Iman Mohammadzaman; Hamiderza Momeni
Volume 8, Issue 2 , September 2011, Pages 69-75
Abstract
In this paper a new nonlinear guidance law with finite time convergence is proposed. The second order integrated guidance and control loop is formulated considering a first order control loop dynamics. By transforming the state equations to the normal form, a finite time stabilizer feedback linearization ...
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In this paper a new nonlinear guidance law with finite time convergence is proposed. The second order integrated guidance and control loop is formulated considering a first order control loop dynamics. By transforming the state equations to the normal form, a finite time stabilizer feedback linearization technique is proposed to guarantee the finite time convergence of the system states to zero or a small neighborhood of zero before the final time of the guidance process. However, some feedback quantities such as high order LOS rate derivatives are not directly measurable and therefore, a finite time observer is proposed to have a finite time output feedback guidance law for more practical applications. Simulation results show the effectiveness of the proposed guidance law.
Farid Shahmiri; Mahsa Baghban Salehi
Volume 8, Issue 2 , September 2011, Pages 77-86
Abstract
In this paper, the application of D-optimal models, as an alternative to response surface models (RS models) for design of experiment (DOE) was examined. Two D-optimal models for tilt-rotors in the wind tunnel experiment, as a form of quadratic functions, were generated based on a chosen optimality criterion. ...
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In this paper, the application of D-optimal models, as an alternative to response surface models (RS models) for design of experiment (DOE) was examined. Two D-optimal models for tilt-rotors in the wind tunnel experiment, as a form of quadratic functions, were generated based on a chosen optimality criterion. This optimality criterion was used to generate the optimized sampled points in the design space in order to minimize the variance of the coefficients for the quadratic functions. The main advantage of D-optimal modeling process is alleviating the high computational burden of constructing the RS models. Error analysis of the developed models was performed using analysis of variance (ANOVA). The ANOVA of the D-optimal thrust and rolling moment models for tilt-rotors showed that lateral position of the downwind tilt-rotor relative to the upwind tilt-rotor is the most significant variable affecting the rolling moment and thrust variations. The results also showed that all the models were significant with more than 95% of confidence level.
Alireza Mohamadifard; Abolqasem Naghash
Volume 8, Issue 2 , September 2011, Pages 87-95
Abstract
A near-optimal midcourse trajectory shaping guidance algorithm is proposed for both air and ballistic target engagement mission attributes for generic long range interceptor missile. This guidance methodology is based on the maximum final velocity as the objective function and maximum permissible flight ...
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A near-optimal midcourse trajectory shaping guidance algorithm is proposed for both air and ballistic target engagement mission attributes for generic long range interceptor missile. This guidance methodology is based on the maximum final velocity as the objective function and maximum permissible flight altitude as the in-flight state constraint as well as the head-on orientation as the terminal state constraint for anti-ballistic trajectory. Guidance algorithm utilizes the combination of the Generalized Vector Explicit Guidance or GENEX guidance with the Bezier curve-generating functions. Nominal Bezier curves are fitted by choosing control points intuitively. Waypoints are then selected on the curve to divide it to suitable portions according to the curve’s length and curvature. These waypoints are then fed into the GENEX guidance law. To avoid acceleration command jumps, an algorithm is designed to switch to the next waypoint at a distance from the current currently-approaching waypoint. To provide near-optimality and meet the in-flight and terminal constraints, all the guidance algorithm parameters including Bezier control points, waypoints, switching distances and the GENEX law gain are optimized using Genetic Algorithm by setting the mentioned cost function and constraints. Simulation results show better performance compared to nominal trajectories while ensuring the flight altitude constraint for air target and head-on orientation for ballistic target.
Soghra Rezazadeh; H. Masumi; E. Esmaeilzadeh
Volume 8, Issue 2 , September 2011, Pages 97-105
Abstract
In this work, the compound flow control method (passive and active) has been described. EHD actuators as wire-plate (active) and splitter plate (passive) were coupled and applied to control fluid flow and heat transfer around cylinder in cross flow. Investigation consists of the interaction between electric ...
