Influence of stiffeners on plate vibration and radiated noise excited by turbulent boundary layers

The influence of stiffeners on plate vibration and noise radiation induced by turbulent boundary layers is investigated by wind tunnel measurements. Plates with and without stiffeners are tested under the flow speed of 60 m/s, 71 m/s and 86 m/s, respectively. The stiffeners are set either perpendicular or parallel to the direction of the free stream. Measured vibration and noise levels are compared with theoretical calculations, where wall pressure cross-spectra are described by the Corcos model. For the plates tested, it is evident that stiffeners perpendicular to the direction of the free stream could increase noise radiation, but have almost no influence on vibration level of plates.     

Noise mitigation action plan of Pisa civil and military airport and its effects on people exposure

The “Galileo Galilei” airport is a civil and military airport quite close to central Pisa. Although the airport brings benefits in terms of tourism and different types of income, the air traffic growth exacerbates the exposition to aircraft noise. This could significantly affect public health. To this day, a small number of studies takes into account the standard indicators of Europe by considering noise emission data for military aircrafts. We estimated the noise impact produced by the airport and we evaluated the related exposed population by using the Integrated Noise Model (INM). The noise power levels of both commercial and military flights have been considered as an input to the model. Predicted levels were validated by means of a noise-monitoring network. A new tracking system (AirNav Radar) that captures Automatic Identification System (AIS) signals emitted by each aircraft has been used to emulate takeoff and landing procedures. This improves the accuracy of the input to the model. We simulated noise maps for present and future scenarios, including those following the application of noise reduction measures. For each situation, we also estimated the exposure of the population and the percentages of highly annoyed and highly sleep disturbed people. We show the utility of AIS data and their specific elaboration to draw up noise abatement measures in order to reduce the noise impact on population and allow the airport development.     

Stress field characteristics of eccentrically loaded aircraft spliced joints

The paper details the stress characteristics in eccentrically loaded aircraft spliced joints. It is shown that the hoop stress (σ_θθ) around each rivet is characterized by two peak values located at θ = (0°, 90°). The magnitude of (σ_θθ) is then reduced to a minimum value between these two peaks. A sharp increase in the axial stress component (σ_xx) along the vertical splice lines occurs in the vicinity of the rivet centerlines followed by a rapid decrease in the areas between the rivets. It is shown that stresses along the first interior rivet row is the most critical. The axial stress (σ_xx) profile along horizontal rivet lines has a “sinusoidal” pattern. It is observed that the transverse stress profile (σ_yy), along the horizontal lines, has different peak and minimum values between the rivets. The magnitude of the peak/minimum values depends upon the line location within the splice region. It is also shown the bending stress component varies significantly and must be accounted for the analysis of the eccentric aircraft joints. Experimental comparisons are made along several lines in the splice region. The numerical model is utilized for analysis of a full frame-bay/splice of aircraft fuselage. The paper provides valuable information that can be utilized by practicing engineers for analysis and design of joints with large number of rivets.     

基于稀疏表示的可见光遥感图像飞机检测算法

为解决当前遥感图像飞机检测方法在复杂背景下准确率低,实现旋转不变困难的问题,结合图像稀疏表示原理,提出一种基于稀疏表示的飞机检测算法.该算法首先利用飞机是刚性目标且具有明显几何外观的特点,构建飞机几何原子库;然后建立飞机轮廓几何逼近的最优化方程,在稀疏表示原理框架下,得到飞机轮廓最优的几何部件组合;最后,以星型结构的部件模型为框架,生成待检测图像的目标显著图并根据显著图定位出飞机.实验结果表明,稀疏表示方法能自适应选取飞机部件,部件数目较少且不易受光照、颜色和复杂背景的影响.与现有算法相比,本文算法准确率达90%以上,检测速度有较大的提高.     

Some results from the investigation of cosmic rays using SSNTD at Dublin

Research based on the use of SSNTD in cosmic ray particle physics continues actively as part of a general research programme at DIAS. The present status of the Ultra Heavy Cosmic Ray Experiment and some recent work on cosmic ray dosimetry are outlined.     

