Journal of Aerospace Science and Technology
Volume:13 Issue: 2, Summer and Autumn 2020

Epoxy is among the most important polymers, which is extensively employed in various technologies and applications. Nevertheless, epoxy polymers present low thermal conductivities and thus the enhancement of their thermal conductivity is an important research topic. Carbon nanotubes (CNTs) owing to their excellent thermal conductivities have been widely considered for the enhancement of the thermal conduction of epoxy polymers. In this work, we developed a combined molecular dynamics finite element multiscale modelling to investigate the heat transfer along CNT/epoxy nanocomposites. To this aim, the heat transfer between the CNT and epoxy atoms at the nanoscale was explored using the atomistic classical molecular dynamics simulations. In this case, we particularly evaluated the interfacial thermal conductance between the polymer and fillers. We finally constructed the continuum models of polymer nanocomposites representative volume elements using the finite element method in order to evaluate the effective thermal conductivity. The developed multiscale modelling enabled us to systematically analyze the effects of CNT fillers geometry (aspect ratio), diameter and volume fraction on the effective thermal conductivity of nanocomposites. Our results suggest that the interfacial thermal conductance between the CNT additives and epoxy polymer dominate the heat transfer mechanism at the nanoscale.The obtained findings in this study provide good vision regarding the enhancement of thermal conductivityof polymeric materials using highly conductive nanofillers.

This study was designed to investigate the ballistic behavior of ceramic-reinforced aluminum composite plates numerically and experimentally and to present an optimal sample design. The parameters studied were ceramic reinforcement percentage and type of matrix alloy. This study used the matrix alloys 6061, 7075, and 5083. The percentage of ceramics used in this study is 15, 30, and 45% by weight. The samples are in three thicknesses of 20, 25, and 30 mm. 27 simulated samples were numerically analyzed with Abaqus finite element software in this study based on existing ballistic protection criteria, one then determines the optimal numerical sample. Using the squeeze casting method, a laboratory sample has been made and experimentally tested to evaluate the numerical results. Lastly, the numerical analysis and the experimental test were compared and the optimal sample was determined.

In this paper, the effect of perturbations of oblate primaries in the Circular Restricted Three-Body Problem is studied, and the equations of satellite orbital motion in the Circular Restricted Three-Body Problem are developed by employing Lagrangian mechanics. Since the equations have no closed-form solution and numerical methods must be applied, the problem can have different periodic or quasi-periodic solutions depending on the equation's initial conditions of orbital state parameters. For this purpose, an algorithm named “orbital correction algorithm” is proposed to correct the initial conditions of orbital state parameters. The limited number of periodic orbits in the study environment indicates the algorithm’s need for suitable initial guesses as input. In the present paper, suitable initial guesses for orbital state parameters are selected from the third-order approximation of the Unperturbed Circular Restricted Three-Body Problem’s periodic solutions, increasing the chance of obtaining desired periodic solutions. The obtained perturbed and unperturbed periodic orbits are compared in order to understand the effect of perturbations. Adding the perturbations brings the study environment closer to the real environment and helps understand satellites' natural motion.

Designing and manufacturing turbine engines have many complexities and challenges that need time and cost. Therefore, reputable companies producing gas turbines have always sought to shorten the design and construction processes, one of which is to use the core of aerial gas turbines in industrial gas turbines. This category of industrial gas turbines is called aero-derivative gas turbines. Aerial gas turbines can be used as industrial gas turbines due to their particular characteristics such as lightweight, relatively small dimensional size, high efficiency, and performance. These characteristics can shorten the design and manufacturing process. In the present work, ALF 502 aero gas turbine has been studied to convert its application to the derived industrial gas turbine. GasTurb software has been used to model this gas turbine for industrial applications. In this study, six different scenarios have been studied for converting aero engines to industrial engines, and results have been discussed. Finally, three scenarios were selected to be implemented on this engine among the studied scenarios.

This paper presents a novel approach to modeling of jet transport aircraft. Initially, basic mathematical models of jet transport are derived. Afterwards by focusing on the bank angle system of the jet transport, considering the aileron as the input, adverse methods of identification are utilized to estimate parameters of the system in an online manner. Then, effects of different types of noise on identification process are analyzed. Eventually, effects of time varying parameters are discussed. Recursive least squares method and its extended version, covariance resetting and forgetting factor methods were the fundamental tools in the system identification process of jet transport. Comprehensive simulations are presented and cast some light on effectiveness and disadvantages of different approaches.

One of the most effective ways of high-speed motion in water is the motion in the supercavitation regime. This way provides the possibility to avoid considerable viscose resistance of boundary layer and consequently reach to very small drag coefficient which can be several times smaller than, that of the continuous flow. In this study the numerical simulation of developed and supercavitating flow is performed. The CFX code which served as a platform for the present work is a three-dimensional code that solves the Reynolds-Averaged Navier-Stokes equations with a finite volume method. The cavitation model is implemented based on the use of Rayleigh-Plesset equation to estimate the rate of vapor production. A high Reynolds number form ĸ-ε model is implemented to provide turbulence closure. For steady state flows and poor mesh resolution near the wall (using log-law wall functions), there is a priori no difference between the two equations formulations. For the different case studies, multi-block structured meshes were generated and the numerical simulation is performed in a wide range of cavitation numbers. Results are presented for steady state flows with natural cavitation about various bodies. Comparisons are made with available measurement of surface pressure distribution, cavitation bubble geometry (cavity length and cavity width) and drag coefficient. The simulated results are in a good agreement with the experimental data. Finally, the three-dimensional results are presented for a submerged body running at several angles of attack.

