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    Automatic droop control for a low voltage DC microgrid

    , Article IET Generation, Transmission and Distribution ; Volume 10, Issue 1 , 2016 , Pages 41-47 ; 17518687 (ISSN) Khorsandi, A ; Ashourloo, M ; Mokhtari, H ; Iravani, R ; Sharif University of Technology
    Institution of Engineering and Technology 
    Abstract
    A DC microgrid (DC-MG) provides an effective mean to integrate various sources, energy storage units and loads at a common dc-side. The droop-based, in the context of a decentralised control, has been widely used for the control of the DC-MG. However, the conventional droop control cannot achieve both accurate current sharing and desired voltage regulation. This study proposes a new adaptive control method for DC-MG applications which satisfies both accurate current sharing and acceptable voltage regulation depending on the loading condition. At light load conditions where the output currents of the DG units are well below the maximum limits, the accuracy of the current sharing process is... 

    Thermoelastic fields of a functionally graded coated lnhomogeneity with sliding/perfect interlaces

    , Article Journal of Applied Mechanics, Transactions ASME ; Volume 74, Issue 3 , 2007 , Pages 389-398 ; 00218936 (ISSN) Hatami Marbini, H ; Shodja, H. M ; Sharif University of Technology
    2007
    Abstract
    The determination of the thermo-mechanical stress field in and around a spherical/ cylindrical inhomogeneity surrounded by a functionally graded (FG) coating, which in turn is embedded in an infinite medium, is of interest. The present work, in the frame work of Boussinesq/Papkovich-Neuber displacement potentials method, discovers the potential functions by which not only the relevant boundary value problems (BVPs) in the literature, but also the more complex problem of the coated inhomogeneities with FG coating and sliding interfaces can be treated in a unified manner. The thermo-elastic fields pertinent to the inhomogeneities with multiple homogeneous coatings and various combinations of... 

    Enhanced frequency droop method for decentralized power sharing control in DC microgrids

    , Article IEEE Journal of Emerging and Selected Topics in Power Electronics ; Volume 9, Issue 2 , 2021 , Pages 1290-1301 ; 21686777 (ISSN) Jafari, M ; Peyghami, S ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Abstract
    This article proposes two novel approaches to improve the superimposed frequency droop scheme for the control of dc microgrids (MGs). Conventional voltage-based control strategies suffer from issues such as undesirable voltage regulations, poor power sharing among the sources, and negative effects of line resistances on the equivalent droop characteristics. To overcome these challenges, a superimposed frequency droop scheme has been introduced. However, this method suffers from three major issues: 1) instability in terms of load variation, which is due to the location of system dominant poles; 2) limitation in system loading due to the limitation in the transferred reactive power; and 3)... 

    Experimental investigation of life-time performance of unbounded natural rubber bearings as an isolation system in bridges

    , Article Structure and Infrastructure Engineering ; July , 2020 , Pages 1-14 Maghsoudi Barmi, A ; Khaloo, A ; Sharif University of Technology
    Taylor and Francis Ltd  2020
    Abstract
    An experimental research study was carried out to investigate the life-time performance of unbounded Steel Reinforced Elastomeric Bearings (SREB), which are designed and used for service limit state in bridges, subjected to seismic demands. Such behaviour was investigated using 13 full-scale specimens in three phases; (1) effects of long-term service, namely the long term presence of vertical loading at service limit state, on the mechanical properties of the bearings, (2) effects of consecutive shear loading at different amplitude in presence of permanent loading, and (3) post-earthquake behaviour of the bearing against service load conditions. An innovative test setup was utilized in which... 

    A study on the plastic properties of unidirectional nanocomposites with interface energy effects

    , Article Acta Mechanica ; Volume 224, Issue 4 , 2013 , Pages 789-809 ; 00015970 (ISSN) Moshtaghin, A. F ; Naghdabadi, R ; Asghari, M ; Sharif University of Technology
    2013
    Abstract
    In this paper, for obtaining an overall size-dependent yield function for nanocomposites containing aligned cylindrical nanofibers, the effects of interface residual stress and interface elasticity are taken into account within a micromechanical framework. Toward this goal, the modified Hill's condition is used, and then, in order to consider effects of the interface residual stress, strains are decomposed into two parts, a part due to the external loadings and the other due to the interface residual stress. Next, utilizing the field fluctuation method, an overall yield function containing effective elastic constants of the material is derived and then simplified for practical loading... 

