Expectations for computational fluid dynamics

This article presents a sampling of the author's expectations for the field of computational fluid dynamics (CFD) in the areas of research, development and application. The primary focus of the discussion herein is related to the non-linear transonic flow regime, and more specifically, for calculations about commercial transport aircraft. However, many of these topics are pertinent to all flow field regimes and aircraft designs. The underlying goal is to enable the automation of multi-disciplinary design processes, which utilize state-of-the-art numerical simulation methods. These include issues pertaining to accuracy, robustness, efficiency, ease-of-use, uncertainty requirements and other challenges.     

Electron beam curing — taking good ideas to the manufacturing floor

Acsion is exploiting several emerging electron beam EB applications ranging from composite curing and repair to viscose manufacturing. EB curing of composite structures offers several advantages: significantly reduced curing times; improvements in part quality and performance; reduced environmental and health concerns; improvements in material handling; and reduced overall manufacturing costs compared to thermal curing. The aerospace industry is developing EB technology in all of their market sectors, including military aviation and space products. Some specific products include cryogenic fuel tanks, improved canopy frames for jet aircraft, and the all-composite military aircraft. This paper discusses each of these opportunities.     

Finding the optimal CSP inventory level for multi-echelon system in Air Force using random effects regression model

Determining the optimal inventory level of CSP (concurrent spare parts) is crucial at the time of acquisition of new aircrafts. Most of the existing optimal CSP models do not take into account the time varying characteristics of CSP even though their demand rates are sensitive to such variation. In this paper, we introduce the CSP inventory model using a two stage approach. At the first stage, we use a random effects model to predict the expected demand of CSP in a multi-echelon system consisting of depot and bases based on CSPs varying characteristics with time. At the second stage, we find the optimal inventory level of CSP by using the optimization algorithm with various constraints under limited budget. The study is expected to contribute to the Air Force establishing the optimal national defense procurement policy for CSP of aircrafts.     

Network design: taxi planning

The effect of managing aircraft movements on the airport’s ground is an important tool that can alleviate the delays of flights, specially in peak hours or congested situations. Although some strategic design decisions regarding aeronautical and safety aspects have a main impact on the airport’s topology, there exists a number of other additional factors that must be evaluated according to the on ground operations, i.e. previous to the taking-off or after landing. Among these factors one can consider capacities at waiting points and directions of some corridors. These factors are related to the demand situation of a given period and influence the aircraft’s routing on the ground or short term Taxi Planning problem (or TP-S). While the TP-S problem studies the aircraft routing and scheduling on the airport’s ground under a dynamic point of view, this paper presents a Taxi Planning network design model (or TPND), attending to these additional factors of the airport’s topology and the conflicting movements of the aircraft on them with the same modelling approach used in the TP-S problem. The TPND model is formulated as a binary multicommodity network flow problem with additional side constraints under a multiobjective approach. The side constraints included are the classical limitations due to capacity and also as a distinctive approach, constraints that restrict the interference of aircraft in order to decrease the intervention of human controllers during the operations or increase their safety margins. The multiobjective approach adopted for the TPND model balances conflicting objectives: airport’s throughput, travel times, safety of operations and costs. In the paper computational results are included on two test airports solving the TPND model by “Branch and Bound” showing the effect of the conflicting objectives in the design decisions. Research supported under Research Project TRA-2005-09068-C03-01/MODAL from the “Ministerio de Educación y Ciencia”.     

The effect of visual stimuli on the horribleness of awful sounds

A mass web-based experiment has been carried out to explore people’s perception of horrible sounds. The advantage of a web-based methodology is that it enables hundreds of thousands of judgements to be obtained over a diverse population. As part of the project, the effect of what people saw on the screen on how they rated the sounds was examined. The sounds were auditioned with images that were either associated or unassociated with the sounds. It was found that images often affected how horrible the sound was perceived to be. For example, the image of finger nails on a blackboard made the associated sound more awful. However, in the case of disgusting sounds, such as the sound of someone eating, the images used had no significant effect on voting behaviour. The colour of the website was also varied. The hue of the website was found to be a significant factor, with a red website making the sounds less horrible than a blue/green website. The brightness and saturation of the website also altered people’s perceptions, with the brighter, more saturated website making the most awful sounds, such as the sound of someone vomiting, less horrible.     

