Search for: aspect-ratio
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    Viscous damping effect on the aeroelastic stability of subsonic wings: Introduction of the U–K method

    , Article Journal of Fluids and Structures ; Volume 73 , 2017 , Pages 1-15 ; 08899746 (ISSN) Beheshtinia, F ; Dehghani Firouz Abadi, R ; Rahmanian, M ; Sharif University of Technology
    This study aims at introduction of a novel method for evaluating the effect of viscous damping on the aeroelastic stability boundaries. The K-method is well-known for being one of the fastest methods in determining the instability conditions (i.e. critical speed and its corresponding frequency). However, formulation of the K-method is developed for aeroelastic systems without viscous damping and solution is valid where the introduced artificial damping is zero. Taking into account the framework of the K-method in general, this study has tried to remove the major shortcoming of the K-method, i.e. investigation of the effect of viscous damping on the aeroelastic stability boundaries. The... 

    Influence of main and outer wings on aerodynamic characteristics of compound wing-in-ground effect

    , Article Aerospace Science and Technology ; Volume 55 , 2016 , Pages 177-188 ; 12709638 (ISSN) Tavakoli Dakhrabadi, M ; Seif, M. S ; Sharif University of Technology
    Elsevier Masson SAS 
    A practical mathematical model with low computational time and good accuracy is applied to investigate theaerodynamic characteristics and static height stability of the compound wing-in-ground effect (WIG). The compound WIG consists of a main wing with low aspect ratio and an endplate, and anouter wing with high aspect ratio. To validate the present mathematical model, a numerical simulation is performed so thatnumerical results had a good agreement with the experimental data. The analysis shows that the main wing is useful in the extreme ground effect zone and the outer wing enhances performance of the compound WIG in the weak ground effect zone. In order to satisfy the static height... 

    The UV photodetection enhancement of tailored ZnO nanorods by controlling the aspect ratio

    , Article Surfaces and Interfaces ; Volume 28 , 2022 ; 24680230 (ISSN) Nazari, N. F ; Rajabi, M ; Moshfegh, A. Z ; Sharif University of Technology
    Elsevier B.V  2022
    ZnO Nanorods (NRs) are deposited on glass substrate using the hydrothermal method by applying a strategic growth control to improve their aspect ratios. In this research, the aspect ratio was tuned by tailoring the synthesis parameters, including the seed layer annealing temperature, absence/presence of polyethylenimine (PEI) in the growth solution, and the solution preheating process. The effects of these parameters on the morphology, crystal structure, room temperature photoluminescence properties, and current-voltage characteristics were examined by FESEM, XRD, PL, and I-V measurements. It was demonstrated that by varying the seed layer annealing temperature and presence of PEI solution... 

    Electroosmotic flow and ionic conductance in a pH-regulated rectangular nanochannel

    , Article Physics of Fluids ; Volume 29, Issue 6 , 2017 ; 10706631 (ISSN) Sadeghi, M ; Saidi, M. H ; Sadeghi, A ; Sharif University of Technology
    Infinite series solutions are obtained for electrical potential, electroosmotic velocity, ionic conductance, and surface physicochemical properties of long pH-regulated rectangular nanochannels of low surface potential utilizing the double finite Fourier transform method. Closed form expressions are also obtained for channels of large height to width ratio for which the depthwise variations vanish. Neglecting the Stern layer impact, the effects of EDL (Electric Double Layer) overlap, multiple ionic species, and association/dissociation reactions on the surface are all taken into account. Moreover, finite-element-based numerical simulations are conducted to account for the end effects as well... 

    Numerical investigation of nozzle geometry effect on turbulent 3-D water offset jet flows

    , Article Journal of Applied Fluid Mechanics ; Volume 9, Issue 4 , 2016 , Pages 2083-2095 ; 17353572 (ISSN) Mohammad Aliha, N ; Afshin, H ; Farahanieh, B ; Sharif University of Technology
    Isfahan University of Technology  2016
    Using the Yang-Shih low Reynolds k-ε turbulence model, the mean flow field of a turbulent offset jet issuing from a long circular pipe was numerically investigated. The experimental results were used to verify the numerical results such as decay rate of streamwise velocity, locus of maximum streamwise velocity, jet half width in the wall normal and lateral directions, and jet velocity profiles. The present study focused attention on the influence of nozzle geometry on the evolution of a 3D incompressible turbulent offset jet. Circular, square-shaped, and rectangular nozzles were considered here. A comparison between the mean flow characteristics of offset jets issuing from circular and... 

