نشریه دانش و فناوری هوافضا
سال نهم شماره 2 (پاییز و زمستان 1399)

One of the challenges in design and construction of satellites is the variation of heat fluxes over the body. Multilayer insulation is used to reduce the impact of environment on the satellite. The connection type of insulation blankets has a considerable effect on the thermal performance. In this paper, the effect of sewing patterns on the thermal performance of multilayer insulators is investigated. The main purpose of this study is to determine the conditions under which the minimum effective emittance coefficient and heat flux of multilayer insulations can be obtained. In this regard, several stitching joint patterns have been modeled and the layer-by-layer model is identified as the best bonding scheme for the insulation blankets. Moreover, the experimental data on no-seam and layer-by-layer patterns are used to validate the numerical models. Deviation of numerical results from experimental data is less than 9%. The effects of the number of layers, thickness and properties of the materials are analyzed. Moreover, due to the temperature cycle in the space, both hot and cold conditions are considered. The results indicate that the layer-by-layer joint pattern with 12 layers has the best thermal performance, i.e. in hot cycle the heat flux and emission coefficient are 2.0216 W / m2 and 0.003653, and in cold cycle the heat flux and emission coefficient are 2.36 W / m2 and 0.004784, respectively.

In this article, the focus is on optimizing solid-fuel grain based on high-speed codes. One of the ways to design a high-performance solid fuel engine is to design the optimal grain for it, so that the highest burning area is provided, and on the other hand other requirements such as mechanical strength and build ability of the grain are provided. One of the most common types of grain is the star shape. To optimize a solid-fuel engine with a star grain, a model is needed to simulate the grain to provide the burning area at any given time. One of the methods of simulating the burning area is modeling it in CAD software and extracting the burning area using cloud points. This method has a high computational volume and its application in optimization algorithm, which is a recurring numerical method, is practically time consuming. To solve this problem, in this paper, a geometric parametric model has been used to calculate the burning area and the Zero-dimensional internal ballistic considering the erosive burning. The distinctive feature of this model is the high speed of its calculations, which is highly efficient in the coupling with optimization algorithms. The results show that this parametric geometric model, in addition to the much lower computational volume than the cloud point model, is also more accurate.

In this paper one stage of a specific turbine with two stages and two different changes in blades, have been studied. Blade change performed in stage, is somehow that at each state of blade rotor and nozzle, both are at a specified bowing with angle of plus 20 degrees or minus 20 degrees. Some parameters like, static pressure, total pressure stream lines, isentropic efficiency, mass flow, turbine power and some other parameters have been studied. Changing the blade shape, cause the change in distribution of the flow in the radial direction. Also making a pressure gradient in radial direction, would result in a force in the same direction. Stream lines showed that, in one cases the secondary flow in the end walls move to the mid span. The radial force has affected on the tip clearance vortexes and intensity and dispersion of them have changed in different cases. Both positive and negative stages had negative effect on the efficiency. The power and mass flow have decreased too. At the end, the effect of the turbine changes on the stability of compressor have studied. The compressor has been closer to the surge line. So should have more accuracy in choosing the blade change.

Convergent-end and Open-end injectors are widely used in internal combustion engines. These types of pressurized swirl injectors include: tangential inputs, rotation chamber, converging section and output orifice. In this paper, simulation and comparison of fluid flow inside Open-end and Convergent-end injectors for spraying kerosene fuel under the same operating conditions has been performed using the fluid volume (VOF) method. The results of time-dependent (unsteady) simulations showed that the exit time of kerosene from the Open-end injector is 1.8 milliseconds and in the Convergent-end injector is 4 milliseconds. The results of time-independent (steady) simulations at different injection pressures showed that the Open-end injector is stable at 0.05 MPa injection pressure, while the convergent-end injector is stable at 0.3 MPa injection pressure. However, the exit rate of kerosene in the Open-end injector is far less than that of the convergence-end injector, which reduces the aerodynamic force applied to the fuel inlet layer of the injector and reduces the fuel atomization in the Open-end injector compared to the convergent-end injector.

In this study, the spray behavior of diesel and biodiesel fuel in a cylinderical fixed volume combustion chamber for a grooved nozzle hole has been investigated using CFD in order to improving the fuel spray characteristics and diesel engine performance. To this end, microscopic and macroscopic diesel and the biodiesel fuel spray characteristics are modeled and investigated using AVL- Fire and Matlab soft ware. Firstly, the liquid fuel flow inside the injector with cylindrical and converged conical nozzle holes have been modeled and then in the following diesel and biodiesel fuels have been used in the grooved nozzle hole. Numerical results show that in this case, the biodiesel spray has smaller penetration length and bigger cone angle and SMD. Thus spray macroscopic and microscopic characteristics can be improved and controlled for different fuels by creating the grooves inside the nozzle hole.Numerical results and experimental data was validated in previous researches.

