On addressing noise constraints in the design of wind turbine blades

Power production from wind energy has been increasing over the past decades, with more areas being used as wind farms and larger wind turbines (WTs) being built. With this development, awareness of the impact of wind energy on the environment and on human health has also raised. There has been a large interest in developing fast turnaround WT blade design frameworks, capable of predicting both aerodynamic and aeroacoustic performance to handle ever stricter noise criteria constraints dictated by site or local authorities. In this work, a blade element momentum theory model is used to predict the aerodynamic performance of a wind turbine, coupled to an empirical aeroacoustic noise model and boundary layer corrections. The aeroacoustic prediction code developed was validated against measurement data of the AOC 15/50 WT and included in an optimization framework using a genetic algorithm. The blade shape was parametrized using NURBS curves for the cross sectional airfoil shapes and Bézier curves for the twist and chord distributions, totaling up to 62 design variables. Two multi-objective optimization cases, both single- and multi-operating point, were performed. Optimal solutions selected from the Pareto fronts are discussed in detail. These solutions ranged from an increase in annual energy production of 15 % to a reduction in noise levels of 9.8 %. It was demonstrated that substantial noise reduction could be obtained at an expense of a minor aerodynamic penalty.     

Development of a structural optimization strategy for the design of next generation large thermoplastic wind turbine blades

This paper presents the development of a structural optimization process for the design of future large thermoplastic wind turbine blades. The optimization process proposed in this paper consists of three optimization steps. The first step is a topology optimization of a short untwisted and non tapered section of the blade, with the inner volume used as the design domain. The second step is again a topology optimization, but on the first half of a blade to study the effect of non symmetry of the structure due to blade twist and taper. Results of this optimization step are then interpreted to build a shell model of the complete blade structure to perform composite size optimization based on a minimum mass objective subjected to constraints on deflection, composite strength and structural stability. Different blade models using ribs are then optimized and compared against conventional blade structure (box spar structure without ribs and single web structure without ribs). The use of ribs in wind turbine blade structures, which is more adapted to thermoplastic composite manufacturing than for thermoset composites, leads to slightly lighter blades than conventional blade structures.     

Optimum section selection procedure for horizontal axis tidal stream turbines

Stochastic behavior of renewable energy sources forces designers to optimize the energy converters for the purpose of capturing the maximum amount of available energy. The performance of horizontal axis wind and tidal turbines mainly depends on the geometrical properties such as chord and twist distributions and also the types of sections which are utilized along the blade. The purpose of presented paper is introducing a procedure which can be utilized in order to select the optimum sections for horizontal axis tidal turbines for the purpose of increasing the turbine performance. The presented procedure also can be applied for horizontal axis wind turbines. For the purpose of evaluating the performance of the proposed method, two design types (chord and twist distributions) of tidal turbines are selected as case studies. Power coefficient is considered as objective function, and three types of hydrofoils namely NACA63-8xx, NACA44xx, and RISO-A1-xx are selected as candidate solutions. A blade element momentum theory model is used for calculating the power coefficient. The discrete ant colony optimization algorithm is selected as optimization tool. The results indicate that the utilization of the proposed method will considerably decrease the required process time for obtaining the optimum sections across the blade span, and also it is shown that using different types of sections across the blade span can increase the power coefficient of the turbine. The importance of the proposed method will be significant when various types of hydrofoils and airfoils can be considered as candidate sections across the blade span.

     

Determination of fault operation dynamical constraints for the design of wind turbine DFIG drives

This paper presents an efficient design tool for the estimation of the transient electromagnetic peak torque and transient rotor over-voltages of wind turbines (WT) doubly-fed induction generators (DFIG) during severe fault conditions on the grid side. This versatile and robust tool is well adapted to the implementation in a DFIG drives CAD environment using iterative optimization procedures. In such an application, it is used to compute the dynamical constraints function during the integrated design process of the whole drive including the generator, the gearbox and the power converters. Results show that it is necessary to take into account the dynamical constraints under fault operation, during the early steps of the system design process. Another application of the tool is also illustrated in the paper: the design of the protection system (i.e. the crowbar resistance) for a given generator, a given gearbox and a given power converter.     

