Marco Rao,Gianluca Falco

This paper deals with a Software Defined Radio (SDR) receiver capable to process GPS and Galileo signals jointly. A large set of possible solution can be implemented, with the main aim of assessing the performance of the receiver for the considered architectures. For this reason, software receivers, either real-time or non-real-time, are fundamental tools to enable research and new developments in the field of GNSSs. In this paper our intent is to discuss some of the choices one can face when implementing an SDR GNSS receiver, switching from the theory to the practice. We focus our attention on the pseudorange construction and the Position, Velocity and Time (PVT) estimation stage, discussing different algorithms to implement these blocks. Our aim is to offer an insight on the options to implement those stages of the receiving chain, in a practical vision which is difficult to find in the available literature.

]]>Venu Gopal Madhav Annamdas

In the last two decades, consciousness of structural health monitoring (SHM) has increased many folds especially after witnessing some aerospace/ aircraft failures. Subsequently many SHM techniques have emerged for crack detections. This paper presents one such technique to monitor a crack using piezoelectric transducer (PZT) via electromechanical impedance (EMI) technique. The basic principle of EMI is to record electromechanical (EM) admittance signatures resulted from the actuations of PZT (bonded on structure to be monitored) in the presence of electric field. Any deviations in these signatures during the monitoring study indicate disturbance/ damage/ crack (for a healthy structure) or increase in severity (if crack/damage is already present). In practice, the occurrence of ‘crack’ and its ‘propagating direction’ are equally important. In this paper, basic crack propagation studies on two metallic beam specimens using EMI are presented. Two PZT transducers, one each was bonded on each specimen. First a small crack was induced at different locations on both specimens, it was allowed to propagate in steps (cracks approaching PZT in one specimen and departing in another). Signatures were acquired for un-cracked and cracked propagation stages. Root mean square deviation index was used to demonstrate the experimental observations related to identification of crack propagating directions. Numerical modal analysis was carried out to understand the shifts in modal frequencies during crack propagation. The existence of crack was successfully predicted by EMI but the propagation of crack was not readily obtained. Hence a signature analysis was carried out to predict the propagation direction. It has been a practice to highlight positive sides of any technology, but limitations of EMI are also discussed in this paper and hence the study is expected to be useful for new and existing researchers in the area of EMI based SHM.

]]>J. E. Jam,Aref A. Fard

Applications of impact damper to reduce machine tools vibration have been investigated analytically, numerically, and experimentally for many years. The reason for this interest lies in the fact that impacts occur very often in many modern technical devices. In different applications, optimal values of impact damper parameters (impact mass, elastic coefficient of barrier etc.) should be found in order to damp vibrations efficiently. We investigate the predictions of a mathematical model for an impact damper consisting of a pendulum and an elastic barrier. Our model incorporates Hertzian contact between the spherical steel pendulum and the barrier. In next step, due to the strong non-linearity of the model, Homotopy Perturbation and iteration perturbation are used to solve the dynamics equation. Homotopy and iteration perturbation method provide analytical solution for strong non-linear equation. To confirm the accuracy of this method, results are compared with numerical solutions in SimMechanics toolbox of MATLAB. Next, a systematic approach based on a Genetic Algorithm optimization method is used to determine the best design parameters for suppressing vibrations. Finally, optimum parameters for complete quenching of vibrations are obtained.

]]>Mohamed B. El Mashade

A constant false alarm rate in the presence of variable levels of noise is usually a requirement placed on any modern radar. The CA- and OS-CFAR detectors are the most widely used ones in the CFAR world. The cell-averaging (CA) is the optimum CFAR detector in terms of detection probability in homogeneous background when the reference cells have identical, independent and exponentially distributed signals. The ordered-statistic (OS) is an alternative to the CA processor, which trades a small loss in detection performance, relative to the CA scheme, in ideal conditions for much less performance degradation in non-ideal background environments. To benefice the merits of these well-known schemes, two modified versions (MX- & MN-CFAR) have been recently suggested. This paper is devoted to the detection performance evaluation of these modified versions as well as a novel one (ML-CFAR). Exact formulas for their false alarm and detection performances are derived, in the absence as well as in the presence of spurious targets. The results of these performances obtained for Rayleigh clutter and Rayleigh target indicate that the MN-CFAR scheme performs nearly as good as OS detector in the presence of outlying targets and all the developed versions perform much better than that processor when the background environment is homogeneous. When compared to CA-CFAR, the modified schemes perform better in an ideal condition, and behave much better in the presence of interfering targets.

