1 Aero-Hydro-Servo-Elastic Analysis of Floating Wind Turbines with Tension Leg Moorings Erin Bachynski, PhD candidate at CeSOS erin.bachynski@ntnu.no January ar 7, 2013 Erin Bachynski CeSOS Centre for Ships and Ocean Structures
2 Floating wind turbine concepts studied at CeSOS We need to understand floating wind turbine behavior so that we can bring the cost down Spar Semi-submersible TLP
3 Tension Leg Platform (TLP) Stability from tension legs, implying motions as an inverted pendulum Small motions (+) Flexible wrt w.r.t. water depth (+) Smaller steel weight (+) Small footprint t area on seabed (+) Challenging installation (-)
4 TLPWT Design Botta, 2009 Shimada, 2011 Moon, 2010 MIT NREL TLPWT (Matha, 2009) Displacement Increases cost Decreases risk of slack Pontoon radius Increases stability Increases hull loads Tendons
5 Integrated aero-hydro-servo-elastic analysis aerodynamics control structural dynamics hydrodynamics Source: NREL/Wind power today, 2010. Challenges: -complexity -tight coupling -nonlinear -time domain -long term periods -transient (faults)
6 Aerodynamics M. D. Pedersen, J. de Vaal, 2012
7 Control system Serves to regulate rotor rotation speed regulate power output protect structure Actions Change generator torque Change blade pitch
8 bine/yr) (%) ilures/turb p ) Blade pitch mechanism failures Contribut tion to failu ure rate (fa Wilkinson et al., 2011 Pitch syste em Jiang, 2012 PhD candidates at CeSOS studying the effects of control system failures on different platforms : Z. Jiang, M. Etemaddar, E. Bachynski, M. Kvittem, C. Luan, A. R. Nejad
9 What happens if one blade stops pitching? 1.5 x TLP, U=20m/s, H 104 s TLP, = 4.8m, EC 5T p = 10.8s 1 Fault occurs Continue operating with B C faulted blade MY, knm Tow wer Top B 0.5 0-0.5 Shut down -1 turbine quickly -1.5-200 -150-100 -50 0 50 100 150 200 time - TF, s
10 What happens if one blade stops pitching (SPAR)? 1.5 x Spar, U=20m/s, H 104 Spar, s = 4.8m, EC 5T p = 10.8s 1 Fault occurs Continue operating with B C faulted blade MY, knm Tow wer Top B 0.5 0-0.5 Shut down -1 turbine quickly -1.5-200 -150-100 -50 0 50 100 150 200 time - TF, s
11 Hydrodynamics y aerodynamics control hydrodynamics Large volume structures: potential flow Slender structures: Morison Equation We have implementations of both unlike many others!
12 Structural aerodynamics control Modeling hydrodynamics structural dynamics Flexible beam elements (tower, blades, mooring system) Rigid hull Global model simplified generator
13 Structural aerodynamics control Modeling hydrodynamics structural dynamics Image: NREL Flexible beam elements (tower, blades, mooring system) Rigid hull Global model simplified generator PhD candidates at CeSOS: Yihan Xing, Amir Nejad, Wenbin Dong, Zhiyu Jiang
14 TLPWT Parametric Design Study: Diameter Water Depth Pontoon Radius Ballast Fraction 45 resulting designs 7 environmental conditions Aerodynamic forces must be transferred to tower bending, inertia, or line tension Stiffness and mass effects Three pontoons, large pontoon radius, and mid-range displacement may give a reasonable design
15 Governing Load Cases Response Spar TLP Tower Base FA Moment storm storm Tower Base SS Moment storm pitch fault/shutdown (not faulted) Blade Flapwise Moment pitch fault/extreme turbulence pitch fault/extreme turbulence (not faulted) Edgewise Moment pitch fault pitch fault/shutdown (faulted) Blade Flapwise Moment pitch fault pitch fault (faulted) Blade Edgewise Moment shutdown shutdown Tendon Tension Variation - storm Fore-aft (FA) Side-side (SS) Image: National Instruments
16 TLPWT + 3 Point Absorbers Preliminary results indicate no significant change in power output for WEC or WT by combining Reduced tendon tension variation (5-10%) and motions % Change in Standa ard De viation 10 % 5 % 0 % 5 % 10 % 15 % 20 % 25 % 30 % EC1 EC2 EC3 %diff difference calculated l as [(TLPWTWEC) TLPWT]/TLPWT
17 Concluding remarks TLP wind turbines present complex, unanswered design and analysis challenges Numerical simulations require coupled aerohydro-servo-elastic tools and expertise A wide variety of environmental and operational conditions must be considered In our studies of floating wind turbines at CeSOS we hope to provide insights that can help inform designers and regulatory bodies
18 Thank you!