Scientia Iranica
Volume:21 Issue: 2, 2014

Radial forging is an open die forging process used for reducing the diameters of shafts, tubes, stepped shafts and axels, and for creating internal profiles in tubes. Due to very large forging load, the tool should withstand large stresses and wear. Therefore, the success of forging process depends upon recognition of the die failure factors and optimization of the tool working conditions that enhance tool life.In this study, the effect of process parameters on the tool life in cold radial forging process is investigated using nonlinear three dimensional finite element modeling. Wear and mechanical fatigue are considered as the main modes of tool failure and a parametric study on the effect of process parameters on tool life is presented.

in this paper a methodology for transporting objects with a group of wheeled nonholonomic mobile manipulators is presented. Full dynamic model of a mobile manipulator with a three wheeled mobile base and a three DOF manipulator is derived using Gibbs-Appell method. Since the dynamical equations of mobile robot are highly nonlinear, Input-output linearization technique is used to control individual robots. Transporting the object is divided into two steps.First, robots use a decentralized behavior-based method to approach and surround the object. Thenvirtual structure method is used to control the robots to transport the object cooperatively. A numerical simulation studyis preformed to show the effectiveness of the control methodology. The results show that group of robots are capable of approaching and grasping unknown shapes and they can also manipulate objects in various manners.

In this paper, particle deposition in the upper airways and five lobes of human lung is simulated. The simulation isbased on a stochastic lung model, derived from detailed morphometric measurements. Pathways are simulated using Monte Carlo methods; consequently the wholestructure changes both stochastically and statistically in each simulation. Iin this investigation the termination phenomena is a function of each daughters’ diameter which best satisfies the lung’s morphometry. Complementary to the previous available assumptions, i.e., flow divisions according to the ratio of daughters’ cross sections or distal volumes, in this investigation flow rates are computed in an upward manner starting from the acini (where suction occurs), following to trachea. Regional expansion and contraction coefficients of acinar airways are taken into account in the airflow distribution analysis. Regional and total deposition fractions in the human respiratory system are computed by astochastic lung deposition model in a full breathing cycle. These fractions are computed in the upper airways as well as the above mentioned stochastic lung instead of a pre-defined lung structure. The effects of Brownian motion, inertial impaction and gravitational sedimentation are simulated in particle deposition analysis in respiratory airways using analytical equations.

In this article, the effects of unsteady parameters, including mean angle of attack, oscillation amplitude, and reduced frequency and pitching axis position, on aerodynamic coefficients of a pitching airfoil are studied. This investigation is implemented for high Reynolds number flows around dynamic stall condition. The employed numerical method is a Coarse Grid CFD (CGCFD) method in which the Euler equations are solved using a coarse grid with no slip boundary conditions and compressible surface vorticity confinement technique. The required computational time for this method is significantly lower compared to that of the full Navier-Stokes equations with a simple one equation turbulence model. In addition, a multi zone adaptive spring grid network is applied to simulate the moving boundary which further reduces the computational time. Using the described numerical setup separates the current work from the others’. The obtained numerical predictions are in very good agreement with experimental datafor the high Reynolds number flow. It is found that moving the pitching axis position to the right or left outside and distancing from trailing edge or leading edge, have inverse effects on aerodynamic characteristics. Further, increasing the reduced frequency, results in a reduction of the lift hysteresis loop slope and the maximum lift and drag coefficients.

Within the elasticity theory the reduced form of displacement field is obtained for general cross-ply composite laminates subjected to a bending moment. The first-order shear deformation theory of plates and Reddy’s layerwise theory are then utilized to determine the global deformation parameters and the local deformation parameters appearing in the displacement fields, respectively. For special set of boundary conditions an elasticity solution is developed to verify the validity and accuracy of the layerwise theory. Finally, various numerical results are presented within the layerwise theory for edge-effect problems of several cross-ply laminates under the bending moment. The results indicate high stress gradients of interlaminar stresses near the edges of laminates.

