نشریه مهندسی هوانوردی
سال بیست و دوم شماره 2 (پاییز و زمستان 1399)

In this article, vibration and supersonic flutter analyses are studied for trapezoidal sandwich panels. Functionally graded trapezoidal panel as well as reinforced sandwich panel by graphene nano platelets are considered. It is assumed that the graphene platelet (GPL) nanofillers are distributed in the matrix either uniformly or non-uniformly in the direction of thickness. UD, FG-X, FG-V, FG-O and FG-A are the distribution patterns of GPLs. Based on the Kant higher-order theories, the dynamic equations of sandwich panels reinforced with graphene nanoplates  are obtained using extended Hamilton’s principle. Dynamic pressure is estimated according to the quasi-stable theory of supersonic piston. Then, using a transformation of coordinates, the governing equations and boundary conditions are converted from the original coordinates into new computational ones. Finally, the differential squares method (DQM) to obtain the natural frequencies, the shape of the modes, and the critical aerodynamic pressure is used. The effect of different porosity distribution, porosity coefficients, distribution of graphene nanoplates, weight fraction, geometry of graphene nanofillers and geometric dimensions on natural frequencies and system instability behavior are studied.

Ring rolling process is used in the production of seamless rings.The most important advantages of these rings are favorable grain flow and crack growth resistance. Aircraft engine spools are usually produced by means of this process. Failure of the work rolls during forming of spools leads to unacceptable geometrical structural and irreparable damages. Evaluation of the work rolls life of the ring rolling machine has a direct effect on the properties of the output ring. Initially, different types of life estimation and cumulative damage assessment methods were studied. By making use of Abaqus simulation, the loading history was extracted and applied to the work rolls. According to the loading history, stress-life method and cumulative damage relations were performed. The results of the research shows that the main roll is significantly affected by mechanical stresses. On the other hand, the mandrel is affected by thermal stresses by applying the thermo-mechanical forces. In general, in order to extend the work roll’s life, of the work rolls and reduce the effects of the thermo-mechanical stresses, the uniformity of temperature during work rolls operation should be maintained. So that proper cooling will have a significant effect on the service life. In addition, the effect of bending stress on the mandrel life is not significant.

The error of the inertial navigation system (INS) increases with time and leads the navigation system to instability. Hence, this paper investigates INS/GPS integration. Kalman filter is the most common way for integrating these two systems, but due to the nonlinear behavior of the INS/GPS integrated navigation system; nonlinear filters are used for data integration. Furthermore, given that GPS is capable of measuring the velocity and position of the object, these measurements are used to estimate system states (position, velocity, and orientation). In the following, we have investigated the observability of the system’s state space. Using practical data from a UAV, simulation results shows that the performance of the particle filter is better than that of the other two estimators for complex nonlinear systems with non-Gaussian noise.

In this paper, static strength analysis of superalloy Rene-80 is studied experimentally in both of the coated and uncoated cases. Superalloy Rene-80 is widely used in manufacturing aircraft turbine blades. The service temperature of this alloy is in the range of 760–982 °C. Although this superalloy has good mechanical properties and acceptable protection against oxidation and hot corrosion, it is coated to improve its resistance to surface degradation factors such as oxidation, hot corrosion and erosion at high temperatures. In this paper, penetrating aluminide coatings were applied to this superalloy with two separate methods of penetration-powder and penetration-slurry, respectively, under the brand names Codep-B and IP1041slurry, respectively and the effect of these coatings on the tensile properties of Rene-80 under ehe temperature range of 25-982 ° C was investigated. For this purpose, the samples according to ASTM-E8 standard are produced and after coating (the two methods mentioned above) along with uncoated samples are carried out a tensile testing in accordance with the ASTM-E21 standard. The results of the present study showed that at low operating temperatures, uncoated samples have better tensile strength than coated samples, but this behavior is reversed at high operating temperatures, which indicates the importance of using nickel-based superalloy coatings for extreme heat environments. Also, the model with IP1041slurry coating at high operating temperature has better yield and ultimate strengths than powder penetration coating.

Cube satellites are small and lightweight satellites a large number of which is launched by each rocket heading into the space and this has led to a rapid increase in the number of these satellites in the Earth orbit. Over the years, many research centers have come up with ways to improve the reliability of the OBC circuits, but so far, no research is entirely focused on the memory module used to record and store loaded satellite data for transmission to the earth station. Given the high cost of manufacturing a satellite, special attention should be paid to increase the reliability of the memory circuit against space radiation and the fault tolerance of these circuits. The STT-MRAM introduced in this paper is now recognized as the most successful alternative to the SRAM. Using software add-ons, the authors have increased the fault tolerance of this type of memory and obtained the fault model based on the Markov Model and the Monte Carlo simulation. The simulations were performed using GEM5 full-system simulator, and the results of the simulation in optimal memory indicate an increase in its fault tolerance in all benchmarks based on the SPEC CPU2006 test standard.

