cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.7510328
title: Matrix Damage Detection in Laminated Composite Structures by Discrete and Continuous Wavelet Transforms Using Vibration Modes

description: ABSTRACT: In this paper it was sought to enhance the potential damage detection, location and quantification of the Discrete and Continuous Wavelet Transforms in thin damaged laminated composite plates by a signal derived from vibration modes. To evaluate the ability of both transforms in the damage prognostic it was also proposed the use of Damage Indexes. The matrix damage level occurs during the impulsive load application over the analyzed structures. The finite element used was a Serendipity-type with rectangular shape, 8 nodes and 5 mechanical degrees-of-freedom per node, which was formulated by First-order Shear Deformation Theory on MATLAB (MathWorks®). The dynamic equation of motion including internal damage was solved by the Newmark implicit integration method. The results have demonstrated that mother wavelets, whether discrete or continuous, applied in dynamic signal processing, can detect a small damage magnitude in the matrix level. Moreover, the proposed Damage Indexes can quantify the damage magnitude as well as determine the most appropriate vibration mode and scalar parameter of the Continuous Wavelet Transform for damage detention.
DOI: 10.6084/m9.figshare.7510328.v1
title: Matrix Damage Detection in Laminated Composite Structures by Discrete and Continuous Wavelet Transforms Using Vibration Modes

description: ABSTRACT: In this paper it was sought to enhance the potential damage detection, location and quantification of the Discrete and Continuous Wavelet Transforms in thin damaged laminated composite plates by a signal derived from vibration modes. To evaluate the ability of both transforms in the damage prognostic it was also proposed the use of Damage Indexes. The matrix damage level occurs during the impulsive load application over the analyzed structures. The finite element used was a Serendipity-type with rectangular shape, 8 nodes and 5 mechanical degrees-of-freedom per node, which was formulated by First-order Shear Deformation Theory on MATLAB (MathWorks®). The dynamic equation of motion including internal damage was solved by the Newmark implicit integration method. The results have demonstrated that mother wavelets, whether discrete or continuous, applied in dynamic signal processing, can detect a small damage magnitude in the matrix level. Moreover, the proposed Damage Indexes can quantify the damage magnitude as well as determine the most appropriate vibration mode and scalar parameter of the Continuous Wavelet Transform for damage detention.
DOI: 10.6084/m9.figshare.7507610
title: A Recursive Methodology to Determine the Mechanical Response of Thin Laminated Plates in Bending

description: ABSTRACT: The paper's objective is to present the development of a recursive methodology which is based on Adomian Decompostion Method in order to evaluate the mechanical response of thin laminated plates in linear bending. By the equivalent layer concept, the linear relation between the equivalent stresses and the strains, namely ABD matrix, is established. When viewed by the Adomian Decompostion Method perspective, it generates an interesting idea: each layer influence on the plate's response can be recursively inserted into a base solution by a rearrangement of the plate's properties. This base solution is previously obtained and it is, in this paper, an isotropic plate response for the same loading and boundary conditions. This approach can significantly increase optimization and delamination studies, given the simplicity on the layers modification, both in fiber orientation and constitutive properties, as these are considered on the recursive procedure. The pb-2 Rayleigh-Ritz Method is used to approximate the solution space and to generate analytic response surfaces. The methodology is applied to symmetrical and unsymmetrical stacking cases for different boundary conditions sets and loading types and the obtained responses are compared to those found on the literature. A study of case complements the methodology analysis: a simplified landing gear door is modeled considering a set of loading conditions as well as different stacking configurations. Good correspondence was found in all studied cases.
DOI: 10.6084/m9.figshare.7507610.v1
title: A Recursive Methodology to Determine the Mechanical Response of Thin Laminated Plates in Bending

