Iranian Journal of Science and Technology Transactions of Mechanical Engineering
Volume:37 Issue: 2, 2013

In this paper, nonlinear free vibration of a micro-beam-based micro electro mechanical oscillator system is studied using He’s frequency amplitude method. Firstly, by considering midplane stretching effects and distributed electrostatic forces and implementing Euler-Bernoulli hypothesis, the governing equations are derived. Then, Galerkin method is used to convert the resulted partial differential equations into an ordinary differential one. At last this nonlinear ordinary differential equation is solved by He''s frequency Amplitude formulation. The proposed method offers an analytical closed form solution which is accurate and simple and in order to study the problem parametrically and in a more general manner the variables are defined in normalized form. A comparison between the obtained results and the one by an accurate numerical method shows the good accuracy of this method in solving this kind of problem. In addition, the relationship between the nonlinear principal frequency and non-dimensional amplitude, electroelastic and axial loads on the beams has been studied.

This article describes an investigation into the free vibration of double-walled carbon nanotubes (DWCNTs) using a nonlocal elastic shell model. Eringen’s nonlocal elasticity is implemented to incorporate the scale effect into the Donnell shell model. Also, the van der Waals interaction between the inner and outer nanotubes is taken into account. A new numerical solution method from incorporating the radial point interpolation approximation within the framework of the generalized differential quadrature (GDQ) method is developed to solve the problem. DWCNTs with arbitrary layerwise boundary conditions are considered in this paper. It is shown that applying the local Donnell shell model leads to overestimated results and one must recourse to the nonlocal version to reduce the relative error. Also, this work reveals that in contrast to the beam model, the present nonlocal elastic shell model is capable of predicting some new noncoaxial inter-tube resonances in studying the vibrational response of DWCNTs.

In this paper, heat dissipation effect of a ferrofluid on natural convection flow in a partially heated cavity in the presence of an external magnetic field outside of the cavity has been analyzed with lattice Boltzmann method (LBM). The cavity is filled with kerosene as the carrier fluid and nanoscale ferromagnetic of cobalt. This study has been carried out for the pertinent parameters in the following ranges: the Rayleigh number of base fluid, Ra=103–105, the volumetric fraction of nanoscale ferromagnetic between 0 and 4%, the size of the nanoscale ferromagnetic is fixed at 45nm. As the size of the heater is equal to H/3, the center of the heater is investigated at Yp= 0.25H, 0.5H and 0.75H. Results show that the heat transfer decreases by the increase of the nanoscale ferromagnetic volume fraction for various Rayleigh numbers. The external magnetic field influences the nanoscale ferromagnetic at Ra=104 more than other Raleigh numbers as the least values are observed at Ra=103. While the heat transfer obtains the greatest value at Yp= 0.5H for multifarious Rayleigh numbers, the greatest effect of the nanoscale ferromagnetic for Ra=104 and 105 is perceived at Yp= 0.75H.

The flow of two-dimensional drops suspended in an inclined channel is studied by numerical simulations at non-zero Reynolds numbers. The flow is driven by the acceleration due to gravity, and there is no pressure gradient in the flow direction. The equilibrium position of a drop is studied as a function of the Reynolds number, the Capillary number, the inclination angle and the density ratio. It is found that the drop always lags the undisturbed flow. More deformable drops reach a steady state equilibrium position that is farther away from the channel floor. For drops that are heavier than the ambient fluid, the equilibrium position moves away from the channel floor as the Reynolds number is raised. The same trend is observed when the inclination angle with respect to horizontal direction increases. The behavior agrees with computational modeling of chute flow of granular materials. A drop that is lighter than the ambient fluid reaches a steady state equilibrium position closer to the channel floor when the Reynolds number or inclination angle increases. Simulations of 40 drops in a relatively large channel, show that drops move away from the channel floor when the density ratio is larger than unity.

Extensive subsonic wind tunnel tests were conducted on a coplanar wing-canard configuration at various angles of attack. In these experiments, a 60° swept canard was placed upstream of a 60° swept main delta wing. This paper deals with the distribution of mean and fluctuating pressure coefficients on the upper surfaces of both the canard and the wing immersed in a variety of angles of attack. According to the results, presence of canard postpones the vortex formation and growth on the wing to higher angles of attack compared to the canard-off case. Due to the canard downwash field, the wing operates at lower effective angles of attack and therefore, its vortex breakdown is delayed. The spectral analysis of the unsteady pressure on both the canard and the wing show the existence of narrow, dominant frequency band containing the majority of the fluctuation energy. This frequency band is believed to be the natural frequency of the leading edge vortex. The results show that the dominant frequency of the wing vortex is lower than that of the canard having the same sweep angle as the wing, which is an indication of the wing vortex attenuation due to canard downwash field.

The main objective of this paper is to predict the warpage of a circular injection moldedpart based on different processing parameters. The selected part is used as spacers in automotive, transmission, and industrial power generation industries. The second goal is facilitating the setup of injection molding machine without (any) need for trial and error and reducing the setup time. To meet these objectives, an artificial neural network (ANN) model was presented. This model is capable of warpage prediction of injection molded plastic parts based on variable process parameters. Under different settings, the process was simulated by Moldflow and the warpage of the part was obtained. Initially, the effects of the melt temperature, holding pressure and the mold temperature on warpage were numerically analyzed. In the second step, a group of data that had been obtained from analysis results was used for training the ANN model. Also, another group of data was applied for testing the amount of ANN model prediction error. Finally, maximum error of ANN prediction was determined. The results show that the R-Squared value for data used for training of ANN is 0.997 and for the test data, is 0.995.

