Aerospace Science and Technology
Shahrokh Zohrabzadeh Bozorgi; Abolghasem Naghash
Abstract
In this paper, a few hybrid satellite constellations including combinations of LEO and GEO satellites for providing satellite navigation and positioning services for users in Iran have been designed and proposed. The performance of the constellations has been analyzed based on DOP values variations. ...
Read More
In this paper, a few hybrid satellite constellations including combinations of LEO and GEO satellites for providing satellite navigation and positioning services for users in Iran have been designed and proposed. The performance of the constellations has been analyzed based on DOP values variations. It is shown that theoretically, it is possible to provide satellite positioning and navigation service with acceptable DOP values based on the introduced hybrid pattern including three GEO satellites and a constellation of about 30 to 60 LEO satellites in 3 or 4 orbit planes. The design has been performed based on studying the skyplot of the Iranian territory considering the GEO satellites as fixed points, and then determining the effect of the instantaneous position of the LEO satellites on the DOP values. A few LEO constellations have been designed to provide best DOP values based on the skyplot analysis results. Then, scenarios including similar GEO satellites and different patterns for LEO satellites have been simulated for half a sidereal day. The performance of the hybrid constellations provides satisfactory results with the average PDOP values of less than 4 which is acceptable. Optimizing the resulted pattern can lead to more desirable performance. In addition to navigation mission, hybrid constellations can perform other missions. Therefore, the proposed constellations can be operated as multi-mission space platforms.
Aerospace Science and Technology
Alireza Sekhavat Banis; Reza Aghaei Togh
Abstract
The compressor blade is responsible for increasing the flow pressure. By adding a blade behind the main blade, the compressor performance can be improved by increasing the pressure ratio and reducing the weight. The tandem improves the performance and increases the compressor absorption coefficient by ...
Read More
The compressor blade is responsible for increasing the flow pressure. By adding a blade behind the main blade, the compressor performance can be improved by increasing the pressure ratio and reducing the weight. The tandem improves the performance and increases the compressor absorption coefficient by increasing the pressure ratio, preventing flow separation and controlling the boundary layer. This has led compressor designers to seek to reduce weight, increase pressure ratio and increase efficiency by using tandem. The geometry of the compressor blade and stage along with its tandem has been obtained from previous valid sources and has been drawn in three dimensions and numerically analyzed. Then the various parameters for the blade and the tandem are examined separately and the pressure and velocity vectors are plotted to show the control of the vortices, which results in improved compressor performance. The characteristic curve of the compressor and the pressure ratio for this particular tandem are also plotted at the end. Calculations show that by using the tandem and removing the excess vortex after the main blade, we will see a 28.5% increase in total pressure, a 15% decrease in relative mach number and a 1.5% decrease in entropy.
Aerospace Science and Technology
Ali Cheraghi; Reza Ebrahimi
Abstract
Feed pumps play a crucial role in the dynamics of hydraulic systems. The surge phenomenon is a common type of instability in pumps and compressors. This phenomenon is a systematic instability and is influenced by the dynamics of all components of a hydraulic system, including tank, valves, suction pipes, ...
Read More
Feed pumps play a crucial role in the dynamics of hydraulic systems. The surge phenomenon is a common type of instability in pumps and compressors. This phenomenon is a systematic instability and is influenced by the dynamics of all components of a hydraulic system, including tank, valves, suction pipes, impeller and the turbomachine itself. Surge emerges when a pump is operating with a positive slope of head and flow curve. The coincidence of the surge phenomenon with cavitation results in a damaging phenomenon called "auto-oscillation." Thus, predicting a pump's behavior outside the design points is of great importance particularly in low flow rates. In this paper, the characteristic curve of a high-speed centrifugal pump is extracted using CFD analysis to determine the stable operating range of the pump. The studied pump consists of an inducer, impeller and volute. The simulation in the pump was carried out three-dimensionally due to the asymmetry of geometry. The simulations are performed over a wide range of flow rates and the characteristic curve of the pump (head coefficient in terms of mass flow rate coefficient) is extracted. Finally, the range of stable operation of the pump is determined using its characteristic curve.
