Hoss Hosseini Toudeshky; Bijan Mohmmadi; Mohammad Dr. Sadr-Lahijani
Volume 6, Issue 2 , June 2009, , Pages 99-113
Abstract
In this paper, progressive damage and global failure of composite laminates under quasi-static, monotonic loading are investigated using 3D continuum damage mechanics. For this purpose, a finite element program has been developed using an eight-node 2D layered element including layer-wise plate theory. ...
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In this paper, progressive damage and global failure of composite laminates under quasi-static, monotonic loading are investigated using 3D continuum damage mechanics. For this purpose, a finite element program has been developed using an eight-node 2D layered element including layer-wise plate theory. Damage analysis of a single orthotropic layer under various uniform in-plane and transverse loading conditions, and laminate problems with diffuse damage under simply supported and distributed transverse loading conditions are performed. The effects of modeling parameters such as hardening rules and mesh densities along the laminate thickness and in-plane surface on the progressive damage response and global failure are also investigated.
Hassan Haddad Pour
Volume 3, Issue 2 , June 2006, , Pages 105-111
Abstract
The present paper describes a set of procedures for the solution of nonlinear static-equilibrium problems in the complex multibody mechanical systems. To find the equilibrium position of the system, five optimization techniques are used to minimize the total potential energy of the system. Comparisons ...
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The present paper describes a set of procedures for the solution of nonlinear static-equilibrium problems in the complex multibody mechanical systems. To find the equilibrium position of the system, five optimization techniques are used to minimize the total potential energy of the system. Comparisons are made between these techniques. A computer program is developed to evaluate the equality constraints and objective function of a general multi-body dynamic system in order to find the equilibrium condition. The obtained results from different approaches are compared together and finally some conclusions are made considering the existing results of the artificial damping method. It is seen that the indirect methods may produce more accurate results with faster convergence.
Neda Eskandari Naddaf; Amir AliAkbarKayyat
Volume 8, Issue 2 , September 2011, , Pages 119-125
Abstract
Pilot-Induced Oscillation (PIO) is an unwanted, inadvertent phenomenon that has the ability to damage the aircraft completely. This paper suggests a novel control method that can damp PIO after predicting its occurrence. The specific point of this control algorithm is that it contains a preprocessor ...
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Pilot-Induced Oscillation (PIO) is an unwanted, inadvertent phenomenon that has the ability to damage the aircraft completely. This paper suggests a novel control method that can damp PIO after predicting its occurrence. The specific point of this control algorithm is that it contains a preprocessor that will not let the controller be activated unless in the case of probable PIOs, so pilot commands will not be disturbed in normal flight situations. Besides, with regard to the unconscious tendency of pilot towards establishing PIO, this control algorithm decides on pilot and controller shares in the control signal. By implementing the suggested method, the control algorithm is able to prevent and suppress a general form of PIO. This paper focuses on those groups of phenomena which take place as a result of a sudden disturbance which perturbs one of the states of Pilot-Vehicle System (PVS). It is also shown that the method can block PIO in cases of complex tracking. As a case study, an airplane model based on F-4 derivatives is presented.
Mohammad Reza Dr. Soltani; M. Masdari; M. Seidjafari; Kaveh Ghorbanian
Volume 7, Issue 2 , September 2010, , Pages 132-137
Abstract
Extensive wind tunnel tests are conducted to evaluate surface pressure distribution of a semi span swept wing. The wing section has a laminar flow airfoil similar to NACA 6-series airfoils. The investigations are conducted at various speeds and angles of attack. Surface pressure distribution over the ...
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Extensive wind tunnel tests are conducted to evaluate surface pressure distribution of a semi span swept wing. The wing section has a laminar flow airfoil similar to NACA 6-series airfoils. The investigations are conducted at various speeds and angles of attack. Surface pressure distribution over the wing upper surface is measured for both chordwise and spanwise sections. Statistical analyses are performed on the data to realize the transition point at each chordwise section. The 3D pressure profiles are compared to the corresponding 2D results at the same conditions. Calculation of the standard deviation, SD, of time variable pressure data shows that SD increases in the transition area and then decreases again when the flow becomes fully turbulent downstream. The measured transition points are further compared with 2D computational results.
hasan Abedi; M. Sohrabian
Volume 5, Issue 3 , July 2008, , Pages 139-144
Abstract
In some aerospace vehicles, the tracking sensors which act in a tracking loop as stabilizer are mounted on a two degree of freedom gyro. The gyro must align its rotor axis with the line of sight in order to remove tracking errors. The tracking precision and sensitivity are functions of the gyros performance. ...
