فصلنامه مکانیک هوافضا
سال نوزدهم شماره 3 (پیاپی 73، پاییز 1402)

Enhancing the failure behavior of laminated composite panels for various industrial, aeronautical and naval applications has been concerned by researchers and engineers. In the present paper, in order to create a fuselage time between the initial failure on the top composite panel and final failure due to failure of the bottom panel, an interlayer elastomeric foam was employed using epoxy adhesive and the failure pattern was compared between the single and sandwich composite panels for various layup methods of the laminates.  The examined layup methods are composed of a stronger direction, cross-ply and woven plies laminates, in which the enhancing influence of an elastomeric foam from PE-EVA blend (28% EVA) was observed in terms of maximum load carrying and energy absorption capacities. The objective for application of an elastomeric foam was omission of disadvantage by inflexible crushable foams. Although, the elastomeric foam supplied aa lower flexural modulus for the sandwich composite panels due to its lower shear rigidity, it could distribute stress concentration areas from the top to the bottom composite panels, to create a considerable fuselage to reach the ultimate strength via absorption of considerable energy. The results showed promising performance for failure response of elastomeric foam cored sandwich panels. Application of the interlayer elastomeric foam in the case of composite panels with lower stiffness showed larger enhancing effect.The objective for application of an elastomeric foam was omission of disadvantage by inflexible crushable foams. Although, the elastomeric foam supplied aa lower flexural modulus for the sandwich composite panels due to its lower shear rigidity, it could distribute stress concentration areas from the top to the bottom composite panels, to create a considerable fuselage to reach the ultimate strength via absorption of considerable energy. The results showed promising performance for failure response of elastomeric foam cored sandwich panels. Application of the interlayer elastomeric foam in the case of composite panels with lower stiffness showed larger enhancing effect.

In this paper, a new method for flocking quadcopters is introduced. For this purpose, the idea of two-level control has been used, where the high-level controller is the same as the flocking algorithm and acts as the path designer of quadcopters. Moreover, tracking of the generated desired path is performed by a low-level controller. The main focus of this paper is on the high-level controller. A novel leaderless flocking algorithm is introduced, where new potential functions are generated using fuzzy logic to achieve a proper lattice. The introduced potential functions have a minimum value in the lattice positions. Therefore, the control signal minimizes its value by using the gradient-descent method to reach the desired situation. A safety radius is defined for every agent such that using the proposed flocking algorithm, the quadcopters do not enter each other's safety region. The stability and convergence of the structural and transitional dynamics of the system are shown. Finally, the proposed method is evaluated through simulations of five quadcopters. The results show that The proposed method provides better performance in creating a lattice, and maintaining obstacle as compared with recently published methods in literature.

Most of the researches on the effect of the step on the hydrodynamics of the stepped vessels have considered uniform step height across the width. This gap prompted the researchers to investigate the effect of the variable height of the step in the width on the hydrodynamic performance of the planing vessels. For this purpose, three Frisma models have been selected, including one model without steps and two models with steps that have variable step height in width. The basis for choosing the triangular change is the uniform change of the height of the step in the width. Comparing the results of the float without steps with other vessels with steps has led to obtaining useful information about the hydrodynamic characteristics of the variable height of the step in width compared to the fixed height of the vessels. In this research, two models with transverse steps and a simple vessel (without steps) were compared in terms of hydrodynamic characteristics such as trim angle value, drag-to-lift ratio, wet surface value and total resistance force, and the most optimal model was determined. Is. The results show that the step with fixed height reduces the resistance force about 30 percent and has a greater drag reduction than the step with variable height. But in the step with variable height, the trim is less than the step with the same height. In the designs, attention should be paid to both.

In order to produce and design parts with high adaptive, 3D printing is a novelty technology. In considering to low hardness of produced parts with PLA filament, using consolidated composite materials with carbon continues fiber, could resolve this problem and increase mechanical characteristic of mentioned produced parts. Base on defense industrial equipment’s, included aerospace industrial, in UAV production procedure, and in order to improve the efficiency of production and quality of produces, employing the 3D printing devices with ability of using the consolidated filament with continues fiber, are needed. So according to the requirement of using consolidated filament with continues fiber, designing a filament-maker device with continues fiber filament with polymer filament structure and carbon consolidator fiber production ability, had started. In order to all right using of the PLA, polymer filament melt experimental effects and extruder device velocity on produced filament surface cut endurance, is analyzed. In this study, 3K carbon fiber is used and factors such as fiber surface coarseness impregnate between fiber and matrix, impregnator temperature effective and filament output velocity are estimated. The results of this study that seen by electronic microscope images shows the coarseness incising of fiber surface in preparation step of   fiber and high-quality carbon fiber impregnate by PLA molten. Besides, by means of TAGOCHI examination design method, filament is produced and samples are tested. With TAGOCHI analysis of results, the best melt temperature is 190 centigrade and the best accumulating velocity is 1 RPM.

