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Volume 25, Number 4, April 2020

In this paper, the design method and experimental validation for the two-degree-of-freedom (2DOF) electromagnetic energy harvester are presented. The harvester consists of the rigid body suspended by four tension springs and electromagnetic transducers. Once the two resonant frequencies and the mass properties are specified, both the constant and the positions for the springs can be determined in the closed form. The designed harvester can locate two resonant peaks close to each other and forms the extended frequency bandwidth for power harvesting. Halbach magnet array is also introduced to enhance the output power. In the experiment, two resonant frequencies are measured at 34.9 and 37.6 Hz and the frequency bandwidth improves to 5 Hz at the voltage level of 207.9 mV. The normalized peak power of 4.587 mW/G2 is obtained at the optimal load resistor of 367 Ω.

Key Words
vibration; energy harvester; resonant frequency; bandwidth; electromagnetic transducer; Halbach array

(1) Shi-Baek Park:
Department of Mechanical Engineering, Yonsei University, Seoul, 03722, Republic of Korea;
(2) Seon-Jun Jang:
School of Mechanical Engineering, Hoseo University, Asan 31499, Republic of Korea.

This paper deals with the problem of global stabilization for a class of nonlinear control systems. An effective approach is proposed for controlling the system interaction of structures through a combination of parallel distributed compensation (PDC) intelligent controllers and fuzzy observers. An efficient approximate inference algorithm using expectation propagation and a Bayesian additive model is developed which allows us to predict the total number of control systems, thereby contributing to a more adaptive trajectory for the closed-loop system and that of its corresponding model. The closed-loop fuzzy system can be made as close as desired, so that the behavior of the closed-loop system can be rigorously predicted by establishing that of the closed-loop fuzzy system.

Key Words
intelligent control function; Bayesian additive model; automated design

(1) Tim Chen:
AI LAB, Faculty of Information Technology, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
(2) Megan Lohnash:
Data Analysis Research Centre, San Jose State University, OneWashington Square; San José, CA 95192-0029, USA;
(3) Emmanuel Owens:
Innovative InformationCentre, Liverpool JohnMoores University, 98Mount Pleasant, Liverpool L3 5UZ, UK;
(4) C.Y.J. Chen:
Faculty of Engineering, King Abdulaziz University, Abdullah Sulayman, Jeddah 21589, Saudi Arabia.

This article deals with the flexural analysis of anti-symmetric cross-ply laminated plates under nonlinear thermal loading using a refined plate theory with four variables. In this theory, the undetermined integral terms are used and the number of variables is reduced to four, instead of five or more in other higher-order theories. The boundary conditions on the top and the bottom surfaces of the plate are satisfied; hence the use of the transverse shear correction factors is avoided. The principle of virtual work is used to obtain governing equations and boundary conditions. Navier solution for simply supported plates is used to derive analytical solutions. For the validation of the present theory, numerical results for displacements and stresses are compared with those of classical, first-order, higher-order and trigonometric shear theories reported in the literature.

Key Words
refined plate theory; flexural analysis; nonlinear thermal loading; cross-ply laminated plates

(1) Nasrine Belbachir, Mohamed Bourada, Kada Draiche, Abdelouahed Tounsi, Fouad Bourada:
Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria;
(2) Kada Draiche:
Département de Génie Civil, Université Ibn Khaldoun Tiaret, BP 78 Zaaroura, 1400 Tiaret, Algérie;
(3) Abdelouahed Tounsi:
Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia;
(4) Fouad Bourada:
Département des Sciences et de la Technologie, Centre Universitaire de Tissemsilt, BP 38004 Ben Hamouda, Algérie;
(5) Abdelmoumen Anis Bousahla:
Laboratoire de Modélisation et Simulation Multi-échelle, Université de Sidi Bel Abbés, Algeria;
(6) Abdelmoumen Anis Bousahla:
Centre Universitaire de Relizane, Algérie;
(7) S.R. Mahmoud:
GRC Department, Jeddah Community College, King Abdulaziz University, Jeddah, Saudi Arabia.

In this paper, a novel but practical approach named series/parallel multi-sensing technique was proposed to evaluate the bolt looseness in a bolt group. The smart washers (SWs), which were fabricated by embedding a Lead Zirconate Titanate (PZT) transducer into two flat metal rings, were installed to the bolts group. By series connection of SWs, the impedance signals of different bolts can be obtained through only one sweep. Therefore, once the loosening occurred, the shift of different peak frequencies can be used to locate which bolt has loosened. The proposed multi input single output (MISO) damage detection scheme is very suitable for the structural health monitoring (SHM) of joint with a large number of bolts connection. Another notable contribution of this paper is the proposal of 3-dB bandwidth root mean square deviation (3 dB-RMSD) which can quantitatively evaluate the severity of bolt looseness. Compared with the traditional naked-eye observation method, the equivalent circuit based 3-dB bandwidth can accurately define the calculation range of RMSD. An experiment with three bolted connection specimens that installed the SWs was carried out to validate our proposed approach. Experimental result shows that the proposed 3 dB-RMSD based multi-sensing technique can not only identify the loosened bolt but also monitor the severity of bolt looseness.

