© Faculty of Mechanical Engineering, Belgrade. All rights reserved FME Transactions (2019) 47, 887-893 887 Received: March 2019, Accepted: May 2019 Correspondence to: Dr Jelena Svorcan Faculty of Mechanical Engineering, Kraljice Marije 16, 11120 Belgrade 35, Serbia E-mail: jsvorcan@mas.bg.ac.rs doi:10.5937/fmet1904887S Jelena Svorcan Assistant Professor University of Belgrade Faculty of Mechanical Engineering Zorana Trivković Research Associate University of Belgrade Faculty of Mechanical Engineering Toni Ivanov Assistant Professor University of Belgrade Faculty of Mechanical Engineering Marija Baltić Research Associate University of Belgrade Faculty of Mechanical Engineering Ognjen Peković Assistant Professor University of Belgrade Faculty of Mechanical Engineering Multi-objective Constrained Optimizations of VAWT Composite Blades Based on FEM and PSO Vertical-axis wind turbines (VAWTs) are attractive tools for wind energy extraction particularly suitable for small consumers or off-grid areas. Although their geometry is simple (here, rectangular blade of constant airfoil is assumed), aerodynamic analysis may be quite complex. Computational fluid dynamics (CFD) approach is employed for the estimation of rotor aerodynamic performances. This paper provides a review of possible multi- objective optimization strategies for the design of small-scale VAWT laminate blades in terms of its main structural parameters: ply-order and ply-number. Numerous structural analyses of the composite turbine blades were performed by finite element method (FEM). Multi-criteria constrained optimizations, by an evolutionary method − particle swarm optimization (PSO), were performed with respect to blade total mass, maximum blade tip deflection under static loading, computed natural frequencies and failure index along the blade. By combining different input and output parameters (cost functions and constraints) a large variety of feasible solutions can be achieved. Keywords: VAWT, Blade, CFD, Laminate, FEM, Multi-objective PSO. 1. INTRODUCTION In accordance with the current industrial and economic trends and the appeal of renewable energy sources, wind turbine blades present one of the contemporary topics of scientific and engineering research [1, 2]. The work pre- sented in [3] gives a good overview of the complete wind turbine rotor blades development process and accentuates the importance of a synchronous coordination between several (equally important) research areas: design (aero- dynamic and structural), regulations and standards, applied materials, manufacturing technologies and verifi- cation testing. It also promotes the use of various contemporary engineering techniques such as: design improvement, optimization, use of novel materials, etc. Throughout the past century several different wind turbine concepts have been tried, usually categorized according to the direction of their rotational axis. Some- what less known, but also interesting and promising type is a vertical-axis wind turbine (VAWT) of a geometri- cally much simpler shape than a conventional horizontal- axis wind turbine (HAWT). The distinctive characteri- stics of VAWTs include: simple design, low production cost, operability in “dirty” winds (of changeable intensity and direction), as well as somewhat lower efficiency than HAWTs. Interesting work on the possible improvement of their aerodynamic performances can be found in [4, 5]. The subject of this investigation, a Darrieus straight- bladed VAWT, contains blades of constant chord and airfoil along their lengths. The research motive is the improvement of its structural design which could ulti- mately lead to the reduced blade mass and cost, pro- longed working life, reduced loading to the tower, etc. (numerous advantages) while preserving structural reli- ability and integrity. Given that contemporary wind tur- bine blades are mostly composite [1-13], particularly in small-scale constructions, the paper investigates the possibilities of applying a multi-objective optimization approach to the blade structural design. Optimization of the blade composite lay-up and ply orientations can be done numerically, by coupling a finite element (FE) solver with a multi-objective optimi- ation method. Given the complexity and nonlinearity of both cost-functions and imposed constraints, usually, one of the evolutionary, heuristic methods is applied [8- 12]. This methodology can be implemented to HAWTs and VAWTs, as well as other mechanical parts/systems. Albanesi et al. [7] performed optimizations of HAWT blade by genetic algorithm (GA), Wang et al. [9] dealt with large VAWT blade also by GA, while Chen et al. [10] used a particle swarm optimization (PSO) method. This research paper communicates several different multi-objective PSO strategies with integer design vari- ables. It is arranged in the following fashion: the follo- wing section describes the initial blade geometry after which the estimation of its aerodynamic performances by computational fluid dynamics (CFD) approach is given. Section “Structural model” clearly explains the assumed blade laminate structure, with its parameterization and optimization algorithm described in detail in the following section. Finally, the gained experiences and results, discussion and conclusions are listed in the end. 2. GEOMETRIC MODEL The starting, reference blade model designed for a straight small-scale Darrieus VAWT of nominal power P nom = 500 W is presented in Fig. 1. Its main charac- teristics and dimensions are: the number of blades N b =