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In some aerospace vehicles, the tracking sensors which act in a tracking loop as stabilizer are mounted on a two degree of freedom gyro. The gyro must align its rotor axis with the line of sight in order to remove tracking errors. The tracking precision and sensitivity are functions of the gyros performance. One of the main factors in reducing the precision and producing instabilities is nutation vibration. This fluctuating motion, which is a dynamical inherent property of the system, is related to the gyro lateral moment of inertia, the length of gyro and its rotating speed. In order to investigate the capabilities of nutation damper and removing the wobble motion of a freely precessing body, this paper analyzes a ring damper partially filled with viscous liquid with taking into account the behavior of the damper and its subsystems. The equations of motion for the dynamical motion of gyro, are obtained using Lagrangian approach, taking into account the friction of dampers and interaction of the liquid with the system equations of motion.
Hamid Parhizkar; Seyed Mohamm Karimian
Volume 3, Issue 3 , September 2006, , Pages 159-166
M. Eftari
Volume 9, Issue 1 , March 2012
Abstract
The performance prediction of axial flow compressors at different speeds and under various pressure ratio conditions are still being developed because of costly empirical experiments. One-dimensional modeling is a simple, fast and accurate method for performance prediction in any type of compressor with ...
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The performance prediction of axial flow compressors at different speeds and under various pressure ratio conditions are still being developed because of costly empirical experiments. One-dimensional modeling is a simple, fast and accurate method for performance prediction in any type of compressor with different geometries. In this approach, inlet flow conditions and compressor geometry are known and by considering various losses of the compressor, velocity triangles at rotor, stator inlets and outlets are determined and, then, compressor performance characteristics are predicted.
Numerous models have been developed theoretically and experimentally for estimating various types of compressor losses. In the present study, the performance characteristics of the axial-flow compressor are predicted based on a one-dimensional modeling approach. Models of Lieblein, Koch-Smith, Aungier, Hawell are implemented to consider the compressor losses. To validate the model, the modeling results are compared with experimental data. This model can be used for various types of axial-flow compressors with different geometries.
Ali Ghamarian; H.R. Zarei
Volume 9, Issue 2 , September 2012
Abstract
This paper investigates the parametric study of the empty and foam-filled end-capped tubes under quasi static and dynamic loadings. The numerical crash analysis of the empty and foam-filled tubes was performed using the explicit finite element code ABAQUS- explicit. Satisfactory agreements were generally ...
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This paper investigates the parametric study of the empty and foam-filled end-capped tubes under quasi static and dynamic loadings. The numerical crash analysis of the empty and foam-filled tubes was performed using the explicit finite element code ABAQUS- explicit. Satisfactory agreements were generally achieved between the numerical and experimental results. In order to determine the crash behavior of the empty and foam filled tubes under dynamic impact, the dynamic amplification factor which relates the quasi-static results to dynamic responses was determined. The influence of the various parameters on the dynamic responses is investigated and then compared with the quasi-static results.
علی جعفرقلی; حسن کریمی مزرعه شاهی
Volume 10, Issue 1 , March 2013
Abstract
A new procedure for deriving nonlinear mathematical modeling for a specific class of aerospace hydro - mechanical control valves is presented. The effects of friction on the dynamic behavior of these types of valves along with the experimental verifictions are also given. The modeling approach is based ...
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A new procedure for deriving nonlinear mathematical modeling for a specific class of aerospace hydro - mechanical control valves is presented. The effects of friction on the dynamic behavior of these types of valves along with the experimental verifictions are also given. The modeling approach is based on the combination of the following three tasks: decomposition of the valve into simple specific subsystems; derivation of the governing equations of each subsystem; and determination of the unknown parameters and coefficients using dynamic and static tests. Dynamic analysis shows that the presence of friction causes the hysteresis phenomenon in these valves and friction force increment causes an increase in the tracking error. On the other hand, excessive reduction of the friction force causes an instable performance. Therefore, a trade-off between the amount of tracking error and stability margins must be considered.
