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    Lower bounds for the blow-up time of nonlinear parabolic problems with robin boundary conditions

    , Article Electronic Journal of Differential Equations ; Vol. 2014 , April , 2014 ; ISSN: 10726691 Baghaei, K ; Hesaaraki, M ; Sharif University of Technology
    Abstract
    In this article, we find a lower bound for the blow-up time of solutions to some nonlinear parabolic equations under Robin boundary conditions in bounded domains of Rn  

    Effect of foundation in dynamic analysis of concrete gravity dams

    , Article Gradjevinar ; Volume 64, Issue 8 , 2012 , Pages 641-646 ; 03502465 (ISSN) Heirany, Z ; Ghaemian, M ; Sharif University of Technology
    Građevinar  2012
    Abstract
    In this paper, nonlinear dynamic analysis of concrete gravity dams was studied. To investigate the effect of dam-reservoir-foundation interaction, a two-dimensional approach was used including the finite element method, and smeared crack approach. The dam-reservoir interaction is solved by staggered solution procedure while the Sharan boundary condition is applied at the reservoir's far-end truncated boundary. The foundation is defined as a part of the structure and some different boundary conditions such as Lysmer, Boulder and damper boundary conditions are applied at its truncated boundaries. Results show that when the nonlinear analysis includes the dam - foundation interaction and the... 

    Preconditioned characteristic boundary conditions for solution of the preconditioned Euler equations at low Mach number flows

    , Article Journal of Computational Physics ; Volume 231, Issue 12 , 2012 , Pages 4384-4402 ; 00219991 (ISSN) Hejranfar, K ; Kamali Moghadam, R ; Sharif University of Technology
    2012
    Abstract
    Preconditioned characteristic boundary conditions (BCs) are implemented at artificial boundaries for the solution of the two- and three-dimensional preconditioned Euler equations at low Mach number flows. The preconditioned compatibility equations and the corresponding characteristic variables (or the Riemann invariants) based on the characteristic forms of preconditioned Euler equations are mathematically derived for three preconditioners proposed by Eriksson, Choi and Merkle, and Turkel. A cell-centered finite volume Roe's method is used for the discretization of the preconditioned system of equations on unstructured meshes. The accuracy and performance of the preconditioned characteristic... 

    Various boundary condition implementation to study microfilters using DSMC simulation

    , Article ASME 2010 International Mechanical Engineering Congress and Exposition, IMECE 2010, Vancouver, BC, 12 November 2010 through 18 November 2010 ; Volume 2 , 2010 , Pages 433-442 ; 9780791844267 (ISBN) Darbandi, M ; Akhlaghi, H ; Karchani, A ; Vakili, S ; Sharif University of Technology
    2010
    Abstract
    In this study, we present a vast boundary condition treatment to simulate gas flow through microfilters using direct simulation Monte Carlo (DSMC) method. We examine the effects of different boundary condition treatments on the density, pressure, and velocity distributions and suggest the best conditions to simulate gas flow through microfilters. We also refine the effects of upstream and downstream locations on the solution. The results show that uniform distributions can be achieved if we apply the inlet/outlet boundary condition at appropriate upstream and downstream distances. We also show that all the suggested boundary conditions suitably predict the pressure drop coefficient factor... 

    A lagged implicit segregated data reconstruction procedure to treat open boundaries

    , Article Journal of Computational Physics ; Volume 229, Issue 14 , July , 2010 , Pages 5418-5431 ; 00219991 (ISSN) Sani, M ; Saidi, M. S ; Sharif University of Technology
    2010
    Abstract
    The problem of treating open boundaries is still a challenging one. Applying fully developed condition is constrained to long enough domains. Without having enough physical evidence about what happens on boundaries, the domain extent could not be shortened and computational costs could not be reduced. From the advent of free (open) boundary conditions, they were confined to mixed finite element procedures. Recent works have extended their application to coupled finite volume solvers based on the shape function data reconstruction. A wider class of flow solvers available, however, rely on the segregated procedure where the velocity components and pressure are solved in succession. Moreover,... 

