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Total 647 records

    Comparison of wellbore stability of UBD in the case of laser drilling and conventional operation

    , Article 76th European Association of Geoscientists and Engineers Conference and Exhibition 2014: Experience the Energy - Incorporating SPE EUROPEC 2014 ; 2014 , Pages 1736-1740 ; ISBN: 9781632666949 Bazargan, M ; Nakhaee, A ; Koohian, A ; Irawan, S ; Habibpour, M ; Shahvar, M ; Sharif University of Technology
    Abstract
    In recent years, growing interest in underbalanced drilling has resulted in the rapid development of its associated equipment technology, practices, and procedures. Underbalanced drilling is used to avoid lost circulation, formation damage, and decreasing weight on bit. However, the risk of wellbore collapse due to lake of hydrostatic mud pressure is high; therefore, using good geo-mechanical model may avoid wellbore instability problems. In order to evaluate the potential for wellbore instability, it is necessary to use an elastoplastic model to compute the stresses and strains around the bore hole. Furthermore, it should be mentioned that the laser drilling process depends extremely on the... 

    All-optical controlled switching in centrally coupled circular array of nonlinear optical fibers

    , Article Applied Optics ; Volume 52, Issue 25 , Sep , 2013 , Pages 6131-6137 ; 1559128X (ISSN) Tofighi, S ; Bahrampour, A. R ; Sharif University of Technology
    Optical Society of American (OSA)  2013
    Abstract
    We show that, in a nonlinear centrally coupled circular array of evanescently coupled fibers, the coupling dynamics of a weak signal beam can be efficiently influenced by a high-power control beam that induces nonlinear defects. When the intense control beam is launched into the central core and one core in the periphery, then localized solitons are formed and cause the fibers with induced defects (defected fibers) to decouple from the other array elements. In the presence of a high-intensity control beam, the propagation of weak signal is restricted to the defected optical fibers. The weak signal periodically couples between the induced defects. This oscillatory behavior depends on the sign... 

    Electromechanical resonator based on electrostatically actuated graphene-doped PVP nanofibers

    , Article Nanotechnology ; Volume 24, Issue 13 , 2013 ; 09574484 (ISSN) Fardindoost, S ; Mohammadi, S ; Zad, A. I ; Sarvari, R ; Shariat Panahi, S. P ; Jokar, E ; Sharif University of Technology
    2013
    Abstract
    In this paper we present experimental results describing electrical readout of the mechanical vibratory response of graphene-doped fibers by employing electrical actuation. For a fiber resonator with an approximate radius of 850 nm and length of 100 m, we observed a resonance frequency around 580 kHz with a quality factor (Q) of about 2511 in air at ambient conditions. Through the use of finite element simulations, we show that the reported frequency of resonance is relevant. We also show that the resonance frequency of the fiber resonators decreases as the bias potential is increased due to the electrostatic spring-softening effect  

    Real time simulation of grasping procedure of large internal organs during laparoscopic surgery

    , Article Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS ; Volume 2012 , 2012 , Pages 924-927 ; 1557170X (ISSN) Dehghani Ashkezari, H ; Mirbagheri, A ; Farahmand, F ; Behzadipour, S ; Firoozbakhsh, K ; Sharif University of Technology
    2012
    Abstract
    Surgical simulation systems facilitate safe and efficient training processes of surgical trainees by providing a virtual environment in which the surgical procedure can be repeated unlimitedly in a wide variety of situations. The present study attempted to develop a real time simulation system for the grasping procedure of large internal organs during laparoscopic surgery. A mass-spring-damper model was developed to simulate the nonlinear viscoelastic large deformations of the spleen tissue while interacting with a triple-jaw grasper. A novel collision detection algorithm was designed and implemented to determine the contact points between the tissue and the grasper jaws. Force or... 