Aerospace Science and Technology
Mahsa Azadmanesh; Jafar Roshanian; Mostafa Hassanalian
Abstract
This paper employs the fast terminal sliding mode control with the sign and the saturation function to track the landing trajectory of a probe on an asteroid and to further improve the dynamic tracking performance. Then the controller is enhanced by adding the fuzzy control to both fast terminals. To ...
Read More
This paper employs the fast terminal sliding mode control with the sign and the saturation function to track the landing trajectory of a probe on an asteroid and to further improve the dynamic tracking performance. Then the controller is enhanced by adding the fuzzy control to both fast terminals. To make fair judgments on the performance of the suggested method, the proportional derivative sliding mode control with both the sign function and the saturation function is simulated as well. The two-point barycentric gravitational model is used to describe the weak gravity around the asteroid. The proposed fuzzy fast terminal method raises the convergence speed, improves the desired trajectory tracking accuracy and ensures that the system modes are placed on the sliding surface in a short, limited time. The absolute errors for the proportional derivative sliding mode controller, fast terminal sliding mode controller and improved fast terminal sliding mode controller are about 244, 139 and 113. The trajectories along all three coordinate axes in the proportional derivative sliding mode controller, fast terminal sliding mode controller and improved fast terminal sliding mode controller were tracked in 8 seconds, 5 seconds and 4 seconds. The results show how the fuzzy-fast terminal sliding mode control with the saturation function is the better choice of controller and how the fuzzy system is able to adapt to the momentary fluctuations and cover them successfully.
Aerospace Science and Technology
Mana Ghanifar; Milad Kamzan; Morteza Tayefi
Abstract
This paper investigates different intelligent methods of tuning feedback-linearization control coefficients. Feedback-linearization technique is an effective method of controlling nonlinear systems. The most critical part of designing this controller is tuning the gains, especially if the plant has complex ...
Read More
This paper investigates different intelligent methods of tuning feedback-linearization control coefficients. Feedback-linearization technique is an effective method of controlling nonlinear systems. The most critical part of designing this controller is tuning the gains, especially if the plant has complex nonlinear dynamics. In this research, to improve the performance of the overall closed-loop system, the feedback linearization method has been integrated with the conventional proportional-integral-derivative (PID) controller. Also, a quadratic performance index was used to compare the functionality of the controllers tuned by the proposed intelligent methods. These intelligent methods include Genetic Algorithms (GA), Particle Swarm Optimization (PSO), Fuzzy Logic, and Neural Network tuning algorithms. A quadrotor aircraft is used as the plant under study in order to evaluate the performance of the controllers tunned in this research. Finally, MATLAB simulation tests demonstrate the effectiveness of the presented algorithms. According to the results, it is demonstrated that the class of online algorithms performs better, even with the specified perturbation.
Aerospace Science and Technology
Amir Akbari; Hossein Khaleghi
Abstract
The use of unshrouded turbine rotor blades can considerably reduce the weight of an aero engine. However, in an unshrouded high-pressure turbine, the tip leakage flow generates about 30% of the turbine total loss. Another factor which affects the loss in axial-flow turbines, is the axial distance between ...
Read More
The use of unshrouded turbine rotor blades can considerably reduce the weight of an aero engine. However, in an unshrouded high-pressure turbine, the tip leakage flow generates about 30% of the turbine total loss. Another factor which affects the loss in axial-flow turbines, is the axial distance between the rotor and stator. The purpose of the current work is to investigate the impacts of the blade tip clearance and the axial distance between rotor and stator on the performance of a high-pressure axial turbine, by using three-dimensional numerical simulations. Comparing the numerical results to the experimental data shows that the numerical simulations can predict the turbine performance fairly accurately. Results reveal that increasing the tip clearance and the axial distance between the rotor and stator reduce the turbine efficiency. The effects of tip clearance and rotor-stator axial distance on the performance and endwall flow field of the studied turbine stage have been presented and discussed.