Sandwich structures due to their mechanical properties and high strength-to-weight ratio used in various applications such as aerospace and fuel cells. In this research, the bending behavior of sandwich structure with aluminum honeycomb core and glass-epoxy faces analyzed. The finite element modeling of the structure done under the three-point bending test and using Abaqus software, to investigate the bending behavior. In addition, the force-displacement diagram and maximum bending force, bending modulus and strength obtained. The parameters of face thickness, core thickness and cell size of the honeycomb core investigated as effective input parameters and the effect of these parameters on the bending behavior of the sandwich panel analyzed. To determine the tests and check these parameters on the structure, the Minitab software and response surface method used by using the central composite design. Finally, the optimal sample introduced. Results show that the sample with face thickness 0.4 mm, cell size 6 mm and core thickness 10 mm has the highest bending modulus and the least weight, and the sample with face thickness of 1.2 mm and cell size 6 mm. In addition, core thickness 20 mm has the highest critical bending load tolerance to the weight.

Aerodynamic interference is one of the phenomena that occurs when two flying objects pass near each other. In this case, the change in the pressure distribution on objects passing near each other causes a change in the aerodynamic forces. In this research, the numerical investigation of the flow field between two narrow bodies at a close distance and the pressure changes along them at supersonic speeds is done. The simulation was done in two-dimensional and three-dimensional form, and the k-omega sst was used to model the flow turbulence. The two slender bodies were placed next to each other at speeds of Mach 1.5, 3, and 4.5 and at intervals of 2, 3, and 4 times the diameter of the body. they were examined in two modes with relative motion and without relative motion. The results show that as the free flow velocity increases, the shock wave deforms from bow to oblique and is reflected between the two bodies.  Also, as the flow Mach number decreases and the distance between two slender bodies increases, the reflected shock wave becomes weaker. At Mach 1.5 the shock wave reflection between two bodies is not very noticeable, while at Mach 4.5 the shock wave is well reflected between two bodies. In the state of relative motion of two slender bodies, separation occurs at the shock wave reflection points and the number of shock wave reflections decreases compared to the state without relative movement.

Maneuvering and controlling the attitude with the highest accuracy, speed and lowest power consumption has always been one of the challenges in the field of spacecraft control system design. The flexibility of satellites causes a change in the dynamics of the whole system. In this article, the Robust Quasi-Sliding Mode Control (RQSMC) method has been utilized to control the attitude of the flexible spacecraft in the presence of disturbances. Considering the non-linearity of the equations of the flexible spacecraft, the impossibility of modeling this system ideally and the inability of mathematical descriptions to fully explain the movement of this flight system, this article uses the RQSMC method as a suitable idea for the attitude control of the flexible spacecraft. For this purpose, the three-degree-of-freedom model of the flexible spacecraft including different disturbances in each direction under quaternion kinematics will be presented in the dynamic modeling section of this article, and then a RQSMC will be designed that also has the ability to control chattering.  The checking of functional parameters such as energy consumption index, agility index and body angular rates constraints showed that this controller has a desirable performance in accurate and fast spacecraft orientation.

Upgrading the thermal efficiency of the cooling system of liquid rocket engines is one of the most significant and intricate problems in designing modern rocket engines in the missile industry. The present study employed the Bees algorithm (BA) to attempt a single-objective optimization of the cooling system of the combustion chamber and nozzle of an LH2/LOX rocket engine considering the overall heat transfer coefficient objective function and four parameters, including the diameter and thickness of the cooling tubes, the radius of the throat, and the mass flow rate of liquid hydrogen (cooling fluid). The optimization was examined by the heat transfer analysis of combustion gases with the chamber walls, the use of the BA optimization algorithm, and the consideration of the sensitivity of the design parameters regarded for the overall heat transfer coefficient objective function. In this respect, these parameters were considered constant in the design ranges, while other parameters were variable. The results show that the overall heat transfer coefficient can increase almost by 17.78% during the optimization process of the cooling system of this rocket engine through the parametric analysis of the four mentioned design parameters.

Oil condition monitoring is an effective method for detecting abnormal erosions or defects in mechanical equipment and systems. One of the issues in the field of condition monitoring with the help of oil analysis is the cost and time required to inspect all samples by an expert. However, not all oil analysis samples need to be reviewed by an expert, and less than 10% of this data indicates a critical situation that requires rapid planning and action. The goal of this article is to turn the oil status into an image so that you can quickly identify the oil status by looking at the image. Also, by processing these images by software, the state of failure can be extracted through artificial intelligence. In this research, the data are taken from the sample test of motor oils of road construction rollers. First, the data were converted to gray scale images using baseline for diesel engines and through MATLAB software. In the next step, these images are processed using the convolution neural network method to determine the oil status. Comparison of the obtained results showed that the visualization of the oil analysis results helps to understand the general condition of the oil for the user and the critical samples and the need for action are identified more quickly among the mass of oil samples.

In this paper, a finite time adaptive sliding mode control is introduced for second order linear multi agent systems (MASs) under unknown nonlinear external disturbance. The distance between agents is constant and the communication graph is undirected. Based on the relative information exchanging between agents, an adaptive sliding mode controller is presented to make the system finite time stable. New adaptive rules are introduced to estimate the upper and lower bounds of the external disturbance. Second Lyapunov stability theorem is employed to finite time stability proof under the proposed decentralized method. We will show that the time derivative of the Lyapunov function along the system’s dynamics is negative under the proposed robust adaptive control law. Moreover, the frequency domain analyses will show that the amplitude of distance error will decrease between the followers. To validate this approach, a numerical system consisting of a leader and 6 followers in two different accelerating and braking maneuvers are presented. The results indicated the satisfactory performance of the proposed approach.