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Comparison of boundary slip for two variants of immersed boundary method in lattice Boltzmann framework
, Article Physica A: Statistical Mechanics and its Applications ; Vol. 404 , 2014 , Pages 200-216 ; ISSN: 03784371 ; Manzari, M. T ; Sharif University of Technology
2014
Abstract
In this paper, the Immersed Moving Boundary-Lattice Boltzmann (IMB-LB) method is compared with the single relaxation time and multiple-relaxation-time versions of the Immersed Boundary-Lattice Boltzmann (IB-LB) method in terms of the amount of numerical velocity slip produced on solid boundaries. The comparisons are performed for both straight and curved boundaries based on the effects of thickness of virtual domain used in the IB method for the first time, and relaxation time parameter(s) of the LB method. For the straight boundaries, a shear flow problem is studied while for the curved boundaries, a falling circular cylinder in an infinite channel is investigated. First, sensitivities of...
An investigation on the body force modeling in a lattice Boltzmann BGK simulation of generalized Newtonian fluids
, Article Physica A: Statistical Mechanics and its Applications ; Vol. 415, issue , 2014 , pp. 315-332 ; Manzari, M. T ; Sharif University of Technology
2014
Abstract
Body force modeling is studied in the Generalized Newtonian (GN) fluid flow simulation using a single relaxation time lattice Boltzmann (LB) method. First, in a shear thickening Poiseuille flow, the necessity for studying body force modeling in the LB method is explained. Then, a parametric unified framework is constructed for the first time which is composed of a parametric LB model and its associated macroscopic dual equations in both steady state and transient simulations. This unified framework is used to compare the macroscopic behavior of different forcing models. Besides, using this unified framework, a new forcing model for steady state simulations is devised. Finally, by solving a...
Production of Globular Structure of Al A356, Using Both Electromagnetic Stirrer and Gas induced Semi Solid (GISS) Process
, M.Sc. Thesis Sharif University of Technology ; Aashuri, Hossein (Supervisor)
Abstract
Production of semi solid slurry and creating the globular alloy structure is possible in the ways of Electromagnetic stirring and Gas induced semi solid, which are used widely in industrial scale. Because of the weak magnetic field in the middle part of stirrer, this part is being emptied of melt. As a result, The porous graphite cone is used in this part in order to inject the gas bubbles.In this research, the semi solid A356 Aluminum alloy, is produced under different durations and stirring flux using a three phase Electromagnetic stirrer and injection of the Argon gas. Consequently the slurry was transferred to a mold and compacted by a drop weight. By investigating and analyzing the...
Prediciton of Suspensions Bulk Viscosity Using Immersed Boundary Approach in the Framework of the Lattice Boltzmann Method
, Ph.D. Dissertation Sharif University of Technology ; Taghizadeh Manzari, Mehrdad (Supervisor)
Abstract
In this study, bulk viscosity of suspensions is predicted using numerical simulation.The elaborated numerical method consists of the lattice Boltzmann (LB) method for fluid matrix simulation and the immersed boundary (IB) method for solid boundary implementation. In order to successfully implement the IB method in the frame-work of the LB method, two important challenges, which are body force modeling in the LB method and numerical velocity slip on solid boundaries, are discussed. As a first challenge, body force modeling in the LB method is studied by using a uni-fied framework which has been devised in this study. Using this unified framework,firstly, errors of different body force...
Testing of Workflow Engine Based Systems: A Model-Based Approach
, M.Sc. Thesis Sharif University of Technology ; Mirian Hosseinabadi, Hassan (Supervisor)
Abstract
As the increased use of workflow engine based systems in various domains, quality assurance and testing them has become critical. The majority of these systems are designed and implemented by a workflow language, so testing these systems is highly dependent of workflow language. In this thesis the common domain of business processes is chosen. In this area, little researches have examined the implemened processes with the second version of BPMN modeling language, and most methods, examined another language called BPEL. For this reason and due to the increased use of BPMN language because of its unique characteristics, this study focuses on testing of systems implemented with this language....
