Journal of Aerospace Science and Technology
Volume:17 Issue: 1, Winter and Spring 2024

In this study, a comprehensive investigation of the fracture parameters in a grooved rotating disc containing a three-dimensional semi-elliptical crack under different working conditions has been investigated. In this regard, three models of radial, circumferential and inclined crack with an angle of 45 degree have been considered in the rotating disk, and the fracture parameters under mixed mode loading (I, II, III) have been extracted. The effects of various parameters such as rotational speed, crack location, aspect ratio, material and presence of grooves on SIFs and crack opening displacement have been studied simultaneously. The finite element results indicated that in the crack with a low aspect ratio (0.4 and 0.6) where the shape of the crack is more like a semi-elliptical, the maximum value of the mode I SIF occurs at the central point of the crack front, while the crack with a high aspect ratio (0.8 and 1) where the shape of the crack is more like a semi-circular, the maximum value of the mode I SIF occurs at the free surface of the crack. The mode II SIF for the rotating disk containing an inclined crack before the central point of the crack front, has the highest value for steel, titanium and aluminium rotating disk, respectively. Also, the numerical results indicated that the highest value of the SIF is related to the grooved rotating disk containing a circumferential crack, and the lowest value of the SIF is for the grooved rotating disk containing a radial crack

The current research was conducted with the aim of identifying the role of unmanned aerial vehicles in future smart cities. The current research was conducted in terms of mixed statistical methods (qualitative-quantitative). The participants of the qualitative part, which was implemented based on the method of thematic analysis, were 14 knowledgeable experts, including specialized and experienced managers in the fields of urban security, transportation, road, and urban development, aviation organization and aviation industry, and The Information and Communication Technology Organization of Greater Tehran cities until reaching theoretical saturation and in the quantitative part, all the expert experts of the relevant devices were 134 people, and using Cochran's formula and targeted sampling method, the number of 99 people was were selected as sample members. The reliability coefficient of the qualitative part was recorded by the method of two coders with the final result (83%) and the reliability of the quantitative part was recorded with Cronbach's alpha coefficient with the final result (0.91). MAXQDA software was used for qualitative data analysis and SPSS software was used for quantitative data analysis. The findings showed that in the process of explaining the role of unmanned aerial vehicles in future smart cities; There are 5 comprehensive themes, 16 organizing themes, and 58 basic themes. The results showed that unmanned aerial vehicles can play a significant role in creating future smart cities through 1- intelligent air transportation, 2- agile monitoring and inspection, 3- smart agriculture, 4- smart urban and citizen services, and 5- smart law enforcement.

This paper aimed to utilize a Deep Neural Network (DNN) to achieve optimal path planning for a spacecraft during a landing mission on an asteroid. A minimum energy-consumption mission is evaluated in which a DNN is utilized to predict the optimal path in case of any failures or unforeseen alterations. The paper uses a DNN and employs a polyhedral model, which is renowned as the most precise method for modelling the irregular shapes of asteroids. The DNN, is utilized for path planning and incorporates data calculated by the network into a spacecraft dynamics equations where an intelligent supporter model has been developed to handle the high computation load of the gravitational field of polyhedral models. Moreover, this study indicates that the prediction errors of final locations are less than 1 kilometer, as the training errors of networks are deemed entirely satisfactory. Eventually, the feasibility of the proposed approach is demonstrated through corresponding simulations

A complete miss distance analysis of true proportional navigation is carried out due to initial heading error, step target maneuver, and seeker noise sources assuming a first-order control system using forward and adjoint methods. For this purpose, linearized equations are utilized for deterministic and stochastic analyses. Worst case analysis shows that the maximum value of the final time-miss distance plots reduces by increasing the value of the effective navigation ratio due to initial heading error and step target acceleration. The number of peaks of these curves obeys the relation of the effective navigation ratio minus 1 (or 2) due to heading error (or step target maneuver). Moreover, the normalized miss coefficients due to seeker noise sources and miss due to random target maneuver are computed and approximate formulas are presented using the curve fitting method. This leads to an approximate formula for miss distance budget. Therefore, optimum values of the effective navigation ratio and control system time constant are obtained. Finally, the preferred values of these parameters are calculated for increased RMS miss of 5%, 10%, and 20% compared to its minimum value for two scenarios.

