A. Moghtadaei Rad
Volume 9, Issue 1 , March 2012
Abstract
This article would study batch and recursive methods that used in terrain navigation systems. Terrain navigation has a lot ofdisadvantages and so researchers have been studied on different method of aided navigation for many years. Therefore, more types of aided navigation systems were introduced with ...
Read More
This article would study batch and recursive methods that used in terrain navigation systems. Terrain navigation has a lot ofdisadvantages and so researchers have been studied on different method of aided navigation for many years. Therefore, more types of aided navigation systems were introduced with advantages and disadvantages in terms of practical and theoretical. One of the main ideas for aided navigation is integration of extended kalman filter and INS[1]. But this integration method has significant weakness in practice that caused to benonsignificant among the aided navigation methods. So in this article, the author introduces more accurate filter (UKF) for integration byINS and other sensors as barometer and radar system. In continue,the use of Aided EKF and UKF navigation schemes would be justified anddeveloping and performing algorithms written for the needed application and simulation results will be presented and compared.Finally, benefit of the proposed methods in this article will be compared with other batch and recursive methods. The most significant of this article is related to its practical application on UAV that was tested in 2010.
M. Mortazavi; A. Askari
Volume 9, Issue 2 , September 2012
Abstract
Improvement of the launch phase of a jet powered Unmanned Aerial Vehicle (UAV) with Jet Assisted Take Off (JATO), has been the subject of attention in the UAV industry. Use of flight simulation tools reduces the risk and required some amount of flight testing for complex aerospace systems. Full nonlinear ...
Read More
Improvement of the launch phase of a jet powered Unmanned Aerial Vehicle (UAV) with Jet Assisted Take Off (JATO), has been the subject of attention in the UAV industry. Use of flight simulation tools reduces the risk and required some amount of flight testing for complex aerospace systems. Full nonlinear equations of motion are used to study and simulate this maneuver and three case studies of their application to UAV launch phase problems are presented. Attempt was made to explain some aspects that were not definite in the test by simulation. The result of the examination was satisfactory. The second and third examples involve the flight test of the UAV. These two applications are typical of launch phase problems. The second example demonstrated a good applicability of this technique to improve and increase the stability of the UAV during launch. In the third example, the UAV in the presence of headwind showed that simulation and real test had a good coincidence.
J. Karimi; M. Shadoud
Volume 10, Issue 1 , March 2013
Abstract
An advanced guidance law is developed for reentry phase of a reentry vehicle. It can achieve small miss distance and desired impact attitude angle, simultanceously. To meet this requirment a guidance law based on the fuzzy logic approach is developed. It is partitioned into three stages. This guidance ...
Read More
An advanced guidance law is developed for reentry phase of a reentry vehicle. It can achieve small miss distance and desired impact attitude angle, simultanceously. To meet this requirment a guidance law based on the fuzzy logic approach is developed. It is partitioned into three stages. This guidance law does not require linearization of missile engagement model. Line-of-sight and flight path angle are used to constitute the rule antecedent of the guidance law to shape an appropriate flight trajectory for engagement. Numerical simulation results and comparsion with an existing algorithm demonstrated that the proposed guidance law offers satisfactory and robustness, fulfilling its design goals.
S.Hamid Jalali -Naini; Sh. Ahmadi Darani
Volume 11, Issue 1 , June 2017
Abstract
In this paper, the preferred region of design parameters for quasi-normalized equations of single-axis attitude control of rigid spacecraft using pulse-width pulse-frequency modulator (PWPFM) is presented for rest-to-rest maneuvers. Using the quasi-normalized equations for attitude control reduces the ...
Read More
In this paper, the preferred region of design parameters for quasi-normalized equations of single-axis attitude control of rigid spacecraft using pulse-width pulse-frequency modulator (PWPFM) is presented for rest-to-rest maneuvers. Using the quasi-normalized equations for attitude control reduces the system parameters, that is, the moment of inertia, the filter gain, and the maximum torque of modulator are merged to other parameters and the total number of parameters is reduced. Therefore, the computational burden is decreased and moreover, the results are usable for grouped parameters, regardless of the value of each parameter separately. The optimization is carried out by grid search method with the performance index of fuel consumption or number of thruster firings for a range of inputs. Finally, the suggested upper and lower bounds of parameters are obtained based on the optimization results.
