Active control of an aircraft tail subject to harmonic excitation

Vibration of structures is often an undesirable phenomena and should be avoided or controlled. There are two techniques to control the vibration of a system, that is, active and passive control techniques. In this paper, a negative feedback velocity is applied to a dynamical system, which is represented by two coupled second order nonlinear differential equations having both quadratic and cubic nonlinearties. The system describes the vibration of an aircraft tail. The system is subjected to multi-external excitation forces. The method of multiple time scale perturbation is applied to solve the nonlinear differential equations and obtain approximate solutions up to third order of accuracy. The stability of the system is investigated applying frequency response equations. The effects of the different parameters are studied numerically. Various resonance cases are investigated. A comparison is made with the available published work. The English text was polished by Keren Wang.     

Experimental investigation on aircraft dynamic stability parameters

In this paper, the design requirements of an experimental apparatus for the measurement of the direct derivatives on an oscillating aircraft model in a wind tunnel are discussed. The elaboration of the signal output of the force transducer is analysed, according to the direct forced oscillation technique. The distorsions of the primary oscillatory motion were previously evaluated and corrected, adopting an open loop control technique. This algorithm is presented and its reliability is verified. Finally, the behaviour of the experimental stability parameters, adopting different oscillation amplitudes and frequencies, is discussed.

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Sommario Nel presente lavoro vengono analizzate le principali caratteristiche di un sistema per l'esecuzione delle prove di oscillazione forzata in galleria del vento, al fine di valutare le derivate aerodinamiche dirette, secondo i gradi di libertá alla rotazione di un velivolo. Inizialmente l'attenzione viene concentrata sul principio di funzionamento e sull'algoritmo di elaborazione dei segnali estensimetrici. L'analisi procede quindi con lo studio delle caratteristiche cinematiche del sistema di movimentazione e supporto, ed in particolare si discutono lc problematiche connesse con il controllo del moto oscillatorio del modello. Infine, viene discusso l'utilizzo dell'apparecchiatura in oggetto con lo acopo di evidenziare come i parametri di stabilitá rilevati sperimentalmente dipendano daile caratteristiche del moto armonico di forzamento.

     

Deep Learning Methods for Heart Sounds Classification: A Systematic Review

The automated classification of heart sounds plays a significant role in the diagnosis of cardiovascular diseases (CVDs). With the recent introduction of medical big data and artificial intelligence technology, there has been an increased focus on the development of deep learning approaches for heart sound classification. However, despite significant achievements in this field, there are still limitations due to insufficient data, inefficient training, and the unavailability of effective models. With the aim of improving the accuracy of heart sounds classification, an in-depth systematic review and an analysis of existing deep learning methods were performed in the present study, with an emphasis on the convolutional neural network (CNN) and recurrent neural network (RNN) methods developed over the last five years. This paper also discusses the challenges and expected future trends in the application of deep learning to heart sounds classification with the objective of providing an essential reference for further study.     

The physics of birdsong production

Human babies need to learn how to talk. The need of a tutor to achieve acceptable vocalisations is a feature that we share with a few species in the animal kingdom. Among those are Songbirds, which account for nearly half of the known bird species. For that reason, Songbirds have become an ideal animal model to study how a brain reconfigures itself during the process of learning a complex task. In the last few years, neuroscientists have invested important resources in order to unveil the neural architecture involved in birdsong production and learning. Yet, behaviour emerges from the interaction between a nervous system, a peripheral biomechanical architecture and environment, and therefore its study should be just as integrated. In particular, the physical study of the avian vocal organ can help to elucidate which features found in the song of birds are under direct control of specific neural instructions and which emerge from the biomechanics involved in its generation. This work describes recent advances in the study of the physics of birdsong production.     

Influence of chromate, molybdate and tungstate on pit formation in chloride medium

It has been characterized and evaluated the 2024-T351 and 7050-T7451 aluminum alloys pitting corrosion in naturally aerated chloride aqueous solutions containing chromate, molybdate and tungstate. It has been carried out electrochemical and non-electrochemical immersion corrosion tests accompanied by surface metallography analysis using an optical microscopy. Chromate for the two alloys and in molybdate for 7050 has corrosion inhibiting effects, whereas tungstate promotes the pitting corrosion for these alloys. Quantitative surface analysis upon the alloys after immersion has indicated that pits are predominantly conical or quasi-conical and irregular. In general, pits have been wider than deep and the widest have been also the deepest. Despite inhibitor presence, when pits have been nucleated, they grow with the same intensity.     

Design of a Structure Composed of a Plate Strengthened by Equidistant Stiffeners

ABSTRACT

An alternative method to the orthotropic plate analogy for analysis of plates strengthened by longitudinal equidistant stiffeners is introduced and is shown to give accurate results, compared with the finite element method. The alternative method uses the concept of undetermined multipliers. Its capabilities in the study of plates strengthened by stiffeners is demonstrated, and design criteria are obtained.     

Real-time aircraft noise likeness detector

One of the most difficult tasks involved in the process of noise monitoring near airports is related to the automatic detection and classification of aircraft noise events.These tasks can be solved by applying pattern recognition techniques to the audio signal captured by a microphone. But now the problem is caused by the background noise, which is present in real environments.This paper proposes a real-time method for continuously tracking the similarity of the input sound and the aircraft’s sounds. Using these facilities, the monitoring unit will be able to mark aircraft events, or to make measurements only when aircraft sound is louder than background noise.A one-class approach has been applied to this detection-by-classification method.Using the default setup, 93% of the aircraft’s events which held an SNR of 6-8 dB were detected, for 30 different locations with diverse soundscapes.     

A systematic design methodology for generating the optimal repairs of aging aircraft

A design methodology which generates optimal mechanical repairs for aging aircraft is presented. Finite element modeling and analysis is used to evaluate the repairs. The repair problem is formulated as an optimization problem using an energy criterion. Optimal locations for rivet placement are found for many different situations.     

Modelling an advanced ManPAD with dual band detectors and a rosette scanning seeker head

Man Portable Air Defence Systems (ManPADs) have been a favoured anti aircraft weapon since their appearance on the military proliferation scene in the mid 1960s. Since this introduction there has been a ‘cat and mouse’ game of Missile Countermeasures (CMs) and the aircraft protection counter counter measures (CCMs) as missile designers attempt to defeat the aircraft platform protection equipment. Magnesium Teflon Viton (MTV) flares protected the target aircraft until the missile engineers discovered the art of flare rejection using techniques including track memory and track angle bias. These early CCMs relied upon CCM triggering techniques such as the rise rate method which would just sense a sudden increase in target energy and assume that a flare CM had been released by the target aircraft. This was not as reliable as was first thought as aspect changes (bringing another engine into the field of view) or glint from the sun could inadvertently trigger a CCM when not needed. The introduction of dual band detectors in the 1980s saw a major advance in CCM capability allowing comparisons between two distinct IR bands to be made thus allowing the recognition of an MTV flare to occur with minimal false alarms. The development of the rosette scan seeker in the 1980s complemented this advancement allowing the scene in the missile field of view (FOV) to be scanned by a much smaller (1/25) instantaneous FOV (IFOV) with the spectral comparisons being made at each scan point. This took the ManPAD from a basic IR energy detector to a pseudo imaging system capable of analysing individual elements of its overall FOV allowing more complex and robust CCM to be developed. This paper continues the work published in [1] and [2] and describes the method used to model an advanced ManPAD with a rosette scanning seeker head and robust CCMs similar to the Raytheon Stinger RMP.