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Esfahani J.A.,Ferdowsi University of Mashhad | Pishbin I.,Khayyam University | Modarres Razavi S.M.R.,Ferdowsi University of Mashhad
Applied Thermal Engineering | Year: 2015

The present experimental study aims to evaluate the stability, thermal and environmental behavior of the natural gas premixed combustion of a 55 kW Low Swirl Burner (LSB). The main focus of this investigation is to clarify the significance of recess length as a controlling factor of combustion performance. The results depicts that by varying the recess length, different flame regimes are distinguished. In terms of heat transfer efficiency and stack losses of the combustion, the lifted stable flame regime has superiority over the attached flames thanks to the more extended flame brush and proper temperature uniformity ratio. The attempt is also made to make an analogy between the effect of recess length and the effect of swirl number on the flame characteristics. The results revealed that the influence of reducing swirl number is proportional to the increase of recess length due to the decaying nature of swirl flow. © 2015 Elsevier Ltd. All rights reserved.

Esfahani S.A.,Khayyam University | Sedaghatnia M.,Khayyam University
Iranian Journal of Physics Research | Year: 2015

In this research, we have investigated the effect of increasing length on the electronic transport of an armchair graphene nano-ribbons with nitrogen atom impurity and without impurity. The semi-infinite, one-dimensional molecular systems are connected to two electrodes and the electron-electron interaction is ignored. The system is described by a simple tight binding model. All calculations are based on the Green's function and Landauer–Buttiker approach, and the electrodes are described in a wide band approximation. © 2015, Iranian Journal of Physics Research. All rights reserved.

Esfahani J.A.,Ferdowsi University of Mashhad | Barati E.,Khayyam University | Karbasian H.R.,Ferdowsi University of Mashhad
Computers and Fluids | Year: 2015

In the present study, the effect of elliptical motion trajectory on the aerodynamic characteristics and propulsive performance of a flapping airfoil is evaluated. A periodic horizontal motion (forward/backward) is combined with vertical motion (upward/downward) of the airfoil to introduce a new kinematic parameter, and of course, an elliptical motion trajectory for flapping airfoil. Similar kinematics is also observed in the flying of birds and swimming of the penguins or turtles. For this modeling, the Navier-Stokes equations are used to simulate the unsteady flow field over a two dimensional NACA0012 airfoil. The Navier-Stokes equations are discretized based on the finite volume method and are solved with a pressure-based algorithm. The flow is assumed to be laminar and incompressible and transient terms are conducted using a second order Euler implicit scheme. It is shown that the combination of horizontal and vertical motions for the flapping airfoil changes the kinematics, motion trajectory and hence the effective angle of attack profile during the flapping cycle. The elliptical motion trajectory will also influence on the fluid structures and change the vortex shedding pattern and wake zone behind the airfoil. Additionally, the introduced kinematics may influence significantly on the aerodynamics and propulsive performance of either pure plunging or pitching/plunging airfoil. © 2014 Elsevier Ltd.

Esfahani J.A.,Ferdowsi University of Mashhad | Karbasian H.R.,Ferdowsi University of Mashhad | Barati E.,Khayyam University
Ocean Engineering | Year: 2015

In the present investigation a new kinematic model for a fish-like swimming is presented. In this model the foil has two rotational motions in order to approach of the fish swimming performance. This kinematic model is a generalized model for flapping foil because it introduces caudal-to-heave ratio (is ratio of caudal length to heave amplitude) which has not been considered. In the present work the proposed kinematic model can be evaluated in Cylindrical coordinate, while it involves with nonlinear hydrodynamic and propulsion models. This kinematic model can switch to Cartesian coordinate when the caudal-to-heave ratio is infinitive value. The foil experiences the diverse effective angle of attack profile due to the influence of the caudal length in association with other kinematic parameters. It is shown that increase in foil-pitch amplitude decreases the angle of attack and hence, thrust reduces in thrust-based condition. Extreme increasing of foil-pitch amplitude leads the angle of attack to switch to drag-based condition and high drag production results from these changes. Moreover, it is shown that in the limited caudal-to-heave ratio the foil may have the better propulsive performance with reasonable thrust. Furthermore, the optimum Strouhal number and foil-pitch amplitude for fish-like swimming are computed from 0.2 to 0.4 and from 30° to 40°, respectively, which are in agreement with observed results in the nature. © 2015 Elsevier Ltd.© 2015ElsevierLtd.Allrightsreserved.