Aerospace Science and Technology
Heshmatollah MohammadKhanlo; Ali Nouri; Seyed Mohammad Kamali
Abstract
Exposure to vibrations of certain frequencies can pose a risk to the pilot's body. During flight, the maneuvers performed by the pilot expose them to sudden and unfavorable accelerations, which can cause physical, physiological, and psychological problems. Research suggests that the use of seat suspension ...
Read More
Exposure to vibrations of certain frequencies can pose a risk to the pilot's body. During flight, the maneuvers performed by the pilot expose them to sudden and unfavorable accelerations, which can cause physical, physiological, and psychological problems. Research suggests that the use of seat suspension systems is effective in reducing high-frequency vibrations. However, for small movements, which occur at low frequencies between 2 to 15 Hz, the cushion of the pilot's seat plays a more significant role. In this research, we investigate the effect of the cushion on reducing vibrations on the pilot's body. Firstly, we compare and validate the results of the biodynamic equations of motion of a 4-degree-of-freedom model of the helicopter pilot's body with the experimental results. Next, we compare the biodynamic response of the motion in the finite element model (numerical solution) with the experimental results. Finally, we obtain and evaluate the biodynamic responses of the pilot's body movement by considering the cushion with different mechanical characteristics and in two stiffness and parallel (Kelvin-Voight model) and series (Maxwell model) damper modes. The Kelvin-Voight model was found to be more accurate than the COMSOL model.
M. Mani
Volume 10, Issue 2 , September 2013, , Pages 25-36
Abstract
Numerous experiments have been conducted on plunging Eppler 361 airfoil in a subsonic wind tunnel. The experimental tests involved measuring the surface pressure distribution over the airfoil at Re=1.5×105. The airfoil was equipped with Gurney flap(heights of 2.6, 3.3 and 5% chord) and plunged at 6cm ...
Read More
Numerous experiments have been conducted on plunging Eppler 361 airfoil in a subsonic wind tunnel. The experimental tests involved measuring the surface pressure distribution over the airfoil at Re=1.5×105. The airfoil was equipped with Gurney flap(heights of 2.6, 3.3 and 5% chord) and plunged at 6cm amplitude. The unsteady aerodynamic loads were calculated from the surface pressure measurements, 51 ports, along with the chord on both upper and lower surfaces of the model. The Gurney flap effects over the loads hysteresis loops of the oscillating airfoil were particularly studied prior to stall, at the stall onset, in light stall, and deep stall conditions. The static results of the flapped and unflapped airfoil were also explored in order to make a reference of comparisonsto the dynamic loads.The results showed that, the addition of the Gurney flap provided no changes in the directions of the Cl, Cd and Cm hysteresis loops for the prior to stall flow conditions; while as a result of the positive camber effects, the lift hysteresis loops shifted upward and the pitching moment’s loops moved vertically downward. Additionally, adding the Gurney flap promoted dynamic stall phenomena.The deep dynamic stall of the flapped airfoil with the height of h/c=5% was seen at ads=13.1deg. This phenomenon was observed at ads=14.8deg for the flapped airfoils of h/c=2.6 and 3.3%.
Masoud Darbandi; S.F. Hosseinizadeh
Volume 2, Issue 1 , March 2005, , Pages 37-44
B. Farhanieh
Volume 4, Issue 1 , March 2007, , Pages 39-47
Abstract
An unsteady two-dimensional finite-volume solver was developed based on Van Leer’s flux splitting algorithm in conjunction with “Monotonic Upstream Scheme for Conservation Laws (MUSCL)” limiters and the two-layer Baldwin-Lomax turbulence model was also implemented. To validate the solver, two test ...