description: ABSTRACT: The paper's objective is to present the development of a recursive methodology which is based on Adomian Decompostion Method in order to evaluate the mechanical response of thin laminated plates in linear bending. By the equivalent layer concept, the linear relation between the equivalent stresses and the strains, namely ABD matrix, is established. When viewed by the Adomian Decompostion Method perspective, it generates an interesting idea: each layer influence on the plate's response can be recursively inserted into a base solution by a rearrangement of the plate's properties. This base solution is previously obtained and it is, in this paper, an isotropic plate response for the same loading and boundary conditions. This approach can significantly increase optimization and delamination studies, given the simplicity on the layers modification, both in fiber orientation and constitutive properties, as these are considered on the recursive procedure. The pb-2 Rayleigh-Ritz Method is used to approximate the solution space and to generate analytic response surfaces. The methodology is applied to symmetrical and unsymmetrical stacking cases for different boundary conditions sets and loading types and the obtained responses are compared to those found on the literature. A study of case complements the methodology analysis: a simplified landing gear door is modeled considering a set of loading conditions as well as different stacking configurations. Good correspondence was found in all studied cases.
DOI: 10.6084/m9.figshare.7516274
title: Comparing an Ensemble Kalman Filter to a 4DVAR Data Assimilation System in Chaotic Dynamics

description: ABSTRACT: In this paper, the Ensemble Kalman Filter is compared with a 4DVAR Data Assimilation System in chaotic dynamics. The Lorenz model is chosen for its simplicity in structure and the dynamic similarities with primitive equations models, such as modern numerical weather forecasting. It was examined if the Ensemble Kalman Filter and 4DVAR are effective to track the Control for 10, 20 and 40% of error at the Initial Conditions. With 10% of noise, the trajectories of both are almost perfect. With 20% of noise, the differences between the simulated trajectories and the observations as well as "true trajectories" are rather small for the Ensemble Kalman Filter but almost perfect for 4DVAR. However, the differences are increasingly significant at the later part of the integration period for the Ensemble Kalman Filter, due the chaotic behavior system. However, for the case with 40% error at the Initial Condition, neither the Ensemble Kalman Filter or 4DVAR could track the Control with only 3 observations ingested. To evaluate a more realistic assimilation application, it was created an experiment in which the Ensemble Kalman Filter ingested single observation at the 180th time step in the X, Y, and Z Lorenz variables and only in the X variable. The results show a perfect fit of 4DVAR and the Control during a complete integrations period, but the Ensemble Kalman Filter has a disagreement after the 80th time step. On the other hand, it was shown a considerable disagreement between the Ensemble Kalman Filter trajectories and the Control as well as a total fail of 4DVAR. Better results were obtained for the case in which observation covers all the components of the model vector.
DOI: 10.6084/m9.figshare.7516274.v1
title: Comparing an Ensemble Kalman Filter to a 4DVAR Data Assimilation System in Chaotic Dynamics

description: ABSTRACT: In this paper, the Ensemble Kalman Filter is compared with a 4DVAR Data Assimilation System in chaotic dynamics. The Lorenz model is chosen for its simplicity in structure and the dynamic similarities with primitive equations models, such as modern numerical weather forecasting. It was examined if the Ensemble Kalman Filter and 4DVAR are effective to track the Control for 10, 20 and 40% of error at the Initial Conditions. With 10% of noise, the trajectories of both are almost perfect. With 20% of noise, the differences between the simulated trajectories and the observations as well as "true trajectories" are rather small for the Ensemble Kalman Filter but almost perfect for 4DVAR. However, the differences are increasingly significant at the later part of the integration period for the Ensemble Kalman Filter, due the chaotic behavior system. However, for the case with 40% error at the Initial Condition, neither the Ensemble Kalman Filter or 4DVAR could track the Control with only 3 observations ingested. To evaluate a more realistic assimilation application, it was created an experiment in which the Ensemble Kalman Filter ingested single observation at the 180th time step in the X, Y, and Z Lorenz variables and only in the X variable. The results show a perfect fit of 4DVAR and the Control during a complete integrations period, but the Ensemble Kalman Filter has a disagreement after the 80th time step. On the other hand, it was shown a considerable disagreement between the Ensemble Kalman Filter trajectories and the Control as well as a total fail of 4DVAR. Better results were obtained for the case in which observation covers all the components of the model vector.
DOI: 10.6084/m9.figshare.7509941.v1
title: Recurrent Algorithm for TDOA Localization in Sensor Networks

