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Total 28 records

    Performance-based assessment of steel jacket platforms by wave endurance time method

    , Article Ships and Offshore Structures ; Oct , 2015 , Page 1-11 ; 17445302 (ISSN) Jahanmard, V ; Diznab, M. A. D ; Mehdigholi, H ; Tabeshpour, M. R ; Seif, M. S ; Sharif University of Technology
    Taylor and Francis Ltd  2015
    Abstract
    In this article, wave endurance time (WET) is addressed as an applicable method for performance-based assessment of fixed offshore structures under extreme waves. In this method, inspired by the endurance time method in the field of earthquake engineering, artificial wave records called wave functions are designed so that their excitations gradually increase with time. Therefore, the main advantage of the proposed method is that it can assess the structural performance under various wave load conditions through a single time-history analysis. Moreover, the reliability of structures can be evaluated on the basis of the time that the structural response is still acceptable. In this study,... 

    Performance-based assessment of steel jacket platforms by wave endurance time method

    , Article Ships and Offshore Structures ; Volume 12, Issue 1 , 2017 , Pages 32-42 ; 17445302 (ISSN) Jahanmard, VR ; Dastan Diznab, M. A ; Mehdigholi, H ; Tabeshpour, M. R ; Seif, M. S ; Sharif University of Technology
    Abstract
    In this article, wave endurance time (WET) is addressed as an applicable method for performance-based assessment of fixed offshore structures under extreme waves. In this method, inspired by the endurance time method in the field of earthquake engineering, artificial wave records called wave functions are designed so that their excitations gradually increase with time. Therefore, the main advantage of the proposed method is that it can assess the structural performance under various wave load conditions through a single time-history analysis. Moreover, the reliability of structures can be evaluated on the basis of the time that the structural response is still acceptable. In this study,... 

    A 32kb 90nm 10T-cell sub-threshold SRAM with improved read and write SNM

    , Article 2013 21st Iranian Conference on Electrical Engineering ; May , 2013 ; 9781467356343 (ISBN) Hassanzadeh, S ; Zamani, M ; Hajsadeghi, K ; Sharif University of Technology
    Abstract
    The constraints of power saving have compelled SRAM designers to consider sub-threshold area as a viable choice. The biggest barrier of this progress is the stability of SRAM's cells and the correct operations. In this paper a 10T cell structure has been proposed with 90% read and 50% write SNM improvement in comparison to the conventional 6T cell. The hold SNM value is about the 6T cell SRAM. Also using differential read method in the proposed structure causes high read performance and using simpler sense amplifier. The symmetric configuration of this structure helps the SRAM has simpler layout and lower transistor mismatch. Using 90nm TSMC CMOS, 32kb 10T cell SRAM in sub-threshold area is... 

    Development of a hybrid reference model for performance evaluation of resolvers

    , Article IEEE Transactions on Instrumentation and Measurement ; Volume 70 , 2021 ; 00189456 (ISSN) Khajueezadeh, M ; Saneie, H ; Nasiri Gheidari, Z ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Abstract
    Resolver is an electromagnetic position sensor typically used in the closed-loop control of permanent magnet synchronous motors (PMSMs). In terms of structure and principle of operation, resolvers are very similar to electrical machines. In this regard, different numerical and analytical models have been developed for the performance prediction of a resolver, with a compromise between computational burden and accuracy. Therefore, a fast and accurate hybrid model of the resolver is presented in this article, which can be used for resolvers with different structures. Additionally, this model can easily be implemented in software such as MATLAB/SIMULINK. The performance of different variable... 

    Distributed multiuser sequential channel sensing schemes in multichannel cognitive radio networks

    , Article IEEE Transactions on Wireless Communications ; Volume 12, Issue 5 , 2013 , Pages 2055-2067 ; 15361276 (ISSN) Shokri Ghadikolaei, H ; Sheikholeslami, F ; Nasiri Kenari, M ; Sharif University of Technology
    2013
    Abstract
    Effective spectrum sensing strategies enable cognitive radios (CRs) to identify and opportunistically transmit on under-utilized spectral resources. In this paper, sequential channel sensing problems for single and multiple secondary users (SUs) networks are effectively modeled through finite state Markovian processes. More specifically, a model for single user case is introduced and its performance is validated through analytical analysis. Then, in order to address multiple SUs case, this model is extended to include the modified p-persistent access (MPPA) protocol. Since the scheme utilized experiences a high level of collision among the SUs, to mitigate the problem appropriately,... 