Karbasian H.R.,Ferdowsi University of Mashhad | Esfahani J.A.,Ferdowsi University of Mashhad | Barati E.,Khayyam University
Wind Energy | Year: 2016

In this paper the effect of accelerated flow over a moving airfoil is considered and based on the flow field around the airfoil the dynamic stall is evaluated. In contrast to ordinary pitching motion, the dynamic stall evaluation in this study is performed with a different motion pattern, in which the airfoil has a heaving motion in one direction. This motion pattern is also similar to rotation of an element of blade in horizontal axis wind turbines (HAWTs). In present investigation, the Reynolds number is changed during simulation time and variations of this parameter from initial to final values are shown by acceleration parameter. The operating Reynolds number is more than 106, and a S809 airfoil is selected to move with accelerations of 1, 4 and 6 m/s2 in normal direction to free stream. To resolve accelerated flow filed in the two-dimensional computational domain and to achieve results within a reasonable computation time, the unsteady Reynolds-Averaged Navier-Stokes (URANS) equations are employed. The governing equations are discretized based on the finite volume approach and semi-implicit method for pressure linked equations algorithm is used for pressure-velocity coupling. Furthermore, turbulence effect on flow field is accounted using shear stress transport (SST) k-ω model. It is shown that the accelerated flow can significantly influence on the aerodynamic loads and dynamic stall trend. This study may introduce a new concept regarding dynamic stall and aerodynamic loads when the rotational acceleration is involved in HAWTs. Copyright © 2014 John Wiley & Sons, Ltd.

Karbasian H.R.,Ferdowsi University of Mashhad | Esfahani J.A.,Ferdowsi University of Mashhad | Barati E.,Khayyam University
Renewable Energy | Year: 2015

In the present study the power extraction possibility by a number of flapping hydrofoils in tandem formation is investigated. A code is developed to predict power extraction capacity for the various number of flapping hydrofoils based on the kinematic and hydrodynamic models. The selected hydrodynamic model follows two dimensional quasi-steady hydrodynamic instability formulation. It is shown that the power extraction is also possible from water stream with the low Reynolds number. As a result of power extraction at low speed flows, the predicted maximum power efficiency is also in lower flapping frequencies. Furthermore, it is found that there are limited number of required flapping hydrofoils in tandem formation, in which the power influence rate drops notably after the second flapping hydrofoil. The flapping hydrofoils at downstream also experience higher hydrodynamic forces, while the flapping hydrofoil kinematics is the key parameter to harness extracted power. As a result of this investigation, the introduced model and code can be used as one of initial tools to predict power capacity for obtaining vast concept regarding tidal sites with the flapping foil hydrokinetic turbines. © 2015 Elsevier Ltd.

Ghafarian T.,Khayyam University | Javadi B.,University of Western Sydney
Future Generation Computer Systems | Year: 2015

Abstract Volunteer computing systems offer high computing power to the scientific communities to run large data intensive scientific workflows. However, these computing environments provide the best effort infrastructure to execute high performance jobs. This work aims to schedule scientific and data intensive workflows on hybrid of the volunteer computing system and Cloud resources to enhance the utilization of these environments and increase the percentage of workflow that meets the deadline. The proposed workflow scheduling system partitions a workflow into sub-workflows to minimize data dependencies among the sub-workflows. Then these sub-workflows are scheduled to distribute on volunteer resources according to the proximity of resources and the load balancing policy. The execution time of each sub-workflow on the selected volunteer resources is estimated in this phase. If any of the sub-workflows misses the sub-deadline due to the large waiting time, we consider re-scheduling of this sub-workflow into the public Cloud resources. This re-scheduling improves the system performance by increasing the percentage of workflows that meet the deadline. The proposed Cloud-aware data intensive scheduling algorithm increases the percentage of workflow that meet the deadline with a factor of 75% in average with respect to the execution of workflows on the volunteer resources. © 2014 Elsevier B.V.

