Scientia Iranica
Volume:19 Issue: 2, 2012

Recently, Shape Memory Alloys (SMAs) have been receiving more attention and further study, due to their ability to develop extremely large, recoverable strains and great forces. In this paper, three major models of SMA behavior, used in the literature, for studying the static performance of SMA components attributed to Tanaka, Liang and Rogers, and Brinson, have been analyzed and compared. The major differences and similarities between these models have also been emphasized and presented in this paper, based on the experimental data of the shape memory and superelastic behavior of an SMA wire. It is shown that these models all agree well in their prediction of the superelastic behavior of SMAs at higher temperatures, but the models developed by Tanaka, and Liang and Rogers cannot be used for predicting the shape memory effect behavior of SMAs. It is also shown analytically that the original evolution kinetics, proposed by Brinson, in a specified region, are inadmissible for some thermomechanical loading and initial conditions. Furthermore, corrected evolution kinetics is addressed here in detail, that is; admissible and valid in this region. According to this research, regarding the validation assessment of three major 1-D constitutive models with experimental data, it will be shown that the Brinson model with the corrected evolution kinetics developed by Chung et al. can be applied for the modeling of SMA smart structures, such as flexible SMA beam structures.

This work simulates the turbulent boundary layer of an incompressible viscous swirling flow through a conical chamber. To model the pressure gradient normal to the wall, the radial and tangential velocity components across the boundary layer have been calculated by both the integral and numerical methods. The numerical solution is accomplished by finite difference, based on the finite volume method. The results show that the radial and tangential boundary layer thicknesses depend on the velocity ratios, Reynolds number and nozzle angle. The peak of radial and tangential boundary layer thicknesses are located at z/L≈0.2 and z/L≈0.8 from the nozzle inlet, respectively. Due to the short length of the nozzle, the contribution of momentum change on pressure loss is more significant than that on the shear stress. Also, the pressure gradient normal to the wall had been considered more accurately than that of the previous attempts.

A novel derivation to transfer an actual domain with circular geometries to the computational domain, which is competent for application to computational fluid dynamics, is derived. Outcome formulas could be employed in cases of gridline transformation in the method of linearized, two dimensional fluid transients, as well. In addition, hydraulic parameters can be computed and handled to achieve high precision results, which is called the polar gridline transformation method. This method is used in cases of other kinds of non-prismatic sections or complex shaped domains, such as the turbine spiral case or the specific shape around wicket gates, and the turbine runner. A real example is also illustrated to verify the necessity and validity of the derived formulas, and logical conclusions are included.

Open jet wind tunnel testing provides an alternative solution to expensive online wind power measurements for researchers and small wind turbine developers. However, there is a lack of knowledge for high Reynolds number and large diameter jet flows. In this paper, the structure of circular open jet flows is reviewed. Theories and experimental correlations are combined to extend our understanding of fully developed turbulent jets. Analytical relations are derived to calculate the correct wind power of the jets. The corresponding reduction in power generated by small wind turbines is explained. The effects of various parameters on the power production of a small wind turbine, such as the jet diameter, the distance of the wind turbine from the jet nozzle and the wind turbine hub diameter, are investigated and the results are discussed.

Prediction of the thermo-mechanical behavior of machine-tool spindles is essential in the reliable operation of high speed machine tools. In particular, the performance of these high speed spindles is dependent on their thermal behavior. The main source of heat generation in the spindle is the friction torque in angular contact ball bearings. This paper presents an effort to develop a comprehensive model of high speed spindles that includes viable models for the mechanical and thermal behavior of its major components, i.e., bearings, shaft and housing. Spindle housing and shaft are treated as six-degree-of-freedom Timoshenko beam elements. Bearings are modeled as two-node elements with five displacements and a thermal load component at each node. Mutual interaction between the thermal and structural behavior of both spindle shaft/housing and bearings is characterized through thermal expansion and the rate of heat generation/transfer. Components are combined to form a finite element model for the thermo-mechanical analysis of spindle-bearing systems.

