Regioselective Nucleophilic Additions to Diiron Carbonyl Complexes Containing a Bridging Aminocarbyne Ligand: A Synthetic, Crystallographic and DFT Study

Diiron µ-aminocarbyne compounds, 1a–e, are prepared in two steps from Fe2Cp2(CO)4, negating the need for difficult purification procedures of intermediate species; they are efficiently isolated by alumina chromatography. Minor amounts of µ-aminocarbyne aryl isocyanide compounds, 2a–c, are obtained as side products. The structures of the cations in 1a,c,e are calculated using DFT; the carbyne carbon is generally predicted to be the thermodynamic site of hydride addition, in agreement with a previous experimental finding concerning 1a. Accordingly, the reaction of 1e with NaBH4affords a bridging aminocarbene complex, 4, in 85 % yield. Otherwise, the reaction of 1c with NaBH4yields the aminocarbyne–cyclopentadiene derivative 3 (70 %), presumably as a consequence of the steric protection exerted by the xylyl–methyl groups towards the carbyne moiety. The sequential treatment of 1a,c with Li2CuCNMe2and MeSO3CF3affords 5a,b, comprising both aminocarbyne and alkoxycarbene ligands. In accordance with DFT calculations, the alkoxycarbene moiety in 5a is the most favourable site for nucleophilic attack. Thus, the reactions of 5a with NH2R (R = Et, iPr) and NBu4CN, respectively, give the aminocarbyne/aminocarbene complexes, 6a,b, and the aminocarbyne-α-cyanoalkyl 7. All the products are fully characterized by spectroscopic and analytical methods; moreover, the structures of 1a, 1d, 6a and 7 are elucidated by single-crystal X-ray diffraction studies

Wind-Tunnel Tests of a Tilt-Rotor Aircraft

A wide aerodynamic test campaign has been carried out on the tiltrotor aircraft ERICA at the Large Wind Tunnel of Politecnico di Milano by means of a modular 1:8 scale model in order to produce a dataset necessary to better understand the aerodynamic behaviour of the aircraft and to state its definitive design. The target of the tests was the measurement of the aerodynamic forces and moments in several different configurations and different attitudes. The test program included some conditions at very high incidence and sideslip angles that typically belong to the helicoptermode flight envelope and measurements of forces on the tail and on the tilting wings. A large amount of data has been collected that will be very useful to refine the aircraft design. In general the aircraft aerodynamics do not present any critical problems, but further optimisation is still possible. From the viewpoint of drag in the cruise configuration, the sponsons of the landing gear seem to be worth some further design refinement since they are responsible for a 20% drag increase with respect to the pure fuselage configuration. On the contrary, the wing fairing has proved to work well when the aircraft longitudinal axis is aligned with the wind, providing just a slight drag increase. Two other interesting aspects are the quite nonlinear behaviour of the side force for the intermediate sideslip angles as well as the noticeable hysteresis in the moment coefficient at very high incidence angles

Stereo particle image velocimetry set up for measurements in the wake of scaled wind turbines

Stereo particle image velocimetry measurements were carried out in the boundary layer test section of Politecnico di Milano large wind tunnel to survey the wake of a scaled wind turbine model designed and developed by Technische Universität München. The stereo PIV instrumentation was set up to survey the three velocity components on cross-flow planes at different longitudinal locations. The area of investigation covered the entire extent of the wind turbines wake that was scanned by the use of two separate traversing systems for both the laser and the cameras. Such instrumentation set up enabled to gain rapidly high quality results suitable to characterise the behaviour of the flow field in the wake of the scaled wind turbine. This would be very useful for the evaluation of the performance of wind farm control methodologies based on wake redirection and for the validation of CFD tools

Wind-tunnel tests of a heavy-class helicopter optimised for drag reduction

Wind-tunnel tests of a heavy-class helicopter model were carried out to evaluate the effectiveness of several components optimised for drag reduction by computational fluid dynamics analysis. The optimised components included different hub-cap configurations, a fairing for blade attachments and the sponsons. Moreover, the effects of vortex generators positioned on the back ramp were investigated. The optimisation effect was evaluated by comparison of the drag measurements carried out for both the original and the optimised helicopter configurations. The comprehensive experimental campaign involved the use of different measurement techniques. Indeed, pressure measurements and stereo particle image velocimetry surveys were performed to achieve a physical insight about the results of load measurements. The test activity confirms the achievement of an overall reduction of about 6% of the original model drag at cruise attitude

Wind-tunnel measurements of the airflow pattern above the collector of different shielded and unshielded precipitation gauges.

