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Probability density evolution for time-varying reliability assessment of wing structures
, Article Aviation ; Volume 22, Issue 2 , 2018 , Pages 45-54 ; 16487788 (ISSN) ; Pourtakdoust, S. H ; Sharif University of Technology
Vilnius Gediminas Technical University
2018
Abstract
Reliability evaluation is a key factor in serviceability and safety analysis of air vehicles. Structural health monitoring methods have grown to a degree of maturity in many industries. However, there is a challenging interest to tie in SHM with reliability assessment. In this respect, consideration of stochastic structural dynamics with SHM data and random loadings opens a new chapter in failure prevention. The current study focuses on the stochastic behavior of structures as a way to relate SHM data with reliability. In this respect, uncertain factors such as atmospheric turbulence, structural parameters, and sensor outputs are considered in the process of reliability assessment. Firstly,...
Utility of probability density evolution method for experimental reliability-based active vibration control
, Article Structural Control and Health Monitoring ; Volume 25, Issue 8 , 2018 ; 15452255 (ISSN) ; Pourtakdoust, S. H ; Sharif University of Technology
John Wiley and Sons Ltd
2018
Abstract
The utility of probability density evolution method for reliability-based active vibration control of a cantilevered flexible beam is experimentally investigated. In this respect, an optimal linear quadratic regulator (LQR) is utilized together with an observer to design an online full-state feedback controller. In order to design a well-performing controller and to simulate the controller performance, a system model is obtained via identification techniques. Reliability tests are consequently performed to verify the effectiveness of the presented reliability assessment method as a foundation for reliability-based control. Subsequently, a hybrid metaheuristic optimization scheme of...
A note on the algebraic connectivity of a graph and its complement
, Article Linear and Multilinear Algebra ; 2019 ; 03081087 (ISSN) ; Akbari, S
Taylor and Francis Ltd
2019
Abstract
For a graph G, let λ2(G) denote its second smallest Laplacian eigenvalue. It was conjectured that (Formula presented.), where (Formula presented.) is the complement of G. In this paper, it is shown that (Formula presented.). © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group
Experimental parametric identification of a flexible beam using piezoelectric sensors and actuators
, Article Shock and Vibration ; Vol. 2014, Issue. 1 , 2014 ; ISSN: 1070-9622 ; Nobahari, H ; Kordkheili, S. A. H ; Sharif University of Technology
2014
Abstract
Experimental system identification of a flexible beam based on sweep square excitation is studied. For the purpose of nonparametric identification, an excitation signal is conducted to evaluate the frequency response of the system. The experiment is designed to excite the beam using a piezo actuator, in a way to raise the chance of exciting first three natural modes. In order to find the best linear representation of the real system, two different identification methods are applied. First, autoregressive moving average eXogenous method is employed to identify the transfer function of the beam. Then, the identification is carried out using the subspace identification method to obtain the...
Investigation of a nonlinear dynamic hydraulic system model through the energy analysis approach
, Article Journal of Mechanical Science and Technology ; Volume 23, Issue 11 , 2010 , Pages 2973-2979 ; 1738494X (ISSN) ; Ehramianpour, M ; Mohammadi, M ; Sharif University of Technology
2010
Abstract
The dynamics of a pressure regulator valve have been studied using the through Bondgraph simulation technique. This valve consists of several elements that can transmit, transform, store, and consume hydraulic energy. The governing equations of the system have been derived from the dynamic model. In solving system equations numerically, various pressure-flow characteristics across the regulator ports and orifices have been taken into consideration. This simulation study identifies some critical parameters that have significant effects on the transient response of the system. The results have been obtained using the MATLAB-SIMULINK environment. The main advantage of the proposed methodology...
Optimization of the shaping function of a tapered piezoelectric energy harvester using tabu continuous ant colony system
, Article Journal of Intelligent Material Systems and Structures ; Volume 30, Issue 20 , 2019 , Pages 3025-3035 ; 1045389X (ISSN) ; Rahimi, G. H ; Saraygord Afshari, S ; Sharif University of Technology
SAGE Publications Ltd
2019
Abstract
During the past years, the development of piezoelectric energy harvesters is extensively increased for providing the required energy of sensor nodes. It has been proven that changing the beam’s cross-section along its length direction may lead to extract more power with less mass. In this article, a hybrid metaheuristic algorithm called tabu continuous ant colony system is employed to optimize the tapered piezoelectric energy harvester in a fast and course manner. The exponential and fourth-order polynomial functions are considered as shaping functions for tapering the beam’s width along its length direction. An experiment is also set up to evaluate the performance of the optimization...
