Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract 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. PubDate: 2023-09-17
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract HEMERA is a large research community which operates in the field of tropospheric and stratospheric balloon-borne research. The Hemera project is aimed to improve the technologies related to the balloons and to favour the research on balloons by offering the opportunity to fly scientific experiment to the international community. The project, described in this paper together with its major outcomes, involves major space agencies dealing with balloon infrastructures, companies operating the balloons, companies providing the necessary technologies and scientific experts. PubDate: 2023-09-15
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The relatively recent decision of NASA and ESA to plan new missions to the so-called Ice Giants, namely Uranus and Neptune, has prompted a resurgence of interest in the experimental analysis of the aero-heating environment that probes entering such atmospheres would experience. In the present study, arc-jet facilities, previously used to simulate space flight in the atmospheres of Earth, Mars, and Titan, are considered as a relevant basis for the implementation of a more complex framework adequately accounting for the atmospheric features of the Ice Giants. It is shown that the key to the successful realization of such an endeavor is a new operating mode for the plasma torch (relying on a nitrogen–hydrogen mixture) together with the inclusion of a new gas control unit, a new mixing chamber to generate relevant gas mixtures (mimicking to a sufficient extent the Ice Giants atmosphere) and a new thermo-chemical model of the overall flow process. The outcomes of some initial tests are presented to demonstrate the adequacy and performances of the implemented approach with respect to typical entry conditions related to these two planets. PubDate: 2023-09-15
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract AstroDART is a Python package that implements a pipeline for processing, analyzing, and managing files derived from observations performed by ground-based optical telescopes. The main goal is to develop a software capable of retrieving information about satellites’ tracklets. In between its functionalities the following are included: perform astrometric reduction using Astrometry.net, detect tracklets using contour tracing techniques with ASTRiDE Python Package, refine the detected tracklets and perform telescope calibration by comparing the observations of known objects with catalogue data and obtaining the celestial coordinates of the object at the observation epoch. In addition, it produces the light curve and TDM files derived from the observations. The computation times are in the order of 15 s per image when no astrometric reduction is performed, increased to 50 s when the astrometric reduction and light curve analysis are included. The average residuals for both right ascension and declination are found to be lower than 9 arcsecs for all of the three test campaigns. PubDate: 2023-09-13
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The aviation accident investigation process includes the detailed examination of the aircraft wreckage, as well as the analysis of both primary and secondary elements of the aircraft structure. This requires examination of the wreckage at the accident site, and is followed by additional analysis, often driven by the first results on the field. Therefore, one of the most important tasks of investigators is to determine the sequence of events of the accident. This means that much evidence should be collected to accurately determine the order in which events occurred. With regard to construction materials involved, the interpretation of fracture surfaces can provide very important information. However, metallic and composite structures demonstrate very different behaviors during the operative service, from corrosion and fatigue to fire and combustion resistance. This paper performs a literature review on the identification of failure mode, damage and safety of polymer composite aircraft structures from a point of view that may be useful to aviation safety investigations, with the aim to provide suggestions for future research. PubDate: 2023-08-30
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract In the era of space exploration, the scientific community is strongly focusing on the analysis of hypersonic flows in the presence of shock wave/boundary layer interaction. In these conditions, the flow field presents a complex shock structure due to the interaction of different shock waves with the boundary layer. The strong adverse pressure gradient makes the boundary layer separate, giving rise to a separation bubble. In the reattachment zone, the temperature can reach very high values, inducing thermochemical non-equilibrium effects. This research field is recently achieving more and more relevance in aerospace research, as the analysis of turbulent shock wave/boundary layer interaction so far has been mainly focused on perfect gas flows. In this manuscript, a Reynolds averaged Navier–Stokes (RANS) approach is considered, the shear stress transport (SST) model being coupled with the multitemperature approach proposed by Park to investigate thermochemical non-equilibrium effects in hypersonic turbulent shock wave/boundary layer interaction. The first part of the manuscript is devoted to the validation of the solver, and results for low enthalpy flat plate and compression ramp flows are presented. The numerical results are shown to be in good agreement with numerical solutions and experimental measurements. Afterward, the free stream conditions are modulated to make non-equilibrium relevant and analyze a reacting flow. PubDate: 2023-08-30
