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Transaction on Civil Engineering

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Transaction on Civil Engineering
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Transaction on Civil Engineering
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Transaction on Civil Engineering
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Transaction on Civil Engineering
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Transaction on Civil Engineering
 
Transaction on Mechanical Engineering

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Transaction on Mechanical Engineering
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Transaction on Mechanical Engineering
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Transaction on Mechanical Engineering
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Transaction on Mechanical Engineering
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Transaction on Mechanical Engineering
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Transaction on Mechanical Engineering
 
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Transaction on Computer Science & Engineering and Electrical Engineering
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Volume 17, Issue 2, 2010
Transaction on Mechanical Engineering


Comparing Sloshing Phenomena in a Rectangular Container with and without a Porous Medium Using Explicit Nonlinear 2-D BEM-FDM
 
        M. Abbaspour (Professor)
  • M. Ghodsi Hassanabad [MSc.]

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The sloshing phenomena in a partially lled tank can a ect its stability. Modi cations of tank instability due to the movement of the tank carrier, are key design points for the stability of a carrier. Even though the sloshing phenomenon has already been investigated using the BEM-FDM technique, the research in this paper covers this phenomenon in a porous media, which is new in 2-D coordinates. For this purpose, a Laplace equation has been used for potential ow, and kinematic and dynamic boundary conditions have been applied to the free surface. Also, a formulation has been developed for a free surface in porous media. BEM has been used for solving the governing equation and FDM discretization has been used for kinematic and dynamic free surface boundary conditions and for time marching. Theoretical results have been veri ed with experimental data collected in this study. The results show an acceptable agreement between theory and experiment, and the rapid damping property in the sloshing phenomena by using porous material in the water, as expected. Also, these results illustrate that the derived formula in this research are applicable and true.

Keywords:
Boundary Element Method (BEM)

    Finite Di erence Method (FDM)
      Porous media; Potential ow
        Liquid free surface.


On the Relationship Between Unsteady Forces and Shock Angles on a Pitching Airplane Model
 
        A.R. Davari (PhD.)
  • M. R. Soltani [Professor]

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series of supersonic visualization tests were performed on an airplane model in both static and dynamic pitching cases. After image processing, the wave angles originating from di erent parts of the model were carefully measured and averaged over several oscillation cycles. These ndings were then compared with the corresponding normal force under similar conditions. The results reveal a hysteresis loop in variations of the model shock angles with instantaneous angles of attack during up-stroke and down-stroke motions. In comparison with the normal force hysteresis loop, it has been found that there is an interesting relationship between the shape of the hysteresis loop of the shock angle and the corresponding loop observed in the normal force data. Further, the oscillation frequency has been shown to have similar e ects on both shock angle and aerodynamic force variations with the instantaneous angle of attack.

Keywords:
Hysteresis

    Pitching motion
      Vortex bursting
        Reduced frequency
          Schlieren
            Up-stroke.


Three-Dimensional Simulation of Turbulent Flow in 3-Sub Channels of a VVER-1000 Reactor
 
        B. Firoozabadi (PhD.)
  • H. Ganjiani [MSc.]

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In this study, the uid dynamics and convective heat transfer for turbulent ows through a 3-sub channel of a rod bundle, which is representative of those used in VVER-1000, are examined. The rod bundle is constructed from parallel rods in a hexagonal array. The rods are on constant pitch by spacer grids spaced axially along the rod bundle. The geometry details of the bundle and heat ux from the fuel rod are similar to that of the Iranian nuclear reactor under construction. A numerical study using Computational Fluid Dynamics (CFD) was carried out to estimate the ow eld, pressure loss and heat transfer coecients in spacer grids and rod bundles. Turbulence has been modeled using the k 􀀀 " turbulence model. At a distance of 2Dh from the beginning of the spacer grids, in the direction of ow, because uid enthalpy and Nusselt numbers have maximum and minimum values, respectively, the probability of nucleate boiling (PNB) is much higher, and a two phase ow will occur. Predicted results are found to be in close agreement with those of the experimental results reported in the literature.

Keywords:
Sub channel

    Rod bundle
      Spacer grid
        Computational Fluid Dynamics (CFD)
          Turbulent ow
            Nusselt number.


