eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2011-01-01
24
1
1
13
71876
Nonlinear Numerical Integration Scheme in Strain Space Plasticity
sina sinaie
sina_sinaie@yahoo.com
1
M. Rezaiee Pajand
rezaiee@um.ac.ir
2
Civil Engineering, Ferdowsi University of Mashhad
Strains are applied to the integration procedure in nonlinear increments todecrease the errors arising from the linearization of plastic equations. Two deformationvectors are used to achieve this. The first vector is based on the deformations obtained bythe first iteration of the equilibrium step, and the second is acquired from the sum of thesucceeding iterations. By applying these vectors and using sub-increments, the total strainincrement can vary nonlinearly during the integration of the flow rule. Four individualvariation schemes are presented for this purpose. In this paper, the strain space formulationis investigated. Numerical examples are analyzed using the traditional linear method andthe suggested schemes. The examples are solved using the von Mises yield criterion andPrager's linear hardening rule. Results indicate that all nonlinear techniques increase theconvergence rate of plastic analysis. In addition, such integration methods are shown toincrease the stability of incremental-iterative analyses.
https://www.ije.ir/article_71876_47c1ffc44420257bcc499cb7858dfb82.pdf
Strain space
Plastic Analysis
Integration methods
Sub
incrementation
Convergence rate
Analysis stability
Numerical methods
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2011-01-01
24
1
15
24
71878
Stochastic Finite Fault Modeling for the 16 September 1978 Tabas, Iran, Earthquake
Saman Yaghmaei-Sabegh
s_yaghmaei@tabrizu.ac.ir
1
Civil Engineering, University of Tabriz
The main objective of this study is estimating acceleration time history of 16 September 1978 Tabas earthquake incorporating the seismological/geological source-path and site model parameters by using finite-fault simulation approach. The method generalizes the stochastic ground-motion simulation technique, developed for point sources, to the case of finite faults. It subdivides the fault plane into subfaults and assumes each subfault to be a point source with a ω-2 spectrum. The length of the fault is taken as 85km and its width as 30km, and the fault plane is divided into 17×6 elements. Geometric spreading, regional anelastic attenuation and local site effect are included in the model. Satisfactory agreements between simulated and observed results validate capability of the method in prediction of ground motion in the study region
https://www.ije.ir/article_71878_bbe0bcb65fb900fe17f4b57b2e6dd495.pdf
Stochastic model
ground motion simulation
Finite
Fault model
Tabas earthquake
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2011-01-01
24
1
25
35
71880
An Improved Pixon-Based Approach for Image Segmentation
Hadi Yousefian
hadi_yousefian18@yahoo.com
1
Hamid Hassanpour
h_hassanpour@yahoo.com
2
Elecctrical Engineering, Tabriz University
An improved pixon-based method is proposed in this paper for image segmentation. In thisapproach, a wavelet thresholding technique is initially applied on the image to reduce noise and toslightly smooth the image. This technique causes an image not to be oversegmented when the pixonbasedmethod is used. Indeed, the wavelet thresholding, as a pre-processing step, eliminates theunnecessary details of the image and results in a fewer pixon number, faster performance and morerobustness against unwanted environmental noises. The image is then considered as a pixonal modelwith a new structure. The obtained image is segmented using the hierarchical clustering method (FuzzyC-Means algorithm). The experimental results in this paper indicate that the proposed pixon-basedapproach has a reduced computational load and a better accuracy compared to the other existing imagesegmentation techniques.
https://www.ije.ir/article_71880_c9bb4bcef741659a548a0979992905c5.pdf
Image Segmentation
Pixon
Wavelet thresholding
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2011-01-01
24
1
37
47
71882
A Mathematical Method for Managing the System Constraint
M.B. Aryanezhad
mirarya@iust.ac.ir
1
Seyed Amin Badri
badri@guilan.ac.ir
2
Industrial Engineering, Iran University of Science and Technology (IUST)
Department of Industrial Engineering, University of Guilan
The goal of theory of constraints (TOC) is to maximize output, which is achieved byidentifying and managing the critically constrained resources. To manage the constraints, Goldrattproposed five focusing steps (5FS). If we increase constrained output, the output of system will beincreased. In this paper, we focus on step four of the 5FS and use the remained capacity of nonconstraintto elevate the system’s constraint.
