نشریه مهندسی مکانیک مدرس
سال دهم شماره 3 (پاییز 1389)

This paper aims to establish a basic understanding of double bulge tube hydroforming process of stainless steel deep drawn cups. The method is briefly reviewed by carrying outexperimental tests and Finite element analysis. After measuring bulge height in both formed curves by CMM and thickness variation of formed tube by ultrasonic thickness measurement unit, it’s found out that thickness variation in this process is less that other traditional methods such as traditional spinning and rubber pad forming. A finite element model is constructed to simulate the double bulge tube hydroforming process and asses the influence of friction coefficient and tube material properties. It is found that material hardening coefficient had the most significant influence on formability characteristics during double bulge tube hydroforming. As similar as other tube hydroforming processes, increasing friction decrease bulge height and thickness.

The dimensionless form of Navier-Stokes equations for two dimensional jet flows are solved using direct numerical simulation. The length scale and the velocity scale of jet flow at the inlet boundary of computational domain are used as two characteristics to define the jet Reynolds number. These two characteristics are jet half-width and centerline velocity. Governing equations are discretized in streamwise and cross stream directions using a sixth order compact finite difference scheme and a mapped compact finite difference method, respectively. Cotangent mapping of is used to relate the physical domain of to the computational domain of. The compact third order Runge-Kutta method is used for time-advancement of the simulation. convective outflow boundary condition is employed to create a non-reflective type boundary condition at the outlet. An inviscid Stuart flow and a completely viscose solutions of Navier Stokes equations are used for the verification of numerical simulations. Results for perturbed jet flow in self-similar coordinates were also investigated which indicate that the time-averaged statistics for velocity, vorticity, turbulence intensities and Reynolds stress distribution tend to collapse on top of each other at flow downstream locations.

In this paper, an analytical formulation of FGM axisymmetric thick-walled cylinders, based on the plane elasticity theory is presented. The stress and displacements in thick cylindrical shell are calculated using the real, double and complex roots of characteristic equation. Solutions are obtained under generalized plane stress, plane strain and closed-ends cylinder assumptions. It is assumed that the material is isotropic and heterogeneous with constant Poissn's ratio and radially varying elastic modulu. The results have been compared with findings of the researcher (2001) [hoop stress is incorrect], and we have present corrected version as well as supplementary findings.

The effect of panel height on performance of ceiling radiant cooling system has been studied. Investigation has been done by employing solution of conservative equations, together with the radiant and thermal comfort equations. Calculation is performed for the typical hottest day of Tehran. Vapour condensation is one of the most important problems whit these systems. Therefore effect of panel height on condensation has been also studied, in a residential place with several different ranges of ventilation rate. The results show that appropriate design of the panel height can significantly reduce the rate of condensation.

Hot wire Anemometer (CTA) can be used to measure instantaneous flow velocity with high frequency. Since the principle of opearation of CTA is based on convective cooling, determination of the air flow direction is difficult. In this Research paper, we have used two cylindrical hot-film sensors placed in parallel to determine the flow direction. The wake effect and the heat due to the upstream sensor on the downstream sensor has been used to identity the flow direction. Effect of wake and presence of the upstream sensor on the downstream sensor has been studied. The results have been used to construct a probe consisting of two parallel sensors, sepereated by 1mm distance. Performance of the probe has been evaluated at various flow angles for laminar and turbulant flows. Findings of this study show that this probe provides the best performance at ±10 flow angles.

In this paper an analytical model for prediction of angular deformation is presented. In this model convective heat losses and a multipoint distributed heat source is used for determination of the inherent strain zone which causes the bending angle. The effects of laser bending process parameters including laser power, beam diameter, scan velocity and pulse duration on the bending angle were investigated experimentally. Main effects of factors were considered and the regression line was derived. An L9 Taguchi’s standard orthogonal array was employed as experimental design and the level of importance of the laser bending process parameters on the bending angle was determined using analysis of variance (ANOVA). Comparison of the analytical model and experimental results has shown a reasonable agreement

Tubular components, such as stepped tubes, conical tubes and box-shape tubes, are mainly produced by tube hydroforming process. Obtaining a sharp corner is the main goal in some of these components. In this paper, corner filling in stepped tubes is studied using a new multistage hydroforming die. The proposed die was simulated and filling of the die cavity was investigated. The finite element software, ABAQUS 6.4, has been used for simulation. In order to verify the simulation results, the new die of stepped tube was manufactured and then experiments have been performed on it. The results of the experiments verified the simulation results. It was shown that by using the new die, parts with sharp corners could be produced. The simplicity of the die and the low internal pressure are among the advantages of this die.Thickness distribution was also examined by FE simulation and via experiments and it is shown that a better distribution could be obtained by the proposed die set.