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.     

Perceived quality features of aircraft sounds: An analysis of the measurement characteristics of a newly created semantic differential

The increasing air traffic in the past has led to the fact that and more and more people were affected by aircraft noise. Since the potential of reducing noise level of current aircraft will be limited in the future after recent developed techniques have been realized in practice.Therefore, additional efforts are necessary to improve the sound quality of aircraft noise and give hints to aircraft manufactures concerning components that have to be acoustically optimized. The present study describes the development of an item list for a semantic differential (SD) that is appropriate for the determination of different perceptive features of aircraft sound quality and focuses on the estimation of the reliability of this new instrument. The selected 10 SD items have relation to the sound components emitted by the different technical devices of airplane engines.The analyses of the measurement characteristics of the different items were based on G-theory. This method presupposes data possessing interval-scale-level characteristics. Therefore, the used rating scales were examined with respect to this attribute. The results verified that the data fulfill this precondition. The results gave evidence that the judgments show large inter-individual differences. The proportion of variance which can be traced back to the factor “aircraft sound” amounted to at most one-fifth of total variance indicating that the differences between the aircraft sounds are rather small. Nevertheless, the findings demonstrate that it is possible to measure not all but several decisive aspects with sufficient reliability and expense.     

民用飞机多级健康状态评估技术研究

健康状态评估技术是实现飞机派遣决策的关键技术。本文提出了一种民用飞机多级健康状态评估方法,该方法充分利用各类工程数据、技术数据和可靠性分析数据,建立飞机技术派遣量化评估方法,甄选影响飞机技术派遣的主要参数,并通过对各参数进行权重分配,建立综合量化分析模型,针对专机、VIP及其他特殊航线运行要求,精准高效地为飞机的技术派遣提供决策依据,保证特殊运行航班的安全性以及签派可靠度。经某航空公司的试用效果良好,验证了提出的方法的可行性。     

Aircraft noise annoyance modeling: Consideration of noise sensitivity and of different annoying acoustical characteristics

Noise annoyance due to aircraft flyover noise was assessed under laboratory conditions. The main objectives of the study were: (i) to identify influential acoustical features of noise annoyance, (ii) to propose noise indices to characterize these acoustical features and (iii) to enhance annoyance models including influential acoustical and non-acoustical variables. Therefore, a verbalization task was performed by the participants of the experiment to collect their whole impression concerning the aircraft flyover noises for which they rated annoyance. This verbalization task highlights that noise annoyance was influenced by three main acoustical features: (i) the spectral content, (ii) the temporal variation and (iii) the perceived sound intensity. Four combinations of noise indices were used to propose multilevel annoyance models, in combination with the individual noise sensitivity. Noise sensitivity was found to highly contribute to annoyance models and should therefore be considered in future studies dealing with noise annoyance due to aircraft noise. Different combinations of noise indices coupled with noise sensitivity were found to be promising for future studies that aim to enhance current annoyance models.     

Hidden corrosion detection in aircraft aluminum structures using laser ultrasonics and wavelet transform signal analysis

Preliminary results of hidden corrosion detection in aircraft aluminum structures using a noncontact laser based ultrasonic technique are presented. A short laser pulse focused to a line spot is used as a broadband source of ultrasonic guided waves in an aluminum 2024 sample cut from an aircraft structure and prepared with artificially corroded circular areas on its back surface. The out of plane surface displacements produced by the propagating ultrasonic waves were detected with a heterodyne Mach-Zehnder interferometer. Time-frequency analysis of the signals using a continuous wavelet transform allowed the identification of the generated Lamb modes by comparison with the calculated dispersion curves. The presence of back surface corrosion was detected by noting the loss of the S(1) mode near its cutoff frequency. This method is applicable to fast scanning inspection techniques and it is particularly suited for early corrosion detection.