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CONTENTS
Volume 32, Number 1, January 2021
 

Abstract
Vortex generators are commonly used in mechanical engineering and the aerospace industry to suppress flow separation owing to their advantages of simple structure, economic viability, and high level of efficiency. Owing to the flow separation of the incoming wind on the leading edge, a suction area is formed on the roof surface, which results in a lifting effect on the roof. In this research, vortex generators were installed on the windward surface of a flat roof and used to disturb to roof flow field and reduced suction based on flow control theory. Computational fluid dynamics (CFD) simulations were performed in this study to investigate the effects of vortex generators on reduce suction. It was determined that when the vortex generator was installed on the top of the roof on the windward surface, it had a significant control effect on reduce suction on the roof leading edge. In addition, the influence of parameters such as size, placement interval, and placement position of the vortex generator on the control effect of the roof's suction is also discussed.

Key Words
CFD (computational fluid dynamics); pressure distribution; roof structure; flow control; vortex generator

Address
Yagebai Zhao, Xiaolong Deng, Hongfu Zhang, Dabo Xin :School of Civil Engineering, Northeast Forestry University, Harbin 150040, China/Lab of Disaster prevention and reduction, Northeast Forestry University, Harbin 150040, China
Zhiwen Liu:Hunan Provincial Key Laboratory of Wind Engineering and Bridge Engineering, Hunan University, Changsha Hunan, 410082, China

Abstract
In recent years, there has been a tendency towards renewable energy sources considering the damages caused by non-renewable energy resources to nature and humans. One of the renewable energy sources is wind and energy is obtained with the help of wind turbines. To determine the behavior of wind turbines under earthquake loads, dynamic characteristics are required. In this study, the differential transformation method is proposed to determine the free vibration analysis of wind turbines with a variable cross-section. The wind turbine is modeled as an equivalent variable continuous flexural beam and blade weight is considered as a point mass at the top of the structures. The differential equation representing the free vibration of the wind turbine is transformed into an algebraic equation with the help of differential transformation method and the angular frequencies and the mode shapes of the wind turbine are obtained by the help of the differential transformation method. In the study, a sample taken from the literature was solved with the presented method and the suitability of the method was investigated. The same wind turbine example also modeled by finite element modelling software, ABAQUS. Results of the finite element model and differential transformation method are compared with each other and the results are in good agreement.

Key Words
differential transformation method; wind turbine; finite element modelling; free vibration; flexural beam

Address
Kanat Burak Bozdogan:Canakkale Onsekiz Mart University, Engineering Faculty, Civil Engineering Department, Canakkale, Turkey
Farshid Khosravi Maleki:Bartin University, Faculty of Engineering, Architecture and Design, Mechanical Engineering Department, Bartin, Turkey

Abstract
This study presents buckling analysis of a simply supported sandwich plate with functionally graded porous layers. In the kinematic relation of the plate, a hyperbolic shear displacement model is used. The governing equations of the problem are derived by using the principle of virtual work. In the solution of the governing equations, the Navier procedure is implemented. In the porosity effect, four different porosity types are used for functionally graded sandwich layers. In the numerical examples, the effects of the porosity parameters, porosity types and geometry parameters on the critical buckling of the functionally graded sandwich plates are investigated.

Key Words
buckling; sandwich plates; functionally graded materials; porosity; higher-order plate theory

Address
Lazreg Hadji:Laboratory of Geomatics and Sustainable Development, University of Tiaret, Algeria/ Department of Mechanical Engineering, University of Tiaret, BP 78 Zaaroura, Tiaret,14000, Algeria

Abstract
The current research deals with, stability/instability and cylindrical composite nano-scaled shell's resonance frequency filled by graphene nanoplatelets (GPLs) under various thermal conditions (linear and nonlinear thermal loadings). The piece-wise GPL-reinforced composites' material properties change through the orientation of cylindrical nano-sized shell's thickness as the temperature changes. Moreover, in order to model all layers' efficient material properties, nanomechanical model of Halpin-Tsai has been applied. A functionally modified couple stress model (FMCS) has been employed to simulate GPLRC nano-sized shell's size dependency. It is firstly investigated that reaching the relative frequency's percentage to 30% would lead to thermal buckling. The current study's originality is in considering the multifarious influences of GPLRC and thermal loading along with FMCS on GPLRC nano-scaled shell's resonance frequencies, relative frequency, dynamic deflection, and thermal buckling. Furthermore, Hamilton's principle is applied to achieve boundary conditions (BCs) and governing motion equations, while the mentioned equations are solved using an analytical approach. The outcomes reveal that a range of distributions in temperature and other mechanical and configurational characteristics have an essential contribution in GPLRC cylindrical nano-scaled shell's relative frequency change, resonance frequency, stability/instability, and dynamic deflection. The current study's outcomes are practical assumptions for materials science designing, nano-mechanical, and micro-mechanical systems such as micro-sized sensors and actuators.