S. Ali S.A. Hosseini Kordkheili; Z. Soltani; A. Merati
Volume 11, Issue 1 , June 2017
Abstract
Thermal buckling behavior of truncated conical liner reinforced by laminated composite is investigated in the presence of a general initial imperfection. For this purpose, the method of virtual work and first-order strain-deformation shell theory are employed to extract equilibrium equations. To this ...
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Thermal buckling behavior of truncated conical liner reinforced by laminated composite is investigated in the presence of a general initial imperfection. For this purpose, the method of virtual work and first-order strain-deformation shell theory are employed to extract equilibrium equations. To this end, a finite element code is developed using the 3D 8-node shell element with six degrees of freedom as an analysis tool. Also, the variation of thickness in conical composite shell is considered. Several problems withc-c, s-s, c-f boundary conditions are solved using code to highlight the effect of imperfection size and position. In this way, the most effective imperfection at each boundary condition is determined.
Aerospace Science and Technology
Reza Mahmoodpoor; Amir Kiyoumarsioskouei; Amin Taraghi Osguei; Leila Donyaparast
Abstract
The focus on different energy harvesting methods has led to various studies on the mechanism of flow-induced vibration phenomena, including vortex-induced vibration, galloping, and wake-galloping. In this study, an experimental investigation on flow around a cylinder with an elastic cantilever beam has ...
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The focus on different energy harvesting methods has led to various studies on the mechanism of flow-induced vibration phenomena, including vortex-induced vibration, galloping, and wake-galloping. In this study, an experimental investigation on flow around a cylinder with an elastic cantilever beam has been conducted to develop new energy harvesting devices based on its dynamic behavior. Therefore, the basic principles for the design of a high resolution open-circuit subsonic wind tunnel were systematically studied and a specific small scale wind tunnel was constructed based on the requirements. The test chamber cross section for the designed wind tunnel is square with a side length of 50 centimeters which can be used for investigation of different micro wind turbines performance up to velocity of 8 m/s with resolution of less than 0.1 m/s. The vibration of two prototype micro-turbines in the presence of obstacles and without obstacles has been studied in different Reynolds numbers. The results show that a circular cylinder oscillates with larger amplitude in the VIV range in comparison to the square cylinder, however, when galloping starts by increasing Reynolds number, the oscillation amplitude of the square cylinder severely increases. The experimental findings show that the presence of an obstacle in upstream of the flow considerably increases the amplitude of oscillation, however, does not have a meaningful effect on the vibration frequency. Also, results indicate that the vibration amplitude of the bluff body in the wake-galloping phenomenon for the square obstacle is greater in comparison to the circular obstacle.
mostafa ghayour; Ahmad Sedaghat; Mohsen Mohammadi
Volume 8, Issue 1 , March 2011, , Pages 57-67
Abstract
Multi-layer orthotropic finite cylindrical shells with a viscoelastic core in contact with fluids are gaining increasing importance in engineering. Vibrational control of these structures is essential at higher modes. In this study, an extended version of the wave propagation approach using first-order ...
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Multi-layer orthotropic finite cylindrical shells with a viscoelastic core in contact with fluids are gaining increasing importance in engineering. Vibrational control of these structures is essential at higher modes. In this study, an extended version of the wave propagation approach using first-order shear deformation theory of shell motion is employed to examine the free vibration of damped finite cylindrical shells in vacuum or in contact with interior or exterior dense acoustic media. For this purpose, a one-layered viscoelastic finite cylindrical shell and a three-layered orthotropic finite cylindrical shell with a viscoelastic core layer were used. Complex natural frequencies have been extracted and the effects of fluid coupling on real and imaginary parts of natural frequencies have been examined. The results reveal that the fluid reduces the imaginary part as much as the real part of the damped natural frequency but that the proportion of the imaginary to the real part (loss factor) remains rather unchanged. Another aspect of the study involves the investigation of the effect of shell parameter, m, when the circumferential mode number, n, increases on both entities of damped natural frequencies. It is found that by increasing n, the real part of the natural frequency follows a u-shape trend; however, the imaginary part reduces and levels off for higher circumferential numbers. The loss factors remain almost constant for these higher modes. The results of the current approach are finally compared with ABAQUS solutions showing superiority of current approach.
Maysam gelveh; S. Mojtaba Mosavi; Mohammad Homayoun Sadr
Abstract
In the last decade, nonlinear normal modes have attracted the attention of many researchers, and many methods and algorithms have been proposed to calculate them. Among the proposed methods, the combination of the shooting method and the continuation of the periodic solution is the strongest methods. ...