    Control of gas metal arc welding by an extended DMC

    , Article Proceedings of the IEEE International Conference on Control Applications ; 2012 , Pages 1430-1434 ; 9781467345033 (ISBN) Sartipizadeh, H ; Haeri, M ; Sharif University of Technology
    Abstract
    Efficient control of gas metal arc welding process enables us to have high quality products in consequence of achieving high quality weld. In this paper, an extended dynamic matrix controller is designed and applied on the gas metal arc welding process, which is considered as a nonlinear multi-inputs multi-outputs system. In order to reach a high quality weld, the outputs, welding current and arc length, are effectively controlled by open circuit voltage and wire feed speed. The structure and performance of the proposed controller are discussed in detail, and then a set of simulation results is presented to verify its efficiencies  

    Kinetic Euclidean minimum spanning tree in the plane

    , Article Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) ; Volume 7056 LNCS , 2011 , Pages 261-274 ; 03029743 (ISSN) ; 9783642250101 (ISBN) Rahmati, Z ; Zarei, A ; Sharif University of Technololgy
    2011
    Abstract
    This paper presents the first kinetic data structure (KDS) for maintenance of the Euclidean minimum spanning tree (EMST) on a set of n moving points in 2-dimensional space. We build a KDS of size O(n) in O(nlogn) preprocessing time by which their EMST is maintained efficiently during the motion. In terms of the KDS performance parameters, our KDS is responsive, local, and compact  

    Enhancing the structural performance of masonry arch bridges with ballast mats

    , Article Journal of Performance of Constructed Facilities ; Volume 31, Issue 5 , 2017 ; 08873828 (ISSN) Mohammadzadeh, S ; Miri, A ; Nouri, M ; Sharif University of Technology
    Abstract
    A large portion of the railway bridge stock in many countries is comprised of masonry arch bridges. During recent years, more attention has been paid to the maintenance of such structures. Rehabilitation and retrofitting methods have been proposed to enhance the performance of masonry arch bridges and extend their service life. Because a large portion of forces exerted on such structures comes from the railway track and passing trains, structural elements are added to the track to reduce the forces transmitted to bridges. One such element is the ballast mat, which, according to suppliers, has a positive impact on the structural performance of the track. This paper tries to assess the effects... 

    A study on the effect of SiO2/Al2O3 ratio on the structure and performance of nano-sized ZSM-5 in methanol to propylene conversion

    , Article Reaction Kinetics, Mechanisms and Catalysis ; Volume 121, Issue 2 , 2017 , Pages 763-772 ; 18785190 (ISSN) Jabbari, A ; Abbasi, A ; Zargarnezhad, H ; Riazifar, M ; Sharif University of Technology
    Abstract
    The effect of SiO2/Al2O3 ratio on high silica content nano-sized HZSM-5 stability and selectivity in conversion of methanol to propylene (MTP) has been investigated in a continuous flow isotherm fixed-bed reactor. Highly crystalline HZSM-5 zeolite samples with SiO2/Al2O3 ratios ranging 150–200 have been prepared and characterized using XRD, ICP-AES analytical techniques, NH3-TPD, BET surface area and SEM imaging for studying their physical and chemical behavior. The reaction was conducted at 480 °C and 1bar with WHSV = 1 h−1 and a solution with 1:1 wt% of methanol and water as feed. Over thoroughly monitoring the catalyst synthesis conditions, the nanocrystal ZSM-5 zeolite samples were... 

    Design of viscous fluid passive structural control systems using pole assignment algorithm

    , Article Structural Control and Health Monitoring ; Vol. 21, issue. 7 , July , 2014 , p. 1084-1099 Zare, A. R ; Ahmadizadeh, M ; Sharif University of Technology
    Abstract
    A methodology is developed for the design of optimum viscous fluid passive energy dissipation systems using pole assignment active control algorithm. In this method, the procedure to assign the new structural poles is slightly modified such that the resulting structural properties (i.e., the optimum locations of system poles) can be achieved merely by modification of structural stiffness and addition of a passive control system. A combination of stiffness reduction and increase of damping is utilized to reduce both acceleration and displacement response. It is shown that the control systems designed using this method provide structural performances slightly better than or close to those of... 

