Aerotecnica Missili & Spazio最新文献

Collision avoidance is a topic of growing importance for any satellite orbiting Earth. Especially those satellites without thrusting capabilities face the problem of not being able to perform impulsive collision avoidance manoeuvres. For satellites in low Earth orbits, though, perturbing accelerations due to aerodynamic drag may be used to influence their trajectories, thus offering a possibility to avoid collisions without consuming propellant. Here, this manoeuvring option is investigated for the satellite Flying Laptop of the University of Stuttgart, which orbits the Earth at approximately ({600},{textrm{km}}). In a first step, the satellite is aerodynamically analysed making use of the tool ADBSat. By employing an analytic equation from the literature, in-track separation distances can then be derived following a variation of the ballistic coefficient through a change in attitude. A further examination of the achievable separation distances proves the feasibility of aerodynamic collision avoidance manoeuvres for the Flying Laptop for moderate and high solar and geomagnetic activity. The predicted separation distances are further compared to flight data, where the principle effect of the manoeuvre on the satellite trajectory becomes visible. The results suggest an applicability of collision avoidance manoeuvres for all satellites in comparable and especially in lower orbits than the Flying Laptop, which are able to vary their ballistic coefficient.

The prediction of pressure fluctuations generated over the external surface of aerospace launchers during the atmospheric flight remains a challenging task due to the complexity of the geometry and the effects of compressibility at high supersonic Mach numbers. An experimental database is here analysed to the scope of providing a procedure to model and predict the relevant statistics of the wall pressure fluctuations generated by a supersonic flow overflowing the VEGA-C Launcher Vehicle. Data have been obtained in an extensive Wind Tunnel test campaign carried out in the trisonic wind tunnel of the National Institute for Aerospace Research (INCAS) in Bucharest. Wall-mounted pressure transducers allowed for the computation of the pressure Auto- and Cross-spectra over the fourth (the payload region) and third stages of the launcher model. Coherence functions are modelled through exponential-like analytical functions following the approaches usually adopted in canonical boundary layer flows, whereas the auto-spectra models are based on polynomial fits. The approach adopted for the achievement of proper non-dimensional quantities as well as the procedure implemented for the full-scale extrapolation is presented and discussed.

This paper presents extended sufficiency results for the local minimality of an extremal of the Bolza problem. These results provide an essential improvement in the state of the art because they are applicable for bang–bang control without requiring the strict Legendre and controllability conditions. Extended sufficient conditions subsume the classic Jacobi conjugate point sufficiency conditions. Necessary conditions of the second order allow to exclude the minimality when sufficiency is not verified. All these results are applicable to space trajectory optimization both in low thrust and in impulsive transfer.

In this manuscript, the authors deeply investigate and test a modern technique that allows the analysis of a structure starting from a photo to identify and locate damage present on it, rapidly and non-destructively without any physical interaction with the analyzed structure. The technique suitability is tested on four statically deformed beams, on which notches represent the defects. The core of the proposed method is the correlation between the curvature that each beam presents under load conditions and its flexural stiffness. The proposed methodology consists in taking a photo of the inflected beam; subsequently, the acquired photo is manipulated with specifically designed image processing tools, and the second derivative of the beam axis is estimated using two distinct numerical differentiator filters (Lanczos filter and Gaussian wavelets) along with suitable processing to reduce border distortions. The tests conducted demonstrate that it is possible, with an opportune static deflection amplitude, to accurately detect the position of the notch with the proposed procedure; a sensitivity analysis is also conducted by testing the procedure with different beam thicknesses, notch positions, and amplitude of the static deflection. Although the authors realize that the technique can generally require sensibly large displacements, the results seem promising.

Re-entry capsules, designed with blunt-body shapes to endure hypersonic air velocities and heat, encounter instability in the low subsonic regime during the final descent phase. Ensuring a controlled descent with the appropriate attitude for deploying deceleration systems becomes paramount. To address this challenge, we employ a cost-effective approach to investigate the dynamic stability of a typical re-entry capsule in free fall. This study involves formulating the aerodynamic model of the system and hypothesizing associated coefficients. A meticulously designed and instrumented prototype is dynamically scaled and subjected to low altitude drop tests to recreate the desired scenario. Subsequently, the data collected during these tests is processed, and stability derivatives are estimated using system identification techniques. Our research contributes to a deeper understanding of the dynamic stability of re-entry capsules during free fall, shedding light on their behavior and providing insights essential for improving their performance and safety during descent.

This paper compares out-of-plane stresses evaluated with Hooke’s Law and the stress recovery technique, focusing on the free edges of composite plates and shells. The Carrera Unified Formulation and the finite element method are adopted to derive the governing equations. Lagrange polynomials are implemented in the equivalent single-layer, layer-wise, and variable kinematics approaches. The latter is used to refine structural models locally and reduce computational overheads. Laminated plates and shells subjected to uniaxial tension are considered. The out-of-plane stresses are compared with references from the existing literature for most cases. The results demonstrate that the stress recovery technique effectively calculates stresses and improves the accuracy of equivalent single-layer models. Furthermore, layer-wise models are needed for accurate results near the free-edge zone. Finally, variable kinematics theories are helpful in accurately detecting local phenomena along the structure’s thickness.

In the past decades, the exponential rise in fossil fuel consumption has led to a pressing need for sustainable energy solutions. This surge in fossil fuel use has not only caused severe environmental repercussions but has also raised questions about our global dependence on such non-renewable resources. Addressing these detrimental effects, NASA has urged the aeronautic industry to reduce aircraft fuel burn by a substantial 70% before 2025. As a result of comprehensive government and industry studies, electric aircraft propulsion has emerged as a pivotal focus of research. This encompasses various architectures, such as full-electric, hybrid electric, and turbo-electric systems. The aim is to significantly diminish the environmental impact of aviation and make it more sustainable for the future of passenger flight. This paper provides an overview of the latest state-of-the-art innovations in propulsion systems. It delves into the operational principles, technological requirements, ongoing research, and development efforts pertaining to all components essential for effecting this transformation in aviation technology. Additionally, the document will showcase existing commercial products, prototypes, and demonstrators to offer a comprehensive picture of the current scenario. Overall, this research is a vital step toward achieving energy sustainability and reducing the environmental footprint of the aviation industry. By exploring and advancing electric aircraft propulsion, humanity can move closer to a cleaner, greener future for air travel.

This article presents a detailed aerodynamic investigation on a transport aircraft with a box-wing lifting system. The aerodynamic development of this configuration is presented through the description of the collaborative and multi-fidelity design approach that took place within PARSIFAL, an European project aiming to develop the box-wing configuration for a civil transonic aircraft. The article starts from an accurate description of the collaborative methodological framework employed and offers an overview of the development of the box-wing aerodynamics together with the highlight on its most significant characteristics and aerodynamic features identified. The design development is detailed step by step, with specific focus on the challenges faced, starting from the conceptual investigations up to the most advanced evaluations. Significant focus is given to the assessment of the aerodynamic performance in transonic flight for the box-wing lifting system, and to the design solutions provided to overcome issues related to this flight regime, such as drag rise and flow separation. In addition, the high-fidelity shape optimisation techniques employed in the advanced stage of the design process are detailed; these allow to define a final configuration with improved aerodynamic performance.