The effect of pre-straining at intermediate temperatures on the mechanical behavior of high-bainite dual phase (HBDP) steels
, Article Materials Science and Engineering A ; Volume 543 , May , 2012 , Pages 224-230 ; 09215093 (ISSN) ; Haghshenas Fatmehsari, D ; Ekrami, A ; Sharif University of Technology
2012
Abstract
High-bainite dual phase (HBDP) steels with 34. vol.% ferrite were subjected to tensile strains of 1%, 3%, and 5% at intermediate temperatures (150-450. °C). Mechanical behavior of pre-deformed steels was then investigated at room temperature. A maximum value for both yield stress and ultimate tensile strength was observed for pre-deformed steels. A minimum elongation was also found in the same pre-deformed specimens at the range of 250-350. °C. It was found that dynamic strain aging (DSA) plays the major role in mechanical properties of pre-strained HBDP steels. The DSA indicator parameter (DSAP) was introduced to evaluate DSA mechanism. Maxima of DSAP were likewise observed at the range of...
Evolutions during synthesis of Al-AlN-nanostructured composite powder by mechanical alloying
, Article Journal of Alloys and Compounds ; Volume 461, Issue 1-2 , 11 August , 2008 , Pages 166-172 ; 09258388 (ISSN) ; Salahi, E ; Farnoush, H ; Pourazrang, K ; Sharif University of Technology
2008
Abstract
High-energy milling technique was used to synthesize Al-10 wt.%AlN-nanostructured composite powder in a planetary ball-mill under argon atmosphere up to 25 h. To show the role of AlN particles, process was conducted for monolithic aluminum. The changes in powder characteristics were investigated by time. Microstructure of powders was studied after different milling times by scanning electron microscope (SEM). The morphological evolutions showed that relative equiaxed powder could be synthesized after 25 h milling. Structural analysis was performed by X-ray diffraction method (XRD) to determine the grain sizes and lattice strain. Furthermore, particle size analysis (PSA) revealed the...
The relationship between an EFL teacher's gender and students' willingness to communicate
, Article International Journal of Communication and Linguistic Studies ; Volume 10, Issue 4 , 2013 , Pages 17-29 ; 23277882 (ISSN) ; Pakzadian, S. S
Common Ground Publishing
2013
Abstract
Learning a foreign language encompasses a process of trial and error that can lead to the progression of the learner's interlanguage, meaning that the learners make use of their language knowledge that receives feedback and brings about progress through diagnosis of the problems and being corrected by the teacher. Therefore, there exists a need to analyze the underlying reasons causing the students to remain taciturn with a low willingness to communicate (WTC) during a language class. There has been much work done investigating the role of the learner's stable personal characteristics (traits) along with their situational changes at a specific time (states) that influence the student's...
An automated simple algorithm for realistic pore network extraction from micro-tomography images
, Article Journal of Petroleum Science and Engineering ; Vol. 123, issue , 2014 , pp. 164-171 ; ISSN: 09204105 ; Jamshidi, S ; Salehi, S
2014
Abstract
Using 3-D scanned data to analyze and extract pore network plays a vital role in investigation of porous media's characteristics. In this paper, a new simple method is developed to detect pores and throats for analyzing the connectivity and permeability of the network. This automated method utilizes some of the common and well-known image processing functions which are widely accessible by researchers and this has led to an easy algorithm implementation. In this method, after polishing and quality control of images, using city-block distance function and watershed segmentation algorithm, pores and throats are detected and 3-D network is produced. This method can also be applied on 2-D images...
Discrimination of heart arrhythmias using novel features in heart rate phase space
, Article Computing in Cardiology ; Volume 40 , Sept , 2013 , Pages 1035-1038 ; 23258861 (ISSN); 9781479908844 (ISBN) ; Rezaei, S ; Salavatian, S
2013
Abstract
In this paper, we try to recognize and distinguish different groups of arrhythmia using novel features which have been obtained from the heart rate's phase space in recent years. For this purpose, we used Triangular Phase Space Mapping (TPSM) and Parabolic Phase Space Mapping (PPSM). For recognition, we used three groups of 15 subjects using the Physionet database (Arrhythmia, Congestive Heart Failure (CHF), and Atrial Fibrillation (AF)) with Normal Sinus Rhythm (NSR). The obtained features discriminate arrhythmia from NSR by p
An intelligent hybrid classification algorithm integrating fuzzy rule-based extraction and harmony search optimization: Medical diagnosis applications
, Article Knowledge-Based Systems ; Volume 220 , 2021 ; 09507051 (ISSN) ; Abdullah, S ; Akhavan Niaki, S. T ; Banihashemi, S ; Sharif University of Technology
Elsevier B.V
2021
Abstract
Uncertainty is a critical factor in medical datasets needed to be overcome for increasing diagnosis efficiency. This paper proposes an intelligent classification algorithm comprising a fuzzy rule-based approach, a harmony search (HS) algorithm, and a heuristic algorithm to classify medical datasets intelligently. Two fuzzy approaches, as well as orthogonal and triangular fuzzy sets, are first utilized to define the attributes of data. Then, an HS algorithm is integrated with a heuristic to generate fuzzy rules to select the best rules in the fuzzy rule-based systems. Moreover, to improve the performance of the proposed classification approach, a three-phase parameter tuning approach is...
