (0.61 m/s) 2.76 (0.84 m/s) 30 1.8 (0.55 m/s) 2.36 (0.72 m/s) 40 1.67 (0.51 m/s) 2.07 (0.63 m/s) 50 1.57 (0.48 m/s) 1.87 (0.57 m/s) 60 1.51 (0.46 m/s) 1.71 (0.52 m/s) 70 1.44 (0.44 m/s) 1.61 (0.49 m/s) 80 1.41 (0.43 m/s) 1.51 (0.46 m/s) 90 1.38 (0.42 m/s) 1.48 (0.45 m/s) 100 1.38 (0.42 m/s) 1.41 (0.43 m/s)
  • 34. Marine Growth Marine Growth  Marine growth is accumulated on submerged members.  Its main effect is to increase the wave forces on the members by increasing not only exposed areas and volumes, but also the drag coefficient due to higher surface roughness.  It increases the unit mass of the member, resulting in higher gravity loads and in lower member frequencies.  Depending upon geographic location, the thickness of marine growth can reach 0,3m or more.  It is accounted for in design through appropriate increases in the diameters and masses of the submerged members.
  • 35. Impact of MG Impact of MG Mass: Submerged Weight CD:
  • 36. MG Design Criteria MG Design Criteria Marine Growth Profile Marine dry density ~ 1400 kg/m^3
  • 37. Corrotion Allowances Corrotion Allowances Considered mostly in splash zone Corrotion allowance shall be included in the in-place analysis as well as in fatigue analysis In general ¼” for in-place analysis and 1/8” for fatigue analysis
  • 38. Seafloor Movements Seafloor Movements  Scour: – Removal of seafloor soil caused by currents and waves  Settlements – Ground motion due to overstressing of foundation elements  Subsidence
  • 39. Scour Scour  Scour is removal of seafloor soils caused by currents and waves. Such erosion can be a natural geologic process or can be caused by structural elements interrupting the natural flow regime near the seafloor.  Scour can result in removal of vertical and lateral support for foundations, causing undesirable settlements of mat foundationsand overstressing of foundation elements  An example impact of scour to pile axial capacity Condition Pile Ultimate Capacity (MN) Reduction (%) As Design 10.37 0.00 Scouring 2.6 m 9.30 10.32 Scouring 4.0 m 8.79 15.34 Scouring 5.0 m 8.42 18.80
  • 40. Ground Subsidence Ground Subsidence  Ground motion due to failure of seafloor slope  Can be defined as the vertical downwards-small movements of the ground.  Several physical causes (like earthquakes, tectonic movements, underground acvitiesetc.) and human activities  Impacts of ground subsidence – Decrease platform structual integrity – Operational problem  Subsidence scenario of Lima Field Subsidence As Built (1975) Measured Jun-2010 Prediction 2015 Prediction 2020 0.0 m 2.36 m 2.86 m 3.36 m
  • 41. Air Gap Air Gap Distance between the underside of the lowest part of the topside (sub cellar deck) and the maximum wave crest elevation of the extreme 100-year wave return period Mnimum air gap: 1.50 m or 5 feet
  • 42. Soil Data Soil Data  Soil data is taken from the soil and foundation / geotechnical investigation reports  Available on- or near-site soil borings and geophysical data should be reviewed  Foundation investigation for pile-supported structures should provide the soil engineering property data needed to determine the following parameters: – axial capacity of piles in tension and compression, – load-deflection characteristics of axially and laterally loaded piles, – pile driveability characteristics, – Mudmat bearing capacity.  Soil data required for jacket structural integrity analysis: P- Y Data, T-Z Data, Q-Z data
  • 43. Seismic Data Seismic Data  Site-specific studies should be considered as a basis for developing the ground motion specification of the design criteria, particularly for sites in areas of high seismicity (Zones 3–5) or in any location where earthquake loading is anticipated to significantly influence structural design.  Design Basis  Peak Ground Acceleration (G) design basis – 200 yr return period (SLE) – 1000 yr return period (DLE)
  • 44. Outline Outline  ASPEK DESAIN  DATA LINGKUNGAN DAN TANAH  TAHAPAN DESAIN  BEBAN
  • 45. DESIGN LOADS CLASSIFICATION DESIGN LOADS CLASSIFICATION  Dead Loads: – Weight of the platform structure in air incl:weight of piles, grout, & ballast – Weight of appurtenant structures permanently mounted on the platform – Hydrostatic forces acting on the structure below the water line incl: external pressure & bouyancy  Functional loads: – Operating Loads: Fluid, contents in piping and equipment – Live Loads: the loads imposed during its use and may change during a mode of operation: static or dynamic functional loads arising form personnel, helicopter, maintenance loads, etc.  Environmental Loads: arise from the action of wave, currents and winds on the structure  Seismic loads: arise as result of the ground motion  Accidental Loads: arise as result of accident or abuse or exceptional conditions: boat impact, dropped objects, deformation, etc  Consctructions Loads: resulting from fabrication, load out, transportation & installation  Dynamic Loads: loads imposed due to response to an excitation of a cyclic nature as wave, wind, earthquake, etc.