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In the last decade, nonlinear normal modes have attracted the attention of many researchers, and many methods and algorithms have been proposed to calculate them. Among the proposed methods, the combination of the shooting method and the continuation of the periodic solution is the strongest methods. However, the computational cost of the method has still limited its application. In this paper, an updated formula is used to reduce the computational costs of the method. Using this updated formula significantly reduced the computation time so that the computational speed of nonlinear normal modes increased tenfold. Also, as the power of nonlinear terms increases in the system, the efficiency of the updated formula increases. In order to evaluate the accuracy of the proposed method, a system with two degrees of freedom was studied, and it was observed that the results obtained are consistent with the results in other works.
F. Javidrad; F. Dabirian
Volume 7, Issue 1 , March 2010, , Pages 59-67
Abstract
In this paper, an approach to aeronautical structural design based on reliability analysis is presented. In this way, the concept of level of safety is discussed and methods of its calculation using statistical data are described. Based on the concept of level of safety, a design procedure is proposed. ...
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In this paper, an approach to aeronautical structural design based on reliability analysis is presented. In this way, the concept of level of safety is discussed and methods of its calculation using statistical data are described. Based on the concept of level of safety, a design procedure is proposed. In order to validate this design procedure, two design cases are studied. In the first case study, using finite element method, a sandwich plate containing a circular disbond between the upper faceplate and core subjected to compressive in-plane load is examined. The calculated critical buckling load and its residual strength versus disbond diameter and design load versus level of safety are compared to the existing data a good agreement is achieved. In the second case study, a delaminated sandwich beam under bending load is considered and the design load (obtained from the strain energy release rate analysis) versus level of safety is determined. The results of the study show that for the adopted visual inspection technique and a high probability of damage occurrence, the design load should be about 25% of the beam strength to achieve a reliability higher than 0.99.
Aerospace Science and Technology
Sina Jahandari; Ahmad Kalhor; Babak nadjar Araabi
Abstract
This paper addresses the adaptive control problem of an aircraft and focuses on the task that the pitch angle of the aircraft is required to follow the desired path. Considering the elevator deflection angle as the input and the pitch angle as the output, a mathematical model of the aircraft is derived ...
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This paper addresses the adaptive control problem of an aircraft and focuses on the task that the pitch angle of the aircraft is required to follow the desired path. Considering the elevator deflection angle as the input and the pitch angle as the output, a mathematical model of the aircraft is derived to specify the structure of the system. Three diverse deterministic self-tuning regulators are designed using direct and indirect methods. Assuming that the system is unknown, recursive least squares method is applied to estimate parameters of the system or that of the controller’s. Diophantine equation and minimum degree pole-placement methods are utilized to calculate the control law. Not only do simulation results clearly demonstrate the privilege and effectiveness of the proposed approaches, but also comprehensive discussion is presented to distinguish advantages and disadvantages of them.
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 ...
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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
Amirali Nikkhah; Moein Ebrahimi; Morteza Tayfi; Navid Mohammadi
Abstract
The paper compares the performance of two altitude controllers, model predictive controller (MPC) and linear quadratic requlator (LQR), for aircraft in cruise flight and height change conditions. The design of the controllers is based on the linearized state space matrix of the aircraft’s longitudinal ...
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The paper compares the performance of two altitude controllers, model predictive controller (MPC) and linear quadratic requlator (LQR), for aircraft in cruise flight and height change conditions. The design of the controllers is based on the linearized state space matrix of the aircraft’s longitudinal motion around the trim conditions. The controllers’ ability to track the desired altitude while satisfying input and state constraints is evaluated, and it is found that both controllers are effective in maintaining the desired height. However, the MPC controller performs less overshoot, settling time and transient error than the LQR controller and achieves a more efficient control input by predicting the future behavior of the system. The proposed altitude controllers provide a promising solution for maintaining the desired aircraft altitude in cruise flight conditions, and the comparative analysis of the two control methods can assist in selecting the appropriate control strategy for a given aircraft system based on the desired performance requirements.
S.H. Jalali Naini; Omid Omidi Hemmat
Abstract
In this study, the static and dynamic analyses of a modified integral pulse-width pulse-frequency (PWPF) modulator with small error-reset integrator (SE-RI) logical circuit are carried out using grid search method. A set of quasi-normalized equations is utilized in order to reduce the number of parameters, ...
