Monitoring of Mooring systems

Transcription

1 Instrumentation of Ocean Devices Monitoring of Mooring systems Christian BERHAULT Centrale Nantes April 2014 MARINET Mooring Monitoring April

2 Presentation EC Devices and Mooring systems Mooring design criteria Rules and recommended practice Design assumptions and methodologies Monitoring : why? Monitoring : strategy and specifications Monitoring : exploitation and survey MARINET Mooring Monitoring April

3 Energy Converter Devices and Mooring systems Offshore wind turbine Wave energy power device Floating current turbine OTEC Two mains configurations: Floater supporting the power energy system Submerged floating system (low wave effect) MARINET Mooring Monitoring April

4 Floating Wind Turbines Hywind Deep draft : spar MARINET Mooring Monitoring April

5 Floating Wind Turbines Semi-submersible multi-columns Main dimensions:10m up to 100m Vertiwind / 2MW Nenuphar /Technip / EDF-EN WINFLOAT Principle Power / EDPR Windfloat Principle Power / EDPR FLOATGEN / IDEOL GAMESA 2MW MARINET Mooring Monitoring April

6 Wave Energy Converter Pelamis Bilboquet / D2M SEAREV Anaconda CETO MARINET Mooring Monitoring April

7 Hydrid technology and large floating platform MLINER Marina Platform / FP7 Poseidon FPP MARINET Mooring Monitoring April

8 OTEC Systems : deep waters ETM/DCNS Lockheed MARINET Mooring Monitoring April

9 Mooring and floater interactions Hull : 2000t to t, steel or concrete, Mooring : tension leg or catenary lines, General field arrangement (lay-out) MARINET Mooring Monitoring April

10 Mooring Design Mooring function and constraints Mooring system, components and lay-out Environmental Conditions : specifications Design rules and methodology Mooring improvement : fatigue, extreme, Installation, Inspection, Maintenance and Repair MARINET Mooring Monitoring April

11 Mooring Main Functions Maintain the floater in place with: limited excursions and motions limited velocities and accelerations limited induced loads on the floater Taking into account environmental constraints: water depth, bathymetry and soil characteristics wind, waves, current, salinity, temperature, bio maritime circulations, fishing, farm arrangement MARINET Mooring Monitoring April

12 Mooring systems and components Mooring systems: Catenary lines Taut lines: cables, rigid pipes Mooring lines components: Chain, steel cable, synthetic ropes, mixted Fairleads, winch, tensioner, chain connector and stopper Anchors: gravity base, suction anchor, standard Mooring lines arrangement: Number and distribution of lines (lay-out) MARINET Mooring Monitoring April

13 Mooring arrangement Horizontal tension on sea bed Large radius of anchoring position Soft mooring stiffness Mooring lines up to 5 or 10 times water depth Large excursions in deep water Vertical tension at sea bed Limited radius of anchoring position High mooring stiffness (vertical component) Reduced excursions in deep water Reduced mooring lines Higher top tensions MARINET Mooring Monitoring April

14 Mooring arrangement Number of lines Lines lay out : environment: most critical directions floater concept: geometry and dimensions soil bathymetry field configuration: other structures, farm Lines fairleads location on the floater (deck, keel, ) MARINET Mooring Monitoring April

15 Mooring components: chain Studlink chain Studless chain Steel characteristics: - weight, corrosion, marine growth - high breaking load - fatigue induced by friction and torsion (OPB) - large fatigue life (tension to tension) MARINET Mooring Monitoring April

16 Mooring components: main characteristics MARINET Mooring Monitoring April

17 Mooring components: steel cables 6 strand (up to 7 years) Spiral strand (10-15 years) 6 strand + zinc wires (up to 10 years) Sheathed spiral strand (>15 years) MARINET Mooring Monitoring April

18 Mooring components: steel cables reduced weight, corrosion reduced axial stiffness (taut lines) fatigue induced by axial dynamic tension lower fatigue life connection with chain MARINET Mooring Monitoring April

19 Mooring components: synthetic ropes - low weight, no corrosion - high breaking load - non linear axial stiffness - sensitive to friction - fatigue life not wellknown Problem : assessement of reliability depending on fibre MARINET Mooring Monitoring April

20 Mooring components: synthetic ropes MARINET Mooring Monitoring April

21 Mooring components: main characteristics MARINET Mooring Monitoring April

22 Mooring components: SN curves MARINET Mooring Monitoring April

23 Mooring components: connections Chain stopper MARINET Mooring Monitoring April

24 Mooring components: anchors Standard anchor or piles for soft soil Suction anchor for liquefied soil (mud) Gravity bases for hard soil (rocks) MARINET Mooring Monitoring April

25 Mooring components: anchors Standard anchor: soft clay, sand horizontal tension (line on the soil) soil resistance required dimensions and weight: max. tension Suction anchor: mud and liquefied soil specific facilities for installation adapted to taut mooring system: vertical tension MARINET Mooring Monitoring April

26 Mooring components: anchors Gravity bases: weight adjusted to compensate line tension resistance to soil friction installation could be difficult in deep water Vertical piles: vertical and horizontal tension length and diameter selected wihin soil cohesion specific facilities for installation MARINET Mooring Monitoring April