Esfahani J.A.,Ferdowsi University of Mashhad | Vahidhosseini S.M.,Ferdowsi University of Mashhad | Barati E.,Khayyam University
Applied Thermal Engineering | Year: 2015

A three-dimensional analytical solution of transport problem of convection-drying is accomplished using Green's function method (GFM). Mass conservation, momentum and energy equations must be solved to obtain convective heat and mass transfer coefficients. In most papers, these equations are solved using numerical methods alike. The mass transfer coefficients are calculated using analogy between the thermal and concentration boundary layers. The results of previous studies are used for these coefficients values. Green's function method has been used as a new simple method to solve equations of transport problem. The heat and mass transfer equations are solved using Green's function method and taking diffusion equation-related adjoint differential operator equal to Delta function. Of course, these equations are coupled with thermal diffusivity, because this parameter is a function of temperature and is used in mass transfer equation. These two coupled equations were solved with a good approximation which is a definition of a weighted function for moisture distribution. Thus, temperature and moisture distributions within the body obtained as functions of x, y, z and an independent time variable t. After these steps it is seen that there is a good consistency between the results and the existing solutions. The prominent advantages of the proposed solution are techniques which are less time and money consuming compared to numerical and experimental methods. © 2015 Elsevier Ltd.

Sabeghi N.,Ferdowsi University of Mashhad | Sabeghi N.,University of Management and Economics | Tareghian H.R.,Ferdowsi University of Mashhad | Demeulemeester E.,University of Management and Economics | Taheri H.,Khayyam University
Computers and Operations Research | Year: 2015

Projects are usually performed in relatively unstable environments. As such, changes to the baseline schedules of projects are inevitable. Therefore, project progress needs to be monitored and controlled. The control process can be assumed as a continuum in which one side is continuous control and the other side is no-control. Continuous control and no-control strategies are cost-wise prohibited. Hence, project progress should be controlled at some discrete points in time during the project's duration. The optimal number and timing of control points are the main issues that should be addressed. In this paper, taking a dynamic view to the project control, for the first time we use an adapted version of the facility location model (FLM) to find the optimal timing of project control points. Initially, the adapted FLM determines the optimum timing of the control points in the project's duration. A simulation model is then used to predict the possible disruptions in the time period between the beginning of the project and the first control point (monitoring phase). If no disruptions are observed, the project's progress is monitored in the second control point, otherwise possible corrective actions are taken using an activity compression model. Whenever due to disruptions, the baseline schedule is to be updated, the FLM is run again to determine the new timing of the control points for the rest of the project's duration. In an iterative manner, this process continues until the timing of the last control point is determined. © 2015 Elsevier Ltd. All rights reserved.

Karbasian H.R.,Pusan National University | Esfahani J.A.,Ferdowsi University of Mashhad | Barati E.,Khayyam University
Renewable Energy | Year: 2016

In the present study the power extraction capability by flapping foil hydrokinetic turbine is investigated. The heaving motion of the foil is considered in two different motion patterns including the simple linear translational motion and the rotation of swing arm on which the foil is mounted. The laminar and incompressible flow around a NACA0012 foil is conducted using Computational Fluid Dynamics (CFD) method. It is shown that the power extraction is possible and more desirable in the lower reduced frequencies. Additionally, the swing arm mode may increase the amount of extracted power and improve the performance of hydrokinetic turbine. Changes in kinematics of flapping foil alter the angle of attack profile and the local Reynolds number on the surface of the foil. These two sensitive changes influence on the sub-layer flow near to surface of the foil and make the vortex structure to be complex during flapping cycle. In the other words, in swing arm mode the vortex creation, growth, separation and shedding occur with an alternative pattern compared to simple mode. Finally, it is shown that the importance of the swing arm mode is in a certain range of swing arm lengths. © 2015 Elsevier Ltd.

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