JOURNAL OF AEROSPACE SCIENCE AND RESEARCH
Year:2009 | Volume:2 | Issue:3|Papers Count:9

In this work, the static and dynamic instabilities of a three-step Timoshinko beam with follower force, considering changes in the stiffness of the joint springs, is investigated. To derive the related equations, Hamiltonian principle has been used. Energy relations are written for the Timoshinko beam considering the rotational inertia and shear deformation. Steady and unsteady follower forces and the kinetic energy of lumped masses and included. It is noted that minor changes in mass and stiffness properties of the beam effect the critical force and the type of istability considerably. Also changing the beam’s length in different cases, critical modes change a considerable amount. Note, dynamic instability occurs because the third and fourth non-tend trequencies are combined, while the first and second frequencies stay stable.

In this work, the performance and the application of vertical combustion chamber in liquid fuel propulsive system have been investigated. In new technology, the related injection inforce a vertical. How inside the combustion chamber, which help the walls, cooling and the mixing & combustion component. This way, a complete combustion is performed in a combustion chamber with small volume.

To estimate the number of required layers for a composite laminate which stands a compound load, a very simple method has been developed and assembled. This method, which is based on superposition theory, the number of layers in each layer-group is settled separately according to the direction and the amount of main stresses and separating them from each other in desired elements. Since the direction of the main stresses and maximum shear stress depend on the amount and the direction of applied loads in this method, determining the strength of singlelayer based on fiber angle (the angle between fiber and applied load in a plan which comprises main stress and or, a plan which comprises maximum shear stress) is needed. In this paper, according to the maximum strain criterion, a very simple method in order to obtain the function of single-layer strength (versus fiber angle) is suggested.

The main objective of this paper is to determine the aerodynamic coefficients of a steady supersonic wing, using boundary element method based on the solution of potential flow. In this regard, the governing partial deferential equation of flow field is first derived and linearized. Then, using boundary element method, in conjunction with the first order shape functions, the system of discrete equations are obtained. However, there are some numerical problems in the evaluation of integral coefficients due to singularity caused by intersection of Mach forecone and the edge of some elements in computational domain. Of course, this problem can be eliminated using some numerical techniques. Finally, the steady supersonic flow analysis is performed for two different wings with identified geometries. Comparison between the numerical results and those obtained using the exact solution indicates good agreements.

In this article, the trend of UAV design using the AerSim software is first described then, different design steps of the autopilot program and the algorithms control tests using software -in-the-loop test in used for choosing the best control methods. In the next step, using the hardware-in-the-loop test, the auto-pilot program is validated. Finally, the flight test results & a real UAV is presented for comparison purpose. Sinse this control algorithm has been designed for a non-linear model aircraft considering the atmospheric noise, the results match well will real data and thus cause considerable decrease in real life tests.

Turbulence is a phenomenon occurring in many flows. Because of the limitations of memory and computational speed, direct numerical simulation of governing equations cannot be implemented in complex situations. On the other hand, the LES and RANS approaches are used more because of their less computational costs. However, in complex problems and also in high Reynolds number flows, LES simulation takes too much CPU time. The hybrid approaches combine the advantages of both LES and RANS, i.e. the accuracy of LES and low numerical effort of RANS. and thus approach can effectively be used in simulation of complex flows. The purpose of this article is to investigate different types of Hybrid LES/RANS approaches used to simulate turbulent flows.

In this article, an innovative method for filling the aircraft wings, farmes with rezin (using VARTM) is presented. This method is a suitable alternative for manual methods. Certain parts are made using both methods and their mechanical properties, speed of their production, and their cost have been compared. The ones made by VARTM have less bubbles and thus more volume fraction. This leads to better mechanical properties. Also, by optimizing the effective properties in VARTM, the production speed is increased compared to the manual method.

The optimal positions of Stewart mechanism joints are obtained using genetic algorithm to maximize the workspace and to minimize the singularity condition within the workspace at the same time. The workspace of Stewart mechanism is obtained by a fully geometric method. The volume of workspace is then calculated with numerical integration. On the other hand, the global dexterity of the workspace is studied by calculating the condition number at each point inside the workspace. Since workspace volume or dexterity is not a suitable design criterion individually, they are combined and a non-dimensional multi-objective cost function is proposed. The suggested cost function involves the ratio of variables to their maximum value. This function is presented as a criterion to reach optimal geometry for different robotic mechanisms. The workspace and the dexterity simulation results are resented. To make sure that the design requirements are achieved, a static force analysis is performed. It is shown that this optimization method increases workspace, stiffness, and dexterity at the same time.

Turbulence models have long been developed and examined for their accuracy and stability in variety of environments. While many flows work with excited turbulence intensity, models have rarely been tested to explore whether their accuracy withstands with augmented free stream turbulence intensity or decline in reasonable solutions. In present study the turbulent intensity of the air, moving parallel to a flat plate is increased from 0.4 to 6.6% for the whole flow, downstream to the screen. Three popular turbulence models are examined by investigating the turbulence penetration into flow field as well as into turbulent boundary layers over the flat plate. Results of numerical solutions for Standard k-e, Realizable k-e and finally two equations Shear Stress Transport k-w model are compared to experimental measurements and results are discussed. Results of variation of free stream turbulence intensity from flow field out of boundary layer, in addition, streamwise mean velocity, streamwise rms velocity and skin friction coefficient from boundary layer are investigated. Conclusion is made that despite restrictions of these turbulent models specially in predicting flow near a turbulent/non-turbulent interface, they have acceptable performance in both low and high intensity turbulent flows.