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In this work, the compound flow control method (passive and active) has been described. EHD actuators as wire-plate (active) and splitter plate (passive) were coupled and applied to control fluid flow and heat transfer around cylinder in cross flow. Investigation consists of the interaction between electric field, fluid flow and temperature field. Experimental tests included various positions of splitter plate and two Re numbers, Re=3500, 7000. EHD actuator was wire-plate. The cylinder and splitter plate were connected to ground and acted as cathode electrodes. Pressure and temperature distributions over the surface of the cylinder have been measured. Results show that two effective corona winds appear in fluid flow around the cylinder. First corona wind is between wires and the cylinder and second one is between wires and splitter plate. Coupled corona winds affected fluid flow and heat transfer. The presence of splitter plate caused decreasing of drag force and increasing of heat transfer. By increasing gap distance, effect of secondary one was reduced and when G=2d, it was found to be negligible.
A. M. Akhlaghi; H. Naseh; Mehran Dr. MirShams; Saeid Irani
Volume 8, Issue 2 , September 2011, Pages 107-117
Abstract
This paper presents an extension of Bayesian networks (BN) applied to reliability analysis of an open gas generator cycle Liquid propellant engine (OGLE) of launch vehicles. There are several methods for system reliability analysis such as RBD, FTA, FMEA, Markov Chains, and etc. But for complex systems ...
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This paper presents an extension of Bayesian networks (BN) applied to reliability analysis of an open gas generator cycle Liquid propellant engine (OGLE) of launch vehicles. There are several methods for system reliability analysis such as RBD, FTA, FMEA, Markov Chains, and etc. But for complex systems such as LV, they are not all efficiently applicable due to failure dependencies between components, computational complexity and state space explosion problems. So to overcome these problems the BN modeling is preferred for OGLE reliability analysis. In this algorithm first the functional models of OGLE is constructed based on expert knowledge and experiments involving system and subsystems interactions. Then failure modes are derived through performing FMEA. Furthermore by using modeling properties of Bayesian networks, a constructional model for failure propagation is obtained based on the acquired functional model and FMEA. Finally, by allocating quantitative properties to the Bayesian model and inference of it, the reliability of OGLE is obtained. The results are verified to the Monte Carlo simulation results. Comparing the values obtained of two applied methods shows the high accuracy and efficiency of introduced algorithm to reliability analysis of launch vehicle OGLE and other complex systems with dependant failure modes.
Neda Eskandari Naddaf; Amir AliAkbarKayyat
Volume 8, Issue 2 , September 2011, Pages 119-125
Abstract
Pilot-Induced Oscillation (PIO) is an unwanted, inadvertent phenomenon that has the ability to damage the aircraft completely. This paper suggests a novel control method that can damp PIO after predicting its occurrence. The specific point of this control algorithm is that it contains a preprocessor ...
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Pilot-Induced Oscillation (PIO) is an unwanted, inadvertent phenomenon that has the ability to damage the aircraft completely. This paper suggests a novel control method that can damp PIO after predicting its occurrence. The specific point of this control algorithm is that it contains a preprocessor that will not let the controller be activated unless in the case of probable PIOs, so pilot commands will not be disturbed in normal flight situations. Besides, with regard to the unconscious tendency of pilot towards establishing PIO, this control algorithm decides on pilot and controller shares in the control signal. By implementing the suggested method, the control algorithm is able to prevent and suppress a general form of PIO. This paper focuses on those groups of phenomena which take place as a result of a sudden disturbance which perturbs one of the states of Pilot-Vehicle System (PVS). It is also shown that the method can block PIO in cases of complex tracking. As a case study, an airplane model based on F-4 derivatives is presented.
sahar noori; Ava Shahrokhi
Volume 8, Issue 2 , September 2011, Pages 127-133
Abstract
To improve the calculation of the flow properties of an aerospike nozzle, different turbulence models were investigated in this study. The primary shape of the nozzle plug is determined through utilizing an approximate method. The flow field is, then, simulated using the Navier-Stokes equations for compressible ...
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To improve the calculation of the flow properties of an aerospike nozzle, different turbulence models were investigated in this study. The primary shape of the nozzle plug is determined through utilizing an approximate method. The flow field is, then, simulated using the Navier-Stokes equations for compressible flows. The commercial computational fluid dynamics code Fluent is used to simulate the flow around an aerospike nozzle. The computational methodology employs steady state density-based formulation and a finite volume cell centered scheme to discretize the flow field equations. To accelerate the solution convergence, the flow field is divided into several zones in order to facilitate each zone with proper unstructured grid and also to offer the appropriate initial conditions for each zone. The accuracy and the robustness of wall function based turbulence schemes, i.e. k-e model, are compared with those of Spalart-Allmaras (S-A) and k-? turbulence models.