•Conduct a non-contact 3D Scanning Laser Doppler Vibrometer (SLDV) test on a three-bladed wind turbine assembly.•Develop a finite element model of the assembly including the composite blade ...modeling.•Correlate modal parameters and dynamic response between the SLDV test and the finite element model.•Investigate high-order complex curvature mode shapes and mode coupling of the wind turbine blade through both experimental and numerical approach.
Experimental and numerical modal analysis on wind turbine blades has been previously studied, considering mainly low order bending modes. However, high-order modes are also critical modes for understanding blade dynamics. The mode coupling is essential because a better understanding of the high-frequency blade dynamics can support advances in model validation, blade aeroelastic simulations, blade design, and structural health monitoring. However, these high-order modes and the associated mode couplings of wind turbine blades have not been studied. This work presents a comprehensive experimental and numerical study based on three modal tests and a correlated finite element simulation to study the complex curvature mode shapes and mode coupling dynamics for a three-bladed wind turbine assembly. Three tests are conducted: Test 1, ten accelerometers are deployed on the whole assembly under impact excitation; Test 2, nine accelerometers are deployed on a single blade under impact excitation; and Test 3, a non-contact 3D Scanning Laser Doppler Vibrometer (SLDV) test is performed on a single blade under shaker excitation. This is the first work to use a 3D SLDV for an experimental modal test on the wind turbine blade. With 300–400 points measured with the 3D SLDV, experimental mode shapes having a high spatial resolution with 3D response are used to characterize the coupling for the low-order and high-order modes with complex curvatures. A reliable finite element model of the three-bladed assembly, including the composite blade modeling, is also developed and is well correlated with Test 2 and Test 3. With the high-fidelity 3D SLDV test and well-correlated finite element model, this is also the first work of using experimental and numerical approaches to investigate the high-order mode shape with complex curvatures and mode coupling of bending and torsional behavior that is present in the wind turbine blade for these high-order modes.
Extreme-size wind turbines face logistical challenges due to their sheer size. A solution, segmentation, is examined for an extreme-scale 50 MW wind turbine with 250 m blades using a systematic ...approach. Segmentation poses challenges regarding minimizing joint mass, transferring loads between segments and logistics. We investigate the feasibility of segmenting a 250 m blade by developing design methods and analyzing the impact of segmentation on the blade mass and blade frequencies. This investigation considers various variables such as joint types (bolted and bonded), adhesive materials, joint locations, number of joints and taper ratios (ply dropping). Segmentation increases blade mass by 4.1%–62% with bolted joints and by 0.4%–3.6% with bonded joints for taper ratios up to 1:10. Cases with large mass growth significantly reduce blade frequencies potentially challenging the control design. We show that segmentation of an extreme-scale blade is possible but mass reduction is necessary to improve its feasibility.
Several key development areas have been identified as having high potential for reducing the levelized cost of energy of offshore wind. Two of the most anticipated developments are future generation ...large wind turbines and the use of floating foundations. There is thus a need for developing large floating substructures that are capable of hosting future generation wind turbines. This work presents the preliminary sizing of two semi-submersible platforms for supporting a 25 MW turbine through a design space search using a simplified parametric analysis. Compared to simple theoretical upscaling, the substructures resulting from the proposed simplified parametric analysis have significantly lower steel mass and stiffer tower.
Abstract As conventional upwind wind turbines grow larger, the increased mass and flexibility of the longer blades present challenges concerning costs, structural loads, and safety constraints such ...as tower clearance. At extreme scales, wind turbines in a downwind configuration may provide a feasible alternative to address these challenges by allowing lightweight, flexible blades that can reduce capital costs and blade loads while maintaining safety margins. Downwind turbine blades suffer from increased fatigue loading due to the tower shadow effect. In this study, novel downwind, three-bladed wind turbine designs at 25 MW rating with lightweight, flexible blades are evaluated and compared in terms of power production and structural loading. To obtain a baseline performance, a standard collective blade pitch wind turbine controller is implemented for the two downwind and one upwind turbine designs. Individual pitch control is then added for the downwind turbines to reduce structural fatigue on the turbine blades. In summary, the two downwind turbine designs that differ in rotor pre-coning and shaft tilt angles using collective and individual pitch control are compared against a conventional upwind turbine with collective pitch control at the same scale under turbulent wind conditions.
