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Total 194 records

    Endurance time method in the linear seismic analysis of shell structures

    , Article International Journal of Civil Engineering ; Volume 10, Issue 3 , 2012 , Pages 169-178 ; 17350522 (ISSN) Tavazo, H ; Estekanchi, H. E ; Kaldi, P ; Sharif University of Technology
    IJCE  2012
    Abstract
    Endurance Time (ET) method is a response history based analysis procedure that can be used for estimating the seismic response of structures at different excitation levels in each response history. This seismic analysis method utilizes specific intensifying acceleration functions to analyze seismic behaviors. One of the potential applications of the ET method is in the seismic assessment of shell structures. In this study, a procedure for linear seismic analysis of shell structures is proposed and applications of this method is investigated for several cases of shell structures. These structures are analyzed under three ET acceleration functions in one direction and the results are compared... 

    Enhanced electromagnetic wave dissipation features of magnetic Ni microspheres by developing core-double shells structure

    , Article Ceramics International ; Volume 48, Issue 1 , 2022 , Pages 446-454 ; 02728842 (ISSN) Zhang, B ; Mahariq, I ; Tran, N ; Mahmoud, M. Z ; Akhtar, M. N ; Sharif University of Technology
    Elsevier Ltd  2022
    Abstract
    Readily oxidization of magnetic particles is a common drawback of these type of materials which reduce their electromagnetic wave dissipation performance. In this study, the magnetic core-double shells structured (Ni/SiO2/Polyaniline) composite has been developed for protection of the core from oxidation and in consequent improvement the complex permittivity. Solvothermal and in-situ polymerization methods were utilized for decorating Ni micro-particles with SiO2 and conductive polyaniline polymer respectively. All physico-chemical, magnetic and electromagnetic features were evaluated via XRD, FTIR, XPS, FESEM, VSM and VNA analysis. The double shells composite possesses significant... 

    Modeling, Control and Simulation of a Swarm of Robots with Shell Structure

    , M.Sc. Thesis Sharif University of Technology Rezaei, Sina (Author) ; Alasty, Aria (Supervisor)
    Abstract
    Swarm robotics has attracted a lot of researches in recent decades due to its ability to overcome complexities despite of simple hardware used in each member of swarm. Developing control algorithms which can address connection, consensus and average consensus, position control, formation and swarm movement, is one of the main problems in the study of multi-agent systems and swarm robotics. Even though such methods have been developed and used by researchers for a few years, theoretical and operational issues still exist in the use of robotic swarms. For example, in leader-follower method, presence of repellent coordinator agent results in disruption in movement of other agents. Also... 

    Synthesis of Conductive Magnetite Nanocomposite based on Polyaniline/Poly(maleic acid-co-acrylic acid) with Core-Shell Structure

    , Article Advances in Polymer Technology ; 2016 ; 07306679 (ISSN) Khodadadi, F ; Najafi Moghadam, P ; Mahmoodi Hashemi, M ; Sharif University of Technology
    John Wiley and Sons Inc  2016
    Abstract
    In this study, a new type of magnetite nanocomposite with a core-shell structure was synthesized using Fe3O4 nanoparticles as a core and polyaniline (PANI) as a shell. For this propose, the surface of Fe3O4 was chemically modified with hexamethylenediisocyanate (HMDI) to improve its compatibility and interphase interaction with the polymeric matrix. Thereafter, the PANI was reacted with modified Fe3O4 to anchor them to PANI by covalent bands which acted as a shell. In the second step, the poly (maleic acid-co-acrylic acid) (P(MAc-co-AA)) as polymeric dopant for the PANI was synthesized. Finally, the PANI anchored to Fe3O4 was immersed in an aqueous solution of poly (maleic... 

    Characterization of yittria stabilized zirconia/titania core-shell powders synthesized via air plasma spray method

    , Article Materials Chemistry and Physics ; Volume 200 , 2017 , Pages 280-286 ; 02540584 (ISSN) Dadfar, M. R ; Rahimipour, M. R ; Vaezi, M. R ; Gholamzadeh, A ; Sharif University of Technology
    Abstract
    In this study, Yittria Stabilized Zirconia/Titania powders synthesized via air plasma spray (APS) method such as morphology changes and phase transformations of core-shell structure characterized. Phase analysis of powders was performed by XRD. The crystallite size and lattice strain of YSZ/TiO2 core-shell structure was calculated by Williamson-Hall method. Morphology was observed with scanning electron microscope. EDS and map analysis were used for core-shell characterization. Results revealed that all TiO2 nano particles were melted around YSZ powders with the thickness between 1 up to 5 μm. After spraying the YSZ/TiO2 mixture in water, strain values increased but crystallite size... 