Distributed Model Predictive Load Frequency Control of Multi-area Power System with DFIGs

Reliable load frequency control (LFC) is crucial to the operation and design of modern electric power systems. Considering the LFC problem of a four-area interconnected power system with wind turbines, this paper presents a distributed model predictive control (DMPC) based on coordination scheme. The proposed algorithm solves a series of local optimization problems to minimize a performance objective for each control area. The generation rate constraints (GRCs), load disturbance changes, and the wind speed constraints are considered. Furthermore, the DMPC algorithm may reduce the impact of the randomness and intermittence of wind turbine effectively. A performance comparison between the proposed controller with and without the participation of the wind turbines is carried out. Analysis and simulation results show possible improvements on closed-loop performance, and computational burden with the physical constraints.      

Design optimization of a laser printer cleaning blade for minimizing permanent set

When a cleaning blade in a laser printer is excessively deformed, immoderate permanent set can result, leading to weaker nip pressure between the cleaning blade and OPC drum that worsens its cleaning performance and printing quality. In this study, the correlation of the permanent set with stress and strain was investigated through tensile tests with rubber test specimens. Based on the experimental results, the maximum von-Mises stress value was used to quantify the permanent set. A design optimization problem was formulated to minimize the maximum von-Mises stress while satisfying the design constraints for maintaining appropriate contact between the cleaning blade and the OPC drum. We employed metamodel-based design optimization using design of experiments, metamodeling and an optimization algorithm to circumvent the difficulty of structural analyses at some design points. Using the proposed design approach, the optimal maximum von-Mises stress was reduced by 40.2 % compared to the initial stress value while all the design constraints were satisfied. In order to verify the validity of our design optimization result, we manufactured the cleaning blades according to the optimum design solution and performed permanent set and printer tests. The test results clearly showed the validity of our design optimization result.     

具有尾缘襟翼风力机的恒功率反步法控制

尾缘襟翼风力机控制技术在大型风力机领域具有巨大的应用潜力.本文首先基于修正的叶素动量方法建立了具有可变尾缘襟翼的风力机气动模型.针对襟翼风力机的非线性模型,采用反步法设计了非线性控制器,保证系统的控制量和状态变量全局有界,并且风机的输出功率可以收敛到额定功率的一个小邻域内.此外,控制器设计过程中没有将实时风速信息纳入反馈系统,因而降低了工程实施的难度.最后针对12 m/s～15 m/s的阶跃风、基于四分量模型模拟的风载扰动、执行机构受到外部扰动以及总转动惯量具有10%不确定性的工况进行了仿真,仿真结果表明所设计的控制器能有效地稳定风力发电系统的输出功率,控制系统具有较强的鲁棒性.     

基于VB的风力机叶片外形优化设计

为了实现风力发电机风轮叶片外形的优化设计,以风场风速分布为基础提出了综合优化目标;以片条理论为基础提出了以展弦比为关键参数的修形约束条件的气动优化目标,建立了叶片外形优化设计的数学模型。采用枚举法和循环结构,选用Access数据库,应用Visual Basic编制程序实现叶片外形的优化设计。针对内蒙古某地区设计了1.5MW风力机叶片,与国外同功率某通用叶片进行了对比分析。结果表明,两种叶片外形基本吻合,而且文中设计的叶片在性能上有明显优势,同时也验证了文中提出数学模型的可靠性和程序的实用性。     

DMTO – a method for Discrete Material and Thickness Optimization of laminated composite structures

This paper presents a gradient based topology optimization method for Discrete Material and Thickness Optimization of laminated composite structures, labelled the DMTO method. The capabilities of the proposed method are demonstrated on mass minimization, subject to constraints on the structural criteria; buckling load factors, eigenfrequencies, and limited displacements. Furthermore, common design guidelines or rules, referred to as manufacturing constraints, are included explicitly in the optimization problem as series of linear inequalities. The material selection and thickness variation are optimized simultaneously through interpolation functions with penalization. Numerical results for several parameterizations of a finite element model of a generic main spar from a wind turbine blade are presented. The different parameterizations represent different levels of complexity with respect to manufacturability. The results will thus give insight into the relation between potential weight saving and design complexity. The results show that the DMTO method is capable of solving the problems robustly with only few intermediate valued design variables.     