Read More
An unsteady two-dimensional finite-volume solver was developed based on Van Leer’s flux splitting algorithm in conjunction with “Monotonic Upstream Scheme for Conservation Laws (MUSCL)” limiters and the two-layer Baldwin-Lomax turbulence model was also implemented. To validate the solver, two test cases were prepared and the computed results had good agreements with reference data. The rotating-stall-like (RS) effect in a multi-blade 2-D stage of an axial compressor was investigated. The RS was captured with a 40% reduction in flow coefficient and a 0.4% increase in load coefficient with respect to normal operating condition. The velocity traces showed a periodic behavior during RS. The same behavior was observed with a stator-free approach, but with different modal characteristics. Finally, the RS vortices and its flow characteristics were observed in detail, and the stator-free approach seemed to be more adequate in stability margin determinations. The same observation is finally prepared for variable number of blades to show the dependency of the RS modal characteristics to number of blades, and to find the minimum required number of blades in numerical analysis of RS.
Volume 2, Issue 2 , June 2005, , Pages 43-47
Jalal Karimi; Seid H. Dr. Pourtakdoust; Hadi Nobahari
Volume 8, Issue 1 , March 2011, , Pages 45-56
Abstract
Performance characteristic of an Unmanned Air Vehicle (UAV) is investigated using a newly developed heuristic approach. Almost all flight phases of any air vehicle can be categorized into trim and maneuvering flights. In this paper, a new envelope called trim-ability envelope, is introduced and sketched ...
Read More
Performance characteristic of an Unmanned Air Vehicle (UAV) is investigated using a newly developed heuristic approach. Almost all flight phases of any air vehicle can be categorized into trim and maneuvering flights. In this paper, a new envelope called trim-ability envelope, is introduced and sketched within the conventional flight envelope for a small UAV. Optimal maneuverability of the intended UAV is evaluated for minimum time pull-up and turn maneuvers. For both the trim and the maneuver problems, the nonlinear 6DOF dynamic models as well as the vehicle constraints are considered. A heuristic based constrained optimization approach is developed to solve both the trim and maneuver problems. Several interesting performance characteristics are extracted. The results are indicative of a good potential for the proposed algorithm to handle complex constrained optimization problems in aerospace engineering .
Fathollah Ommi; Hamidreza Khodayari; Zoheir Saboohi
Abstract
Butterfly valves as control valves are used when a small pressure drop is required in the valve. The results of numerical studies of solving the incompressible flow equations around the butterfly valve in three dimensions are presented in this paper. ANSYS CFX commercial software is used to solve the ...
Read More
Butterfly valves as control valves are used when a small pressure drop is required in the valve. The results of numerical studies of solving the incompressible flow equations around the butterfly valve in three dimensions are presented in this paper. ANSYS CFX commercial software is used to solve the flow equations. The ε-k turbulence model is used to simulate flow disturbances. Velocity, pressure distribution, kinetic energy, and turbulence intensity profiles are the factors that provide flow characteristics. The position of the disk at the opening angles of 0˚, 15˚, 30˚, 45˚, 60˚, and 75˚ as well as the inlet velocities of 1, 2, and 3 m/s have been investigated. Torque and valve performance factors such as flow coefficient and Hydrodynamics torque coefficient have been calculated for these different opening angles. The results of this simulation have been compared with the available experimental results for validation. The results show that the pressure drop across the valve, the flow coefficient, and the hydrodynamic torque coefficient depend on the opening angle. As the opening angle increases, the flow coefficient and the hydrodynamic torque coefficient decrease, and the torque and pressure drop increase across the valve. Flow separation has also been investigated at the mentioned opening angles.
Mousa Farhadi
Volume 3, Issue 1 , March 2006, , Pages 51-60
Abstract
Turbulent flow over wall-mounted cube in a channel was investigated numerically using Large Eddy Simulation. The Selective Structure Function model was used to determine eddy viscosity that appeared in the subgrid scale stress terms in momentum equations. Studies were carried out for the flows with Reynolds ...
