S. Moammad Bag Malaek
Volume 2, Issue 2 , June 2005, , Pages 11-18
Seyyed Amir Mahdi Ghannadpour; H.R. Ovesy; M. Nassirnia
Volume 8, Issue 1 , March 2011, , Pages 11-19
Abstract
ABSTRACT This paper presents the theoretical developments of two finite strip methods (i.e. semi-analytical and full-analytical) for the post-buckling analysis of isotropic plates. In the semi-analytical finite strip approach, all the displacements are postulated by the appropriate shape functions while ...
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ABSTRACT This paper presents the theoretical developments of two finite strip methods (i.e. semi-analytical and full-analytical) for the post-buckling analysis of isotropic plates. In the semi-analytical finite strip approach, all the displacements are postulated by the appropriate shape functions while in the development process of the full-analytical approach, the Von-Karman’s equilibrium equation is solved exactly to obtain the buckling loads and the out-of-plane buckling deflection modes. The investigation of plates buckling behaviour is then extended to the post-buckling study with the assumption that the deflected form after the buckling is the combination of first, second and higher (if required) modes of buckling. Thus, the full-analytical post-buckling study is effectively a multi term analysis. In this method the Von-Karman compatibility equation is used together with a consideration of the total strain energy of the strut. Through the solution of the compatibility equation, the in-plane displacement functions which are themselves related to the Airy stress function are developed in terms of the unknown coefficients in the assumed out-of-plane deflection function. The in-plane and out-of-plane deflection functions are substituted in the total strain energy expressions and the theorem of minimum total potential energy is applied to solve for the unknown coefficients.
Aerospace Science and Technology
Ali Khavari; S. Mohammad Reza Moosavi; Amir Tabatabaee; Hadi Shahriyar Shahhosseini
Volume 12, Issue 2 , October 2019, , Pages 11-18
Abstract
Abstract: Urban canyon is categorized as hard environment for positioning of a dynamic vehicle due to low number and also bad configuration of in-view satellites. In this paper, a tuning procedure is proposed to adjust the important factors in Kalman Filter (KF) using Genetic Algorithm (GA). The authors ...
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Abstract: Urban canyon is categorized as hard environment for positioning of a dynamic vehicle due to low number and also bad configuration of in-view satellites. In this paper, a tuning procedure is proposed to adjust the important factors in Kalman Filter (KF) using Genetic Algorithm (GA). The authors tested the algorithm on a dynamic vehicle in an urban canyon with hard condition and compared the results with traditional KF and Weighted Least Square (WLS) methods. The outputs showed that this algorithm could be more reliable more than 114% and 61% against WLS and traditional KF. ---------------------------------------------------------------------------------------Abstract: Urban canyon is categorized as hard environment for positioning of a dynamic vehicle due to low number and also bad configuration of in-view satellites. In this paper, a tuning procedure is proposed to adjust the important factors in Kalman Filter (KF) using Genetic Algorithm (GA). The authors tested the algorithm on a dynamic vehicle in an urban canyon with hard condition and compared the results with traditional KF and Weighted Least Square (WLS) methods. The outputs showed that this algorithm could be more reliable more than 114% and 61% against WLS and traditional KF.
Aerospace Science and Technology
Jafar Roshanian; Ehsan Rahimzade
Abstract
In this research, new adaptation law for updating parameters of the model reference adaptive control and the model reference adaptive control with feedback integrators for a specific class of nonlinear systems with additive parametric uncertainty are presented. The innovation presented in this paper ...
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In this research, new adaptation law for updating parameters of the model reference adaptive control and the model reference adaptive control with feedback integrators for a specific class of nonlinear systems with additive parametric uncertainty are presented. The innovation presented in this paper is the consideration of a new form for Lyapunov functions candidate to prove the stability of the closed-loop system. In general, Lyapunov functions candidate, which is used to prove stability and to derive rules for updating control parameters, include two sets of quadratic expressions. The first quadratic expression contains the trajectory tracking error and the second category includes the error of estimating the controller parameters. In this research, it is proved that by selecting quadratic expressions including the variable of trajectory tracking error in the form of power series, a new adaptation law is obtained that includes quadratic expressions in terms of the variable of tracking error in the form of power series. This type of adaptation law can be considered as an adaptation law derived from quadratic Lyapunov functions, except that the gain adaptation matrix parameters vary with time. It has been shown that by using an adaptive controller with a feedback integrator, the tracking error tends to zero faster and the flying object roll angle tracks the reference trajectory after a shorter time. In order to evaluate the control performance of the designed controllers, the system of one degree of freedom of the Wing Rock phenomenon has been used.
