Seyed Saied Bahrainian
Volume 5, Issue 2 , June 2008, , Pages 81-90
Abstract
Making an initial tetrahedral grid for complex geometry can be a tedious and time consuming task. This paper describes a novel procedure for generation of starting tetrahedral cells using hexahedral block topology. Hexahedral blocks are arranged around an aerodynamic body to form a flow domain. Each ...
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Making an initial tetrahedral grid for complex geometry can be a tedious and time consuming task. This paper describes a novel procedure for generation of starting tetrahedral cells using hexahedral block topology. Hexahedral blocks are arranged around an aerodynamic body to form a flow domain. Each of the hexahedral blocks is then decomposed into six tetrahedral elements to obtain an initial tetrahedral grid around the same aerodynamic body. This resulted in an algorithm that enables users to produce starting tetrahedral grids for variety of aerodynamic bodies. To construct an initial starting tetrahedral grid suitable for computational flow simulations, representing a solid surface geometry (fuselage or a wing section) attached to a plane-of-symmetry, a topology containing at least 5 hexahedral blocks is required. The resulting initial starting grid consists of 30 tetrahedral cells with 74 faces and 16 vertices, which is the same number of vertices as for the hexahedral blocks. A face-based global data structure is then produced for the tetrahedral cells. To represent multiple surface definitions a topology containing nine hexahedral blocks is required. When decomposed, the nine hexahedral blocks, produce a tetrahedral grid consisting of 54 cells and 24 vertices.
Volume 3, Issue 2 , June 2006, , Pages 87-95
Abstract
This study was carried out using two sets of numerical weather forecast data and flight reports for Clear Air Turbulence (CAT) over Iranian Plato to find atmospheric flow patterns favorable to the formation of CAT. The numerical data include five months of AVN analysis with horizontal resolution of 1 ...
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This study was carried out using two sets of numerical weather forecast data and flight reports for Clear Air Turbulence (CAT) over Iranian Plato to find atmospheric flow patterns favorable to the formation of CAT. The numerical data include five months of AVN analysis with horizontal resolution of 1 degree(about 100 km) and four months forecast data of MM5 model with resolution of 50 km. Important indices associated with conditions favorable for CAT formation include wind shear, flow deformation fields and atmospheric static stability (or joint effects such as Richardson number). These indices were estimated and also some algorithms such as Dutton to find their threshold values for CAT occurrence. The best selected algorithms are determined in the 5 months period using AVN outputs. In another 4 months period the MM5 outputs were used for the forecast of CAT using the POD method. The results for there periods indicated that severe CAT rarely occurred over Iran and condition for moderate CAT are often in upstream of troughs ridges, near straight jet stream with cold advection and upper region of ridges. The POD method shows Dutton and Ellrod-2 are the best selected algorithms for CAT forecasting and have good consistency with observations. Their typical threshold values (associated with wind shears) are about 3 and 20 for moderated CAT respectively.
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.
Ali Ashrafizadeh; A. A. Hosseinjani
Volume 7, Issue 2 , September 2010, , Pages 107-122
Abstract
The classical panel method has been extensively used in external aerodynamics to calculate ideal flow fields around moving vehicles or stationary structures in unbounded domains. However, the panel method, as a somewhat simpler implementation of the boundary element method, has rarely been employed to ...
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The classical panel method has been extensively used in external aerodynamics to calculate ideal flow fields around moving vehicles or stationary structures in unbounded domains. However, the panel method, as a somewhat simpler implementation of the boundary element method, has rarely been employed to solve problems in closed complex domains. This paper aims at filling this gap and discusses the numerical solution of the Laplace equation in bounded domains via the numerical panel method. It is shown that the panel method is an efficient and accurate computational algorithm for the solution of this class of problems. Several test cases in heat conduction and internal ideal flow are presented to show that the numerical panel method can be used in closed domains regardless of the complexities in the geometry and/or boundary conditions.
fariborz saghafi; Seyed Mohammad Khansari Zadeh
Volume 5, Issue 3 , July 2008, , Pages 123-128
Abstract
In the present paper, an efficient method for three dimensional aircraft pattern recognition is introduced. In this method, a set of simple area based features extracted from silhouette of aerial vehicles are used to recognize an aircraft type from its optical or infrared images taken by a CCD camera ...
