Iranian Journal of science and Technology (B: Engineering)
Volume:35 Issue: 5, August 2011

This paper presents a simple Cartesian practical technique named blocked-off-region procedure to study the combined conductive and radiative heat transfer in three-dimensional irregular geometries. By a concept of blocked-off method previously applied in the problems of computational fluid dynamics, both straight and curvilinear boundaries can be treated. The set of equations consisting of gas energy equation and also the radiative transfer equation are solved simultaneously to obtain the temperature and radiative heat flux distributions inside the participating medium. The finite volume method has been adopted to solve the energy equation and the discrete ordinates method (DOM) is used to model the radiative transfer in an absorbing-emitting and linear anisotropic scattering medium. The radiative conductive model is validated by comparison with test cases solutions from the literature and is applied to analyze the effect of thermoradiative parameters such as conduction-radiation parameter, optical thickness and scattering albedo on the temperature and radiative flux distributions for three-dimensional enclosures. Results confirm that the proposed method is a good general way for studying combined conductive and radiative heat transfer in three-dimensional complex enclosures.

The effect of density ratio on the hydrodynamic interaction between two drops in simple shear flow at finite Reynolds numbers is studied considering the gravity influence. In this study the full Navier-Stokes equations are solved by a finite difference/front tracking method. The interaction of two drops contains approach, collision, and separation. For a range of density ratios, the interaction between deformable drops increases the cross-flow separation of their centres. The distance between the drop centres along the velocity gradient direction increases irreversibly after collision and reaches a new steady-state value after separation. The interaction between drops is affected by the density ratio. As the density ratio increases, the final equilibrium position of drops moves to the higher velocity region and the drop deformation increases. Drop deformation prevents drop coalescence at finite Reynolds numbers; the reduced collision cross-section of the drops allows them to glide past each other. The drops accelerate while sliding over each other. As the density ratio decreases, drops rotate more slowly, and the point at which the drops separate is delayed.

In this paper the turbulent natural convection flow is investigated through Large Eddy Simulation (LES) turbulence model, which is applied in Lattice Boltzmann, and the results for high Rayleigh numbers between 106 and 109 are represented. Air with Pr=0.71 is considered in this study. In this investigation we have tried to present Large-eddy turbulence model by Lattice Boltzmann Method (LBM) with a clear and simple statement. The results confirm that this method is in acceptable agreement with other verifications of such a flow. The effects of increase in Rayleigh number are displayed on streamlines, isotherm counters, local Nusselt number and average Nusselt number.

This paper formulates a method that provides an index for evaluating the coupling effects between the degree-of-freedom motions of six-degrees-of-freedom parallel manipulators. The aim is to provide guidance for the initial design of mechanisms in which the decoupling of the displacement with respect to degrees of freedom motion is required. It is based on singular-value decomposition to the properties of the joint space inverse mass matrix. The method uses a transformation matrix, the product of transposed Jacobian matrix and an orthogonal unitary matrix. Each element of the matrix quantifies the degree of coupling effects between degree-of-freedom motions with respect to the physical task space frame. A mathematical description of the method is presented, with the analysis supported by results from simulations and experiments. The results of the simulations show good agreement with the experimental results, indicating the good potential of the proposed method to provide guidance to mechanism designers in assessing the magnitude of the coupling effects at the initial design stage.

The in-service cracks of the continuous casting machine roll are studied. The effects of high temperature fatigue crack growth were investigated for 25Kh1M1F steel, which is widely used for continuous casting rolls. In general, fatigue crack growth rates increased with increasing temperatures. At high crack growth rates, crack-tip plasticity was significant and propagation proceeded by ductile striation formation processes.

In this paper, a computational technique is presented based on the natural element method (NEM) for large plastic deformation simulation of the metal forming problems. NEM is a numerical technique in the field of computational mechanics and can be considered as a meshless method. The selected process is backward extrusion for circular shape hollow components from round billets. The punch stroke value is divided into sub-steps, whereas a new set of nodes become active at the end of each sub-step of deformation. Solutions are obtained for different area reductions under friction condition. Hollman-Ludwik law is selected to explain the material behavior after the yielding point. The experiments are carried out with fully annealed commercial aluminum alloy billets at room temperature, using various punch sizes. A set of die and punches are designed and constructed for experimental works. The validity of the proposed method is verified by comparing the results from deformed geometry, contours of equivalent strain and forming loads with those obtained from finite element simulation and experimental measurements. It is concluded that the results obtained by NEM are in good agreement with those from FEM and experiments and therefore, the meshless natural element method is capable of handling large plastic deformation.

The accuracy and precision of computer numerical control (CNC) machine tools directly affect the dimensional accuracy of machined parts. Accurate detection of machine tool errors with respect to positioning and orientation is imperative to the accuracy of the manufacturing process and, further, to eliminate errors through error compensation techniques. This paper presents a method to measure and determine angular errors resulting from drive axis out-of-straightness. Measurement of errors in discrete steps has been carried out via laser autocollimator and the method of neural networks (NN) has been employed to predict the amount of errors in the range between the steps. The results from this study can be used as a model for industrial applications to identify errors prior to the programming of the manufacturing process.