Aerospace Science and Technology
Shayan Dehkhoda; Mohammad-Ali Amiri Atashgah
Abstract
This paper is dedicated to the optimal path-planning of a quadrotor to deliver the goods in the form of a round-trip mission. At first, quadrotor modeling is performed by the Newton-Euler method and then the problem is formulated as an optimal control effort problem. Then, by discretization of the equations ...
Read More
This paper is dedicated to the optimal path-planning of a quadrotor to deliver the goods in the form of a round-trip mission. At first, quadrotor modeling is performed by the Newton-Euler method and then the problem is formulated as an optimal control effort problem. Then, by discretization of the equations using the direct colocation method, the problem becomes a nonlinear programming system that can be solved by available optimization methods. This discretization helps to make the derivative values in the equations of motion as simple algebraic expressions and the path optimization problem becomes a standard form of nonlinear programming problem (NLP). In this method, instead of obtaining state and control functions, state and control values are obtained at the beginning and endpoints of smaller time intervals. This method is one of the most explicit methods for the numerical solution of differential equations. It should be noted that in this research, safe areas around urban obstacles are considered fixed cylinders. Extensive simulations are evidence of the usefulness of this method, while the vehicle realizes all geometric, dynamic, and kinematic constraints.
Aerospace Science and Technology
Seyedeh sepideh Madani; mohammad ali shahi ashtiyani
Abstract
Nowadays, operational usage of the unmanned aerial vehicles (UAVs) in various missions is on the increase considering their capabilities. Provided that there is coordination between the UAV, navigation and control system, operational capability of the UAVs increases. Since there is no pilot in UAVs, ...
Read More
Nowadays, operational usage of the unmanned aerial vehicles (UAVs) in various missions is on the increase considering their capabilities. Provided that there is coordination between the UAV, navigation and control system, operational capability of the UAVs increases. Since there is no pilot in UAVs, the task of guidance and control of the UAV for carrying out the mission depends on the ability of the autopilot and guidance system. This paper regards the control and the guidance as two separate entities in way point tracking problem. To do so, backstepping controller design for inner loop to track the commands is generated by the outer loop. The outer loop is designed based upon fuzzy logic. The proposed system uses standard Mamdani fuzzy controllers that provide speed, heading, and flight path angle references for the autopilots. Nonlinear six-degree-of-freedom equations of motion are used to model the vehicle dynamics. Simulations were carried out to verify the performance of the system. The results indicate the ability of way point tracking system to track the desired set of waypoints.
Aerospace Science and Technology
Jafar Jafari; hamid Parhizkar; Sajad Ghasemlooy
Abstract
This research investigates the effect of optimization of blade cross-section on the performance of the Darrieus wind turbine. The fluid flow around a Darrieus wind turbine is simulated by URANS (Unsteady Reynolds Averaged Navier Stokes) method. And blade cross-section was modeled by the Bezier curve ...
Read More
This research investigates the effect of optimization of blade cross-section on the performance of the Darrieus wind turbine. The fluid flow around a Darrieus wind turbine is simulated by URANS (Unsteady Reynolds Averaged Navier Stokes) method. And blade cross-section was modeled by the Bezier curve and optimized to increase the average torque of the wind turbine. We used a novel, simple way for remeshing new design points in the optimization process. The Nelder-Mead simplex method was used for optimization, which enhanced the Turbine's performance by 33.7 percent. Results show that optimization of the blade cross-section is effective for increasing the performance of a VAWT (Vertical Axis Wind Turbine), and Nelder-Mead simplex is a proper and fast optimization method to be used in this case. Finally, the optimized airfoil was analyzed and compared with the initial one to understand optimization effects. It was concluded that optimization was more effective in azimuth positions of 90 to 160 degrees. And it decreased the performance in some regions according to changing nature of flow around each blade because of rotational motion. Analyzes show that optimization increased the Turbine's performance by increasing lift force of airfoil in some positions or affecting interaction flow -even accompanied by decreasing lift force of airfoil- in other positions, and it decreased performance in some other azimuth points.
Aerospace Science and Technology
Sahar Noori; Armin Sheidani; Djavad Kamari
Abstract
In this study the effect of different configurations of three plates located in an air-filled container, which included vertical, horizontal and tilted, on coupled radiation and natural convection heat transfer has been numerically investigated. The side walls of the cavity were kept a constant temperature, ...