Wind is the first environmental source of precipitation undercatch for catching-type precipitation gauge. This work presents an aerodynamic investigation on different precipitation gauge geometries and on a wind shield by means of wind tunnel tests. Experiments have been jointly performed by University of Genoa, DICCA, and Politecnico di Milano within the Italian project PRIN 20154WX5NA \u201cReconciling precipitation with runoff: the role of understated measurement biases in the modelling of hydrological processes\u201d. The airflow, around precipitation gauges, was measured employing two different experimental techniques: a traversing system equipped with \u201cCobra\u201d multi hole pressure probes and the Particles Image Velocimetry PIV. Cobra probes allow to measure the three components of the local flow velocity in the measuring points, while PIV technique provides two-dimensional velocity fields on the investigated planes. The airflow velocity and direction were investigated for different wind speed values and different precipitation gauge geometries: the \u201cchimney\u201d, the \u201ccylindrical\u201d and the \u201cinverted conical\u201d shapes. The effect of a traditional Single Alter windshield was also assessed on the cylindrical shape. These experiments allow to detect qualitatively and quantitatively the main features of the flow, speed-up and updraft, above the collector which influence the particle trajectories and their collection. Results confirm the dependency of the airflow disturbance on the gauge geometry, especially in terms of maximum local velocity and distribution of the upward and downward components of the vertical velocity. PIV velocity fields and Cobra velocity profiles show the expected attenuation of the flow velocity above a gauge located inside the windshield due to the break of the flow induced by the shield slats. The experimental campaign provided a wide dataset suitable for the validation of numerical Computational Fluid Dynamics simulations. This work is propaedeutic to the quantification of the precipitation undercatch and the elaboration of correction curves to obtain the actual precipitation in windy conditions

A global-local meta-modelling technique for model updating

The finite element model updating procedure of large or complex structures is challenging for engineering practitioners and researchers. Iterative methods, such as genetic algorithms and response surface models, have a high computational burden for these problems. This work introduces an enhanced version of the well-known Efficient Global Optimisation technique to address this issue. The enhanced method, refined Efficient Global Optimisation or rEGO, exploits a two-step refinement and selection technique to expand the global search capability of the original method to a global–local, or hybrid, search capability. rEGO is tested and validated on four optimisation test functions against the original methods and genetic algorithms with different settings. Good results in terms of precision and computational performance are achieved, so an application for model updating is sought. A penalty function for the finite element model updating is identified in residuals of the modified total modal assurance criterion. Finally, rEGO for finite element model updating is implemented on a hybrid, numerical and experimental, case study based on a well-known experimental dataset and on a higher dimension finite element model of a wing spar. Satisfactory results in terms of precision and computational performance are achieved when compared to the original methods and genetic algorithms, needing two orders of magnitude fewer evaluations and achieving comparable results in terms of precision.Engineering and Physical Sciences Research Council (EPSRC): 227762

A Loewner-based system identification and structural health monitoring approach for mechanical systems

Data-driven structural health monitoring (SHM) requires precise estimates of the target system behaviour. In this sense, SHM by means of modal parameters is strictly linked to system identifcation (SI). However, existing frequency-domain SI techniques have several theoretical and practical drawbacks. Tis paper proposes using an input-output system identifcation technique based on rational interpolation, known as the Loewner framework (LF), to estimate the modal properties of mechanical systems. Pioneeringly, the Loewner framework mode shapes and natural frequencies estimated by LF are then applied as damage-sensitive features for damage detection. To assess its capability, the Loewner framework is validated on both numerical and experimental datasets and compared to established system identification techniques. Promising results are achieved in terms of accuracy and reliability.Engineering and Physical Sciences Research Council (EPSRC): 227762

Ground vibration testing of a high aspect ratio wing with revolving clamp

The advancements in the aeronautical industry and research on materials and manufacturing methods in the last 70 years have been shifting the paradigm of wing design to high aspect ratio flexible wings. These wings can show a varying behaviour in different operating conditions, as per the nature of their geometry and materials. This work proposes a case study of a high aspect ratio flexible wing in order to study the effect of operating conditions on its structural properties. To test different operating conditions on the ground, a revolving clamp is designed to attach the specimen to a clamp-on shaker. A clear relationship between the wing’s modal properties, and so structural properties, and the angle the clamp sets is found

Ground vibration testing of a flexible wing: a benchmark and case study

Beam-like flexible structures are of interest in many fields of engineering, particularly aeronautics, where wings are frequently modelled and represented as such. Experimental modal analysis is commonly used to characterise the wing’s dynamical response. However, unlike other flexible structure applications, no benchmark problems involving high-aspect-ratio flexible wings have appeared in the open literature. To address this, this paper reports on ground vibration testing results for a flexible wing and its sub-assembly and parts. The experimental data can be used as a benchmark and are available to the aeronautical and structural dynamics community. Furthermore, non-linearities in the structure, where present, were detected. Tests were performed on the whole wing as well as parts and sub-assembly, providing four specimens. These were excited with random vibration at three different amplitudes from a shaker table. The modal properties of a very flexible high-aspect-ratio wing model, its sub-assembly and parts, were extracted, non-linear behaviour was detected and the experimental data are shared in an open repository

The SSDC Role in the LICIACube Mission: Data Management and the MATISSE Tool

Light Italian Cubesat for Imaging of Asteroids (LICIACube) is an Italian mission managed by the Italian Space Agency (ASI) and part of the NASA Double Asteroid Redirection Test (DART) planetary defense mission. Its main goals are to document the effects of the DART impact on Dimorphos, the secondary member of the (65803) Didymos binary asteroid system, characterizing the shape of the target body and performing dedicated scientific investigations on it. Within this framework, the mission Science Operations Center will be managed by the Space Science Data Center (ASI-SSDC), which will have the responsibility of processing, archiving, and disseminating the data acquired by the two LICIACube onboard cameras. In order to better accomplish this task, SSDC also plans to use and modify its scientific webtool Multi-purpose Advanced Tool for Instruments for the solar system Exploration (MATISSE), making it the primary tool for the LICIACube data analysis, thanks to its advanced capabilities for searching and visualizing data, particularly useful for the irregular shapes common to several small bodies