نشریه مهندسی هوانوردی
سال بیست و چهارم شماره 2 (پاییز و زمستان 1401)

Welding is very important in the aerospace industry and is widely used in aerospace structures. One of the problems that most industries are facing is created residual stress by the welding process. Residual stresses in the surrounding areas of welding can cause cracks and crack growth so identifying and evaluating residual stresses in the welded structures is necessary. There are different methods for determining residual stress. In this paper, laboratory and numerical methods were presented for determining the residual stress. Then, the welding process of two aluminum sheets of 6061-T6 alloy has been done and the residual stresses have been obtained by drilling method. Welding is done in two passes and by spot welding, the first, the end and the middle of the weld line are connected to prevent the sheets from moving. Also, the welding process of the two aluminum sheets was simulated in 3D in the ABAQUS finite element software and the residual stresses were extracted. All conditions in the finite element analysis are similar to the welding conditions in the laboratory. Results show high accuracy in the modeling of finite element processes in the welding process. Finally, in the finite element method, thermal stress is modeled and optimal parameters are extracted for the above operations.

In this study, to investigating the efficiency of the Curle and the compact form of the acoustic analogy in the far-field noise prediction, the flow around a square, a circular and an elliptic cross-sectional geometry at Reynolds numbers of 46000 and 69000 are simulated in the open-source software, OpenFOAM. The large eddy simulation approach has been used to simulate the incompressible flow around the geometries. To predict the far-field sound pressure levels with the Curle acoustic analogy, the data of the surface pressure fluctuations has been used, which were saved during the simulations through the probe utility of OpenFOAM, while with the compact form of the Curle acoustic analogy, the fluctuations of the lift coefficient have been used. To validate the numerical approach in the study, in the first part of the results, the average aerodynamic coefficients (lift, drag coefficients), mean pressure coefficient, Strouhal number and the formation of the coherent structures of the flow through Q-criterion are investigated.In the second part of the results of the present study, the far-field sound pressure level due to the interaction of the flow with the geometries were investigated. To validate the results in this section, the far-field sound pressure level of the geometry with square cross-section has been investigated and the proper precision of the approach has been evaluated. Finally, the results of the study have shown that the geometry with the square cross-section produces the maximum and the geometry with the elliptical cross-section produces the minimum far-field sound pressure level.

In this paper, the strength analysis of composite sandwich structures under buckling load as well as composite polyurethane foam core in composite sandwich structures has been studied experimentally. For better performance of the shell and core in the sandwich structure as well as to increase their strength against buckling compressive load, a reinforcer with new geometry of hourglass and square with foam and without foam has been used. Having a negative Poisson's ratio and greater flexural stiffness as well as maximum load bearing capacity is the reason for using hourglass geometry. The new VARTM method has been used to create better and more uniform quality samples. The results of this study show that corrugated sandwich structures with hourglass filled with polyurethane foam withstand more load against buckling load and also have good efficiency in energy absorption. In a foamless composite sandwich structure, the core is distorted (separation of the shell from the core), and local buckling occurs due to the empty core. While in the sandwich structure with foam, due to the presence of foam in the core, the distortion of the structure is prevented. Also, despite its light weight, foam is able to withstand the compressive load due to local buckling. As a result, the structure has only suffered general buckling.

An investigation has been conducted to determine the optimum blade planform required to minimize the rotor power, maximize the lift-to-drag ratio, and maximize roll attitude quickness of the helicopter using numerical optimization techniques. The optimization process is based on response surface method, I-optimal design expriment, and helicopter inverse simulation program (HISP), developing mathematical model of performance, and Turning a multi-objective optimization problem into a one-objective problem using Desirability approach that the optimal numerical solution will eventually be calculated. The effects of helicopter weight and blade planform parameters (i.e., root chord, taper ratio, the taper starting point on the blade, and blade twist) on the performance and handling quality of the helicopter are therefore investigated. Responses of helicopter were obtained through a HISP developed for rotors with quasi-steady aerodynamic formulations. The resulting system provides a systematic evaluation to examine the rotor blade design variables and their interactions, thus reducing the time and cost of designing rotor blades. The results also confirm that the optimum tapered blade lowers the power required by about 7% and enhances the lift-to-drag ratio and roll attitude quickness up to 10% and 36% with a satisfactory improvement relative to the helicopter with rectangular planform a NACA 0012 cross-section in slalom maneuver, which is a good improvement for rotor blade design.