Read More
In this study the effect of different configurations of three plates located in an air-filled container, which included vertical, horizontal and tilted, on coupled radiation and natural convection heat transfer has been numerically investigated. The side walls of the cavity were kept a constant temperature, while the upper and the lower walls were thermally insulated. In addition, non-uniform temperature distribution was applied to each of the plates. Moreover, in this study the effect of coupled heat transfer on flow separation and local Nu number was studied. The flow separation on the heated plates due to the thermal gradients was captured and the subsequent the effects were discussed. Also, the results reveal there are two main flow patterns known as separation of the convective flow and stretching of the CW vortex which are created by combined heat transfer. It was also demonstrated that these flow patterns are the main responsible for variations in the heat transfer.
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 ...
Read More
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.
Aerospace Science and Technology
Amir Moghtadaei Rad
Abstract
In this article, a complete model including cross-coupling of azimuth and elevation axes, the effect of axis friction, non-perpendicularity and imbalance of axes was implemented for the platform with two degrees of freedom. Since this model includes 3 loops of current, stability and tracking from the ...
Read More
In this article, a complete model including cross-coupling of azimuth and elevation axes, the effect of axis friction, non-perpendicularity and imbalance of axes was implemented for the platform with two degrees of freedom. Since this model includes 3 loops of current, stability and tracking from the inside to the outside, it was necessary to design a suitable controller for each loop separately from the inside to the outside after linearizing the obtained model. Also, due to the presence of two channels, azimuth and elevation, it was necessary to repeat and design 3 controllers for both channels separately. Since the purpose of this article is to compare the performance of different controllers, PID, Fuzzy, Fuzzy PID and Fuzzy self-tuning controllers for both channels and all loops, their design and performance in time and frequency domains were analyzed. At the end, relative advantages of each controller according to different parameters of the system were presented in a comparative table.
Aerospace Science and Technology
کامران رئیسی چرمکانی; غلامرضا مرادی
Abstract
Knowledge of aircraft last position and trajectory is of the utmost importance for search and rescue in aviation today. In case of an accident, this information is necessary for rapid response.
The existing method of reporting the whereabouts depend upon pilot reports during flight or signals from special ...
Read More
Knowledge of aircraft last position and trajectory is of the utmost importance for search and rescue in aviation today. In case of an accident, this information is necessary for rapid response.
The existing method of reporting the whereabouts depend upon pilot reports during flight or signals from special equipment such as emergency location transmission. Future renovation to Air Traffic Control system has been planned which requires the installation of automatic Dependent Surveillances – Broadcast. However, it will take some time to implement such systems in all aircrafts and providing the necessary infrastructure. This paper proposes Geo-tagging the pilot communication using Code Division Multiple Access (CDMA) method. It is an intermediate, yet inexpensive, solution for worldwide application in aviation which can be implemented quickly. It takes advantage of the existing equipment both in the air as well as on the ground. The simulations presented show the applicability and efficiency of the proposed routine.
Aerospace Science and Technology
Hassan Naseh; Mehran MirShams; Hamid Reza Fazeley
Abstract
Recently, engineering systems are quite large and complicated. Conceptual design process of Space Transportation Systems (STSs) is a multidisciplinary task which must take into account interactions of various disciplines and analysis codes. Current approach for the conceptual design of STSs requires ...