Read More
Turbulent flow over wall-mounted cube in a channel was investigated numerically using Large Eddy Simulation. The Selective Structure Function model was used to determine eddy viscosity that appeared in the subgrid scale stress terms in momentum equations. Studies were carried out for the flows with Reynolds number ranging from 1000 to 40000. To evaluate the computational results, data was compared with experimental results at Re=40000, showing a good correspondence. In this study the effect of Reynolds numbers on flow characteristics such as time-averaged streamlines, turbulent intensity and Reynolds stresses were investigated. Results of computations show that the flow with higher Reynolds number has a shorter reattachment length and by increasing the Reynolds number, the number of horseshoe vortex in the upstream decreases. The vortex structures were similar in the upstream of the cube for time-averaged and instantaneous flow field. While on the downstream, the vortex structure does not show any similarity and had complex flow field structure. Reynolds stress was became stronger at the sides of the cube where the horseshoe vortexes were built and its become more significant at the higher Reynolds number.
hamid fazeli; M.R. Soltani; alireza davari
Volume 7, Issue 1 , March 2010, , Pages 51-57
Abstract
Unsteady dynamic behavior of TTCP model with different wrap around fin sets were investigated in a trisonic wind tunne. The aerodynamic coefficient force measurement in this wind tunnel shows good agreement in comparison with that of the NASA Langley Research Center in static case. The model was sinusoidally ...
Read More
Unsteady dynamic behavior of TTCP model with different wrap around fin sets were investigated in a trisonic wind tunne. The aerodynamic coefficient force measurement in this wind tunnel shows good agreement in comparison with that of the NASA Langley Research Center in static case. The model was sinusoidally oscillated at three different frequencies of 1, 3 and 8 Hz at M=2.0 and the effects of these frequencies on the shock angle were investigated and compared with the corresponding static case. Experimental data indicates that the static shock angle does not fall between the upstroke and down stroke dynamic shock angle at different frequencies which is different from experimental findings for flat fin configurations. This unsteady behavior could be added to the other anomalies frequently seen in the aerodynamic characteristics of wrap around fin configurations. Also shock development mechanism over the nose and several fin sets was investigated and the shock-boundary layer interaction near the fin/body juncture which leads to shock likes ? was clearly observed in this investigation.
A. nouri; S. Astaraki
Volume 11, Issue 2 , October 2017, , Pages 53-63
Abstract
In this paper, optimization of the sound transmission loss of finite rectangular anisotropic laminated composite plate with simply supported boundary conditions has been developed to maximize transmission loss. Appropriate constraints were imposed to prevent the occurrence of softening effect due to ...
Read More
In this paper, optimization of the sound transmission loss of finite rectangular anisotropic laminated composite plate with simply supported boundary conditions has been developed to maximize transmission loss. Appropriate constraints were imposed to prevent the occurrence of softening effect due to optimization. For this purpose, optimization process was incorporated into comprehensive finite element software. The transmission loss (TL) obtained from the numerical solution was compared with those of other authors indicated good agreement. The discrete frequencies have been chosen based upon the sound transmission class with A-weighting constant. Several traditional composite materials have been studied and the results have shown that in the mass control region, the optimization of stacking sequence and optimal thickness has not been an effective contribution to improve the transmission loss. The results also show that, the lamina thickness optimization has an important effect on improving the transmission loss, but the advantage of low weight composite material is compromised by optimization.
Aerospace Science and Technology
Ali Cheraghi; Reza Ebrahimi
Abstract
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 ...
Read More
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.
Mohammad Javad Maghrebi
Volume 2, Issue 4 , December 2005, , Pages 55-63
Abstract
Linear stability analysis of the three dimensional plane wake flow is performed using a mapped finite di?erence scheme in a domain which is doubly infinite in the cross–stream direction of wake flow. The physical domain in cross–stream direction is mapped to the computational domain using a cotangent ...