    Effects of sex, age, body height and body weight on spinal loads: Sensitivity analyses in a subject-specific trunk musculoskeletal model

    , Article Journal of Biomechanics ; Volume 49, Issue 14 , 2016 , Pages 3492-3501 ; 00219290 (ISSN) Ghezelbash, F ; Shirazi Adl, A ; Arjmand, N ; El Ouaaid, Z ; Plamondon, A ; Meakin, J. R ; Sharif University of Technology
    Elsevier Ltd 
    Abstract
    Subject-specific parameters influence spinal loads and the risk of back disorders but their relative effects are not well understood. The objective of this study is to investigate the effects of changes in age (35–60 years), sex (male, female), body height (BH: 150–190 cm) and body weight (BW: 50–120 kg) on spinal loads in a full-factorial simulation using a personalized (spine kinematics, geometry, musculature and passive properties) kinematics driven musculoskeletal trunk finite element model. Segmental weight distribution (magnitude and location along the trunk) was estimated by a novel technique to accurately represent obesity. Five symmetric sagittal loading conditions were considered,... 

    A combined passive and active musculoskeletal model study to estimate L4-L5 load sharing

    , Article Journal of Biomechanics ; 2017 ; 00219290 (ISSN) Azari, F ; Arjmand, N ; Shirazi Adl, A ; Rahimi Moghaddam, T ; Sharif University of Technology
    Elsevier Ltd  2017
    Abstract
    A number of geometrically-detailed passive finite element (FE) models of the lumbar spine have been developed and validated under in vitro loading conditions. These models are devoid of muscles and thus cannot be directly used to simulate in vivo loading conditions acting on the lumbar joint structures or spinal implants. Gravity loads and muscle forces estimated by a trunk musculoskeletal (MS) model under twelve static activities were applied to a passive FE model of the L4-L5 segment to estimate load sharing among the joint structures (disc, ligaments, and facets) under simulated in vivo loading conditions. An equivalent follower (FL), that generates IDP equal to that generated by muscle... 

    A combined passive and active musculoskeletal model study to estimate L4-L5 load sharing

    , Article Journal of Biomechanics ; Volume 70 , March , 2018 , Pages 157-165 ; 00219290 (ISSN) Azari, F ; Arjmand, N ; Shirazi Adl, A ; Rahimi Moghaddam, T ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    A number of geometrically-detailed passive finite element (FE) models of the lumbar spine have been developed and validated under in vitro loading conditions. These models are devoid of muscles and thus cannot be directly used to simulate in vivo loading conditions acting on the lumbar joint structures or spinal implants. Gravity loads and muscle forces estimated by a trunk musculoskeletal (MS) model under twelve static activities were applied to a passive FE model of the L4-L5 segment to estimate load sharing among the joint structures (disc, ligaments, and facets) under simulated in vivo loading conditions. An equivalent follower (FL), that generates IDP equal to that generated by muscle... 

    Effect of thermal treatment on fracture behavior of solder joints at various strain rates: Comparison of cyclic and constant temperature

    , Article Engineering Failure Analysis ; Volume 128 , 2021 ; 13506307 (ISSN) Honarvar, S ; Nourani, A ; Karimi, M ; Sharif University of Technology
    Elsevier Ltd  2021
    Abstract
    Fracture tests on Sn93Pb37 solder joints in a double cantilever beam (DCB) configuration were performed at two different strain rates of 10−5 and 0.03 s−1 under mode I loading conditions. In each case, the critical strain energy release rate for crack initiation, Jci, was obtained. Effects of storing specimens at a constant temperature of 75 °C and cyclic temperature varying between 32 and 75 °C were examined at these strain rates. In the strain rate of 0.03 s−1, storing samples in a constant or cyclic temperature caused the fracture energy to decrease significantly with respect to the specimens maintained in ambient temperature. The significant reduction in fracture energy by placing the... 

    State estimation, positioning and anti-swing robust control of traveling crane-lifter system

    , Article Applied Mathematical Modelling ; March , 2015 ; 0307904X (ISSN) Moradi, H ; Vossoughi, G ; Sharif University of Technology
    Elsevier Inc  2015
    Abstract
    Under different loading conditions, the over-head cranes may experience a wide range of model parameters variation. A robust control strategy is developed to achieve the high positioning accuracy, short transportation time and suppression of swing angle for an uncertain over-head crane system. Over-head crane is modeled as a three degrees of freedom system and control problem is investigated for two cases: a system with a single control input (the force on trolley) and a system with two control inputs (the force on trolley and the torque on lifter). Regulator and observer systems are designed. To achieve the tracking objectives, an optimal robust controller is designed based on μ-synthesis... 