Aerospace Science and Technology
Mohammadreza Varshavi; Sahar Noori
Abstract
Air-breathing hypersonic flight is presumed by many of the savants in the field of aeronautical engineering as the last boundary of aerial vehicle design to be pushed back. An auspicious design configuration for the prospective hypersonic transport vehicles of the future is a “Waverider,” ...
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Air-breathing hypersonic flight is presumed by many of the savants in the field of aeronautical engineering as the last boundary of aerial vehicle design to be pushed back. An auspicious design configuration for the prospective hypersonic transport vehicles of the future is a “Waverider,” using the Scramjet engine cycle as its propulsive system. Two-dimensional CFD Analysis and case-to-case study of three pre-defined waverider configurations with 2-ramp, 3-ramp, and 4-ramp inlet geometries are carried out in the hypersonic flight regime of Mach numbers 5, 6, and 7. This is done in an attempt to study the single-oriented and also correlative-oriented impacts of increasing/decreasing the number of inlet ramps and increasing/decreasing the flight Mach number upon the behavior of final aerodynamic coefficients and ratios. The paramount outcome of the present work is the generation of some tables which can be utilized as primary guidelines for aeronautical design engineers who are designing waverider configurations on a preliminary basis.
Mohammad Farshchi
Volume 4, Issue 2 , June 2007, , Pages 13-22
Abstract
A theoretical study analyzing three-dimensional combustion acoustic instabilities in a liquid propellant rocket engine combustor has been conducted. A linear theory based on Crocco’s pressure sensitive time lag model is used. To apply this theory the combustor is divided into two main components, including ...
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A theoretical study analyzing three-dimensional combustion acoustic instabilities in a liquid propellant rocket engine combustor has been conducted. A linear theory based on Crocco’s pressure sensitive time lag model is used. To apply this theory the combustor is divided into two main components, including the combustion chamber and the converging part of the nozzle. The assumption of concentrated combustion zone is used and the governing perturbation equations describing oscillations of flow variables are considered. To solve these equations appropriate boundary conditions at both ends of the combustion chamber are required. Combustion zone boundary condition at one end and the nozzle admittance relation at other end are used. To obtain the nozzle admittance the three dimensional flow perturbation equations are solved in the converging part of the nozzle. This approach is capable of predicting acoustic stability behavior of a combustor at a wide range of Mach numbers and frequencies. Also, this analysis enables the rocket engine designer to observe the effects of different parameters such as nozzle entrance Mach number, chamber geometry, nozzle geometry, and gas properties on stability characteristics of an engine combustor. In case of instability observation; one can predict the acoustic mode which causes the instability and achieve an optimum design before conducting any expensive and time consuming experimental tests. This paper presents the stability analysis results and a parametric study of the effect of design parameters on stability characteristics of a typical combustor.
Volume 4, Issue 3 , September 2007, , Pages 13-24
Abstract
In this paper a general formulation for finding the maximum allowable dynamic load (MADL) of flexible link mobile manipulators is presented. The main constraints used for the algorithm presented are the actuator torque capacity and the limited error bound for the end-effector during motion on the given ...
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In this paper a general formulation for finding the maximum allowable dynamic load (MADL) of flexible link mobile manipulators is presented. The main constraints used for the algorithm presented are the actuator torque capacity and the limited error bound for the end-effector during motion on the given trajectory. The precision constraint is taken into account with two boundary lines in plane which are equally offset due to the given end-effector trajectory, while a speed-torque characteristics curve of a typical DC motor is used for applying the actuator constraint. Finite element method (FEM) is utilized for deriving the kinematic and dynamic equations which considers the full nonlinear dynamic of mobile manipulator. In order to verify the effectiveness of the presented algorithm, two simulation studies considering a flexible two-link planar manipulator mounted on a mobile base are presented and the results are discussed.