27 Anchor capacity under tension MARINET Mooring Monitoring April

28 Anchor capacity under tension MARINET Mooring Monitoring April

29 Environmental conditions Soil characteristics and bathymetry Wave conditions: Wave statistics: wave description / scatter diagram Long term distribution:1-year, 100-years return period Current conditions: Tide, from wind, oceanic, rivers, Current profile along water depth Statistics: scatter diagram, long term distribution Wind conditions: Statistics: short term and long term distributions, gusts Joint probability distribution: wind, wave, current MARINET Mooring Monitoring April

30 Site conditions : Current tide, oceanic, river, wind, variation with depth short and long term statistics in time MARINET Mooring Monitoring April

31 Wave conditions Origins: wind, swell, cyclone, freak waves Height, period, direction Energy distribution: wave spectra Short and long term statistics in tim Interaction with current Global parameters: Hs, Tp, mean direction MARINET Mooring Monitoring April

32 Wave parameters distributions MARINET Mooring Monitoring April

33 Wave conditions: scatter diagram Hs\Tp Tp=3s Tp=4s Tp=5s Tp=6s Tp=7s Tp=8s Tp=9s Tp=10s Tp=11s Tp=12s Tp=13s Tp=14s Tp=15s Tp=16s Tp=17s Tp=18s Hs=0.5m Hs=1m Hs=1.5m Hs=2m Hs=2.5m Hs=3m Hs=3.5m Hs=4m Hs=4.5m Hs=5m Hs=5.5m Hs=6m Hs=6.5m Hs=7m Hs=7.5m Hs=8m Hs=8.5m 1 2 Hs=9m 1% des états de mer les moins fréquents de 95% à 99 % des états de mer les plus fréquents 95% des état de mer les plus fréquents MARINET Mooring Monitoring April

34 Wind conditions Velocity and direction Variation with height (above sea level) Energy distribution: wind spectra, turbulence Short and long term statistics Reference: mean wind on 10mn at 10m MARINET Mooring Monitoring April

35 Wind : Vmoy + Spectrum + Gust N v V ( t, Z ) V ( Z ). V ( f ).cos( 2.. f. t ) mean i i i j 1 V ( f i ) V ( Z ) mean is the mean velocity at the Z elevation point is deduced from the wind time history Example: The Harris spectrum is defined using reduced frequency : ~ f ~ f. Lv f V mean f. S ( f ) Harris V mean ~ f 4. Cd. ~ ( 2 f ) Lv =1800m a reference distance Cd=0.003, V V ( 10m, 1hr) mean mean MARINET Mooring Monitoring April

36 Environmental conditions Basis of the mooring analysis is the Specifications of the metocean conditions including: long term statistics vs required exploitation life: return period (20-years?) distribution of short term statistics for fatigue life analysis of all mooring components, for installation and IMR Specification are derived in accordance with selected certification rules requirements MARINET Mooring Monitoring April

37 Design and tools Environmental loads Floater response Mooring loads Fatigue life Model Tests Global simulation Marine growth Corrosion Global Numerical simulation In-situ tests and Monitoring MARINET Mooring Monitoring April

38 Design rules and Methodology Design rules and criteria: Maximum breaking loads Fatigue life for all components, S/N curves Anchor and soil resistance Marine growth and Corrosion effects Methodology: Static and quasi-static response: current, mean wind load, wave drift, stabilization systems (ballast, thrusters, ) Dynamic loads and response induced by the floater motions, wave kinematics, VIV, TIV, MARINET Mooring Monitoring April

39 Certification rules DNV-GL, BV, API Rules for mooring design are applied to: maximum loads and stresses in the lines and components within the specified return period (100-y, including a safety coefficient) fatigue life within the exploitation period (100-y to 200-y including a safety coefficient) maximum loads in accidental conditions: defined in the rules (line broken, floater compartment flooded) maximum environmental conditions needed for installation Rules recommend design methodologies and safety coefficients for each kind of conditions MARINET Mooring Monitoring April

40 Sea keeping - Mooring analysis Top line motion : Basic Roll motions : process, DIODORE lines : a wide connexion range of application Offset and Slow drift : mooring Low frequency pitch/heave Slow drift : mooring Vortex Induced Motions : Mooring Line tensions MARINET Mooring Monitoring April

41 Example : Floating Wind Turbine Mast material, height, Connexion to the hull wind, floater motion Mooring lines material, components, lay-out, fairlead Current, waves, floater motions Wind turbine Power, mass Blades and rotor Control Wind, floater motion Hull Geometry and structural design, ballast, stabilization, towing, installation, damaged conditions Waves, wind, current, tidal, staic and dynamic stability, offset, motions Mooring lay-out Soil, water depth, bathymetry MARINET Mooring Monitoring April

42 Example : Floating Wind Turbine Mass, inertia Aerodynamic drag / lift Aeroelasticity, VIV Blades / mast interaction Mass, inertia Rotor drag Blades drag / lift Blade deformation Rotation control Pitch control or imposed position Mass, apparent weight, stifness Added mass, viscous drag Mass, inertia, Hydrostatic loads (tidal, shape) Stabilization Diffraction/radiation/drag VIM, instability Hydroelastic response Soil interaction at TDP contact/stiffness/friction MARINET Mooring Monitoring April