description: ABSTRACT: Using the mathematical apparatus of the extended Kalman Filter, the recurrent algorithm of the passive location in sensor networks - based on the Time Difference of Arrival method in case of correlated errors of measurements - is developed. The initial estimates of Radio Frequency Sources coordinates and the correlation matrix of the vector estimation are determined based on the method of the least squares in case of 3 difference measurement distances. Efficiency analysis of recurrent adaptive algorithm and its comparison with the quadratic correction one are performed by statistical modeling. A comparison of them with the lower limit of the Cramer-Rao was carried out. The implementation of the recurrent adaptive algorithm requires 2.7 times less computational cost than the quadratic correction one.
DOI: 10.6084/m9.figshare.7509941
title: Recurrent Algorithm for TDOA Localization in Sensor Networks

description: ABSTRACT: Using the mathematical apparatus of the extended Kalman Filter, the recurrent algorithm of the passive location in sensor networks - based on the Time Difference of Arrival method in case of correlated errors of measurements - is developed. The initial estimates of Radio Frequency Sources coordinates and the correlation matrix of the vector estimation are determined based on the method of the least squares in case of 3 difference measurement distances. Efficiency analysis of recurrent adaptive algorithm and its comparison with the quadratic correction one are performed by statistical modeling. A comparison of them with the lower limit of the Cramer-Rao was carried out. The implementation of the recurrent adaptive algorithm requires 2.7 times less computational cost than the quadratic correction one.
DOI: 10.6084/m9.figshare.7508273
title: Higher Education Aviation Programs in Greece: A Missed Opportunity or a Challenge to Meet?

description: Abstract: The air transport industry in Greece has been experiencing a significant growth. However, higher education has missed so far this export opportunity. Public universities and technological educational institutes have very limited undergraduate offerings in the fields of aeronautical engineering and aircraft maintenance technology, respectively. These programs are offered only in the local language, practically restricting them to the indigenous market. Postgraduate offerings are currently inexistent. This study proposes a generic model for undergraduate and postgraduate aviation programs. This model, aligning with the world’s best practice in aviation education, would have to be adjusted to meet the Greek aviation industry. A preliminary investigation to identify the characteristics of the model was conducted in the Greek aviation industry, through a survey supported with in-depth interviews. The research findings suggest that it is necessary to invest in the strengths of the Greek aviation industry (aviation services and aircraft maintenance) and the strategic advantages of the country (climate favorable for flight training and touristic attractiveness). The need for a postgraduate aviation program is highlighted, in contrast to the introduction of an undergraduate program, which came up as less desirable. Moreover, the need for export-driven target-oriented synergies between industry and academia has been a key observation.
DOI: 10.6084/m9.figshare.7508273.v1
title: Higher Education Aviation Programs in Greece: A Missed Opportunity or a Challenge to Meet?

description: Abstract: The air transport industry in Greece has been experiencing a significant growth. However, higher education has missed so far this export opportunity. Public universities and technological educational institutes have very limited undergraduate offerings in the fields of aeronautical engineering and aircraft maintenance technology, respectively. These programs are offered only in the local language, practically restricting them to the indigenous market. Postgraduate offerings are currently inexistent. This study proposes a generic model for undergraduate and postgraduate aviation programs. This model, aligning with the world’s best practice in aviation education, would have to be adjusted to meet the Greek aviation industry. A preliminary investigation to identify the characteristics of the model was conducted in the Greek aviation industry, through a survey supported with in-depth interviews. The research findings suggest that it is necessary to invest in the strengths of the Greek aviation industry (aviation services and aircraft maintenance) and the strategic advantages of the country (climate favorable for flight training and touristic attractiveness). The need for a postgraduate aviation program is highlighted, in contrast to the introduction of an undergraduate program, which came up as less desirable. Moreover, the need for export-driven target-oriented synergies between industry and academia has been a key observation.
DOI: 10.6084/m9.figshare.7508279
title: Operational Measurements for Infrared Camera Characterization