H.R. Ovesy
Volume 5, Issue 1 , March 2008, , Pages 13-22
Abstract
In this paper, the compressive behavior of composite laminates with multiple through-the-width delaminations is investigated analytically. The analytical method is based on the CLPT theory and its formulation is developed on the basis of the Rayleigh-Ritz approximation technique to analyze the buckling ...
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In this paper, the compressive behavior of composite laminates with multiple through-the-width delaminations is investigated analytically. The analytical method is based on the CLPT theory and its formulation is developed on the basis of the Rayleigh-Ritz approximation technique to analyze the buckling and post-buckling behavior of the delaminated laminates. The method can handle both local buckling of the delaminated sublaminates and global buckling of the whole plate. Also the three-dimensional finite element analysis is performed by using ANSYS5.4 general purpose commercial software, and the results are compared with those obtained by the analytical model. The agreement between the results is very good.
S. Forouzan-sepehr; Soheil Dr. Mohammadi
Volume 6, Issue 1 , March 2009, , Pages 13-23
Abstract
The element-free Galerkin method is employed for two-dimensional analysis of steady-state heat transfer. The unknown response of the system, i.e. temperature is approximated using the moving least squares technique. Numerical integration of governing simultaneous system of equations is performed by Gauss ...
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The element-free Galerkin method is employed for two-dimensional analysis of steady-state heat transfer. The unknown response of the system, i.e. temperature is approximated using the moving least squares technique. Numerical integration of governing simultaneous system of equations is performed by Gauss quadrature and new modified nodal integration techniques. Numerical examples and tests have proved that the new methods remain in an acceptable level of accuracy while providing less expensive and much faster approaches.
M. Noorabadi; N. Namdaran; M. Rahnama; Jafar Eskandari Jam
Volume 11, Issue 2 , October 2017, , Pages 13-22
Abstract
The aim of this study is to investigatethe effective parameters on vibrations of circular cylindrical shells with fixed rotary speed andresting elastic foundation by means of analytical and finite element numerical simulation. First, the governing equations are derived using the theory of Donnell, considering ...
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The aim of this study is to investigatethe effective parameters on vibrations of circular cylindrical shells with fixed rotary speed andresting elastic foundation by means of analytical and finite element numerical simulation. First, the governing equations are derived using the theory of Donnell, considering the centrifugal forces,Coriolis acceleration, and the initial annular tension. Then, the analytical solution for cylindrical shells isintroduced under simply supported conditions. Further, the effect of parameters such as therotational speed of the shell, its lay-up, fiber angle, and the stiffness of the elastic foundation on the values of natural frequency and the critical velocity of the shells are studied. The analytical solution results are in good compatibility with the results achieved from the finite element method.
Aerospace Science and Technology
Morteza Sharafi; Nasser Rahbar; Ali Moharrampour; Abdorreza Kashaninia
Abstract
This study proposes a new non-linear guidance law for a Falcon 9 missile booster landing's terminal phase using a non-linear vectorized high expansion method. For this purpose, At first, the dynamic modeling of the landing problem is presented, assuming mass, gravity, and density are variables. Then, ...
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This study proposes a new non-linear guidance law for a Falcon 9 missile booster landing's terminal phase using a non-linear vectorized high expansion method. For this purpose, At first, the dynamic modeling of the landing problem is presented, assuming mass, gravity, and density are variables. Then, sensitivity variables are extracted using the vectorized high order expansion method and assuming the parameters constant. Then, the guidance law is extracted to update the path and optimal commands using sensitivity variables. The path and commands of the near-optimal guidance are extracted online using the proposed guidance law. Considering initial deviations, the guidance law performance in simulations are studied using a combination of various initial deviations. The results shown as charts and numerical values of errors indicate that the landing point errors are insignificant, and the vectorized high order expansion method has a desirable performance for the reusable booster's vertical landing.
M. Manshadi; A. Sharafi; M.H. Soltani
Volume 9, Issue 2 , September 2012, , Pages 15-24
Abstract
An extensive experimental investigation is conducted to study the effect of canard position relative to the fuselage reference line on the aerodynamic forces of a fighter type configuration model. Aerodynamic forces at different flight conditions are measured in a subsonic wind tunnel. The wing and the ...