Read More
Linear stability analysis of the three dimensional plane wake flow is performed using a mapped finite di?erence scheme in a domain which is doubly infinite in the cross–stream direction of wake flow. The physical domain in cross–stream direction is mapped to the computational domain using a cotangent mapping of the form y = ?cot(??). The Squire transformation [2], proposed by Squire, is also used to relate the three–dimensional disturbances to the equivalent two– dimensional disturbances. The compact finite di?erence scheme of Lele [3] and the chain rule of di?erentiation are used to solve the Orr Sommerfeld equation. The results of linear stability analysis indicates that streamwise and the span- wise component of velocity eigenmodes are antisymmetric and the cross stream velocity eigenmode is symmetric. This is consistent with the DNS requirement of plane wake flow pertaining to solvability conditions[5]
Aerospace Science and Technology
Sevda Rezazadeh Movahhed; Mohammad Ali Hamed
Abstract
The fixed-wing unmanned aerial vehicles (UAVs) have gained significant attention across diverse civilian and military applications in recent years, where precision control, advanced manoeuvrability, and elevated stealth capabilities are paramount. In order to design a robust control system to enable ...
Read More
The fixed-wing unmanned aerial vehicles (UAVs) have gained significant attention across diverse civilian and military applications in recent years, where precision control, advanced manoeuvrability, and elevated stealth capabilities are paramount. In order to design a robust control system to enable different tracking and path-following purposes, it is desired to establish a precise aerodynamic model. The research introduces a straightforward approach for accurately computing aerodynamic coefficients, essential for deriving aerodynamic forces and moments, particularly focusing on the rudderless flying-wing UAV models. Utilizing Digital DATCOM software, the study outlines a procedure for calculating the requisite aerodynamic coefficients of fixed-wing aircrafts. The data input card is prepared based on the design and physical attributes of the rudderless flying-wing Freya UAV model and its associated airfoil structure. Through the utilization of the input card in DATCOM software, computations are performed to determine static longitudinal/lateral stability, dynamic stability, and control coefficients, along with their derivatives. Additionally, a 3D model is constructed. The ensuing output file is then imported into the MATLAB environment for comprehensive analysis and integration into dynamic modelling for the design of control systems. The open-loop and closed-loop system performance analysis based on the obtained aerodynamic coefficients, shows acceptable values in terms of control surfaces and flight dynamics variables in the category of small-sized rudderless flying-wing UAVs which proves the reliability of the obtained results.
Aerospace Science and Technology
Karim Dastgerdi; Farshad Pazooki; Jafar Roshanian
Volume 12, Issue 2 , October 2019, , Pages 61-70
Abstract
airplane in presence of asymmetric left-wing damaged. Variations of the aerodynamic parameters, mass and moments of inertia, and the center of gravity due to damage are all considered in the nonlinear mathematical modeling. The proposed discrete-time nonlinear MRAC algorithm ...
Read More
airplane in presence of asymmetric left-wing damaged. Variations of the aerodynamic parameters, mass and moments of inertia, and the center of gravity due to damage are all considered in the nonlinear mathematical modeling. The proposed discrete-time nonlinear MRAC algorithm applies the recursive least square (RLS) algorithm as a parameter estimator as well as the error between the real damaged dynamics and a model of nominal undamaged aircraft to generate the desired control commands. The discrete-time adaptive control algorithm is augmented with a Nonlinear Dynamic Inversion (NDI) control strategy and is implemented on the NASA generic transport model (GTM) airplane while considering the effect of wing damage and un-modeled actuator dynamics. The stability of the proposed nonlinear adaptive controller is demonstrated through Popov’s hyperstability theory. Simulation results of the introduced controller are compared with the classical discrete-time adaptive control strategy. The results demonstrate the effective performance of the proposed algorithm in controlling the airplane in presence of abrupt asymmetric damage.
Aerospace Science and Technology
Mohammad Reza Salimi; Mohammad Taeibi Rahni; Abolfazl Amiri Hezaveh; Mehdi Zakyani Rodsari
Abstract
In present research, the interaction between single liquid droplet with particles inside a porous media is investigated numerically in two dimensions. The He’s model is used to simulate two phase flow and multiple relaxation time collision operator is implemented to increase numerical stability. ...