A stabilized piezolaminated nine-nodded shell element formulation for analyzing smart structures behaviors
, Article Mechanics of Advanced Materials and Structures ; Volume 23, Issue 2 , 2016 , Pages 187-194 ; 15376494 (ISSN) ; Salmani, H ; Afshari, S. S. G ; Sharif University of Technology
Taylor and Francis Inc
2016
Abstract
An explicit hybrid stabilization method is utilized together with a reduced order integration scheme to stabilize spurious zero energy modes from the sub-integrated degenerated shell element. This stabilization is achieved after employing appropriate contravariant higher order stress modes. The relevant finite element formulation of the piezolaminated nine-nodded shell element is then derived to analyze smart structures behaviors. To show the capabilities of the presented formulation, it has been implemented in a finite element code. The developed code is used to analyze some typical problems. The results are compared with those obtained from other schemes in the literature and experiments
Simulation of static recrystallization after cold side-pressing of low carbon steels using cellular automata
, Article Journal of Materials Engineering and Performance ; Volume 21, Issue 8 , 2012 , Pages 1553-1561 ; 10599495 (ISSN) ; Serajzadeh, S ; Sharif University of Technology
2012
Abstract
In this article, the finite element and cellular automata models are coupled to determine static recrystallization kinetics after cold deformation of low carbon steels. The deformation analysis is first performed to predict the strain, stress, and stored energy distributions within the deformed steel employing the finite element software, ABAQUS. Then, the kinetics of static recrystallization and distribution of recrystallized grain size are evaluated by means of a cellular automata model together with the stored energy calculated by the deformation analysis. To examine the predictions, the experimental results of recrystallized fractions and grain sizes after cold side-pressing of low...
Information resource management maturity model
, Article World Academy of Science, Engineering and Technology ; Volume 37 , 2009 , Pages 258-262 ; 2010376X (ISSN) ; Khosravi, Sh ; Sharif University of Technology
2009
Abstract
Nowadays there are more than thirty maturity models in different knowledge areas. Maturity model is an area of interest that contributes organizations to find out where they are in a specific knowledge area and how to improve it. As Information Resource Management (IRM) is the concept that information is a major corporate resource and must be managed using the same basic principles used to manage other assets, assessment of the current IRM status and reveal the improvement points can play a critical role in developing an appropriate information structure in organizations. In this paper we proposed a framework for information resource management maturity model (IRM3) that includes ten best...
Directed functional networks in Alzheimer's disease: disruption of global and local connectivity measures
, Article IEEE Journal of Biomedical and Health Informatics ; Volume 21, Issue 4 , 2017 , Pages 949-955 ; 21682194 (ISSN) ; Jalili, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2017
Abstract
Techniques available in graph theory can be applied to signals recorded from human brain. In network analysis of EEG signals, the individual nodes are EEG sensor locations and the edges correspond to functional relations between them that are extracted from EEG time series. In this paper, we study EEG-based directed functional networks in Alzheimer's disease (AD). To this end, directed connectivity matrices of 25 AD patients and 26 healthy subjects are processed and a number of meaningful graph theory metrics are studied. Our data show that functional networks of AD brains have significantly reduced global connectivity in alpha and beta bands (P < 0.05). The AD brains have significantly...
Some results on the Laplacian spread conjecture
, Article Linear Algebra and Its Applications ; Volume 574 , 2019 , Pages 22-29 ; 00243795 (ISSN) ; Akbari, S ; Sharif University of Technology
Elsevier Inc
2019
Abstract
For a graph G of order n, let λ 2 (G) denote its second smallest Laplacian eigenvalue. It was conjectured that λ 2 (G)+λ 2 (G‾)≥1, where G‾ is the complement of G. For any x∈R n , let ∇ x ∈R (n2) be the vector whose {i,j}-th entry is |x i −x j |. In this paper, we show the aforementioned conjecture is equivalent to prove that every two orthonormal vectors f,g∈R n with zero mean satisfy ‖∇ f −∇ g ‖ 2 ≥2. In this article, it is shown that for the validity of the conjecture it suffices to prove that the conjecture holds for all permutation graphs. © 2019 Elsevier Inc
A note on the algebraic connectivity of a graph and its complement
, Article Linear and Multilinear Algebra ; 2019 ; 03081087 (ISSN) ; Akbari, S ; Sharif University of Technology
Taylor and Francis Ltd
2019
Abstract
For a graph G, let λ2(G) denote its second smallest Laplacian eigenvalue. It was conjectured that (Formula presented.), where (Formula presented.) is the complement of G. In this paper, it is shown that (Formula presented.). © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group
A note on the algebraic connectivity of a graph and its complement
, Article Linear and Multilinear Algebra ; Volume 69, Issue 7 , 2021 , Pages 1248-1254 ; 03081087 (ISSN) ; Akbari, S ; Sharif University of Technology
Taylor and Francis Ltd
2021
Abstract
For a graph G, let (Formula presented.) denote its second smallest Laplacian eigenvalue. It was conjectured that (Formula presented.), where (Formula presented.) is the complement of G. In this paper, it is shown that (Formula presented.). © 2019 Informa UK Limited, trading as Taylor & Francis Group
New Jacobian matrix and equations of motion for a 6 d.o.f cable-driven robot
, Article International Journal of Advanced Robotic Systems ; Volume 4, Issue 1 , 2007 , Pages 63-68 ; 17298806 (ISSN) ; Meghdari, A ; Sharif University of Technology
InTech Europe
2007
Abstract
In this paper, we introduce a new method and new motion variables to study kinematics and dynamics of a 6 d.o.f cable-driven robot. Using these new variables and Lagrange equations, we achieve new equations of motion which are different in appearance and several aspects from conventional equations usually used to study 6 d.o.f cable robots. Then, we introduce a new Jacobian matrix which expresses kinematical relations of the robot via a new approach and is basically different from the conventional Jacobian matrix. One of the important characteristics of the new method is computational efficiency in comparison with the conventional method. It is demonstrated that using the new method instead...