This paper addresses the adaptive control problem of an aircraft and focuses on the task that the pitch angle of the aircraft is required to follow the desired path. Considering the elevator deflection angle as the input and the pitch angle as the output, a mathematical model of the aircraft is derived to specify the structure of the system. Three diverse deterministic self-tuning regulators are designed using direct and indirect methods. Assuming that the system is unknown, recursive least squares method is applied to estimate parameters of the system or that of the controller’s. Diophantine equation and minimum degree pole-placement methods are utilized to calculate the control law. Not only do simulation results clearly demonstrate the privilege and effectiveness of the proposed approaches, but also comprehensive discussion is presented to distinguish advantages and disadvantages of them.

In this paper, using the Abaqus finite element software, the torsional hysteresis of X52, X60, X65 steels under loadings with different torsion values, has been numerically investigated and they are compared to each other. The shear stress, effective stress, residual stress and elastic and plastic shear strain distribution are presented in the numerical results. In this analysis, the “chaboche” kinematic hardening theory has been used to predict the behavior of the material in the plastic region. By comparing the difference percentage graphs of the steels under the same load, it has been concluded that the hysteresis loops in X65 steel will become stable sooner than X60 and in X60 steel they become stable sooner than X52.

In the course of all-round advancement of engineering science, space research can be considered as the drivers of this forward movement. In the field of space propulsion, this trend can be seen as a backward trend, not in the sense of regression, but in the sense of optimizing the original designs used for space systems, which not only lead to the re-invention of these systems based on the acquisition of specific modern manufacturing technologies, but also strengthened the link between sciences such as Materials science and Mechanics science. In this research, according to the space propulsion system roadmap and also the review of old and reference designs, an attempt has been made to study some of the optimizations made in recent years and to express the weaknesses and challenges ahead. One of the ideas that optimizes, minimizes and increases the reliability of the space propulsion system is the injection of fuel through the porous media. The study of a type of showerhead injector expresses the formation path of the idea of using porous materials in the injection system and then the efficiency of these two types of injections is compared in a design that connects the porous material with the coaxial injector design.

In order to reduce cost and time along with enhancing the safety issues, numerical computer modelling and simulations are widely used for analyzing complex systems such as launch vehicle or spacecraft propulsion system. The objective of this research is to obtain an algorithm for simulation of staged combustion cycle liquid propellant engines. For this purpose the space shuttle main engine (SSME), as one of the world’s most complicated engines, is selected as a case study. A total of 34 elements is taken into account and using more than 100 linear/non-linear equations, the engine’s steady state system model has been established in MATLAB SIMULINK software. The simulation method uses eleven nested loops for iteration. The algorithm is based on the known parameters at the inlet of engine main feed lines namely mass flow rate and pressure, similar to the known conditions during hot test of engine on test stand. The simulation is capable of predicting the engine’s operation in wide range of thrust throttling levels from 69 percent to 109 percent of the nominal thrust. In order to validate the suggested method, SSME main component parameters, operating at 109 percent of rated thrust is presented. Simulation result mean error is less than 5 percent.

The weaknesses of liquid propellants have led to special attention to gelled propellants in the last two decades as a way to overcome the weaknesses of these propellants. Previous studies have shown that the addition of gel-forming agents to liquid propellants converts these propellants, mainly Newtonian fluids, into non-Newtonian fluids, which greatly affects the physical properties of these propellants. In order to better understand the changes occurred in the physical properties of liquid propellants due to their gelled structure, on factors such as spraying and atomization, in this study, impinging jet injectors have been used to spray and atomize a non-Newtonian gelled fluid with rheological properties similar to gelled propellants. Analysis of the results of the present study shows that the use of impinging jet injectors causes different regimes of spraying and atomization (due to the jets’ high Reynolds number) for non-Newtonian gelled fluids, some of which being fundamentally different from the regimes formed for Newtonian fluids. In general, 4 regimes including stable closed rim, unstable closed rim with the formation of vermicular ligaments, open rim with successive formation of bow-shaped ligaments and a turbulent regime have been identified in this study. The properties of each of these regimes and their details will be explained in this paper.

In this paper, a new methodology to develop an optimum flying law using model predictive control algorithm for a third order non-minimum phase system is presented. The guidance law of the optimum line of sight strategy may be extracted for an ideal non-minimum phase control model of first, second and third order. Optimization algorithm of controller has been introduced and the simulation results for the non-minimum phase system is provided. The results indicate efficiency of the proposed controller in alleviating the adverse effect of the non-minimum phase system and the proposed method could be extended to use in other systems with higher order and complexity in online applications.