Seyed Hamid Jalali Naini
Volume 6, Issue 2 , June 2009, Pages 55-61
Kaveh Amiri; Mohammad Reza Dr. Soltani; H. Haghiri; Mahmood Mani
Volume 6, Issue 2 , June 2009, Pages 63-70
Abstract
A trisonic wind tunnel has been modified to improve its flow quality when operating at transonic speeds through perforated walls and side suctions. The usefulness of such a perforated wall, already known, is reduction of the blockage effect as well as the shock elimination. Two types of perforated walls ...
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A trisonic wind tunnel has been modified to improve its flow quality when operating at transonic speeds through perforated walls and side suctions. The usefulness of such a perforated wall, already known, is reduction of the blockage effect as well as the shock elimination. Two types of perforated walls have been used in this investigation. The first wall had a porosity of about 22% and the holes were drilled perpendicular to the surface. However, the second wall had a variable porosity, 0 to 6%, and the holes were drilled at an angle of 60 degrees with respect to the normal vector of the plate. The flow in the test section of the wind tunnel was surveyed extensively at various Mach numbers ranging from 0.6 up to 1.2. Effect of porosity has been studied by comparing results related to the present perforated with the previous closed wall data for various conditions as. Te amount of suction could be adjusted through the side walls. Flow quality along the nozzle and test section has been studied by a long tube installed in the center of the wind tunnel test section.
M.A. Sharbafi; A. Mohammadinejad Mohammadinejad; Jafar Dr. Roshanian; Seddigh Khaki
Volume 6, Issue 2 , June 2009, Pages 71-78
Abstract
Gain scheduling is one of the most popular nonlinear control design approaches which has been widely and successfully applied in fields ranging from aerospace to process control. Despite the wide application of gain scheduling controllers, there is a notable lack of analysis on the stability of these ...
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Gain scheduling is one of the most popular nonlinear control design approaches which has been widely and successfully applied in fields ranging from aerospace to process control. Despite the wide application of gain scheduling controllers, there is a notable lack of analysis on the stability of these controllers. The most common application of these kinds of controllers is in the field of flight control and autopilots. The main goal of this paper is to apply a methodology to prove stability of a gain scheduled controller used in directing Skid-to-Turn missiles. One of the most widespread applications of gain scheduling controller is the main problem of this paper. To design the controller we use pole placement in state feedback controllers and a kind of innovative interpolation to reduce jumping in gains related to changing the flight conditions. Finally we utilize root locus and Kharitonov’s Theorem to prove stability of the linearized plant. The presented approach for stability analysis is distinctive in the literature.
I. Shafieenejad; Alireza Novinzadeh
Volume 6, Issue 2 , June 2009, Pages 79-85
Abstract
A new guidance scheme for the problem of Low-thrust transfer between inclined orbits is developed within the framework of optimal control theory. The objective of the guidance scheme is to provide the appropriate thrust steering program that will transfer the vehicle from an inclined low earth orbits ...
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A new guidance scheme for the problem of Low-thrust transfer between inclined orbits is developed within the framework of optimal control theory. The objective of the guidance scheme is to provide the appropriate thrust steering program that will transfer the vehicle from an inclined low earth orbits to the high earth orbits. The presented guidance scheme is determined using Pontryagin’s principle such that three desired performance measures are minimized and boundary conditions for this unspecified final time problem are satisfied. One of the novelties of this work is changing independent variable from time to thrust angle and considering properties of autonomous system equations to reduce to one where exact analytical solution is obtained.
Soghra Rezazadeh; Esmaeil Esmaeilzadeh
Volume 6, Issue 2 , June 2009, Pages 87-97
Abstract
In this paper, effects of EHD actuators on hydrodynamic behavior and heat transfer of air flow over a circular cylinder were considered. Pressure and temperature distributions around the cylinder were measured in presence of wire-plate EHD actuators. The Reynolds number based on cylinder diameter (d) ...
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In this paper, effects of EHD actuators on hydrodynamic behavior and heat transfer of air flow over a circular cylinder were considered. Pressure and temperature distributions around the cylinder were measured in presence of wire-plate EHD actuators. The Reynolds number based on cylinder diameter (d) were 3500, 7000. Experiments were performed for various configurations. Based on obtained results, the flow field around the cylinder was affected significantly by EHD actuation. The flow visualization confirmed the formation of separation bubble because of EHD actuation and affected pressure distribution dramatically. Measured temperatures showed that the excess flow, resulted from corona wind, enhanced local and average heat transfer over the cylinder.
Hoss Hosseini Toudeshky; Bijan Mohmmadi; Mohammad Dr. Sadr-Lahijani
Volume 6, Issue 2 , June 2009, Pages 99-113
Abstract
In this paper, progressive damage and global failure of composite laminates under quasi-static, monotonic loading are investigated using 3D continuum damage mechanics. For this purpose, a finite element program has been developed using an eight-node 2D layered element including layer-wise plate theory. ...
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In this paper, progressive damage and global failure of composite laminates under quasi-static, monotonic loading are investigated using 3D continuum damage mechanics. For this purpose, a finite element program has been developed using an eight-node 2D layered element including layer-wise plate theory. Damage analysis of a single orthotropic layer under various uniform in-plane and transverse loading conditions, and laminate problems with diffuse damage under simply supported and distributed transverse loading conditions are performed. The effects of modeling parameters such as hardening rules and mesh densities along the laminate thickness and in-plane surface on the progressive damage response and global failure are also investigated.
S. Amirahmadi; R. Ansari
Volume 6, Issue 2 , June 2009, Pages 115-120
Abstract
The main focus of this paper is on efficiency analysis of two kinds of approximating functions (characteristic orthogonal polynomials and characteristic beam functions) that have been applied in the Rayleigh-Ritz method to determine the non-dimensional buckling and frequency parameters of an angle ply ...
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The main focus of this paper is on efficiency analysis of two kinds of approximating functions (characteristic orthogonal polynomials and characteristic beam functions) that have been applied in the Rayleigh-Ritz method to determine the non-dimensional buckling and frequency parameters of an angle ply symmetric laminated composite plate with fully elastic boundaries. It has been observed that orthogonal polynomials yield superior results for the lower modes. Also, the overall CPU time consumed to perform the calculations by the two different procedures for constructing the approximating functions showed that orthogonal polynomials are computationally more time efficient. A novel approach is devised for the construction of characteristic beam functions for buckling and vibration analysis of an angle ply symmetric laminated composite plate. Numerical results are presented and discussed
