Scientia Iranica
Volume:24 Issue: 5, Nove-Dec 2017

Laser ablation is a novel non-mechanical wheel preparation method for optimizing the treatment costs of superabrasive tools. In this study, the thermal effects of picosecond laser radiation on vitrified and resin bond CBN superabrasive grinding wheel surfaces was analytically and experimentally investigated. The analytical approach is intended to find threshold process parameters for selective ablation of cutting grains and bond material. A picosecond Yb:YAG laser device was integrated with a cylindrical grinding machine which facilitates the treatment of grinding wheel as it is mounted on the grinding spindle. It has been shown that, the extent of material ablation is defined by the maximum surface temperature induced by the laser radiation which is in turn defined by the laser pulse energy. It is also suggested that, the depth of laser thermal effects is governed by the relative speed of the laser scanner with respect to the wheel surface.

Based on the recent photographs of microstructures of anacinus a novel 3D computational model for airflow and particle transport and deposition was developed. To model the entireacinar region simultaneously, an approach was proposed to reduce the computational space. The airflow was solved using numerical simulations for the cases of expanding and contracting the asinus wall. The volume change of the lung was imposed based on the normal breathing condition with 15% volumetric expansion ratio. Since the entire acinar region was modeled, realistic pressure type boundary conditions were used and the use of earlier unrealistic boundary conditions was avoided. The simulation results showed that the flow patterns in an acinus with moving walls were significantly different from those for the rigid wall case. Furthermore, due to the asymmetric configuration, the flow patterns were not quite symmetric. It was shown that the ratio of alveolar flow to ductal flow rate controlled the dominant flow regime in each generation. Ratios below 0.005led to recirculation regime where flow separation occurred, while values above this threshold led to flows with radial streamlines. In summary, while the flow in the primary generations was characterized by the formation of recirculation regions in the alveoli, the terminal generations were characterized by radial streamlines which move towards the alveolar wall. Both flow regimes had substantial effects on particle deposition in the acinus.

In this study, the optimal distribution of Wall Shear Stress (WSS) in a bifurcation and its effect on the morphology of blood vessels were investigated. The optimal WSS was obtained through minimization of energy loss due to friction and metabolic consumption. It was shown that the optimal WSS is a function of metabolic rate, fluid properties, diameter, and flow regime. For fully developed laminar and turbulent flows different patterns of WSS were observed. For laminar flows WSS is constant but for turbulent flows WSS is a function of diameter such that the exponent of diameter varies by tube relative roughness. Based on the optimal WSS and conservation of mass, the optimal relationship between diameters of mother and daughters’ vessels was obtained for different flow regimes. Also, it was theoretically shown that the optimal distribution of WSS in a bifurcation minimizes flow resistance as well as energy loss. In addition, it was demonstrated that the specific relationship between the length and diameters of a blood vessel and optimal relationship between diameters lead to optimal WSS distribution. Finally, the numerical simulation was used to investigate the effect of Reynolds number on the optimal WSS and flow resistance, and to verify the theoretical formula predictions, obtained in this work.

Piezoelectric Energy harvesting (PEH) from fluid flow energy has attracted significant attention throughout the last decade. In the previous PEH from fluid flow, a piezoelectric beam placed behind a bluff body such as circular cylinders. Hence, the piezoelectric beam oscillated due to the vortex shedding behind of the bluff body. Subsequently, this vibration generates voltage in the beam. In many engineering vehicles such as airplanes the strong vortex shedding caused by bluff body is destructive and reduces the efficiency of devices, therefore; it is not proper to attach a bluff body to these devises.
In this paper PEH from vertical beams in low speeds and high speed flows are investigated. Current work shows that in contrast to the low speed flows the extracted power from vertical beam in the high speed flows are considerable. Moreover, for a practical example of vertical beam in high speed flows the energy harvesting from piezoelectric Gurney flap attached to a NACA2412 airfoil is investigated. Finally, this study proposes a piezoelectric vertical beam with attached end cylinder as an energy harvester in the low speed flows. It is indicated that this device has strong vibration and therefore produces a remarkable electrical power

In the present study a rule-based fuzzy inference system is used to predict heat transfer and entropy generation of stratified air-water flow in horizontal mini-channel as a function of a wide range of important parameters. Numerical data of our recent study are used to develop and test the system. The GK clustering algorithm is used to cluster the data. Fuzzy rules are generated based on the Sugeno-Yasukawa algorithm by using trapezoidal membership functions. The FATI and FITA approaches are implemented in the inference engine and finally the combination of the two approaches is defuzzified. The Mamdani and logical methods with the Yager operators are used and unified in both approaches. The parametric form of the system is a feature of the present study which can be used as an effective tool to improve the accuracy of the results. The novelty of the present study is the presentation of the generalized diagrams for the developing region of the channel which seems to be useful for engineering applications. In addition, generalized diagrams of average Nusselt numbers as well as total entropy generation can identify the appropriate range of volumetric flow rate ratio and the Reynolds number.

This paper aims to analyze fluid flow characteristics and heat transfer augmentation in the air duct of a solar air heater using CFD techniques. The air duct has a rectangular section, the top wall is the glazing and the bottom one is the absorber provided with transverse rectangular or squared ribs. The simulations are performed in the turbulent regime and RANS formulation is used to modelize the flow and resolve mass, momentum and energy equations using Finite Volumes method. The air flow analysis shows that the velocity profile was not disturbed by the ribs outside the laminar sublayer. Heat transfer analysis based on the calculation of Nusselt Number, friction factor and thermo-hydraulic performance has highlighted the heat transfer enhancement, and no big friction losses were recorded. A comparative study between two ribs shape (square and rectangular) was achieved and showed a better thermohydraulic performance for rectangular ribs.