    Buoyancy effects on gaseous slip flow in a vertical rectangular microchannel

    , Article Microfluidics and Nanofluidics ; Vol. 16, issue. 1-2 , 2014 , pp. 207-224 ; ISSN: 16134982 Sadeghi, M ; Sadeghi, A ; Saidi, M. H ; Sharif University of Technology
    Consideration is given to the buoyancy effects on the fully developed gaseous slip flow in a vertical rectangular microduct. Two different cases of the thermal boundary conditions are considered, namely uniform temperature at two facing duct walls with different temperatures and adiabatic other walls (case A) and uniform heat flux at two walls and uniform temperature at other walls (case B). The rarefaction effects are treated using the firstorder slip boundary conditions. By means of finite Fourier transform method, analytical solutions are obtained for the velocity and temperature distributions as well as the Poiseuille number. Furthermore, the threshold value of the mixed convection... 

    Pressure effects on electroosmotic flow of power-law fluids in rectangular microchannels

    , Article Theoretical and Computational Fluid Dynamics ; Vol. 28, issue. 4 , 2014 , pp. 409-426 ; ISSN: 09354964 Vakili, M. A ; Sadeghi, A ; Saidi, M. H ; Sharif University of Technology
    In this paper, the fully developed electroosmotic flow of power-law fluids in rectangular microchannels in the presence of pressure gradient is analyzed. The electrical potential and momentum equations are numerically solved through a finite difference procedure for a non-uniform grid. A complete parametric study reveals that the pressure effects are more pronounced at higher values of the channel aspect ratio and smaller values of the flow behavior index. The Poiseuille number is found to be an increasing function of the channel aspect ratio for pressure assisted flow and a decreasing function of this parameter for pressure opposed flow. It is also observed that the Poiseuille number is... 

    Joule heating effects in electrokinetically driven flow through rectangular microchannels: An analytical approach

    , Article Nanoscale and Microscale Thermophysical Engineering ; Volume 17, Issue 3 , 2013 , Pages 173-193 ; 15567265 (ISSN) Sadeghi, A ; Kazemi, Y ; Saidi, M. H ; Sharif University of Technology
    This is a theoretical study dealing with mixed electroosmotic and pressure-driven flow of a Newtonian liquid in a rectangular microchannel. Both and thermal boundary conditions are considered and the Debye-Hückel linearization is invoked. The governing equations are made dimensionless assuming fully developed conditions and then analytically solved using an infinite series solution. The governing factors are found to be the dimensionless Debye-Hückel parameter, velocity scale ratio, dimensionless Joule heating parameter, and channel aspect ratio. The results indicate that the Nusselt number is an increasing function of the channel aspect ratio, whereas the opposite is true for the velocity... 

    Study of Biomolecules Imaging Using Molecular Dynamics Simulations

    , Article Nano ; Volume 10, Issue 7 , October , 2015 ; 17932920 (ISSN) Kheirodin, M ; Nejat Pishkenari, H ; Moosavi, A ; Meghdari, A ; Sharif University of Technology
    World Scientific Publishing Co. Pte Ltd  2015
    The process of imaging a biomolecule by atomic force microscope (AFM) is modeled using molecular dynamics (MD) simulations. Since the large normal force exerted by the tip on the biosample in contact and tapping modes may damage the sample structure and produce irreversible deformation, the noncontact mode of AFM (NC-AFM) is employed as the operating mode. The biosample is scanned using a carbon nanotube (CNT) as the AFM probe. CNTs because of their small diameter, high aspect ratio and high mechanical resistance attract many attentions for imaging purposes. The tip-sample interaction is simulated by the MD method. The protein, which has been considered as the biomolecule, is ubiquitin and a... 

    Axis-switching and breakup of rectangular liquid jets

    , Article International Journal of Multiphase Flow ; Volume 126 , May , 2020 Morad, M. R ; Nasiri, M ; Amini, G ; Sharif University of Technology
    Elsevier Ltd  2020
    The behavior of low-speed liquid jets emerging from rectangular orifices into a quiescent air is studied numerically. After ejection, the rectangular cross-section transforms into an elliptical form along the jet and while axis-switching includes elliptical cross-sections only, the rectangular shape never establishes again. The optimum wavenumber, corresponding to the most dominant wave, is found to be greater in orifices with higher aspect ratios and, as a result, breakup length of the jet will be shorter. The breakup length decreases exponentially with the initial amplitude of disturbances. Moreover, it is observed that the form of final breakup leads to elimination of the satellite... 