    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) Zahedi, E ; 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  

    Neural networks control of autonomous underwater vehicle

    , Article ICMEE 2010 - 2010 2nd International Conference on Mechanical and Electronics Engineering, Proceedings, 1 August 2010 through 3 August 2010 ; Volume 2 , August , 2010 , Pages V2117-V2121 ; 9781424474806 (ISBN) Amin, R ; Khayyat, A. A ; Ghaemi Osgouie, K ; Sharif University of Technology
    2010
    Abstract
    This paper describes a neural network controller for autonomous underwater vehicles (AUVs). The designed online multilayer perceptron neural network (OMLPNN) calculates forces and moments in earth fixed frame to eliminate the tracking errors of AUVs whose dynamics are highly nonlinear and time varying. Another OMLPNN has been designed to generate an inverse model of AUV, which determine the appropriate propeller's speed and control surfaces' angles receiving the forces and moments in the body fixed frame. The designed approximation based neural network controller with the use of the backpropagation learning algorithm has advantages and robustness to control the highly nonlinear dynamics of... 

    Design and development of a hand robotic rehabilitation device for post stroke patients

    , Article Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference ; 2009 , Pages 5026-5029 ; 1557170X (ISSN) Rashedi, E ; Mirbagheri, A ; Taheri, B ; Farahmand, F ; Vossoughi, G. R ; Parnianpour, M ; Sharif University of Technology
    Abstract
    Robot-mediated rehabilitation is a rapidly advancing discipline that seeks to develop improved treatment procedures using new technologies, e.g., robotics, coupled with modern theories in neuroscience and rehabilitation. A robotic device was designed and developed for rehabilitation of upper limbs of post stroke patients. A novel force feedback bimanual working mode provided real-time dynamic sensation of the paretic hand. Results of the preliminary clinical tests revealed a quantitative evaluation of the patient's level of paresis and disability  

    Selecting dryer type using fuzzy logic

    , Article CHISA 2006 - 17th International Congress of Chemical and Process Engineering, Prague, 27 August 2006 through 31 August 2006 ; 2006 ; 8086059456 (ISBN); 9788086059457 (ISBN) Shariati, R. P ; Sharif University of Technology
    2006
    Abstract
    Due to variety of industrial dryers and also importance of selecting appropriate dryer to achieve the required quality of product as well as considering economical aspects, using methods and algorithms which take all effective factors into account and present the best selection is regarded by engineers and researchers. In this paper selection of dryer applying fuzzy logic is presented and the advantages of this method are investigated. For this a program is written using MATLAB programming software and its result compared with real cases. It has been found that there is a good agreement between the prepared program results and industrial experiences. Selection of dryer for a specific... 

    Design of an stable GPC for nonminimum phase LTI systems

    , Article Wec 05: Fourth World Enformatika Conference, Istanbul, 24 June 2005 through 26 June 2005 ; Volume 6 , 2005 , Pages 88-91 ; 9759845857 (ISBN); 9789759845858 (ISBN) Yaghobi, M ; Haeri, M ; Sharif University of Technology
    2005
    Abstract
    The current methods of predictive controllers are utilized for those processes in which the rate of output variations is not high. For such processes, therefore, stability can be achieved by implementing the constrained predictive controller or applying infinite prediction horizon. When the rate of the output growth is high (e.g. for unstable nonminimum phase process) the stabilization seems to be problematic. In order to avoid this, it is suggested to change the method in the way that: first, the prediction error growth should be decreased at the early stage of the prediction horizon, and second, the rate of the error variation should be penalized. The growth of the error is decreased... 

    Iterative interference cancellation for a coded multicarrier frequency-hopping CDMA (MC-FH-CDMA) system

    , Article Scientia Iranica ; Volume 11, Issue 3 , 2004 , Pages 248-254 ; 10263098 (ISSN) M. Ebrahimi, T. M ; Nasiri Kenari, M ; Sharif University of Technology
    Sharif University of Technology  2004
    Abstract
    In this paper a low complexity iterative multi-user receiver for the coded MC-FH-CDMA system, is considered, which has been introduced in [1]. The structure of the proposed receiver consists of a Multi-User Likelihood Calculator (MULC) and a bank of SISO channel decoders, one for each active user. Based on the received signal and a priori information about code bits, provided by SISO decoders in the previous iteration, MULC computes the extrinsic information of the coded symbols of active users in the form of a Log-Likelihood Ratio (LLR). This information is used by channel decoders as a priori information to compute an update of LLRs. The processing proceeds in an iterative manner, similar... 

