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    Dynamic based cost functions for TF/TA flights

    , Article IEEE Transactions on Aerospace and Electronic Systems ; Volume 48, Issue 1 , 2012 , Pages 44-63 ; 00189251 (ISSN) Malaek, S. M ; Kosari, A. R ; Sharif University of Technology
    Abstract
    In this work we present a systematic approach to incorporating the dynamic capabilities of an aircraft via suitable cost functions while planning for terrain following-terrain avoidance trajectories. We further show that use of nondimensional parameters related to the dynamics of an aircraft within the cost function provides a better understanding of how they could affect the resulting trajectories. Different case studies for arbitrary three-dimensional flights show that the current approach provides more realistic trajectories and so helps alleviate the design process of relevant controllers as well as tracking systems over the desired terrain. We further introduce two new parameters of... 

    Formation and breakup patterns of falling droplets

    , Article Numerical Heat Transfer; Part A: Applications ; Volume 68, Issue 9 , Jun , 2015 , Pages 1023-1030 ; 10407782 (ISSN) Sharafatmandjoor, S ; Taeibi Rahni, M ; Azwadi Che Sidik, N ; Sharif University of Technology
    Taylor and Francis Ltd  2015
    Abstract
    Some interface front patterns of falling droplets are studied via direct numerical solution of the full Navier-Stokes equations governing the system of droplets and the ambient surrounding media as a single-fluid model. We focus on the mutual interactions of the effects of characterizing nondimensional parameters on the formation and break-up of large cylindrical droplets. The investigation of droplet cross sections and deformation angles shows that for moderate values of the Atwood number, increasing the Eötvös number explicitly increases the deformation rate in formation and breakup phenomena. Otherwise, increasing the Ohnesorge number basically amplifies the viscous effects  

    Oscillatory behavior of the nonlinear clamped-free beam microgyroscopes under electrostatic actuation and detection

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 10 , 2013 ; 9780791856390 (ISBN) Mojahedi, M ; Firoozbakhsh, K ; Ahmadian, M. T ; Barari, A ; ASME ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2013
    Abstract
    Vibratory micromachined gyroscopes use suspending mechanical parts to measure rotation. They have no gyratory component that require bearings, and for this reason they can be easily miniaturized and batch production using micromachining methods. They operate based on the energy interchange between two modes of structural vibration. The objective of this paper is to study the oscillatory behavior of an electrostatically actuated vibrating microcantilever gyroscope with proof mass at its end. In the modelling, the effects of different nonlinearities, fringing field and base rotation are considered. The microgyroscope is subjected to coupled bending oscillations around the static deflection... 

    Equivalent linear model for existing soil-structure systems

    , Article International Journal of Structural Stability and Dynamics ; Volume 16, Issue 2 , 2016 ; 02194554 (ISSN) Sameti, A. R ; Ghannad, M. A ; Sharif University of Technology
    World Scientific Publishing Co. Pte Ltd 
    Abstract
    The concept of equivalent linearization is extended for the soil-structure systems, in which the strength ratio (defined as the ratio of the yielding strength to the elastic strength demand) is known rather than the ductility ratio. The nonlinear soil-structure system is replaced by a linear single-degree-of-freedom (SDOF) system, which can capture the response of the actual system with sufficient accuracy. The dynamic characteristics of the equivalent linear SDOF system are determined through a statistical approach. The super-structure is modeled by an inelastic SDOF system with bilinear behavior, and the homogeneous half space beneath the structure by a discrete model, following the Cone... 

    A new non-dimensional parameter to obtain the minimum mixing length in tree-like concentration gradient generators

    , Article Chemical Engineering Science ; Volume 195 , 2019 , Pages 120-126 ; 00092509 (ISSN) Rismanian, M ; Saidi, M. S ; Kashaninejad, N ; Sharif University of Technology
    Elsevier Ltd  2019
    Abstract
    Microfluidic-based concentration gradient generators (CGGs) have a number of applications in chemical, biological and pharmaceutical studies. Thus, precise design of the microfluidic system is crucial to maintaining the desired concentration gradient in microchannels. One of the design considerations is the length of microchannels in the structure of a CGG. A CGG with a short length fails to provide the complete diffusive mixing, while the size of the microchip would unfavorably increase by incorporating a long CGG. Considering a CGG as a tree-like structure consisting of T-shaped micromixers, the mixing process of the species at a straight microchannel has been solved analytically. Herein,... 