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In the present paper, an efficient method for three dimensional aircraft pattern recognition is introduced. In this method, a set of simple area based features extracted from silhouette of aerial vehicles are used to recognize an aircraft type from its optical or infrared images taken by a CCD camera or a FLIR sensor. These images can be taken from any direction and distance relative to the flying aircraft. A multilayer perceptron neural network has been used for the purpose of aircraft classification. The network training has been carried out using a library of images generated by a 3D model of each aircraft. The neural network is successfully trained and used to recognize and classify arbitrary real aircraft images. The results show more than 90% accuracy in ideal conditions and very good robustness in the presence of noise.
Volume 3, Issue 3 , September 2006, , Pages 143-149
Abstract
An analysis of on-line autonomous robust tracking controller based on variable structure control is presented for an aerospace launch vehicle. Decentralized sliding-mode controller is designed to achieve the decoupled asymptotic tracking of guidance commands upon plant uncertainties and external disturbances. ...
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An analysis of on-line autonomous robust tracking controller based on variable structure control is presented for an aerospace launch vehicle. Decentralized sliding-mode controller is designed to achieve the decoupled asymptotic tracking of guidance commands upon plant uncertainties and external disturbances. Development and application of the controller for an aerospace launch vehicle during atmospheric flight in an experimental setting is presented to illustrate the performance of the control algorithm against wind gust and internal dynamics variations. The proposed sliding mode control is compared to non-linear and time-varying gain scheduled autopilot and its superior performance is illustrated by simulation results. Furthermore, the proposed sliding-mode controller is convenient for implementation.
S.A. Sina; Hassan Haddad Pour
Volume 5, Issue 4 , December 2008, , Pages 180-182
Abstract
Two 2-D aeroelastic models are presented here to determine instability boundary (flutter speed) and gust response of a typical section airfoil with degrees of freedom in pitch and plunge directions. To build these 2-D aeroelastic models, two different aerodynamic theories including Indicial Aerodynamic ...
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Two 2-D aeroelastic models are presented here to determine instability boundary (flutter speed) and gust response of a typical section airfoil with degrees of freedom in pitch and plunge directions. To build these 2-D aeroelastic models, two different aerodynamic theories including Indicial Aerodynamic Theory and Vortex Lattice Method (VLM) have been employed. Also, a 3-D aeroelastic framework constructed of Boundary Element Method (BEM) and modal technique is used to show the accuracy and reliability of the presented 2-D aeroelastic models. The methods reviewed in this study are used to predict the non-dimensional flutter speed and its corresponding frequency for a typical section airfoil (for the 3-D model a high aspect ratio wing with the same cross-sectional characteristics is used) Then, a group of figures show how different time-marching schemes can change the dynamic responses due to the sharp edge gust. Also, a set of figures provide some comparisons between the 2-D aeroelastic models, and also, with the 3-D model. As seen from the results presented in this study 2-D aeroelastic models give lower non-dimensional flutter speed than the 3-D model. In addition, the dynamic responses due to the sharp edge gust predicted by the 2-D models show larger amplitudes than the 3-D model. It means that since the 2-D aeroelastic models can overestimate the dynamical behavior such as flutter speed and responses to the sharp edge gust, they can be used in the preliminary design steps to reduce the cost and save time.
Soheil Dr. Mohammadi
Volume 3, Issue 4 , December 2006, , Pages 195-204
Abstract
A combined finite/ discrete element method is presented for modelling of composite specimens subjected to dynamic/impact loadings. The main task is set on developing an algorithm for simulation of potential bonding and debonding/delamination phenomena during impact or general dynamic loading conditions. ...
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A combined finite/ discrete element method is presented for modelling of composite specimens subjected to dynamic/impact loadings. The main task is set on developing an algorithm for simulation of potential bonding and debonding/delamination phenomena during impact or general dynamic loading conditions. In addition, full fracture analysis can also be performed. The proposed approach adopts a general node to face nonlinear frictional contact algorithm to enforce bonding/debonding constraints between composite plies. The method is also capable of analysing progressive fracture and fragmentation behaviour as well as potential post cracking interactions caused by the newly created crack sides and segments. A local remeshing technique is adopted every time a new crack is formed, while an overall remeshing is performed anytime a certain criterion of error estimation is violated. The special local remeshing technique is designed to model geometrically an individual crack by splitting the element, separating the failed node, creating new nodes and dividing the neighbouring elements to preserve the compatibility conditions. The same procedure is capable of modelling application of fibre reinforced polymer (FRP) layers to other engineering structures in order to improve their flexible behaviour in static and dynamic loading conditions.
