71 research outputs found
Helicopter Noise Footprint Prediction in Unsteady Maneuvers
No full textThis paper investigates different methodologies for the evaluation of the acoustic disturbance emitted by helicopter’s main rotors during unsteady maneuvers. Nowadays, the simulation of noise emitted by helicopters is of great interest to designers, both for the assessment of the acoustic impact of helicopter flight on communities and for the identification of optimal-noise trajectories. Typically, the numerical predictions consist of the atmospheric propagation of a near-field noise model, extracted from an appropriate database determined through steady-state flight simulations/measurements (quasi-steady approach). In this work, three techniques for maneuvering helicopter noise predictions are compared: one considers a fully unsteady solution process, whereas the others are based on quasi-steady approaches. These methods are based on a three-step solution procedure: first, the main rotor aeroelastic response is evaluated by a nonlinear beam-like rotor blade model coupled with a boundary element method for potential flow aerodynamics; then, the aeroacoustic near field is evaluated through the 1A Farassat formulation; finally, the noise is propagated to the ground by a ray tracing model. Only the main rotor component is examined, although tail rotor contribution might be included as well. The numerical investigation examines the differences among the noise predictions provided by the three techniques, focusing on the assessment of the reliability of the results obtained through the two quasi-steady approaches as compared with those from the fully unsteady aeroacoustic solver.Air Transport & Operation
Modeling stochastic behavior of state variables within the optimization of departure procedures
No full textAerospace Engineerin
Experimental/Numerical Acoustic Correlation of Helicopter Unsteady Manoeuvres
No full textThis paper presents one of the main objective of WP1 of Clean Sky GRC5 MANOEUVRES project, which consists in the correlation of ground noise data measured during flight tests, with numerical predictions obtained by a numerical process aimed at the analysis of the acoustic field emitted by helicopter rotors in arbitrary unsteady manoeuvring flight. Two of the helicopter trajectories analysed by the dedicated GRC5 flight test campaign are considered. Noise measurements obtained by microphones located on the ground at several positions along and aside the ground projection of the vehicle fly-over trajectory are used for correlation. The numerical simulation starts with the aeromechanic identification of the flown trajectory, followed by the corresponding prediction of aerodynamic loads, rotor noise radiation and far field atmospheric propagation.</p
Design of robust terminal procedures: By optimization of arrival and departure trajectories
No full textWith the growth of the air traffic movements and the population of people living around airports, the number of awakenings due to aircraft noise has increased. ICAO has defined four research fields to reduce noise and one of them is implementation of noise abatement operational procedures. This includes different trajectory optimization methods, one of which is rerouting of trajectories around noise sensitive areas. Research has proven that rerouting has a positive effect on reducing the number of people getting disturbed while keeping the fuel consumption as low as possible. Until now these trajectory optimization problems focused on either a departure or an arrival trajectory. When implementing these optimized routes, it may result in a conflict with other existing routes and this is the problem that is the main focus of this research. Within this research trajectories will be combined and optimized for number of awakenings and fuel consumption while assessing the effect of terminal operations. The model that combines trajectories is based on existing models, including a point-mass model and a noise model. These are combined in a multi-objective evolutionary algorithmwhere the objectives are the number of awakenings and the fuel consumption. The results of the optimization problems are presented as Paretooptimal solutions. To contribute to the field of noise abatement terminal operations, two trajectories are combined in an optimization problem. To assure enough distance between the two trajectories the minimum separation constraint is used. When a loss of separation happens, the flight path angle of one of the trajectories is adjusted. The designed model is used to optimize four trajectory optimization problems. The first being a departure trajectory, this is the current Spijkerboor standard instrumental departure that departs from runway 24 at Amsterdam Airport Schiphol. The second problem is the current night standard terminal arrival route starting at sea and landing on runway 18R at Schiphol. For the third optimization problem the two trajectories of the previous optimization problems are combined with keeping the minimumseparation constraint in mind. The final case study was used to focus more on the effect of the minimum separation constraint. From the departure optimization problem can be concluded that there is a big diversity in the vertical and horizontal trajectory between the minimum fuel andminimumawakening solution. For the arrival optimization problem the difference between these two solutions is not significant. The vertical trajectory is for both solutions almost the same, the main difference is caused by the ground trajectory. When combining the trajectories the results of the objective functions for the combined problemare the sum of the arrival and departure objective functions. This results in a bias to the departure trajectory because these numbers are atleast twice the value compared to the arrival trajectory. This also results in the arrival trajectory always being created around the departure trajectory. From the final case study can be concluded that when designing the trajectories the influence of the minimum separation constraint is mostly on the vertical profile of the departure trajectory. Also can be observed that small rerouting of the trajectories sometimes is needed to give both trajectories enough space to cross each other.Aerospace EngineeringControl & OperationsAir Transport and Operation