https://www.ije.ir/article_71882_0d197409fe19aa667ab5d9c7b2825ccf.pdf
theory of constraints
five focusing steps
Queueing system
Threshold
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2011-01-01
24
1
49
53
71884
Effect of Mold Preheating on the Microstructure of the Investment Cast Astm F-75 Implant Alloy
Mohsen Fatahi
mohsen.fatahy@yahoo.com
1
Ahmad Kermanpur
ahmad_k@cc.iut.ac.ir
2
Mahmood Meratian
mmeratian@yahoo.com
3
Hossein Ghazvinizadeh
hogha168@yahoo.com
4
Hossein Minouei
h_minouie@yahoo.com
5
Faculty of Engineering, Islamic Azad University Ahvaz Branch
Materials Science and Engineering, Isfahan University of Technology
Materials Science and Engineering, Isfahan University of Technology
Materials Engineering, Isfahan University of Technology
Materials Science and Engineering, Isfahan University of Technology
The ASTM F-75 (Co-28%Cr-6%Mo) is widely used as a biocompatible alloy in medicinefor manufacturing implants. In this study, effect of mold preheating on the as-cast microstructure of thealloy was investigated using the solid investment casting process. Several mold preheating temperaturesof 550, 700, 850 and 1000 °C were selected at the same melt superheat. The samples were characterizedby optical microscopy, electron microscopy and macro-hardness test. The results showed that the size ofgrains and secondary carbides of the matrix was increased by increasing the mold preheatingtemperature. In addition, morphology of the M23C6 carbides was changed from the eutectic carbidesprecipitated in grain boundaries to the blocky shape precipitated in both carbide interface and dendriticmatrix. The appropriate microstructure with nearly fine grains with homogeneous distribution ofsecondary phases was obtained at mold preheating temperature of about 850 °C.
https://www.ije.ir/article_71884_d37b6eb246c12de2e1e9ad63140d7562.pdf
Investment cast
Mold preheating
Microstructure
Co alloy
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2011-01-01
24
1
55
63
71885
Mathematical Modeling of Potential Flow over a Rotating Cylinder (RESEARCH NOTE)
Salar Askari Lasaki
bas_salaraskari@yahoo.com
1
M. H. Shojaefard
mhshf@iust.ac.ir
2
Mechanical Engineering Department, Amir Kabir University of Technology
School of Automotive Engineering, Iran University of Science and Technology (IUST)
Potential flow over rotating cylinder is usually solved by the singularity method. However,in this paper a mathematical solution is presented for this problem by direct solution of the Laplace’sequation. Flow over the cylinder was considered non-viscous. Neumann and Dirichlet boundaryconditions were used on the solid surfaces and in the infinity, respectively. Because of non-viscous flow,the Laplace equation is the governing equation of the flow field. The entire flow field was divided intotwo parts including free stream over a stationary cylinder and flow over a rotating cylinder with no freestream. Because of linearity of the governing equation, solutions of these flows were superposed toobtain velocity potential function from which velocity and pressure distribution was obtained. Pressureforces acting on the cylinder were obtained by integrating pressure distribution over the cylinder surfacethat was exactly the same as the results of the singularity method. Present work achieved the famousKutta-Joukowski theorem in the aerodynamics and fluid mechanics. In addition, the proposed analyticalmodel was validated by numerical solution.