Read More
Recently, engineering systems are quite large and complicated. Conceptual design process of Space Transportation Systems (STSs) is a multidisciplinary task which must take into account interactions of various disciplines and analysis codes. Current approach for the conceptual design of STSs requires the evaluation of a large number of different configurations and concepts. With existing legacy codes, estimating the performance of all design combinations becomes very time consuming and computationally expensive. A possible solution to this problem could be employing of surrogates during design tasks. This paper describes an effort to optimize the design of an entire STS to achieve a low Earth orbit, consisting of multiple stages using an efficient surrogate-based Multidisciplinary Design Optimization (MDO) framework with the goal of minimizing vehicle weight and ultimately vehicle cost. Furthermore, a combination of Response Surface Methodology (RSM) and Kriging surrogates has been used for building surrogate models. The disciplines of aerodynamics, propulsion, trajectory simulation, geometry, and mass properties, have been integrated to produce an engineering system model of the entire vehicle. In addition, the system model has been validated using the existing design data of STS’s trajectory and their subsystems. For the design optimization, in order to ensure that the payload achieves the desired orbit, a hybrid algorithm has been used to minimize the deference between the actual and desired orbital parameters. The objective function of the optimization problem is to minimize the overall system mass, thus minimizing the system cost per launch. The proposed design and optimization methodology provides designers with an efficient and powerful approach in computation during designing space transportation systems and can also be developed for more complex industrial design problems with comparable characteristics.
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 ...
Read More
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
Mohammad Hossein Khalesi
Abstract
Unmanned Aerial Vehicles (UAVs) have numerous applications in military, commercial and hobby fields. Among these vehicles, drones with vertical take-off and landing (VTOL) capability have attracted more attention due to their specific capabilities such as better maneuverability and hover flight. In recent ...
Read More
Unmanned Aerial Vehicles (UAVs) have numerous applications in military, commercial and hobby fields. Among these vehicles, drones with vertical take-off and landing (VTOL) capability have attracted more attention due to their specific capabilities such as better maneuverability and hover flight. In recent years, numerous concepts emerged which trying to propose new configurations to enhance UAVs performance. In this paper, we propose a novel concept which integrates single main rotor helicopter and quadrotor structure to overcome some difficulties exist in those applications. This suggested configuration, include a variable pitch main rotor equipped with four smaller counterrotating rotors to overcome its opposite torque (instead of a tail rotor in helicopters) and also sustain a portion of the UAV weight which make it possible to use a smaller main rotor. This design preserves maneuverability of helicopters, while eliminates tail rotor power loss and its asymmetric lateral force and also enhances the flight stability and maneuverability by properly using other four rotors’ thrusts. Preliminary dynamic modeling and control system design are presented in the text and the results show that this idea can be investigated further. The next steps are planned to be studied in next researches.
Aerospace Science and Technology
Sarallah Abbasi; MohammadAmin Daraei
Abstract
In this research, the thermodynamic analysis of a three-spool mixed-flow turbofan engine has been studied by examining parameters such as flight altitude, flight Mach number, fan pressure ratio, high and Intermediate-pressure compressor pressure ratios, bypass ratio and burner exit temperature. First, ...
Read More
In this research, the thermodynamic analysis of a three-spool mixed-flow turbofan engine has been studied by examining parameters such as flight altitude, flight Mach number, fan pressure ratio, high and Intermediate-pressure compressor pressure ratios, bypass ratio and burner exit temperature. First, the effect of these parameters on the thrust, thrust specific fuel consumption (TSFC) and engine efficiency was investigated and then in the exergy analysis, it was found that the lowest exergy efficiency with a value of 85.45% belongs to the combustion chamber; Therefore, a parametric study was conducted to improve the performance and exergy efficiency of the burner; For example, in the case of bypass ratio of 2.2 and fan pressure ratio of 2, the exergy efficiency of the burner is increased by 12.23% compared to the base case. In addition, the results of sensitivity analysis show that the burner exit temperature and the HPC pressure ratio with 21.81 and 2.2%, respectively, have the most and the least effect on the engine net thrust; Also, the burner exit temperature and the flight altitude with 4.57% and 0.11%, respectively, have the most and the least effect on the TSFC.
Aerospace Science and Technology
Amir Moghtadaei Rad
Abstract
Inertial navigation amplifies the noise of the input sensors over time due to the presence of an integrator in the output path to determine the position and attitude of the object. This system has high bandwidth and good short-term accuracy. On the other hand, GPS navigation has low bandwidth, low noise ...