    Dispute in photocatalytic and photoluminescence behavior in ZnO/graphene oxide core-shell nanoparticles

    , Article Materials Letters ; Volume 240 , 2019 , Pages 117-120 ; 0167577X (ISSN) Haghshenas, S. S. P ; Nemati, A ; Simchi, A ; Kim, C. U ; Sharif University of Technology
    Elsevier B.V  2019
    Abstract
    ZnO/graphene oxide core-shell nanoparticles (ZGNPs) were prepared by via in-situ chemical synthesis and electrolysis. This report addresses the disagreement in the photocatalytic and photoluminescence behavior in this system. XRD, Raman, HRTEM, PL and UV–Vis were able to confirm ZnO nanoparticles and core-shell structures formation at various temperatures. A little shift was observed in Raman for ZGNPs after conjugating. PL showed a few peaks that were not related to the graphene, which depends on the synthesis route and defects. After conjugating between ZnO and Graphene, two mechanisms are suggested. The first is band structure modification in the boundary of core and shell. The second one... 

    Interlaminar stress analysis of composite shell structures using a geometrically nonlinear layer-wise shell finite element

    , Article Composite Structures ; Volume 257 , 2021 ; 02638223 (ISSN) Soltani, Z ; Hosseini Kordkheili, S. A ; Sharif University of Technology
    Elsevier Ltd  2021
    Abstract
    This work aims to calculate interlaminar stress distribution through the thickness of multilayered composite shell structures by employing a novel nonlinear layer-wise shell finite element formulation. Adapting the Mindlin– Reissner theory in each layer, the shear-deformable layer-wise shell element presents the interlaminar shear stress distributions by increasing the number of layers. The interlaminar normal stress distribution is then determined using the finite difference solution of the general form of equilibrium equation in the non-orthogonal curvilinear grid along the Gaussian points. Two boundary conditions at the bottom and the top surfaces are satisfied by adopting the linear... 

    Numerical evaluation of the ultimate load of concrete funicular shells of circular plan

    , Article Proceedings of the Institution of Civil Engineers: Structures and Buildings ; Volume 174, Issue 1 , 2021 , Pages 5-11 ; 09650911 (ISSN) Javid, A ; Mofid, M ; Sharif University of Technology
    ICE Publishing  2021
    Abstract
    A special type of shell structure - a concrete shallow funicular shell of circular plan - is considered in this paper. Funicular shells carry their dead weight only by in-plane compression forces. Numerical analysis of funicular shells was performed using the non-linear finite-element method, considering both geometric and material non-linearities. A circular-plan concrete funicular shell unit was also constructed and its ultimate central concentrated load is determined. The ultimate load of the shell unit predicted by the numerical model was very close to the experimentally determined ultimate load, thus confirming the validity of the numerical model. The numerical results revealed the... 

    Synthesis, Characterization and Photocatalytic Application of Sol-gel Derived ZnO@CdS Coreshell Nanorods

    , M.Sc. Thesis Sharif University of Technology Zirak, Mohammad (Author) ; Moshfegh, Alireza (Supervisor)
    Abstract
    Synthesis, characterization and photocatalytic applications of core-shell like ZnO@CdS nanorods have been studied in this research. The synthesis of core-shell like ZnO@CdS nanorods was carried out in three different steps. At first, ZnO seed layer was formed on glass substrate via sol-gel process under optimum conditions using absolute ethanol solution containing zinc acetate and a stabilizer ( either Monoethanolamine (MEA) or diethanolamine (DEA)). When MEA used as stabilizer, the optimum concentration of sol was found 0.2 M, while increasing the sol concentration caused the seed layer to be grown in a string-like structure. The RMS surface roughness of seed layer prepared by 0.2 M sol... 

    The Photocatalytic and Photoluminescence Properties of Quasi Core-shell ZnO-graphene Oxide Nanoparticles

    , Ph.D. Dissertation Sharif University of Technology Pourseyed Haghshenas, Siamak (Author) ; Nemati, Ali (Co-Supervisor) ; Simchi, Abdollreza (Co-Supervisor) ; Kim, Choong-Un (Co-Supervisor)
    Abstract
    In this report, a combination of in-situ chemical synthesis and electrolysis methods was applied for the preparation of zinc oxide/graphene quasi core-shell nanoparticles. Pure zinc oxide was also prepared using the same method at different temperatures. The degree of 100 ◦C was selected for synthesizing of ZnO-GO quasi core-shell (zinc oxide as a core and few layer of graphene oxide as a shell). The particle size was 15±2 nm in all samples. In both processes, oxygen was the main reason for the connection between the core and the shell. Unlike chemical process that has all kind of functions in electrolysis process, one kind of function was produced and confirmed by FTIR. XRD patterns also... 