]]>Inder Krishen Panditta

Derivative theorems of Principle of Quasi Work, a powerful pseudo energy principle, are derived. These theorems, viz. Applied Load Theorem, Deflection Theorem and Unit Load Theorem are applicable to a pair of topologically similar structural systems. One more theorem referred to as Relative Deflection Theorem along with its two corollaries are also derived from this principle for facilitating truss analysis. Using these theorems, a new methodology for calculating nodal deflections of a truss from its internal member forces and vice versa is presented in this paper. This methodology is amazingly simple, easy, and fast. These theorems form the basis of present methodology. Thirteen nodal deflections of a four bay truss included in this paper were calculated by hand in less than fifteen minutes.

]]>Santosh Joteppa,Bhoopendrakumar Singh,Satyanarayana Prasad,Vinod S Chippalkatti,R. N. Garvalia,K. G. Domadia,R. M. Parmar,R. K. Dave,DRM Samudraiah

Space grade subsystems require judicious combination of design, analysis and testing to realize a flight worthy hardware. These subsystems operate in an environment considerably different from that in which they are built and after launch they are inaccessible to routine maintenance and repair. The thermal vacuum test is one of the most critical environmental tests and all the subsystem have to pass this test in order to maintain the high reliability. Finite element method approach is used for the thermal analysis of the power supply by considering the thermo vacuum boundary conditions for the study of behaviour of highly dissipating components and the temperature profile. This paper presents the design considerations for realizing a space grade Power supply from its thermal and vacuum performance perspective. Comparison is made between the results of the thermal analysis and actual test under vacuum conditions of Flight model. Also the result of the qualification model which is tested at higher temperature is discussed. Design margins are also established through actual testing in thermo vacuum chamber to achieve the onboard performance of the Power supply under vacuum in geo-stationary environment for a product life of 15 years.

]]>J. E. Jam,S. Maleki,A. Andakhshideh

Linear and non-linear bending analysis of moderately thick functionally graded (FG) rectangular plates with different boundary conditions are presented using generalized differential quadrature (GDQ) method. The modulus of elasticity of plates is assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. Based on the first-order shear deformation theory and Von Karman type non-linearity, the governing system of equations include a system of thirteen partial differential equations (PDEs) in terms of unknown displacements, forces and moments. To derive linear system of equations, non-linear terms are omitted in former equations. Presence of all plate variables in the governing equations provides a simple procedure to satisfy different boundary conditions. Successive application of the GDQ technique to the governing equations resulted in a system of non-linear algebraic equations. The Newton–Raphson iterative scheme is then employed to solve the resulting system of non-linear equations. Illustrative examples are presented to demonstrate accuracy and rapid convergence of the presented GDQ technique. Accuracy of the results for both displacement and stress components are verified with comparing the present results with those of analytical and finite element methods. It is found that the theory can predict accurately the displacement and stress components even for small number of grid points.

]]>Marco Rao,Gianluca Falco

This paper deals with a Software Defined Radio (SDR) receiver capable to process GPS and Galileo signals jointly. A large set of possible solution can be implemented, with the main aim of assessing the performance of the receiver for the considered architectures. For this reason, software receivers, either real-time or non-real-time, are fundamental tools to enable research and new developments in the field of GNSSs. In this paper our intent is to discuss some of the choices one can face when implementing an SDR GNSS receiver, switching from the theory to the practice. We focus our attention on the pseudorange construction and the Position, Velocity and Time (PVT) estimation stage, discussing different algorithms to implement these blocks. Our aim is to offer an insight on the options to implement those stages of the receiving chain, in a practical vision which is difficult to find in the available literature.

