4 - Structural Optimization of Offshore Wind Turbines - Petrini

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ASCE Earth & Space 2010 OWT Symposium

http://content.asce.org/files/pdf/EarthSpace2010Prelim-FINAL.pdf

http://ascelibrary.org/doi/book/10.1061/9780784410967

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4 - Structural Optimization of Offshore Wind Turbines - Petrini

  1. 1. Structural Optimization of Offshore Wind Turbines Mario Torcinaro, Francesco Petrini, Stefania Arangio francesco.petrini@uniroma1.it Department of Structural and Geotechnical Engineering Sapienza University of Rome
  2. 2. MotivationsEARTH&SPACE 2010 2 Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010 Motivations 1. Offshore wind farms are relatively new structural facilities located in challenging environment, the preliminary design of the structural elements is usually very conservative. A refinement is needed. 2. An offshore wind farm is formed by a number of wind turbines (50-200 elements) and, consequently, a small individual reduction of structural material amount can lead to significant saving of money if regarding the whole farm. 3. A new support structure is proposed here, and the correct sizing of its structural parts is crucial in this phase.
  3. 3. EARTH&SPACE 2010 INTRODUCTION System design approach for complex structural systems optimization Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  4. 4. z y x,x’ z’ y’ Waves Mean wind Current P (t)vP (t)w P (t)uP Turbulent wind Vm(zP) P H h vw(z’) Vcur(z’) z y x,x’ z’ y’ Waves Mean wind Current P (t)vP (t)w P (t)uP Turbulent wind Vm(zP) P H h vw(z’) Vcur(z’) d Complex system 3 EARTH&SPACE 2010 Introduction Part I Part II A “Complex System” Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  5. 5. z y x,x’ z’ y’ Waves Mean wind Current P (t)vP (t)w P (t)uP Turbulent wind Vm(zP) P H h vw(z’) Vcur(z’) z y x,x’ z’ y’ Waves Mean wind Current P (t)vP (t)w P (t)uP Turbulent wind Vm(zP) P H h vw(z’) Vcur(z’) d 3 EARTH&SPACE 2010 Introduction Part I Part II A “Complex System” NonLinearities Uncertainty Interactions Complex system Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  6. 6. System Engineering 4 Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.it A System Engineering Approach Since the structural behavior of offshore wind turbines is influenced by nonlinearities, uncertainties or interactions, they can be defined as complex structural system “a set of interrelated components which interact one with another in an organized fashion toward a common purpose” (NASA, 1995) Structure Structural system “a device to channeling loads” Decomposition Structure Actions Performances Structural System A fundamental task concerns the Structural System and Structural Performance decomposition EARTH&SPACE 2010 Introduction Part I Part II Bontempi F., Li H., Petrini F., Gkoumas K., (2008). Basis of Design of Offshore Wind Turbines by System Decomposition, Proceedings of the ASEM'08, Jeju , Korea, 26-28 May 2008.
  7. 7. System Engineering 5 Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.it Structural decomposition EARTH&SPACE 2010 Introduction Part I Part II Macro - LevelDetail - Level Structure decomposition Main structure (carrying loads) Secondary structure Auxiliary structure Rotor-nacelle assembly Support structure Energy production Energy transfer Operation Maintenance Emergency Substructure Tower Rotor Nacelle Blades Foundations Meso - Level Junctions Junctions Micro - Level Bontempi F., Li H., Petrini F., Gkoumas K., (2008). Basis of Design of Offshore Wind Turbines by System Decomposition, Proceedings of the ASEM'08, Jeju , Korea, 26-28 May 2008.
  8. 8. Optimization in design process 6 EARTH&SPACE 2010 Introduction Part I Part II Structural design and structural optimization Topological Optimization Design Optimization Structural check Best design config? Refine No STOP PBD Pre sizing Performance requirements Advanced Model Basic Models Conceptual design START Yes Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  9. 9. 7 EARTH&SPACE 2010 Introduction Part I Part II Structural design and structural optimization Topological Optimization Design Optimization PBD No Structural check Best design config? Refine STOP Pre sizing Performance requirements Advanced Model Basic Models Conceptual design START Refinement of the design configuration with the goal of obtaining satisfaction performances in economical way Shape optimization (Options definition) Parameters optimization (Options refinement) Feasible configuration selection (Option selection) Yes Optimization in design process Present Work Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  10. 10. EARTH&SPACE 2010 PART I, Case study structure: Modeling and Optimization aspects Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  11. 11. Support Structures 9 EARTH&SPACE 2010 Introduction Part I Part II Typologies of support structures Westgate, Z.J. and DeJong, J.T. (2005). Geotechnical considerations for offshore wind turbines. Report for MTC OTC Project Water depth (m) Foundation type 0-10 Gravity based 0-30 Mono-pile >20 Tripod/Jacket >50 Floating Bontempi, F. (2010). Advanced topics for offshore wind turbines. Earth&Space 2010 Conference Strutted Quadruped Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  12. 12. Objective Funcrion Analytics 10 EARTH&SPACE 2010 Introduction Part I Part II Optimization problem formulation Unconstrained Design spaceConstrains Constrained Design space We must find the minimum of a certain Objective Function f, depending on certain Design Variables (DV) x1,…,xn subjected to a number of constrains and by bounding the values of a certain number of state variables (SV) nn11 n LSV,,LSV,RXx,0)x(g,0)x(hbeing)x(fmin   Constrains Design variables State variables Objective Functions Von Mises stresses Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  13. 13. 