A comparison between the elastic modulus of carbon nanotube (CNT) polymer nano composites predicted by classical micromechanics theories, based on continuum mechanics and experimental data, was made and the results revealed a great di erence. To improve the accuracy of these models, a new two-step semi-analytical method was developed, which allowed consideration of the e ect of the interphase, in addition to CNT and matrix, in the modeling of nanocomposites. Based on this developed method, the in fluence of microstructural parameters, such as CNT volume fraction, CNT aspect ratio, partial and complete agglomerations of CNTs, and overlap and exfoliation of CNTs, on the overall elastic modulus of nanocomposites was investigated.

Identification and minimization of error sources is one of the important issues in experimental investigations. Mainly in micro-scale problems, precise settings should be applied in high-tech test beds to reduce disturbances and induced motions.An experimental study is conducted to assess the role of induced forces and velocity fields in a particulate system which is used for particle identification and separation. Two main effects caused by disturbances are sampling errors and induced motion in the channel either on fluid or dispersed phases. Different disturbance scenarios are implemented on the test bed and then the system response is reported. In order to assess the induced motion as a result of applied forces, microscopic imaging of particles movement in the channel and image processing of the results is performed.Results of particle sampling indicate that optimized pneumatic settings should be implemented to secure safe level of sampling error. Results for induced flow show that the velocity filed can affect the operation of the manipulation mechanism. Methods for capturing the induced force and velocity fields can be implemented in the relevant applications such as micro-particle systems and cellular studies.

This paper describes how one can design a computer program and implement it on an ordinary PC or PDA for detecting very long duration electrocardiogram (ECG) PQRST events with processing capability (time complexity) less than 1300 clock/samples along with the accuracy more than 99.86%. For detecting and delineating QRS complexes, a noise-robust instantaneous concavity analysis was applied. For detecting and delineating P- and T- waves, the analysis of local extremums of the QRS-eliminated signal was used. The proposed method was applied to several databases (more than 1,000,000 beats which were normal or abnormal) with different sampling frequencies and bit-rates. After application of the algorithm, the average detection sensitivity Se=99.96% and positive predictivity P+=99.94%, were obtained for QRS complex. The average delineation error were about -3.0 msec, 2.5 msec, and 2.8 msec, for P-QRS-T events, respectively. By implementing the proposed algorithm computer program to selected databases, the required variation for the core parameters set of the program was about 0.0% for all sampling frequencies and bit rates. The maximum computational complexity required during application of the method to databases was estimated to be lower than 1300 clocks/sample. These merits make the algorithm eligible to be implemented by a mobile-phone or PDA.

The Computational Fluid Dynamics (CFD) method is employed to gain further insight into the characteristics of the in-cylinder flow fi eld. Comparison between the measured and predicted results of the in-cylinder tumble flow and flow coecient generated by a port-valve-liner assembly, on a steady- flow test bench, is presented, and a reasonably good level of agreement is achieved. A CAD parametric model of port geometry is created to enable variations, practically and quickly. Employing CFD analysis, the relationship between design parameters and port ow characteristics is established. The in uence of new blockage patterns on in-cylinder flow is also studied.

Dynamic modeling of a double-pipe heat exchanger has been the subject of current study. The basis of this study is the same velocity of vapor and liquid phases or in other words, homogeneous phase in the annulus part of exchanger. The model can predict the temperature and vapor quality along the axial pipe from pipe inlet up to a distance where steady state conditions achieved. The simulation would be conducted for two modes of co- and counter- flow in a one dimensional transient system. The physical properties of water were estimated from empirical correlation and saturated vapor table with cubic Spline interpolation. The exchanger model which is a set of ordinary differential equations (ODEs), ordinary differential equations and algebraic equations has been solved numerically. Modeling results have been investigated for different operating times and two modes of co- and counter-current.