نشریه دانش و فناوری هوافضا
سال پنجم شماره 1 (بهار و تابستان 1395)

This paper discusses the flight control strategy based on Adaptive Dynamic Inversion (ADI) with two-time-scale separation for airplane. Because of nonlinear behavior of flight dynamics, the flight control problem is a rather important and complex issue. In addition to traditional methods, e.g., classic controller, Dynamic inversion methods, fuzzy and neural networks have been used. After reviewing these methods, Combination Adaptive dynamic inversion Method is designed. In this structure, the control system attempts to track the angle of attack, the sideslip angle and the roll angle in wind frame ( ). Six degree-of-freedom nonlinear equations of motion are considered for tracking the input commands. Dynamic inversion technique needs an exact and accurate flight dynamics, and to avoid this problem, we use an adaptive controller. Two-timescale based system dynamics are divided into slow outer variables and fast inner variables. Adaptive controller and Dynamic inversion algorithm are used in inner and outer loops, respectively. The performance of the proposed method compares with Full Dynamic Inversion (DI) method. Simulation results demonstrated the efficacy of Adaptive Dynamic Inversion controller.

In this paper, a new method on the base of the indirect solution of optimal control problem is presented for trajectory planning of Free-Floating Space Robot (FFSR) in point to point motion. To this end, dynamic equations of the system beside the non-holonomic constraints due to angular momentum conservation low are derived in the state space form. Then the necessary conditions for optimality are derived using the fundamental theorem calculus of variations. The obtained equations lead to a two-point boundary value problem (BVP) which its solution result in optimal trajectory and optimal control function. In the proposed method, both manipulator and base moves from the initial pose to the final pose in such a way that all the boundary conditions, dynamic equations and non-holonomic constraints are satisfied, and a given performance index such as consumed power or torque is also minimized. Simulations are performed for a two-link free-floating space manipulator and the obtained results are compared with the previous works, and the efficiency of proposed method to reduce the base movement is illustrated.

In this article, effect of magnetic field on hydrogen diffusion flame (30% hydrogen volume fraction and 70% nitrogen volume fraction) in terms of flame shape, heat of reaction source and amount of unburnt hydrogen in products parameters is investigated. The magnetic field is applied directly to the flame region for the magnitude of 0.5, 1, 1.5, 2, 2.5, and 3 tesla. It is found that the flame shape and the flame height become smaller with the application of magnetic field. It is also found that the magnetic field reduces the obtained unburnt hydrogen quantity at Y=1 mm. In fact, magnetic field presence produces Lorentz force which opposes the flow direction. Consequently, the more the magnitude of magnetic field, the more the reaction source heat and the shorter the flame height will become. These results represent that the magnetic field causes more complete combustion and less pollutant production. It is noted that magnetic field effect on governing equations, Lorentz force and Joule heating are added to the momentum and energy equation respectively by using C programming.

In this paper, an experimental study and numerical simulation with openfoam software have been done. In this study effects of flow condition and geometrical parameters on spray characteristics of airblast atomizer have been investigated. In experimental, the droplet sizes (Sauter Mean Diameter) and their distributions have been determined in different Weber number 727 to 2250 and Reynolds number 1650, with using Malvern Master Sizer x. Numerical simulation was done based on discrete particle tracking method and Eulerian-Lagrangian approach. The results show that in constant Weber number, increasing of liquid injection port can increase SMD but in high Weber numbers has less effect. Numerical simulation shows that liquid injection angle and mixing length have low effect on penetration length of spray. On the other hand, increasing in liquid injection port diameter can decrease penetration length of spray strongly. Numerical simulation and experimental results have little difference and very similar to each other.

Performance of a aerospace vehicle or spacecraft during the re-entry have great dependency to flow-field physics around it. Aerothermodynamics heating in high velocity is highly dependent on geometry and flow-field physics. It is a big challenge of these vehicles for re-entry phase and engineers for reduction of these inappropriate effects use thermal protection systems with much expensive prices. In this Concern, the effects of flow control using counter flow axial jet ahead of a 2.6% scale model of Apollo capsule are investigated in order to decreasing the undesirable effects of aerothermodynamics heating. The aerodynamics performance of this capsule has been studied at free stream Mach number of 3.48 with 5 different flow rates of counter flow jet. The results show that two flow regimes can be seen by increasing the jet mass flow rate; Long Penetration Mode (LPM) and Short Penetration Mode (SPM). LPM that appears in low mass flow rates causes the increment of the shock-detachment distance, unsteadiness and flow oscillations and SPM that appears in high mass flow rates causes the decrement of the shock-detachment distance. Transition of LPM to SPM occurs in mass flow rate between 0.0145kg/s and 0.113kg/s. The results indicate that the counter flow jet decreases the drag about 80%. Moreover, the effects of excitation in counter flow pulsed jets at 1000Hz and 2000Hz frequency have been investigation for decrement of mass of fluid injection in this study. The results of this investigation shows that increment of excitation frequency to 2000Hz reduces drag near to 60%.

Topology optimization of structural is among optimization method. That goal is to find best geometric and structural performance. In this way optimal geometry and material distribution of a structure that must pass Space generated. In other Hand, initial shape of structure production by loads applies to the optimization. The finite element method is created to help Sections of elements that can be removing namely. They will not enter in to Tension According to the Requirements defined in the analytical cycle model Delete And the optimal way possible for the Considered to be able to maintain the operating condition Recommended. In this study, topology analysis was performed on a Plate Structures Where changes in boundary conditions, loads and constraints are checked and optimized geometry is extracted in each case.

Composite applications are very wide in most industrial fields. Today, polymer matrix composites are used in the automotive industry, aerospace, oil, gas and petrochemical Industries and etc. Glass / epoxy composite is one of the most useful composites that has special properties such as high strength-to-weight ratio, high hardness, high corrosion resistance, low thermal expansion, resistance to nuclear radiation and absorption of energy. Composite beams may be used as flexural elements. In flexural loading, the crack initiation and failure can occur in a variety of modes that each ones has special frequencies. In this research, acoustic emission method was used to evaluate and check the different failure mechanisms of glass epoxy composite beam under three point bending loading. In order to determine different failure mechanisms, wavelet transform analysis was used for acoustic signal processing by using only one sensor. Three types of dominant failure mechanisms (matrix fracture, debonding and fiber breakage) in composite beam under bending were identified and the frequency ranges corresponding to these failure mechanisms were determined. Wavelet transform results showed that these three types of dominant failure mechanisms (matrix fracture, debonding and fiber breakage) have frequency ranges of 0-125 KHz, 125-250 KHz and 375-500 KHz respectively. Finally, the observations of scanning electron microscope from fracture surface of specimen validated the obtained results. This research showed the possibility of acoustic emission technique as a monitoring tool of glass/epoxy composite beam in flexural failure.