    Assessment of foundation mass and earthquake input mechanism effect on dam–reservoir–foundation system response

    , Article International Journal of Civil Engineering ; Volume 17, Issue 4 , 2019 , Pages 473-480 ; 17350522 (ISSN) Ghaemian, M ; Noorzad, A ; Mohammadnezhad, H ; Sharif University of Technology
    Springer International Publishing  2019
    Abstract
    Concrete dams are one of the most important infrastructures in every country and the seismic safety assessment of them is a major task in dam engineering field. Dam–foundation–reservoir system analysis is a complex interaction problem because this system consists of three domains with different behaviors. For accurate analysis of this system, some important factors should be considered such as foundation mass and earthquake input mechanism. In this paper, the effect of foundation mass and earthquake input mechanism on seismic response of concrete gravity dam is investigated. For this purpose, two different methods are introduced for modeling of massed semi-infinite foundation in finite... 

    Gaseous slip flow mixed convection in vertical microducts with constant axial energy input

    , Article Journal of Heat Transfer ; Vol. 136, issue. 3 , 2014 ; ISSN: 00221481 Sadeghi, A ; Baghani, M ; Saidi, M. H ; Sharif University of Technology
    Abstract
    The present investigation is devoted to the fully developed slip flow mixed convection in vertical microducts of two different cross sections, namely, polygon, with circle as a limiting case, and rectangle. The two axially constant heat flux boundary conditions of H1 and H2 are considered in the analysis. The velocity and temperature discontinuities at the boundary are incorporated into the solutions using the first-order slip boundary conditions. The method considered is mainly analytical in which the governing equations in cylindrical coordinates along with the symmetry conditions and finiteness of the flow parameter at the origin are exactly satisfied. The first-order slip boundary... 

    Dynamic green function for response of timoshenko beam with arbitrary boundary conditions

    , Article Mechanics Based Design of Structures and Machines ; Volume 42, Issue 1 , 2 January , 2014 , Pages 97-110 ; ISSN: 15397734 Ghannadiasl, A ; Mofid, M ; Sharif University of Technology
    Abstract
    This paper presents the dynamic response of uniform Timoshenko beams with arbitrary boundary conditions using Dynamic Green Function. An exact and direct modeling technique is stated to model beam structures with arbitrary boundary conditions subjected to the external load that is an arbitrary function of time t and coordinate x and the concentrated moving load. This technique is based on the Dynamic Green Function. The effect of different boundary conditions, load, and other parameters is assessed. Finally, some numerical examples are shown to illustrate the efficiency and simplicity of the new formulation based on the Dynamic Green Function  

    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
    Abstract
    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... 

    Gaseous slip flow forced convection in microducts of arbitrary but constant cross section

    , Article Nanoscale and Microscale Thermophysical Engineering ; Vol. 18, issue. 4 , 2014 , p. 354-372 Baghani, M ; Sadeghi, A ; Sharif University of Technology
    Abstract
    This is a theoretical study that extends a classical method of treating the convection heat transfer in complex geometries to gaseous slip flow forced convection in microchannels with H1 thermal boundary condition. Through this line, the momentum and energy equations in cylindrical coordinates are made dimensionless. Afterward, solutions are presented that exactly satisfy the dimensionless differential equations along with the symmetry condition and finiteness of the flow parameter at the origin. The first-order slip boundary conditions are then applied to the solution utilizing the least squares matching method. Though the method is general enough to be applied to almost any arbitrary cross... 