Key Words
various thermal distributions; graphene nanoplatelet; resonance frequency; stability/instability; modified couple stress model

Address
Zhigang Yao:Department of Electronic and Optic Engineering, Army Engineering University, Shijiazhuang 050003, China/ School of Automation and Electrical Engineering, University of Science and Technology, Beijing 100083, China
Hui Xie :Department of Electronic and Optic Engineering, Army Engineering University, Shijiazhuang 050003, China
Yulei Wang:Institute of Electronics and Information Engineering, Tongji University, Shanghai 200082, Shanghai, China

Abstract
This paper proposes a novel diffuser design for Diffuser Augmented Wind Turbines (DAWT) based on the blunt trailing edge airfoil AF300. Computational Fluid Dynamics (CFD) simulations are carried out to measure the performance of the AF300 diffuser against diffusers made with the shape of other high performance low wind speed airfoils. The results show that the proposed diffuser produces a greater air mass flow increase through the plane of the turbine than the other diffusers and it can be used to increase the performance of a horizontal axis wind turbine.

Key Words
DAWT; high performance airfoil diffuser; small wind turbines; CFD simulation

Address
Arturo Alanis:CIDESI-Centro de Ingeniería y Desarrollo Industrial, Av. Pie de la Cuesta No. 702, Desarrollo San Pablo, 76125, Qro, Mexico
Jesus Alejandro Franco:CIDESI-Centro de Ingenieria y Desarrollo Industrial, Av. Pie de la Cuesta No. 702, Desarrollo San Pablo, 76125, Qro, Mexico/Escuela Nacional de Estudios Superiores Juriquilla, UNAM, Queretaro 76230, Mexico
Saul Piedra :CONACYT-CIDESI- Centro Nacional de Tecnologias Aeronauticas Carretera Estatal 200 Querétaro-Tequisquiapan Km. 23, No. 22547, Colon, Qro. Mexico
Juan Carlos Jauregui:Universidad Autonoma de Queretaro, Cerro de las Campanas S/N, Queretaro, Qro. Mexico

Abstract
Ultrapure ferritic stainless steel provides a new generation of long-span metal roof systems with continuous welding technology, which exhibits many unknown behaviors during wind excitation. This study focuses on the wind-resistant capacity of a new continuous welding stainless steel roof (CWSSR) system. Full-scale testing on the welding joints and the CWSSR system is performed under uniaxial tension and static ultimate wind uplift loadings, respectively. A finite element model is developed with mesh refinement optimization and is further validated with the testing results, which provides a reliable way of investigating the parameter effect on the wind-induced structural responses, namely, the width and thickness of the roof sheeting and welding height. Research results show that the CWSSR system has predominant wind-resistant performance and can bear an ultimate wind uplift loading of 10.4 kPa without observable failures. The welding joints achieve equivalent mechanical behaviors as those of base material is produced with the current of 65 A. Independent structural responses can be found for the roof sheeting of the CWSSR system, and the maximum displacement appears at the middle of the roof sheeting, while the maximum stress appears at the connection supports between the roof sheeting with a significant stress concentration effect. The responses of the CWSSR system are greatly influenced by the width and thickness of the roof sheeting but are less influenced by the welding height.

Key Words
metal roof system; continuous welding; wind resistance performance; full-scale testing; numerical simulation

Address
Dayang Wang,Mingming Wang and Yongshan Zhang:School of Civil Engineering, Guangzhou University, 510006, P.R. China
Zhendong Zhao:State Key Laboratory of Nuclear Power Safety Monitoring Technology and Equipment, China Nuclear Power Engineering Co. Ltd., Shenzhen 518172, China
Tong Ou:Architectural Design and Research Institute of Guangdong Province, 510000, P.R. China
Zhiyong Xin:Zhuhai Envete Engineering Testing Co., LTD, 519000, P.R. China

Abstract
In steel cable bridges, the use of magnetorheological (MR) dampers between butt cables is constantly increasing to dampen vibrations caused by rain and wind. The biggest problem in the actual applications of those devices is to launch a kind of appropriate algorithm that can effectively and efficiently suppress the perturbation of the tie through basic calculations and optimal solutions. This article discusses the optimal evolutionary design based on a linear and quadratic regulator (hereafter LQR) to lessen the perturbation of the bridges with cables. The control numerical algorithms are expected to effectively and efficiently decrease the possible risks of the structural response in amplification owing to the feedback force in the direction of the MR attenuator. In addition, these numerical algorithms approximate those optimal linear quadratic regulator control forces through the corresponding damping and stiffness, which significantly lessens the work of calculating the significant and optimal control forces. Therefore, it has been shown that it plays an important and significant role in the practical application design of semiactive MR control power systems. In the present proposed novel evolutionary parallel distributed compensator scheme, the vibrational control problem with a simulated demonstration is used to evaluate the numerical algorithmic performance and effectiveness. The results show that these semiactive MR control numerical algorithms which are present proposed in the present paper has better performance than the optimal and the passive control, which is almost reaching the levels of linear quadratic regulator controls with minimal feedback requirements.

Key Words
semiactive intelligent control; magnetorheological; optimal equivalent controller design; vibrational control and numerical algorithmic design

Address
Tim Chen:Faculty of Information Technology, Ton Duc Thang University, Ho Chi Minh City, Vietnam
Yu-Ching Huang:Department of Earth Science, National Taiwan Normal University, Taipei, China/Center of Natural Science, Kaohsiung Municipal Fushan Junior High School, Kaohsiung, China
Zhao-Wang Xu :Department of Earth Science, National Taiwan Normal University, Taipei, China
J.C.Y. Chen:Faculty of Information Technology, University of California, Irvine, U.S.A.

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