    Photocatalytic and photoluminescence properties of ZnO/graphene quasi core-shell nanoparticles

    , Article Ceramics International ; Volume 45, Issue 7 , 2019 , Pages 8945-8961 ; 02728842 (ISSN) Pourseyed Haghshenas, S ; Nemati, A ; Simchi, R ; Choong Un, C ; Sharif University of Technology
    Elsevier Ltd  2019
    Abstract
    In this paper, a combination of in-situ chemical synthesis and electrolysis methods was applied for the preparation of zinc oxide/graphene oxide quasi core-shell nanoparticles. Pure zinc oxide was also prepared using the same method at different temperatures. 100 °C was selected for synthesizing the ZnO/GO quasi core-shell (zinc oxide as a core and few layers of graphene oxide as a shell). The particle size was 15 ± 2 nm in all samples. In both processes, oxygen was the main reason for the connection between the core and the shell. XRD patterns also confirmed the formation of ZnO (with regular wurtzite structure) and ZnO/GO quasi core-shell structures. Raman spectroscopy results confirmed... 

    Plasma-enhanced chemical vapor deposition for fabrication of yolk-shell SnO2@Void@C nanowires, as an efficient carbon coating technique for improving lithium-ion battery performance

    , Article Materials Science in Semiconductor Processing ; Volume 149 , 2022 ; 13698001 (ISSN) Habibi, A ; Mousavi, M. R ; Yasoubi, M ; Sanaee, Z ; Ghasemi, S ; Sharif University of Technology
    Elsevier Ltd  2022
    Abstract
    This manuscript describes the implementation of plasma-enhanced chemical vapor deposition (DC-PECVD) and vapor-liquid-solid (VLS) techniques to fabricate a yolk-shell SnO2@Void@C nanowire (NW) structure. SnO2 nanowires have been synthesized on the stainless steel mesh substrate through the VLS method. The PECVD-assisted growth of carbon nanolayer on the SnO2 and SiO2 coated SnO2 NWs has been performed to fabricate SnO2@C core-shell and SnO2@SiO2@C yolk-shell structures, respectively. A consequent silica etching process converted the SnO2@SiO2@C into SnO2@Void@C structure. The electrochemical performance of bare SnO2 NWs, SnO2 NWs @ C, and SnO2 @Void @ C coaxial NWs structures have been... 

    Application of Endurance Time Method in Seismic Analysis of RC Cooling Towers

    , M.Sc. Thesis Sharif University of Technology Tavazo, Hassanali (Author) ; Esmaeil Pourestekanchi, Homayoon (Supervisor)
    Abstract
    In the earthquake conditions, the collapse of cooling towers can stop power station activities and heavy financial losses that can be led increasing disaster dimentions finally. In this thesis for analysis of concrete hyperbolic cooling towers and generally for analysis of shell structures, the endurance time (ET) method benefits are used. Also with comparision between ET and standard time history method (THA), accuracy and probable errors of ET method are discussed. It should be noted that ET method is a new time history based method of seismic analysis expect that in this method, structure is imposed under specific intensifying acceleration functions. ET method is capabable for nonlinear... 

    Behavior of a Single-layer Latticed Cylinder Steel Shell with a Long Span under Wind Load

    , M.Sc. Thesis Sharif University of Technology Daghestani, Shahrooz (Author) ; Khalu, Alireza (Supervisor)
    Abstract
    Single-layer steel grid shell structures are a good structural solution to new buildings by specific properties that are required by long-span structures and provide at the same time the opportunity to produce immense verity of design shapes and free form architecture; complex curved surfaces expect to be covered with low weight material. A grid shell is essentially a shell with its structure concentrated into individual linear element in relatively thin grid compared to the overall dimension of the grid shell. This research investigates single-layer grid structures with emphasis on design of load details. The application of single-layer for transparent structures enhances use of glazed... 

    Free vibration analysis of joined cross-ply laminated conical shells

    , Article International Journal of Mechanical Sciences ; Vol. 78, issue , 2014 , pp. 118-125 ; ISSN: 00207403 Kouchakzadeh, M. A ; Shakouri, M ; Sharif University of Technology
    Abstract
    The present study deals with vibrational behavior of two joined cross-ply laminated conical shells. The natural frequencies and mode shapes are investigated. The joined conical shells can be considered as the general case for joined cylindrical-conical shells, joined cylinder-plates or cone-plates, cylindrical and conical shells with stepped thicknesses and also annular plates. Governing equations are obtained using thin-walled shallow shell theory of Donnell type and Hamilton's principle. The appropriate expressions among stress resultants and deformations are extracted as continuity conditions at the joining section of the cones. The equations are solved assuming trigonometric response in... 