Davoud Hassanzadeh
Volume 9, Issue 1 , March 2012
Abstract
An implicit unsteady upwind solver including a mesh motion approach was applied to simulate a helicopter including body, main rotor and tail rotor in hover flight. The discretization was based on a second order finite volume approach with fluxes given by the Roeand#39;s scheme. Discretization of Geometric ...
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An implicit unsteady upwind solver including a mesh motion approach was applied to simulate a helicopter including body, main rotor and tail rotor in hover flight. The discretization was based on a second order finite volume approach with fluxes given by the Roeand#39;s scheme. Discretization of Geometric Conservation Laws (GCL) was devised in such a way that the three-dimensional flows on arbitrary moving grids could be solved. The accurate geometric representation together with the flexibility required for grid displacement was achieved by using a tetrahedral grid. First, the numerical methodology was validated through experimental test data; then, our supposed helicopter configuration was utilized. At the same time, the main rotor loading measurements were done through flight tests. Two methods of moving reference frame (MRF) and viscous/inviscid Dynamic Mesh were compared resulting in robustness of Dynamic Mesh approach. Ultimately, our calculationsyieldedvalid solutions to the blade loading and wake structure.
Abolfazl Mokhtari; A.A. Nikkhah; Mahdi Sabze Parvar; A.R. Novinzadeh
Volume 9, Issue 2 , September 2012
Abstract
There is a growing interest in the modeling and control of model helicopters using nonlinear dynamic models and nonlinear control. Application of a new intelligent control approach called Brain Emotional Learning Based Intelligent Controller (BELBIC) to design autopilot for an autonomous helicopter is ...
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There is a growing interest in the modeling and control of model helicopters using nonlinear dynamic models and nonlinear control. Application of a new intelligent control approach called Brain Emotional Learning Based Intelligent Controller (BELBIC) to design autopilot for an autonomous helicopter is addressed in this paper. This controller is applied to a nonlinear model of a helicopter. This methodology has been previously proved to present robust characteristics against disturbances and uncertainties existing in the system. The simulation results of this controller has compared with a PID controller. The policies for PID and BELBIC controller are the same. The controller design goal is that the helicopter tracks a special maneuver to reach the commanded height and heading. The performance of the controllers is also evaluated for robustness against perturbations with inserting a high frequency disturbance. Simulation results show a desirable performance in both tracking and improved control signal by using BELBIC controller.
M.H Djavareshkian; A.M. Faghihi
Volume 10, Issue 1 , March 2013
Abstract
A pressure based implicit procedure to solve the Euler and Navier-Stokes equation is developed to predict transonic viscous and inviscid flows around the pitching and heaving airfoils with a high reslution scheme. In this process, nonorthogonal and non moving mesh with collocated finite volume formulation ...
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A pressure based implicit procedure to solve the Euler and Navier-Stokes equation is developed to predict transonic viscous and inviscid flows around the pitching and heaving airfoils with a high reslution scheme. In this process, nonorthogonal and non moving mesh with collocated finite volume formulation are used. In order to simulate pitching or heaving airfoil, oscillation of flow boundary condition is applied. The boundedness criteria for this procedure are determined from Normalized Variable Diagram (NVD) scheme. The procedure incorporates the K-E eddy- viscosity turbulence model. This process is tested for inviscid and turbulent transoinc aerodynamic flows around oscillation airfoil. The results are compared with other existing numerical solutions and with the experimental data. The comparisons show that the resolution quality of the developed algorithm is significant.
H. Fazeli
Volume 10, Issue 2 , September 2013
Abstract
This paper studies theuncertain nonlinear dynamics of a MEMS optical switch addressing electrical, mechanical and optical subsystems. Recently, MEMS optical switch has had significant merits in reliability, control voltage requirements and power consumption. However, an inherent weakness in designing ...