Read More
Inertial navigation amplifies the noise of the input sensors over time due to the presence of an integrator in the output path to determine the position and attitude of the object. This system has high bandwidth and good short-term accuracy. On the other hand, GPS navigation has low bandwidth, low noise processing power, and long-term accuracy. However, it can only determine the position and does not give us information about the object's attitude. Most papers have presented integrated algorithms related to GPS/INS tightly coupled navigation and have provided relatively acceptable results. Nevertheless, the main problem in this integration model is when there is an intentional or stochastical signal interference for GPS, which is not far from the mind in military applications. Therefore, navigation faces a problem. This article provides a solution with a tightly coupled integrated algorithm for high accuracy in integrated navigation.
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
Seyyed S Moosapour; Amin Keyvan
Abstract
This paper provides an academic insight into the design of a three-dimensional guidance law which can be utilized to reach the maneuvering targets in definite angles. Firstly, the theoretical phenomenon of a conventional dynamic inversion which can be implemented for reaching targets with constant velocity ...
Read More
This paper provides an academic insight into the design of a three-dimensional guidance law which can be utilized to reach the maneuvering targets in definite angles. Firstly, the theoretical phenomenon of a conventional dynamic inversion which can be implemented for reaching targets with constant velocity will be addressed. However, given that this method is not applicable for reaching accelerated targets, a combination of dynamic inversion method and sliding mode control is presented. These mechanisms can impact maneuvering targets with bounded acceleration. Proceeding the discussion of these observations, an improved form of the proposed controller will be introduced as this method guarantees a finite reaching time. Furthermore, the chattering phenomenon, which is the predominant disadvantage of the sliding mode, will be analysed. Given these findings, a second terminal sliding surface will be presented. This approach will be able to generate continuous guidance law whilst effectively eliminating the chattering problem that was evident in the sliding mode mechanism. Finally, through the application of numerical simulations, the effectiveness of the proposed guidance laws against maneuvering targets will be demonstrated.
Aerospace Science and Technology
Amir reza Kosari; Elahe Khatoonabadi; Vahid Bohlouri
Abstract
In this paper, the control of a three-axis rigid satellite attitude control system with a fractional order proportional-integral-derivative (PID) controller is investigated in the presence of disturbance and parametric uncertainties. The reaction wheel actuator with the first-order dynamic model is used ...
Read More
In this paper, the control of a three-axis rigid satellite attitude control system with a fractional order proportional-integral-derivative (PID) controller is investigated in the presence of disturbance and parametric uncertainties. The reaction wheel actuator with the first-order dynamic model is used to control the attitude of the satellite. Uncertainties are considered on satellite moment inertia, actuator model and amplitude and frequency of external disturbances. External disturbances are modeled with two fixed and periodic parts and uncertainty is also considered on the disturbances model. The integer order controller is also used for the same conditions to compare the results with the fractional order controller. The usual Granwald-Letinkov definition is used to solve integrals and fractional order derivatives. The mean absolute of the pointing error of the satellite pointing maneuver has been selected as an objective function of the optimization problem. The controller gains in integer and fractional order are obtained by particle swarm evolution algorithm (PSO) optimization method. The performance criterion has been studied in terms of the controller time response and also in terms of the standard deviation of the mentioned uncertainties and external disturbance. The results show that the fractional order controller performs more accurate and robustness than the integer order controllers in the face of uncertainty and disturbance.
Aerospace Science and Technology
Hamed Arhami; Mohammad Mazidi Sharfabadi
Abstract
In this research, combustion modeling inside the combustion chamber of a typical turboprop engine has been investigated. The complex geometry of this combustion liner was modeled according to the technical drawings and the turbulent flow and internal combustion were simulated numerically and three-dimensionally. ...
Read More
In this research, combustion modeling inside the combustion chamber of a typical turboprop engine has been investigated. The complex geometry of this combustion liner was modeled according to the technical drawings and the turbulent flow and internal combustion were simulated numerically and three-dimensionally. The non-premixed combustion model is used to simulate combustion and the K-ω method is used to simulate turbulent flow. This study investigated how the combustion phenomenon occurs, the internal temperature distribution, the outlet, and the wall of the combustion tube, for which comprehensive three-dimensional data were not previously available. These simulations have identified the weaknesses of the combustion tube and by eliminating these weaknesses, the problem of reducing the efficiency of several gas turbine engines has been solved. Comparison of the results of the present study with a similar numerical analysis showed that the results of this study are more in line with laboratory results. The results of the simulation of combustion pipe defects show that the combustion liner that had a welding line near the outlet had a 25% higher pressure drop than a typical combustion liner and the effective cross-sectional area of the fluid flow was reduced by 11%. The output of a repaired combustion tube is different from a typical type.