    Optimal design of adjustable air-gap, two-speed, capacitor-run, single-phase axial flux induction motors

    , Article IEEE Transactions on Energy Conversion ; Volume 28, Issue 3 , May , 2013 , Pages 543-552 ; 08858969 (ISSN) Nasiri Gheidari, Z ; Lesani, H ; Sharif University of Technology
    2013
    Abstract
    -In this paper, a new optimized structure for two-speed, capacitor-run, single-phase axial flux induction motor (AFIM) for direct-drive operation is presented. Although, there are many advantages for direct-drive systems, their axial forces between the stator and rotor increases with reduction in air-gap length and is of serious concern. An increase in the air-gap length will result in the deterioration of performance characteristics of the motor. In this paper, a new construction technique is proposed to fabricate an AFIM with adjustable air-gap length. After presenting a comprehensive design algorithm, all geometrical dimensions and electrical equivalent circuit parameters are analytically... 

    Simulation of a carbon nanotube field effect transistor with two different gate insulators

    , Article Scientia Iranica ; Volume 20, Issue 6 , 2013 , Pages 2332-2340 ; 10263098 (ISSN) Fallah, M ; Faez, R ; Jafari, A. H ; Sharif University of Technology
    Sharif University of Technology  2013
    Abstract
    In this paper, a novel structure for MOSFET like CNTFETs (MOSCNTs) is proposed, combining the advantages of both high and low dielectrics to improve output characteristics. In this structure, the gate dielectric at the drain side is selected from a material with low dielectric constant to form smaller capacitances, while a material with high dielectric constant is selected at the source side to improve on current and reduce leakage current. The new structure is simulated based on the Schrödinger-Poisson formulation. Obtained results show that the proposed configuration has lower off and higher on current in comparison with low-k MOSCNTs. Also, using a two-dimensional model, a wide range of... 

    Structural health monitoring of buried pipelines under static dislocation and vibration

    , Article Proceedings of 2010 IEEE/ASME International Conference on Mechatronic and Embedded Systems and Applications, MESA 2010, 15 July 2010 through 17 July 2010 ; 2010 , Pages 325-329 ; 9781424471010 (ISBN) Dezfouli, S ; Zabihollah, A ; Sharif University of Technology
    Abstract
    Buried pipe lines are an efficient way of transporting of water, sewage, oil, and gas resources in all over the world. Since the buried pipe lines are exposed to many unexpected conditions, such as landslides, corrosion, fatigue, earthquakes, material flaws or even intentional damaging, so the inspection requirements lead to adoption of new method of maintenance, protection and conserving. This report aims to improve the trustworthiness, reliability, yet economical technologies for monitoring of behavior and manner of buried pipe lines during operation and assessing the risk of pipe lines failure. Distributed sensors (piezoelectric) are surface designed and embedded to investigate the... 

    Multidisciplinary optimization of a car component under NVH and weight constraints using RSM

    , Article 2009 ASME International Mechanical Engineering Congress and Exposition, IMECE2009, Lake Buena Vista, FL, 13 November 2009 through 19 November 2009 ; Volume 15 , 2010 , Pages 315-319 ; 9780791843888 (ISBN) Azadi, M ; Zahedi, F ; Azadi, S ; Moradi, M ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2010
    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 (NVH) etc. In this paper, a multidisciplinary optimization (MDO) of a car back-bonnet is investigated by using trie Response Surface Method (RSM). Firstly, a car body is fully surface modeled in CATIA and meshed in HYPERMESH software. Then, modal analysis of the finite element model is performed by NASTRAN software to find natural frequencies. Frequency map of that component is extracted and compared with a reference map to detect defects. Design of Experiments (DOE) methodologies is used for a... 

    Two quasi orthogonal space-time block codes with better performance and low complexity decoder

    , Article 10th International Symposium on Communication Systems, Networks and Digital Signal Processing, CSNDSP 2016, 20 July 2016 through 23 July 2016 ; 2016 ; 9781509025268 (ISBN) Lotfi Rezaabad, A ; Talebi, S ; Chizari, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    Abstract
    This paper presents two new space time block codes (STBCs) with quasi orthogonal structure for an open loop multi-input single-output (MISO) systems. These two codes have been designed to transmit from three or four antennas at the transmitter and be given to one antenna at the receiver. In this paper first, the proposed codes are introduced and their structures are investigated. This is followed by the demonstration of how the decoder decodes half of transmitted symbols independent of the other half. The last part of this paper discusses the simulation results, makes performance comparison against other popular approaches and concludes that the proposed solutions offer superiority  