    Effects of surface residual stress and surface elasticity on the overall yield surfaces of nanoporous materials with cylindrical nanovoids

    , Article Mechanics of Materials ; Volume 51 , 2012 , Pages 74-87 ; 01676636 (ISSN) Moshtaghin, A. F ; Naghdabadi, R ; Asghari, M ; Sharif University of Technology
    Elsevier  2012
    Abstract
    Mechanical properties of a material near the surfaces and interfaces are different from those of the same material far from the surfaces/interfaces. The effect of this difference on the effective mechanical properties of heterogeneous materials becomes significant when the size of inhomogeneities is at the scale of nanometers. In this article, within a micromechanical framework, the effects of surface residual stress and surface elasticity are taken into account to obtain a macroscopic size-dependent yield function for nanoporous materials containing aligned cylindrical nanovoids. Based on the modified Hill's condition, the strains are decomposed into two parts, a part due to the external... 

    Molecular dynamics investigation of β-SiC behavior under three-axial tensile loading

    , Article Journal of Computational and Theoretical Nanoscience ; Volume 8, Issue 11 , 2011 , Pages 2187-2192 ; 15461955 (ISSN) Mortazavi, B ; Simchi, A ; Besharati Givi, M. K ; Rajabpour, A ; Sharif University of Technology
    2011
    Abstract
    Molecular dynamics (MD) simulations were used to study the mechanical behaviour of β-SiC at nano-scale under tensile loading. Effects of loading rate and tensile temperature on the mechanical properties and failure were studied. Modified embedded-atom method (MEAM) potential and Berendsen thermostat were utilized for modelling. Periodic boundary conditions were employed and the behaviour of material was analyzed under three-axial loading condition at which the stress- strain relation was acceptably size independent. It is shown that with increasing the loading rate from 5 m/s to 70 m/s, the failure strain increases without a remarkable change in the stress-strain relationship. The MD... 

    Simulating the crack propagation mechanism of pre-cracked concrete specimens under shear loading conditions

    , Article Strength of Materials ; Volume 47, Issue 4 , July , 2015 , Pages 618-632 ; 00392316 (ISSN) Haeri, H ; Sharif University of Technology
    Springer New York LLC  2015
    Abstract
    The mechanism of crack propagation in concrete specimens containing cracks under shear loading conditions is studied. The shear box test of pre-cracked (double edge cracks) concrete specimens is carried out under laboratory conditions. The higher order displacement discontinuity formulation and the special crack tip elements for the treatment of crack ends is used to numerically simulate the crack propagation mechanism of brittle solids under direct shear loading. A special modeling technique is also proposed to take into account the effect of crack overlapping on the fracturing process of the bridge area in between the two parallel cracks. In this study, the wing cracks are produced at the... 

    State estimation, positioning and anti-swing robust control of traveling crane-lifter system

    , Article Applied Mathematical Modelling ; Volume 39, Issue 22 , 2015 , Pages 6990-7007 ; 0307904X (ISSN) Moradi, H ; Vossoughi, G ; Sharif University of Technology
    Elsevier Inc  2015
    Abstract
    Under different loading conditions, the over-head cranes may experience a wide range of model parameters variation. A robust control strategy is developed to achieve the high positioning accuracy, short transportation time and suppression of swing angle for an uncertain over-head crane system. Over-head crane is modeled as a three degrees of freedom system and control problem is investigated for two cases: a system with a single control input (the force on trolley) and a system with two control inputs (the force on trolley and the torque on lifter). Regulator and observer systems are designed. To achieve the tracking objectives, an optimal robust controller is designed based on μ-synthesis... 

    Prediction of machining chatter based on FEM simulation of chip formation under dynamic conditions

    , Article International Journal of Machine Tools and Manufacture ; Volume 50, Issue 7 , July , 2010 , Pages 611-620 ; 08906955 (ISSN) Mahnama, M ; Movahhedy, M. R ; Sharif University of Technology
    2010
    Abstract
    Machining chatter is an inherently nonlinear phenomenon that is affected by many parameters such as cutting conditions, tool geometry e.g., nose radius and clearance angle and frictional conditions at the tool/workpiece interface. Models for chatter prediction often ignore nonlinearities or introduce them through simple models for friction and geometry. In particular, the effect of chiptool interaction on the occurrence of chatter is not investigated thoroughly. This paper presents a novel approach for prediction of chatter vibration and for investigation of the effects of various conditions on the onset of chatter. This approach uses finite element simulation to investigate the... 