Effects of blade tip modifications on wind turbine performance using vortex model

The effects of blade tip modifications on a wind turbine blade are studied with the design code developed previously, by taking into account the curving of the blade axis in or out of the plane of rotation. This is an area of interest for manufacturers of wind turbines to improve the aerodynamic performance, as has been done with airplane wings and also to use the swept tips to unload the blades during wind gusts by changing the local incidences with a nose-down torsional moment.The vortex model, based on Goldstein approach, treats each blade as a lifting line generating a helicoidal vortex sheet, supporting the trailed vorticity along prescribed helices whose pitch is determined to satisfy the wake equilibrium condition. As the lifting line is given sweep in the plane of rotation or dihedral in the plane containing the blade and the rotor axis, the induced velocities by the bound vortex at the lifting line are no longer zero and the blade flow is also affected by the modified vortex sheet geometry, according to the Biot-Savart formula. The study is performed with a two-bladed rotor with the NREL blade as point of reference.A series of tests is carried out with the design code, comparing the design of a rotor blade with straight axis or with a ±10% (forward or backward) sweep, dihedral or winglet. Results indicate that the aerodynamic performance are in general enhanced with these tip modifications, although the trends differ between forward and backward orientations, with some nonlinear effects associated with the wake geometry.     

Optimization of geometry described by curves

In CAD, the shape of a design is often described by an interpolating curve. In this paper, an automated method for finding the optimal geometry of such a curve is used to study the blade geometry of vertical axis wind turbines. To minimize bending moments due to centrifugal loads during rotation the blades are often curved in the shape of the troposkien (Greek for ‘turning rope’). From a fabrication point of view a simpler shape is preferred. An optimal number of interpolating points along the curve are used as design variables and their movements controlled by an optimization algorithm. During the optimization, the shape of the curve is successively recomputed and current objective and constraint functions are analysed. Stresses along the beam are computed using the finite element method by regarding the curve as a plane elastic beam.     

考虑风力发电批特征的电力机组调度问题

电力机组组合问题是在给定的计划周期内确定火电、风电和蓄 电池机组的开关机状态及发电量, 以满足系统的负荷需求、旋转备用等约束要求. 为了降低风电在电网中的供电不稳定 性, 引入蓄电池储能系统与风机进行协调调度. 由于大数量风机的介入, 明显增加了问 题处理的难度和复杂性. 本文从一个新的视角 将相近物理位置的风机进行组批, 基于批的视角对问题建立了批模型. 为 了提高批模型的性能, 提出了批模型参数的变换方法. 根据问题的NP-难特征和模 型的复杂结构, 开发了拉格朗日松弛(Lagrangian relaxation, LR)算法进 行求解. 为了加速算法的求解效率, 提出了子 问题近似求解的代理次梯度的拉格朗日松弛算法. 实验结果表明, 提出的批模型明 显优于传统的单机模型. 基于批模型开发的拉格朗日松弛算法与CPLEX优化软 件相比, 能够在较短的时间内获得高质量的解.     

Synthesis of nonlinear controller for wind turbines stability when providing grid support

This paper presents a new nonlinear polynomial controller for wind turbines that assures stability and maximizes the energy produced while imposing a bound in the generated power derivative in normal operation (guarantees a smooth operation against wind turbulence). The proposed controller structure also allows eventually producing a transient power increase to provide grid support, in response to a demand from a frequency controller. The controller design uses new optimization over polynomials techniques, leading to a tractable semidefinite programming problem. The ability of the wind turbine to increase its power under partial load operation has been analysed. The aforementioned optimization techniques have allowed quantifying the maximum transient overproduction that can be demanded to the wind turbine without violating minimum speed constraints (that could lead to unstable behaviour), as well as the total generated energy loss. The ability to evaluate this shortfall has permitted the development of an optimization procedure in which wind farm overproduction requirements are divided into individual turbines, assuring that the total energy loss in the wind farm is minimum, while complying with the maximum demanded power constraints. Copyright © 2013 John Wiley & Sons, Ltd.     