    Coreless self-centering braces as retrofitting devices in steel structures

    , Article Journal of Constructional Steel Research ; Volume 133 , 2017 , Pages 485-498 ; 0143974X (ISSN) Attari Dezfuli, M ; Dolatshahi, K. M ; Mofid, M ; Sadeghi Eshkevari, S ; Sharif University of Technology
    Elsevier Ltd  2017
    Abstract
    Conventional lateral resisting systems can provide sufficient strength and ductility for design based earthquakes, although the considerable residual deformation remaining in the plasticized regions undermines the resiliency of the structures. In order to resolve this problem, various self-centering systems have been proposed and tested in recent years, most of which are specified for new buildings and are not simply suitable for retrofitting applications. Moreover, the available self-centering systems are costly and complex to assemble, which can be considered as a serious barrier for practical application. To address these drawbacks, an innovative Core-Less Self-Centering (CLSC) brace is... 

    Probabilistic analysis of soil-structure interaction effects on the seismic performance of structures

    , Article Earthquake Engineering and Structural Dynamics ; Volume 46, Issue 4 , 2017 , Pages 641-660 ; 00988847 (ISSN) Mirzaie, F ; Mahsuli, M ; Ghannad, M. A ; Sharif University of Technology
    Abstract
    This paper revisits the phenomenon of dynamic soil-structure interaction (SSI) with a probabilistic approach. For this purpose, a twofold objective is pursued. First, the effect of SSI on inelastic response of the structure is studied considering the prevailing uncertainties. Second, the consequence of practicing SSI provisions of the current seismic design codes on the structural performance is investigated in a probabilistic framework. The soil-structure system is modeled by the sub-structure method. The uncertainty in the properties of the soil and the structure is described by random variables that are input to this model. Monte Carlo sampling analysis is employed to compute the... 

    Application of endurance time analysis in seismic evaluation of an unreinforced masonry monument

    , Article Journal of Earthquake Engineering ; Volume 21, Issue 2 , 2017 , Pages 181-202 ; 13632469 (ISSN) Chiniforush, A. A ; Estekanchi, H ; Dolatshahi, K. M ; Sharif University of Technology
    Taylor and Francis Ltd  2017
    Abstract
    In this article, seismic behavior of the main dome of a well-known middle-eastern historical- monument, “Imam Reza Shrine” (Mashhad, Iran) which is located in a high seismic area in Iran is evaluated. This study focuses on the response history analysis using intensifying dynamic excitations in the framework of Endurance Time Method. Endurance Time Analysis gives acceptable results for a wide range of earthquake intensities and considerably reduces the computational demand in comparison to the conventional Time History Analysis and Incremental Dynamic Analysis. The aim of this study is to investigate the applicability and efficiency of Endurance Time Analysis for masonry monuments and to... 

    More efficient lateral load patterns for seismic design of steel moment-resisting frames

    , Article Proceedings of the Institution of Civil Engineers: Structures and Buildings ; Volume 171, Issue 6 , 2018 , Pages 472-486 ; 09650911 (ISSN) Moghaddam, H ; Hajirasouliha, I ; Hosseini Gelekolai, S. M ; Sharif University of Technology
    ICE Publishing  2018
    Abstract
    The preliminary design of building structures is normally based on the equivalent lateral forces provided in seismic design guidelines. The height-wise distribution of these loads is predominantly based on elastic vibration modes. However, as structures exceed their elastic limits in severe earthquakes, these design load patterns may not necessarily lead to efficient distribution of strength within the structures. To address this issue, several alternative load patterns have been proposed for the seismic design of non-linear structures. However, due to the simplifications involved in the development of these design load patterns, their adequacy needs to be assessed for different structural... 

    Correlation between structural performance levels and damage indexes in steel frames subjected to earthquakes

    , Article Scientia Iranica ; Volume 16, Issue 2 A , 2009 , Pages 147-155 ; 10263098 (ISSN) Arjomandi, K ; Estekanchi, H ; Vafai, A ; Sharif University of Technology
    2009
    Abstract
    Various damage indexes have been introduced in recent years incorporating different parameters for estimating structural damage. Amongst these indexes, Plastic Ductility and Drift have been the center of attention of standards and building codes, like FEMA-356, because of their straightforward physical interpretation and ease of calculation. In this paper, several steel moment frames have been considered and their responses have been evaluated under a set of scaled earthquakes. A group of various damage indexes, which included cumulative and non cumulative, cyclic fatigue based, deformation based and modal parameter based, has been considered and the damage to structures has been evaluated...