The quest for reduced levelized cost of energy has driven significant growth in wind turbine size; however, larger rotors face significant technical and logistical challenges. The largest published ...rotor design is 25 MW, and here we consider an even larger 50 MW design with blade length over 250 m. This paper shows that a 50 MW design is indeed possible from a detailed engineering perspective and presents a series of aero-structural blade designs, and critical assessment of technology pathways and challenges for extreme-scale rotors. The 50 MW rotor design begins with Monte Carlo simulations focused on optimizing carbon spar cap and root design. A baseline design resulted in a 250-m blade with mass of 502 tonnes. Subsequently, an aero-structural design and optimization were performed to reduce the blade mass/cost with more than 25% mass reduction and 30% cost reduction by determining optimal blade chord and airfoil thickness for best aero-structural performance.
Abstract
The goal of further reducing the Levelized Cost of Energy (LCOE) has driven the investigation of large-scale wind turbines. This work presents a simple, rapid and detailed approach for the ...structural design of the tower and monopile without a controller, but with frequency and high fidelity structural verification. The approach uses an optimization to reduce the mass of the structures while meeting strength, buckling and geometric constraints by using analytical equations. A verification of frequency constraints is performed with BModes, and ANSYS Mechanical APDL is used for high fidelity verification of stress and buckling. The approach is applied to study the design space of three 25 MW offshore wind turbines with different rotor diameters and cone angles, and to evaluate the nacelle center of mass fore-aft location effect. Results obtained show that the tower and monopile are more susceptible to changes in the rotor thrust than the overturning moment even for designs with high pre-cone angle and large distance of the nacelle center of mass from the tower axis. But it is possible to obtain structurally feasible tower and monopile designs for the three 25 MW turbines studied while not exceeding diameter and wall thickness limits. However, mass penalties can be decreased by 0.8-14%, to further reduce the cost of energy, by increasing the diameter limit which may require manufacturing technology development. The approach applied and studies serve to understand the design space of the tower and monopile for a 25 MW turbine, and provide baseline designs that can be used in the development of a controller and evaluation of a full suite of design load cases.
Offshore floating wind foundations supporting a large wind turbine require a large yard facility or significant facility upgrades for their fabrication. To overcome the cost increase associated with ...facility upgrades, an innovative lightweight modular floating foundation is developed. The foundation comprises multiple modules to enable their assembly on water, offering many benefits and expanding fabrication options for a reduction in the overall cost of the platform. In this paper, the foundation modules and their assembly are briefly described, and an analysis of the platform’s dynamic responses is presented. The modular foundation includes a modular and lightweight tension leg platform (TLP) called “MarsVAWT” which supports a Darrieus 10 MW vertical axis wind turbine (VAWT). The platform is moored with highly pretensioned wire rope tendons. The responses of the platform are analyzed in the time domain in a semi-coupled manner under the turbine operating and parked conditions for an offshore site in the US Northeast. The tower base shear forces and bending moments increase considerably with the combination of wind and waves, compared to those with wind only. The tendon tensions on the weatherside in the operating condition at high wind speeds are comparable to the values of the 50-year extreme (parked). The tendon tension increases are highly correlated to the platform pitch, as well as the horizontal and vertical velocities and vertical acceleration at the tendon porch. The modular platform performances and tendon designs are confirmed to comply with industry standards and practices.
The quest for reduced levelized cost of energy has driven significant growth in wind turbine size; however, larger rotors face significant technical and logistical challenges. The largest published ...rotor design is 25 MW, and here we consider an even larger 50 MW design with blade length over 250 m. This paper shows that a 50 MW design is indeed possible from a detailed engineering perspective and presents a series of aero-structural blade designs, and critical assessment of technology pathways and challenges for extreme-scale rotors. The 50 MW rotor design begins with Monte Carlo simulations focused on optimizing carbon spar cap and root design. A baseline design resulted in a 250-m blade with mass of 502 tonnes. Subsequently, an aero-structural design and optimization were performed to reduce the blade mass/cost with more than 25% mass reduction and 30% cost reduction by determining optimal blade chord and airfoil thickness for best aero-structural performance.