43 Example : Floating Wind Turbine Wind Wind Turbine / Mast Mean and time varying loads Offset and tilt Aeroelastic response Couplings : heel, tilt, stabilization Floater motions induced by Wind variation, control, Vibrations Current, Waves Current, Waves, Tidal Hull + Mooring Mean offset and set-down Slow drift and set-down Wave frequency motions Slamming / whipping VIV, VIM, galop, «mathieu» Couplings : Mast/blades bending modes Top velocity, accelation Control algorithm MARINET Mooring Monitoring April

44 Mooring line stiffness Horizontal tension Working point Mean position Distance Fairlead -anchor Mean offset MARINET Mooring Monitoring April

45 Mooring line design Stiffness law : Fx Taut (linear +Fdynamic Catenary Fmean + Flf SALM F0 X MARINET Mooring Monitoring April

46 S( ) Slow drift Second order diffraction Irregular waves Period 3 to 25s WF response (25s) (3s) Wave frequency response Mean drift X( ) LF WF Low frequency response LF response Global response MARINET Mooring Monitoring April

47 Vortex Induced Motions MARINET Mooring Monitoring April

48 Tools for Design Numerical tools: Standard sea-keeping and mooring tools Fully coupled analysis in time domain Non-linear response in extreme waves: small floaters Specific approaches: wind or current turbine, wave energy device Farm arrangement FE analysis for local strain/stress, chain OPB Model tests in wave tanks: Modeling full environment conditions Calibration / Validation of numerical models MARINET Mooring Monitoring April

49 Non linear time domain MARINET Mooring Monitoring April

50 Non linear time domain MARINET Mooring Monitoring April

51 Numerical Modeling Beam : drag loads HDB : added mass, 1 st order WF loads, LF-QTF MARINET Mooring Monitoring April

52 Numerical Modeling Assumption : diffraction-radiation + time domain simulation Drag loads on each hull component: excitation, damping Inertia and drag loads on mooring lines and umbilical d ancrage : BV Aerodynamic loads from wind turbine, wind drag loads on mast Heave Tension MARINET Mooring Monitoring April

53 Design Basis Typical range of floater natural periods Heave : 6 to 10 sec. Pitch / Roll : 15 to 30 sec. Surge / Sway : 80 to 250 sec. Yaw : 30 to 50 sec. MARINET Mooring Monitoring April

54 Mooring Design Methodology for selection: Tension vs horizontal offset Loads on the anchor Maximum top tension Maximum line angles: top fairlead and TDP Connections design Installation and IMR MARINET Mooring Monitoring April

55 Monitoring Requirements Top Tension Top angle Anchor tension TDP angle MARINET Mooring Monitoring April

56 Mooring improvement Static analysis for mooring design: screening study Operational conditions: fatigue life Extreme and survival conditions Installation conditions Accidental Line broken Floater compartment flooded MARINET Mooring Monitoring April

57 Monitoring: Why? Uncertainty in the design prediction methodology imposes large safety coefficients both for extreme and fatigue response: from 3 to 10 depending of RP Reducing safety coefficients = cost reduction both for procurement and installation In-situ measurements will be required: To validate (or not!), in real conditions, the methodology and standard numerical models To follow the real occurred damage and to re-estimate the fatigue life MARINET Mooring Monitoring April

58 Monitoring: Why? In-situ measurements will be required: To follow risk of line broken (due to severe conditions or collisions) To program hot-line safety operation MARINET Mooring Monitoring April

59 Monitoring Requirements Measurements : wave, current and wind conditions floater motions top lines tension (3 dofs or top angles) tension and angle at TDP continue time series, with a large frequencies range (to include VIV, WF and LF components) Hot-line data transmission (VHF, Optical fibers, ) Hot-line post-processing to provide alarm messages MARINET Mooring Monitoring April

60 Monitoring Requirements Associated numerical models: for calibration and re-estimation of extremes to re-estimated fatigue life with a given period to estimate evolution of marine growth Selection of gauges: load, acceleration, motions, Reliability and redundancy of measurement systems Existing measurements systems to be tested regarding performance and reliability in marine conditions? MARINET Mooring Monitoring April

61 Monitoring Difficulties Bad return experience from oil&gaz (FPSO, Calm buoy): reliability of measurement systems no coherent times series between environment parameters, motions and tensions line failures not anticipated More severe conditions for MREs: High dynamic response in the mooring lines Large top angle variations induced by pitch/roll motions New material as synthetic ropes MARINET Mooring Monitoring April

62 Conclusions Specific R&D project on mooring lines monitoring is required. ECN proposes the MOORSURV project with two steps : monitoring of a SEMREV meteo data buoy: motions and mooring lines to develop and to validate methologies and tools (alarm, fatigue, ) monitoring of a full scale MRE system during a 2-years test period Identification and tests of existing loads gages regarding requirements MARINET Mooring Monitoring April

63 MERCI MARINET Mooring Monitoring April