MULTIDISCIPLINARY DESIGN OPTIMIZATION OF A LARGE SCALE HYBRID COMPOSITE WIND TURBINE BLADE STRUCTURE

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1 16th International Conference on Composite Structures ICCS 16 A. J. M. Ferreira (Editor) FEUP, Porto, 2011 MULTIDISCIPLINARY DESIGN OPTIMIZATION OF A LARGE SCALE HYBRID COMPOSITE WIND TURBINE BLADE STRUCTURE Jin Woo Lee *, Sathya N. Gangadharan and Maj Mirmirani * Graduate Student, Department of Aerospace Engineering lee2b6@my.erau.edu Professor, Department of Mechanical Engineering sathya@erau.edu Dean, College of Engineering mirmiram@erau.edu Key words: Hybrid Composite Structures, Multidisciplinary Design Optimization. Summary. A multidisciplinary design optimization (MDO) of a large scale hybrid composite wind turbine blade is performed. Multiple objectives are considered in this design optimization: maximize length of blade, minimize weight and manufacturing cost. A wind turbine blade is divided into regions and the layup sequences for each region are considered as design variables. Applied load due to extreme wind condition for rotor rotation and rotor stop condition are considered for finite element analysis (FEA) to evaluate the structural strength. The structural stiffness is designed and illustrated so that the natural frequency of the blade does not coincidence with the excitation frequency of the wind turbine. A process of obtaining an optimum hybrid composite laminate layup and an optimum length of wind turbine blade is developed in this research. 1 INTRODUCTION In recent years, the demand for renewable energy sources is rapidly growing to reduce the emission of greenhouse gases. The energy production using wind turbine is one of the promising solutions to generate electricity from a reusable source. As the demand of energy generation using wind turbine increases, a demand for developing technology to build large scale wind turbine blades also increases to generate high capacity wind turbine generator because longer blades sweep larger area and can harness more energy from the wind. At present, conventional wind turbine blades are produced using glass/epoxy composite materials because of its high strength, light weight and reduced manufacturing cost. However, the use of glass/epoxy to build large scale wind turbine blades has reached its limit, because of limited material characteristics of glass/epoxy. Graphite/epoxy is a good candidate

2 composite material for manufacturing wind turbine blades because it has higher strength and lower weight compared to a glass/epoxy composite blade structure. Although graphite/epoxy has better performance characteristics compared to glass/epoxy, higher cost (more than 10 times) of graphite/epoxy limits the used of the material in practical applications. Chamis et al. [1] illustrated that the hybrid composites, which are combination of different composite materials, can yield combined performance and properties of composite materials. An accurate analysis will allow to identify specific combinations of separate composite materials to be used to form an laminated structure known as a hybrid laminate composite structure (HLCS). Precise design and incorporation of the HLCS in wind turbine blades could improve efficiency of the system and reduce manufacturing costs. This research work will yield effective methods and processes for the multidisciplinary design optimization of the hybrid laminated composite based wind turbine blade structures. 2 METHOD OF APPROACH A baseline analysis is conducted and multidisciplinary design optimization process is developed and illustrated SERI-8 wind turbine blade [2] is used as a geometric model in our study. Baseline analysis is performed using NASTRAN [3]. PCOMP composite laminate elements are used for finite element modeling. Clamped boundary conditions are applied at root of blade and a point load is applied at the tip of blade in the flapping direction. A multidisciplinary design optimization process is developed using HEEDS [4] optimizer software. A series of processes were setup using CATIA [5] for geometric modeling, FEMAP [6] for pre and post processing, NASTRAN for structural analysis, SEER-Mfg [7] for manufacturing cost estimation and [8] for data management. The block diagram of MDO process is shown in Figure 1. Multiple objectives to maximize the length of the blade, minimize the weight and the cost of blade are considered simultaneously. The blade model is divided into 8 segments in the span direction, 2 segments in the thickness direction and 3 segments in the chord direction. 1 spar is divided into 8 segments and 4 ribs are considered as 1 region for each rib. The orientation, thickness, material and number of hybrid composite laminate layer of each region is set as design variables. PCOMP elements are used for laminate elements and CBUSH spring elements are used as relaxed constraints at blade root. Aerodynamic forces are applied on the blade for each extreme condition of rotor rotation and rotor stop cases. MO-SHERPA method is used in the MDO process. 3 RESULTS AND DISCUSTIONS For baseline model, percent difference for the blade tip displacement between our FEA results and Ong et al. [2] is about 3.2%. The results of the baseline model modal analysis are shown in Table 1. As shown in Campbell diagram (Figure 2), there is a possibility that resonance could occur because of two interferences: first interference between the first order excitation due to rotation of rotor and first natural frequency and the second interference between the third order excitation due to rotation of 3 blades and third natural frequency. Therefore, based on the preliminary results, the stiffness of blade needs to be optimized to avoid resonance. 2

3 REFERENCES [1] C. C. Chamis and R. F. Lark, Hybrid Composites State-of-The-Art Review: Analysis, Design, Application and Fabrication, NASA, (1977). [2] Cheng-Huat Ong and Stephen W. Tsai, The Use of Carbon Fibers in Wind Turbine Blade Design, Sandia National Laboratories, SAND , (2000). [3] NX NASTRAN, Ver. 6, Siemens, Washington DC, (2009). [4] HEEDS, Ver. 5.3, Red Cader Technology, East Lansing, Mi, (2009). [5] CATIA V5 R20, Dassault Systems, Lowell, MA, (2010). [6] FEMAP Ver. 10.1, Siemens, Washington DC, (2009). [7] SEER-MFG, Ver. 6.1, Galorath Inc., El Segundo, CA, (2010). [8] EXCEL Ver. 2007, Microsoft, Sand Leandro, CA, (2007). ACKNOWLEDGEMENT Thanks to Dr. Somanath, Nagendra of Pratt & Whitney for all his help and support in this research project. 3

4 CATIA Modeling FEMAP Import.stp Model Meshing HEEDS Program File Change Scale.pro Apply Load & Constraint DV Pre Processing Define Material Define Layup Values of Design Variables Input DVs in SEER Server Mode Define Properties Export.dat Nastran Input File MO-SHERPA SEER-Mfg Cost Calculation NX Nastran Execute Nastran Export.op2 file Values of Responses Write Output of Cost Calculation Result FEMAP Program File.pro Import.op2 Nastran Result File RV Post Processing List Response Variables and export to.lst File Figure 1 : Block diagram of multidisciplinary design optimization process 4

5 Modes Hz Table 1 : SERI-8 baseline blade model natural frequencies Figure 2: Campbell diagram of SERI-8 baseline blade model 5