]]>Venu Gopal Madhav Annamdas

In the last two decades, consciousness of structural health monitoring (SHM) has increased many folds especially after witnessing some aerospace/ aircraft failures. Subsequently many SHM techniques have emerged for crack detections. This paper presents one such technique to monitor a crack using piezoelectric transducer (PZT) via electromechanical impedance (EMI) technique. The basic principle of EMI is to record electromechanical (EM) admittance signatures resulted from the actuations of PZT (bonded on structure to be monitored) in the presence of electric field. Any deviations in these signatures during the monitoring study indicate disturbance/ damage/ crack (for a healthy structure) or increase in severity (if crack/damage is already present). In practice, the occurrence of ‘crack’ and its ‘propagating direction’ are equally important. In this paper, basic crack propagation studies on two metallic beam specimens using EMI are presented. Two PZT transducers, one each was bonded on each specimen. First a small crack was induced at different locations on both specimens, it was allowed to propagate in steps (cracks approaching PZT in one specimen and departing in another). Signatures were acquired for un-cracked and cracked propagation stages. Root mean square deviation index was used to demonstrate the experimental observations related to identification of crack propagating directions. Numerical modal analysis was carried out to understand the shifts in modal frequencies during crack propagation. The existence of crack was successfully predicted by EMI but the propagation of crack was not readily obtained. Hence a signature analysis was carried out to predict the propagation direction. It has been a practice to highlight positive sides of any technology, but limitations of EMI are also discussed in this paper and hence the study is expected to be useful for new and existing researchers in the area of EMI based SHM.

]]>J. E. Jam,Aref A. Fard

Applications of impact damper to reduce machine tools vibration have been investigated analytically, numerically, and experimentally for many years. The reason for this interest lies in the fact that impacts occur very often in many modern technical devices. In different applications, optimal values of impact damper parameters (impact mass, elastic coefficient of barrier etc.) should be found in order to damp vibrations efficiently. We investigate the predictions of a mathematical model for an impact damper consisting of a pendulum and an elastic barrier. Our model incorporates Hertzian contact between the spherical steel pendulum and the barrier. In next step, due to the strong non-linearity of the model, Homotopy Perturbation and iteration perturbation are used to solve the dynamics equation. Homotopy and iteration perturbation method provide analytical solution for strong non-linear equation. To confirm the accuracy of this method, results are compared with numerical solutions in SimMechanics toolbox of MATLAB. Next, a systematic approach based on a Genetic Algorithm optimization method is used to determine the best design parameters for suppressing vibrations. Finally, optimum parameters for complete quenching of vibrations are obtained.

]]>Mohamed B. El Mashade

A constant false alarm rate in the presence of variable levels of noise is usually a requirement placed on any modern radar. The CA- and OS-CFAR detectors are the most widely used ones in the CFAR world. The cell-averaging (CA) is the optimum CFAR detector in terms of detection probability in homogeneous background when the reference cells have identical, independent and exponentially distributed signals. The ordered-statistic (OS) is an alternative to the CA processor, which trades a small loss in detection performance, relative to the CA scheme, in ideal conditions for much less performance degradation in non-ideal background environments. To benefice the merits of these well-known schemes, two modified versions (MX- & MN-CFAR) have been recently suggested. This paper is devoted to the detection performance evaluation of these modified versions as well as a novel one (ML-CFAR). Exact formulas for their false alarm and detection performances are derived, in the absence as well as in the presence of spurious targets. The results of these performances obtained for Rayleigh clutter and Rayleigh target indicate that the MN-CFAR scheme performs nearly as good as OS detector in the presence of outlying targets and all the developed versions perform much better than that processor when the background environment is homogeneous. When compared to CA-CFAR, the modified schemes perform better in an ideal condition, and behave much better in the presence of interfering targets.

]]>Inder Krishen Panditta

Derivative theorems of Principle of Quasi Work, a powerful pseudo energy principle, are derived. These theorems, viz. Applied Load Theorem, Deflection Theorem and Unit Load Theorem are applicable to a pair of topologically similar structural systems. One more theorem referred to as Relative Deflection Theorem along with its two corollaries are also derived from this principle for facilitating truss analysis. Using these theorems, a new methodology for calculating nodal deflections of a truss from its internal member forces and vice versa is presented in this paper. This methodology is amazingly simple, easy, and fast. These theorems form the basis of present methodology. Thirteen nodal deflections of a four bay truss included in this paper were calculated by hand in less than fifteen minutes.

]]>Santosh Joteppa,Bhoopendrakumar Singh,Satyanarayana Prasad,Vinod S Chippalkatti,R. N. Garvalia,K. G. Domadia,R. M. Parmar,R. K. Dave,DRM Samudraiah

Space grade subsystems require judicious combination of design, analysis and testing to realize a flight worthy hardware. These subsystems operate in an environment considerably different from that in which they are built and after launch they are inaccessible to routine maintenance and repair. The thermal vacuum test is one of the most critical environmental tests and all the subsystem have to pass this test in order to maintain the high reliability. Finite element method approach is used for the thermal analysis of the power supply by considering the thermo vacuum boundary conditions for the study of behaviour of highly dissipating components and the temperature profile. This paper presents the design considerations for realizing a space grade Power supply from its thermal and vacuum performance perspective. Comparison is made between the results of the thermal analysis and actual test under vacuum conditions of Flight model. Also the result of the qualification model which is tested at higher temperature is discussed. Design margins are also established through actual testing in thermo vacuum chamber to achieve the onboard performance of the Power supply under vacuum in geo-stationary environment for a product life of 15 years.