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This paper studies theuncertain nonlinear dynamics of a MEMS optical switch addressing electrical, mechanical and optical subsystems. Recently, MEMS optical switch has had significant merits in reliability, control voltage requirements and power consumption. However, an inherent weakness in designing control for such systems is unavailability of switch position information at all times due to the saturated output characteristics, which is aggravated by considering disturbances. In order to circumvent this problem, two nonlinear observers based on the first order and second order sliding mode approach are designed to estimate the state variables of the device subject to external disturbances. The nonlinear observers are then utilized in the control system to maintain robust stability and tracking performances. The newly invented second order sliding mode controller can remove the chattering phenomena as the main drawback of the first order sliding mode controller. Furthermore, since second order sliding mode control is not robust against disturbances/uncertainties which vary with states, a new time-varying second order sliding mode control is proposed to enhance the robust performance of the controller without estimating any switching time. Simulation results show that the proposed observer and control have good tracking ability and robustness against disturbances
I. Mohammadzaman; H. Dehghani Firouzabadi
Volume 11, Issue 1 , June 2017
Abstract
In this paper, a robust autopilot is proposed using stable interpolation based on Youla parameterization. The most important condition of stable interpolation between local controllers is the preservation of stability so that each local controller can ensure stability for an open neighborhood around ...
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In this paper, a robust autopilot is proposed using stable interpolation based on Youla parameterization. The most important condition of stable interpolation between local controllers is the preservation of stability so that each local controller can ensure stability for an open neighborhood around a nominal point. The proposed design used fixed-order robust controller with parameter-dependent central polynomial for each vertex of the polytope to decrease the conservation of each local controller. A stability-preserving gain-scheduled controller was designed using a newly proposed algorithm in the flight envelop for a parameter varying model. The results of simulation confirm the efficiency of the proposed method.
Aerospace Science and Technology
Ali Alizadeh; Mohsen Heydari Beni; Jafar Eskandari Jam
Abstract
In this research, aluminum/alumina/graphite hybrid composite was prepared by horizontal centrifugal casting method, and the microstructure and distribution of alumina and graphite particles in the radial direction of the cross-sectional area of the samples were investigated. The distribution of graphite ...
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In this research, aluminum/alumina/graphite hybrid composite was prepared by horizontal centrifugal casting method, and the microstructure and distribution of alumina and graphite particles in the radial direction of the cross-sectional area of the samples were investigated. The distribution of graphite and alumina particles has led to the creation of a gradual structure (FGM) along the cross section. As a result of the centrifugal force, the graphite particles separated in the inner part of the sample and the alumina particles gradually increased from the inner region to the outer region. The samples were obtained with 3, 5 and 7% by volume of graphite particles added to the melt and with the rotation speed of the mold RPM1000, RPM1500 and RPM2000, and the formation of the inner zone rich in graphite was investigated. In all samples, 3% by volume of alumina particles were used and the effect of the presence of alumina particles on the distribution of graphite particles was studied. Optical microscope (OM) was used to investigate the microstructure and distribution of graphite and alumina particles. By increasing the amount of graphite from 3 to 7 percent by volume, the collision and interaction between graphite particles increases and leads to an increase in the thickness of the inner layer rich in graphite, and increasing the speed of rotation of the mold first causes an increase in the thickness of the inner layer and then leads to It was reduced. The presence of alumina particles prevented the complete separation of graphite particles
M. R. Mosavi; A. R. Baziar; M. Moazedi
Volume 10, Issue 2 , September 2013, , Pages 9-16
Abstract
Spoofing could pose a major threat to Global Positioning System (GPS) navigation, so the GPS users have to gain an in-depth understanding of GPS spoofing. Since spoofing attack can influence position results, spoof compensation is possible through reducing position deviations. In this paper, a novel ...
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Spoofing could pose a major threat to Global Positioning System (GPS) navigation, so the GPS users have to gain an in-depth understanding of GPS spoofing. Since spoofing attack can influence position results, spoof compensation is possible through reducing position deviations. In this paper, a novel processing technique is proposed and the wavelet transform is used to eliminate the impact of spoofing on the stationary GPS receivers. We assumed that the spoofing attack was immediately detected, and then the position residuals of the last authentic and new spoofing signals were passed to the statistic wavelet transform at the first level. By denoising in the next step, position deviations due to the spoofing attack can be extracted. Then, the estimated position solution of the received signal is corrected. Finally, the receiver coordinates are calculated by averaging the corrected positions. For validation of the suggested algorithm, five different data sets are investigated. We mitigated the spoofing in all data sets more than 93%. The test results show that the proposed technique supremely improves the performance of the GPS receiver and attenuates the spoofing effect.