Key Words
bolt looseness detection; PZT; impedance; series/parallel multi-sensing technique; equivalent circuit; 3 dB-RMSD

(1) Dongdong Chen, Linsheng Huo:
State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, Liaoning, 116023, People's Republic of China;
(2) Gangbing Song:
Smart Materials and Structures Laboratory, Department of Mechanical Engineering, University of Houston, Houston, TX, 77004, United States of America.

In this paper the effect of confining pressure and tunnel depth on the ground vertical settlement has been investigated using particle flow code (PFC2D). For this perpuse firstly calibration of PFC2D was performed using both of tensile test and triaxial test. Then a model with dimention of 100 m × 100 m was built. Acircular tunnel with diameter of 20 m was drillled in the middle of the model. Also, a rectangular tunnel with wide of 10 m and length of 20 m was drilled in the model. The center of tunnel was situated 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m and 60 m below the ground surface. these models are under confining pressure of 0.001 GPa, 0.005 GPa, 0.01 GPa, 0.03 GPa, 0.05 GPa and 0.07 GPa. The results show that the volume of colapce zone is constant by increasing the distance between ground surface and tunnel position. Also, the volume of colapce zone was increased by decreasing of confining pressure. The maximum of settlement occurs at the top of the tunnel roof. The maximum of settlement occurs when center of tunnel was situated 15 m below the ground surface. The settlement decreases by increasing the distance between tunnel center line and measuring circles in the ground surface. The minimum of settlement occurs when center of circular tunnel was situated 60 m below the surface ground. Its to be note that the settlement increase by decreasing the confining pressure.

Key Words
direct tensile strength; PFC2D; confining pressure; settlement; tunnel

(1) Hadi Haeri:
State Key Laboratory for Deep GeoMechanics and Underground Engineering, Beijing, 100083, China;
(2) Vahab Sarfarazi:
Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran;
(3) Mohammad Fatehi Marji:
Mine Exploitation Engineering Department, Faculty of Mining and Metallurgy, Institution of Engineering, Yazd University, Yazd, Iran.

In this study, a simple two-dimensional shear deformation model is employed for buckling analysis of functionally graded (FG) plates. The proposed theory has a kinematic with integral terms which considers the influence of shear deformation without using "shear correction factors". The impact of varying material properties and volume fraction of the constituent on buckling response of the FG plate is examined and discussed. The benefit of this theory over other contributions is that a number of variables is reduced. The basic equations that consider the influence of transverse shear stresses are derived from the principle of virtual displacements. The analytical solutions are obtained utilizing the "Navier method". The accuracy of the proposed theory is proved by comparisons with the different solutions found in the literature.

Key Words
functionally graded plate; shear deformation theory; buckling

(1) Karima Bakhti, Mohamed Sekkal, Abdelouahed Tounsi:
Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria;
(2) Karima Bakhti:
Département de génie civil, Ecole Nationale Polytechnique d'Oran, Algérie;
(3) E.A. Adda Bedia, Abdelouahed Tounsi:
Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia.

The presence of cracks in mechanical components is a very important problem that, if it is not detected on time, can lead to high economic costs and serious personal injuries. This work presents a methodology focused on identifying cracks in unbalanced rotors, which are some of the most frequent mechanical elements in industry. The proposed method is based on Artificial Neural Networks that give a solution to the presented inverse problem. They allow to estimate unknown crack parameters, specifically, the crack depth and the eccentricity angle, depending on the dynamic behavior of the rotor. The necessary data to train the developed Artificial Neural Network have been obtained from the frequency spectrum of the displacements of the well- known cracked Jeffcott rotor model, which takes into account the crack breathing mechanism during a shaft rotation. The proposed method is applicable to any rotating machine and it could contribute to establish adequate maintenance plans.

Key Words
rotor diagnosis; neural networks; crack identification; breathing mechanism; frequency spectrum

Department of Mechanical Engineering, University Carlos III of Madrid, Av. de la Universidad, 30, 28911, Leganes, Madrid, Spain.