Read More
In present research, the interaction between single liquid droplet with particles inside a porous media is investigated numerically in two dimensions. The He’s model is used to simulate two phase flow and multiple relaxation time collision operator is implemented to increase numerical stability. Simulations have performed in three non-dimensional body forces of 0.000108, 0.000144, 0.000180, porosity values of 0.75, 0.8, 0.85 and Ohnesorge range of 0.19-0.76. In the range of investigated non-dimensional parameters, two distinct physics of droplet trapping and break up have observed. The related results revels that for every values of investigated non-dimensional body forces and porosity, there is a critical Ohnesorge number that droplet breaks up occurs for larger values. This critical value decreases as non-dimensional body force and porosity increases. Based on these results, a droplet trapping or break up behavioral diagram is drown with respect to the investigated density ratio, Ohnsorge, Reynolds and Capilary numbers.
Aerospace Science and Technology
Morteza Sharafi; Mahdi Jafari; mojtaba alavipour
Abstract
In this paper, optimal guidance law design considering fixed final state and time for the final phase a spacecraft or launch vehicle is investigated and studied. This guidance law, not only satisfied a specific optimality criterion, but it also has the least sensitivity to the initial state’s deviations; ...
Read More
In this paper, optimal guidance law design considering fixed final state and time for the final phase a spacecraft or launch vehicle is investigated and studied. This guidance law, not only satisfied a specific optimality criterion, but it also has the least sensitivity to the initial state’s deviations; which is due to the inclusion of the nonlinear terms in the mathematical modeling using the high order expansions method. The main goal of this research, is to investigate the development and to augment the capability of the high order expansions method for guidance law design. Different implementations of this approach including the differential algebra high order, the generating function based high order and vectorized high order expansions methods have been investigated. After reviewing the implementation concepts of the high order expansions method, the effectiveness of this method has been studied. Then a 3-dimensional injection of a satellite problem has been chosen as the case study and after extracting the mathematical model and nominal optimal solution, the sensitivity variables have been extracted up to the 3rd order. Afterwards, to investigate the performance of the designed guidance law, the Monte Carlo simulations have been performed and it has been shown that the designed guidance law on the basis of the Taylor series and high order expansions method has a good accuracy and is a valuable alterative to the nominal trajectory tracking guidance approach.
Aerospace Science and Technology
Mohammad Hossein Bayat; Mohammad Shahbazi; Bahram Tarvirdizadeh
Abstract
The use of Unmanned Aerial Vehicles (UAVs) with different features and for a variety of applications has grown significantly. Tracking generic targets, especially human, using the UAV's camera is one of the most active and demanding fields in this area. In this paper we implement two vision-based tracking ...
Read More
The use of Unmanned Aerial Vehicles (UAVs) with different features and for a variety of applications has grown significantly. Tracking generic targets, especially human, using the UAV's camera is one of the most active and demanding fields in this area. In this paper we implement two vision-based tracking algorithms to track a human by using a 2D gimbal which can be mounted on UAVs. To ensure smooth movements and reduce the effect of common jumps on the trackers output, the gimbal motion control system is equipped with a Kalman filter followed by a proportional-derivative (PD) controller. Various experimental tests have been designed and implemented to track a human. The evaluation results show success in tracking the high speed movements with one of the algorithms and high accuracy in tracking the challenging movements in the other algorithm. Also in both methods, the tracking computation time is short enough and suitable for real-time implementation. The favorable performance of both algorithms indicate the ability of designed system to be implemented on the UAVs for practical applications.
Aerospace Science and Technology
Hamid Reza Talesh Bahrami; Sajad Ghasemlooy; hamid Parhizkar
Volume 12, Issue 1 , March 2019, , Pages 65-74
Abstract
Rotating cylinders have wide applications in different areas, especially the aerodynamic area. However, the acoustic behaviors of these components have not been widely studied. The generating noise from a spinning cylinder is mainly due to the detached vortices from the leeward of the body. In this study, ...
Read More
Rotating cylinders have wide applications in different areas, especially the aerodynamic area. However, the acoustic behaviors of these components have not been widely studied. The generating noise from a spinning cylinder is mainly due to the detached vortices from the leeward of the body. In this study, the large eddy simulation technique is used to simulate the flow field over a three-dimensional cylinder. In the following, the Ffowcs Williams and Hawkings equation is used to estimate the noise at the specified locations using the oscillating pressure components on the cylinder wall. The acoustic behavior of both stationary and rotating cylinders are studied. Results show that the acoustic behaviors of cylinders rotating with smaller frequencies (up to f=16f0, where f0 is the dominant detaching frequency of vortices on a stationary cylinder) are nearly the same. However, at higher rotational frequencies (24f0) where vortices are omitted, OASPL of the generated noise is reduced considerably (about 20 dB at different angles with constant radial positions, r=26D, at mid-span plane). On the other hand, when the rotational frequency is increased over this limit, the pressure oscillation on the wall becomes significant and the OASPL approaches higher values.