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An extensive experimental investigation is conducted to study the effect of canard position relative to the fuselage reference line on the aerodynamic forces of a fighter type configuration model. Aerodynamic forces at different flight conditions are measured in a subsonic wind tunnel. The wing and the canard have triquetrous shapes. Experiments are conducted at Reynolds number of 342209 and at 0 to 40 degree angles of attack. The results show that canard increases the lift and drag forces while it decreases the static stability of the model. The canard at itandrsquo;s up position increases the aerodynamic forces and decreases the static stability i.e., superior maneuver capability. Furthermore, when the forward position of the canard is considered, both lift and drag are increased; however, the overall aerodynamic efficiency and also more static stability are improved. The canard at up and forward position respect to the wing-body is an appropriate selection for the best performance at moderate to high angles of attack among the various wing-canard-body configurations.
Aerospace Science and Technology
S. Amir M. Ghannadpour; M. Barekati
Volume 12, Issue 1 , March 2019, , Pages 15-26
Abstract
In this paper, a method based on Chebyshev polynomials is developed for examination of geometrically nonlinear behaviour of thin rectangular composite laminated plates under end-shortening strain. Different boundary conditions and lay-up configurations are investigated and classical laminated plate theory ...
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In this paper, a method based on Chebyshev polynomials is developed for examination of geometrically nonlinear behaviour of thin rectangular composite laminated plates under end-shortening strain. Different boundary conditions and lay-up configurations are investigated and classical laminated plate theory is used for developing the equilibrium equations. The equilibrium equations are solved directly by substituting the displacement fields with equivalent finite double Chebyshev polynomials. Using this method allows one to analyze the composite laminated plates with combination of different boundary conditions on all edges. The final nonlinear system of equations is obtained by discretizing both equilibrium equations and boundary conditions with finite Chebyshev polynomials. Nonlinear terms caused by the product of variables are linearized by using quadratic extrapolation technique to solve the system of equations. Since number of equations is always more than the number of unknown parameters, the least squares technique is used to solve the system of equations. Some results for angle-ply and cross-ply composite plates with different boundary conditions are computed and compared with those available in the literature, wherever possible.
Aerospace Science and Technology
Hamzeh Eshraghi
Abstract
In the current article, using results of previous researches, a guideline has been developed to select a proper value for solidity of a tandem blade row in an axial flow compressor stage. Next, using this guideline, a highly loaded tandem compressor stage has been designed. To verify the selected solidity ...
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In the current article, using results of previous researches, a guideline has been developed to select a proper value for solidity of a tandem blade row in an axial flow compressor stage. Next, using this guideline, a highly loaded tandem compressor stage has been designed. To verify the selected solidity value, some other cases have been designed with different solidity values. Other geometrical parameters have been selected similarly in all cases. At the next stage, a three dimensional numerical model is developed to predict the characteristic performance of each tandem stage. The model is validated with the experimental results of NASA Stage and Rotor 37, and the level of the accuracy of the model is presented. Using a similar model, the performance of all cases has been derived and the effect of solidity variation on the overall performance of machine has been discussed. Lastly, the effect of solidity variation on the tip leakage flow structure near peak efficiency point is discussed for all cases.
Hamid Parhizkar
Volume 3, Issue 1 , March 2006, , Pages 17-21
Abstract
The present study is devoted to an approximate modeling for numerical simulation of flows past oscillating airfoils. In this study, it is shown that the harmonic oscillating objects can be studied by simple numerical codes that are not able to solve moving grids. Instead of using moving grid for the ...
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The present study is devoted to an approximate modeling for numerical simulation of flows past oscillating airfoils. In this study, it is shown that the harmonic oscillating objects can be studied by simple numerical codes that are not able to solve moving grids. Instead of using moving grid for the simulation of flowfield around an oscillating airfoil, this unsteady flow is solved on a fixed grid having oscillated its free stream velocity vector on the boundaries. It is shown that, with a time shift, resulting airfoil forces have a good agreement with moving grid results. This time shift, which is not noted by others, is the time that takes for the flow to move from upstream boundary and pass the airfoil completely. Resulting - ellipse diameter using this approximate modeling, is only a little bigger than the experimental results. This modeling is applicable in simple codes that are not able to model moving grids.
