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Multidisciplinary optimisation of a car component under NVH and weight constraints using RSM
, Article International Journal of Vehicle Noise and Vibration ; Volume 5, Issue 3 , 2009 , Pages 261-270 ; 14791471 (ISSN) ; Azadi, S ; Moradi, M ; Zahedi, F ; Sharif University of Technology
2009
Abstract
One of the important challenges in the auto industry is to reduce the mass of the vehicle while meeting structural performance requirements for crashworthiness, noise, vibration and harshness, etc. In this paper, a multidisciplinary optimisation of a car back-bonnet is investigated by using the response surface method. A car body is fully surface modelled in CATIA and meshed in software. Then, modal analysis of the finite element model is performed by NASTRAN software to find natural frequencies. A frequency map of that component is extracted and compared with a reference map to detect defects. Design of experiments methodology is used for a screening of the design space and for the...
Dissolution and conformational behavior of functionalized cellulose chains in the bulk, aqueous and non-aqueous media: A simulation study
, Article Carbohydrate Research ; Volume 496 , October , 2020 ; Moghbeli, M. R ; Rasouli, S ; Gharib Zahedi, M. R ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
In the present study, we employ all-atom molecular dynamics simulations to investigate the dynamic behaviors and structural properties of the native and modified cellulose chains in the bulk, aqueous, and organic media. Particular attention has been directed to the role of different hydrophobic and hydrophilic functional groups as linear and branched aliphatic and also cyclic pendent groups on the solubility and packing of the cellulose chain. The various properties related to density profile, mean squared displacement, intramolecular entropy, radius of gyration, and radial distribution function were calculated. The results showed that the chain tendency toward crystallinity decreased when...
Antepartum fetal heart rate feature extraction and classification using empirical mode decomposition and support vector machine
, Article BioMedical Engineering Online ; Volume 10 , 2011 ; 1475925X (ISSN) ; MA, M. A ; Zahedi, E ; Ahmed, S ; Hassan, F. M ; Sharif University of Technology
2011
Abstract
Background: Cardiotocography (CTG) is the most widely used tool for fetal surveillance. The visual analysis of fetal heart rate (FHR) traces largely depends on the expertise and experience of the clinician involved. Several approaches have been proposed for the effective interpretation of FHR. In this paper, a new approach for FHR feature extraction based on empirical mode decomposition (EMD) is proposed, which was used along with support vector machine (SVM) for the classification of FHR recordings as 'normal' or 'at risk'.Methods: The FHR were recorded from 15 subjects at a sampling rate of 4 Hz and a dataset consisting of 90 randomly selected records of 20 minutes duration was formed from...
Optimal control of nonlinear dynamical systems using direct solution of neural network controllers
, Article AIAA Guidance, Navigation, and Control Conference and Exhibit 2002, Monterey, CA, 5 August 2002 through 8 August 2002 ; 2002 ; 9781563479786 (ISBN); 9781624101083 (ISBN) ; Jalali, M. A ; Ghorbani, R ; Zahedi, A ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2002
Abstract
Due to inherent potential of General Regression Neural Network(GRNN) to approximate nonlinear functions, it can be implemented as a nonlinear state-feedback controller. In this paper the methodology of direct collocation and nonlinear programming is utilized in combination with GRNN to determine the optimal control of dynamical systems. Application of this method to the design of an optimal controller for a chaotic flexible beam as a non-autonomous, nonlinear system is investigated. © 2002 The American Institute Aeronautics and Astronautics Inc. All rights reserved
Network immunization under limited budget using graph spectra
, Article International Journal of Modern Physics C ; Volume 27, Issue 8 , 2016 ; 01291831 (ISSN) ; Khansari, M ; Sharif University of Technology
World Scientific Publishing Co. Pte Ltd
2016
Abstract
In this paper, we propose a new algorithm that minimizes the worst expected growth of an epidemic by reducing the size of the largest connected component (LCC) of the underlying contact network. The proposed algorithm is applicable to any level of available resources and, despite the greedy approaches of most immunization strategies, selects nodes simultaneously. In each iteration, the proposed method partitions the LCC into two groups. These are the best candidates for communities in that component, and the available resources are sufficient to separate them. Using Laplacian spectral partitioning, the proposed method performs community detection inference with a time complexity that rivals...