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In this study, the static and dynamic analyses of a modified integral pulse-width pulse-frequency (PWPF) modulator with small error-reset integrator (SE-RI) logical circuit are carried out using grid search method. A set of quasi-normalized equations is utilized in order to reduce the number of parameters, that is, the integrator gain and the maximum torque of modulator are merged to other parameters. The output of the modified integral PWPF (IPWPF) modulator is limited to 50 Hertz.The preferred regions of the IPWPF are chosen by the amount of limitation on fuel consumption and thruster firings. These preferred regions are obtained for different dead zone values of SE-RI circuit. The analyses are performed in two methods with different choices of Schmitt-trigger parameters (i.e., hysteresis or threshold ratio). The proposed regions described by simple inequality relations represent the rectangular regions, which does not give the whole preferred region. As an advantage of the study, the preferred regions are presented graphically instead of rectangular regions by inequality relations.
Aerospace Science and Technology
G. R. Abdizadeh; Sahar Noori; Mohammad Saeedi; Hamidreza Tajik
Abstract
Designing flattened miniature heat pipes (FMHPs) for electronic devices is a challenging issue due to high heat flux and limited heat dissipation space. It requires understanding the combined effects of the sintered-grooved wick structure, double heat sources, and flat thickness on heat pipes' thermal ...
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Designing flattened miniature heat pipes (FMHPs) for electronic devices is a challenging issue due to high heat flux and limited heat dissipation space. It requires understanding the combined effects of the sintered-grooved wick structure, double heat sources, and flat thickness on heat pipes' thermal efficiency. Therefore, the aim of this study is to numerically investigate the effects of the FMHP with a hybrid wick on the thermal performance of its double heat sources acting as the CPU and GPU in notebook PCs. A transient 3D finite volume method was used to solve the governing equations and assisted boundary conditions. The cylindrical heat pipe with a 200 mm length and 6 mm outside diameter is flattened into 2, 2.5, 3, and 4 mm final thicknesses (FT). The obtained results show that the final critical thicknesses with the lowest thermal resistance are 2.5 and 3 mm for hybrid and grooved wick structures, respectively. Therefore, FMHP with hybrid wicks can be flattened about 8% more. Hybrid wick structures have the best effect on FMHP thermal performance at FT=2.5 mm
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. ...
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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
Hamed Alisadeghi; Parsa Abbasrezaee
Abstract
In this article, we analyze the existing de-orbiting mechanisms in the world and analyze different types of these mechanisms for Nano satellites, also known as CubeSats. Moreover, a new passive and efficient design of the de-orbiting mechanism for the CubeSats have been proposed. Utilizing de-orbiting ...
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In this article, we analyze the existing de-orbiting mechanisms in the world and analyze different types of these mechanisms for Nano satellites, also known as CubeSats. Moreover, a new passive and efficient design of the de-orbiting mechanism for the CubeSats have been proposed. Utilizing de-orbiting mechanisms are important in Nano satellites or CubeSats to prevent production of space debris in LEO (low-earth orbit), and in NASIR-1 CubeSat, Sail Drag method was used to do so. In this method, the satellite is deorbited using passive two-sided de-orbiting approach in 1.7 years on average, or less than a maximum of 2 years. Software analysis is used to calculate membrane size and the required boom mechanisms in LEO, 600 km from the earth’s surface. Drag sail is designed using software and the prototype as well as the final version for engineering model are made and tested. The passive two-sided sail drag design of NASIR-1 is a more efficient mechanism compared to active, four-sided models in terms of volume, weight and the required electrical power and it offers a larger available externa surface on CubeSat’s surfaces.
Aerospace Science and Technology
Bahram Ghorbani Rezaei; Jafar Eskandari Jam
Abstract
While the composite pipes and cylinders manufacture by filament wound system, there are a lot of parameters that influence on the strength and mechanical behavior of them. This various mechanical behavior causes various buckling behavior. One of the most important parameters is winding pattern ...
