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CONTENTS
Volume 7, Number 1, January 2022
 


Abstract
In this study, a new strategy is presented to transmit the fundamental elastic beam problem into the modern optimization platform and solve it by using artificial intelligence (AI) tools. As a practical example, deflection of Euler-Bernoulli beam is mathematically formulated by 2nd-order ordinary differential equations (ODEs) in accordance to the classical beam theory. This fundamental engineer problem is then transmitted from classic formulation to its artificial-intelligence presentation where the behavior of the beam is simulated by using neural networks (NNs). The supervised training strategy is employed in the developed NNs implemented in the heuristic optimization algorithms as the fitness function. Different evolutionary optimization tools such as genetic algorithm (GA) and particle swarm optimization (PSO) are used to solve this non-linear optimization problem. The step-by-step procedure of the proposed method is presented in the form of a practical flowchart. The results indicate that the proposed method of using AI tools in solving beam ODEs can efficiently lead to accurate solutions with low computational costs, and should prove useful to solve more complex practical applications.

Key Words
artificial neural networks; elastic beam deflection; euler-bernoulli beam; genetic algorithm; ordinary differential equation; particle swarm optimization

Address
Mehdi Babaei: Department of Civil Engineering, University of Bonab, Bonab, Iran

Arman Atasoy: Department of Civil Engineering, Istanbul Rumeli University, Istanbul, Turkey

Iman Hajirasouliha: Department of Civil & Structural Engineering, The University of Sheffield, Sheffield, U.K.

Somayeh Mollaei: Department of Civil Engineering, University of Bonab, Bonab, Iran

Maysam Jalilkhani: Department of Civil Engineering, Urmia University of Technology, Urmia, Iran

Abstract
In this paper, the optimum location of the belt truss-outrigger for a combined system of framed tube, shear core and outrigger-belt truss is calculated. The optimum location is determined by maximization of the first natural frequency. The framed tube is modeled using a non-prismatic cantilever beam with hollow box cross section. The governing differential equation is solved using the weak form integral equations and the natural frequencies of the structure are calculated. The graphs are introduced for quick calculation of the first natural frequency. The location of the belt truss-outrigger that maximizes the first natural frequency of the structure is introduced as an optimum location. The structure is modeled using SAP-2000 finite elements software. In the modelling, the location of the belt truss-outrigger is changed along the height of the structure. With various locations of the outrigger, the lateral deflection of the all stories and axial force in the columns of the outer tube are calculated. The analysis is repeated by locating the outrigger-belt truss at the optimum location. The analysis results are compared and effect of the optimum location on the lateral deflection and the shear lag phenomena are investigated.

Key Words
framed tube; lateral deflection; natural frequency; optimum location; outrigger-belt truss; shear lag

Address
Mehrdad Mohammadnejad: Department of Civil Engineering, Birjand University of Technology, Birjand, Iran

Hasan Haji Kazemi: Department of Civil Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

Abstract
Phase-type distributions are the distributions of the time to absorption in finite and absorbing Markov chains. They generalize, while at the same time, retain the tractability of the exponential distributions and their family. They are widely used as stochastic models from queuing theory, reliability, dependability, and forecasting, to computer networks, security, and computational design. The ability to fit phase-type distributions to intractable or empirical distributions is, therefore, highly desirable for many practical purposes. Many methods and tools currently exist for this fitting problem. In this paper, we present the results of our investigation on using orthogonal-distance fitting as a method for fitting phase-type distributions, together with a comparison to the currently existing fitting methods and tools.

Key Words
acyclic; fitting; orthogonal distance; phase-type distributions; traces

Address
Reza Pulungan: Department of Computer Science and Electronics, Faculty of Mathematics and Natural Sciences, Universitas Gadjah Mada, Yogyakarta, Indonesia

Holger Hermanns: Dependable Systems and Software, Saarland University, Saarbrücken, Germany