In this study, the effect of FG porous on the free vibration behavior of sandwich plate with piezoelectric face sheets and FG core is studied. A new hyperbolic shear deformation function is presented in this paper. The properties of the FG core varied along the thickness according to power law. The properties of the FG material change with the power distribution as a function of the changes in properties along the thickness. The structure of porous materials has cavities and pores. Therefore, in this research, a linear porous model and two types of nonlinear porous models are considered for the property change function. The governing differential equations are derived using the Hamilton principle. The obtained equations were solved using the Navier method for simple boundary conditions. The effects of important geometric and mechanical parameters including thickness to length ratio, length to width ratio, ratio of FG core thickness to piezoelectric face sheets and the effect of electrical potential on the natural frequency response of porous FG sandwich and piezoelectric face sheets have been investigated. To verification, the analytical results obtained in this study are compared with the results presented in the literature, and in this comparison, a good agreement was obtained, which shows the correctness theory, deriving and solving equations.

In this paper, attitude control of a rigid satellite in the presence of external perturbations and considering the parametric uncertainties with the fractional order controller is investigated. To control the attitude of the satellite, a reaction wheel actuator with a first-order dynamic model is used and uncertainty is considered in the parameters of the satellite’s moment of inertia, the actuator model and external perturbations. For comparative purposes, in addition to the fractional order controller, the integer order controller is also used. Numerical solution is performed by Euler method and Granwald-Letinkov definition is used to solve the fractional order integral and derivative. The coefficients of the integer order and fractional order controllers were extracted by the particle swarm optimization method with the performance criterion of mean of absolute value of error. Fractional order controllers have more degree of freedom than integer order controllers due to their more design parameters. Therefore, according to the results, the appropriate performance of fractional order controllers can be seen in overshoot, settling time and against of perturbations and uncertainty in the satellite attitude control.

In this research, a model for detecting targets and classifying the pulses received by the 6-antenna radar system using artificial neural networks optimized by genetic algorithm is presented. The proposed model consists of two main parts: clustering and classification. In the clustering process, the different pulses received by each of the radar antennas are clustered in such a way that the pulses of each target are placed in the cluster of the same target, and finally the results of clustering with different algorithms are evaluated by Dunn index. In the classification process, using the neural network, the target angle is predicted, the characteristics of which are received by the antennas, and the weights and biases of the neural network are optimized by a genetic algorithm. To adjust the parameters, Taguchi method has been used to select the best values of the parameters and the neural network has been trained with these values, and as a result, the accuracy of predicting the received pulse angle has increased to 98.55%.

The use of accurate and reliable navigation systems for determine the exact position and attitude of aerospace equipment is of great importance. Magnetometer is one of these types of sensors which is a low cost and reliable tool for determining exact position. The purpose of this study is based on use a magnetic field sensor to determine the position and estimate the orbit of a typical satellite. By using magnetometer measurements and an independent algorithm, the position of the device is first estimated. This is done by reading magnetometers and using models of the Earth's magnetic field. The use of the above technique is associated with errors that have been reduced by using the extended Kalman filter. The filter used overcomes the initial errors and provides the desired accuracy approximation for determining exact position of device. The results for a circular orbit will indicate the high accuracy of these estimates for low-altitude orbiting satellites.

Today, the use of composite materials has become widespread. Composite parts are subjected to different loading rates under mechanical loads and therefore must have sufficient strength against such various loads. In this paper, the behavior of hybrid composite with layers of glass and kenaf fibers under impact loading is investigated and analyzed. The effect of a number of layers on energy absorption, initial peak force as well as damage area was discussed. In the following, the results of experimental tests are compared with the numerical method by ABAQUS/EXPLCIT software, and the results show that the two methods are in good agreement and close to each other. The results showed that increasing the number of layers from 5 to 13 layers increases the initial strength and peak force by 85%. Also, by studying the specific energy absorption (SEA), it was found that increasing the number of layers at the optimal point increases the SEA so that increasing the number of layers from 5 to 9 layers causes a decrease of 3% and then increasing the number of layers up to 13 layers Increases SEA by 26%. It was observed that the energy absorption improved by 51% with the proper arrangement of layers of glass fibers and kenaf. At the end of the study, the failure mode of composites showed that the main mechanism of energy absorption in the back surface of composite plates is the debonding of layers with matrix fracture and fiber breakage.

