Journal of Aerospace Science and Technology
Volume:7 Issue: 1, Winter and Spring 2010

The purpose of this paper is to examine the multidisciplinary design optimization (MDO) of a reentry vehicle. In this paper, optimization of a RV based on, minimization of heat flux integral and minimization of axial force coefficient integral and maximization of static margin integral along reentry trajectory is carried out. The classic optimization methods are not applicable here due to the complexity of the equations, therefore in this research, the genetic algorithm technique is utilized for optimization of the RV. In addition, the results of the genetic algorithm, are validated with those of two other methods, Pareto genetic algorithm and response surface method. In the present paper, in order to decrease the computational time, parallel processing strategy is employed

The method of lattice boltzmann equation(LBE) is a kinetic-based approach for fluid flow computations. In the last decade, minimal kinetic models, and primarily the LBE, have met with significant success in the simulation of complex hydrodynamic phenomena, ranging from slow flows in grossly irregular geometries to fully developed turbulence, to flow with dynamic phase transitions. In the present work, a computer code, based on the LBM has been developed to show the capability of the method for simulating fluid flows. The confined flow around a cylinder with square cross-section mounted inside a plane channel (blockage ratio B=1/8) was investigated in detail with LBM method. The largest Reynolds number chosen was Re=300 based on the maximum inflow velocity and the chord length of the square cylinder. The LBE was built up on the D2Q9 model and the single relaxation time method called the lattice-BGK method. Both velocity profiles and integral parameters such as drag coefficient and Strouhal number were investigated

Ionospheric tomography is a method to investigate the ionospheric electron density in two or three dimensions. In this study, the function-based tomographic technique has been used for regional reconstruction of a 3D tomographic model of the ionospheric electron density using the GPS measurements of the Iranian Permanent GPS Network. Two-dimensional Haar wavelets and empirical orthogonal functions are used as base functions to model the horizontal and the vertical structure of the electron density, respectively. Sparseness of data and data gaps make ionospheric tomography an ill-posed inverse problem. The truncated singular value decomposition (TSVD) method is used to come up with solution. The data analysis results show that the latitudinal sections of the electron density in ionosphere obtained from the tomographic technique supports the expected time and height variations in the electron density. Moreover, these findings show that the height of maximum electron density is changed during the day. This confirms the efficiency of the developed multilayer model in comparison to the traditional single-layer ones. The relative error between the reconstructed electron density and the electron density obtained from ionosonde data varies between 5 to 35 percent. The difference between the reconstructed electron density (as well as the corresponding estimations of the IRI-2001 model) and the direct estimates of this quantity increases when the electron density reaches to its maximum value. Assuming that the ionosonde station in Tehran produces reliable results, this proves that the reconstructed image as well as the IRI-2001 model does not efficiently constraint the electron density during this period of time.

In the following paper, the effects of a choked jet exhausted from the base of a non-lifting body on its total and base drags at sub-sonic and transonic regimes has been numerically investigated. Having surveyed the results of some turbulence models and after comparing with experimental results, an appropriate turbulence model i.e. SST K-, has been chosen and this model has been used in the subsequent analysis. The analysis have been conducted in the free stream Mach number range of 0.4

Abstract View Paper Original: English

The main purpose of this paper is concerned with the sensitivity analysis of main rotor dynamic response pertaining to variation of some relevant system parameters effectively supports the preliminary design of both articulated and hingeless helicopter rotor configurations. The methodology is laid out based on Galerkin solution of partial differential equation (PDE) of main rotor with flexible blades in modal space, and developing of some significant expressions useful for direct and cross-coupled damping and control response prediction. The methods followed in this particular discipline supports the derivation of main rotor PDE for flexible flapping in non-linear closed form accompanied with procurement of response derivatives, Galerkin method of solution, linearization, modal analysis and harmonic balance application. The main advantage of this approach is to render main rotor direct, cross damping and control derivatives for each harmonic of the blade deformations associated with the calculated pitching and rolling moments. The sensitivity expressions enables the prediction of direct, cross damping and control derivatives of main rotor response in terms of the most expressive system parameters, including flap frequency ratio, stiffness number, blade response Lock number, and physical hinge offset, necessary for design of modern helicopters. Finally, the results are depicted in graphical forms for a range of system parameters and operating conditions. Comparison of damping and control derivatives in hover, shows a small effect of offset hinge on the main rotor direct response, whereas, the cross derivatives have a strong dependence on combination of stiffness and offset. Furthermore, Comparison with the full aeroelastic analysis shows that the obtained predictions approximate the true elastic of the main rotor behavior.

Unsteady dynamic behavior of TTCP model with different wrap around fin sets were investigated in a trisonic wind tunne. The aerodynamic coefficient force measurement in this wind tunnel shows good agreement in comparison with that of the NASA Langley Research Center in static case. The model was sinusoidally oscillated at three different frequencies of 1, 3 and 8 Hz at M=2.0 and the effects of these frequencies on the shock angle were investigated and compared with the corresponding static case. Experimental data indicates that the static shock angle does not fall between the upstroke and down stroke dynamic shock angle at different frequencies which is different from experimental findings for flat fin configurations. This unsteady behavior could be added to the other anomalies frequently seen in the aerodynamic characteristics of wrap around fin configurations. Also shock development mechanism over the nose and several fin sets was investigated and the shock-boundary layer interaction near the fin/body juncture which leads to shock likes λ was clearly observed in this investigation.

In this paper, an approach to aeronautical structural design based on reliability analysis is presented. In this way, the concept of level of safety is discussed and methods of its calculation using statistical data are described. Based on the concept of level of safety, a design procedure is proposed. In order to validate this design procedure, two design cases are studied. In the first case study, using finite element method, a sandwich plate containing a circular disbond between the upper faceplate and core subjected to compressive in-plane load is examined. The calculated critical buckling load and its residual strength versus disbond diameter and design load versus level of safety are compared to the existing data a good agreement is achieved. In the second case study, a delaminated sandwich beam under bending load is considered and the design load (obtained from the strain energy release rate analysis) versus level of safety is determined. The results of the study show that for the adopted visual inspection technique and a high probability of damage occurrence, the design load should be about 25% of the beam strength to achieve a reliability higher than 0.99.