Organisatiegericht huisvesten
No full textElke organisatie komt vroeg of laat voor de vraag te staan, welke huisvesting het beste past bij de organisatie. Of dit nu is naar aanleiding van een noodzakelijke renovatie van het bestaande gebouw, verhuizing naar een ander gebouw, nieuwbouw, of als onderdeel van de normale bedrijfsvoering. Wat werkt beter: een traditioneel cellenkantoor of een kantoorconcept met gebruik van flexibele werkplekken, al dan niet in een meer open setting? Hoe stemmen we de huisvesting af op het bedrijfsbeleid, de organisatiedoelen, de werkprocessen en wensen van de medewerkers? Kortom: hoe realiseren we een op onze organisatie toegespitste huisvesting? In dit hoofdstuk geven we concreet handen en voeten aan het begrip organisatiegericht huisvesten. Er wordt eerst kort stilgestaan bij het begrip organisatiegericht huisvesten en verwante termen. Vervolgens introduceren we twee tools ter ondersteuning van de planontwikkeling en besluitvorming: een huisvestingkeuze model dat relevante componenten in de besluitvorming op overzichtelijke wijze en procesmatig in de tijd positioneert, en een keuzematrix waarin huisvestingsdoelstellingen gekoppeld worden aan conceptuele keuzes voor de plaats, de lay-out en het gebruik van werkplekken en andere voorzieningen. Deze instrumenten zijn ontwikkeld op basis van literatuurstudie, participatie in huisvestingsprocessen en evaluatieve studies naar gebruik en beleving van verschillende kantooromgevingen (Koppejan, Van der Voordt, Hartjes-Gosselink, 2008).Accepted ManuscriptReal Estate Managemen
Multi-aircraft Trajectory Optimization for Continuous Descent Arrivals
No full textIT is a known fact that aircraft noise and fuel emissions are the most constraining factors for the growth of aviation. Continuous Descent Arrivals (CDAs) provide significant reductions in fuel consumption and noise footprint on the ground, by following idle thrust descent and eliminating low altitude leveling off. However, limitations such as unpredictability of the trajectory and separation management for CDAs prevent wide-spread implementation. The thesis focuses on overcoming some of these limitations. Optimal control theory is used to optimize the descent trajectory of the aircraft by using fuel and time as the performance index. The problem is formulated as amulti-phase optimal control and is solved by using a pseudospectral method. The theory is also the backbone of General Pseudospectral OPtimal Control Software (GPOPS). The main focus of the thesis is to enable multi-aircraft trajectory optimization for CDAs and ensure sufficient separation between all aircraft along the entire trajectory by implementing the separation algorithm. The possibility of using both distance based and the time based separation is explored in detail. It is demonstrated using Amsterdam Schiphol (AMS) airport’s real-time inbound flight data that it is feasible to apply the separation algorithm to separate aircraft along the entire lateral path while still being able to performCDAs during the peak and non-peak periods. All the limitations pertaining to the separation algorithmare analyzed and discussed in detail. By addressing some of these shortcomings, the simulation environment can be improved to bring itmore close to a real-time scenario. Although a lot of other factors have to be considered for a practical wide-spread implementation, success of this method will result in the aircraft trajectory being more predictable to the ground controller, effectively addressing one of the major shortcomings of CDAs. On a more important note, the success of this method will also result in reduced noise footprint and fuel consumption by aircraft, benefiting both the environment and airlines.Aerospace EngineeringControl & Operation
Optimal long-haul Trajectories in a Wind Field
No full textThe long-haul flights of airlines are impacted by the en-route wind fields. Flights on the same route with different directions may have significantly different flight performances. It may benefit to airlines in terms of fuel cost and on-time performance if the optimal long-haul routes are able to plan. However, the wind direction and strength are varying in different regions, at different altitudes and different times. It is difficult to identify the most suitable trajectory in a complex wind field. Consequently, the trajectory optimization problem is proposed. The main goal of this study is to develop an optimization model to identify the near optimal trajectory with minimum consumption for long-haul flights taking into account en-route winds and a set of constraints based on ATC regulations. One of the methods to solve the problem is the genetic algorithm since it is a global search method. For this purpose the software tool NSGA is applied in this study. However, the computational process of NSGA is not very efficient due to the computational loss for infeasible solutions. In order to overcome the computational inefficiency of NSGA, a 2-phase approach is proposed. Phase 1 is to reduce the search scope for Phase 2, while the outcomes of Phase 2 are detailed solutions with the accurate fuel consumption and flight time of the trajectories. Moreover, approaches based on parameterization are introduced to minimize the number of infeasible solutions and the control parameters. The control variables of Phase 1 are the coordinates of waypoints, true airspeeds of segments, distances of vertical segments, and the altitude changing locations. Infeasible solutions may be generated with excess flight distance and/or random terminated locations. In order maintain the feasibility of evaluated solutions, an algorithm is