In this study, after introducing the concept of smartening and examining various models of how to do this, a cantilever beam has been used for the smartening,using MATLAB. Then, the smart code is applied to the desired airfoil and after the flap modeling process, at different flap angles, the meshing process using the H-grid method was done in Gambit software. The flow is assumed to be constant, turbulent, adiabatic and incompressible, and the equation solving algorithm is selected pressure-based. The reason for the three-dimensional study in this research is to create more accurate simulation conditions and to consider three-dimensional effects. In addition, due to the special position the wing is attached to the body at the root, modeling the wing separately imposes a lot of complexity. The turbulence model is also considered k-ε. In this research, the performance of the smart flap has been investigated in both near ground and open conditions. Comparison of the results and aerodynamic characteristics of the wing with the smart flap and the wing with the normal flap in Fluent software, shows that the lift coefficient has increased significantly (about 16%), but the changes in the drag coefficient are very small. Finally, it has led to a significant improvement in the ratio of lift to drag (L/D). Also, the study of pressure and velocity gradients at different sections shows that the intelligentization process is very successful and has a better distribution compared to conventional flaps.

This study investigates the effects of cascade blades that are passed through the flow. To this end, the characteristics of boundary layer flow is obtained on a fixed plate in downstream. A special moving grid has been introduced for the numerical simulation of flow. In this method, a zone of the grid moves inside the main grid. Regarding the defined plan, the regular changes of grid connections can be carried out by the program. Therefore, movement of different bodies in the flow can be simulated even in large sizes without reducing the quality of grid. In the written code, the unsteady form of the Navier-Stokes equations is solved using an averaging method. For turbulent modeling, a two-equation k −ε model is used. Velocity profile at the boundary layer on the flat plate is calculated. The results are validated with experimental data and good agreements among the results are observed. The results are validated with experimental data and good agreements among the results are observed.

The current study is dedicated to free vibration and aeroelastic stability analysis of truncated conical ‎panels in supersonic flows. Governing equations of motion and the corresponding boundary conditions are ‎derived using Hamiltonian formulations. The aeroelastic stability problem is formulated based on first-order ‎shear deformation theory as well as classical shell theory with the linearized first-order piston theory for ‎aerodynamic loading. Based on the Galerkin truncation, the coupled fluid-solid interaction equation ‎transferred to ordinary differential equations.‎‏ ‏By solving the eigenvalue problem, frequencies and damping ‎of the system have been obtained versus supersonic flows‎. ‏ ‏The results are validated using numerical and theoretical data ‎available in the literature.‎ The study has been accomplished for truncated ‎conical shells with various geometries. The flutter boundaries are obtained for truncated conical shells with different ‎semi-vertex cone angles, different subtended angles, and different thicknesses. In all cases, the truncated conical shell ‎loses its stability through coupled-mode flutter.‎

In the last decade, the use of plasma actuators for the application of flow control has been very interested. One of plasma actuators types is the Dielectric Barrier discharge (DBD) plasma actuator. Its properties include simple structure, fast response time, low power consumption and lack of moving parts. In this study, the changes of pressure distribution before and after plasma formation at different frequencies and voltages were investigated just above surface at the bottom of the flat plate model and the location of the last plasma actuator. Also the effect of voltage and frequency changes on the pressure distribution has been surveyed. The results of the experimental tests indicate that the plasma produces the ionic jet just above surface, in fact, the plasma actuators produce momentum flow in the boundary layer and produce ionic wind. By increasing the voltage and frequency - more than the breakdown voltage - the momentum flow is created in the direction of the plasma actuator. As the voltage increases and the plasma becomes visible and vortexes are formed on the flat plate.

Designing the suitable autopilot for the quadrotors is very important in how the flight vehicle moves and follows the specified reference path. One of the suitable controllers for autopilot design is the predictive controller, which is the most well-known Generalized Predictive Controller method. In the autopilot design, constraints on inputs as well as communication delays must be taken into account, and if these two issues are not addressed in the controller design, the autopilot will not function properly and may even lead to instability. In this paper, a generalized predictive controller with consideration for delayed input data for a quadrotor autopilot is presented. Also, in order to determine the predictive control parameters, the Metaheuristic method, particle swarm optimization, has been used and these parameters have been optimally adjusted. In adjusting the controller parameters, the objective function is used based on the performance indicators such as settling time, peak time, overshoot, and steady-state error. By adjusting the weights of this function, the controller performance indicators can be determined. Also, the simulation results show that the controller performance based on the defined objective function is much improved compared to the cost function based on the integral of the error.