Aerospace Science and Technology
Sam Mohamad Hassan Pouryoussefi; Sohrab Gholamhosein Pouryoussefi
Abstract
Importance of study of pulsating heat pipes (PHPs) behavior and limitations in conducting experimental studies, the necessity of numerical simulations is getting critical in this area. In present work, numerical simulations are carried out for pulsating heat pipes. Thermal performance of closed loop ...
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Importance of study of pulsating heat pipes (PHPs) behavior and limitations in conducting experimental studies, the necessity of numerical simulations is getting critical in this area. In present work, numerical simulations are carried out for pulsating heat pipes. Thermal performance of closed loop pulsating heat pipes is investigated at different operating conditions such as evaporator heating power and filling ratio. Water, ethanol, methanol and acetone are employed as working fluids. A two-dimensional single loop PHP is used for present study. Computational Fluid Dynamics (CFD) video technique is employed for flow visualization purpose. Perfect match was observed between the present CFD video clip and previous experimental video-based studies in terms of flow pattern and behavior. Present study shows how researchers can benefit from developments of numerical tools to test pulsating heat pipes behavior at different operating conditions or different working fluids without facing difficulties and limitations of applying laboratory thermal measurement equipment or high-speed cameras. The CFD video clip as result of numerical simulation was found very informative for flow visualization purpose. The simulated clip made it much easier to capture phenomena occur in a pulsating heat pipe. The thermal performance investigation at different operating conditions and working fluids was found very informative in terms of application and design purposes especially for experimental studies. By increasing heating power greater than 60 W, circulation velocity was increased for most cases. Phase contour videos are inserted at the bottom of the article.
Aerospace Science and Technology
Alireza Ekrami Kivaj; Alireza Novinzadeh; farshad pazooki; Ali Mahmoodi
Abstract
This study aims to investigate the spacecraft returning from the atmosphere. Due to high speed, prolonged flight duration, and numerical sensitivity, returning from the atmosphere is regarded as one of the more challenging tasks in route design. Our suborbital system is subjected to a substantial thermal ...
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This study aims to investigate the spacecraft returning from the atmosphere. Due to high speed, prolonged flight duration, and numerical sensitivity, returning from the atmosphere is regarded as one of the more challenging tasks in route design. Our suborbital system is subjected to a substantial thermal load as a result of its return at high speed and the presence of uncertainty. In addition, the current study aims to lessen the thermal load in the system to meet the needs of the initial and final conditions through multi-subject optimization, comparison of the two fields of aerodynamics and flight dynamics, assistance from optimal control theory, and consideration of uncertainties The heat load in the sub-orbital system could be reduced by around 9.6% using these algorithms and optimum control theory. Artificial bee colonies, genetic algorithms, and the combined genetic algorithms and particle swarm algorithms were utilized as exploratory optimization techniques. The objective of the flight mechanics system is also to create the best trajectory while taking into account uncertainty and minimizing thermal load. The conduction law based on heat reduction is described in the search for the ideal trajectory. We reduced the heat rate during the first part of the spacecraft's return journey from the atmosphere by concentrating on the angle of attack. By more accurately specifying the angle of attack and the angle of the bank in the second stage of the split guidance legislation, the ultimate return requirements could be achieved significantly .
Reza Dr. Taghavi
Volume 5, Issue 2 , June 2008, , Pages 57-66
Abstract
Occurrence of laminar separation bubbles on solid walls of an elliptic cylinder has been simulated using a recently developed transitional model for boundary layer flows. Computational method is based on the solution of the Reynolds averaged Navier-Stokes (RANS) equations and the eddy-viscosity concept. ...
