Journal of Aerospace Science and Technology
Volume:14 Issue: 1, Winter and Spring 2021

Airships usually have low cruising speed due to their large volume and high drag level. This makes the aerodynamic design of the vehicle, including the surfaces shape, the length-to-diameter ratio and the position of the fins, all very important. Furthermore, an important parameter in the vehicle aerodynamic drag is determining the flow separation area at the rear of the air vehicle. The flow separation plays an essential role in the amount of drag and lift force, so the location of the fins and the design of the rear of the airship will be very important. By using both analytical and numerical methods, this study examines the aerodynamic efficiency of an airship in three different configurations, focusing on the location, type, and angle of attack of the fin, and compares analytical and numerical results. According to studies conducted among the types of fins, the cross-type will have the best performance among the fins in terms of lift-drag ratio. Also, moving the fins forward and distancing them from the rear of the vehicle disrupts the flow pattern at the rear of the vehicle and delays separation. This will improve aerodynamic efficiency and improve the lift-drag ratio of the vehicle.

In this research, new adaptation law for updating parameters of the model reference adaptive control and the model reference adaptive control with feedback integrators for a specific class of nonlinear systems with additive parametric uncertainty are presented. The innovation presented in this paper is the consideration of a new form for Lyapunov functions candidate to prove the stability of the closed-loop system. In general, Lyapunov functions candidate, which is used to prove stability and to derive rules for updating control parameters, include two sets of quadratic expressions. The first quadratic expression contains the trajectory tracking error and the second category includes the error of estimating the controller parameters. In this research, it is proved that by selecting quadratic expressions including the variable of trajectory tracking error in the form of power series, a new adaptation law is obtained that includes quadratic expressions in terms of the variable of tracking error in the form of power series. This type of adaptation law can be considered as an adaptation law derived from quadratic Lyapunov functions, except that the gain adaptation matrix parameters vary with time. It has been shown that by using an adaptive controller with a feedback integrator, the tracking error tends to zero faster and the flying object roll angle tracks the reference trajectory after a shorter time. In order to evaluate the control performance of the designed controllers, the system of one degree of freedom of the Wing Rock phenomenon has been used.

The composite lattice cylindrical shells are analyzed in this research while they are subjected to transient dynamic loading. The equilibrium equations for the composite cylindrical shell are expressed in terms of classical shell theory. Additionally, due to the discontinuous distribution of stiffness and shell mass between reinforcing ribs and their proximity to one another (empty or filled with filler material), this issue has been expressed using an appropriate distribution function. On the basis of Lowe's first approximation theory, the strain-displacement and curvature-displacement relationships are considered. The Galerkin method is used to calculate the natural frequencies and shapes of structural modes for the boundary conditions, as well as the transient dynamic response of the composite cylindrical lattice shell to lateral impulsive loading applied extensively and uniformly on a specific rectangular surface. The convolution and a method for summing the effects of the modes are also obtained, and the obtained results are validated using references and ABAQUS finite element software. The effects of various parameters on free and forced vibrations are investigated, including geometric ratios, material properties, cross-sectional dimensions and distances, and lattice configuration. Finally, the effect of strengthening the cylindrical shell with lattice structures is investigated.

Compared to the enormous costs of laboratory experiments, numerical approaches to improving the performance of turbomachines are less costly and more practical. In the present study, by using the Taguchi method and orthogonal arrays while doing a limited number of simulations (according to the Taguchi method), the sensitivity level of objective functions have been investigated to optimization variables in a fan of a high-bypass ratio turbofan engine (JT9D-7 Engine). a mathematical parameterized algorithm coupled to a computational fluid dynamic solution  is employed to modify the geometry and calculate the objective functions. 15 optimization variables are defined by varying:The radial distribution of the chord length from the hub to the tip of the blade and alsoeach profile's lean and sweep in five control points compared to hub profile.The lean, sweep and chord length are parameterized by a spline algorithm. The objective functions included the pressure ratio, isentropic efficiency and mass flow rate of the fan in the design point. The results showed that the lean angle affects the isentropic efficiency, and the sweep angle affects the mass flow rate of the fan. The pressure ratio was sensitive to both variables. Concerning the design variables, 2-level L16 and L32 arrays of the Taguchi method were used for running the sensitivity analysis. Assuming a fixed number of blades, a fixed angle of incidence, and a fixed camber angle, distributing the chord length did not significantly affect the objective functions compared to the lean and sweep distribution.

In this paper, a semi-analytical solution for three-dimensional transient analysis of an annular plate with piezoelectric layers is investigated. The core is a functionally graded material with an exponential distribution. This method, which is a combination of the state space method, Laplace transform and its inversion, and the one-dimensional differential quadrature method, is used to obtain the response of three-dimensional motion equations plate and the stress-displacement relations of the state space equations obtaining an analytical solution in the direction of the thickness and by applying the differential quadrature method to the equations of state space, a semi-analytical solution of the plate is obtained. To obtain a solution in the time domain, the Laplace transform and its numerical inversion are used. Analyzing the convergence of the present method, the obtained numerical results have been compared with the results of articles and with results obtained from using finite element analysis. Various parameters were studied including boundary conditions, piezoelectric properties, voltage applied to the actuator, the ratio of core thickness to layers, the ratio of outer to inner radius, and the functionally graded material variations index.

This paper deals with the problem of optimal selection of orbital parameters for an Earth observation mission in the absence of the possibility of injection into sun-synchronous orbit by considering the requirements and limitations of the mission and the satellite platform. By modeling the existing relationships between each of the three areas of orbit, mission and platform, the effects of changes in each of the parameters have been analyzed and tracked. One of the important advantages of the proposed solution is that in the process of optimal selection of relevant parameters, all aspects of the orbit, mission and platform are considered simultaneously. This, in turn, can lead to an implementable and operational option for accomplishing the mission. In evaluation of effects of changing orbital parameters on the mission characteristics and requirements of the satellite platform, a developed computer code has been used.