A new immunization algorithm based on spectral properties for complex networks
, Article 2015 7th Conference on Information and Knowledge Technology, IKT 2015, 26 May 2015 through 28 May 2015 ; May , 2015 , Page(s): 1 - 5 ; 9781467374859 (ISBN) ; Khansari, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2015
Abstract
Nowadays, we are facing epidemic spreading in many different areas; examples are infection propagation, rumor spreading and computer viruses in computer networks. Finding a strategy to control and mitigate the spread of these epidemics is gaining much interest in recent researches. Due to limitation of immunization resources, it is important to establish a strategy for selecting nodes which has the most effect in mitigating epidemics. In this paper, we propose a new algorithm that minimizes the worst expected growth of an epidemic by reducing the size of the largest connected component of the underlying contact network. The proposed algorithm is applicable to any level of available resources...
Stability analysis of descriptor systems with multiple commensurate time-delays
, Article Journal of the Franklin Institute ; Volume 356, Issue 15 , 2019 , Pages 8690-8705 ; 00160032 (ISSN) ; Haeri, M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
A new method is proposed to analyze stability of descriptor systems with multiple commensurate time-delays. In this method, purely imaginary roots of the system are calculated, asymptotic behavior of root path at these roots is studied, and unstable regions of the system in the space of delays are determined. Moreover, the number of roots in each unstable region is calculated. Also necessary and sufficient conditions for τ-stabilizability of these systems are presented. Examples are provided to illustrate the effectiveness and validity of the proposed method. © 2019 The Franklin Institute
Decomposition and robust non-fragile stabilisation of singular time-delay systems
, Article IET Control Theory and Applications ; Volume 12, Issue 13 , 2018 , Pages 1882-1888 ; 17518644 (ISSN) ; Haeri, M ; Sharif University of Technology
2018
Abstract
This study presents a new approach to decompose singular time-delay systems (STDSs) in a way that they can be transformable to normal time-delay systems (TDSs) with a lower order. Necessary and sufficient conditions are provided to determine which STDSs can be transformed to TDSs. Also, a stabilisation method is provided to stabilise the system, while the time delay in the system can belong to several distinct intervals or even everywhere. The proposed method is non-fragile towards controller parameters. This method also reveals one of the many applicable situations of the proposed decomposition. The effectiveness of the proposed method is illustrated through some examples. © 2018 The...
Asymptotic stability of linear descriptor systems with time-delay by designing delay margin
, Article 5th International Conference on Control, Instrumentation, and Automation, ICCIA 2017 ; Volume 2018-January , 2018 , Pages 23-29 ; 9781538621349 (ISBN) ; Haeri, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
In this paper a new approach is developed to stabilize descriptor systems with time-delay, while time-delay can belong to a given interval. This approach takes the advantages of system's singularity to simplify the model and uses the so-called Rekasius substitution to compute the controller parameters in a way that the asymptotic stability of the closed-loop system in the given interval of the delay can be guaranteed. Finally, a numerical example is provided to evaluate the proposed method's effectiveness. © 2017 IEEE
Investigating the effect of geometric parameters on hydrodynamic and hydro-acoustic performances of submerged propellers
, Article Applied Ocean Research ; Volume 114 , 2021 ; 01411187 (ISSN) ; Ebrahimi, A ; Zahedi, F ; Javanmardi, M. R ; Seif, M. S ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
The hydro-acoustic analysis of submerged propellers is an important issue in marine industries, which is examined to reduce the vibrations and noise level of vessels alongside reducing fuel consumption and improving hydrodynamic efficiency. B-series propellers are common propellers whose hydrodynamic and acoustic investigation through applying suitable rake, and skew angle can offer proper results to designers for enhancing the hydrodynamic performance and reducing noise. In this study, a model of the five-bladed B-series propeller with the normal skew angle is chosen. The effects of geometric parameters, including the rake angle, skew angle, geometric pitch ratio, and the number of blades...
