نشریه دانش و فناوری هوافضا
سال نهم شماره 1 (بهار و تابستان 1399)

Solar-powered generator is one of the critical parts in designing and manufacturing of the satellites. Achieving a high degree of reliability and maximum absorption in the Solar-powered generator are two key factors considered by designers.   In this paper, designing and manufacturing different components of a charging part of a nano-satellite have been evaluated by considering environmental constraints.  Simplicity and high degree of reliability are the main aspects of the proposed method that lead to maximum amount of power absorption. The innovation of this paper is detecting the optimal operating point of the solar panel based on the measurement of the solar cell temperature. In addition, an I2C communication protocol has been implemented between PMU and C&DH in order to simultaneously monitor of voltage and current of various points and receiving controlling orders from the stations on earth.  After designing and simulating of the controller of the charging part of the satellite, various necessary components for building of each subsystem have been prepared. In the next step, prototype of the charging circuit board was built and tested.  According to the test results, necessary modifications were implemented on the final circuit board.  Finally, the last version of the PMU circuit board was designed and built. Utilizing the boost synchronous converter, the efficiency of the converter section is improved up to 95%.

The flight mechanism of a bird is rather similar to that of an airplane because they both follow the same aerodynamic rules. For migratory birds that sustain flight without flapping their wings for very long periods and have relatively higher Reynolds numbers of flight, this similarity is very impressive. This paper aims to analyze flight performance of migratory birds using flight mechanics equations and to compare the results with the bird flight data. In that way, the obtained model can be validated, and used to estimate the performance of the flapping unmanned aerial vehicles. To that end, the flight performance of a brent goose, a migratory bird, is examined: Firstly, the flight of migratory birds is modeled. Then, the chemical and mechanical powers of the bird is obtained and analyzed. Afterwards, several performance parameters such as the aerodynamic efficiency coefficient, rate of climb, climb gradient, optimum airspeed interval and range are attained. Also, a comparison is made between the results of this study and real acquired data for a brent goose in order to validate the method. Finally, the effects of the altitude and weight on the performance parameters are studied. The results of this study indicate that the flight dynamic equations are capable to predict flight performance of migratory birds with acceptable precision.

In this paper, a fault-tolerant control system is designed for a quadrotor system. First, a control system was designed in the healthy mode then the system is upgraded to a fault-tolerant control system by using an analytical redundancy. This control system consists of two parts: (1) attitude control and, (2) position control. The inner loop is related to the control of the quadrotor attitude, and it is responsible for the stabilization and control of the Euler's Angles (azimuth, pitch and roll) and height. The outer loop is also related to the position control. This loop, according to the command of position, calculates the angles required to execute them and transmit them to the attitude control. The attitude and position control were implemented by using fuzzy and PD controllers respectively. Then, Parity space relations are used to detect and estimate actuator faults. As follow as these, control redesign is performed for fault tolerance and correction inputs by using fault signals. The difference between the healthy and faulty outputs approximately are reached to zero by using the PID controller. Two scenarios are considered for actuator faults. The first one is, the fault occurs in motor 1 and 2, and the second scenario is, fault happens in all motors. Finally, according to the actuator saturation, the critical value (maximum) of fault tolerance is estimated.

The main goal of this research is the conflict resolution and collision avoidance between multi low altitude aircraft using differential game theory. The conflict resolution is investigated as a cooperative differential game using a non-inferior method. In this study, the problem is considered as a constrained nonlinear differential game and is transformed into a single objective function using the weighted combination of aircraft objective functions. The objective function obtained along with all functional and environmental constraints will be solved in nonlinear programming using the pseudo-spectral method. The three degrees of freedom with performance constraints are used to model the problem. Also for the validation, the problem of conflict resolution will be solved in four different examples using the performance characteristics of a real aircraft based on low altitude flight rules. In these examples, the impact of priority coefficients on the flight path, the impact of the presence and constraint of the flight space on two-dimensional and three-dimensional space will be examined. The results show that in order to resolution of conflict base on the flight priority, it affects the control effort and flight path of each of the conflicting aircraft. This flight priority can be based on the need for airlines, flight delay, number of passengers or etc.