This paper carries out the integration of the 1 3 dimensional Gross-Pitaevskii equation (GPE) in presence of quadratic potential term to ob tain the 1-soliton solutions. The solitary wave ansatz method is employed to integrate the considered equation. Parametric conditions for the existence of the soliton solutions are determined. Both non-topological (bright) and topological (dark) solitonsolutions are reported and we observed that the existence condition for bright and dark soliton solutions are opposite to each other. Finally, the two integrals of motion of the governing model equation have been extracted.

The purpose of this study is to define a simple model and discuss the main effects due to the use of the sensors with imperfect mounting in experimental measurements. This paper presents a theoretical and experimental investigation for the effects of different mounting methods of accelerometers on signal transmissibility in modal testing. In the theoretical part, a two degree-of-freedom (2-DOF) model is used, where the first DOF accounts for the accelerometer seismic mass and Piezo-crystal and the second DOF represents the mounting interface dynamics. An experimental modal analysis is conducted on a simple steel free-free beam using impact hammer excitation. The time domain signals and frequency response functions (FRFs) are measured in the case of magnetic, wax and stud mounting. It is found that the method of mounting has a significant effect on damping rates of measured responses. Although natural frequencies have no important changes, but the quality of measured FRFs is degraded considerably.

In this paper, an experimental study on the flow patterns of two-phase air-light oil flow is performed in a 20 mm diameter pipe with a length of 6 m in different orientations with pipe angles in the range of -45 to . The flow regimes are captured by a high speed camera. In the experiments, the air with the viscosity of 0.019 mPa.s and the density of 1.2 Kg/m3 and a light oil with the viscosity of 2.6 mPa.s and the density of 840 Kg/m3 are used. During the experiments, different flow patterns are observed such as bubbly, slug, smooth stratified, wavy stratified, and annular flows. Flow regimes in different pipe inclination angles are inspected in two-phase air-light oil flow and flow pattern maps are proposed for every pipe inclination angle. In addition, a comprehensive study on major forces acted on dispersed phase are presented theoretically to perform a thorough discussion on effects of pipe inclination angle on transition boundaries between flow patterns in two-phase air-light oil flow. It is inferred that non-stratified flows are dominant flow patterns in the upward flows and stratified flows are dominant flow patterns in the downward flows.

An extensive experimental investigation was performed to explore the shock waves formation and development process in transonic flow. Shadowgraph visualization technique was employed to provide visual description of the flowfield features. Based on the visualization, the formation process was categorized into two intrinsically different phases, subsonic and supersonic. The characteristics of subsonic phase are well known; however, those of the supersonic ones are far less studied. The supersonic phase itself is made up of two consecutive phases, namely approaching and sweeping. The effects of each phase on the flowfield characteristics and on shaping the supersonic regime have been studied in details. In order to generalize the results, three different models were tested. Moreover, a special terminology is suggested by authors to ease the process description and to pave a way for future studies. Above all, as the transition from transonic regime to supersonic one is a vague concept in terms of physical reasoning, a new explanation was proposed that could be used as a criterion for distinguishing between transonic and supersonic regimes.

In this paper, a series solution is obtained for MHD flow of linear visco-elastic fluid over a shrinking/stretching sheet by using homotopy perturbation method (HPM). The governing Navier-Stokes equations of the flow are transformed to an ordinary differential equation by a suitable similarity transformation and stream function. The influence of various parameters such as Hartman number and Deborah number on the velocity field is analyzed by appropriate graphs. Finally, the validity of results is verified by comparing with numerical results. Results are presented graphically and in tabulated forms to study the efficiency and accuracy of the homotopy perturbation method.

In this paper, integrated optimization of the guidance and control parameters of a dual spin flying vehicle is presented. The vehicle is composed of two parts: a free rolling aft body including the engine and the stabilizing fins and a roll isolated front body including all necessary guidance and control equipments such as onboard computer, control fins and an inertial navigation system. After developing the governing equations of motion, control loops and the guidance algorithm are constructed. Controllers are designed for two operating points and the guidance algorithm consists of a midcourse and a terminal phase. In midcourse phase, a virtual target, located on the nominal trajectory, is followed using proportional navigation law; while in the terminal phase, the vehicle is guided toward the real target. A new nonlinear saturation function is defined in order to saturate the maximum lateral acceleration command, as a function of dynamic pressure. Finally, the integrated tuning of 23 guidance and control parameters is formulated as an optimization problem. The optimization problem is solved using a metaheuristic algorithm, called tabu continuous ant colony system. The performance of the optimized guidance and control system is evaluated using Monte Carlo simulations, based on the complete nonlinear model.

Two new techniques are proposed to enhance the estimation abilities of the conventional neural network (NN) method for its application to the fitness function estimation of aerodynamic shape optimization with the genetic algorithm (GA). The first technique is pre-processing the training data in order to increase the training accuracy of the multi-layer perceptron (MLP) approach. The second technique is a new structure for the network to improve its quality through a modified growing and pruning method. Using the proposed techniques, one can obtain the best estimations from the NN with less computational time. The new methods are applied for optimum design of a transonic airfoil and the results are compared with those obtained from the accurate Computational Fluid Dynamics (CFD) fitness evaluator and also with the conventional MLP NN approach. The numerical experiments show that using the new method can reduce the computational time significantly while achieving the improved accuracy.