Milling is a competitive manufacturing process that is widely used in automotive, aerospace, biomechanical and die/mould industries. Due to the complex geometry and intricate mechanics of milling, the realistic simulation of various milling processes is a challenging research task. Accurate simulation of the milling process requires a proper knowledge of its dynamics. In this paper, a method is developed for the accurate prediction of cutting forces and surface texture in the end-milling operation, based on Time Series Analysis (TSA). In the proposed approach, an equivalent damping ratio is defined for the cutting zone, while the damping ratio of the non-cutting zone is determined by experimental modal analysis. Using a correlation sum criterion, the simulation and experimental force signals are compared to anticipate the value of process damping inside the cutting zone, by assessing the variations in correlation dimensions for both signals. The simulation algorithm incorporates the Time Finite Element Analysis (TFEA) for predicting the dynamics of the milling system. It also takes into account the effect of cutter deflections and run out. The feasibility of the proposed algorithm is verified experimentally for the side wall machining of aluminum 7075-T6, using a High Speed Steel (HSS) helical end mill. The implemented model can accurately predict cutting forces and a 3D surface texture for low radial immersion cutting.

This work applied the Lattice Boltzmann Method (LBM) to investigate the effect of CuO nanoparticles on natural convection with magnetohydrodynamic (MHD) flow in a square cavity. The left and right vertical walls of the cavity were kept at constant temperatures, Th and Tc, respectively, with two insulated walls at the top and bottom. A uniform magnetic field was used in a horizontal direction. Results were carried out for different Hartmann numbers ranging from 0–100, Rayleigh numbers from 103–105 and the solid volume fraction from 0 to 0.05. Effects of the solid volume fraction and magnetic field on hydrodynamic and thermal characteristics were investigated and discussed. The averaged Nusselt numbers, on hot wall, streamlines, temperature contours, and the vertical component of velocity for different values of a solid volume fraction, Hartmann and Rayleigh numbers were illustrated. The results indicate that the averaged Nusselt number increases for nanofluids when increasing the solid volume fraction, while, in the presence of a high magnetic field, this effect decreases.

This paper presents a C2 Pythagorean-Hodograph (PH) spline curve interpolator for high speed contouring applications. With the knot vector and control points given, the C2 PH quintic spline curve is a “good” interpolant to the nodal points of the cubic B-spline curve, with the same knot vector and control points. To generate the C2 PH quintic spline curves, a uniform knot sequence is employed. The S-curve motion planning architecture, with variable feedrate for a planar C2 PH quintic spline curve, is also developed. In particular, C1 cubic feed acceleration/deceleration is imposed on the first and last PH quintic spline segments. Several closed C2 PH quintic spline curve contouring tasks, along with a simple position loop controller, were conducted to verify the effectiveness of the proposed interpolation algorithm. The experimental results were analyzed and discussed. It is found that the proposed CNC interpolator is not only feasible for machining the complicated parametric curves represented in the C2 PH quintic spline form, but also yields a satisfactory contouring performance for variable feedrate control.

This paper presents the direct kinematics solution of a 4PUS + 1PS parallel manipulator. The mechanism consists of a fixed base and moving platform connected by five serial chains. The solution of its direct kinematics yields an eighth-degree polynomial in a single variable, which indicates that there may be up to eight different configurations for the moving platform for a given set of joint variables. A numerical example with eight real solutions is included. Therefore, the polynomial is minimal.

A control strategy on a hybrid vehicle can be implemented through different methods. In this paper, the Cerebellar Model Articulation Controller (CMAC) and Radial Basis Function (RBF) neural networks were applied to develop an optimal control strategy for a split parallel hydraulic hybrid vehicle. These networks contain a nonlinear mapping, and, also, the fast learning procedure has made them desirable for online control. The RBF network was constructed with the use of the K-mean clustering method, and the CMAC network was investigated for different association factors. Results show that the binary CMAC has better performance over the RBF network. Also, the hybridization of the vehicle results in considerable reduction in fuel consumption.

In this paper, the nonlinear oscillation of a pendulum wrapping and unwrapping on two cylindrical bases is studied, and an analytical solution is obtained using the multiple scales method. The equation of motion is derived based on an energy conservation technique. By applying the perturbation method to the differential equation, the nonlinear natural frequency of the system is calculated, along with its time response. Analytical results are compared with numerical findings and good agreement is found. The effect of large amplitude and radius of cylinders on system frequency is evaluated. The results indicate that as the radius of the cylinder increases, the system frequency is increased. Also, it is illustrated that initial amplitude plays a dual role in the frequency. As the initial amplitude increases up to a certain point, the frequency is increased, while by increasing it to higher values, the system frequency decreases.