Todays, one of the topics that is of particular importance in the field of navigation is the use of navigation error propagation equations in order to integrate the output of an inertial navigation system with an external measurement to take advantages of both the inertial navigation mechanism and the external measurement. Study of past research Show that error propagation equations are generally extracted in a geographic frame that can have weaknesses. This paper demonstrates how to extract the error propagation equations in a tangent frame that not only have more simplicity than the geographic frame but also have a higher accuracy in describing the inertial navigation error propagation and thus increase the efficiency of the integrated navigation system. Finally, simulations in two cases using the tangent error propagation model and the geographic error propagation equations are performed by considering the hypothetical values for the acceleration and angular velocities and random error of the sensors. The results of the simulations also confirm the increasing of accuracy of the proposed error propagation model in this paper.ns in this paper also confirm the validity of this issue.

This paper concerned with the performance improvement of quad rotor using by variable pitch control system. The methodology was laid out based on dynamic modeling of six degree of freedom motion, trim calculations, linearization, and robust control system design for a candidate variable pitch quad-rotor at hover. Therefore, a comprehensive mathematical model of rotors was derived based on the blade element-momentum theory (BEMT) at low Reynolds number, and then, the engine and propulsion models were appended to form the real quad-rotor as a whole. Two control loops including of an inner loop for attitude control system and the outer loop for motion control applied with the robust control system, is the main structure of control system design. Linear controller and feedback linearization controller was also implemented to cover the stability of the quad rotor and compensation of fixed and variable pitch control mechanisms.. Variable pitch quad rotor helped the user to made bigger quad rotor with the less problem in control system which prepared from gyroscopic effect in fixed pitch quad rotor.

The use of thin plates with grid reinforcements has a widespread application in the design of lightweight structures. In this paper, the effect of the presence of a central crack on the critical buckling load of a thin plate reinforced with an isogrid lattice under pressure load is evaluated. The plate is reinforced by four horizontal and three diagonal ribs, which create hexagonal grids. The modeling and analysis is preformed numerically by finite element method using Abaqus software; and the influences of crack length and orientation, and Poisson's ratio on buckling load coefficients are investigated. The results show that the effect of these parameters is strongly influenced by the boundary conditions. In plates with simple supports on all four edges, increasing the length of the crack increases the critical buckling load and increasing the crack angle reduces the load. On the other side, when the longitudinal edges of the plate are free, the previous trend changes. As the increase in the length of the crack decreases the critical buckling load and the increase in the crack angle increases the critical buckling load. Also, the change in Poisson's ratio in both of the supporting conditions has little effect on stability of the plate; and the results show that increasing the Poisson's ratio slightly reduces the critical buckling load.

In this paper, a three-phase micromechanical model of short fiber composites considering interphase is developed to analyze the stress field in aramid fiber reinforced rubber composites. Due to the importance of the interphase in this type of composites, the modified shear-lag model and the imaginary fiber technique have been applied to investigate the load transfer mechanism and stress distribution. The results obtained from the analytical model indicate that the maximum tensile stress is occurred at the center of the fiber, whereas the shear stress of the interface at the end of the fiber reaches the maximum value. In the present model, the mechanical properties of the interphase, such as the elastic modulus, are obtained by averaging the radius-dependent mechanical properties. Also, the effects of the modulus ratio, aspect ratio, interphase thickness and Young modulus on the axial and shear stresses of interface have been investigated. The importance of the present model compared to the previous models is to use of imaginary fiber technique for short fiber composites with a three-phase micromechanics model. Note that the mechanical properties of these composites can be determined by obtaining the distribution of stresses in the matrix. There is also good agreement between the FEM results of full continuum micromechanical three-phase model and the results of the present analytical model.

In this paper, the three dimensional bending analysis of a multi-directional functionally graded annular sector plate is considered. The material properties are assumed to be graded in all three spatial directions following introduced power law functions. Governing Equations and boundary equations are derived based on three-dimensional theory of elasticity. The differential quadrature method is employed to discretize and solve the governing equations. Numerical results for different gradient indices are calculated. The results obtained from this research show that the direction of material variation has a noticeable effect on bending of an annular sector plate. In fact it indicates that the direction of material variation in a multi-directional annular sector plate can use as an effective variable for design optimization. Also the results of this paper can be used as benchmark for following studies. Moreover three dimensional bending analysis for an annular sector plate even for a common functionally graded plate (one directional FGM) has novelty and doesn’t considerate in literature. Comparisons are made with the solutions resulted by simulation in ABAQUS and show good agreement. Comparisons are made with the solutions resulted by simulation in ABAQUS and a good agreement was observed between the results.