Centrifugal pumps in most industries are responsible for transporting fluids and significant role in the amount of energy consumed. One of the most important issues in explaining centrifugal pumps is the start-up stage. As this point, the pump performs at transient mode. The period when it is necessary for the pump to rotate at a constant speed is called the start-up time of the pump. All the start-up stage, hydraulic equipment may be damaged due to pressure fluctuations. Therefore, it seems necessary to study the performance of the pump at transient stage. In the present study, using the computational fluid dynamics tools, the performance of the pump during the start-up period has been studied. The result show that due to the increase in pump start-up time, the maximum pressure created in pump decreases. And by increasing the length of the pipe downstream, the amount of pressure created in the pump increases. Finally, by adding a certain amount of impurities to the water and performing a two-phase flow analysis, the power required by the pump increases.

Spin is one of the most important phases of aircraft design. Therefore one of the important tests for taking the pilot certification is entry and recovery from spin. The spin of PC-21 is investigated numerically and theoretically at the developed spin phase and is compared with results of flight test. The spin type of this airplane is counterclockwise and maximum rudder deflection is 25 degree. According to theoretical results, the spin of this aircraft should be happen at angle of attack 30 degree; however the flight test results show that spin must be happen at angle of attacks between 40 to 65 degrees. Numerical results show good agreement with flight test data. This research describes the ability of computational fluid dynamics to prediction of the behavior of airplanes in the spin conditions. The proper turbulence modeling, strong hardware, accuracy evaluation and significant experience in CFD procedures are requirements of the approach.

In this paper, the effect of aerodynamic heating on temperature distribution inside supersonic bird cabin in different insulation conditions, the existence of gravity force and different flight height has been investigate using a computational fluid dynamics method with the finite volume approach. The coupling boundary condition in the shell wall use to simultaneously to solve the equations in solid and fluid. The air assumed as an ideal gas and the Boussinesq approximation used to changes density with temperature. In - cabin temperature distribution changes in terms of the free Convection heat transfer is simulated transiently up to a flying time of 70 seconds. The results are presented as temperature contour in the middle section of the model, temperature - time and temperature - location diagrams for different times. In this research, experimental and numerical method s are validated the temperature distribution inside and outside the model, which shows good accuracy.

A vertical take-off and landing (VTOL) aircraft is one that can hover, take off, and land vertically. VTOL UAVs have high maneuverability and their users are after maintaining this maneuverability. This alongside with their extreme nonlinearities and under actuating control system rises the importance of the control of flight. In this paper, the effect of using stabilizing mechanisms in trajectory tracking of quad-rotor unmanned aerial vehicles under wind gusts is studied. Two mechanisms that are simulated and used in this paper are very rare and introduced their usage for first time in this study. The first one is a spherical pendulum stabilizer and the second one is a cross stabilizer. Also appropriate controller is designed for each stabilizer mechanism. The performance of the systems are investigated in the presence of disturbing forces. The results show that instead of using complicated nonlinear control methods, the proposed stabilizer mechanism yields a desired performance. Acceptable trajectory tracking shows the successful effectiveness of the proposed stabilizers.

Several research efforts have been directed towards better understanding the causes of accidents. While some studies provide useful insights into accidents, they do not provide an accurate understanding of accidents if viewed from an event-based perspective. Air accidents in Iran, especially in the last two decades, do not show a significant decrease in the number of accidents or casualties; In this study, we deal with the most important causes of helicopter aviation accidents in Iran. To better understand the causes of aviation accidents, this study offers a state-based approach to examining existing logical gaps or neglected cases. For this purpose, first, using statistica software, situations and factors that are possibly related to fatal and non-fatal accidents are identified; In this software, accident states, signs and accident information codes are automatically detected in a database and the information is automatically classified. We apply the model to 6200 helicopter accidents that occurred between 1982 and 2020. To better understand the causes of accidents, a state-based approach is proposed to examine existing logical gaps or omissions and examines records that are potentially full of errors. Also, the method of air accident ontology and model-based modeling with machine learning tools, which is a new method in this field, has been used to achieve more desirable results.