Weight optimization for flexural reinforced concrete beams with static nonlinear response

The weight optimization of reinforced concrete (RC) beams with material nonlinear response is formulated as a general nonlinear optimization problem. Incremental finite element procedures are used to integrate the structural response analysis and design sensitivity analysis in a consistent manner. In the finite element discretization, the concrete is modelled by plane stress elements and steel reinforcement is modelled by discrete truss elements. The cross-sectional areas of the steel and the thickness of the concrete are chosen as design variables, and design constraints can include the displacement, stress and sizing constraints. The objective function is the weight of the RC beams. The optimal design is performed by using the sequential linear programming algorithm for the changing process of design variables, and the gradient projection method for the calculations of the search direction. Three example problems are considered. The first two are demonstrated to show the stability and accuracy of the approaches by comparing previous results for truss and plane stress elements, separately. The last one is an example of an RC beam. Comparative cost objective functions are presented to prove the validity of the approach.     

A coupled Navier-Stokes/Vortex-Panel solver for the numerical analysis of wind turbines

The present paper introduces a coupled Navier-Stokes/Vortex-Panel solver for the computational study of incompressible high Reynolds number flow around horizontal axis wind turbines. The Navier-Stokes solver is confined to the near-field around one wind turbine blade; the Vortex-Panel method accounts for the far-field of a two-bladed rotor. A robust coupling between both methods is achieved through the spanwise distribution of bound circulation determined by Stokes’ theorem. The coupled solver reduces both artificial dissipation and computational cost compared to a full-domain Navier-Stokes analysis. Results obtained for inviscid and attached viscous flow around an optimal wind turbine blade are compared to a vortex model based on strip theory. Good agreement is found between both models that serves as a validation of the coupled solver for future applications to wind turbines.     

兆瓦级风力发电机功率特性的模拟测试及分析

风力发电机的功率及其效率特性对风力机气动特性有很大影响。针对我国兆瓦级风力机风轮叶片研究中存在的问题,制作了1．5MW风轮叶片模型并根据相关国标进行了实验室及车载测试,根据测试数据风力发电机组的效率特性曲线及功率特性曲线,最后通过数据分析,提出了叶片模型的改进方案。     

Control co-design of 13 MW downwind two-bladed rotors to achieve 25% reduction in levelized cost of wind energy

Wind energy is recognized worldwide as cost-effective and environmentally friendly and is among the fastest-growing sources of electrical energy. To further decrease the cost of wind energy, wind turbines are being designed at ever larger scales, which is challenging due to greater structural loads and deflections. Large-scale systems such as modern wind turbines increasingly require a control co-design approach, whereby the system design and control design are performed in a more integrated fashion. We overview a two-bladed downwind morphing rotor concept that is expected to lower the cost of energy at wind turbine sizes beyond 13 megawatts (MW) compared with continued upscaling of traditional three-bladed upwind rotor designs. We describe an aero-structural-control co-design process that we have used in designing such extreme-scale wind turbines, and we discuss how we were able to achieve a 25% reduction in levelized cost of energy for our final turbine design compared to a conventional upwind three-bladed rotor design.     

Optimum design of space structures with active and passive damping

This paper investigates the effects of passive damping on the optimum structural design with active controllers. An integrated design of structure and active control system is performed. The minimum weight design is obtained by imposing constraints on the closed-loop damping and the imaginary part of the closed-loop eigenvalues of the active control system. The mathematical optimization problem is solved by using the NEWSUMT-A program, which is based on quadratic extended interior penalty function method. The ACOSS-FOUR model is selected for the numerical studies. The active control effort, performance index, and optimum weights are presented as a function of the passive damping.     

Wind Farm Layout Design Using Cuckoo Search Algorithms

Wind energy has emerged as a strong alternative to fossil fuels for power generation. To generate this energy, wind turbines are placed in a wind farm. The extraction of maximum energy from these wind farms requires optimal placement of wind turbines. Due to complex nature of micrositing of wind turbines, the wind farm layout design problem is considered a complex optimization problem. In the recent past, various techniques and algorithms have been developed for optimization of energy output from wind farms. The present study proposes an optimization approach based on the cuckoo search (CS) algorithm, which is relatively a recent technique. A variant of CS is also proposed that incorporates a heuristic-based seed solution for a better performance. The proposed CS algorithms are compared with genetic and particle swarm optimization (PSO) algorithms, which have been extensively applied to wind farm layout design. Empirical results indicate that the proposed CS algorithms outperformed the genetic and PSO algorithms for the given test scenarios in terms of yearly power output and efficiency.