A compact optimization model for the tail assignment problem

This paper investigates a new model for the so-called Tail Assignment Problem, which consists in assigning a well-identified airplane to each flight leg of a given flight schedule, in order to minimize total cost (cost of operating the flights and possible maintenance costs) while complying with a number of operational constraints. The mathematical programming formulation proposed is compact (i.e., involves a number of $0?1$ decision variables and constraints polynomial in the problem size parameters) and is shown to be of significantly reduced dimension as compared with previously known compact models. Computational experiments on series of realistic problem instances (obtained by random sampling from real-world data set) are reported. It is shown that with the proposed model, current state-of-the art MIP solvers can efficiently solve to exact optimality large instances representing 30-day flight schedules with typically up to 40 airplanes and 1500 flight legs connecting as many as 21 airports. The model also includes the main existing types of maintenance constraints, and extensive computational experiments are reported on problem instances of size typical of practical applications.     

Predicting noise from aircraft operated on the ground

Averaged data for sound levels due to aircraft engine testing out to a distance of 3 km obtained under low wind speed conditions are presented. Predictions of standard analytical approximations are compared with these averaged data. The measured average sound levels are shown to be consistent with the predicted influence of ground effect including impedance discontinuities. There is a noticeable influence of directionality also.     

Noise abatement measures at airports: Contributing factors and mutual dependence

Airports are known to cause noise-related environmental concerns, mostly because significant environmental impact correlated with operation of airports arises from aircraft generated noise. In order to address this concern, many airports have applied a variety of actions that alleviate negative effects of noise i.e. noise abatement measures (NAMs). Although there are similarities between airports applying some of the NAMs, numbers and types of applied measures are quite different among them. This paper focuses on finding statistical evidence to support the hypothesis that there is a significant correlation between applied NAMs and specific characteristics related to airports. To determine the reasons why airports apply NAMs, a logistic regression method was used on the data set for 246 European airports. As predictor variables, five specific characteristics related to airports (number of runways, number of aircraft movements, distance from the city, population of the city it serves, per capita gross domestic product (GDP) of the country an airport is located in), and ten NAMs based on their mutual dependencies were used. The results demonstrate a significant correlation between the applied NAMs and particular airport-related characteristics, but also between NAMs themselves. These findings can be used to determine the likelihood of applying a particular NAM to any airport, based on the characteristics that show a significant correlation with the corresponding NAM.     

The effect of proximity of the landing gear lights on its turbulent wake

A simplified model of a landing gear is tested in a wind tunnel to investigate the effect of the landing light location on the resulting noise generation. Examination of the near-field pressure fluctuations, combined with phase-locked stereoscopic particle imaging velocimetry of the unsteady wake identified two distinct sources of pressure fluctuations. The higher frequency source has a wide frequency band and is situated in the outer regions of the wake near the lights. On the other hand, the lower frequency source is found to be stronger, has a narrower frequency band and is developed further downstream in the wake, closer to the wake centreline. The lower frequency source is observed to be rather robust as it is hardly affected by the location of the landing lights, whereas the higher frequency source becomes weaker as the spacing between the lights is reduced. The effect of a splitter plate positioned downstream of the landing gear strut is also investigated as a means of reducing the lower frequency pressure fluctuations. Although the lower frequency source is considerably weakened by the splitter plate, substantial enhancement of the higher frequency source is observed.     

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.     

Aircrafts’ taxi noise. Sound power level and directivity frequency band results

When noise mapping airports, the main noise sources are take offs and landings. But aircrafts’ taxi noise can also be important, and should be considered, for instance when there are residential buildings near the airport’s terminal.Main prediction tools, like Integrated Noise Model (INM), do not consider taxiing and standard outdoors noise predictions software applications must be used, to model taxi as industrial noise sources.This technical note shows frequency band sound power levels and directivity data for several aircrafts’ classes; so that an acoustic consultant can include taxi for noise mapping an airport.     

The effect of the number of aircraft noise events on sleep quality

BackgroundBoth the WHO and the EC recommend the use of L_night as the primary indicator for sleep disturbance. Still, a key question for noise policy is whether the prediction of sleep quality could be improved by taking the number of events into account in addition to L_night.ObjectivesThe current paper investigates the association between sleep quality and the number of aircraft noise events. The first aim of this study was to investigate whether, for the purpose of predicting sleep quality measured by motility, the nummer of events is adequately represented in L_night for the purpose of predicting sleep quality measured by motility. The second aim was to investigate whether the number of events at a given L_night has an additional predictive value. In addition, it was explored whether the total number of events should be taken into account for the production of sleep quality, or only the number of events exceeding a certain sound pressure level.MethodsThis study is based on data of a field study among 418 people living within a range of 20 km from Amsterdam Airport Schiphol. The data from this study are well suited for this purpose, since for every subject both the number and the exposure level of events are available. Sleep quality was measured by motility, derived from actimeters worn on the wrist, and by self-reported sleep quality scored on a 11-point scale. Mixed linear regression models were built in a stepwise manner to predict sleep quality during a sleep period time.ResultsThe results show that, given a certain equivalent noise level, additional information on the overall number of events does not improve the prediction of sleep quality. However, the number of events above L_Amax of 60 dB was related to an increase in mean motility, indicating lower sleep quality. No effect of number of events was found on self-reported sleep quality.ConclusionsThis study suggests that the number of events is more or less adequately represented in L_night and only the number of high noise level events may have additional effects on sleep quality as measured by motility. This may be viewed as an indication that, in addition to L_night, the number of events with a relatively high L_Amax could be used as a basis for protection against noise-induced sleep disturbance.     

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.