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Low-Earth-Orbit (LEO) region congestion is becoming one of the big issues of the modern space era. To avoid the Kessler syndrome, now more than ever it is needed to improve awareness about space traffic, and upgrade the entire monitoring process. Extensive literature is available covering the topics of orbital conjunction filtering techniques and computation of the Minimum Orbital Intersection Distance (MOID). The present paper investigates Funding and/or Conflicts of interests/Conflict of interest. An alternative filtering method exploits the near-circularity of certain orbits (a condition often verified in LEO), to improve conjunction analysis performance. Elliptical orbits are reshaped through an auxiliary deferent model, inspired by C. Ptolemy’s orbital theory, replacing the real motion along conjunction analysis. To recover satellites’ averaged mean orbital elements, CelesTrack LEO catalogue was considered and propagated. Based on averaged parameters, off-centric circular orbits are considered instead of elliptical ones. The resulting deferents (off-centric circles) are not far from osculating orbits due to LEOs low eccentricities, becoming the basis for the conjunction analysis algorithm. The algorithm is conceived as a sequence of pre-filters and a final MOID computation. Performances are inspected through an all-vs-all analysis, taking as reference a combination of Hoots’ and Gronchi’s algorithms. This method achieves good performance as compared with these traditional benchmarks. Adopting this approach could reduce the time needed for a preliminary conjunction inspection during the first phases of the Collision Avoidance (CA) process, especially in LEO, where pre-filtering aims to reduce the number of orbit couples where precise MOID computation is needed. PubDate: 2023-08-21
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract A novel high-order accurate approach to the analysis of beam structures with bulk and thin-walled cross-sections is presented. The approach is based on the use of a variable-order polynomial expansion of the displacement field throughout both the beam cross-section and the length of the beam elements. The corresponding weak formulation is derived using the symmetric Interior Penalty discontinuous Galerkin method, whereby the continuity of the solution at the interface between contiguous elements as well as the application of the boundary conditions is weakly enforced by suitably defined boundary terms. The accuracy and the flexibility of the proposed approach are assessed by modeling slender and short beams with standard square cross-sections and airfoil-shaped thin-walled cross-sections subjected to bending, torsional and aerodynamic loads. The comparison between the obtained numerical results and those available in the literature or computed using a standard finite-element method shows that the present method allows recovering three-dimensional distributions of displacement and stress fields using a significantly reduced number of degrees of freedom. PubDate: 2023-08-18
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The meshing technique represents the capability to discretize the domain of interest, to fit the real physical continuum in the best possible way. The most used approach is the finite-element method (FEM), a numerical method to solve partial differential equations. To overcome the classical issues presented by FEM, other models are investigated. The goal is to allow the problem domain to be discretized by elements represented by arbitrary polygons, which can be concave and convex. Moreover, different polynomial consistency is sought within these methods with the possibility to handle non-conforming discretizations, mainly for local refinement and so on. This work aims to present the new adaptive elements, which are finite elements based on Carrera unified formulation, to demonstrate that all the previous capabilities can be done with these new elements, with easy implementation of the relative model. First, a classical patch test is done to investigate the mesh distortion sensitivity. Then, different study cases are presented with more complex meshes combining very distorted concave and convex elements. PubDate: 2023-08-08
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract This paper presents an application of the functional resonance analysis method (FRAM) to the risk assessment of low-speed legs of a helicopter flight mission. A combination of low forward speed and a specific rate of vertical descent could lead to meet a region of the helicopter’s flight envelope that shall be avoided to prevent the vortex ring state, an aerodynamic phenomenon which could cause uncontrolled high rates of descent. A fully developed vortex ring state (VRS) is characterized by an unstable situation in which the helicopter experiences uncommanded pitch and roll oscillations, with a reduced or no collective authority, and a helicopter descent rate that may approach more than 5000 feet per minute. If the recognition of VRS signs is performed early by the pilot in a condition of sufficient altitude, then the required recovery may be performed. However, some mission legs require to descend close to the ground, as the case of a firefighting mission, in which one of the fundamental task requires to fill a tank with water. This type of mission has been selected as the case study of this paper, and a qualitative risk assessment is performed using FRAM. The model developed using FRAM is systemic, where both accidents and successes are seen to emerge in the system from combinations of normal variability. Moreover, the model is complex and non-linear, providing a complete overview of functions and tasks performed by the whole system and the related couplings. The paper presents the potential events related to the mission selected and provides results in terms of possible safety barriers. PubDate: 2023-08-08
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract This paper addresses the development of an attitude determination and control system (ADCS) for a sounding rocket using thrust vector control (TVC). To design the ADCS, a non-linear 6 degrees-of-freedom (DoF) model for the rocket dynamics and kinematics is deduced and implemented in simulation environment. An optimal attitude controller is designed using the linear quadratic regulator (LQR) with an additional integral action (LQI), and relying on the derived linear, time-varying, state-space representation of the rocket. The controller is tested in the simulation environment, demonstrating satisfactory attitude tracking performance, and robustness to model uncertainties. A navigation system is designed, based on measurements available on-board, to provide accurate real-time estimates on the rocket’s state and on the aerodynamic forces and moments acting on the vehicle. These aerodynamic estimates are used by an adaptive version of the controller that computes the gains in real time after correcting the state-space model. Finally, the ADCS is the result of the integration of the attitude control and navigation systems, with the complete system being implemented and tested in simulation, and demonstrating satisfactory performance. PubDate: 2023-07-08 DOI: 10.1007/s42496-023-00161-w