    The effect of soil-structure interaction on damage index of buildings

    , Article Engineering Structures ; Volume 30, Issue 6 , 2008 , Pages 1491-1499 ; 01410296 (ISSN) Nakhaei, M ; Ali Ghannad, M ; Sharif University of Technology
    2008
    Abstract
    The effect of Soil-Structure Interaction (SSI) on Park and Ang Damage Index in a Bilinear-SDOF model is investigated under seismic loading. This is done through an extensive parametric study. Two non-dimensional parameters are used as the key parameters which control the severity of SSI: (1) a non-dimensional frequency as the structure-to-soil stiffness ratio index and (2) the aspect ratio of the structure. The soil beneath the structure is considered as a homogeneous elastic half space and is modeled using the concept of Cone Models. The system is then subjected to three different earthquake ground motions as the representative motions recorded on different soil conditions. The analysis is... 

    Inelastic displacement ratios for soil-structure systems allowed to uplift

    , Article Earthquake Engineering and Structural Dynamics ; Vol. 43, issue. 9 , July , 2014 , p. 1401-1421 ; ISSN: 00988847 Ghannad, M. A ; Jafarieh, A. H ; Sharif University of Technology
    Abstract
    The simultaneous effects of soil-structure interaction, foundation uplift and inelastic behavior of the superstructure on total displacement response of soil-structure systems are investigated. The superstructure is modeled as an equivalent single-degree-of-freedom system with bilinear behavior mounted on a rigid foundation resting on distributed tensionless Winkler springs and dampers. It is well known that the behavior of soil-structure systems can be well described using a limited number of nondimensional parameters. Here, by introducing two new parameters, the concept is extended to inelastic soil-structure systems in which the foundation is allowed to uplift. An extensive parametric... 

    Alternative solution for kinematic interaction problem of soil-structure systems with embedded foundation

    , Article Structural Design of Tall and Special Buildings ; Volume 22, Issue 3 , 2013 , Pages 251-266 ; 15417794 (ISSN) Jahankhah, H ; Ghannad, M. A ; Rahmani, M. T ; Sharif University of Technology
    2013
    Abstract
    An effective procedure to incorporate kinematic interaction (KI) aspects in seismic analysis of soil-structures systems was presented. In this regard, first, the effect of KI on the structural response was investigated with special focus on the role of rocking component of foundation input motion (FIM). This was performed parametrically for a wide range of selected nondimensional parameters, which well define the introduced simplified soil-structure model. It was observed that ignoring the effect of rocking input motion may introduce errors, which can be on the unsafe side especially for slender structures with large embedment ratios. On the other hand, it was known that introducing the... 

    Development of Nusselt number and friction factor correlations for the shell side of spiral-wound heat exchangers

    , Article International Journal of Thermal Sciences ; Volume 139 , 2019 , Pages 105-117 ; 12900729 (ISSN) Mostafazade Abolmaali, A ; Afshin, H ; Sharif University of Technology
    Elsevier Masson SAS  2019
    Abstract
    This research aims to investigate the thermo-hydraulic characteristics of flow in the shell side of spiral-wound heat exchangers with consistent shell geometry. To achieve this end, three-dimensional computational fluid dynamics is employed. Geometrical configuration of spiral-wound heat exchangers can be completely determined by knowing six primary parameters including start factor, tube outside diameter, number of tubes in the first layer, number of layers, longitudinal pitch, and radial pitch. Dividing the longitudinal and radial pitches by tube outside diameter, the six primary geometrical parameters reduce to five non-dimensional parameters. The effects of number of tubes in the first... 

    Phenomenological investigation of drop manipulation using surface acoustic waves

    , Article Microgravity Science and Technology ; Volume 32, Issue 6 , 2020 , Pages 1147-1158 Sheikholeslam Noori, M ; Shams Taleghani, A ; Taeibi Rahni, M ; Sharif University of Technology
    Springer Science and Business Media B.V  2020
    Abstract
    This paper aims at the investigation of acoustic streaming produced by surface acoustic waves (SAWs) in a drop. Computational simulation of acoustofluidic phenomenon, using lattice Boltzmann method (LBM), presenting acoustic applications in flow control, and a relatively complete parametric study are the motivations of this work. For this purpose, a computational fluid dynamics modeling based on multi-relaxation time multi-component multiphase color gradient lattice Boltzmann method was used. The simulations were carried out at wave frequencies ranging from 20 MHz to 271 MHz and wave amplitudes ranging from 0.5 nm to about 350 nm. First, the non-dimensional form of Navier-Stokes equations...