description: ABSTRACT: The detection, location, identification and recognition are very important activities for the air forces. Imaging systems are tools used for those functions, so it is mandatory to characterize those systems to really know their actual operational limits. This paper presents a set of measurements for spectral, radiometric and spatial camera characterization to be applied to imaging systems operating in the thermal infrared. A SC5600 camera manufactured by FLIR® Systems was used and assembled with lenses of 27 or 54 mm equivalent focal length. The camera spectral characterization was done by comparison to a calibrated system composed by thermal source, monochromator and a broadband reference detector. The radiometric characterization was performed using an extensive blackbody (CI Systems) for temperatures between 10 and 55 ºC to evaluate the camera accuracy and obtain the calibration curves. The spatial characterization was carried out using the same extensive blackbody and 2 standard USAF 1951 machined targets, one made of steel and other of aluminum, serving as masks for the blackbody. Using recycled material, a homemade extended blackbody for outdoor use was built. The results obtained using the 2 blackbodies in laboratory were similar.
DOI: 10.6084/m9.figshare.7508279.v1
title: Operational Measurements for Infrared Camera Characterization

description: ABSTRACT: The detection, location, identification and recognition are very important activities for the air forces. Imaging systems are tools used for those functions, so it is mandatory to characterize those systems to really know their actual operational limits. This paper presents a set of measurements for spectral, radiometric and spatial camera characterization to be applied to imaging systems operating in the thermal infrared. A SC5600 camera manufactured by FLIR® Systems was used and assembled with lenses of 27 or 54 mm equivalent focal length. The camera spectral characterization was done by comparison to a calibrated system composed by thermal source, monochromator and a broadband reference detector. The radiometric characterization was performed using an extensive blackbody (CI Systems) for temperatures between 10 and 55 ºC to evaluate the camera accuracy and obtain the calibration curves. The spatial characterization was carried out using the same extensive blackbody and 2 standard USAF 1951 machined targets, one made of steel and other of aluminum, serving as masks for the blackbody. Using recycled material, a homemade extended blackbody for outdoor use was built. The results obtained using the 2 blackbodies in laboratory were similar.
DOI: 10.6084/m9.figshare.5930893
title: Space Propulsion: a Survey Study About Current and Future Technologies

description: ABSTRACT: Current Space Launch Vehicles use chemical reactions (solid and liquid propellants) to achieve sufficient thrust to launch artifacts and humans into space. Propulsion technologies can be framed in three different categories: "escape propulsion", "in-space propulsion", and "deep space propulsion". The launch vehicles currently used for "escape propulsion" rely on mature technologies, which experienced only small incremental improvements over the last five decades, and breakthroughs for this kind of propulsion are not foreseen for the next two decades. This research gathered information on the main operational heavy-lift space launch vehicles with capacity over 5,000 kg that are used to reach GEO (Geostationary Earth Orbit) by the United States, Russia, Europe, China, Japan and India and compared their thrust capability. The results show that performance was improved mainly by adding boosters, increasing gross propellant weight, with larger diameter rocket motors and using more efficient liquid propellant pairs. Information regarding the frequency of published scientific articles and patents on Space Vehicles Propulsion Systems since the 1960s was also gathered, which demonstrates some progress in the last years, mainly in USA and Europe. "In-space" and "Deep space" spacecraft were also briefly examined in this article, resuming the main features of some new promising developments, mainly regarding the latter, which present prospects of significant technological advances; however, real progress in interplanetary missions will be possible only when technological breakthroughs towards other propulsion types become possible and feasible. So, two questions motivated the authors: why space propulsion development seems stagnant? Are there prospects for progress?
DOI: 10.6084/m9.figshare.5930893.v1
title: Space Propulsion: a Survey Study About Current and Future Technologies