Abstract
A simulation study of the distribution of magnetic flux induced by a U-shaped electromagnet into a two- layer massive object with variations in the depth and properties of the surface layer has been carried out. It has been established that the hardened surface layer "pushes" the magnetic flux into the bulk of the magnetized object and the magnetic flux penetration depth monotonically increases with increasing thickness of the hardened layer. A change in the thickness and magnetic properties of the surface layer leads to a redistribution of magnetic fluxes passing between the poles of the electromagnet along with the layer and the bulk of the steel object. In this case, the change in the layer thickness significantly affects the magnitude of the tangential component of the field on the surface of the object in the interpolar space, and the change in the properties of the layer affects the magnitude of the magnetic flux in the magnetic "transducer-object" circuit. This difference in magnetic parameters can be used for selective testing of the surface hardening quality. It has been shown that the hardened layer pushes the magnetic flux into the depth of the magnetized object. The nominal depth of penetration of the flow monotonically increases with an increase in the thickness of the hardened layer.

Key Words
bulk; hardware-software system of magnetic testing; layer; magnetic flux; simulation; surface hardening

Address
A.V. Byzov: Department of nondestructive testing, M.N. Miheev Institute of Metal Physics of Ural Branch of Russian Academy of Sciences, 18 Sof'i Kovalevskoy St, Ekaterinburg, 620108, Russia

D.G. Ksenofontov: Department of nondestructive testing, M.N. Miheev Institute of Metal Physics of Ural Branch of Russian Academy of Sciences, 18 Sof'i Kovalevskoy St, Ekaterinburg, 620108, Russia

V.N. Kostin: Department of nondestructive testing, M.N. Miheev Institute of Metal Physics of Ural Branch of Russian Academy of Sciences, 18 Sof'i Kovalevskoy St, Ekaterinburg, 620108, Russia

O.N. Vasilenko: Department of nondestructive testing, M.N. Miheev Institute of Metal Physics of Ural Branch of Russian Academy of Sciences, 18 Sof'i Kovalevskoy St, Ekaterinburg, 620108, Russia

Abstract
In this research, the aeroelastic instability of a tail section manufactured from aluminum isotropic material with different shell thickness investigated. For this purpose, the two degrees of freedom flutter analytical approach are used, which is accompanied with simulation by finite element analysis. Using finite element analysis, the geometry parameters such as the center of mass, the aerodynamic center and the shear center are determined. Also, by simulation of finite element method, the bending and torsional stiffnesses for various thickness of the airfoil section are determined. Furthermore, using Lagrange's methods the equations of motion are derived and modal frequency and critical torsional/bending modes are discussed. The results show that with increasing the thickness of the isotropic airfoil section, the flutter and divergence speeds increased. Compared of the obtained results with other research, indicates a good agreement and reliability of this method.

Key Words
aeroelastic instability; aluminum airfoil section; finite element analysis; flutter speed

Address
Amin Gharaei: Faculty of Engineering, Yazd University, Yazd, Iran

Hamid Rabieyan-Najafabadi: Faculty of New Sciences and Technologies, University of Tehran, Tehran, Iran

Hossein Nejatbakhsh: Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran

Ahmad Reza Ghasemi: Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran

Abstract
This study presents the application of two indices for the locating of cracks in Reinforced Concrete (RC) structures, as well as the development of their modified forms to overcome limitations. The first index is based on mode shape curvature and the second index is based on the fourth derivative of the mode shape. In order to confirm the indices' effectiveness, both eigenvalues coupled with nonlinear static analyses were carried out and the eigenvectors for two different damage locations and intensities of load were obtained from the finite element model of RC beams. The values of the damage-locating indices derived using both indices were then compared. Generally, the mode shape curvature-based index suffered from insensitivity when attempting to detect the damage location; this also applied to the mode shape fourth derivative-based index at lower modes. However, at higher modes, the mode shape fourth derivative-based index gave an acceptable indication of the damage location. Both the indices showed inconsistencies and anomalies at the supports. This study proposed modification to both indices to overcome identified flaws. The results proved that modified forms exhibited better sensitivity for identifying the damage location. In addition, anomalies at the supports were eliminated.

Key Words
crack identification; damage locating indices; mode shape curvature; mode shape fourth derivatives

Address
Moatasem M. Fayyadh: Asset Lifecycle, Sydney Water, 2150 NSW, Australia

Hashim Abdul Razak: Department of Civil Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia


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