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Occurrence of laminar separation bubbles on solid walls of an elliptic cylinder has been simulated using a recently developed transitional model for boundary layer flows. Computational method is based on the solution of the Reynolds averaged Navier-Stokes (RANS) equations and the eddy-viscosity concept. Transitional model tries to simulate streamwise fluctuations, induced by freestream turbulence, in pre-transitional boundary layer flows by introducing an additional transport equation for laminar kinetic energy term. It includes three transport equations of turbulent kinetic energy, KT, laminar kinetic energy, KL, and dissipation rate frequency, ?. Numerical results show that the model is capable of predicting each of subcritical (final separation in laminar), critical (existence of bubble/bubbles) and supercritical (final separation in turbulent) flow regimes. Laminar separation bubble is simulated precisely, due to the modeling of transition from laminar to turbulent in separated free shear layer. Separation bubble region and its characteristics were detected by inspection on the distributions of surface pressure and skin friction, and also by streamlines pattern. Excellent agreements were observed between results obtained through current mathematical modeling with available experimental data for all the flow regimes. In addition, some of the results of the present numerical method are compared to those obtained through application of conventional fully laminar and fully turbulent standard k-? models.
Kaveh Amiri; Mohammad Reza Dr. Soltani; H. Haghiri; Mahmood Mani
Volume 6, Issue 2 , June 2009, , Pages 63-70
Abstract
A trisonic wind tunnel has been modified to improve its flow quality when operating at transonic speeds through perforated walls and side suctions. The usefulness of such a perforated wall, already known, is reduction of the blockage effect as well as the shock elimination. Two types of perforated walls ...
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A trisonic wind tunnel has been modified to improve its flow quality when operating at transonic speeds through perforated walls and side suctions. The usefulness of such a perforated wall, already known, is reduction of the blockage effect as well as the shock elimination. Two types of perforated walls have been used in this investigation. The first wall had a porosity of about 22% and the holes were drilled perpendicular to the surface. However, the second wall had a variable porosity, 0 to 6%, and the holes were drilled at an angle of 60 degrees with respect to the normal vector of the plate. The flow in the test section of the wind tunnel was surveyed extensively at various Mach numbers ranging from 0.6 up to 1.2. Effect of porosity has been studied by comparing results related to the present perforated with the previous closed wall data for various conditions as. Te amount of suction could be adjusted through the side walls. Flow quality along the nozzle and test section has been studied by a long tube installed in the center of the wind tunnel test section.
Mehrzad Shams; Reza Ebrahimi
Volume 3, Issue 2 , June 2006, , Pages 67-75
Abstract
A Lagrangian-Eulerian numerical scheme for the investigation of bubble motion in turbulent flow is developed. The flow is analyzed in the Eulerian reference frame while the bubble motion is simulated in the Lagrangian one. Finite volume scheme is used, and SIMPLEC algorithm is utilized for the pressure ...
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A Lagrangian-Eulerian numerical scheme for the investigation of bubble motion in turbulent flow is developed. The flow is analyzed in the Eulerian reference frame while the bubble motion is simulated in the Lagrangian one. Finite volume scheme is used, and SIMPLEC algorithm is utilized for the pressure and velocity linkage. The Reynolds stresses are modeled by the RSTM model of Launder. Upwind scheme is used to model convective fluxes. The Guassian Filter White Noise is incorporated to simulate the turbulent fluctuation velocities. The bubble diameter is found by the use of Rayleigh-Plesset equation. Various forces in the equation of motion of the bubble are considered. The Buoyancy, Saffman lift, drag, pressure, and change of volume forces are carefully applied. The effects of all of these forces on bubble path are also examined. The bubbles are created in the low pressure zones, and then traced in the flow field. It is observed that the bubble diameter is highly dependent on the mean stream pressure, and its location. The results are compared with the other published works, and have an acceptable accuracy.
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.
maryam malekzadeh; Abolqasem Naghash; H.Ali Talebi
Volume 7, Issue 2 , September 2010, , Pages 81-91
Abstract
Two robust nonlinear controllers along with a nonlinear observer have been developed in this study to control a 1D nonlinear flexible spacecraft. The first controller is based on dynamic inversion, while the second one is composed of dynamic inversion and µ-synthesis controllers. The extension of dynamic ...