In this paper, a reference trajectory tracking control is designed for a typical quadrotor. For this purpose, two control ‎loops is proposed as follow: the inner loop is based on state feedback control technique and optimal control which ‎coefficients are obtained as a function of system states using the genetic algorithm. Then, optimal control coefficients ‎functions are extracted‏ ‏using the optimally stored data and least square method. The mentioned control function is ‎based on a linear relationship between system state space and control coefficients. In the outer control loop, the PID ‎control is utilized. Since, in this approach, the control coefficients are ‎obtained from the genetic algorithm, the ‎properties of the fitness function are considered. The ‎performance of the proposed controller is evaluated by a ‎comparative study especially to the PID ‎controller, which is widely used in the literature. The simulation results show ‎the effective performance of this technique in controlling Euler angles, reduction in summation of tracking error and ‎optimization in power consumption.‎

In this research,the most important causes of helicopter accidents are discussed.For this aim,the data of aviation accidents that occurred in Iran and the data registered in ICAO are used.Several research efforts have been directed towards betters understanding the causes of accidents.Many of these efforts use ICAO accident reports and data.Unfortunately,while these studies easily identify the top types of accidents(e.g.,inflight loss of control (LOC)),they usually cannot identify why these accidents are happening.Most ICAOnarrative reports for accidents are very short(many are only one paragraph long),and do not contain much information on the causes(likely because the causes were not fully identified).Unfortunately,in our country, the efforts made in this field for various reasons have not been given much attention so far,which has led to the lack of clear and citationable results of the correct causes of aviation accidents.Aviation accidents in Iran,especially in the last two decades,do not show a significant reduction in the number of accidents or casualties.To better understand the causes of aviation accidents,this study offers a state-based approach to examining existing logical gaps or neglected cases and a computer program(in STATISTICA)that automatically builds states,signs,and information codes related to accidents These rules also help identify and count causes for accidents that were not discernable from previous analyses of historical accident data.State-based approach shows that distraction of pilots to objects in the environment often results in loss of flight control(16.7%),which is not directly distinguishable from conventional analysis.State-based modeling is a new method in this field.Also,machine learning tools are used to achieve more desirable results.

In the present study, optimum design of a semi-active oleopneumatic shock absorber equipped with MR valve in order to use in the airplane main landing gear will be discussed. In the first phase of design, based on the force-displacement diagram design criterion and considering a maximum value of gas pressure, dimensions of the main cylinder, piston cylinder, orifice width, valve radius, and length are determined in the passive state of shock absorber. In the following and in the second phase of design, by the use of obtained information from the first phase, and according to performance criteria of MR valve and the principle of using the maximum working capacity of MR fluid without magnetic saturation of MR valve, the optimum design of MR valve in the constant volume and the active state of shock absorber will be done. In the design procedure, the effect of geometric parameters on shock absorber force is also examined and will be shown that orifice width is the most effective and sensitive geometric parameter in this regard. Optimum design of airplane main landing gear MR shock absorber based on performance criteria of MR valve and investigating the effect of MR valve parameters on shock absorber forces and magnetic properties of valve are the novelties of this research. Due to the importance and the application of MR shock absorber, the results and the achievements of the present study can be used in other industries, in addition to the airplane landing gear as a specific case study.

Recent developments in mission implementation and agent control have drawn attention to the performing of cooperative missions. Decision-making systems are among the most important parts of such missions. The aim of these systems is efficient task assignment and path planning. This paper combines a task assignment approach and a path planning method to tackle collaborative problems. The task assignment approach, used in this paper, is based on an improved linear programming approach for its high accuracy. The path planning method is based on Dubins curve to handle the limitation movements of fixed-wing fighters, investigated in this paper. The proposed methods perform based on the utilized fighter’s performance characteristics and flight constraints in a dynamic environment with moving targets. The path planning approach is based on specific constraints, including certain output vectors of each point as well as input ones to the target points, minimum rotational angle, and performance factors of fighters. In the next step, Dubins path planning output is used as the necessary coefficient to solve the task assignment problem of cooperative fighters. By using a heuristic hierarchical approach based on linear programming, a comprehensive path planning and task assignment of a fleet of fighters is completed. The presented results show optimal performance and higher speed to solve rather than the classical approaches, which is capable to cover the dynamic environment as well.