Aerospace Science and Technology
Mahdi Karami Khorramabadi; Ali Reza Nezamabadi
Abstract
In this paper, the buckling behavior of functionally graded simply supported nanocomposite beams reinforced by nano clay is studied. The specimens were prepared and the experimental tensile and buckling tests are carried out. The elastic modulus of epoxy/clay nanocomposite for functionally graded and ...
Read More
In this paper, the buckling behavior of functionally graded simply supported nanocomposite beams reinforced by nano clay is studied. The specimens were prepared and the experimental tensile and buckling tests are carried out. The elastic modulus of epoxy/clay nanocomposite for functionally graded and uniformly distributed of nanoclay are estimated through a model based on the genetic algorithm approach. The results show that GA can be considered as an acceptable optimization research technique to identify Young’s modulus of nanocomposites with maximum accuracy. For simply supported beam, the first order shear deformation beam theory is applied for displacement field and the governing equations are derived by using Hamilton principle. The influence of nanoparticles for functionally graded and uniform distribution on the buckling load of a beam is presented. Comparison study is conducted to assess efficacy and accuracy of the present analysis. A comparison for theoretical analysis with the experimental results demonstrated the high accuracy.
Aerospace Science and Technology
Mahdi Miralam; Amir Rahni
Abstract
In multi-stage Missiles, stabilizer wings are responsible for stabilizing the Missile. The control fins located upstream of the stabilizer wings affect the flow by spinning, which influences stability as well as control. One method for resolving this problem is to design stabilizer wings with less affectability ...
Read More
In multi-stage Missiles, stabilizer wings are responsible for stabilizing the Missile. The control fins located upstream of the stabilizer wings affect the flow by spinning, which influences stability as well as control. One method for resolving this problem is to design stabilizer wings with less affectability against the upstream flow. The present paper deals with this issue by considering multiple planar fins and grid fins. Once validation is performed, after selecting the appropriate turbulence model and choosing the planar and grid fins, the appropriate Missile model is established; then, on a model with speeds of 0.6, 0.7, and 0.8 Mach, at attack angles of 0, 2, 4, and 6 degrees, and with control fins, variation at angles of 0, 1, 3, and 6 degrees, the aerodynamic coefficients as well as the effects of the upstream stabilizer wings are investigated in pitch and roll modes at an appropriate trim angle . The obtained results indicated that the use of grid fin downstream of the control surfaces would be less affected due to its physical nature; thus, the lower capacity of the control surface would be used for control during the flight, which would significantly facilitate the process of designing.
Aerospace Science and Technology
seyed sam Saham; Saeed Karimian Aliabadi
Abstract
The use of urban and rural scale wind turbines that in addition to generating power can play the role of old wind turbines in arid areas will be very attractive. In this research it has been tried to first evaluate the wind energy potential in Zahedan city and then to evaluate a sample of vertical axis ...
Read More
The use of urban and rural scale wind turbines that in addition to generating power can play the role of old wind turbines in arid areas will be very attractive. In this research it has been tried to first evaluate the wind energy potential in Zahedan city and then to evaluate a sample of vertical axis wind turbine. First, a three-dimensional semi-analytic code based on the DMST method was developed, the validation of which was studied and presented. Using this tool, the performance of the turbine in terms of power and ventilation has been investigated and in the results of this parametric study, the effect of the cone angle on the power and ventilation coefficient has been explained in detail. Based on the results of this study, it can be seen that increasing the cone angle to 20 degrees, although it reduces the power of the turbine, but does not have a significant effect on the power coefficient and at the same time causes a ventilation coefficient of about 1.6 percent. It was also observed that at a conical angle of 10 degrees and at the working point of the turbine, the output power will be 30 kW and the ventilation flow will be 30,000 m^3⁄h.