Thermo-mechanical modeling of high speed spindles
, Article Scientia Iranica ; Volume 19, Issue 2 , 2012 , Pages 282-293 ; 10263098 (ISSN) ; Movahhedy, M. R ; Sharif University of Technology
2012
Abstract
Prediction of the thermo-mechanical behavior of machine-tool spindles is essential in the reliable operation of high speed machine tools. In particular, the performance of these high speed spindles is dependent on their thermal behavior. The main source of heat generation in the spindle is the friction torque in angular contact ball bearings. This paper presents an effort to develop a comprehensive model of high speed spindles that includes viable models for the mechanical and thermal behavior of its major components, i.e., bearings, shaft and housing. Spindle housing and shaft are treated as six-degree-of-freedom Timoshenko beam elements. Bearings are modeled as two-node elements with five...
The dilemma of BME research projects in developing countries: A case study
, Article Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS ; 2011 , Pages 3631-3635 ; 1557170X (ISSN) ; 9781424441211 (ISBN) ; Attar, H. M ; Sharif University of Technology
2011
Abstract
Researchers are faced with huge challenges when undertaking BME research projects in developing countries. Various administrative, technical, economic and even cultural barriers have to be overcome whereas the quality and quantity of the output has to be comparable with the developed world in order to make results publishable. This paper uses a real project context to highlight the major problems and the necessity of a holistic approach which would take into consideration all stakeholders interests. It is only by tackling problems such as relationship between academia-industry and administration efficiency at their root that significant progress can be achieved
The dilemma of BME research projects in developing countries: a case study
, Article Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference ; Volume 2011 , 2011 , Pages 3631-3635 ; 1557170X (ISSN) ; Attar, H. M ; Sharif University of Technology
2011
Abstract
Researchers are faced with huge challenges when undertaking BME research projects in developing countries. Various administrative, technical, economic and even cultural barriers have to be overcome whereas the quality and quantity of the output has to be comparable with the developed world in order to make results publishable. This paper uses a real project context to highlight the major problems and the necessity of a holistic approach which would take into consideration all stakeholders interests. It is only by tackling problems such as relationship between academia-industry and administration efficiency at their root that significant progress can be achieved
Operational strategy optimization of a hybrid green power system based on fuzzy logic controller with considering for optimal sizing and analysis of different priorities for energy storage
, Article Sustainable Energy, Grids and Networks ; Volume 32 , 2022 ; 23524677 (ISSN) ; Moeini Aghtaie, M ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
Renewable energy (RE) as a new player in the generation sector of power systems imposes new challenges to the system operators. The intermittent nature of REs for systems where are autonomous calls for new operational and planning strategies to reach more efficient power management. An autonomous hybrid green power system (HGPS) should be able to meet the load while keeping the cost of the HGPS as low as possible. Many studies have presented different un-optimal and optimal operational strategies, a few of which were optimally sized. In this regard, this paper develops a new thorough framework for designing and optimizing an autonomous HGPS. To reach this goal, the proposed model (a)...
Numerical and experimental investigations for design of a high performance microhydro-kinetic turbine
, Article International Journal of Engineering, Transactions B: Applications ; Volume 30, Issue 5 , 2017 , Pages 785-790 ; 1728144X (ISSN) ; Rad, M ; Khayat, M ; Sharif University of Technology
2017
Abstract
Design and manufacturing of a high performance micro-hydro-kinetic turbine is discussed in the present paper. The main goal is manufacturing an equipped experimental model of hydro-kinetic turbine with highest energy absorption from water current. A multi-shape ducted turbine comprised of a multi-part diffuser was manufactured that can be converted to many experimental models for studying various diffuser enhancing effects. Turbine's rotor included a three-blade axial propeller and a mixed six-blade propeller with high power coefficient. Simple experiments on propeller were performed for flow visualization, torque measurement and illustrating dynamic balance at high speed rotation in air and...
