نشریه علوم کاربردی و محاسباتی در مکانیک
سال بیست و نهم شماره 1 (پاییز و زمستان 1396)

Poly methyl methacrylate (PMMA) is one of the transparent polymers prevalently formed through thermoforming process. One of the important factors in this production is its optical quality. Using finite element simulation is very important to this aim. In this paper, PMMA thermoforming process is simulated using elastic-plastic model and accuracy of the results is verified by comparison with that of experimental data optained from tests. Then, thickness distribution and final shear strain are controlled by forming with rubber and a product with appropriate properties and quality is obtained. By choosing rubber with properties similar to the sheet, the rubber effects on sheet can be prevented..

In this study, the numerical analysis of turbulent flow and heat transfer of oscillating impinging circular jet on concave cylindrical surface has been investigated. In this way, the averaged Navier-Stocks equations for turbulent incompressible flow in an unsteady state with RNG k-ε turbulent model and in 3D computational space were solved. The effects of oscillation frequency, amplitude of oscillation and Reynolds number on Time-averaged Nusselt number Distribution in concave surface were studied. The obtained results show that applying the pulsating jet in the range of 50 to 200 Hz can increasing heat transfer from concave surface in comparison with the steady jet. Furthermore, increasing Re number from 10000 to 40000 and amplitude of oscillation from 0.4 to 1, leads to the increase of time-averaged Nusselt number..

In this research a linear time- invariant lumped mass model, LTI, in three-dimensional space for a double- helical gear pair is developed and effects of gyroscopic moment on the dynamics and vibrations are studied. In this model, each member has six degrees of freedom and both of the mesh stiffness and bearing stiffness are undertaken. The dynamic response due to transmission errors excitations is calculated by using the modal summation technique. The results of this research show that, by taking the gyroscopic effects in double- helical gear pair, most of the natural frequencies are reduced. In addition, the gyroscopic moment have an important role on the dynamic response of a high- speed double- helical gear pair. In order to verify the equations and solution methodology, the obtained dynamic response from a pair of double- helical gear pair is compared with the empirical results of other researches.

Accurate natural gas measurement is an important issue especially in domestic usage levelCapillary tube thermal mass flow meter is one of the most common types of mass flow meters which are mostly used for low mass flow rates. In this work, a capillary tube flow meter was simulated numerically. A three-dimensional steady state heat transfer in its sensor tube was numerically analyzed and the sensitivity of this type of flow meter was investigated. In order to validate the simulation approach and conditions taken in this study, the simulation was also accomplished for Nitrogen, for which experimental data was available in the literature, leading to satisfactory results. Considering all the possible effective parameters, the uncertainty of the flow meter was also calculated. Numerical results show that the maximum amount of uncertainty in measurement for this type of flow meter is less than 1.24% that is acceptable for residential customers.

In this paper, effect of the nanoparticles diameter on the forced convection heat transfer of turbulent flow of Al2O3-water nanofluids in a circular tube under constant heat flux on the wall using of two phase mixture model numerically investigated and was statistical analysis. The Volume fraction of nanoparticles is %3, the Reynolds number is 5×104 and the variation of diameter of nanoparticles is assumed in the range of 20- 110nm. In the statistical analysis, from the continuous probability distribution functions such as Gamma, Normal, Lognormal, Gumbel, Weibull and Frechet were used. After reviewing the results, it was found that by increasing the diameter of nanoparticles, the Nusselt number is reduced and this parameter due to changes in the nanoparticles of diameter has followed of the Frechet probability distribution function.

In this paper, a new sealing method has been applied to eliminate the friction force between the tube and the die. The new sealing method was experimentally examined in the free bulge test of AA6063 aluminum tubes and necking limit strains, thickness and bulge height of specimens were measured. Results showed that the new sealing method compared to the conventional sealing method improves the material flow to the deformation zone and, therefore, increases the bulge height of aluminum tubes. Finite element simulations of the free bulge test were performed in ABAQUS software under the different process parameters. In these simulations, forming limit curve obtained from the experimental tests was utilized to predict of the necking. Results showed that an increase of friction coefficient, axial feed and initial length tub increases the bulge height of aluminum tubs in the new sealing method compared to the conventional sealing method.

In this paper the two-dimensional unsteady flow within the elastic pipes is modelled based on a Godunov-type wave propagation algorithm. The numerical solver applied herein treats the friction source term within the flux-differencing of the finite volume neighboring cells to calculate the relevant flux-waves. In order to include the unsteady friction term the Baldwin-Lomax turbulence model is utilized. First, the method is examined to model the water hammer problem for a pipe connected to reservoir and the obtained numerical results are compared with the exact solution with both frictionless and steady friction terms. Then, the proposed scheme is employed to simulate the flow within two pipes with different Reynolds number (Re=15800, Re=5800) and the numerical simulations are validated with the available experimental data.

In this paper, free convection heat transfer is completely analyzed in a closed cavity containing internal conducting blocks with arbitrary arrangement. Free convection heat transfer in the cavity is studied according to the variations of Rayleigh number, number of conducting blocks, arrangements of blocks and the porosity. The overall Nusselt number as a criterion of heat transfer is reported on the walls of the cavity. The obtained results show that the thermal effects of porosity and the arrangements of blocks in the cavity are less than the effects of Rayleigh number. However, increasing the number of blocks inside the cavity leads to a decrease in the overall Nusselt number.

In this paper a new ejector pump for using in textile and carpet knitting industries has been designed and optimized by numerical method. One of the customary methods in carpet knitting is tufting through which strings are deployed by fluid (air) and particular needles. In this study, a new method for sucking strings into the needles by employing air ejector has been proposed. Navier-Stokes equations for two-dimensional domain for a compressible turbulent steady flow have been solved. Furthermore, the Realizable k-ε method has been employed for the turbulent flow. The numerical method is verified by prior experimental data for similar ejector pump and good agreements are achieved. In this study, geometric parameters as length and divergence angle in mixing chamber, diffuser outlet diameter and initial inlet pressure are investigated. Numerical results suggest optimum values for divergence angle and length of the mixing chamber.