While the composite pipes and cylinders manufacture by filament wound system, there are a lot of parameters that influence on the strength and mechanical behavior of them. This various mechanical behavior causes various buckling behavior. One of the most important parameters is winding pattern that have effects on critical buckling loads. So this parameter should be controlled since it effects on mechanical behavior of pipes and cylinders. In the present work the influence of winding patterns on the critical buckling load of filament wound pipes exposed by pure axial loading have been studied. The studied specimens are Glass/Epoxy tubes with [+55,-55]6 lay-up(diameter to thickness ratio d/t of 10 and length of 280mm). Parameters were all considered to be consistent to investigate the effects of winding patterns there is just difference in winding pattern between three the experimental specimens. The lay-up is the result of classical theories. Love model and Galerkin’s method were used to provide buckling equations and solve theoretically the resulted equation respectively. Although the results illustrate that there is a difference, about 2-4 percent, in terms of critical buckling load between disparate winding patterns, 16 unit cells winding pattern bears higher buckling load than other patterns. Also the results show that no evident patterns influence on buckling modes of pipes. Later, the maximum lateral buckling loads of the patterns are verified with experimental data.

This paper aims to present an investigation on determining the critical cavitation number of a high-speed centrifugal pump by computational fluid dynamics. In doing so, characteristic curves of the pump used in this study were obtained in the presence and absence of cavitation. The critical cavitation number was calculated based on the cavitation breakdown characteristic curve. Two-phase flow inside the pump was simulated using the homogenous mixture method and the Rayleigh-Plesset model. The SST turbulence model and MRF rotating model were used to simulate turbulence and rotation of the flow throgh the pump, respecively. The critical cavitation number that was the outcome of numerical analysis results was compared to the experimental data. This comparison implied the necessity of considering the safety factor for determining the critical cavitation number and inlet pressure required to uninterrupted operation of the pump cavitation, using the results of numerical analysis.

The primary objective of this study was to demonstrate how plasma actuators could be used to discharge a perpendicular dielectric barrier as a virtual Gurney flap. This study utilized wind tunnel experiments on a flat plate airfoil. Each experiment is conducted at two different free flow velocities of ten and twenty meters per second. To study and extract the aerodynamic phenomena generated by plasma actuators and to compare them to the Gurney phenomena of a physical flap, velocity profiles in the model sequence were measured using a hot wire flow meter in two different longitudinal positions relative to the model. All experiments were conducted from five distinct vantage points, 0, 2, 4, 6, and 8, and plasma actuators were activated in two distinct settings to extract concepts under a variety of conditions. Wind tunnel experiments indicate that downward sequence transfer occurs when plasma actuators are used. Additionally, there are two distinct types of vortex shedding on the model's back: one that resembles Karman vortex shedding and another that occurs below the model. The observation of velocity profiles demonstrates that the deformation of the sequence caused by the use of plasma actuators is very similar to that caused by an airfoil sequence equipped with a physical Gurney flap.

This study focuses on improving performance of a supercritical wing equipped with winglets at different cant angles. This study aims to experimentally investigate the variation of aerodynamic performance of a supercritical wing of NASA Sc (2)-0410 airfoil at lower Reynolds numbers with winglets at various cant angles. The tests were performed by measuring the lift and drag force using a three-component balance within a broad range of angle of attack from -4 to 20 degrees and at three different subsonic flow velocities. Results include changes in lift, drag, and aerodynamic performance for each winglet cant angle compared to the baseline wing. The results show that winglets generally increase the lift force and decrease the drag force by decreasing the size and strength of the wingtip vortices. Moreover, the optimal winglet for each case is extracted based on the aerodynamic performance provided by each winglet. In order to better and more accurately compare the effect of different mounting angles of the winglet on the aerodynamic performance of the base wing, the impact of each winglet is shown separately. Accordingly, it is observed that the winglets with angles of 0o and 15 o, namely W0 and W15, have shown good performance in increasing the lift coefficient. Also, the winglet with 90 degrees has shown good performance in creating the least drag force.

The purpose of this paper is to present a Multi-Input Multi-Output (MIMO) linear controller based on the eigenstructure assignment method for a fixed-wing Unmanned Aerial Vehicle (UAV) in longitudinal and lateral-directional channels. To this end, a six degree-of-freedom model of the aerial vehicle is considered, where dynamic modes of the system in each channel are analyzed, and the effect of each dynamic mode on state and output variables of the system is investigated. Then, the eigenvalue and eigenvector parameters of the designed controller are appropriately assigned for the system dynamic modes in each channel. In addition, the system requirements of each dynamic mode are satisfied with the proposed controller, and the adverse interaction between the system state variables is minimized. The capability and effectiveness of the designed controller in a desired maneuver are demonstrated with a nonlinear model simulation of a fixed-wing UAV. In this regard, the results in longitudinal and lateral-directional channels are presented.

The purpose of this paper is to propose a method for the dual space tether system to continue its mission in the event of a failure by using fault-tolerant control. To accomplish this, a new and accurate model of a space tether with two tethers has been introduced, which can demonstrate the effects of the tensile force more precisely in the model. One of the features of this model is the ability to modify the junction of the tethers to the subsatellite, which can be included as a control parameter in the problem. As a result, the fuel required to control the mission can be decreased. To mitigate the effects of tether failure, a fault-tolerant control strategy based on model predictive control (MPC) has been developed for the nonlinear space tether system. This control method has the advantage of being both optimal and capable of controlling the system in the event of a failure. The simulation results demonstrate that the proposed control method is capable of controlling the dual spatial tether system despite thruster and tether failure.