Journal of Aerospace Science and Technology
Volume:5 Issue: 1, Spring 2008

Today, Flapping Micro Aerial Vehicles (MAV) are used in many different applications. Reynolds Number for this kind of aerial vehicle is about 104 ~ 105 which shows dominancy of inertial effects in comparison of viscous effects in flow field except adjacent of the solid boundaries. Due to periodic flapping stroke, fluid flow is unsteady. In addition, these creatures have some complexities in kinematic modeling. Although numerical methods are widely used for unsteady aerodynamic problems, it is highly difficult to solve the full 3D Navier–Stokes equations for complex flows like the ones of the flapping insect wings. Actually, the numerical simulation of flapping wings for different conditions of flapping frequencies and wing shapes has not been done yet. This is done in the present study. In present study, a computer code based on the unsteady Panel Method has been developed for flow analysis. The prepared algorithm and the computer code are capable of modeling MAV''s flapping wings in different unsteady conditions. The results of aerodynamic design coefficients have been drew. At the end the optimum wing shape and flapping frequency are chosen as another result of this study.

In this paper, the compressive behavior of composite laminates with multiple through-the-width delaminations is investigated analytically. The analytical method is based on the CLPT theory and its formulation is developed on the basis of the Rayleigh-Ritz approximation technique to analyze the buckling and post-buckling behavior of the delaminated laminates. The method can handle both local buckling of the delaminated sublaminates and global buckling of the whole plate. Also the three-dimensional finite element analysis is performed by using ANSYS5.4 general purpose commercial software, and the results are compared with those obtained by the analytical model. The agreement between the results is very good.

A computational study of partial cavitation over axisymmetric bodies is presented using two numerical methods. The first method is based on the VOF technique where transient 2D Navier-Stokes equations are solved along with an equation to track the cavity interface. Next, the steady boundary element method (BEM) based on potential flow theory is presented. The results of the two methods for a disk cavitator are compared with each other and with those of the available experiments and analytical relations. The two methods are then used to predict the partial cavity over an axisymmetric body consisting of a disk cavitator followed by a conical section and ending in a cylindrical shape. The effects of various parameters such as cone length, cone angle, cavitator radius and cylinder diameter are investigated. The results show that as the cone length is increased, the cavity region covers a larger portion of the body. Reducing the cone angle increases both the length and diameter of the cavity region. For an axisymmetric body with a larger radius the cavity detachment is more likely to occur.

The effect of airfoil shape parameterization on optimum design and its influence on the convergence of the evolutionary optimization process is presented. Three popular airfoil parametric methods including PARSEC, Sobieczky and B-Spline (Bezier curve) are studied and their efficiency and results are compared with those of a new method. The new method takes into consideration the characteristics of viscous transonic flows particularly around the trailing edge. The methods are applied to airfoil shape optimization at high Reynolds number turbulent flow conditions using Genetic Algorithm. An unstructured grid Navier-Stokes flow solver with a two-equation K-ε turbulence model is used to evaluate the objective function. The original mesh movement strategy (Spring analogy) is modified particularly inside the boundary layer in order to maintain the quality of cells in this area. The aerodynamic characteristics of the optimum airfoil obtained from the proposed parametric method are compared with those from alternative methods. It is concluded that the new method is capable of finding efficient and optimum airfoils in fewer number of evaluations.

In this paper the effect of different hardening models in simulating the U-bending process for AA5754-O and DP-Steel, taking a benchmark of NUMISHEET''93 2-D draw bending, has been discussed. The hardening models considered in simulations are: isotropic hardening, pure (linear) kinematic hardening and combined (nonlinear kinematic) hardening. The influence of hardening models on predicting springback and final state variables such as equivalent plastic strain, sheet thickness and punch force has been studied. The combined hardening model predicted the springback parameters well and the isotropic hardening over predicted the springback. The results of springback prediction have been compared with the results reported in the literature. A relation between the level of the final equivalent plastic strain and the amount of springback has been found. The obtained results show that attaining higher amount of equivalent plastic strain in the sheet leads to the less springback after unloading. Comparison between the two materials demonstrates that the aluminum alloy requires lower punch force which means superior formability and exhibits smaller springback.