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Mixed flow compressor stage designs are becoming increasingly popular for use in Micro Gas Turbine (MGT) engines. Due to manufacturing constraints and structural considerations, such compressors typically feature unshrouded impeller designs. A numeric investigation of the effect of impeller-shroud tip clearance on the performance of a MGT mixed flow compressor stage fitted with a crossover diffuser is presented. Three baseline test compressors are designed using an in-house-developed application based on one-dimensional mean line theory. These cover a wide range of design mass flow rates, design speeds, and impeller meridional exit (mixed flow) angles. The performance of each of the test compressors are evaluated at an impeller-shroud tip clearance of 0.1 mm, 0.3 mm, and 0.6 mm. Commercial CFD software is used to verify the performance results of the various test compressor configurations. It is found that an increase in impeller tip clearance negatively impacts both compressor performance (total-to-total pressure ratio and efficiency) and choke margin. Conversely, stall margin increases with an increase in impeller tip clearance. PubDate: 2023-06-24 DOI: 10.1007/s42496-023-00160-x
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The technologies and demonstrators for space exploration (TEDS) Program is an essential part of the Italian Aerospace Research Program (PRORA), for which execution was assigned to the Italian Aerospace Research Centre (CIRA) by the Italian Minister of Research. It was conceived in 2020 as a technology program aimed to mature several technologies, demonstrators, and engineering tools considered enabling for future space exploration and colonization missions. Indeed, Martian colonization and lunar colonization are foreseen to be the next steps in human space exploration, and long-term manned spaceflight and extra-terrestrial planet settlement are the inevitable trends of space technologies and will enhance human knowledge in several scientific fields, leading to better understanding of the wider universe and our place within it. But the robotic and manned exploration, for both short- and long-term missions and, above all, the possible habitation and the future colonization of the Moon, require to overcome numerous critical challenges e.g., protection from radiation and micro-meteorites, energy supply, extraction and recycling of water, food production, and much more. Moreover, the environmental issues that could negatively impact lunar surface missions include temperature fluctuations, triboelectrification, airless conditions, energetic particle exposure, and the lunar regolith dust particles. The present paper gives an overview of the (CIRA) development plan related to the (TEDS) program, focusing on the development of enabling technologies, both actual achievements and future perspectives. PubDate: 2023-06-24 DOI: 10.1007/s42496-023-00159-4
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract This paper presents a novel approach to developing 2D structural theories for composite shells. The proposed approach uses the capabilities of the Carrera Unified Formulation (CUF) in conjunction with the Axiomatic/Asymptotic Method (AAM) to obtain the best theories for given structural layouts. Different structural cases are considered to analyze the influence of factors such as boundary conditions, lamination, and thickness on the accuracy of a model. The parameter chosen to evaluate a model’s performance is based on the Failure Indexes (FI) defined by the Hashin Failure criteria for unidirectional fiber composites. The outcome of this procedure is the Best Theory Diagram (BTD), containing the graphical representation of the highest accuracy as a function of the number of adopted unknowns. The results show the importance of higher-order terms to capture stress fields and the influence of thickness on the definition of the best theories. PubDate: 2023-06-19 DOI: 10.1007/s42496-023-00158-5
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract On August 22, 2014, the first two Full Operational Capacity satellites of the Galileo constellation were launched from Kourou on a Soyuz ST-B rocket. Shortly after the insertion into the final orbit, the on-board telemetry showed the achieved orbit was different from the target highly inclined circular orbit, due to a failure in the Fregat upper stage attitude control system. This anomaly precluded nominal operations in the Galileo constellation, as well as introducing limitations in the use of several of on-board subsystems. A recovery campaign took place in the winter of 2014 to change the two satellites’ trajectories, so to reduce the entity of operative constraints and provide better communication with the ground segment. With no dedicated orbital thruster available, attitude thrusters were used effectively to modify and enhance the orbit and recover from a multi-system failure, making reinsertion in a GNSS constellation possible. This work investigates, by means of a numerical model, the best combination and sequence of maneuvers that could have been implemented in the recovery campaign to satisfy most proposed drivers with the given \(\Delta v\) budget. The results show that different final orbits with the same resonance but lower eccentricity could have been achieved. PubDate: 2023-06-07 DOI: 10.1007/s42496-023-00157-6
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract An extension has been made with the popular Rayleigh–Ritz method by integrating the Lagrangian functional of a nonlinear vibration equation of motion over one period of vibrations to eliminate harmonics from the simplification. A set of successive nonlinear equations of coupled higher order amplitudes of deformation is obtained, and a nonlinear eigenvalue problem is presented for the frequency–amplitude dependence of nonlinear vibrations of successive displacements. The subsequent solutions of vibration frequencies and deformation are actually consistent with other successive approximate methods such as the harmonics balance method. This is an extension of the powerful Rayleigh–Ritz method which has broad applications for approximate solutions for vibration problems in solid mechanics. This extended Rayleigh–Ritz method can now be utilized for the analysis of free and forced nonlinear vibrations of structures as a new technique with significant advantages. PubDate: 2023-03-24 DOI: 10.1007/s42496-023-00153-w
Hybrid journal (It can contain Open Access articles)