Since, monocular vision sensor cannot accurately measure relative range between the target and itself, it is difficult for UAVs equipped with this kind of sensors to track a target. This is exacerbated by the tracking a maneuvering aerial target in a three-dimensional space. To solve this problem, the accuracy of dynamic models is very important for predicting the movement and maneuvering of the target. This accuracy can be achieved by complicating and bringing the dynamic equations closer to the real dynamics of the vehicle, or by using appropriate models of the target acceleration. In this paper, we compare the performance three different dynamic models in tracking a mass-point maneuvering target. To do this, we used the UKF filter along with the monocular camera measurement model These models differ in terms of the coordinate system and the target acceleration model. The time spent and Root mean square error (RMSE) are considered as comparison criteria between these models.

Todays, determining the maximum time it takes to keep navigation blocks in stock before re-calibration is one of the major concerns in the aerospace industry, as increasing this time helps to save a large part of costs. Reduce the transportation of blocks from the warehouse to the calibration laboratory and return them. On the other hand, reducing the storage time of the block in the warehouse, as it results in fewer changes in the calibration coefficients, will result in increased navigation accuracy when the blocks need to be used on the system. Therefore, choosing the right time for a compromise between cost and error rate will be essential. In this paper, by selecting a sensitivity analysis, called Monte Carlo analysis and having information on monthly calibration coefficients of navigation sensors over a period of one to two years, the calibration interval of navigation and navigation blocks is extracted analytically. Be. To achieve this goal, it is first shown that the sensitivity of the navigation error to the changes of the calibration coefficients is independent of the uncertainty range of the calibration coefficients, and then Monte Carlo analysis for each of the bias and scale factors of the various sensor blocks and a sampled navigation block. Finally, the results of this analysis show the relationship between the storage time of the block in the warehouse and the maximum error uncertainty.

This paper presents the design and construction of a laboratory model for tracking a moving target object using image processing. The aerial robot is used as a follower and the ground robot is used as a target object. A one-degree-of-freedom robot is used instead of an aerial robot, and a moving mobile robot is used as a ground robot to move at different speeds. The distance error between the ground robot and the aerial robot is calculated using image processing and fed back to the aerial robot controller. The dynamic model is used to design the position controller. PID, PID-fuzzy controllers, and optimal linear integral control are designed using a dynamic model, and simulation is performed in MATLAB software. Using simulation to evaluate the performance of three controllers has been designed. The controller is selected using 4 criteria. The performance of the proposed controller is evaluated by implementing the controller on a laboratory model. The aerial robot controller for real-time tracking of the target object and the object of sight is not out air Robot. The novelty of this paper is the design of an inexpensive laboratory model for the real-time implementation of moving a target object with a moving tracker.

Considering uncertainty is an Inseparable part of industrial design and close to real issues. Ignoring these uncertainties in design can reduce system performance and even worse lead to failing the mission completely in some cases. In the present study, one of the design methods under uncertainty, namely the worst-case optimization for the design of a hydrogen peroxide monopropellant propulsion system, has been implemented. The proposed method in this study includes two types of epistemic and aleatory uncertainty. This method searches for the optimal point using the genetic algorithm by separating design parameters and variables for all three types of sparse points, single-interval, and multi-interval uncertainty representations. The designer is ineffective in choosing the type of distribution and the type of distribution is determined depending on the available data. In other words, even uncertainty in the type of distribution and its parameters has been considered. Also, the method of maximum likelihood-based is used to estimate the distribution parameters.

In this paper, an improved trajectory design to reach LEO orbit to an orbital near the moon called Lunar is investigated in the presence of disturbances using Lagrangian points of the Earth-Moon system. For this purpose, the Lagrangian L1 point in the system, due to its proper position, plays the role of the mediator for the desired transfer, so that, first, the equations of motion of three finite objects to reach the LEO orbit to the adjacency of L1 and then to go to the Lunar orbit L1 is solved, eventually the periodic orbits around L1 are used to connect two trajectories to achieve the desired trajectory. In the following, the disturbance model is also added to the equations of motion of the restricted 3-body problem in order to evaluate its effect on the results. The simulation results show that the required impulse is better than the Hohmann transfer method even in the presence of disturbances.