    Optimum Process Unit Layout via Risk Assessment

    , M.Sc. Thesis Sharif University of Technology Kareshki, Hamid (Author) ; Rashtchian, Davood (Supervisor)
    Abstract
    One of the most important stages to designing a process plant is layout of equipment in unit area. There are plenty of routine procedures to find out equipment arrangement and their separation distances based on process and cost criteria. Although some studies have been carried out to enter safety parameters to conventional procedures, the problem complexity because of the number of involved equipment is still of concern. To clear these ambiguities, the new approach presented in this thesis is aimed at quantifying the effects of adjacent equipment on each other. In this way, fire radiation and explosion have been selected as the major hazard that any equipment can expose on the other items,... 

    Identification And Assessment of Major Risks Associated with Heavy Equipment Transportation in Iranian Oil, Gas and Petrochemical Projects

    , M.Sc. Thesis Sharif University of Technology Seyedi, Amin (Author) ; Eslami, Hossein (Supervisor)
    Abstract
    Transportation of heavy and super heavy equipment is one of the issues that have been discussed in recent years. High cost and required expertise of Transportation for oil and gas projects has caused many organizations and Iranian companies turn to outsourcing strategy and have invested a lot of money in this field without regard to its Risks. Unfortunately, the lack of risk management in transportation projects has led to an increase in refractive index. In this thesis, have been identified the risks of heavy and super-heavy transport equipment in the oil, gas and petrochemical industries then prioritize the risks identified. Finally, each of the identified risks in Iran is investigated.... 

    A novel approach for assessing the impacts of voltage sag events on customer operations

    , Article PQ 2012: 8th International Conference - 2012 Electric Power Quality and Supply Reliability, Conference Proceedings ; 2012 , p. 125-130 ; ISBN: 9781470000000 Yasir, M ; Kazemi, S ; Lehtonen, M ; Fotuhi-Firuzabad, M ; Sharif University of Technology
    Abstract
    The business activities of the majority of industrial and commercial customers are dependent on some critical equipments that are susceptible to voltage sag events. This paper aims to propose a novel approach to estimate the financial impacts of voltage sag events on customer operations. The proposed technique is based on the event tree method. Using this approach, it is possible to consider the impacts of operational failure of various sensitive equipments, involved in the customer operations, on the financial losses expected from voltage sag events. A quantitative case study is conducted in the paper to illustrate the applicability of the proposed approach  

    Modeling and velocity control of a-shape microrobot with adaptive neural network controller

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Vol. 4A, issue , 2014 Nojoumian, M. A ; Shirazi, M. J ; Vossoughi, G. R ; Salarieh, H ; Sharif University of Technology
    Abstract
    Design and control of micro robots have been one of the interesting fields in robotics in recent years. One class of these micro robots is the legged robots. Various designs of legged robots have been proposed in the literature. All designs rely on friction for locomotion. In this paper dynamic model of a planar two-legged micro robot is presented using Luger friction model, and an adaptive neural controller used to control the robot to improve robustness and velocity of the robot. As mentioned earlier, friction plays an important role in locomotion of the legged robots. However, especially in legged micro robots, it is difficult to model the frictional force correctly since environmental... 

    Diesel engine maintenance system, using trend analysis of histroical data

    , Article Advanced Materials Research, 16 September 2011 through 18 September 2011, Singapore ; Volume 383-390 , September , 2012 , Pages 6755-6761 ; 10226680 (ISSN) ; 9783037852958 (ISBN) Sayyah, A ; Nikbakht, M ; Sayyah, M ; Baharudin, B. T .H. T ; Ismail, N ; Singapore Institute of Electronics ; Sharif University of Technology
    2012
    Abstract
    Contaminant materials in lubricants are signs for prediction and measurement of wear in engines. Therefore oil monitoring is considered as one of the most effective techniques for maintaining the heavy equipments. However based on oil analysis data, the identification of engine problem is very hard due to different contribution factors. Hence, this paper is purposed to analyze the wear behavior of some sets of selected heavy equipment engine based on documented oil analysis data during two years in different conditions to track engine failures using trend analysis. Furthermore the selected equipments are divided into two major groups (plantation and forestry, and general construction) based... 