This research was conducted with the aim of comparative comparisons of pilot training at Shahid Sattari Air University (from the point of view of the source of the planned courses, the planned time of each lesson and the order and sequence of each lesson presentation) with selected international, regional and national universities.This research is a applied research in terms of the purpose and is descriptive-analytical regarding method. Data were collected by library method and analyzed using Breddy's comparative study model and qualitative method. The statistical population of the study consisted of American AOT pilot training institutes, Maxwell American University, Arizona University, Pakistan War University, and Israeli War University and Applied Scientific University. The method of selecting the statistical population is Purposeful sampling. Research findings indicate that there was no significant difference between the samples in the exact courses of flight, aerodynamics, engine and aircraft systems, physiology, navigation, and meteorology in terms of curriculum planning. Shahid Sattari Air Force University has a better program in the fields of warfare, military science and electronic warfare than other other universities studied.In the University of Pakistan, more specifically in the field of war and military science, especially in ballistic missile program, more action were observed.Basic courses and aviation laws in Arizona's educational centers were seen more powerful than other selected institutes.

In this research, a different view of the study of the pattern and behavior of turbulent flow on the two full-span wings of baseline and sinusoidal leading-edge with periodic boundary condition by a numerical method is introduced. In this simulation, the Navier-Stokes equations are discretized by the finite volume method and solved using the improved turbulence model (IDDES). In other words, in the current study, to enhance the maneuverability of a fix-winged MAV, a passive flow control method was employed, which was inspired by the buoyancy fin of a special species of whale called a humpback. In order to study the performance of this type of infinite wing, the Reynolds number was considered equal to 140000. The results show extensive variations between these two types of full-span wings. The sinusoidal leading-edge full-span wing, in contrast to the baseline infinite wing, has severe fluctuations in pressure distribution and flow pattern at the pre-stall region. These variations are caused by the dominance of lateral flows over longitudinal flows on this type of infinite wing. Therefore, researching the patterns and analysis of vortices formed on this type of aerofoil as well as the associated frequencies is always a useful tool for understanding physics of flow on them, which will provide designers with a new perspective on flying objects.

Continuous aerial patrolling of long borders of a country requires a group of cooperative unmanned aerial vehicles (UAVs). Previous research based on the spatio-temporal virtual plane provided a framework for comparing different patterns and scenarios of patrolling from the point of view of criteria such as revisit time, percentage of spatio-temporal coverage and the degree of uniformity of coverage. Continuing previous research, the present paper uses the concept of spatio-temporal coverage to provide an automated process for patrolling scenario design with the ability to focus on priority areas such as intruder’s corridors. The designed scenario is described based on the number and distribution of the UAVs at each airport, the time difference between their take-offs, the movement pattern of each UAV and their speed along the path. More focus on priority areas is provided by adjusting the time difference between taking-off the UAVs from the airports or changing their speed on the interested areas. The proposed process considers practical constraints such as minimum speed and maximum flight duration of UAVs, path specifications, payload specifications, and etc. in the production of feasible paths. In the following, the user's priorities regarding reducing the number of UAVs, increasing the coverage percentage, and the reduction of the maximum and average revisit time is considered in selecting the final scenario among the produced feasible path. The proposed process is implemented as a toolbox and the results show the ability of this method to design an appropriate scenario based on user requirements and existing constraints.

Vibroacoustic behavior of graphene reinforced composite plate (GRCP) is studied to investigate the sound transmission loss (STL), Due to the importance of the behavior of the structure against sound waves. Many materials have been used to increase the stiffness and improve the vibroacoustic behavior of sandwich structures. which in recent years, Graphene has prompted many researchers to use it in sandwich structures. Governing equations are derived based on three-dimensional elasticity and state vector method is used to solve equations of motion. To evaluate the validity of the results from previous studies, two studies that have examined the sound transmission loss of plate have been used. To find the effective parameters on the amount of plate STL, changes in graphene weight fraction, plate thickness, incidence angle, thickness of graphene nanoplatelets (GPLs) and width of GPLs are investigated. Finally, numerical results show that adding a small amount of GPLs to the composite matrix increases its stiffness and thus improves the behavior of the structure against the pressure of sound waves. Also, Increasing the plate thickness has a good effect on the STL, and increasing width of GPLs with constant length has no effect on the vibroacoustic behavior of the structure.