In the current research, four different configurations of plasma streamwise vortex generators (PSVGs) for compressible flow control have been experimentally investigated to analyze their capabilities in controlling compressible flow (M=0.428) at the different excitation voltages and frequencies. The impacts of electrical parameters on the performance and efficiency of plasma actuators have been studied. Power spectrum analysis of pressure fluctuations in the boundary layer has been employed to determine the unsteady forcing frequencies of PSVGs. The presence of a dominant frequency in power spectrum diagrams is a strong indication of flow separation in the region from which the pressure signal has been extracted. As such, it was observed that the separation bubble was created in front of the comb-type PSVG when it starts its operation; however, using the T-type configuration diminished the separation bubble. T-type and mesh-type PSVGs, in similar experimental conditions, were observed to be more efficient than the comb-type and saw-type geometries in controlling compressible flow.

In this paper, the Fluidic anti-ice system performance for protective of ice formation on the aircraft wing leading edge is investigated numerically. The main parameters in this paper is checked, behavior of the flow, see the leak or spray flow out of the hole, and the fluid distribution range by volume of fluid method. This study helps us to distribute fluid anti-ice over the zone of wing so as to prevent ice formation in that area. Then the effect of various parameters such as fluid flow rate and inlet pressure, air velocity and angle of attack was studied and observed that if these parameters changed, it can be sensible effects on the fluid distribution and its range. Finally, in order to validate of numerical method by using the Euler and Lagrange method in this analysis, two experimental results were used and compared them. There is a good agreement between the numerical and experimental results.

The design of space launch vehicles that can be reused can significantly reduce the cost of space missions. These launch vehicles should be equipped with engines that are capable of proper operation in the supersonic and hypersonic flow regimes. The design of the air intake of these engines is a key challenge. One of the most important issues affecting the performance of these engines is the shocks that are expected at the entrance to the engine. The flow of air from these shocks provides conditions for stable combustion in the engine. The air intake efficiency of these engines is optimized in several ways. In this study, the attempt to optimize a supersonic air intake using the magnetohydrodynamic method has been developed as an advanced flow control technique. The results of this study showed that the MFR parameter increased by 21.62%, the mean temperature increased by 10.51%, pressure recovery of the exhaust particles towards the combustion chamber increased by 14.5%, and the flow distortion decreased by 18.93%.

Transverse fuel injection in supersonic crossflow of scramjet combustors is one of the common methods for fuel-air mixing. Air jet injection before fuel jet can improve fuel penetration but with the excess stagnation pressure loss. In this paper, the position of air jet is changed to find the position that maximum fuel jet penetration height and minimum stagnation pressure loss is achieved. For numerical simulations, Two-dimensional Navier-Stokes equations and k-ω sst turbulence model and the perfect gas equation are solved. Then the results of the numerical solution are compared and validated with experimental data. Numerical results showed good agreement with the experimental values. In the experimental test, Helium is injected into supersonic crossflow and so numerical simulation is started with Helium injection. In scramjet usually, hydrogen was used as fuel. Therefore, hydrogen fuel injection is used for the parametric study. In the case of air injection near the fuel injection, maximum fuel penetration with minimum stagnation pressure loss is achieved.

In this research study the transient process in expansion cycle rocket engines. For this purpose, the RL-10 expansion cycle rocket engines has been selected as the study sample. In expansion cycle engines, the start-up process is complex due to the use of fluid passing through the heat transfer path in the cooling system instead of using the gas generator to move the turbine. This process is managed by control valves.It is important to know the effect of the process and the timing of the opening and closing of the valves in the analysis of this type of system. In this paper, the dynamic model of the expansion cycle rocket engines was first developed and validated using experimental test results.Finally, using this model, the effect of valve opening and closing on the dynamic behavior of the motor was measured by measuring the time characteristics of the system.This study showed that the process and order of opening and closing valves in the oxidizing path in expansion cycle rocket engine is very important.

In this paper, designing, implementation and validation of a laboratory for sun sensor test and calibration would be presented. In this laboratory, power, spectrum, uniformity, subtending angle, and the parallelism of the sunbeams and also the angular motion of sun sensor with respect to sun simulator are accurately simulated. Using the simulator, test and calibration of sun sensors in different angular maneuvering would be possible. This capability depends on a method for precise calibration of 3DOF motion simulator and sun simulator with respect together. This calibration method is used to make the sunbeams and optical axes of sun sensors, which is perpendicular to the sun sensor surface, parallel and coaxial. In the beginning of the paper, the detailed description and adjustment methods for each of the components of the simulator are presented. Afterwards, an algorithm for making the optical axes of the sun sensor coaxial with the axis of the sun simulator beams will be developed. Furthermore, each of the specifications of the produced beams is compared with the sunbeams specifications using the existent peripheral or some heuristic methods. Finally, a referenced calibrated sun sensor is evaluated in a known angular maneuver by the developed simulator. Comparing the known angular maneuver to the measured angles shows the adequate accuracy of the implemented simulator in order to test and calibration of the analog sun sensor. Considering the specification of the produced beams, it seems that digital sun sensor can also be calibrated.