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Two robust nonlinear controllers along with a nonlinear observer have been developed in this study to control a 1D nonlinear flexible spacecraft. The first controller is based on dynamic inversion, while the second one is composed of dynamic inversion and µ-synthesis controllers. The extension of dynamic inversion approach to flexible spacecraft is impeded by the non-minimum phase characteristics when the panel tip position is taken as the output of the system. To overcome this problem, the controllers are designed by utilizing the modified output re-definition approach. It is assumed that only one torque on the hub is used. In particular, the assumption that all sate variables are measurable is not realistic; hence sliding mode observers is used to estimate states. Actuator saturation is considered in the design of controllers. The performances of the proposed controllers are compared in terms of nominal performance, robustness to uncertainties, vibration suppression of panel, sensitivity to measurement noise, environment disturbance and nonlinearity in large maneuvers. To evaluate the performance of the proposed controllers, an extensive number of simulations on a nonlinear model of the spacecraft are performed. Simulation results show the ability of the proposed controller in tracking the attitude trajectory and damping panel vibration. It is also verified that the perturbations, environment disturbance and measurement errors have only slight effects on the tracking and damping responses.
Mohammad J. Sadigh; Ali Salehi
Volume 5, Issue 3 , July 2008, , Pages 107-113
Abstract
Many space applications require robotic manipulators which have large workspace and are capable of precise motion. Micro-macro manipulators are considered as the best solution to this demand. Such systems consist of a long flexible arm and a short rigid arm. Kinematic redundancy and presence of unactuated ...
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Many space applications require robotic manipulators which have large workspace and are capable of precise motion. Micro-macro manipulators are considered as the best solution to this demand. Such systems consist of a long flexible arm and a short rigid arm. Kinematic redundancy and presence of unactuated flexible degrees of freedom, makes it difficult to control micro-macro manipulators. This paper presents a closed-loop control based on artificial constrained motion which helps to keep the end-effector on the prescribed trajectory, while the flexible arm can freely vibrate. The robustness of algorithm is checked against uncertainties of the system, which shows good performance except in the presence of gravity. A gravity compensating term is added to eliminate the drift due to gravity.
fariborz saghafi
Volume 3, Issue 3 , September 2006, , Pages 125-133
Abstract
The feasibility of using a stand alone Fluidic Thrust-Vectoring (FTV) system for the purpose of longitudinal trim of an unmanned aerial vehicle is the focus of the research presented in this paper. Since the fluidic thrust vectoring requires high pressure secondary air to deflect the engine exhaust gases, ...
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The feasibility of using a stand alone Fluidic Thrust-Vectoring (FTV) system for the purpose of longitudinal trim of an unmanned aerial vehicle is the focus of the research presented in this paper. Since the fluidic thrust vectoring requires high pressure secondary air to deflect the engine exhaust gases, this research also provides an analytical toolset for preliminary sizing of a suitable secondary air supply. The study is based on a conceptual model of a VTOL tail-sitter type unmanned aerial vehicle in three common phases of flight named as Hovering, Transition and Cruise. A relationship is finally presented between the thrust-vectoring angle and the required secondary mass flow rate. It is found that the aircraft trim is possible only by using fluidic thrust-vectoring. In addition, the mathematical model developed in this study can be used as a preliminary tool for overall performance evaluation of such a conceptual aircraft, especially for sensitivity analysis of thrust-vectoring control and finding the optimum values of the parameters like centre of gravity and engine location.
G. Yuan
Volume 5, Issue 4 , December 2008, , Pages 161-166
Abstract
The dynamic characteristics of deflectable nose missiles with rotary single-channel control were investigated in this paper. Firstly, the effective angle of attack, effective angle of sideslip and quasi-body coordinates were introduced based on the spin characteristics of the missile’s body. Secondly, ...
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The dynamic characteristics of deflectable nose missiles with rotary single-channel control were investigated in this paper. Firstly, the effective angle of attack, effective angle of sideslip and quasi-body coordinates were introduced based on the spin characteristics of the missile’s body. Secondly, considering the interaction between the missile’s nose and body, the rigid kinetic model of missile with deflectable nose control was set up in the quasi-body coordinates utilizing rootless multi-rigid-body system dynamics. Finally, computer simulation was performed to investigate and analyze the interaction between the missile’s nose and body. Academic analysis and simulation results indicate that the nose deflection will cause a motion of body on the opposite direction, and the kinetic model established in this paper is correct and reasonable.