Journal of Applied and Computational Sciences in Mechanics
Year:2013 | Volume:24 | Issue:2 (8)|Papers Count:8

Drilling is one of the main machining processes carried out in the assembly stage of automobile manufacturing and aerospace components. Generally, delamination is considered as a major problem during drilling of composite materials. In this paper, the effects of feed rate, cutting speed and drill point angle on thrust force and delamination factor have been studied by using full factorial design. According to the results, feed rate has the most significant effect on thrust force followed by drill point angle. Moreover, the Half-Normal plot was used to identify which experiment factors have significant effects on the delamination factor; According to the results, feed rate has the most important effect. Acoustic emission signals and wavelet analysis were employed to monitor drilling process and discriminate frequency distributions of different cutting mechanisms. After time-frequency analyzing of AE signals, component 2 (EPC2) with frequency range of 62.5-125 kHz was attributed to matrix cracking and component 5 (EPC5) with frequency range of 250-312.5 kHz and average energy of 32% was attributed to fiber cutting.

In high-pressure axial turbines, when the fluid mass flow is low, the supersonic blades are being used to obtain a high specific work output. To prevent losses due to low blade aspect ratio, the turbine is used in partial admission conditions. The turbine stator is a group of convergence-divergence nozzles that provides the supersonic flow. The design of these nozzles is important, because there is a direct relationship between the degree of partial admission and nozzle design parameters. The turbine efficiency is highly dependent on partial admission degree. To assess, in first step, an evaluation was carried out using an appropriate turbine efficiency correlation; then, a three-dimensional numerical analysis was implemented, and finally a series of experimental tests were carried out to validate the above assessments. The experimental results showed a good agreement with 1D and 3D numerical predicted results of turbine performance. The results showed that even small changes in the nozzle geometric parameters and partial admission degree, have a significant impact on the turbine performance and the flow distribution in the axial gap.

In this paper, an analytical study of the forced vibrations of hexapod table is studied. Considering external force as a time sinusoid force, forced vibrations of the platform are investigated. Resonance frequencies and vibrations of the moving platform are also calculated in different directions. The results of the analytical approach are verified using FEM simulation. Modelling the harmonic milling forces, a careful examination of the forced vibration are carried out in different cutting conditions and different configurations. Resonance frequencies and the range of vibrations are then calculated. Finally, knowing the resonance frequencies and the vibrations of hexapod table, different configurations of the table, which results in dynamic instability, are investigated.

Natural convection heat transfer from a vertical heated plate in a saturated porous medium is analyzed under thermal non-equilibrium assumptions. The plate is maintained at a non uniform temperature and the fluid is considered to be with internal heat generation. The coupled momentum and energy equations for fluid and solid phases are transformed to a similarity format, and solved numerically. The resulting velocity and temperature distributions are shown for different values of the problem parameters. Also the values of the local Nusselt numbers for both solid and fluid phases are shown. The effect of suction/injection on the free convection boundary layer is also studied. The obtained results are compared with those presented in the literature in the case of thermal equilibrium model.

Laminar counter flow diffusion flames provide useful information about basic properties of non-premixed combustion. A lot of studies have been performed on H2/O2 counter flow. Most of previous studies include undiluted or diluted systems of hydrogen (with CO2 or N2) against an air flow under a variety of conditions such as strain rates, inlet temperature and pressure. The main purpose of this research is to investigate the extinction limits and also to see how the temperature changes against the strain rate. The effect of Ar and He gases as diluents on combustion and extinction limits of H2/O2 is also investigated. Numerical simulations have been done with the OPPDIF code from CHEMKIN software. The obtained numerical results are compared with the others results and show the accuracy of numerical solution. Increasing the diluent percent causes decreasing of the maximum temperature and also the maximum mole fraction of active radicals of H and OH. Decreasing of producing H radical causes the fuel be slightly influenced by this species and thus the fuel diffuses more to oxide side. Increasing the diluent percent also causes decreasing of blow off and quenching limits in hydrogen combustion and accordingly narrows the flammability; But the increasing of inlet temperature flows and ambient pressure extend the flammability limits.

In this paper, the transient inertial viscoelastic flow around a circular cylinder is investigated numerically. A second order finite-volume method is used to increase the numerical accuracy. Here, the Giesekus model is used as the constitutive equation. This nonlinear model has prominent ability in describing normal stress differences and viscosity in power-law regions. The impacts of the elasticity and Reynolds number on the shedding frequency are discussed. Also, drag reduction phenomenon in the viscoelastic flow is studied by extracting pressure distribution on the cylinder surface. The obtained results are in good agreement with recent experimental and numerical investigations reported in the literature for Newtonian fluids.

In this work, Harmony Search Meta-Heuristic Optimization Algorithm has been developed for aerodynamic shape optimization problem for the first time. The aerodynamic shape, which has been investigated, is an airfoil with Parces method for its shape parameterization. The problem was minimization of aerodynamic objective function using inverse design method and the objective function has been the deviation of pressure distribution between investigated airfoil and the target airfoil. The 2-Dimensional compressible Navier-Stokes equations have been considered for simulation of flow using Spalart-Almaras turbulence model. A global improvement has been carried out to enhance the efficiency of Harmony Search Algorithm. In improved Harmony Search Algorithm one obtains the optimum design values and target airfoil by changing the airfoil shape design variables. To do this, algorithm starts from NACA0012 airfoil and reconstructs the target airfoil (RAE2822) by making pressure distribution closer to the target airfoil pressure distribution. For more accurate investigation and to make sure about the accuracy of algorithm, this optimization process has also been done in inverse direction. It means that, NACA0012 airfoil has been reconstructed starting from RAE2822 airfoil. The obtained results show that the utilization of Harmony Search Algorithm allows us to obtain an efficient and powerful tool for Aerodynamic Shape Optimization.

Improving mechanical properties of composites based on strength-to-weight ratio has been gained much attention in various applications. Having the most resistant and at the same time the lightest and the most economical structure is believed as an aim in these applications. These three factors are usually opposed to each other. So, applying optimization algorithms for improving mechanical properties of composites is very important. Particle swarm optimization (PSO) is used in balanced symmetric hybrid laminated composites for accessing the lowest weight and cost based on the first natural frequency. In this research, the objective function is a combination of the weight and cost which are both functions of the numbers and material of layers, while the natural frequency, in addition to the above factors, is a function of the fibers angle and the stacking sequenc, too. The results obtained from PSO algorithm (including optimized stacking sequences and the number of plies reinforced by either glass or graphite fibers) are compared with obtained results from genetic algorithm (GA) and ant colony optimization (ACO). The results confirme the advantages of hybrid composites and reveale that PSO provide the same results and in some cases even better sequences relative to the mentioned algorithms. This algorithm is so useful and competitive with respect to other heuristic algorithms.