    Thickness optimization of polyurethane floor insulation based on analysis of the heat transfer in a multi-layer

    , Article ASME 2014 12th Biennial Conference on Engineering Systems Design and Analysis, ESDA 2014 ; Vol. 3, issue , 2014 Moosavi, A ; Saidi, M. H ; Reshadi, M ; Sharif University of Technology
    Abstract
    During the year, due to weather conditions, the temperature fluctuations at surface level cause problems in underground pipes as a result of freezing water. One of the best prevention strategies is the use of polyurethane floor insulation for keeping the temperature of clay above zero degrees Celsius. In this study to calculate the minimum thickness of polyurethane insulation layer, the differential equation of energy is solved based on principle of separation of variables using imaginary eigenvalues for consistency with the temperature distribution in multi-layer consist of asphalt, gravel and polyurethane with finite thickness and clay as a semiinfinite medium with periodic thermal... 

    Blow-up phenomena for a system of semilinear parabolic equations with nonlinear boundary conditions

    , Article Mathematical Methods in the Applied Sciences ; Volume 38, Issue 3 , 2015 , Pages 527-536 ; 01704214 (ISSN) Baghaei, K ; Hesaaraki, M ; Sharif University of Technology
    John Wiley and Sons Ltd  2015
    Abstract
    This paper deals with the blow-up phenomena for a system of parabolic equations with nonlinear boundary conditions. We show that under some conditions on the nonlinearities, blow-up occurs at some finite time. We also obtain upper and lower bounds for the blow-up time when blow-up occurs. Copyright  

    Free vibration analysis of general stepped circular plates with internal elastic ring support resting on Winkler foundation by green function method

    , Article Mechanics Based Design of Structures and Machines ; Volume 44, Issue 3 , 2016 , Pages 212-230 ; 15397734 (ISSN) Ghannadiasl, A ; Mofid, M ; Sharif University of Technology
    Taylor and Francis Inc 
    Abstract
    Natural frequencies are important dynamic characteristics of a structure. Therefore, the exact solution pertaining to free vibration of stepped circular plate elastically restrained against rotation, translation, and internal elastic ring support resting on an arbitrary variable elastic foundation using Green Function is presented in this paper. Thus, an accurate and direct modeling technique is introduced for modeling stepped circular plate on an arbitrary variable elastic foundation with arbitrary boundary conditions and internal elastic ring support. The effect of the translational along with rotational support flexibilities, as well as, the elastic coefficient of Winkler foundation and... 

    Dynamics and stability of conical/cylindrical shells conveying subsonic compressible fluid flows with general boundary conditions

    , Article International Journal of Mechanical Sciences ; Volume 120 , 2017 , Pages 42-61 ; 00207403 (ISSN) Rahmanian, M ; Firouz Abadi, R. D ; Cigeroglu, E ; Sharif University of Technology
    Elsevier Ltd  2017
    Abstract
    A fast and efficient reduced order formulation is presented for the first time to study dynamics and stability of conical/cylindrical shells with internal fluid flows. The structural and fluid formulations are developed based on general assumptions to avoid any deficiency due to modeling. Their respective solutions and the final solution to the coupled field problem are also developed in a way to be capable of capturing any desirable set of boundary conditions. In addition to the flexibility provided by the solution methodology and generalization provided by the formulation, current solution proposes an additional advantage over others which is the minimal computational cost due to the... 

    An analytical solution for bending of axisymmetric circular/annular plates resting on a variable elastic foundation

    , Article European Journal of Mechanics, A/Solids ; Volume 74 , 2019 , Pages 462-470 ; 09977538 (ISSN) Foyouzat, M. A ; Mofid, M ; Sharif University of Technology
    Elsevier Ltd  2019
    Abstract
    In this paper, an analytical method is presented in order to determine the static bending response of an axisymmetric thin circular/annular plate with different boundary conditions resting on a spatially inhomogeneous Winkler foundation. To this end, infinite power series expansion of the deflection function is exploited to transform the governing differential equation into a new solvable system of recurrence relations. Singular points of the governing equation are effectively treated by applying the Frobenius theorem in the solution, which in turn permits the use of more-general analytical functions to describe the variation of the foundation modulus along the radius of the plate. Moreover,... 