Comparative analysis of agricultural water pricing between Azarbaijan Provinces in Iran and the state of California in the US: A hydro-economic approach
, Article Agricultural Water Management ; Volume 223 , 2019 ; 03783774 (ISSN) ; Zakeri, Z ; Esfandiari, M ; Behzadian, K ; Zahedi, S ; Razavi, V ; Sharif University of Technology
Elsevier B.V
2019
Abstract
Iranian water authority has recently announced that one of the effective ways to avoid unprecedented high water consumption in Iran's agriculture sector is to increase water price. This paper analyzes the feasibility of this policy by using a hydro-economic approach with the aim to consider the role of water pricing in agricultural water management. Such an analysis was conducted through comparing price of water consumed for producing selected agricultural crops (i.e. wheat, sugar beets, onion, tomato, barley, potato, corn, alfalfa hay and watermelon) in a case study on two provinces (East Azarbaijan and West Azarbaijan) in Iran to that in the state of California (CA) in the USA. According...
NVH analysis and improvement of a vehicle body structure using DOE method
, Article Journal of Mechanical Science and Technology ; Volume 23, Issue 11 , 2010 , Pages 2980-2989 ; 1738494X (ISSN) ; Azadi, M ; Zahedi, F ; Sharif University of Technology
2010
Abstract
The improvement of a vehicle body structure under the constraint of noise, vibration and harshness (NVH) behavior is investigated by using design of experiments (DOE) method. First, car body geometry is modeled in CATIA and meshed in HYPERMESH software. Then, a modal analysis between 0-50 Hz is done by MSC NASTRAN. A frequency map of the body is extracted and compared with a reference map to identify shortcomings. By using factorial and response surface Methods (RSM), optimization of the NVH performance is accomplished. An algorithm is proposed to improve the car NVH behavior. At last, in order to verify the present algorithm, forced vibration is analyzed under real road inputs for the model...
A comprehensive study on noise reduction methods of marine propellers and design procedures
, Article Applied Acoustics ; Volume 150 , 2019 , Pages 55-69 ; 0003682X (ISSN) ; Razaghian, A. H ; Seif, M. S ; Zahedi, F ; Nouri Borujerdi, A ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
The noise generated by the propeller is one of the most important components of the vessels noise. Therefore, reducing this noise will significantly decrease the total noise of the vessel. Underwater noise of vessels has destructive effects on marine life. In addition, this noise affects the health and comfort of the crew and passengers of the ship. Moreover, high noise may cause warships to be detected easily. In this paper, first, common methods of noise reduction, including blade coating, modern propellers, propeller hub modification and ducted propellers are investigated. Then, relevant optimization methods are presented. Next, the effects of the geometric parameters like number of...
Transversal thermal transport in single-walled carbon nanotube bundles: Influence of axial stretching and intertube bonding
, Article Journal of Chemical Physics ; Volume 139, Issue 18 , 2013 ; 00219606 (ISSN) ; Tafazzoli, M ; Böhm, M. C ; Alaghemandi, M ; Sharif University of Technology
2013
Abstract
Using reverse nonequilibrium molecular dynamics simulations the influence of intermolecular bridges on the thermal conductivity (λ) in carbon nanotube (CNT) bundles has been investigated. The chosen cross linkers (CH 2, O, CO) strengthen the transversal energy transport relative to the one in CNT bundles without bridges. The results showed that λ does not increase linearly with the linker density. The efficiency of the heat transport is determined by the number of linkers in the direction of the heat flux, the type of the linker, and their spatial ordering. The influence of a forced axial stress on the transversal λ has been also studied. The observed λ reduction with increasing axial...
Interfacial thermal transport and structural preferences in carbon nanotube-polyamide-6,6 nanocomposites: How important are chemical functionalization effects?
, Article Physical Chemistry Chemical Physics ; Volume 17, Issue 22 , 2015 , Pages 14502-14512 ; 14639076 (ISSN) ; Tafazzoli, M ; Böhm, M. C ; Alaghemandi, M ; Sharif University of Technology
Royal Society of Chemistry
2015
Abstract
We employ reverse nonequilibrium molecular dynamics simulations to investigate the interfacial heat transfer in composites formed by an ungrafted or a grafted carbon nanotube which is surrounded by oligomeric polyamide-6,6 chains. The structural properties of the polymer matrix and the grafted chains are also studied. The influence of the grafting density, the length of the grafted chains as well as their chemical composition on the interfacial thermal conductivity (λi ) are in the focus of our computational study. For the considered grafted polyethylene and polyamide chains we do not find a sizeable difference in the observed λi values. In contrast to this...