A novel Integrated Vehicle Dynamics Control (IVDC) scheme is presented to coordinate active steering and braking subsystems. The multi-stage coordination scheme is based on the phase-plane Method. The first stage includes the high-level controller which integrates three individual controllers according to vehicle states in the phase plane. In the next stage, an optimized scheme is established to allocate the control objectives to individual braking and steering forces.To achieve this, an inequality-constrained optimization problem, including driver''s brake demand, is solved analytically. Coefficients of the cost function are adapted based on the vehicle phaseplane trajectory to realize a proper coordination of braking and steering subsystems. Simulation results validate the effectiveness of the proposed method to enhance the vehicle dynamics control.

In recent years much research has been conducted to study the variations in welding parameters and consumables on the mechanical properties of steels to optimize weld integrity. The quality of weld is a very important working aspect for the manufacturing and construction industries. In the present work, an attempt has been made to apply an efficient technique, fuzzy based desirability method to solve correlated multiple response optimization problems, in the field of flux cored arc welding. This approach converts the complex multiple objectives into a single fuzzy reasoning grade. Based on fuzzy reasoning grade, optimum levels of parameters (Welding current, arc voltage and electrode stickout) were identified. Experiments were performed based on Taguchi method. Weld bead hardness and material deposition rate are selected as quality targets. Significant contributions of parameters are estimated using Analysis of Variance (ANOVA). Confirmation test is conducted and reported. It is found that the electrode stickout is the most significant controlled factor for the process according to the weighted fuzzy reasoning grade of the maximum weld bead hardness and material deposition rate. The proposed technique allows manufacturers to develop intelligent manufacturing system to achieve the highest level of automation.

One of the most important design parameters in extrusion process is the shape of die profile. In the present research work, an optimum extrusion die profile has been obtained through implementation of slab analysis in a computational algorithm. Moreover, extrusion process through both optimum conical and curved die has been performed experimentally and also by finite element method. It has been demonstrated that material work hardening characteristics and friction condition have remarkable effects on the optimum streamlined die profile. Also, results prove that the streamlined die profile designed based on the developed approach, is superior to the conventional conical dies from both metallurgical and manufacturing perspectives. Consequently, the proposed method can be regarded as an efficient and reliable tool for designing streamlined die profiles. Hence, this technique can be used to produce desirable conditions in both process and product quality in terms of extrusion force, deformation homogeneity and die wear.

In the present work, three extrusion profiles have been investigated objectively, these are a conical, a cosine which is proposed in this study and a profile designed to impose equal strain increments over the equi-spaced sections. Each of them reduces a portion of the required power for extrusion. Conical profile provides the least frictional surface, cosine profile omits the surfaces of velocity discontinuity and the other profile reduces the power attributed to redundancy during deformation. However, the capability of these profiles in reducing the total power of the process is very different. Results suggest that cosine profile is the best energy-wise, whereas the profile which imposes equal strain increments over the equi-spaced sections provides the best distribution of strain in the product. In addition, a simple exponential equation as a function of die geometry is presented for the case of the profile which imposes equal strain increments over the equi spaced sections.

A linear instability analysis of an inviscid annular liquid sheet emanating from an atomizer subjected to inner and outer swirling air streams and a non-swirl round liquid jet has been carried out. The dimensionless dispersion equation that governs the instability was derived and was solved by Numerical method to investigate the effects of the liquid-gas swirl orientation on the maximum growth rate and its corresponding unstable wave number that produces the finest droplets. To understand the effect of air swirl orientation with respect to liquid swirl direction, four possible combinations with both swirling air streams with respect to the liquid swirl direction have been considered. Results show that at low liquid swirl Weber number a combination of co inner air stream and counter-outer air stream has the largest most unstable wave number and shortest breakup length. The combination of inner and the outer air stream co-rotating with the liquid has the highest growth rate. Also, the results for round liquid jet and planar liquid sheet show that the linear theory accurately predicts the variation in breakup length with jet velocity.

This paper presents the total heat transfer rate by Elliptical Annular Fin (EAF) and Circular Annular Fin (CAF) by experimental set-up, validated CFD analysis and optimization of EAF using Genetic Algorithm (GA). The experimental result of EAF shows that, the surface temperature of EAF goes on decreasing gradually along with the projected surface area in the direction of the major axis. The STE decreases with the Biot number (Bi) and Shape factor (SF). The rate of reduction of STE with increasing Bi is higher for Bi < 0.013. The experimental results are validated with CFD result. The deviation is within acceptable range for surface temperature, STE and fin effectiveness are 5-8%. The GA developed is validated with the experimental result. It is observed that, the fin effectiveness is higher when the minor axis touches the circumference of the CT, and for smaller values of SF and smaller values of the radius of the CT. This optimization method is universal and may be used for optimization of EAF under specified volume.