In this study, the mechanical properties of polymeric hybrid nanocomposites based polypropylene (PP) and ethylene-propylene dine monomer (EPDM) reinforced with graphene nanosheets, a nano clay, and glass fiber by response surface methodology is investigated. Compounds include 0, 1, and 2 wt% graphene nanosheets, 0, 3, and 6 wt% nano clay 0, 10, and 20 wt% glass fibers, and 0, 5, and 10 wt% EPDM which were prepared by an internal mixer. Samples for mechanical testing were made by a hot press machine. The tensile tests were performed to determine the tensile strength and tensile modulus and the impact test was performed to assess the impact strength of the compounds. SEM images were also used to observe how the nanoparticles and glass fibers dispersed in the polymer. It was observed that graphene and clay nanoparticles had well dispersion at low wt% but aggregation was observed at high wt% of them. Graphene nanosheets at low wt% increased impact strength, tensile strength, and tensile modulus by 23% 46%, and 16%, respectively. However, high weight percentages, it has reduced them. With addition of nanoclay at low wt% has increased the tensile strength by 21% and reduced it at high wt% and reduced impact strength and tensile modulus. With the addition of glass, fibers has increased the impact strength and tensile modulus by 18% and 24% and the tensile strength is increased at low wt% and reduced at high wt%. The addition of EPDM increased the impact strength by 57% while reducing the tensile properties.

In this paper, the nonlinear free vibrations of viscoelastic solid and annular circular microplates are investigated. These microplates are rested on a viscoelastic symmetrical and asymmetric nonlinear foundations. The small scale effect is considered using the modified coupling stress theory. The nonlinear equations of the microplates is obtained using Hamilton's principle and first order shear deformation theory (FSDT). The finite element method (FEM) and Newton iteration algorithm are used to obtain the nonlinear natural frequency. The obtained results are compared with the results of the researchers and a good agreement is observed between them. Then, the effects of various parameters such as length scale parameter, outer radius to thickness ratio, maximum deflection to thickness ratio, softening and hardening nonlinear foundation, symmetric and asymmetric nonlinear foundation, different boundary conditions, structure and foundation damping were investigated. The results show that free and clamped boundary conditions have the highest and lowest nonlinear frequencies of solid and hollow circular microplates, respectively. Also, symmetric and asymmetric nonlinear viscoelastic foundations have a significant effect on the nonlinear nonlinear frequency and the nonlinear frequency of the hollow circular microplate changes to higher values for each amplitude ratio in the presence of a hardened asymmetric foundation.

The purpose of aerial refueling is to solve the problem of limiting the amount of fuel carried, a technique to increase range and endurance. In this paper, the control design of an air refueling system using a combination of machine vision and GPS with iterated uncented Kalman filter is, taking into account the vortex effects of the tanker aircraft and atmospheric turbulence. Since the docking phase between two aircraft is very sensitive, challenging and has a direct effect on the success of the aerial refueling process, a control is designed to guide the probe to the moving drogue and then hold the probe at that stage until the air refueling process is complete. For this purpose, first, the receiver aircraft is modeled in the presence of atmospheric turbulence effects and the vortex of the tanker aircraft. Then an LQR control system between probe and drogue based on the combination of machine vision and GPS for aerial refueling was proposed. An iterated uncented Kalman filter method for data integration is also proposed to obtain the exact relative position between the receiver aircraft and the drogue. After software implementation and simulation, good performance is obtained with the LQR control rule for connecting the receiving aircraft to the refueling aircraft. The simulation results show that the proposed control scheme can achieve exactly the relative position and realize a safe and successful connection between the two flying devices.