Scientia Iranica
Volume:18 Issue: 4, 2011

The response of a rod-stabilized, V-shaped, premixed flame to upstream velocity and equivalence ratio perturbations was characterized as a function of excitation frequency. The response of the flame to equivalence ratio perturbations was calculated, assuming that the heat release response is controlled by contributions from three disturbances. These disturbances include flame speed, heat of reaction and flame area. Using an analytical model, based on linearization of the front tracking equation for inclined flames, the kinematics of a V-flame anchored on a central obstacle was investigated and its response was compared with that of a conical flame. The results suggest that the phase response of the V-flame increases quasi-linearly with excitation frequency, indicating that the fluctuations require a certain time to reach the flame surface. Longer V-flames exhibit more sensitivity to the convected flow disturbances. The stronger contribution of the flame-area perturbations in the case of a V-flame, which is due to the intensified effect of displacement at the tip of the flame, leads to higher values of the overall response of the flame, compared with that of the conical flame. The flame response to equivalence ratio perturbations indicates that V-flames behave as an amplifier at a certain range of frequencies, and they are more susceptible to flow oscillations than conical flames.

In this study, the flow patterns of air–water, two-phase flows have been investigated experimentally in a vertical mini pipe. The flow regimes were observed by a high speed video recorder in pipes with diameters of 2, 3 and 4 mm and length 27, 31 and 25 cm, respectively. The comprehensive visualization of air–water, two-phase flow in a vertical mini pipe has been performed to realize the physics of such a two-phase flow. Different flow patterns of air–water flow were observed simultaneously in the mini pipe at different values of air and water flow rates. Consequently, the flow pattern map was proposed for flow in the mini-pipe, in terms of superficial velocities of liquid and gas phases. The flow pattern maps are compared with those of other researchers in the existing literature, showing reasonable agreement.

This paper presents a methodological approach to traffic condition recognition, based on driving segment clustering. Traffic condition recognition has many applications to various areas, such as intelligent transportation, adaptive cruise control, pollutant emissions dispersion, safety, and intelligent control strategies in hybrid electric vehicles. This study focuses on the application of driving condition recognition to the intelligent control of hybrid electric vehicles. For this purpose, driving features are identified and used for driving segment clustering, using the k-means clustering algorithm. Many combinations of driving features and different numbers of clusters are evaluated, in order to achieve the best traffic condition recognition results. The results demonstrate that traffic conditions can be correctly recognized in 87 percent of situations using the proposed approach.

Sedimentation tanks are designed for the settling of floated solids in water. These tanks are one of the most important parts of water treatment plants and their performance directly affects the functionality of these plants. One challenging method for increasing the performance of sedimentation tanks is to use baffles. A useful baffle should be installed in a suitable place with a proper height. In this work, an experimental study of particle-laden flow in a rectangular sedimentation tank has been performed and kaolin is used as solid particles. The effects of baffle configurations on the velocity and concentration profiles along the tank were studied. Sedimentation tank performance was directly investigated by measurement of the mean concentration along the tank. In order to determine the best baffle configuration, two positions of single and double-baffle arrangements with various heights were investigated. Results show that the best baffle position and proper baffle height relates to the inlet concentration. In any case, the middle baffle, with suitable height, is efficient and increases sedimentation tank performance.

The main purpose of this paper is to design a decentralized controller for some car-like (wheeled) multi robots to follow and hunt a moving target. Considering geometric dimensions, mass and moment of inertia, robots are very similar to actual cars in which the outputs of the controller are steering and driving wheel torques. All robots are equipped with range and bearing sensors along with antenna, to communicate radio wave signals. A Kalman filter is implemented to estimate relative position, state variables of the target and state variables of other robots. The controller is designed to carry out the group maneuver of the system, based on the system dynamics analysis of inertial agents, as well as minimizing the norm of the error between desired and actual acceleration. A simulation study considering the group maneuver of four robots has been carried out, and the achieved results in positions, velocities and other relevant state variables of agents are depicted in the paper. The control torques of the steering system and driving wheels are derived and depicted appropriately. These results guarantee the performance of the addressed controller coupled with the Kalman filter, despite the existence of nonholonomics in dynamics, inertial behaviors, etc.

In this paper, the conjugate gradient method, coupled with the adjoint problem, is used in order to solve the inverse heat conduction problem and estimation of the time-dependent heat flux, using temperature distribution at a point in a two layer system. Also, the effect of noisy data on the final solution is studied. The numerical solution of the governing equations is obtained by employing a finite-difference technique. For solving this problem, the general coordinate method is used. The irregular region in the physical domain (r,z) is transformed into a rectangle in the computational domain (ξ,η). The present formulation is general and can be applied to the solution of boundary inverse heat conduction problems over any region that can be mapped into a rectangle. The obtained results for few selected examples show the good accuracy of the presented method. Also, the solutions have good stability even if the input data includes noise. The problem is solved in an axisymmetric case. Applications of this model are in the thermal protect systems (t.p.s.) and heat shield systems.

The present article encompasses the laminar ascending flow and combined mixed (free and forced) convective-radiative heat transfer within symmetrically heated vertical parallel plates. Radiative heat transfer between two opposite walls is considered and the gas is assumed as gray, absorbing, emitting and scattering. Elliptic governing equations for the case of buoyancy assisted flow are solved numerically employing a home-made CFD code based on the finite volume method. The radiative transfer equation is solved using the discrete ordinates method, adopting its S6 quadrature scheme. The influence of two important radiative parameters, namely, wall emissivity and scattering albedo, while the extinction coefficient is either constant or not, on the occurrence of flow reversal, fanning friction coefficient, flow and thermal fields, is investigated. Present results show that the occurrence of reversed flow enhances both heat transfer and the fanning friction coefficient, and the radiation mode amplifies heat transfer, while reducing the fanning friction coefficient. As wall emissivity increases from 0 to 1, effects of radiation on flow and thermal fields rise. However, there is no linear relationship for the whole range of ε. As scattering albedo varies between 0 and 0.75, radiation effects on flow and thermal fields for the constant and variable extinction coefficient are entirely opposite.

Analysis of the static bending, free vibration and dynamic response of functionally graded piezoelectric plates has been carried out by the finite element method under loadings. The FGPM (Functionally Graded Piezoelectric Material) plate is assumed to be graded through the thickness and simple power law distribution, in terms of the volume fractions of the constituents used for formulation. The electric potential is assumed linear through the thickness of the plate. The governing equations are obtained, using potential energy and Hamilton’s principle, based on the First order Shear Deformation Theory (FSDT), which can include thermo-piezoelectric effects. The finite element model is derived based on the constitutive equation of the piezoelectric material, accounting for coupling between the elasticity and electric effect, by four node elements. The present finite element is modeled with displacement components and electric potential as nodal degrees of freedom. Results are presented for two constituent FGPM plates under different mechanical boundary conditions. Numerical results for a PZT-4/PZT-5H plate are given in both dimensionless tabular and graphical forms. Effects of material composition and boundary conditions on static bending, free vibration and dynamic response are also studied. The numerical results obtained by the present model are in good agreement with the solutions reported in the literature.