A note on the algebraic connectivity of a graph and its complement
, Article Linear and Multilinear Algebra ; Volume 69, Issue 7 , 2021 , Pages 1248-1254 ; 03081087 (ISSN) ; Akbari, S ; Sharif University of Technology
Taylor and Francis Ltd
2021
Abstract
For a graph G, let (Formula presented.) denote its second smallest Laplacian eigenvalue. It was conjectured that (Formula presented.), where (Formula presented.) is the complement of G. In this paper, it is shown that (Formula presented.). © 2019 Informa UK Limited, trading as Taylor & Francis Group
On Dinur’s Proof of the PCP Theorem
, M.Sc. Thesis Sharif University of Technology ; Daneshgar, Amir (Supervisor)
Abstract
The PCP theorem is the result of a line of work on interactive proofs and probabilistically checkable proofs. The first theorem relating standard proofs and probabilistically checkable proofs is NEXP?PCP[poly(n),poly(n)] . Subsequently, the method used in the proof of this statement were extended to yield a proof of the PCP theorem. However, this proof is relatively long and complicated. The PCP theorem is equivalent to hardness of approximation of some optimization problems. In 2006, Irit Dinur discovered a different proof of the PCP theorem. Dinur’s proof is a rather shorter and simpler than original proof. The main purpose of this survey is to present the main concepts and tools used in...
Application of a Thermo-Plastic Constitutive Model for Coupled THM Analysis of Behavior of Saturated Soils
, M.Sc. Thesis Sharif University of Technology ; Pak, Ali (Supervisor)
Abstract
Effects of temperature on the behavior of soils and rocks have been studied widely in recent years. Following the need for understanding the effects of temperature on the behavior of clayey soils, several experimental and numerical studies on thermo-mechanical behavior of clayey soils have been carried out and a number of thermo-mechanical constitutive models have been developed for saturated and unsaturated clayey soils. In this research, a two-yield surface thermo-plastic constitutive model developed by Abuel-Naga et al. (2007, 2009), has been chosen for THM analysis of the behavior of saturated clayey soils. This constitutive model is based on Modified Cam-Clay (MCC) model. The MCC model...
Experimental Study of Bond in Curved FRP-Strengthed Beams
, M.Sc. Thesis Sharif University of Technology ; Vafai, Abolhassan (Supervisor)
Abstract
Through the recent years application of FRP material in structural engineering has been developed significantly. According to possible changes of a building function during its lifetime or alteration of the building codes, building structures usually need to be strengthened. Referring to merits of FRP material, its application seems to be a convenient idea toward the cited requirement. Curved beam and slab are known as highly used elements in building structures. Bridges composed of horizontal or vertical arches could be noted as common examples which need to be reinforced by FRP. However curved concrete surfaces, reinforced by FRP plates, seem to be studied than it is really required; For,...
Investigating the Response Reduction Factor of Steel 3-D Braced Frames with Eccentricity
, M.Sc. Thesis Sharif University of Technology ; Khonsari, Vahid (Supervisor)
Abstract
Studying the performance of irregular structures in past earthquakes reveals that due to their severe vulnerability, we need to accurately assess the behavioral characteristics of such structures. On the other hand, all existing seismic codes recommend the use of response modification factor to determine the base shear, design forces of the members, and the design drift ratios, which seem to have limited comprehensiveness. Moreover, the response modification factor for a structural system is discussed in a general manner and the effect of factors such as number of bays, number of stories, span length, story height and irregularities are not considered. In this research, the effects of...
Influence of Beta Nucleation Method with the Use of Calcium Pimelate on Low-Temperature Toughness of Polypropylene Block Copolymer
, M.Sc. Thesis Sharif University of Technology ; Bagheri, Reza (Supervisor)
Abstract
One drawback of polypropylene (PP) as a widely-used semicrystalline thermoplastic is its low toughness at sub-zero temperatures. Along with adding elastomers to PP as impact modifiers, modification of PP’s crystalline structure by means of beta-phase nucleating agents —beta being the toughest polymorph of PP —is a standard method of improving PP’s toughness. Nucleation efficiency is highly dependent on the optimum dispersion of the nucleating agent. Therefore, improving the dispersion of the nucleating agents assumes an essential role. The objective of this study is to determine the influence of the incorporation method of calcium pimelate (CaPi), a highly-selective beta nucleating agent, on...