]]>J. E. Jam,S. Maleki,A. Andakhshideh

Linear and non-linear bending analysis of moderately thick functionally graded (FG) rectangular plates with different boundary conditions are presented using generalized differential quadrature (GDQ) method. The modulus of elasticity of plates is assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. Based on the first-order shear deformation theory and Von Karman type non-linearity, the governing system of equations include a system of thirteen partial differential equations (PDEs) in terms of unknown displacements, forces and moments. To derive linear system of equations, non-linear terms are omitted in former equations. Presence of all plate variables in the governing equations provides a simple procedure to satisfy different boundary conditions. Successive application of the GDQ technique to the governing equations resulted in a system of non-linear algebraic equations. The Newton–Raphson iterative scheme is then employed to solve the resulting system of non-linear equations. Illustrative examples are presented to demonstrate accuracy and rapid convergence of the presented GDQ technique. Accuracy of the results for both displacement and stress components are verified with comparing the present results with those of analytical and finite element methods. It is found that the theory can predict accurately the displacement and stress components even for small number of grid points.

]]>Marco Rao,Gianluca Falco

This paper deals with a Software Defined Radio (SDR) receiver capable to process GPS and Galileo signals jointly. A large set of possible solution can be implemented, with the main aim of assessing the performance of the receiver for the considered architectures. For this reason, software receivers, either real-time or non-real-time, are fundamental tools to enable research and new developments in the field of GNSSs. In this paper our intent is to discuss some of the choices one can face when implementing an SDR GNSS receiver, switching from the theory to the practice. We focus our attention on the pseudorange construction and the Position, Velocity and Time (PVT) estimation stage, discussing different algorithms to implement these blocks. Our aim is to offer an insight on the options to implement those stages of the receiving chain, in a practical vision which is difficult to find in the available literature.

]]>Venu Gopal Madhav Annamdas

In the last two decades, consciousness of structural health monitoring (SHM) has increased many folds especially after witnessing some aerospace/ aircraft failures. Subsequently many SHM techniques have emerged for crack detections. This paper presents one such technique to monitor a crack using piezoelectric transducer (PZT) via electromechanical impedance (EMI) technique. The basic principle of EMI is to record electromechanical (EM) admittance signatures resulted from the actuations of PZT (bonded on structure to be monitored) in the presence of electric field. Any deviations in these signatures during the monitoring study indicate disturbance/ damage/ crack (for a healthy structure) or increase in severity (if crack/damage is already present). In practice, the occurrence of ‘crack’ and its ‘propagating direction’ are equally important. In this paper, basic crack propagation studies on two metallic beam specimens using EMI are presented. Two PZT transducers, one each was bonded on each specimen. First a small crack was induced at different locations on both specimens, it was allowed to propagate in steps (cracks approaching PZT in one specimen and departing in another). Signatures were acquired for un-cracked and cracked propagation stages. Root mean square deviation index was used to demonstrate the experimental observations related to identification of crack propagating directions. Numerical modal analysis was carried out to understand the shifts in modal frequencies during crack propagation. The existence of crack was successfully predicted by EMI but the propagation of crack was not readily obtained. Hence a signature analysis was carried out to predict the propagation direction. It has been a practice to highlight positive sides of any technology, but limitations of EMI are also discussed in this paper and hence the study is expected to be useful for new and existing researchers in the area of EMI based SHM.

]]>J. E. Jam,Aref A. Fard

Applications of impact damper to reduce machine tools vibration have been investigated analytically, numerically, and experimentally for many years. The reason for this interest lies in the fact that impacts occur very often in many modern technical devices. In different applications, optimal values of impact damper parameters (impact mass, elastic coefficient of barrier etc.) should be found in order to damp vibrations efficiently. We investigate the predictions of a mathematical model for an impact damper consisting of a pendulum and an elastic barrier. Our model incorporates Hertzian contact between the spherical steel pendulum and the barrier. In next step, due to the strong non-linearity of the model, Homotopy Perturbation and iteration perturbation are used to solve the dynamics equation. Homotopy and iteration perturbation method provide analytical solution for strong non-linear equation. To confirm the accuracy of this method, results are compared with numerical solutions in SimMechanics toolbox of MATLAB. Next, a systematic approach based on a Genetic Algorithm optimization method is used to determine the best design parameters for suppressing vibrations. Finally, optimum parameters for complete quenching of vibrations are obtained.