Rotational diffusion of tungstic acid colloids in microgravity as studied by aircraft experiments

 Rotational relaxation times (τ) of anisotropic tungstic acid colloids (3.24 μm in major axis) in aqueous suspension are measured in microgravity (0G), normal gravity (1G) and at 2G. The measurements at 0G and 2G are achieved by parabolic and circular flights, respectively. The limiting slopes of the relaxation curves in the plots of the transmitted light intensity against time are close to zero at 0G irrespective of the flow directions in the flow cell, whereas those at 1G and especially at 2G depend on the flow direction by the convection of the suspension and particle sedimentation. Experimental errors at the τ values at 0G are small compared with those at 1G and 2G, which is ascribed to the lack of movement of impurities in the suspension such as quite small air bubbles, which cannot be recognized with the naked eye, and the convection of the suspension in microgravity. More reliable rotational relaxation times are obtained in microgravity; however, the relaxation times themselves are quite insensitive to gravity. Theτ values observed are larger than those calculated from the particle size, which indicates the important contribution of the electrical double layers formed around the colloidal particles. Received: 22 February 2001 Accepted: 13 June 2001     

Interaction of torsion and lateral bending in aircraft nose landing gear shimmy

In this paper we consider the onset of shimmy oscillations of an aircraft nose landing gear. To this end we develop and study a mathematical model with torsional and lateral bending modes that are coupled through a wheel-mounted elastic tyre. The geometric effects of a positive rake angle are fully incorporated into the resulting five-dimensional ordinary differential equation model. A bifurcation analysis in terms of the forward velocity and the vertical force on the gear reveals routes to different types of shimmy oscillations. In particular, we find regions of stable torsional and stable lateral shimmy oscillations, as well as transient quasiperiodic shimmy where both modes are excited.     

Airport management: taxi planning

The Taxi Planning studies the aircraft routing and scheduling on the airport ground. This is a dynamic problem, which must be updated almost every time that a new aircraft enters or exits the system. Taxi Planning has been modelled using a linear multicommodity flow network model with side constraints and binary variables. The flow capacity constraints are used to represent the conflicts and competence between aircrafts using a given airport capacity. The “Branch and Bound” and “Fix and Relax” methodologies have been used. The computational tests have been run at the Madrid-Barajas airport, using actual data from the airport traffic.     

NMR detection of thermal damage in carbon fiber reinforced epoxy resins

Composite materials of epoxy resins reinforced by carbon fibers are increasingly being used in the construction of aircraft. In these applications, the material may be thermally damaged and weakened by jet blast and accidental fires. The feasibility of using proton NMR relaxation times T1, T1rho, and T2 to detect and quantify the thermal damage is investigated. In conventional spectrometers with homogeneous static magnetic fields, T1rho is readily measured and is found to be well correlated with thermal damage. This suggests that NMR measurements of proton T1rho may be used for non-destructive evaluation of carbon fiber-epoxy composites. Results from T1rho measurements in the inhomogeneous static and RF magnetic fields of an NMR-MOUSE are also discussed.     

Influence of mesoscale urban morphology on the spatial noise attenuation of flyover aircrafts

The influence of urban morphology of low-density built-up areas on spatial noise level attenuation of flyover aircrafts is investigated at a mesoscale. Six urban morphological parameters, including Building Plan Area Fraction, Complete Aspect Ratio, Building Surface Area to Plan Area Ratio, Building Frontal Area Index, Height-to-Width Ratio, and Horizontal Distance of First-row Building to Flight Path, have been selected and developed. Effects of flight altitude and horizontal flight path distance to site, on spatial aircraft noise attenuation, are examined, considering open areas and façades. Twenty sampled sites, each of 250 m * 250 m, are considered. The results show that within 1000 m horizontal distance of flight path to a site, urban morphology plays an important role in open areas, especially for the buildings with high sound absorption façades, where the variance of average noise level attenuation among different sites is about 4.6 dB at 3150 Hz. The effect of flight altitude of 200–400 ft on average noise level attenuation is not significant, within about 2 dB at both 630 Hz and1600 Hz in open areas. Urban morphological parameters influence the noise attenuation more in open areas than that on façades. Spatial noise attenuation of flyover aircrafts is mainly correlated to Building Frontal Area Index and Horizontal Distance of First-row Building to Flight Path.