Alireza Jahangirian
Volume 2, Issue 1 , March 2005, , Pages 29-36
G. Atashbaz
Volume 1, Issue 1 , October 2004, , Pages 31-39
Abstract
It is generally believed that, on slender delta wings, there is a critical state at which strong asymmetric vortices are found along the leading edge on the lee-side of the delta wing. These asymmetric vortices can lead to high lateral forces even when slender delta wing is at the zero angle of yaw. ...
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It is generally believed that, on slender delta wings, there is a critical state at which strong asymmetric vortices are found along the leading edge on the lee-side of the delta wing. These asymmetric vortices can lead to high lateral forces even when slender delta wing is at the zero angle of yaw. Some experimental studies reported recently, cast considerable doubt as to the validity of the above explanations. A wind tunnel investigation was, therefore, performed to study afresh this phenomenon. The flow over four sharp edged delta wings with aspect to a ratio ranging of 0.56 to 1.46 was investigated using flow visualization with laser light sheet and some surface pressure as well as hot wire measurement. The tests were conducted for angles of attack ranging from 0 to 30 deg and at a free-stream velocity of 30m/s corresponding to a Reynolds number of $4.8 times10^{5}$ based on the center line chord of the wing. The results obtained suggest the absence of asymmetry in the vortex core position in the flow.
Asghar Dashti Rahmatabadi
Volume 4, Issue 1 , March 2007, , Pages 33-38
Abstract
This paper presents the effect of preload on static and dynamic performance characteristics of several gas-lubricated noncircular journal bearing configurations. The linearized system approach using finite element method is used to obtain both steady state and dynamic characteristics. The results of ...
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This paper presents the effect of preload on static and dynamic performance characteristics of several gas-lubricated noncircular journal bearing configurations. The linearized system approach using finite element method is used to obtain both steady state and dynamic characteristics. The results of the investigation shows that preload has a significant effect on frictional power loss and the stability margin. It is observed that increased preload, lowers the stability margin while it will increase the amount of power loss in noncircular gas lubricated bearing systems. The results also show that the preload effect on stability margin is more pronounced at lower compressibility numbers.
M. Ziaei- Rad; Javad Abolfazli Esfahani
Volume 2, Issue 2 , June 2005, , Pages 37-42
fariborz saghafi
Volume 4, Issue 4 , December 2007, , Pages 37-46
Abstract
In this research, an automatic control system is designed for landing of a small helicopter on a 4 DOF moving platform. The platform has three translational and one directional degree of freedom. The controller design approach is based on development of helicopter nonlinear dynamic model into the SDC ...
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In this research, an automatic control system is designed for landing of a small helicopter on a 4 DOF moving platform. The platform has three translational and one directional degree of freedom. The controller design approach is based on development of helicopter nonlinear dynamic model into the SDC (State Dependent Coefficient) form and real time solving of state dependent Riccati equation (SDRE). To compensate the simplifications and term eliminations done to make the SDC form, a nonlinear compensator is added. The performance of the control system in automatic landing is evaluated by computer simulation in different scenarios. The results show a satisfactory tracking performance of the controller during landing on a moving platform.
Mohammad Reza Seif; mohammad ali sharifi; M. Najafi Alamdari
Volume 8, Issue 1 , March 2011, , Pages 37-44
Abstract
Linearization of the nonlinear equations and iterative solution is the most well-known scheme in many engineering problems. For geodetic applications of the LEO satellites, e.g. the Earth’s gravity field recovery, one needs to provide an initial guess of the satellite location or the so-called reference ...
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Linearization of the nonlinear equations and iterative solution is the most well-known scheme in many engineering problems. For geodetic applications of the LEO satellites, e.g. the Earth’s gravity field recovery, one needs to provide an initial guess of the satellite location or the so-called reference orbit. Numerical integration can be utilized for generating the reference orbit if a satellite’s state vector i.e., position and velocity is known at a reference epoch. However, the numerically integrated orbit deviated from the real orbit due to imperfect force models. The more accurate reference orbit the less linearization error occurs. The deviation between the reference and real orbit can be minimized using the least squares method. Different analytical and numerical techniques have been developed for calculation of the design matrix of the least squares method. Herein, we have generalized the idea of the Lagrange coefficients for the determination of the design matrix’s entries in the gravitational field an attracting inhomogeneous mass body. Numerical implementation of the proposed method shows its high performance.
kosar Mokhtari; Alireza Naderi
Abstract
The present study investigates the flow around two tandem spheres and their aerodynamic optimization. In a systematic view, the downstream sphere is regarded as the projectile and the upstream sphere is the sensor. The aim of this study is to find the most appropriate configuration with lowest drag force. ...