    Two-dimensional warranty cost analysis for second-hand products

    , Article Communications in Statistics - Theory and Methods ; Volume 40, Issue 4 , 2011 , Pages 684-701 ; 03610926 (ISSN) Shafiee, M ; Chukova, S ; Saidi-Mehrabad, M ; Niaki, S. T. A ; Sharif University of Technology
    2011
    Abstract
    In spite of the recent steady increase of the volume of the second-hand markets, often customers remain in doubt regarding the quality and durability of the secondhand products. Aiming to reduce and share this uncertainty, dealers offer warranty on their products. Offering warranty for second-hand products is a relatively new marketing strategy employed by dealers of used electronic equipment, furniture, automobiles, etc. Usually, for used products, the dealer's expected warranty cost is a function of product reliability, past age and usage, servicing strategy and conditions and terms of the warranty policy/contract. Sometimes the offered policy is limited by two parameters, typically the... 

    DC partial discharge characteristics for corona, surface and void discharges

    , Article Proceedings of the IEEE International Conference on Properties and Applications of Dielectric Materials, 19 July 2015 through 22 July 2015 ; Volume 2015-October , July , 2015 , Pages 260-263 ; 9781479989034 (ISBN) Rahimi, M. R ; Javadinezhad, R ; Vakilian, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Abstract
    Measurement of partial discharges (PDs) current pulses is found to be one of the most efficient methods to evaluate the high voltage electrical equipment insulation condition. Generators, transformers, cables and transmission lines are especially tested for the presence of PDs. In AC, the solution is well known. Phase-resolved method can be used to detect and determine partial discharge activities. Although phase-resolved method works well under AC voltage; due to lack of a cyclic variation in DC voltage and current this cannot be used when studying partial discharges in DC voltage systems. Therefore, other methods are employed to interpret the partial discharge in DC. For this purpose, the... 

    Structure-aware online virtual machine consolidation for datacenter energy improvement in cloud computing

    , Article Computers and Electrical Engineering ; Volume 42 , 2015 , Pages 74-89 ; 00457906 (ISSN) Esfandiarpoor, S ; Pahlavan, A ; Goudarzi, M ; Sharif University of Technology
    Abstract
    The necessity and significance of improving the energy efficiency of cloud implementations have increased due to the rapid growth and proliferation of cloud computing services around the world. Virtual machines (VMs) comprise the backend of most, if not all, cloud computing services. Several VMs are often consolidated on a physical machine to efficiently utilize its resources. In this paper, we take into account the cooling and network structure of the datacenter host ing the physical machines when consolidating the VMs so that fewer racks and routers are employed, without compromising the service-level agreements; consequently, idle routing and cooling equipment can be turned off in order... 

    Designing a LQR controller for an electro-hydraulic-actuated-clutch model

    , Article Proceedings of 2016 2nd International Conference on Control Science and Systems Engineering, ICCSSE 2016, 27 July 2016 through 29 July 2016 ; 2016 , Pages 82-87 ; 9781467398725 (ISBN) Pourebrahim, M ; Selk Ghafari, A ; Pourebrahim, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    Abstract
    During the past decade, Electro-Hydraulic system has performed a significant role in industrial engineering as an actuator for high performance and precision positioning applications. In this case, many control methods have been developed for an electro-hydraulic actuated clutch. In this paper a Linear Quadratic Regulators (LQR) is proposed to trajectory control of a wet clutch actuated by a hydraulic servo valve mechanism. Simulation study was performed using linearized mathematical model of the system implemented in MATLAB software. Based on the simulation results performance of the proposed controller was evaluated and discussed  

    Project scheduling and equipment planning with random breakdowns

    , Article RAIRO - Operations Research ; Volume 51, Issue 4 , 2017 , Pages 1189-1209 ; 03990559 (ISSN) Shafikhani, A ; Najafi, A. A ; Akhavan Niaki, S. T ; Sharif University of Technology
    Abstract
    Most of the research works conducted on Project Scheduling Problem (PSP) especially Resource Constrain Project Scheduling Problem (RCPSP) either ignore equipment planning or schedule the activities first, and then plan for the required equipment. Moreover, little works that consider simultaneous PSP and Equipment Planning (EP) are based on the assumption that the equipment is continuously available. However, in reality, equipment is subject to either random breakdowns or deterministic maintenance programs that make it not being available all the time. In this paper, the PSP and EP problems are simultaneously considered in closer to reality situations in which the equipment is not always...