The noise of wind turbines is mainly of aerodynamic origin and is caused by the impact of the flow on the turbine blade. Therefore, improving the behaviour of the flow around the turbine and reducing aeronoise can result in reducing its annoying noise. In the first step of this research, a suitable serration is selected according to the physics of the flow, and then it is installed on the leading edge of the blade in such a way that it does not cause the power loss of the turbine. All the studies have been done experimentally in the wind tunnel and with the help of power, pressure and air velocity measurements in the wake and in the different free stream velocities. The results showed that the pressure fluctuations in the model equipped with a serrated blade have decreased by 4-9% on average in different areas compared to the simple Savonius. On the other hand, the results of the frequency analysis of the anemometer sensors also showed that in the dominant frequencies, the serration caused the range of phenomena to decrease. These results were obtained in such a way that the power measurement showed that the maximum power value of the turbine equipped with serrated blade experienced an increase of nearly 19%. On the other hand, the velocity profile in the wake also shows a greater deficit in the flow around the modified Savonius, which confirms the decrease in the output momentum from the turbine and consequently the increase in power.

Air-breathing hypersonic flight is presumed by many of the savants in the field of aeronautical engineering as the last boundary of aerial vehicle design to be pushed back. An auspicious design configuration for the prospective hypersonic transport vehicles of the future is a “Waverider,” using the Scramjet engine cycle as its propulsive system. Two-dimensional CFD Analysis and case-to-case study of three pre-defined waverider configurations with 2-ramp, 3-ramp, and 4-ramp inlet geometries are carried out in the hypersonic flight regime of Mach numbers 5, 6, and 7. This is done in an attempt to study the single-oriented and also correlative-oriented impacts of increasing/decreasing the number of inlet ramps and increasing/decreasing the flight Mach number upon the behavior of final aerodynamic coefficients and ratios. The paramount outcome of the present work is the generation of some tables which can be utilized as primary guidelines for aeronautical design engineers who are designing waverider configurations on a preliminary basis.

Computerized Ionospheric Tomography (CIT) is a method to reconstruct ionospheric electron density image by computing Total Electron Content (TEC) values from the recorded GPS signals. Due to the poor spatial distribution of GPS stations, limitations of signal viewing angle and discontinuity of observations in time and space domain, CIT are an inverse ill-posed problem. In order to solve these problems, two new methods are developed and compared with the initial method of Residual Minimization Training Neural Network (RMTNN). Modified RMTNN (MRMTNN) and Ionospheric Tomography based on the Neural Network (ITNN) is considered as new methods of CIT. In all two methods, Empirical Orthogonal Functions (EOFs) are used to improve accuracy of vertical domain. Also, Back Propagation (BP) and Particle Swarm Optimization (PSO) algorithms are used to train the neural networks. To apply the methods for constructing a 3D-image of the electron density, 23 GPS measurements of the International GNSS Service (IGS) with different geomagnetic indexes are used. For validate and better assess reliability of the proposed methods, 4 ionosondee stations have been used. Also the results of proposed methods have been compared to that of the NeQuick empirical ionosphere model. Based on the analysis and comparisons, the RMSE of the ITNN model at high geomagnetic activity in DOUR, JULI, PRUH and WARS ionsonde stations are 1.22, 1.46, 1.18 and 1.19 (1011 ele./m3), respectively. The results show that RMSE of the ITNN model is less than other models in both high and low geomagnetic activities and in ionosonde stations.