]]>Mohamed B. El Mashade

A constant false alarm rate in the presence of variable levels of noise is usually a requirement placed on any modern radar. The CA- and OS-CFAR detectors are the most widely used ones in the CFAR world. The cell-averaging (CA) is the optimum CFAR detector in terms of detection probability in homogeneous background when the reference cells have identical, independent and exponentially distributed signals. The ordered-statistic (OS) is an alternative to the CA processor, which trades a small loss in detection performance, relative to the CA scheme, in ideal conditions for much less performance degradation in non-ideal background environments. To benefice the merits of these well-known schemes, two modified versions (MX- & MN-CFAR) have been recently suggested. This paper is devoted to the detection performance evaluation of these modified versions as well as a novel one (ML-CFAR). Exact formulas for their false alarm and detection performances are derived, in the absence as well as in the presence of spurious targets. The results of these performances obtained for Rayleigh clutter and Rayleigh target indicate that the MN-CFAR scheme performs nearly as good as OS detector in the presence of outlying targets and all the developed versions perform much better than that processor when the background environment is homogeneous. When compared to CA-CFAR, the modified schemes perform better in an ideal condition, and behave much better in the presence of interfering targets.

]]>Inder Krishen Panditta

Derivative theorems of Principle of Quasi Work, a powerful pseudo energy principle, are derived. These theorems, viz. Applied Load Theorem, Deflection Theorem and Unit Load Theorem are applicable to a pair of topologically similar structural systems. One more theorem referred to as Relative Deflection Theorem along with its two corollaries are also derived from this principle for facilitating truss analysis. Using these theorems, a new methodology for calculating nodal deflections of a truss from its internal member forces and vice versa is presented in this paper. This methodology is amazingly simple, easy, and fast. These theorems form the basis of present methodology. Thirteen nodal deflections of a four bay truss included in this paper were calculated by hand in less than fifteen minutes.

]]>Santosh Joteppa,Bhoopendrakumar Singh,Satyanarayana Prasad,Vinod S Chippalkatti,R. N. Garvalia,K. G. Domadia,R. M. Parmar,R. K. Dave,DRM Samudraiah

Space grade subsystems require judicious combination of design, analysis and testing to realize a flight worthy hardware. These subsystems operate in an environment considerably different from that in which they are built and after launch they are inaccessible to routine maintenance and repair. The thermal vacuum test is one of the most critical environmental tests and all the subsystem have to pass this test in order to maintain the high reliability. Finite element method approach is used for the thermal analysis of the power supply by considering the thermo vacuum boundary conditions for the study of behaviour of highly dissipating components and the temperature profile. This paper presents the design considerations for realizing a space grade Power supply from its thermal and vacuum performance perspective. Comparison is made between the results of the thermal analysis and actual test under vacuum conditions of Flight model. Also the result of the qualification model which is tested at higher temperature is discussed. Design margins are also established through actual testing in thermo vacuum chamber to achieve the onboard performance of the Power supply under vacuum in geo-stationary environment for a product life of 15 years.

]]>J. E. Jam,S. Maleki,A. Andakhshideh

Linear and non-linear bending analysis of moderately thick functionally graded (FG) rectangular plates with different boundary conditions are presented using generalized differential quadrature (GDQ) method. The modulus of elasticity of plates is assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. Based on the first-order shear deformation theory and Von Karman type non-linearity, the governing system of equations include a system of thirteen partial differential equations (PDEs) in terms of unknown displacements, forces and moments. To derive linear system of equations, non-linear terms are omitted in former equations. Presence of all plate variables in the governing equations provides a simple procedure to satisfy different boundary conditions. Successive application of the GDQ technique to the governing equations resulted in a system of non-linear algebraic equations. The Newton–Raphson iterative scheme is then employed to solve the resulting system of non-linear equations. Illustrative examples are presented to demonstrate accuracy and rapid convergence of the presented GDQ technique. Accuracy of the results for both displacement and stress components are verified with comparing the present results with those of analytical and finite element methods. It is found that the theory can predict accurately the displacement and stress components even for small number of grid points.

]]>