JOURNAL OF AEROSPACE SCIENCE AND TECHNOLOGY
Year:2024 | Volume:17 | Issue:2|Papers Count:10

Flexible ropes have wide-ranging applications in aerospace engineering, yet accurately measuring their motion state without disrupting dynamic characteristics remains a challenge. This study introduces a visual measurement method aimed at precisely assessing flexible rope motion to support the development and validation of an accurate cable dynamics model. Addressing non-uniform movement speeds attributed to the rope's large length-diameter ratio, a novel tether edge segmentation operator is proposed to delineate motion blur regions into exposure beginning and ending time tethers. This operator enhances accuracy over existing centerline extraction methods, particularly in asymmetric motion blur regions. The proposed approach not only resolves accuracy issues during high-speed motion but also leverages the camera's inherent image acquisition frame rate, reducing system complexity and cost. Validation of the material point tracking algorithm through mathematical and physical simulations underscores its effectiveness in monitoring any point on the tether. Furthermore, verifying the tether dynamics model through the absolute nodal coordinate method highlights the novelty and significance of this research in advancing aerospace engineering applications.

Exposure to vibrations of certain frequencies can pose a risk to the pilot's body. During flight, the maneuvers performed by the pilot expose them to sudden and unfavorable accelerations, which can cause physical, physiological, and psychological problems. Research suggests that the use of seat suspension systems is effective in reducing high-frequency vibrations. However, for small movements, which occur at low frequencies between 2 to 15 Hz, the cushion of the pilot's seat plays a more significant role. In this research, we investigate the effect of the cushion on reducing vibrations on the pilot's body. Firstly, we compare and validate the results of the biodynamic equations of motion of a 4-degree-of-freedom model of the helicopter pilot's body with the experimental results. Next, we compare the biodynamic response of the motion in the finite element model (numerical solution) with the experimental results. Finally, we obtain and evaluate the biodynamic responses of the pilot's body movement by considering the cushion with different mechanical characteristics and in two stiffness and parallel (Kelvin-Voight model) and series (Maxwell model) damper modes. The Kelvin-Voight model was found to be more accurate than the COMSOL model.

In this research, aluminum/alumina/graphite hybrid composite was prepared by horizontal centrifugal casting method, and the microstructure and distribution of alumina and graphite particles in the radial direction of the cross-sectional area of the samples were investigated. The distribution of graphite and alumina particles has led to the creation of a gradual structure (FGM) along the cross section. As a result of the centrifugal force, the graphite particles separated in the inner part of the sample and the alumina particles gradually increased from the inner region to the outer region. The samples were obtained with 3, 5 and 7% by volume of graphite particles added to the melt and with the rotation speed of the mold RPM1000, RPM1500 and RPM2000, and the formation of the inner zone rich in graphite was investigated. In all samples, 3% by volume of alumina particles were used and the effect of the presence of alumina particles on the distribution of graphite particles was studied. Optical microscope (OM) was used to investigate the microstructure and distribution of graphite and alumina particles. By increasing the amount of graphite from 3 to 7 percent by volume, the collision and interaction between graphite particles increases and leads to an increase in the thickness of the inner layer rich in graphite, and increasing the speed of rotation of the mold first causes an increase in the thickness of the inner layer and then leads to It was reduced. The presence of alumina particles prevented the complete separation of graphite particles

This study introduces a hybrid algorithm designed for trajectory tracking control during thetransition flight of a tailsitter Unmanned Aerial Vehicle (UAV), employing an integration ofneural networks and a genetic optimization algorithm. The tailsitter UAV ducted fan tailsitter, which has been augmented with two additional wings to enhance its flight capabilities. Thefoundation of the intelligent controller lies in the feedback linearization method, withperformance enhancements achieved through online neural network training coupled with agenetic optimization algorithm. To validate the effectiveness of the proposed algorithm incontrolling the UAV during transition flight, simulations were conducted within the Matlab-Simulink software environment.

By carefully investigating the motion of birds of prey, it is seen that in addition to the legs, the claws and their gimbal dynamics play an important role in successful grasping of the specified target. Therefore, in order to achieve an avian-inspired robot, it is essential to consider these degrees of freedom. Having added these degrees of freedom, a precise dynamic analysis is needed to extract the auxiliary equations of motion by which the control design for such an under-actuated multiple-servo articulated flying vehicle system will be possible and in turn, servos’ signals are producible. In this respect, the aim of this study is presenting an extended model of a hunting quadrotor in planar motion and showing the significance of detailed kinetic analysis in designing a model-based controller for the system in pursuit phase. Given the high nonlinearity and dynamic coupling in this integrated system, along with the presence of intense uncertainties and atmospheric and impulsive disturbances, super-twisting sliding mode control (STSMC) is designed and its performance compared with SMC is evaluated through simulation based on some standard metrics.