Stability analysis of three-layered piezoelectric doubly curved nano shell with accounting size dependency is performed in this paper based on first order shear deformation theory and curvilinear coordinate system relations. The elastic core is integrated with sensor and actuator layers subjected to applied electric potentials. The principle of virtual work is employed for derivation of governing equations of stability. The critical electrical and mechanical buckling loads are evaluated in terms of important parameters of the problem such as size-dependent parameter, two principle angle of doubly curved shell and two parameters of Pasternak's foundation. One can conclude that mechanical buckling loads are decreased with increase of nonlocal parameter while the electrical buckling loads are increased.

Key Words
stability analysis; electrical and mechanical buckling loads; three-layered nano shells; doubly curved piezoelectric; size dependent parameter; first-order shear deformation theory; applied electric potential

Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, I.R. Iran.

This paper proposes a novel approach to model updating for a large-scale cable-stayed bridge based on ambient vibration tests coupled with a hybrid metaheuristic search algorithm. Vibration measurements are carried out under excitation sources of passing vehicles and wind. Based on the measured structural dynamic characteristics, a finite element (FE) model is updated. For long-span bridges, ambient vibration test (AVT) is the most effective vibration testing technique because ambient excitation is freely available, whereas a forced vibration test (FVT) requires considerable efforts to install actuators such as shakers to produce measurable responses. Particle swarm optimization (PSO) is a famous metaheuristic algorithm applied successfully in numerous fields over the last decades. However, PSO has big drawbacks that may decrease its efficiency in tackling the optimization problems. A possible drawback of PSO is premature convergence leading to low convergence level, particularly in complicated multi-peak search issues. On the other hand, PSO not only depends crucially on the quality of initial populations, but also it is impossible to improve the quality of new generations. If the positions of initial particles are far from the global best, it may be difficult to seek the best solution. To overcome the drawbacks of PSO, we propose a hybrid algorithm combining GA with an improved PSO (HGAIPSO). Two striking characteristics of HGAIPSO are briefly described as follows: (1) because of possessing crossover and mutation operators, GA is applied to generate the initial elite populations and (2) those populations are then employed to seek the best solution based on the global search capacity of IPSO that can tackle the problem of premature convergence of PSO. The results show that HGAIPSO not only identifies uncertain parameters of the considered bridge accurately, but also outperforms than PSO, improved PSO (IPSO), and a combination of GA and PSO (HGAPSO) in terms of convergence level and accuracy.

Key Words
model updating; evolutionary algorithm; cable-stayed bridge; improved particle swarm optimization; ambient vibration measurements; genetic algorithm; hybrid algorithm

(1) Tran N. Hoa, S. Khatir:
Soete Laboratoy, Department of Electrical Energy, Metals, Mechanical Constructions, and Systems, Faculty of Engineering and Architecture, Ghent University, 9000 Gent, Belgium;
(2) Tran N. Hoa, Nguyen N. Long, Bui T. Thanh:
Department of Bridge and Tunnel Engineering, Faculty of Civil Engineering, University of Transport and Communications, Hanoi, Vietnam;
(3) G. De Roeck:
Department of Civil Engineering, KU Leuven, B-3001 Leuven, Belgium;
(4) M. Abdel Wahab:
Division of Computational Mechanics, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
(5) M. Abdel Wahab:
Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam.

This article presents a comprehensive model to investigate a free vibration and resonance frequencies of nanostructure perforated beam element as nano-resonator. Nano-scale size dependency of regular square perforated beam is considered by using nonlocal differential form of Eringen constitutive equation. Equivalent mass, inertia, bending and shear rigidities of perforated beam structure are developed. Kinematic displacement assumptions of both Timoshenko and Euler-Bernoulli are assumed to consider thick and thin beams, respectively. So, this model considers the effect of shear on natural frequencies of perforated nanobeams. Equations of motion for local and nonlocal elastic beam are derived. After that, analytical solutions of frequency equations are deduced as function of nonlocal and perforation parameters. The proposed model is validated and verified with previous works. Parametric studies are performed to illustrate the influence of a long-range atomic interaction, hole perforation size, number of rows of holes and boundary conditions on fundamental frequencies of perforated nanobeams. The proposed model is supportive in designing and production of nanobeam resonator used in nanoelectromechanical systems NEMS.

Key Words
resonance frequencies; free vibration; perforated nonlocal nanobeam; analytical solution; frequency equations

(1) Mohamed A. Eltaher:
Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia;
(2) Mohamed A. Eltaher:
Mechanical Design and Production Department, Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Egypt;
(3) Norhan A. Mohamed:
Engineering Mathematics and Physics Department, Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Egypt.

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