    The effect of nanopores geometry on desalination of single-layer graphene-based membranes: A molecular dynamics study

    , Article Journal of Molecular Liquids ; Volume 339 , 2021 ; 01677322 (ISSN) Sarvestani, A. B ; Chogani, A ; Shariat, M ; Moosavi, A ; Kariminasab, H ; Sharif University of Technology
    Elsevier B.V  2021
    The water desalination process using nanoporous single-layer graphene membranes is simulated through classical molecular dynamics. The effect of nanopores shapes on the capacity of the membrane for filtration of water is investigated. According to the results, the geometry of the nanopores considerably affects the performance of the membrane and can completely change the water flow rate and salt rejection. The results reveal that the effective area of the nanopores plays a critical role and for a better understanding of the impact of this parameter, aspect ratio and the equal diameter of noncircular pores based on different methods such as equal area, equal perimeter, and hydraulic diameter... 

    Aeroelastic optimization of the high aspect ratio wing with aileron

    , Article Computers, Materials and Continua ; Volume 70, Issue 3 , 2022 , Pages 5569-5581 ; 15462218 (ISSN) Ghalandari, M ; Mahariq, I ; Ghadak, F ; Accouche, O ; Jarad, F ; Sharif University of Technology
    Tech Science Press  2022
    In aircraft wings, aileron mass parameter presents a tremendous effect on the velocity and frequency of the flutter problem. For that purpose, we present the optimization of a composite design wing with an aileron, using machine-learning approach. Mass properties and its distribution have a great influence on the multi-variate optimization procedure, based on speed and frequency of flutter. First, flutter speed was obtained to estimate aileron impact. Additionally mass-equilibrated and other features were investigated. It can deduced that changing the position and mass properties of the aileron are tangible following the speed and frequency of the wing flutter. Based on the proposed... 

    Evaluating of Geometric Factors Effects on Seakeeping Performance of HARTH Vessels

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Mostafa (Author) ; Seif, Mohammad Saeed (Supervisor)
    Performing research and development in the field of modern vessel types which serve several functions is considerably necessary because of their importance and rapid development. HARTH vessel is considered one of the important ships which has been recently attracted much attention from the world. In this respect, a full investigation of its performance could make a big contribution to its optimum design and appropriate exploitation.“HARTH” ship is the abbreviation for “High Aspect Ratio Twin Hull” is included in the catamaran vessel category with a high aspect ratio with respect to their underwater cross-section’s ratio of length to width.A host of crucial issues should be considered for... 

    An efficient method for nonlinear aeroelasticy of slender wings

    , Article Nonlinear Dynamics ; Volume 67, Issue 1 , 2012 , Pages 659-681 ; 0924090X (ISSN) Shams, S ; Sadr, M. H ; Haddadpour, H ; Sharif University of Technology
    This paper aims the nonlinear aeroelastic analysis of slender wings using a nonlinear structural model coupled with the linear unsteady aerodynamic model. High aspect ratio and flexibility are the specific characteristic of this type of wings. Wing flexibility, coupled with long wingspan can lead to large deflections during normal flight operation of an aircraft; therefore, a wing in vertical/forward-afterward/torsional motion using a third-order form of nonlinear general flexible Euler-Bernoulli beam equations is used for structural modeling. Unsteady linear aerodynamic strip theory based on the Wagner function is used for determination of aerodynamic loading on the wing. Combining these... 

    A comprehensive study on the critical ventilation velocity in tunnels with different geometries

    , Article International Journal of Ventilation ; Volume 14, Issue 3 , Mar , 2015 , Pages 303-320 ; 14733315 (ISSN) Kazemipour, A ; Afshin, H ; Farhanieh, B ; Sharif University of Technology
    VEETECH Ltd  2015
    Longitudinal ventilation is a common technique for smoke management during a fire accident within tunnels. In this paper, fire and smoke movement behaviour in longitudinally ventilated tunnels is investigated focusing on critical ventilation velocity. Firstly, critical velocity (VC) is evaluated for different heat release rates and results are compared and verified with model scale experimental data. Secondly, two fire scenarios inside tunnels with different cross sections are arranged and the reliability of some existing correlations for VC is explored. Results illustrate that using a combined geometric scale rather than the traditional single length-scale ones results in better estimation... 

