Journal of Applied and Computational Sciences in Mechanics
Year:2011 | Volume:22 | Issue:1 (3)|Papers Count:8

In establishing of similarity conditions, dimensional analysis and direct use of governing equations are two existing major methods. These methods are frequently used in elastic domains. In this study, both methods are applied in inelastic domains. Their applicability is illustrated through the study of buckling response of impacted composite plates by using the progressive damage modeling technique. In order to establish the similarity conditions between impacted plates under buckling loading, similitude theory is applied in two following stages. First similarity condition is established for impacted plates. Then the similarity condition between impacted plates under buckling loading is established. For development of similarity conditions in impact loading, dimensional analysis is used while in buckling loading governing equations are applied directly. This method is called “Sequential Similitude”. In the next stage, progressive damage modeling was conducted on scaled down models to verify the accuracy of predicted results from similitude equations. Results show the validity of this procedure for simulation with acceptable errors in predicted results.

The present study numerically assesses two and three dimensionally, of the flow pattern inside channels and around impulse blades of a supersonic turbine. Also the effects of edge-sharpening on the aerodynamics of blades have been of concern. Primary studies show that with geometric modification of blades, optimization of the efficiency of turbine is possible. The numerical and experimental results suggest that edge-sharpening modifies flow pattern and improves shock field on the area between nozzle and. Supersonic turbines do not need cooling system and their flow is of compressible, supersonic, highly turbulent and complex flow field type. Turbulence flows may have different oscillating velocity fields. Since these oscillations may be very small and haveing a high frequency, their direct simulation will be too costly in regard to practical engineering computations. In numerical studies, correct simulation and the proper turbulence model selection for these flows are very important in obtaining reliable results in reasonable amount of time. The Two turbulence models, k-e/RNG and, k-w, have been widely used for the numerical analysis of these turbo machines. The present study also aimed to comparatively assess the two models to determine which one is superior for the simulations of impulse turbines. Accurate measurements of the mean characteristics and oscillating of the velocity field have been carried out in boundary layers with y+£50. The results of the computations have been compared to those of the experimental analysis.

The main goal for this research is to analyze a transversely isotropic half-space under the effect of a circular rigid disc attached on the surface of the domain. To do so, the potential method is used to uncouple the Navier’s equilibrium partial differential equations. Utilizing Hu-Nowakii-Lekhnitskii potential functions and both Fourier series and Hankel transform, the displacements and stresses Green’s functions are determined for a surface ring load in a cylindrical coordinate system attached to the domain. Then, the effect of circular rigid disc is seen by applying some ring loads of unknown amplitudes, depends on the direction of displacement of the disc, which may be vertical, horizontal or rocking displacement. The amplitudes of the different ring loads are determined by satisfying the displacement boundary conditions. It is shown that the results are identical to the existing ones for the isotropic case. To assess the effect of anisotropy, the results are numerically evaluated for different transversely isotropic materials and compared.

Gas lubricated bearings are of tremendous use especially in the biomedical and aerospace industries. Analytical treatment of gas lubrication is tedious due to high nonlinearity of the pressure equation as the consequence of lubricant compressibility. Howevere, in this paper a feed-forward neural network approach is employed to investigate the performance of circular as well as two, three and four-lobe noncircular gas lubricated bearings. The performance parameters considered are stability margins, power loss, bearing load capacity and attitude angle for various values of bearing aspect ratio, eccentricity and compressibility numbers. The results of the neural network analyses are compared with those obtained from the finite element model. It is observed that results are in good agreement. It is believed that the neural network model can easily compete with the available theoretical model in predicting the solution of lubrication problems in respect to its simplicity,  as well as its capability of producting accurate results with lesser computer time.

In this paper the performance of a Savonius wind turbine has been studied both experimentally and theoretically using the FloEFD software. Two different types of vertical axis Savonius rotor, namely, conventional and advanced rotors, have been compared. It is shown that the coefficient of static moment for an advanced Savonius rotor is about 11% more than that for a conventional one. A study has also been conducted to investigate the variation of the power coefficient for the advanced Savonius rotor installed in MERC and recommendations have been presented to enhance its performance.

Good understanding of In-Cylinder Fluid Flow during the operation process has effective role in the engine design. To aid the best operation, fuel consumption and environment pollution must be decreased. In recent years, various turbulence models are widely developed and used to predict the flow turbulence. In this paper, the effect of turbulence models in simulation of In-Cylinder fluid flow in a combustion chamber has been investigated from the Inlet Valve Closing (IVC) to Exhaust Valve Opening (EVO). Comparison of the present simulation with the experimental data shows a considerable difference for various models. The results of simulation show that the Reynolds Stress Turbulence Model is better than the other turbulence models.

The Functionally Graded Materials (FGM) have been introduced in the last few decades. In these materials the modulus of elasticity can vary as a continuous function throughout the domain of the problem. Due to some weaknesses of the Finite Element Method (FEM) in dealing with these problems, a slightly different version of the recently developed Isogeometric Analysis (IA) method is employed to overcome some of the deficiencies of the FEM. Amongst the benefits of the proposed method, elimination of the burden of mesh generation and a considerable reduction in the size of unknowns and consequently the number of the resulted equations can be named. Finally, the accuracy and robustness of the method is illustrated by a couple of examples.