https://www.ije.ir/article_71885_0b6b7470c715fe37d23591dcc6c800d1.pdf
Bernoulli equation
Laplace Equation
potential flow
Kutta
Joukowski theorem
Singularity method
CFD
Finite Volume Method (FVM)
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2011-01-01
24
1
65
78
71887
A Particle Swarm Optimization Algorithm for Mixed-Variable Nonlinear Problems
Iman Mohagheghian
imaniut81@me.iut.ac.ir
1
Hassan Nahvi
hasnahvi@yahoo.com
2
Mechanical Engineering, Isfahan University of Technology
Mechanical Engineering, Isfahan University of Technology
Many engineering design problems involve a combination of both continuous anddiscrete variables. However, the number of studies scarcely exceeds a few on mixed-variableproblems. In this research Particle Swarm Optimization (PSO) algorithm is employed to solve mixedvariablenonlinear problems. PSO is an efficient method of dealing with nonlinear and non-convexoptimization problems. In this paper, it will be shown that PSO is one of the best optimizationalgorithms for solving mixed-variable nonlinear problems. Some changes are performed in theconvergence criterion of PSO to reduce computational costs. Two different types of PSO methods areemployed in order to find the one which is more suitable for using in this approach. Then, severalpractical mechanical design problems are solved by this method. Numerical results show noticeableimprovements in the results in different aspects.
https://www.ije.ir/article_71887_02550045c1cb50fad4968d10650fefa4.pdf
Particle Swarm Optimization
mixed
variable
engineering design
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2011-01-01
24
1
79
86
71890
Postbuckling Equilibrium Path of a Long Thin-Walled Cylindrical Shell (Single-Walled Carbon Nanotube) under Axial Compression Using Energy Method
ali Ghorbanpour
aghorban@kashanu.ac.ir
1
Ali Saidi
saidi@mail.uk.ac.ir
2
Mehdi Mohammadimehr
mmohammadimehr@yahoo.com
3
Qiang Han
emqhan@scut.edu.cn
4
mechanical Engineering, Kashan university
Mechainical Engineering, Shahid Bahounar university of Kerman
mechanical Engineering, S. Bahonar University
School of Civil Engineering and Transportation, South China University of Technology
In this paper, an elastic shell model is presented for postbuckling prediction of a long thinwalledcylindrical shell under axial compression. The Ritz method is applied to solve the governingequilibrium equation of a cylindrical shell model based on the von-Karman type nonlinear differentialequations. The postbuckling equilibrium path is obtained using the energy method for a long thin-walledcylindrical shell. Furthermore, the postbuckling relationship between the axial stress and end-shorteningis investigated with different geometric parameters. Also, this theory is used for postbuckling analysis ofa single-walled carbon nanotube without considering the small scale effects. Numerical results revealthat the single-walled carbon nanotube under axial compression has an unstable postbuckling behavior.
https://www.ije.ir/article_71890_8224c93e34903b2ba3937f525b261956.pdf
Postbuckling
Long Thin
Walled Shell
Axial Compression
Ritz Method
SWCNT
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2011-01-01
24
1
87
105
71892
Frequency Analysis for a Timoshenko Beam Located on an Elastic Foundation
Hamid Ekhteraei Toussi
ekhteraee@um.ac.ir
1
Mojtaba Sadeghian
mo_sa257@stu-mail.um.ac.ir
2
Mech. Engr., Ferdowsi University of Mashhad
Mech. Eng., Ferdowsi University of Mashhad
It is quite usual to encounter a beam with different types of cross section or even structuraldiscontinuities such as a crack along its length. Furthermore, in many occasions such a beam mayhappen to be exposed to the oscillatory fluctuations. Therefore, any information about its naturalfrequencies may be worthwhile. Amongst the problems of discontinues beam analysis, in this paper aspecial kind of frequency analysis for a cracked and stepped beam located on an elastic foundation isconsidered. Accordingly, following a look out at the definition of Timoshenko beams, a specialmodeling trend known as the wave method is introduced. Based on the d'Alembert’s approach for thesolution of wave differential equations, the technique of wave method is mainly depended on the studyof transmission and reflection of waves colliding to a barrier. The method results in a global frequencymatrix, which its determinant gives out the natural frequencies. The wave method is employed for thefrequency analysis in some kinds of cracked and stepped beams with different types of boundaryconditions. In some typical cases, the results are compared to other similar works and confirmed to beconvincing.
https://www.ije.ir/article_71892_25c5e352f544660370c43644a1c49362.pdf
Timoshenko beam
Elastic Foundation
Wave approach
Cracked stepped beam
Frequency analysis