    Stability analysis of joined isotropic conical shells under axial compression

    , Article Thin-Walled Structures ; Volume 72 , 2013 , Pages 20-27 ; 02638231 (ISSN) Shakouri, M ; Kouchakzadeh, M. A ; Sharif University of Technology
    2013
    Abstract
    In this study, the buckling of two joined isotropic conical shells under axial compression and simply supported boundary conditions is investigated. The governing equations are obtained using thin-walled shallow shell theory of Donnell-type and theorem of minimum potential energy. The continuity conditions at the joining section of the cones are appropriate expressions among stress resultants and deformations. The equations are solved by assuming trigonometric response in circumferential and series solution in meridional direction. The results are validated in comparison with the available results in the literature. Effects of semi-vertex angles and meridional lengths on the buckling load... 

    Whirling frequencies of thin spinning cylindrical shells surrounded by an elastic foundation

    , Article Acta Mechanica ; Volume 224, Issue 4 , 2013 , Pages 881-892 ; 00015970 (ISSN) Firouz Abadi, R. D ; Torkaman Asadi, M. A ; Rahmanian, M ; Sharif University of Technology
    2013
    Abstract
    In this paper, the whirling frequencies of simply supported and clamped rotating cylindrical shells surrounded by an elastic foundation are investigated. The Love's shell theory is used along with the Winkler foundation to obtain the governing equations of motion. An exact power series solution is obtained for arbitrary boundary conditions and the results are verified with the literature. Several case studies are performed, and the effect of spinning speed, foundation stiffness, and geometrical dimensions of the cylinder on the whirling frequencies are investigated  

    Comparison of natural frequencies of composite cylindrical shells: A squared lattice with its equivalent seamless one

    , Article Proceedings of the ASME Design Engineering Technical Conference, 15 August 2010 through 18 August 2010 ; Volume 5 , 2010 , Pages 835-841 ; 9780791844137 (ISBN) Kargarnovin, M. H ; Jam, J. E ; Hashemian, A. H ; Sharif University of Technology
    Abstract
    Modern Latticed composite materials whose high specific strength and stiffness are utilized in spacecraft and rocket structures to a sufficiently high extent are now widely used in primary airframe structures. In this work a comparison between squared latticed composite cylinder shells and the equivalent hollow cylinder with same weight, outer radius, length and material is done. An analytical equation is derived for natural frequency of square latticed composite shells. The first fifth modes are taken to be compared. The analytical and FEM results are shown and compared to each other. Also, as discussed, the squared lattice cylinder shell reaches to their natural frequencies easily than the... 

    A novel method for production of foamy core@compact shell Ti6Al4V bone-like composite

    , Article Journal of Alloys and Compounds ; Volume 656 , 2016 , Pages 416-422 ; 09258388 (ISSN) Ahmadi, S ; Sadrnezhad, S. K ; Sharif University of Technology
    Elsevier Ltd 
    Abstract
    This paper presents a novel method for fabrication of bone-like Ti6Al4V foamy core@compact shell composite for utilization as substitutive implant for cortical bone having porous core. Seven prototypes with core-diameters of 0, 6, 8, 10, 12, 14 and 16 mm surrounded by dense shells of respective thicknesses 8, 5, 4, 3, 2, 1 and 0 were produced by an innovative two-stage packing/compaction sintering method. Density, porosity, Young's modulus and compression strength of the prototypes depended on the core diameter. Mechanical strength and Young's modulus of 10@16 (10 mm core, 16 mm diameter prototypes) resembled that of the human ulna bone. Creation of foam at the center was achieved by... 

    Free vibration analysis of functionally graded cylindrical shells including thermal effects

    , Article Thin-Walled Structures ; Volume 45, Issue 6 , 2007 , Pages 591-599 ; 02638231 (ISSN) Haddadpour, H ; Mahmoudkhani, S ; Navazi, H. M ; Sharif University of Technology
    2007
    Abstract
    Free vibration analysis of simply supported FG cylindrical shells for four sets of in-plane boundary conditions is performed. The material properties are assumed to be temperature-dependant and gradually changed in the thickness direction of the shell. The effects of temperature rise are investigated by specifying arbitrary high temperature on the outer surface and the ambient temperature on the inner surface of the cylinder. Distribution of temperature across the shell thickness is found from steady state heat conduction only in the thickness direction. The equations of motion are based on Love's shell theory and the von Karman-Donnell-type of kinematic nonlinearity. The static analysis is...