AEROSPACE KNOWLEDGE AND TECHNOLOGY JOURNAL
Year:2017 | Volume:6 | Issue:1 |Papers Count:10

The use of spiral atomizers is one of the common and appropriate methods to produce liquid sprays. In this paper, we have investigated the performance of these single-base atomizers experimentally. Then, the effects of two important geometrical parameters in these type of atomizers, orifice diameter and spiral angle as quantities that have dominant effects were studied. After this, the numerical simulation of spray was conducted using the open-source Open FOAM code and helping of experimental results, parameters in numerical models compatible with these results are presented in the low pressure range. Experimental results show that decreasing spiral angle and output orifice diameter, increases Sauter mean diameter of droplets. In addition, the numerical simulation of spiral atomizer predicts velocity and size distribution of spray droplets with good accuracy that shows validity of the experimental parameters used in numerical models. In this paper using experimental results, numerical model parameters that are compatible with hollow cone spray of these atomizers have presented that with the presented parameters, Hereinafter simulation of hollow cone spray in pressure range of this paper could be done independent of the experimental results.

Vortex combustion chamber which is a new generation of liquid fuel engine with different arrangements of injectors generated a vortex flow into the combustion chamber. This vortex contributed to increased cooling and mixing the components of the propellant in the combustion chamber and can be generated a complete combustion in a small volume chamber. In this chamber several type of injector used in various locations including, centrifugal, flow and vortex injectors. In this study, the design of these injectors and then experimental test to investigate the effect of geometrical parameters on their hydrodynamic characteristics is done using water flow. Spry forming process, flow measurement, pressure drop and injector spray angle including hydrodynamic characteristics that have been studied. The results show acceptable agreement of the predicted design with performance of injectors. Accordingly, centrifugal and flow injectors that injected the fuel and oxidizer into the chamber were selected and shown that increasing the number of tangential vortex injectors to 6, generated more uniformity in the rising vortex flow in the chamber but the entry angle to 5 degrees no significant effect on rising flow.

In this paper, the effects of swirling air and primary aeration on NOx production are numerically investigated. In this regard, a combustion chamber with two-dimensional axisymmetric geometry and non-premixed combustion is considered. The k–e Realizable model is adopted as a turbulence closure model. Also, the Presumed PDF and EDM models with Zeldovich mechanism are considered for combustion modeling. Comparisons of numerical results with available experimental data show that the PDF model is capable of predicting the combustion characteristics. Results show that for every swirl number a specific aeration exists that consequences the minimum NO emissions. As the result, the increase of swirl number in without aeration will lead first to an increase and then a slight decrease of combustion temperature and NO at the exit. The effect of aeration in constant stoichiometric ratio shows that, swirl number of 0.48 and 2.5% aeration, leads to the complete combustion and minimum NO emissions.

Missile’s vertical launchers are one of the ground equipment of tactical missiles used to hold them in launching position, vertical position and servicing them for launching. Tower launchers’ dimension and configuration depend on effective loads, dimension and weight of the missile. In the majority of tower launchers two bars connected to each other with crossbar connectors are considered as basic parts. Space frame element is used for designing and a finite element code has been written in MATLAB Software to calculate stress and deformities of the structure. A Genetic algorithm which is codified in MATLAB has been used for optimization. This code uses the finite element code to calculate the stress and deformation of the structure. All of the written codes have been compared to experimental data and results confirm the accuracy and exactness of the outcome. In this design weight of the tower launcher was the target equation, displacement and yield stress were constraints and geometrical specifications of the cross section were variables.

Thin-walled tubes have been widely used as energy absorbing devices for decades in trains, passenger cars, ships and other high-volume industrial products since they are relatively cheap and weight efficient. This paper investigates the energy absorption responses of bitubular conical tubes under quasi-static axial and oblique loading. In experimental approach, aluminum bitubular conical tubes were made by the process of spinning. The bitubular conical tubes were fixed at both ends. These samples are compressed between two rigid platens under quasi-static loading conditions and axial and oblique load was realized by applying a load at the upper end of specimens and the collapse mechanism, the variations of crushing load and absorbed energy are determined. A numerical model is presented based on finite element analysis to simulate the collapse process considering the non-linear responses due to material behavior, contact and large deformation. The comparison of numerical and experimental results showed that the present model provides an appropriate procedure to determine the collapse mechanism, crushing load and the amount of energy absorption. The validated finite element model was then used for the parametric studies, in order to determine the effect of bitubular conical tube loading parameters i.e. effect of boundary condition and crush angle. The results of this paper highlight the advantages of using bitubular conical tubes as energy absorber.