This paper has investigated the flow interference between four circular cylinders of equal diameters in a square arrangement in a cross-flow. Wind tunnel experiments were conducted to measure the mean force coefficients and Strouhal numbers (St) for six spacing ratios (l/d) varying from 1. 5 to 4 at five subcritical Reynolds numbers (Re) ranging from 1. 26×〖10〗^4 to 6. 08×〖10〗^4. The pressure distributions on the surface of the cylinders were measured using pressure transducers. Furthermore, the hot-wire anemometer was employed to measure the vortex shedding frequencies behind each cylinder. It is revealed that for l/d=1. 5, due to severe flow interference between cylinders, there is a difference between lift coefficients for the upstream cylinders. Also, for l/d≤2, the mean drag coefficients for downstream cylinders are negative. In addition, for l/d=2 and l/d=2. 5, there is no vortex shedding from the upstream cylinders. Moreover, it is found that the effects of variations in this range of the Reynolds numbers, on the quality of the vortex shedding and Strouhal numbers are negligible,whereas the variations in l/d, strongly affect the flow pattern around the cylinders and aerodynamic coefficients. Also, by decreasing the amount of l/d, the effects of the flow interference between the cylinders increase.

In this research designing the damper and control of system vibrations with the piezoelectric layers accommodation in studying the Flutter phenomenon will be considered. Accordingly, system structural modeling will be done in a continuous model of unmanned airplane wing. By considering all parameter of the wing, the regions which have piezoelectric layers are modeled as beam with degree of torsion and bending freedom. Also, modeling the airflow behavior as quasi-steady will be done. By considering linear theory for piezoelectric structural equations, two layers will be bonded on the top and bottom of the beam. Due to design the damper and control of the vibration, Negative Feedback Control (NFC) algorithm will be used. To perform this algorithm, the lower piezoelectric layer acts as sensor. In fact, it has to measure the harvesting voltage. On the other hand, the upper piezoelectric layer, is the actuator of the system. In the other words, with feedback of measured voltage of the sensor to the controller, it applies new voltage to the system to control the stability of the system and at the end the flutter phenomenon can be postponed by using this algorithm. The results will presented for different values of feedback coefficient. Additionally, the effect of system main parameters on postponing flutter in each case of algorithm will investigated and optimized value of each parameter will showed based on postponing flutter phenomena.

The focus on different energy harvesting methods has led to various studies on the mechanism of flow-induced vibration phenomena, including vortex-induced vibration, galloping, and wake-galloping. In this study, an experimental investigation on flow around a cylinder with an elastic cantilever beam has been conducted to develop new energy harvesting devices based on its dynamic behavior. Therefore, the basic principles for the design of a high resolution open-circuit subsonic wind tunnel were systematically studied and a specific small scale wind tunnel was constructed based on the requirements. The test chamber cross section for the designed wind tunnel is square with a side length of 50 centimeters which can be used for investigation of different micro wind turbines performance up to velocity of 8 m/s with resolution of less than 0. 1 m/s. The vibration of two prototype micro-turbines in the presence of obstacles and without obstacles has been studied in different Reynolds numbers. The results show that a circular cylinder oscillates with larger amplitude in the VIV range in comparison to the square cylinder, however, when galloping starts by increasing Reynolds number, the oscillation amplitude of the square cylinder severely increases. The experimental findings show that the presence of an obstacle in upstream of the flow considerably increases the amplitude of oscillation, however, does not have a meaningful effect on the vibration frequency. Also, results indicate that the vibration amplitude of the bluff body in the wake-galloping phenomenon for the square obstacle is greater in comparison to the circular obstacle.

The present paper strives for optimization of the Liquid-Propellant Engine (LPE)’s feed system. To this end, the new hybrid meta-model methodology by utilizing the Design of Experiment (DOE) method and the Response Surface Method (RSM) were developed and implemented as two effective means of designing, analyzing and optimizing. The input design variables, constraints, objective function, and their surfaces were identified. Then, the design and development strategy was clarified by utilizing the combination of RSM, DOE and regression analysis. Hence, 64 different experiments were carried out on the RD-253 propulsion system. The response surface curves were drawn and the related objective function equation was obtained. The Analysis of Variance (ANOVA) results indicate that, the developed hybrid model is capable to predict the responses adequately within the limits of input parameters. In addition, the precision of the model was assessed by comparing with the existing samples and the output was interpreted and analyzed that shown highly accuracy. Therefore, desirability function analysis has been applied to LPE’s feed system for achieving to maximize the power and minimize the weight, simultaneously. Finally, confirmatory tests have been conducted with the optimum parametric conditions to validate the optimization techniques. In conclusion, the methodology capability is to optimize the LPE system, an 11% increase in the power to feed system weight ratio and a 2% increase the thrust to engine weight ratio. These values are considerably large for LPE design.

In this research, for the first time, two types of conventional plain and single-slotted aerodynamic control surfaces have been compared and investigated from an aeroelastic point of view. For aeroelastic modeling, geometrically exact fully intrinsic beam equations are combined with Peter’s unsteady aerodynamic model in an incompressible flow regime. In order to check the aeroelastic stability of the wing, first the resulting non-linear partial differential equations are discretized by using the central finite difference method, and then linearized about the static equilibrium. Finally by using the eigenvalue analysis of linearized equations, the stability of the system versus different parameters are evaluated. The validation of the results has been achieved through comparison with the results presented in the references. Then the effects of various important parameters of the control surface on the speed and frequency of flutter instability have been investigated for two types of conventional aerodynamic control surfaces for the first time and hence this is the main novelty of this study. It is found that the improving trend of the single-slotted control surface is more pronounced at lower chord ratios and the location closer to the wingtip than the plain control surface. Also, the importance of paying attention to the type of control surface in aeroelastic stability became more clear.