نشریه دانش و فناوری هوافضا
سال سوم شماره 1 (بهار و تابستان 1393)

Star trackers as an example of celestial based sensors are specifically designed to perform accurate and absolute attitude determination. This requires us to measure the camera optical axis with respect to the local direction of the gravity and to have knowledge of time. This paper modifies the standard algorithms are implemented in star trackers so that they can estimate the local coordinates of the platform as well as the azimuth along with attitude data using observations from an accurate tilt meter and a clock. In order to validate our proposed method، different tests have been performed using developed simulator system. Results of the research described that proposed method has the capability of implementing in navigation purposes as an efficient alternative for GPS when it is not available and also periodic augmentation of Inertial Navigation Systems.

Skilled pilot training in aviation industry is of great importance. This in real terms due to high costs and safety considerations، is facing with serious obstacles. Thus providing low cost، efficient and repeatable flight training conditions attracted a broad range of researches. Flight simulators are such devices for training the skilled pilots. These tools aim to provide the same feeling of real flying for pilots، and give the opportunity to pilot to react under terms of the flight conditions. Motion cueing design algorithm is of the salient challenges in the design of these devices. The algorithm receives the linear acceleration and angular velocity of the real flight as the inputs and is due to calculate the appropriate movements of the actuators such that the infinite plane motions to get constricted to finite motions in the limited work space of the flight simulator. This has to be done in a way that the pilot in flight simulator feels as could as the same sense of motion of the pilot in aircraft. The authors aim to develop an optimal motion cueing algorithm for 6 DoF flight simulator with fuzzy compensated system specially focusing on the maximum use of workspace of the simulator to obtain more appropriate sense of motion. Comparing the results of the proposed fuzzy compensated and the conventional optimal motion cueing algorithms، shows an evident improvements in terms of smaller movements of actuators while achieving more appropriate motions of the flight simulator.

In this paper، plastic behavior of thin-walled conical shell under static internal pressure has been investigated analytically. In order to simplification، stress resultant along the slant of cone has been neglected and rigid-perfectly plastic model is used for material behavior. Common rectangular surface has been used as yielding criterion. According to present approach، cones are categorized into «long» and «short» based on their geometry. For each case، required pressure for initiation of plastic flow is formulated and is named collapse pressure. Maximum collapse pressure occurs at specific angle. The results coincide with collapse pressures of cylinder and circular plate at angels near 0º and 90º، respectively. The results have been depicted for various ratios of the larger radius of cone to the thickness. The differences between long and short cone have been distinguished.

In this paper، free vibration of the thick sandwich beams with flexible cores is investigated using the dynamic stiffness method and a new higher order theory. First the governing partial differential equations of motion for one element are derived using Hamilton’s principle. Closed form analytical solution of these equations is determined. After applying the effect of boundary condition of the element on the obtained equations، the element dynamic stiffness matrix is developed. These matrices are assembled and the boundary conditions of the beam are applied، so that the dynamic stiffness matrix of the beam is derived. Natural frequencies and mode shapes are computed by the use of numerical techniques and the well-known Wittrick–Williams algorithm. Finally، some numerical examples are discussed using the dynamic stiffness method and the analytical formulation. For verification of the present model، the obtained results are compared with the latest exact analytical and approximate finite element results.

A numerical dynamic-aerodynamic interface code for the separation dynamics simulation of constra­in­ed strap-on boosters jettisoned in the atmosphere is presented. This code includes a main environme­nt which connects both dynamic and aerodynamic subsystems together at one time. The first part، consists of a 6-DOF multi body dynamic solver and the second part، contains a numeric­al aerodynamic flow solver، which is automatically used the dynamic mesh updating algorithm for adaption of the body motion in the discrete computa­tion­al field. The relationship between dynamic and aero­dyn­a­m­i­c solver is such that the resultant separation software، can simulates mult­­i body separation with complete mechanisms such as springs separation، Thrusters، joints، etc، in the presence of the aero­dyna­mic effects. The flow solver is validated by the Titan-IV launch vehicle experimental data. After all، this method is used in simulation of strap-on booster separation for a typical launch vehicle with use of spring separation system and constraint joints in presence of aerodynamic effects and without them. Hence the aim of presented interface is to facilitate integration of complicated separation mechanisms simulation with a full numerical CFD aerody­n­a­m­ic solver.

Shock formation on the surface of flying objects due flow compressibility and its interaction with boundary layer cause undesirable effects such as drag increment and flow separation. Various methods for reducing the effects have been suggested in the past like vortex generators، suction & blowing، and etc. This paper investigates numerically using of porous media for flow control and decreasing the shock effects. Porous media by increasing flow cross section and by combination suction & blowing reduces these undesirable effects. The numerical method is finite volume، the equations are Navier-Stokes and the geometric model is NACA0012 airfoil. The flow is assumed to be turbulent and steady in transonic regime. In addition، the geometrical modeling of porous media is validated in this paper. Results show that by decreasing the shock wave effects and consequently wave drag decrement، total drag coefficient decrease 20% and 16% using porous surface and porous media، respectively. The weaken shock is moved to the upstream and Mach number behind the shock decrease from 1. 34 to 1. 29. By decreasing the shock-boundary layer interaction effects، separation bubble is postponed from 0. 58 to 0. 78 chord length.

In this paper، the main goals are investigation of missile with grid fins، determination of aerodynamics coefficient and calculation of fin span effects on performance of missile. We solved Navier-Stokes equations for achieving of them. Nowadays، with improvement of numerical algorithms and speeding up of computers processors، CFD is one of the most convenient and high accuracy methods for analysis. The first، we introduce the grid fins and then analyze a fin with different span to investigation of fin span effect on performance of missile. Finally، we mount two grid fins on missile body and carry out CFD calculations on total missile at different Mach and angle of attack to compute the flow field and aerodynamics coefficient for a missile with grid fins. The results have been validated by comparing the computed aerodynamic coefficients for the missile and individual grid fins against wind tunnel measurement data. Very good agreement with the measured data was observed for all investigated configurations.