Aerotecnica Missili & Spazio最新文献

Hall effect thruster (HET) is nowadays one of the most used and attractive electric propulsion (EP) technologies for satellite applications because of its relatively high specific impulse, efficiency, high thrust-to-power ratio, simplicity and possibility to down-scale. The increasing demand for a higher lifetime pushes research efforts toward the optimization of these devices. The erosion of the accelerating channel is the main limiting lifetime phenomena. Computational modelling is commonly used to study it. The behaviour of plasma heavy particles, namely neutrals and ions, has been analysed by means of axisymmetric particle-in-cell (PIC) code, developed to be coupled with a module solving fluid equations for electrons (i.e. hybrid approach for plasma). The PIC module has been developed to work with non-Cartesian mesh to consider the variation of wall profile due to erosion. The discharge within the accelerating channel of the SPT-100 thruster was selected as a cornerstone test because of the great availability of numerical and experimental data. The study shows that the code is able to describe accurately densities and velocities of ions and neutrals, reproducing with consistency the physics within the accelerating channel and near-plume of HETs with eroded and non-eroded walls. profile.

Passengers’ safety in unconventional situations, such as those of an emergency landing, has become more and more important due to the increase of air traffic. To improve passengers’ safety, certification authorities have imposed specific crashworthiness requirements in airworthiness regulations as defined in Title 14 of Federal Regulations Code—Part 25 for transport aircraft. Over the years, a series of drop tests were carried out to evaluate the structural performance of the airframe and seats and their effects on the occupants. However, the development of a single test is not only time-consuming but also very expensive. In this context, computer modelling and simulation have become increasingly popular for efficient and quick investigations on aircraft’s dynamic behaviour. This study aims to develop a numerical procedure to assess passengers’ safety during a crash landing and optimize the occupant lumbar load for which the impacts of different seat cushion foams are analysed. The experimental data have been collected as part of the research project, which involved the Department of Industrial Engineering Federico II on a drop test of a full-scale fuselage section equipped with two Anthropomorphic Test Devices (ATDs). The finite element model of the test article is generated through the pre/post-processor LS-PREPOST® and is solved using the non-linear explicit dynamic finite element code LS-DYNA®. The parametric study confirms the importance of choosing the appropriate foam material of the aeronautical seat cushion, as it has been observed that DAX 55 foams resulted in a lumbar load peak reduced by 20.6% with reference to the conventional polyurethane foam.

This work presents the experimental results of launching of Fénix I-2 “Alejandro Pedroza Meléndez” (F2APM), a Mexican manufacture single-stage solid propellant rocket motor from Cabo Tuna Range in Charcas, San Luis Potosí, México. The solid fuel sounding rocket motor was KN-Sorbitol propellant type. The rocket performed its flight at perfect weather and visibility conditions, reaching a maximum altitude of about 6 000 m. Engine and flight trajectory showed very good agreement with the theoretical data measurement obtained from captive-fired experiment. At burnt-out, locked-in resonance increased drag limiting the maximum vertical reach.

Impact testing is a critical activity for many aerospace activities. Data on impacts can be employed to evaluate materials survivability, operations safety, and, if possible, to plan prompt maintenance. A classical impact testing facility usually employs Light-Gas Guns (LGGs) to evaluate the effect of collisions in a controlled laboratory environment. In particular, single stage LGGs are relatively simple in their working principle, as they consist in a pressurized gas reservoir and a barrel with a projectile placed in front of the experiment target. When the shot command is executed, the gas from the reservoir accelerates the projectile through the barrel; in first approximation, its velocity is related to the reservoir pressure, the barrel geometry, and the projectile velocity. In this context, The Malta College of Arts, Science and Technology (MCAST) and the Centre of Studies and Activities for Space CISAS “Giuseppe Colombo” of the University of Padova have started a collaboration to develop a single stage LGG impact facility in Malta. In this paper, the conceptual evaluation and the development of the facility is introduced. First, the potential application of such facility in the framework of Malta aviation market as well as the business opportunities in the emerging space sector are presented. In a second part of this work, the LGG main design drivers are defined and a preliminary evaluation of the achievable projectile velocities is performed.

Recent years have seen an increasing interest towards similitude methods. In fact, the possibility of testing a scaled model, instead of a full-scale prototype, leads to many advantages: financial and time savings, easier experimental setups, etc. However, similitudes have drawbacks, too, mainly due to non-scalable effects and partial similitude, which prevent from an accurate reconstruction of the prototype response. For these reasons, an alternative method which can bypass these limitations is needed. A new method, called VOODOO (Versatile Offset Operator for the Discrete Observation of Objects), is herein proposed: it is based on the definition of a transformation matrix which links the outputs of a given linear systems to those belonging to another system, which may be a scaled model. The responses are acquired on a discrete number of points for both the systems. This work aims at investigating the method’s strengths and limitations of the method. The results show that, although VOODOO exhibits some lack of accuracy in off-design conditions due to the loss of spatial correlation, it is able to overcome some major restrictions that affect all similitude methods.

The prediction of dynamic crushing behavior of aerospace-grade composites is a hard challenge for researchers. At coupons scale, such behavior implies the understanding of the initiation and propagation of the elementary damage mechanisms. Many results of the research confirm that the modulus and strength of composites increases with strain-rate. This paper presents the improvement of the constitutive model UL-Crush by adding dynamic stiffness modulus and strengths. The improved tool uses new approach by updating the stiffness and the strength values depending on strain-rates. In addition, parameter sensitivity investigations were conducted to assess the specific energy absorption capabilities of different material configurations. A new on-axis compression fixture was designed and manufactured to carry out tests of plain weave fabric composites, under quasi-static (QS) and low-velocity compression using MTS Insight 100 loading frame and drop tower CEAST Instron9340 facility. Two types of cross-section geometries were used: flat-plate and Hat-Shape coupons. Four types of triggering mechanism were adopted, including saw teeth, chamfer45°, steeple and corrugated, to ensure a continuous and stable crushing mode of failure. Detailed parameter sensitivity investigations were performed, including dimension scale, stacking sequences, trigger types and strain-rates. It was shown that the crush response is strain-rate dependent, and dynamic load decreases absorbed energy, which is indicative of microstructure disintegrating. Globally, big dimension scale, corrugated trigger, [0/45/45/0]s layup and decreasing strain-rate are the parameters to enhance the energy absorption capability of composite coupons. It has been observed that the improved numerical tool UL-Crush was able to significantly capture most crush mechanisms, reasonably correlate with experiments, and give an accurate dynamic response for crashworthy structures.

Sustainable air transportation requires aerodynamically efficient airplanes. Thus, reduction of drag is of paramount importance. From a pure induced drag perspective, this goal can be achieved by the adoption of nonplanar configurations such as C-Wings, Joined Wings or with other design options such as wingtip devices (winglets). Under the assumption of inviscid flow with wake aligned with the freestream velocity, several winglet designs are investigated and general properties are demonstrated. In particular, under optimal conditions, given a closed simply connected wingtip region bounded by a curve, any winglet design geometrically included in that region will be less efficient than the winglet whose lifting line is represented by the bounding curve. Moreover, closed winglets are characterized by undetermined optimal aerodynamic load but unique and global minimum for the induced drag. Finally the Box Winglet and several variations of it are proposed as effective forms to reduce induced drag.