Thang Le-Duc

In this paper, we explore the advantages of heuristic mechanisms and devise a new optimization framework named Sequential Motion Optimization (SMO) to strengthen gradientbased methods. The key idea of SMO is inspired from a movement mechanism in a recent metaheuristic method called Balancing Composite Motion Optimization (BCMO). Specifically, SMO establishes a sequential motion chain of two gradientguided individuals including a leader and a follower to enhance the effectiveness of parameter updates in each iteration. A surrogate gradient model with low computation cost is theoretically established to estimate the gradient of the follower by that of the leader through chain rule during training process. Experimental results in terms of training quality on both fully-connected multilayer perceptrons (MLPs) and convolutional neural networks (CNNs) with respect to three popular benchmark datasets including MNIST, Fashion-MNIST and CIFAR-10 demonstrate the superior performance of the proposed framework in comparison with the vanilla stochastic gradient descent (SGD) implemented via back-propagation (BP) algorithm. Although this study only introduces the vanilla gradient descent (GD) as a main gradientguided factor in SMO for deep neural networks (DNNs) training application, it is greatly potential to combine with other gradientbased variants to improve its effectiveness and solve other largescale optimization problems in practice.

In this work, a new approach for aerodynamic optimization of horizontal axis wind turbine (HAWT) airfoil is presented. This technique combines commercial computational fluid dynamics (CFD) codes with differential evolution (DE), a reliable gradient-free global optimization method. During the optimization process, commercial CFD codes are used to evaluate aerodynamic characteristics of HAWT airfoil and an improved DE algorithm is utilized to find the optimal airfoil design. The objective of this research is to maximize the aerodynamic coefficients of HAWT airfoil at the design angle of attack (AOA) with specific ambient environment. The airfoil shape is modeled by control points which their coordinates are design variables. The reliability of CFD codes is validated by comparing the analytical results of a typical HAWT airfoil with its experimental data. Finally, the optimal design of wind turbine airfoil is evaluated about aerodynamic performance in comparison with existing airfoils and some discussions are performed.