    An analytical approach in dynamic calibration of strain gauge balances for aerodynamic measurements

    , Article IEEE Sensors Journal ; Volume 18, Issue 9 , May , 2018 , Pages 3572-3579 ; 1530437X (ISSN) Bighashdel, A ; Zare, H ; Pourtakdoust, S. H ; Sheikhy, A. A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    Abstract
    Strain gauge balances (SGBs) are efficient and accurate means of static force measurement. However, due to their inherent elastic characteristics, they lack desired performance when used in dynamic loading conditions. In this paper, a novel technique is presented that remedies their inherent weakness in measuring dynamic periodic forces. The proposed method produces a correction factor to compensate the measured loading in dynamic situations. For this purpose, first an analytical investigation is performed to determine the structural dynamic behavior of a typical SGB system via the modal approach. This analytical investigation leads to identification of the structural interference effects... 

    Estimation of human lower extremity musculoskeletal conditions during backpack load carrying

    , Article Scientia Iranica ; Volume 16, Issue 5 B , 2009 , Pages 451-462 ; 10263098 (ISSN) Selk Ghafari, A ; Meghdari, A ; Vossughi, G. R ; Sharif University of Technology
    2009
    Abstract
    This paper focuses on the biomechanical aspects of the human lower extremity loading condition during backpack load carrying. A biomechanical framework was generated with the aim of employing a block-oriented structure of Simulink integrated with the Virtual Reality Toolbox of MATLAB software to provide a simulation study of the musculoskeletal system in a virtual environment. In this case, a ten-degrees-of-freedom musculoskeletal model actuated with sixteen muscles in each leg was utilized to simulate movement in the sagittal plane. An inverse dynamics based optimization approach was employed to estimate the excitation level of the muscles. In addition, distributions of the mechanical power... 

    Constitutive equations for micropolar hyper-elastic materials

    , Article International Journal of Solids and Structures ; Volume 46, Issue 14-15 , 2009 , Pages 2765-2773 ; 00207683 (ISSN) Ramezani, S ; Naghdabadi, R ; Sohrabpour, S ; Sharif University of Technology
    2009
    Abstract
    In this paper, the concept of hyper-elasticity in the micropolar continuum theory is investigated. The restrictions on the fourth-order elasticity tensors are investigated. Using the representation theorems, a general form of constitutive equations for micropolar hyper-elastic isotropic materials is presented. As some special cases, generalizations of the neo-Hookean and Mooney-Rivlin type materials to the micropolar continuum theory are presented. The generalized constitutive equations reduce to those of the microplar linear elasticity theory when the deformations are infinitesimal. Also, Updated Lagrangian finite element formulations for the micropolar hyper-elastic materials are... 

    Modeling IEEE 802.11 DCF using parallel space-time Markov chain

    , Article IEEE Transactions on Vehicular Technology ; Volume 57, Issue 4 , 2008 , Pages 2404-2413 ; 00189545 (ISSN) Ghaboosi, K ; Hosain Khalaj, B ; Xiao, Y ; Latva-aho, M ; Sharif University of Technology
    2008
    Abstract
    Many performance evaluations for the IEEE 802.11 Distributed Coordination Function (DCF) have been previously reported in the literature; most studies are based on saturation analysis, and a few models under a finite-load condition adopt an M/G/1 queuing system. However, using M/G/1 queuing only considers the first moment of the frame service time to derive the probability of the transmission queue being vacant. In this paper, we model the DCF using the parallel space-time Markov chain, where the frame arrivals are tracked by monitoring the transmission queue during transitions between successive states of the space-time Markov chain. The proposed framework provides the possibility of... 

    Room- and high-temperature torsional shear strength of solid oxide fuel/electrolysis cell sealing material

    , Article Ceramics International ; Volume 45, Issue 2 , 2019 , Pages 2219-2225 ; 02728842 (ISSN) Fakouri Hasanabadi, M ; Kokabi, A. H ; Faghihi Sani, M. A ; Groß Barsnick, S. M ; Malzbender, J ; Sharif University of Technology
    Elsevier Ltd  2019
    Abstract
    The structural integrity of the sealant material is critical for the reliability of solid oxide fuel/electrolysis stacks. In the current study, a torsion test is implemented to evaluate and compare its shear strength with a partially crystallized glass sealant at room- and operation relevant high-temperatures. Hourglass-shaped specimens with different configurations of hollow- and full-halves are utilized for testing. The fracture surfaces are visualized via optical microscopy and complementary scanning electron microscopy. In addition, cyclic loading is used to investigate potential subcritical crack growth effects in the sealants. Both, the specimens with a hollow-half as well as the ones...