Despite of outstanding properties of cellular materials, their properties cannot be well controlled, and their applications are limited due to irregular pores. Although the use of cellular lattice structures repels this difficulty, complex geometry of these materials makes it impossible to produce metallic ones using conventional manufacturing methods. In addition, additively manufactured metallic samples are expensive. In this study, in order to fabricate and characterize inexpensive metallic cellular lattices, an indirect additive manufacturing process, including fused deposition modeling and gravity casting, is utilized and the effects of different parameters on the quality of the final part are assessed through experimental and numerical methods. Simulations’ results show that decreasing the melt load time, and increasing molten Al temperature, mold temperature, mesh height, and struts’ diameter increase the mold filling percentage. For the fabricated samples, the difference between the struts’ diameter of the sacrificial patterns and designed ones increases by decreasing the struts’ diameter, especially for horizontal struts. For metallic samples, the struts’ diameter’s difference is mainly related to the sacrificial patterns so that the error arisen from casting process is just about 2.2 percent. Also, using the utilized method, cellular lattices with struts’ diameter smaller than 3 mm cannot be fabricated. Microscopic images demonstrate that the samples’ defects are mainly of misrun type which are located on the top plate of BCC and BCCZ samples and on the horizontal struts of SC ones.

The composite structures have many applications in military, aerospace, marine, transportation, and sporting goods industries where the strength to weight performance of the structure is especially important. The quality and strength of composite plates are always decreased due to defects arisen during construction and service. One of the important and most common defects in composite plates is delamination and its propagation. In the present research the delamination propagation of a composite circular plate is investigated. The geometry of delamination is also assumed to be circular and the plate is subjected to a bending load. The nonlinear governing equations are first obtained using third order shear deformation theory. Then, these equations are coded and solved using spectral homotopy analysis method (SHAM). Moreover, the effects of radius and depth of the delamination on energy release rate are studied. It can be seen that the radius of delamination increases, the strain energy release rate increases to a critical radius 0.7 and then decreases. Also, with increasing delamination depth from 0.14 to 0.48, the the strain energy release rate increases. The results of the present research are in good agreement with the FE results and also the available analytical results.

The application of continuum robots with flexible mechanical structures is becoming more widespread in the aerospace . These types of robots have recently used to inspect aircraft fuel tanks and space probes. In this paper, the kinematic behavior and working space of a one-segment continuum robot with a tendon mechanism is studied. The theory for kinematic analysis is the fixed curvature method which is the most effective for analyzing continuum robots especially in the case of weightlessness. Also, the amount of tension and bending of the secondary backbones of the continuum robot in the one-dimensional and three-dimensional were investigated as a time dependent functions. Results showed the rate of change of link lengths is about 39.1% increase of back link, and 17.8%, and 21.2% decrease in others with an initial length of 40 mm . Based on this results , it is possible to estimate the amount of tension and bending over a certain period for different types of materials. Additionally, the error of reaching to target point in the obtained optimal values of bending and rotation angles,equal to 67.35 and -40.89, was almost zero which shows the very high accuracy of model. Also, the results of the working spacecover the surface of the sphere of the working space with an accuracy of 1 mm, The obtained results increase accuracy of robot moving in environments with complex structures and limited spaces. The proposed model can be used as a base for continuum multi-part robots.

In this paper, the Three-dimensional (3-D) theory of elasticity has been used for sound transmission loss (TL) of a thin-walled cylindrical shell with infinite length. This structure is excited by an obliquely plane wave. Governing equations of the thin shell have been derived in radial, axial, and circumferential directions. Then, Helmholtz decomposition is applied to solve the equations. Therefore, the displacement field is considered in terms of Lame potential functions This method describes the vibrational behavior of the shells more accurately than other theories, including the classical theory and the first and third order of shear, due to the consideration of the effects of rotation and shear. A comparison of the present method results with those obtained from classical shell theory (CST) indicates an excellent agreement. However, at the high frequencies the classical encounter insufficient accuracies as a result of increasing the rotational terms as well as shear wave effects. The results show that with increasing shell thickness, due to increased flexural stiffness of the shell, the sound transmission loss has increased. By increasing the Mach number, due to the negative stiffness, reduces the sound transmission loss in the stiffness-controlled region and conversely increases the sound transmission loss in the mass-controlled region due to damping in the structure. Finally, it is shown that the critical and coincidence frequencies increase with the growing up Mach number.

With the growth of technology and population, the human need for energy is constantly increasing. Renewable energy sources are the best option to supply this. In this regard, the use of piezoelectric materials to convert environmental vibrations into electrical energy as an energy source for electrically powered electronic components is one of the available options. In the present paper, the shape of a unimorph piezoelectric actuator has been optimized. It is assumed that this beam is triggered by a harmonic base. In this paper, the energy harvesting system, along with its electrical circuit, is simulated in Comsol software. In this software, frequency responses of the voltage, current, and electrical power of the system are obtained and power sensitivity analysis has been performed in regard to the shape parameters of the beam. The goal of this paper is to obtain a more optimal state for the beam shape in order to gain more power. This is usually done through optimization methods. In this research, the adopted optimization techniques are all zero-order, which use only the value of the objective function.