This paper investigates the effect of limited geometrical changes on the combustion chamber performance of a specifically upgraded gas microturbine. The fuel used in this chamber is gas-methane. The purpose of this paper is to improve the performance of the chamber in terms of fuel consumption and to reduce NO and CO2 emissions concentrations. For this purpose, based on the relevant calculations, a combustion chamber was designed for the upgraded engine and later, with changes in the volume of primary combustion zones (PZ) and dilution zone (DZ), two additional geometries were created. Then, using three-dimensional numerical analysis, the combustion performance was tested and evaluated in all three geometries. The numerical simulation uses the PDF interaction model and the k-epsilon turbulence model. The results show that the chamber with a reduced geometry of 25% by volume, with a 10% reduction in FAR ratio, has an acceptable flow pattern and performance, and the amount of contaminants in it has decreased by more than 30% on average.

The fuel spray analysis in the combustion chamber, as a significant parameter in optimizing nozzle performance, is associated with complexity, both numerical and experimental, due to the high pressure and speed of the fuel flow. In this paper, the simulation of the effect of nozzle geometry and the needle lift on the Diesel fuel spray has been done by usage of Fluent software. The spray penetration length is considered as a major criterion for improving the performance of the Diesel engine. The size and location of cavitation phenomena within the nozzle will change with the deformation of the nozzle geometry and the needle lift, under constant conditions. Accordingly, firstly the effect of nozzle geometry and needle lift on the formation of cavitation in the Diesel nozzle was simulated transiently with moving mesh and using the scanner-Saur method. Then, using the obtained results, fuel spray was simulated by SSD method. In this paper, the aim of increasing the accuracy of problem solving is investigated for laboratory and experimental values. The process of flow changes in the nozzle is solved unsteady, and then the outlet results at the upstream are used as input values for flow downstream and spray. This article shows that how the penetration length of spray will change with the deformation of the nozzle geometry and needle lift.

One of the critical challenges in the satellite is thermal management of the electronic unit and preventing the formation of hotspots, which requires proper heat transfer for structures used in spacecraft. One way to increase heat conduction is to use heat pipes in these structures. Heat pipes are passive heat control methods that can be used in aerospace applications due to their reliability, cost and power consumption, lifetime, and high thermal conductivity. The main goal of this study is to apply a heat pipe in thermal management of the satellite. We use a 3D cylindrical numerical model of the wicked heat pipe for comprising with experimental data. Heat pipe simulation is performed using the multi-phase volume of the fluid model (VOF) method, and user-defined function in the numerical model in Fluent software. We use transient mode for solving equations. The simulations results show that after 120 s the heat pipe operation is stabled. The results confirm reducing the porosity, the thermal resistance in the heat pipe increases, and the heat transfer performance decreases. The results also show that the methanol has the lowest thermal resistance among other coolants.

In the present work, in order to improve performance characteristics such as power output and reduce fuel consumption in spark ignition engines and engines used in the aerospace industry, combined gasoline fuels with dimethyl ether and iron oxide nano catalysts that can be synthesized at lower prices than other catalysts , Has been studied in a gasoline spark ignition engine. In order to achieve the steady state in the experimental stages, the temperature of the water and engine oil before each test of the EF7 spark ignition engine at engine speed of 2800 rpm is about 10 to 15 minutes to reach the various parts of the engine. The tests are carried out at full load conditions and engine speed rpm 2800 and between torques 0 to N.m 100. The output power and fuel consumption of the engine, with the combination of gasoline with 10% of the dimethyl ether, increased by 22.5% and 28.28% respectively, and in the case of gasoline in combination with 10% of dimethyl ethyl and 10ppm of iron oxide nano additive, lead to output power 19.44% increased and fuel consumption 19.5% reduced. in the case of gasoline in combination with 10% of dimethyl ether and 20ppm nano additive of iron oxide lead to output power 13.93% increased and fuel consumption 11.08% reduced, compared to the base fuel gasoline. emissions have also been reduced by combined fuel with iron oxide nano catalysts.