    The effect of soil-structure interaction on hysteretic energy demand of buildings

    , Article Structural Engineering and Mechanics ; Volume 24, Issue 5 , 2006 , Pages 641-645 ; 12254568 (ISSN) Nakhaei, M ; Ghannad, M. A ; Sharif University of Technology
    Techno-Press  2006
    The effect of soil-structure interaction (SSI) on hysteresis energy demand of buildings using an ensemble of alluvium site records was investigated. The structure and the soil were molded separately and then combined to constitute the soil-structure model using the sub-structure method. The key parameters effecting the response of the soil-structure system were found to be a non-dimensional frequency as a representative of structure to soil stiffness ratio; and aspect ratio of the building. It was found that the hysteric energy dissipated in a structure under an earthquake can be highly effected when the stiffness of the soil beneath the structure is altered  

    Effect of varying aspect ratio on relative stability for graphene nanoribbon interconnects

    , Article Applied Mechanics and Materials, 24 July 2012 through 26 July 2012 ; Volume 229-231 , November , 2012 , Pages 205-209 ; 16609336 (ISSN) ; 9783037855102 (ISBN) Farrokhi, M ; Faez, R ; Nasiri, S. H ; Davoodi, B ; Sharif University of Technology
    Achieving dense off-chip interconnection with satisfactory electrical performance is emerging as a major challenge in advanced system engineering. Graphene nanoribbons (GNRs) have been recently proposed as one of the potential candidate materials for both transistors and interconnect. In addition, development is still underway for alternative materials and processes for high aspect ratio (AR) contacts. Studding the effect of varying aspect ratio on relative stability of graphene nanoribbon interconnects is an important viewpoint in performance evaluation of system. In this paper, Nyquist stability analysis based on transmission line modeling (TLM) for GNR interconnects is investigated. In... 

    Corrected formulation for estimation of ripple in large aspect ratio tokamaks

    , Article Journal of Fusion Energy ; Volume 31, Issue 2 , 2012 , Pages 195-197 ; 01640313 (ISSN) Dini, F ; Khorasani, S ; Sharif University of Technology
    The finite number of toroidal field coils of a tokamak destroys the perfect axisymmetry of the device. The coils produce a short wavelength ripple in the toroidal magnetic field strength as a field line follows round the torus, which becomes important in transport and confinement properties of plasma. Hence, a quick and accurate estimation of ripple becomes important. We have noticed that a previously reported analytical formulation by Princeton Plasma Physics Laboratory team is not applicable to our large aspect ratio tokamak, and have devised a slightly modified form which has greatly improved the accuracy of the analytical fit  

    Determination of Protein Absorption Profile at the Surface of Biocompatible Superparamagnetic Iron Oxide Nanoparticles using Gel Electrophoresis

    , M.Sc. Thesis Sharif University of Technology Ghasemi, Forough (Author) ; Hormozi Nezhad, Mohammad Reza (Supervisor) ; Mahmoudi, Morteza (Supervisor)
    Superparamagnetic Iron Oxide NPs (SPIONs) because of their multi-task capabilities (e.g. magnetic labeling, cell isolation, hyperthermiaand controlled drug release) have been recognized as one of the most promising NPs for theranosis applications.When NPs come in contact with a biological medium, the surfaces of them are covered by biomolecules (e.g., proteins, natural organic materials, and enzymes). Therefore, what a biological entity, such as cells, tissues, and organs, sees when interacting with NPs is different original pristine surface of the NPs and actually is hard protein corona. Shape of NPs has a great impact on proteins adsorb onto its surface and consequently on the way that... 

    Investigating the Effects of Specimen Size and Dimensions Ratio on Compressive Strength of Concrete

    , M.Sc. Thesis Sharif University of Technology Zabihi, Alireza (Author) ; Kazemi, Mohammad Tagi (Supervisor)
    Concrete is one of the most widely used building materials. Compressive strength of concrete is the most important property in designing reinforced concrete structures. Compressive strength test should be carried out on specimens with standard dimensions. In practice, dimensions of structural elements could be different from the dimensions of standard specimen. The dimensions’ ratio influences the strength of concrete specimen and the coefficient of strength variation. In the present study it is tried to obtain a meaningful relationship between size and strength based on the results of the tests on the specimens with different dimension ratios. Specimens examined in this study are C25 grade...