Performance evaluation of shared hosting security methods
, Article Proc. of the 11th IEEE Int. Conference on Trust, Security and Privacy in Computing and Communications, TrustCom-2012 - 11th IEEE Int. Conference on Ubiquitous Computing and Communications ; 2012 , Pages 1310-1315 ; 9780769547459 (ISBN) ; Arshad, S ; Khoshkdahan, S ; Sharif University of Technology
2012
Abstract
Shared hosting is a kind of web hosting in which multiple websites reside on one webserver. It is cost-effective and makes the administration easier for websites' owners. However, shared hosting has some performance and security issues. In default shared hosting configuration, all websites' scripts are executed under the webserver's user account regardless of their owners. Therefore, a website is able to access other websites' resources. This security problem arises from lack of proper isolation between different websites hosted on the same webserver. In this survey, we have examined different methods for handling mentioned security issue. Also we evaluated the performance of mentioned...
The behaviour of an artificially cemented sandy gravel
, Article Geotechnical and Geological Engineering ; Volume 23, Issue 5 , 2005 , Pages 537-560 ; 09603182 (ISSN) ; Hosseini, S. M ; Toll, D. G ; Yasrebi, S. S ; Sharif University of Technology
2005
Abstract
The major section of the city of Tehran, Iran has been developed on cemented coarse-grained alluvium. This deposit consists of gravely sand to sandy gravel with some cobbles and is dominantly cemented by carbonaceous materials. In order to understand the mechanical behaviour of this soil, a series of undrained triaxial compression tests and unconfined compression tests were performed on uncemented and artificially cemented samples. Portland cement type I was used as the cementation agent for preparing artificially cemented samples. Uncemented samples and lightly cemented samples (1.5% cement) tested at high confining pressure showed contractive behaviour accompanied with positive excess pore...
An imperialist competitive algorithm approach for multi-objective optimization of direct coupling photovoltaic-electrolyzer systems
, Article International Journal of Hydrogen Energy ; Vol. 39, Issue 33 , 11 November , 2014 , pp. 18743-18757 ; ISSN: 03603199 ; Sayedin, F ; Khavas, S. S
2014
Abstract
In the context of sustainable clean hydrogen production pathways, photovoltaic-electrolyzer systems are one of the most promising alternatives for acquiring hydrogen from renewable energy sources. In fact, determining the optimal set of design and operating variables are always a key issue while coupling directly renewable electricity sources to PEM electrolyzers. Few previous studies have attempted to find the optimal size and operational condition of directly coupled photovoltaic-electrolyzer (PV/El) systems in order to maximize the hydrogen production or to minimize energy transfer loss between photovoltaic devices and the electrolyzer. Nevertheless an easy and efficient approach still...
Kalman filter based packet loss replacement in presence of additive noise
, Article 2012 25th IEEE Canadian Conference on Electrical and Computer Engineering: Vision for a Greener Future, CCECE 2012 ; 2012 ; 9781467314336 (ISBN) ; Ghorshi, S ; Tahaei, A
2012
Abstract
A major problem in real-time packet-based communication systems, is misrouted or delayed packets which results in degraded perceived voice quality. If packets are not available on time, the packets are considered as lost. The easiest solution in a network terminal receiver is to replace silence for the duration of lost speech segments. In a high quality communication system, to avoid degradation in speech quality due to packet loss, a suitable method or algorithm is needed to replace the missing segments of speech. In this paper, we introduce an adaptive filter for replacement of lost speech segment. In this method Kalman filter as a state-space based method will be used to predict the...
Investigation of Mesh Sensitivity Influence to Determine Crack Characteristic by Finite Element Methods
, Article Journal of Failure Analysis and Prevention ; Volume 16, Issue 3 , 2016 , Pages 506-512 ; 15477029 (ISSN) ; Mirjavadi, S. S ; Asli, S. A ; Sharif University of Technology
Springer New York LLC
2016
Abstract
In this research, an extended finite element model has been investigated. Investigation of opening and closure stress always has been one of the difficult parameters to analysis of results; therefore, the utilization of finite element methods would be a good and logical alternative for this purpose. In addition, linear elastic fracture criteria are used for validation of numerical results from the simulation. In this work, a detailed analysis of the influence of different parameters in the results of a specific specimen with a semi-elliptical tooling groove in terms of closure and opening stress is presented, and the impact of optimum element size in fracture characteristic in various load...