Dynamic Response of Floating Wind Turbine
 
        M. Karimirad (MSc.)

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Like other o shore structures, oating wind turbines are subjected to stochastic wave and wind loads that cause a dynamic response in the structures. Wind turbines should be designed for di erent conditions, such as Operational and Survival conditions. In high sea states, the response can be quite di erent from the operational condition. The present paper deals with coupled wave and wind induced motion in harsh conditions, up to 15 m signi cant wave height and 50 m/sec average wind speed. There are several ways to deal with the dynamic response of oating wind turbines. The Coupled Time domain dynamic response analysis for a moored spar wind turbine subjected to wave and wind loads is carried out using DeepC. DeepC is well known software for calculating the coupled dynamic response of moored oating structures. The aerodynamic forces on a parked wind turbine are calculated, based on the strip theory, and imported to the DeepC through a MATLAB interface. At each time step, the relative wind velocity, based on the response of the structure, is calculated.

Keywords:
O shore

    Floating wind turbine
      Stochastic dynamic response
        Aero-hydro-elastic.


Maximum Dynamic Load Determination of Mobile Manipulators via Nonlinear Optimal Feedback
 
        M. H. Korayem (Professor)
  • M. Irani [MSc.]

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In this paper, a nonlinear optimal feedback control law is designed to nd the maximum load carrying capacity of mobile manipulators for a given trajectory task. The optimal state feedback law is given by the solution to the nonlinear Hamilton-Jacobi-Bellman (HJB) equation. An iterative procedure is used to nd a sequence of approximate solutions of the HJB equation. This is done by solving a sequence of Generalized HJB (GHJB) di erential equations. The Galerkin procedure is applied to nd a numerical solution to the GHJB equation. Using this method, a nonlinear feedback is designed for the mobile manipulator and, then, an algorithm is developed to nd the maximum payload. In mobile base manipulators, the maximum allowable load is limited by their joint actuator capacity constraints, nonholonomic constraints and redundancy that arise from base mobility and increased Dofs. To solve the extra Dofs of the system, an extended Jacobian matrix and additional kinematic constraints are used. The validity of the methodology is demonstrated via simulation for a two-link wheeled mobile manipulator and linear tracked Puma arm and the results are discussed.

Keywords:
Maximum payload

    Manipulator
      Optimal control
        Closed loop controller
          HJB.


Numerical Modeling of Transient Turbulent Gas Flow in a Pipe Following a Rupture
 
        A. Nouri-Borujerdi (Professor)
  • M. Ziaei-Rad [MSc.]

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The transient ow of a compressible gas generated in a pipeline after an accidental rupture is studied numerically. The numerical simulation is performed by solving the conservation equations of an axisymmetric, transient, viscous, subsonic ow in a circular pipe including the breakpoint. The numerical technique is a combined nite element- nite volume method applied on the unstructured grid. A modified  􀀀 " model with a two-layer equation for the near wall region and compressibility correction is used to predict the turbulent viscosity. The results show that, for example, after a time period of 0.16 seconds, the pressure at a distance of 61.5 m upstream of the breakpoint reduces about 8%, while this value for the downstream pressure located at the same distance from the rupture is about 14% at the same time. Also, the mass ow rate released from the rupture point will reach 2.4 times its initial value and become constant when the sonic condition occurs at this point after 0.16 seconds. Also, the average pressure of the rupture reduced to 60% of its initial value and remained constant at the same time and under the same condition. The results are compared with available experimental and numerical studies for steady compressible pipe ow.

Keywords:
Transient compressible ow

    Gas pipeline
      Numerical modeling
        Sudden rupture
          Combined nite element- nite volume method.


E ects of Canard Position on Wing Surface Pressure
 
        M. R. Soltani (Professor)
  • F. Askari [MSc.]
  • A.R. Davari [PhD.]
  • A. Nayebzadeh [MSc.]

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A series of wind tunnel tests were performed to study the e ects of a canard and its position on the downstream ow eld over the wing surface. The wing surface pressure was measured for both canard-o and canard-on con gurations. In addition, the canard position e ects on the wing were investigated at di erent angles of attack. The canard was installed at three vertical positions and at two di erent horizontal distances from the wing apex. The results show a remarkable increase in the wing suction peak for the canard-on con gurations. At low to moderate angles of attack, among the various con gurations examined in the present experiments, the mid-canard con guration developed a higher suction on the wing while, at high angles of attack, the upper-canard was found to induce the most favorable ow eld on the wing. In addition, higher suctions were achieved on the wing at moderate to high angles of attack, as the wing-canard distance was increased.

Keywords:
Canard

    Delta wing
      Downwash
        Leading edge vortex.