description: ABSTRACT: Current Space Launch Vehicles use chemical reactions (solid and liquid propellants) to achieve sufficient thrust to launch artifacts and humans into space. Propulsion technologies can be framed in three different categories: "escape propulsion", "in-space propulsion", and "deep space propulsion". The launch vehicles currently used for "escape propulsion" rely on mature technologies, which experienced only small incremental improvements over the last five decades, and breakthroughs for this kind of propulsion are not foreseen for the next two decades. This research gathered information on the main operational heavy-lift space launch vehicles with capacity over 5,000 kg that are used to reach GEO (Geostationary Earth Orbit) by the United States, Russia, Europe, China, Japan and India and compared their thrust capability. The results show that performance was improved mainly by adding boosters, increasing gross propellant weight, with larger diameter rocket motors and using more efficient liquid propellant pairs. Information regarding the frequency of published scientific articles and patents on Space Vehicles Propulsion Systems since the 1960s was also gathered, which demonstrates some progress in the last years, mainly in USA and Europe. "In-space" and "Deep space" spacecraft were also briefly examined in this article, resuming the main features of some new promising developments, mainly regarding the latter, which present prospects of significant technological advances; however, real progress in interplanetary missions will be possible only when technological breakthroughs towards other propulsion types become possible and feasible. So, two questions motivated the authors: why space propulsion development seems stagnant? Are there prospects for progress?
DOI: 10.6084/m9.figshare.5930911
title: Low Subsonic Wind Tunnel - Design and Construction

description: ABSTRACT: This paper describes the design and the construction details of a medium size subsonic low-speed wind tunnel, which has been designed to achieve 90 m/s in the working section with expected low intensity turbulence level, making it available for researching in areas such as low speed aerodynamics (flight and terrestrial vehicles), sport activities, civil engineering applications, fundamental research in Fluid Mechanics and other possibilities. To accomplish such objectives a very detailed design was carried on using theoretical analyses, CFD simulations and semi-empirical methods, all of them applied to improve the flow quality along the wind tunnel sections. A very careful attention has been focused to the design of the fan blades and the electrical engine assembly, which has been inserted in a "pusher" configuration. Flow control and stabilization also took place using screens, honeycombs and corner vanes, all of them optimized to induce low turbulence levels in the working section. The design and construction of each wind tunnel section has been presented and discussed shedding light to the most relevant technical aspects and an attempt is made here to present some design and manufacture guidance for the main components of a low subsonic wind tunnel.
DOI: 10.6084/m9.figshare.5930911.v1
title: Low Subsonic Wind Tunnel - Design and Construction

description: ABSTRACT: This paper describes the design and the construction details of a medium size subsonic low-speed wind tunnel, which has been designed to achieve 90 m/s in the working section with expected low intensity turbulence level, making it available for researching in areas such as low speed aerodynamics (flight and terrestrial vehicles), sport activities, civil engineering applications, fundamental research in Fluid Mechanics and other possibilities. To accomplish such objectives a very detailed design was carried on using theoretical analyses, CFD simulations and semi-empirical methods, all of them applied to improve the flow quality along the wind tunnel sections. A very careful attention has been focused to the design of the fan blades and the electrical engine assembly, which has been inserted in a "pusher" configuration. Flow control and stabilization also took place using screens, honeycombs and corner vanes, all of them optimized to induce low turbulence levels in the working section. The design and construction of each wind tunnel section has been presented and discussed shedding light to the most relevant technical aspects and an attempt is made here to present some design and manufacture guidance for the main components of a low subsonic wind tunnel.