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While the composite pipes and cylinders manufacture by filament wound system, there are a lot of parameters that influence on the strength and mechanical behavior of them. This various mechanical behavior causes various buckling behavior. One of the most important parameters is winding pattern that have effects on critical buckling loads. So this parameter should be controlled since it effects on mechanical behavior of pipes and cylinders. In the present work the influence of winding patterns on the critical buckling load of filament wound pipes exposed by pure axial loading have been studied. The studied specimens are Glass/Epoxy tubes with [+55,-55]6 lay-up(diameter to thickness ratio d/t of 10 and length of 280mm). Parameters were all considered to be consistent to investigate the effects of winding patterns there is just difference in winding pattern between three the experimental specimens. The lay-up is the result of classical theories. Love model and Galerkin’s method were used to provide buckling equations and solve theoretically the resulted equation respectively. Although the results illustrate that there is a difference, about 2-4 percent, in terms of critical buckling load between disparate winding patterns, 16 unit cells winding pattern bears higher buckling load than other patterns. Also the results show that no evident patterns influence on buckling modes of pipes. Later, the maximum lateral buckling loads of the patterns are verified with experimental data.
S. Amirahmadi; R. Ansari
Volume 6, Issue 2 , June 2009, , Pages 115-120
Abstract
The main focus of this paper is on efficiency analysis of two kinds of approximating functions (characteristic orthogonal polynomials and characteristic beam functions) that have been applied in the Rayleigh-Ritz method to determine the non-dimensional buckling and frequency parameters of an angle ply ...
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The main focus of this paper is on efficiency analysis of two kinds of approximating functions (characteristic orthogonal polynomials and characteristic beam functions) that have been applied in the Rayleigh-Ritz method to determine the non-dimensional buckling and frequency parameters of an angle ply symmetric laminated composite plate with fully elastic boundaries. It has been observed that orthogonal polynomials yield superior results for the lower modes. Also, the overall CPU time consumed to perform the calculations by the two different procedures for constructing the approximating functions showed that orthogonal polynomials are computationally more time efficient. A novel approach is devised for the construction of characteristic beam functions for buckling and vibration analysis of an angle ply symmetric laminated composite plate. Numerical results are presented and discussed
sahar noori; Ava Shahrokhi
Volume 8, Issue 2 , September 2011, , Pages 127-133
Abstract
To improve the calculation of the flow properties of an aerospike nozzle, different turbulence models were investigated in this study. The primary shape of the nozzle plug is determined through utilizing an approximate method. The flow field is, then, simulated using the Navier-Stokes equations for compressible ...
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To improve the calculation of the flow properties of an aerospike nozzle, different turbulence models were investigated in this study. The primary shape of the nozzle plug is determined through utilizing an approximate method. The flow field is, then, simulated using the Navier-Stokes equations for compressible flows. The commercial computational fluid dynamics code Fluent is used to simulate the flow around an aerospike nozzle. The computational methodology employs steady state density-based formulation and a finite volume cell centered scheme to discretize the flow field equations. To accelerate the solution convergence, the flow field is divided into several zones in order to facilitate each zone with proper unstructured grid and also to offer the appropriate initial conditions for each zone. The accuracy and the robustness of wall function based turbulence schemes, i.e. k-e model, are compared with those of Spalart-Allmaras (S-A) and k-? turbulence models.
Mohammad Reza Mosavi; Azadeh Nakhaei; Sh. Bagherinia
Volume 7, Issue 2 , September 2010, , Pages 139-150
Abstract
Global Positioning System (GPS) is proven to be an accurate positioning sensor. However, there are several sources of errors such as ionosphere and troposphere effects, satellite time errors, errors of orbit data, receivers errors, and errors resulting from multi-path effect which reduce the accuracy ...
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Global Positioning System (GPS) is proven to be an accurate positioning sensor. However, there are several sources of errors such as ionosphere and troposphere effects, satellite time errors, errors of orbit data, receivers errors, and errors resulting from multi-path effect which reduce the accuracy of low-cost GPS receivers. These sources of errors also limit the use of single-frequency GPS receivers due to their less accurate data. Therefore, its important to reduce the effect of errors on GPS systems. In order to cope with these errors and enhance GPS systems accuracy, Differential GPS (DGPS) method can be used. The problem with this method is slow updating process of differential corrections. In this paper, three algorithms based on Kalman Filtering (KF) are proposed to predict real-time corrections of DGPS systems. The efficiency of proposed algorithms is verified based on the collected of actual data. The experimental results carried out in field tests assure the high potential of these methods to get accurate positioning data. The results show that KF with variable transition matrix is better than other methods; so that its possible to reduce the Root Mean Square (RMS) of positioning errors in low-cost GPS receivers to less than one meter.
