نشریه علوم کاربردی و محاسباتی در مکانیک
سال بیست و سوم شماره 1 (پاییز و زمستان 1390)

Cage roll forming is one of the new methods of cold roll forming process which is widely used for producing ERW pipes. In addition to less production cost and time, using cage roll forming provides smooth deformation on the strip. Few studies can be found about cage roll forming because of its complexity, and the available knowledge is more experience-based and not science-based. In this paper, deformation of pipes with small thickness/diameter ratio is investigated by 3D finite element simulation in Marc-Mentat software. Edge buckling defect in roll forming of pipes with small thickness/diameter ratio is very important. Due to direct effect of longitudinal strain on the edge buckling phenomenon, longitudinal strains at the edge and center line of the deformed strip are investigated and the high risk stands are introduced. Deformation flower pattern and curvature of the deformed strip are predicted using the simulation results and the effects of each cage forming stage on the deformed strip profile are specified. In order to verify the simulation results, circumferential length, opening distance of the two edges and forming power in different forming stages are obtained from the simulations and are compared that of the experimental data which were measured from the production line. A good agreement between the experimental and simulated results is observed.

In studies done on porous burner, generally burners with axial flow are considered. In this paper, porous burners with radial and axial flow have been modeled numerically and results of radial and axial porous burners with equal fuel consumptions are compared. The mechanism used in combustion phenomenon is 15 stage mechanisms which predict the pollutions production precisely. The results show a significant enhancement of the radial burner performance from viewpoint of temperature distribution, velocity distribution, amount of emissions, and thermal radiation efficiency. The CO and NO emissions are lower and the output radiative power in the radial burner is higher than those of the axial burner.

The objective of this research is geometrical optimization of Half Toroidal Continuously Variable Transmission (CVT) in order to achieve high power transmission efficiency and low weight. After dynamic analysis of the system, the contact between the disk and the roller is modeled according to elasto-hydrodynamic lubrication principles. Accordingly, a computer model is created with geometric, thermal and kinetic parameters as inputs of the system, to determine the efficiency and the weight of CVT. Results are compared to those obtained from models in other articles to confirm its validity. Geometric parameters are obtained by means of genetic optimization algorithm, while optimization parameters are power transmission efficiency and system weight. It is observed that regardless of weight coefficients assigned to power transmission efficiency and weight, difference between results are negligible. Also, the effect of oil film temperature, speed ratio and rotational speed of input disk on power transmission efficiency for optimized geometry is shown.

In this paper the effect of braking force error on the dynamic behavior of the truck is investigated. In the previous studies concerning the braking force error on the vehicle lateral deviation, to avoid complexity, researchers have assumed that the vehicle velocity during the braking process remains constant. In the present work, based on the realistic assumption that the vehicle velocity would decrease during the braking process, and by considering the linear bicycle model for the vehicle, the equations of motion are derived. The equations are solved numerically and the results are compared with those reported in the literature and those obtained experimentally. It is shown that the implication of the realistic assumption leads to more accurate results. The results have been validated by conducting experimental tests on Azarakhsh 6-ton truck.

Use of Tailor-Welded Blanks (TWBs) in production has significant advantages such as weight and cost reduction. However, their application requires processes that increase their poor formability in comparison to base materials. One of these procedures is the use of fluid pressure in sheet metal forming. In this paper hydro-mechanical deep drawing process of tailor-welded low carbon steel (St12) blanks with different thicknesses is studied using FEM and verified experimentally, and effect of fluid pressure on weld-line movement and thickness distribution is investigated. Results of FEM are in good agreement with experiments. Results show that there is an optimum value of final pressure in which the least maximum thinning occurs. Furthermore, using fluid pressure we can obtain higher drawing ratios and also reduce the weld-line movement compared to conventional deep drawing.

High temperatures are often encountered in almost all of the combustion systems, therefore, thermal radiation heat transfer can influence the droplets heat up rate and consequently their life time. In this paper, the effect of thermal radiation heat transfer is investigated for two cases of directional and spherically symmetric illuminations. The flow and temperature fields insdie and outside of the droplet are solved numerically using control volume approach in the presence of thermal radiation. Mie theory is used for the case of directionally illuminated droplet and Dombrovsky’s simplified model is employed for the spherically symmetric illumination to determine the amount and distribution of the absorbed thermal heat inside the droplet. Maximum absorption for a dodecane droplet occurs at the back of the droplet when subjected to directional illumination, while it happens on the surface of the droplet for spherically symmetric illumination. Results show that the heat up rate is less affected by directional radiation whereas spherically symmetric radiation enhances the heat up rate.

Various methods for parametric interpolation of NURBS curves have been proposed in the past. However, the errors caused by the approximate nature of the NURBS interpolator were rarely taken into account. This paper proposes an integrated look-ahead algorithm for parametric interpolation along NURBS curves. The algorithm interpolates the sharp corners on the curve with the Pythagorean-hodograph (PH) interpolation. This will minimize the geometric and interpolator approximation errors simultaneously. The algorithm consists of four different modules: a sharp corner detection module, a PH construction module, a feedrate planning module, and a dynamics module. Simulations are performed to show correctness of the proposed algorithm. Experiments on an X-Y table confirm that the developed method improves contour accuracy significantly compared to previously proposed adaptive-feedrate and curvature-feedrate algorithms.

This paper presents the application of the generalized differential quadrature (GDQ) method for the hydrodynamic analysis of circular and noncircular, two lobe and three lobe, journal bearings. GDQ is a simple, efficient, high-order numerical technique and it uses the information on all grid points to approach the derivatives of the unknown function. The effectiveness of the solution technique is verified by comparing the GDQ computed results with that of analytical solutions and FDM results from the published literature. It is found that GDQ method can easily compete with the existing methods of solution of lubrication problems for its analytical simplicity; smaller computer storage requirements and capability of producing accurate results with very high computational efficiency. Also the effects of design and assemble parameters, namely the eccentricity ratio, preload factor, mount and tilt angles on the performance parameters of these bearings have been investigated using GDQ method. Results show that the variation of mount and tilt angles can has variable effects on noncircular lobed journal bearing performance parameters. Among the two types of noncircular bearings considered, the effect of the mount and tilt angles is more significant for two lobe bearings in comparison with the three lobe bearings.