Significant attention has been given to the field of multi-agent systems in recent years due to its potential to solve complex problems that cannot be addressed by a single agent. One such problem is the cooperative search and coverage application, which requires multiple agents to efficiently search and cover a given area. However, the effectiveness of such systems is dependent on various factors, including mission definition parameters and the approach used to achieve mission performance optimality. In this paper, an optimal strategy for segregating multi-agent missions for search and coverage applications is proposed. The proposed strategy involves dividing a single mission into several simultaneous missions based on the optimal division of the environment that ensures system performance optimality while achieving a common goal. The mission area is divided into sub-areas, and each sub-area is assigned to specific agents to improve overall system performance. The effectiveness of the proposed strategy is demonstrated through simulations and relevant comparisons.

This research delves into the intricate realm of supersonic inlet design for ramjet engines, honing in on the critical aerodynamic considerations and optimization of performance factors. At Mach 2.5, the study meticulously scrutinizes pivotal design parameters, including the placement and number of inclined shocks, cowl-lip positioning, throat area, spike location, and diffuser length. Computational fluid dynamics simulations are harnessed to unravel the intricate flow dynamics and assess the proposed inlet geometry's performance.The findings reveal a nuanced relationship between back pressure and shock wave positioning, where increasing back pressure initiates a shift in the shock wave, impacting the flow state. The paper delineates this transition, emphasizing the pivotal back pressure range of 300,000 to 350,000 pascals, where optimal shock wave alignment corresponds with design parameters, achieving a supercritical state.However, elevating back pressure beyond this range triggers a sub-critical state and mass flow overflow as the shock exits the throat.the study explores various performance metrics, encompassing drag coefficient, distortion coefficient, mass flow ratio and total pressure recovery under varying back pressure conditions. The outcomes underscore the merits of higher back pressures, which mitigate drag coefficient and distortion while amplifying TPR.In the sub-critical state, MFR diminishes due to shock wave displacement beyond the intake opening.This research illuminates the intricate dance of aerodynamics within ramjet engine inlets and underscores the paramount significance of optimizing inlet geometry to unlock heightened performance. It effectively encapsulates the essence of the full article, enticing readers to embark on a deeper exploration of this crucial area of aerospace engineering.

The fixed-wing unmanned aerial vehicles (UAVs) have gained significant attention across diverse civilian and military applications in recent years, where precision control, advanced manoeuvrability, and elevated stealth capabilities are paramount. In order to design a robust control system to enable different tracking and path-following purposes, it is desired to establish a precise aerodynamic model. The research introduces a straightforward approach for accurately computing aerodynamic coefficients, essential for deriving aerodynamic forces and moments, particularly focusing on the rudderless flying-wing UAV models. Utilizing Digital DATCOM software, the study outlines a procedure for calculating the requisite aerodynamic coefficients of fixed-wing aircrafts. The data input card is prepared based on the design and physical attributes of the rudderless flying-wing Freya UAV model and its associated airfoil structure. Through the utilization of the input card in DATCOM software, computations are performed to determine static longitudinal/lateral stability, dynamic stability, and control coefficients, along with their derivatives. Additionally, a 3D model is constructed. The ensuing output file is then imported into the MATLAB environment for comprehensive analysis and integration into dynamic modelling for the design of control systems. The open-loop and closed-loop system performance analysis based on the obtained aerodynamic coefficients, shows acceptable values in terms of control surfaces and flight dynamics variables in the category of small-sized rudderless flying-wing UAVs which proves the reliability of the obtained results.

The paper compares the performance of two altitude controllers, model predictive controller (MPC) and linear quadratic requlator (LQR), for aircraft in cruise flight and height change conditions. The design of the controllers is based on the linearized state space matrix of the aircraft’s longitudinal motion around the trim conditions. The controllers’ ability to track the desired altitude while satisfying input and state constraints is evaluated, and it is found that both controllers are effective in maintaining the desired height. However, the MPC controller performs less overshoot, settling time and transient error than the LQR controller and achieves a more efficient control input by predicting the future behavior of the system. The proposed altitude controllers provide a promising solution for maintaining the desired aircraft altitude in cruise flight conditions, and the comparative analysis of the two control methods can assist in selecting the appropriate control strategy for a given aircraft system based on the desired performance requirements.