Investigation of the effect of nanosilica on rheological, thermal, mechanical, structural, and piezoelectric properties of poly(vinylidene fluoride) nanofibers fabricated using an electrospinning technique
, Article Industrial and Engineering Chemistry Research ; Volume 56, Issue 44 , 2017 , Pages 12596-12607 ; 08885885 (ISSN) ; Ahmad Ramazani, S. A ; Talebi, S ; Fattahpour, S ; Hasany, M ; Sharif University of Technology
2017
Abstract
The effects of different nano-SiO2 contents on the rheological properties of poly(vinylidene fluoride) (PVDF) solution and mechanical, thermal, structural, and piezoelectric properties of composite nanofibers were investigated. Results showed an increase in fiber diameter (∼125 to 350 nm) and ∼450% increase in tensile strength as the content of nano-SiO2 particles increased. The degree of crystallinity decreased by 19% as the nano-SiO2 content increased by 2% (w/w). Further investigation demonstrated that silica could significantly improve the piezoelectric properties of PVDF nanofibers as the output voltage showed an increase in the presence of silica attributed to change in the crystalline...
A method for real-time safe navigation in noisy environments
, Article 2013 18th International Conference on Methods and Models in Automation and Robotics, MMAR 2013, Miedzyzdroje ; 2013 , Pages 329-333 ; 9781467355063 (ISBN) ; Kamali, E ; Niknezhad, M. R ; Monfared, S. S. M. S ; Sharif University of Technology
2013
Abstract
The challenge of finding an optimized and reliable path dates back to emersion of mobile robots. Several approaches have been developed that have partially answered this need. Satisfying results in previous implementations has led to an increased utilization of sampling-based motion planning algorithms in recent years, especially in high degrees of freedom (DOF), fast evolving environments. Another advantage of these algorithms is their probabilistic completeness that guarantees delivery of a path in sufficient time, if one exists. On the other hand, sampling based motion planners leave no comment on safety of the planned path. This paper suggests biasing the Rapidly-exploring Random Trees...
A generalization of the swartz equality
, Article Glasgow Mathematical Journal ; Vol. 56, issue. 2 , May , 2014 , pp. 381-386 ; ISSN: 00170895 ; Fakhari, S. A. S ; Yassemi, S ; Sharif University of Technology
2014
Abstract
For a given (d-1)-dimensional simplicial complex Γ, we denote its h-vector by h(Γ)=(h 0(Γ),h 1(Γ),...,hd (Γ)) and set h -1(Γ)=0. The known Swartz equality implies that if Δ is a (d-1)-dimensional Buchsbaum simplicial complex over a field, then for every 0 ≤ i ≤ d, the inequality ihi (Δ)+(d-i+1)h i-1(Δ) ≥ 0 holds true. In this paper, by using these inequalities, we give a simple proof for a result of Terai (N. Terai, On h-vectors of Buchsbaum Stanley-Reisner rings, Hokkaido Math. J. 25(1) (1996), 137-148) on the h-vectors of Buchsbaum simplicial complexes. We then generalize the Swartz equality (E. Swartz, Lower bounds for h-vectors of k-CM, independence, and broken circuit complexes, SIAM J....
Hardware-in-the-loop optimization of an active vibration controller in a flexible beam structure using evolutionary algorithms
, Article Journal of Intelligent Material Systems and Structures ; Vol. 25, issue. 10 , 2014 , p. 1211-1223 ; Hosseini Kordkheili, S. A ; Afshari, S. S ; Sharif University of Technology
2014
Abstract
In this study, active vibration control of a cantilevered flexible beam structure equipped with bonded piezoelectric sensor/actuators is investigated. The linear quadratic regulator technique together with an observer is adopted to design the controller as well as to provide the full-state feedback. Two different approaches are subsequently used for simultaneously integrated optimization of the controller and observer parameters. In the first approach, a linear experimental model of the system is obtained using identification techniques, and the optimization is then performed based on a computer simulation of the system. However, in the second approach, a hardware-in-the-loop optimization...