In this paper, governing equations of transverse vibration of single-layer graphene sheet with different boundary conditions under 2D in-plane magnetic field action, considering its consequent forces and moments, are investigated for the first time using differential quadrature method (DQM). Governing equations of motion are obtained using non-local theory and considering Lorentz's force. The partial differential equations of system are changed to the ordinary differential equations using separation of variables method. Using differential quadrature method, the obtained governing equations are solved for different boundary conditions. The effects of elastic foundation stiffness, non-local parameter, plate aspect ratio and 2D magnetic field effects on the natural frequency of graphene sheet are evaluated. The results show that increase of foundation stiffness, non-local parameter and aspect ratio result in increase of fundamental frequency, in all boundary conditions. But, action of in-plane magnetic field results in decrease of fundamental frequency, because of decreasing flexural stiffness and increasing in-plane pressure loading.

In this study, a new guidance law for high maneuver targets is designed by using state dependent Riccati equation. The reason of using this equation is: no need to linearization of equations and simplification of implementation. The aim of this research is presenting a guidance law that compensate the depletion of classic guidance laws for high maneuver targets and in the second, the comparison among proportional navigation law, pure pursuit law and new guidance law. It is worth noting that the criterions of analyzing are: total of incoming acceleration and required time for hitting the target. So these laws have been compared for fixed target, moving target with constant speed and moving target with variable speed and for different initial conditions. Finally a sensitivity analysis has been done for investigation of laws behavior.

In this paper, a new enhanced backstepping controller is presented for control of quadrotors. Dynamic equations of the robot are nonlinear. Therefore, a convenience controller is required to stabilize the robot on desired motion. Here, backstepping method is used for control of the robot. In the conventional backstepping method, nonlinear terms of dynamic equations appear in the control law. Therefore, control law depends on accuracy of the nonlinear terms in the dynamic equations. In this research, nonlinear terms in the backstepping controller are estimated by function approximate method and adaptive laws based on projection operator. Therefore, in the proposed controller, the nonlinear terms of the dynamic model is not required to know accurately. This is the main novelty of the paper. The stability analysis is performed by Lyapanov theory. In order to validation of the proposed approach, several numerical simulation results are presented. Simulation results show the proposed controller can force the quadrotors in neighborhood of the desired motion in presence of dynamic model uncertainties and external disturbances.

In this paper, a capacitive 3-DOF vibratory rate micro gyroscope with 2-DOF oscillator in the sense mode and 1-DOF in the drive mode was studied. A complete model of the micro gyroscope, including mechanical and electrical parts was utilized. Based on the graphical and differential sensitivity analyses methods, variations of the system parameters were analyzed. In the first step, governing equations of the micro gyroscope were derived. In order to simulate the sensor operation, working frequency has been determined and then, output voltage of the sensor versus changes in mechanical and electrical elements is studied. According to the sensitivity analysis results, secondary mass (m2), permittivity, length and width of the electrostatic capacitors, also DC and AC components of the actuation voltage have been clustered as the most sensitive parameters. Initial gap of the electrostatic capacitors and stiffness are fairly sensitive. Primary mass (m1), mass of the decoupling frame (mf), and young module are considered as non-sensitive parameters. Variations of the output voltage based on secondary mass (m2), stiffness and initial gap are completely non-linear and in some areas have severe slopes. Wise choices in selecting appropriate values for these parameters will lead to the better performance and more output voltage of the sensor

This paper presents a methodology for conceptual design of long endurance stratospheric airships and establish a baseline of specifications for a conventional configuration stratosphere airship, according to given performance and operational requirements. The methodology is validated by other design concepts, which previously developed for similar missions. The shape optimization of airship was introduced into the design process, and several optimum objectives can be selected including minimum drag, minimum surface area and minimum weight. Also, a multi-objective function was used to take account of various factors which influence airship subsystems- e.g. aerodynamics, structures, energy and weight- to determine the optimal shape of airship. An algorithm for generating the shape is developed and appropriate mathematical models for subsystems are constructed. Simulation results show the optimized shape gives an improvement in the multi-objective function compared with a reference shape. The baseline specifications of stratosphere airships designed for various shapes by this methodology are presented.