    Buckling of laminated composite plates with elastically restrained boundary conditions

    , Article Structural Engineering and Mechanics ; Volume 74, Issue 5 , June , 2020 , Pages 577-588 Kouchakzadeh, M. A ; Rahgozar, M ; Bohlooly, M ; Sharif University of Technology
    Techno-Press  2020
    Abstract
    A unified solution is presented for the buckling analysis of rectangular laminated composite plates with elastically restrained edges. The plate is subjected to biaxial in-plane compression, and the boundary conditions are simulated by employing uniform distribution of linear and rotational springs at all edges. The critical values of buckling loads and corresponding modes are calculated based on classical lamination theory and using the Ritz method. The deflection function is defined based on simple polynomials without any auxiliary function. The verifications of the current study are carried out with available combinations of classic boundary conditions in the literature. Through... 

    Buckling of Laminated Composite Plates with Elastically Restrained Boundary Conditions

    , M.Sc. Thesis Sharif University of Technology Rahgozar, Meysam (Author) ; Kochakzadeh, Mohammad Ali (Supervisor)
    Abstract
    This paper presents a unified solution to buckling analysis of rectangular symmetrically laminated composite plates with elastically restrained edges. The plates are subjected to biaxial compression and boundary conditions are simulated by employing uniform distribution of linear and rotational springs at all edges. The buckling loads and corresponding mode shapes are obtained based on classical lamination theory and using the Ritz method with simple polynomials as deflection function without any auxiliary functions. The verifications of current study are carried out with available combinations of classic boundary conditions in the literature. Through parametric study with wide range of... 

    Physically based wall boundary condition for dissipative particle dynamics

    , Article Microfluidics and Nanofluidics ; Vol. 17, issue. 1 , July , 2014 , p. 181-198 Mehboudi, A ; Saidi, M. S ; Sharif University of Technology
    Abstract
    In this paper, we present a novel wall boundary condition model, which stands just on the physical facts, for the dissipative particle dynamics (DPD) method. After the validation of this model by means of the common benchmarks such as the Couette and the Poiseuille flows, we study the effects of this model on the diffusion coefficient in a wide variety of different coarse-graining levels. The obtained results show that the proposed model preserves the thermodynamics of the system, also eliminates the spurious effects of the wall, and consequently is able to preserve the accurate structural characteristics of the working DPD fluid in the wall's vicinity. We also study the fluid flow through a... 

    Simulation and optimization of a semi spherical air bearing

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 7, Issue PARTS A, B, C, D , 2012 , Pages 153-159 ; 9780791845233 (ISBN) Saidimanesh, M ; Shahiri, A ; Nikparto, A ; Sharif University of Technology
    2012
    Abstract
    It is important to test the attitude control systems on satellites before they are launched in space. Traditionally this has been done by dropping the satellite, and firing the thrusters before the satellite makes a soft landing in a net. This method only allows a few seconds of testing and does not lend itself to the measurement of pointing accuracy. A better method is to mount the satellite on a spherical air bearing. In this paper behavior of a semi spherical air bearing is studied and analyzed in various conditions. These bearings are used in different applications such as simulation of approximately frictionless condition which is the satellite's situation in space. In this analysis... 

    A unified approach to the mathematical analysis of generalized RKPM, gradient RKPM, and GMLS

    , Article Computer Methods in Applied Mechanics and Engineering ; Volume 200, Issue 5-8 , January , 2011 , Pages 540-576 ; 00457825 (ISSN) Behzadan, A ; Shodja, H. M ; Khezri, M ; Sharif University of Technology
    2011
    Abstract
    It is well-known that the conventional reproducing kernel particle method (RKPM) is unfavorable when dealing with the derivative type essential boundary conditions [1-3]. To remedy this issue a group of meshless methods in which the derivatives of a function can be incorporated in the formulation of the corresponding interpolation operator will be discussed. Formulation of generalized moving least squares (GMLS) on a domain and GMLS on a finite set of points will be presented. The generalized RKPM will be introduced as the discretized form of GMLS on a domain. Another method that helps to deal with derivative type essential boundary conditions is the gradient RKPM which incorporates the...