  • 46. LOADING CONDITIONS LOADING CONDITIONS  The environmental conditions combined with appropriate dead and live loads  Operational (Normal) Condition:  1-year return period environmental loads  Allowable stresses max 1.0  Storm Condition  100-year return period environmental loads  Allowable stresses: increased by 1/3  Seismic Condition  Consider the effects of all gravity loads in combinations with simulatanous and collinear of loads due to ground motion  Allowable stresses: increased by 70%  Accidental Loads  Consider the effects of collision loads and due to dropped objects  Allowable stresses: increased by 1/3  For local design of elements, a dynamic load factor of 2.0 shall be used
  • 47. Wind loads Wind loads Fw = (1/2) ρ V2 Cs A ρ : the wind density (ρ ~ 1.225 Kg/m3) Cs : the shape coefficient – Cs = 1,5 for beams and sides of buildings, – = 0,5 for cylindrical sections – = 1,0 for total projected area of platform. Shielding and solidity effects can be accounted for
  • 48. WAVE & CURRENT LOADS WAVE & CURRENT LOADS  Represented by their static equivalent using Morisson’s equation  For deep water: requires a load analysis involving the dynamic action of the structure  For global structure: ignored lift forces, slam forces, and axial Froude-Krylov forces  If D/L >0.2, use diffraction theory  Total base shear and overturning moment are calculated for global structure forces  Local member stresses: due to local hydrodynamic forces (incl. slam, lift, Froude-Krylov, buoyancy) and loads transferred due to global fluid-dynamic force and dynamic response of the structure
  • 49. PROCEDURE FOR CALCULATION OF WAVE PLUS PROCEDURE FOR CALCULATION OF WAVE PLUS CURRENT FORCES CURRENT FORCES
  • 51. WAVE PARAMETER WAVE PARAMETER  Wave Kinematic factor: – Consider wave directional spreading or irregularity in wave profile shape – Tropical storm: 0.85 – 0.95 – Extra tropical storm: 0.95 – 1.0  Current Blockage Factor: – Reducing current speed due to the presence of the structure  Conductor shielding – Depending upon the configuation of the structure and the number of conductor  Marine Growth: Increased in cross sectional area  Drag and Inertia Coefficient, depend on: – Reynold Number : R = Um D/ν – K-C number : K = 2 Um T2/D – Roughness : e = k/D – Current/Wave velcity : r = V1/Vmo – Member Orientation
  • 52. WAVE PARAMETER WAVE PARAMETER Members with marine growth Cd = 0.8 Cm = 2.0 Members without marine growth Cd = 0.5 Cm = 2.0 IN-PLACE ANALYSIS FATIGUE ANALYSIS
  • 53. Wave lift and slamming Loads Wave lift and slamming Loads In addition to the forces given by Morison's equation, the lift forces FL and the slamming forces FS, typically neglected in global response computations, can be important for local member design. – FL = (1/2) ρ CL Dv2 – FS = (1/2) ρ Cs Dv2 CL ≈1,3 CD. Cs ≈ π  For tubular members
  • 54. Seimic Loads Seimic Loads  Two levels of earthquake intensity: – strength level (SLE) – ductility level (DLE).  SLE: reasonable likelihood of not being exceeded during the platform's life (mean recurrence interval ~ 200 - 500 years), the structure is designed to respond elastically.  DLE: maximum credible earthquake at the site, the structure is designed for inelastic response and to have adequate reserve strength to avoid collapse.  API-RP2A recommends: X, Y, 0.5 Z  DNV rules: 0,7X, O,7 Y and 0,5 Z  The value of a max and often the spectral shapes are determined by site specific seismological studies.
  • 56. Accidental Loads Accidental Loads Impact loads, incl dropped object and collision loads Unintended flooding Loads caused by extreme weather Heat loads Explosion loads
  • 57. Dropped Object Dropped Object E = M.g0.h E : impact energy (kJ) M : mass of object (tonnes) go : gravity (9.81 m/s2) h : Drop height in air (m)
  • 58. Collision Loads Collision Loads E = ½ (M+a).ν2 E: Collision energy (kJ) M: Displacement of vessel a : added mass of vessel – Sideway collision~ 0.4 M – Bow/ stern collision ~ 0.1 M V : impact speed (m/s)
  • 59. DAFTAR PUSTAKA DAFTAR PUSTAKA  API RP 2A Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms, 1993.  Bramlette Mc. Cleland: Planning and Design of Fixed Offshore Structure, Van Nostrand Reinhold Co, New York, 1986  Wardenier. J: Offshore and Hydraulic Steel Structrures, Delfi University of Technology, Deift, Netherlands, 1998  Murdjito: Bangunan Lepas Pantai, Diktat Kuliah, FT Kelautan ITS 1998  Chakrabarti, S.K.: Hydrodynamics of Offshore Structures, Springer-Verlag, berlin, 1987  DET NORSKE VERITAS, Offshore standard: structural design of offshore units (wsd method), APRIL 2002, DNV-OS-C201  BS6235, "Code of Practice for Fixed Offshore Structures", British Standards Institution, London, 1982.  DOE-OG, "Offshore Installation: Guidance on Design and Construction", U.K., Dept. of Energy, London 1985.  Clauss, G. T. et al: "Offshore Structures, Vol 1 - Conceptual Design and Hydromechanics", Springer, London 1992.  Hsu, H.T., "Applied Offshore Structural Engineering", Gulf Publishing Co., Houston, 1981.  Graff, W.J., "Introduction to Offshore Structures", Gulf Publishing Co., Houston, 1981.