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The present study investigates the flow around two tandem spheres and their aerodynamic optimization. In a systematic view, the downstream sphere is regarded as the projectile and the upstream sphere is the sensor. The aim of this study is to find the most appropriate configuration with lowest drag force. Therefore, the results of the effects of the center-to-center (CC) distance of the spheres, and the reduction of the sensor’s diameter were investigated in 15 different cases. The results show that as the distance between the spheres decreases, the drag force of the spheres decreases too; reduction in the sensor’s diameter would increase the projectile’s drag while decreasing the sensor’s drag. The highest effects on drag reduction were induced by constant distance between spheres and a change in sensor’s diameter. Consequently, in the last stage of the study, the adjoint solution of the FLUENT software was used to reduce the drag of the whole set through optimization of the sensor frontal hemisphere. However, due to systematic limitations, only the shape of the forepart of the sensor can be changed. Since the sphere is a bluff body, efficient options are needed for the adjoint optimization algorithm and it’s worth noting that the optimized shape in each case is different from other cases. The highest drag reduction happened in the case with a CC distance of 2.5 m and sensor diameter of 0.75 m. Furthermore, the case with CC distance of 1m and sensor diameter of 0.25 is the only case after optimization in which simultaneously the drag force of both spheres has been reduced.
farid Shahmiri
Volume 7, Issue 1 , March 2010, , Pages 41-49
Abstract
The main purpose of this paper is concerned with the sensitivity analysis of main rotor dynamic response pertaining to variation of some relevant system parameters effectively supports the preliminary design of both articulated and hingeless helicopter rotor configurations. The methodology is laid out ...
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The main purpose of this paper is concerned with the sensitivity analysis of main rotor dynamic response pertaining to variation of some relevant system parameters effectively supports the preliminary design of both articulated and hingeless helicopter rotor configurations. The methodology is laid out based on Galerkin solution of partial differential equation (PDE) of main rotor with flexible blades in modal space, and developing of some significant expressions useful for direct and cross-coupled damping and control response prediction. The methods followed in this particular discipline supports the derivation of main rotor PDE for flexible flapping in non-linear closed form accompanied with procurement of response derivatives, Galerkin method of solution, linearization, modal analysis and harmonic balance application. The main advantage of this approach is to render main rotor direct, cross damping and control derivatives for each harmonic of the blade deformations associated with the calculated pitching and rolling moments. The sensitivity expressions enables the prediction of direct, cross damping and control derivatives of main rotor response in terms of the most expressive system parameters, including flap frequency ratio, stiffness number, blade response Lock number, and physical hinge offset, necessary for design of modern helicopters. Finally, the results are depicted in graphical forms for a range of system parameters and operating conditions. Comparison of damping and control derivatives in hover, shows a small effect of offset hinge on the main rotor direct response, whereas, the cross derivatives have a strong dependence on combination of stiffness and offset. Furthermore, Comparison with the full aeroelastic analysis shows that the obtained predictions approximate the true elastic of the main rotor behavior.
Volume 3, Issue 1 , March 2006, , Pages 43-49
Abstract
This paper presents an application of the nonlinear optimal control techniques to the design of launch vehicle autopilots. The optimal control is given by the solution to the Hamilton-Jacobi-Bellman (HJB) equation, which in this case cannot be solved explicity. A method based upon Successive Galerkin ...
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This paper presents an application of the nonlinear optimal control techniques to the design of launch vehicle autopilots. The optimal control is given by the solution to the Hamilton-Jacobi-Bellman (HJB) equation, which in this case cannot be solved explicity. A method based upon Successive Galerkin Approximation (SGA), is used to obtain an approximate optimal solution. Simulation results involving three degrees of freedom (3DOF) model of a launch vehicle during atmospheric flight are reported to demonstrate the performance of the considered autopilot. Alternative results are also presented for classical and linear optimal approaches.
M.J. Nategh
Volume 4, Issue 2 , June 2007, , Pages 43-51