Aerospace Science and Technology
M.E. Golmakani; M. Moravej; M. Sadeghian
Volume 14, Issue 2 , October 2021, , Pages 66-79
Abstract
In this paper, the nonlinear thermal buckling of moderately thick functionally graded cylindrical panels is analyzed based on the first-order shear deformation theory (FSDT) and large deflection von Kármán equations. The highly coupled nonlinear governing equations are solved using the ...
Read More
In this paper, the nonlinear thermal buckling of moderately thick functionally graded cylindrical panels is analyzed based on the first-order shear deformation theory (FSDT) and large deflection von Kármán equations. The highly coupled nonlinear governing equations are solved using the combination of dynamic relaxation approach with the finite-difference discretization method at various boundary conditions. The material properties of the constituent components of the FG shell are considered to vary continuously along the thickness direction based on simple power-law and Mori-Tanaka distribution methods, separately. The critical thermal buckling load is considered based on the thermal load-displacement curve derived by solving the incremental form of nonlinear equilibrium equations. In order to consider the accuracy of the present results, a comparison study has been carried out. The effects of the boundary conditions, rule of mixture, grading index, radius-to-thickness ratio, length-to-radius ratio and panel angle are studied on the thermal buckling loads. It is observed from the results that in high values of radius-to-thickness ratios, there is no difference between the values of critical buckling temperature differences for linear and nonlinear distributions.
Aerospace Science and Technology
Mahsa Azadmanesh; Jafar Roshanian; Mostafa Hassanalian
Abstract
This study aims to control a space robot's soft-landing trajectory on the asteroid EROS433 considering a weak, yet effective gravitational field. As the research innovation, the study employs a fast terminal sliding mode control (FTSMC) to manage the landing trajectory and enhance the dynamic tracking ...
Read More
This study aims to control a space robot's soft-landing trajectory on the asteroid EROS433 considering a weak, yet effective gravitational field. As the research innovation, the study employs a fast terminal sliding mode control (FTSMC) to manage the landing trajectory and enhance the dynamic tracking performance for the soft landing of the space robot on the asteroid. This controller can ensure that the system modes are positioned on the sliding surface within a limited time. As an advantage over the PD sliding mode controller, the proposed controller raises the speed and improves the accuracy of tracking the desired trajectory and enhances the robustness of the control system. The study further compares the results of simulations performed in MATLAB to evaluate the proposed controller design. The results show that the absolute error value for FTSMC is significantly lower than the PD sliding mode controller, and when the sign function is replaced by a hyperbolic tangent, it makes the system behavior smoother and reduces the oscillations.
Aerospace Science and Technology
Asad Saghari; Amirreza Kosari; Masoud Khoshsima
Abstract
This paper deals with the problem of optimal selection of orbital parameters for an Earth observation mission in the absence of the possibility of injection into sun-synchronous orbit by considering the requirements and limitations of the mission and the satellite platform. By modeling the existing relationships ...
Read More
This paper deals with the problem of optimal selection of orbital parameters for an Earth observation mission in the absence of the possibility of injection into sun-synchronous orbit by considering the requirements and limitations of the mission and the satellite platform. By modeling the existing relationships between each of the three areas of orbit, mission and platform, the effects of changes in each of the parameters have been analyzed and tracked. One of the important advantages of the proposed solution is that in the process of optimal selection of relevant parameters, all aspects of the orbit, mission and platform are considered simultaneously. This, in turn, can lead to an implementable and operational option for accomplishing the mission. In evaluation of effects of changing orbital parameters on the mission characteristics and requirements of the satellite platform, a developed computer code has been used.