11 EARTH&SPACE 2010 Introduction Part I Part II First order Optimization method One introduces the following unconstrained objective function:                     2 31 m 1i m 1i iwih m 1i ig n 1i ix 0 wPhPgPqxPq,Q f f x   λ2 ii i ig αg g gP         λ is a large integer so that the function will be very large when the constraint is violated and very small when it is not Q is the dimensionless unconstrained objective function, Px is the exterior penalty functions applied to the design variables, Pg, Ph, and Pw are penalties applied to the constrained design and state variables, f0 is the reference objective function value that is selected from the current group of design sets q is the response surface parameter . For each optimization iteration (j) a search direction vector d(j) is devised. The next iteration (j+1) is obtained from the following equation:      j j j1j s dxx         1j 1jk jj rq,Q   dxd                  21j jT1jj 1j q,Q q,Qq,Qq,Q r       x xxx where sj is the line search parameter, and The key to the solution of the global minimization of Q relies on the sequential generation of the search directions and on internal adjustments of the response surface parameter (q). ANSYS Inc. (2008). ANSYS Theory reference Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010 Analytics
  14. 14. 12 EARTH&SPACE 2010 Introduction Part I Part II Optimization problem algorithm Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010 Algorithm
  15. 15. Modeling 13 EARTH&SPACE 2010 Introduction Part I Part II Structural system modeling Structure Actions Interactions Modeling levels Systemic Macro Meso Micro Model level Scale Detail level Type of Finite Elements Systemic level wind farm approximate shape of the structural components BEAM elements Macro level single turbine approximate shape of the structural components, correct geometrical ratios between the components BEAM elements Meso level single turbine detailed shape of the structural components SHELL, BRICK elements micro level individual components detailed shape of the connecting parts SHELL, BRICK elements Differentiation of the modeling levels Bontempi F., Li H., Petrini F., Manenti S., (2008). Numerical modeling for the analysis and design of offshore wind turbines, Proceedings of ASEM'08, Jeju, Korea, 26-28 May 2008 Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  16. 16. 1°1° Macro Global response Meso Micro Levels of modeling and results detail level Jacket - Tower connection Detailed global response and medium-detailed local response Detailed local response and analysis of connections ModelingIntroduction Part I Part II 14 EARTH&SPACE 2010 Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  17. 17. EARTH&SPACE 2010 PART II, Case study structure: Problem definition and results Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  18. 18. Design variables 15 EARTH&SPACE 2010 Introduction Part I Part II Application x1 x2 • Structure and piles 180 m • Structure height: 140 m • Immersed: 35 m • Over water level: 105 m Local constraints: •maximum Von Mises ideal stress equals to 300MPa (strength criterion); •maximum compression stress equals to 200MPa (local instability criterion); •maximum ratio diameter/thickness equals to 100 (local instability criterion); Global constraints: •Eulerian buckling multiplier greater that 5; •maximum horizontal displacement permitted 4 m. • Objective Function: TOTAL VOLUME
  19. 19. Results 16 EARTH&SPACE 2010 Introduction Part I Part II Macro-level model: Design variables trend Diameters Thicknesses Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  20. 20. 17 EARTH&SPACE 2010 Introduction Part I Part II Macro-level model: State variables trend Compression stresses Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010 Von Mises stresses Results
  21. 21. 18 EARTH&SPACE 2010 Introduction Part I Part II Macro-level model: Configuration evolution Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010 Results
  22. 22. 19 EARTH&SPACE 2010 Introduction Part I Part II Macro-level model: Objective function Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010 Results
  23. 23. 20 EARTH&SPACE 2010 Introduction Part I Part II Meso-level model Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010 Results
  24. 24. 21 EARTH&SPACE 2010 Introduction Part I Part II Meso-level model: Effective buckling modes detection Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010 Macro-level model Meso-level model Results 1° buckling mode load multipler = 9,08 1° buckling mode load multipler = 10,12
  25. 25. Optimal configuration Optimal ConfigIntroduction Part I Part II 22 EARTH&SPACE 2010 Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010 VOLUME=116 [m3] Diamet ers[m] Thicknesses[m] d/t D1 2.25 T1 3.1E-02 72.5 D2 3.14 T2 4.2E-02 75.5 D3 4.03 T3 4.2E-02 96.9 D4 4.56 T4 4.2E-02 109.5 D5 5.09 T5 5.2E-02 97.5 D6 2.37 T6 3.3E-02 71.8 D7 5.09 T7 5.2E-02 97.5 D8 5.30 T8 5.4E-02 98.3 D9 5.05 T9 5.4E-02 93.7 D10 4.80 T10 5.4E-02 89.1 D11 4.55 T11 5.4E-02 84.5 D12 4.31 T12 4.4E-02 97.9 D13 3.84 T13 4.4E-02 87.3 D14 3.37 T14 4.4E-02 76.7 D15 2.91 T15 4.4E-02 66.0 D16 2.44 T16 3.8E-02 64.8 D17 1.52 T17 1.6E-02 95.9 D18 2.32 T18 2.3E-02 99.4
  26. 26. Monopile-Quadruped comparison Quadruped:  VOLUME = 116 [m3]  Weight = 904 [t]  D max = 5 [m] Monopile:  VOLUME = 234 [m3]  Weight = 2377 [t]  D max = 9 [m] Optimal ConfigIntroduction Part I Part II 23 EARTH&SPACE 2010 Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010
  27. 27. EARTH&SPACE 2010 24 Structural Offshore Wind Turbines Optimization francesco.petrini@uniroma1.itEARTH&SPACE 2010 Conclusions 1. The Design Optimization of Owts is a fundamental step in the design of Offshore Wind Farms. 2. The Design Optimization of such a complex structural systems has been carried out by assuming simplified models for the actions. 3. Multi level detail models are needed in order to capture the main physical aspects. 4. A new support structure is proposed here, the optimization produced good results in terms of weight if compared with another feasible solution (a monopile support structure).

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