introduced to locate the latitude feasible range of each waypoint. Additionally, approaches based on parameterization are introduced to ensure that the evaluated trajectories terminate at the city pair. By applying these approaches, the number of infeasible solutions due to the excess flight distance and/or random terminated locations is significantly reduced. Although the approaches proposed are able to reduce the number of the control parameters, long computational time is still required to evaluate each solution with a small time or distance step. In order to increase the computational speed, the equivalent wind speed and equivalent weight concepts are proposed in Phase 1. By applying this approach, the distance step is able to increase to a segment distance. The computational efficiency is increased. The outcomes of Phase 2 are detailed solutions. With the involved climbing and descent phases, the number of parameters in Phase 2 is more than the number of parameters in Phase 1. The search scope of Phase 2 is based on the outcomes of Phase 1 to obtain detailed solution within an acceptable computational time. In this study, the forward simulation is applied to ensure the feasibility of the flight altitude. However, the constant landing weight is hardly achieved by applying this algorithm. The transport losses may occur if there is fuel left when the aircraft arrives at the destination. In order to solve this problem, an iterative algorithm is proposed to adjust the initial take-off weight if the final landing weight is not within the expected range. The verification in this study shows that the designed tool is quality and credible. The tool is able to detect the tailwind and headwind in a real wind field. The outcomes of the tool are a little deviated to the optimal solution, but the deviation is acceptable after analysing. In this study, three routes are researched, which are Amsterdam and New York, Amsterdam and Johannesburg, Amsterdam and Singapore. The average saving in terms of flight time and fuel consumption of the optimized solutions are 3.16% and 3.1% respectively compared to the solutions with the great circle path and optimized vertical profile. The results achieved in this study are promising, but enhancements can be made in the some areas. The optimization processes discussed in this study were only performed for one type of aircraft. More aircraft models can be analysed to further prove the performance of the designed tool. The current program assumes a standard atmosphere. As the pressure and temperature are of great influence on both the air density which further impacts the performance of the engine. A more elaborate atmospheric model could be introduced to obtain more accurate solutions. The tool designed in this study is based on Matlab. With more efficient software, the computational time can be dramatically decreased. Additionally, the use of a better equipped computer with multi processers will significantly increase the computational efficiency. In addition, well-designed termination criterions are recommended when there are multi closed local optimal solutions in the search space, which will increase the computational efficiency during the optimization process.Air Transport and OperationsControl & OpeationsAerospace Engineerin
Development of a Multi-Event Trajectory Optimization Tool for Noise-Optimized Approach Route Design
No full textThis paper presents preliminary results from an ongoing research effort towards the development of a multi-event trajectory optimization methodology that allows to synthesize RNAV approach routes that minimize a cumulative measure of noise, taking into account the total noise effect aggregated for all inbound flight movements taking place within an operational year. This new development is an extension of a tool called NOISHHH which was developed earlier for the synthesis of single-event noise abatement RNAV trajectories into and out of airports. Although the presented numerical examples pertain to a specific airport in the Netherlands, viz. Rotterdam the Hague airport, this study focuses on the development of a generic methodology that can be applied to any given airport. Initial application of the adapted optimization framework to the design of noise abatement RNAV approach routes at Rotterdam The Hague airport reveals a significant potential for reducing the number of people highly annoyed due to annual noise exposure relative to the existing situation.Control & OperationsAerospace Engineerin
An Optimal Control Approach to Helicopter Noise and Emissions Abatement Terminal Procedures
No full textCivil aviation plays an irreplaceable role in the current global civilization. Even though the 2008 economic crisis has limited growth in the western world, it can only be expected that due to continuing development in the Far East, South America and Africa this role will increase further over the years to come. Also in the field of helicopter operations continuous growth is predicted, mainly attributed to the growth of the private and corporate transport sectors. To reduce and control the negative impacts of aviation – mainly noise nuisance and pollutant emissions – both in Europe and the United States major research efforts have been initiated with the main objective to provide step changes in the development of environmentally friendly or green aircraft. Although the larger part of the research effort has been focused on the development of new air vehicles, also the development of green operations is being researched, especially with a focus on noise abatement. Researchers have mainly focused on the development of noise abatement departure and arrival procedures for fixed-wing aircraft in an effort to reduce the noise impact in near-airport communities, with promising results. With the current fleet of helicopters the total noise nuisance caused by helicopter operations is significantly smaller than that of fixed-wing aircraft. However, due to their specific types of operations – often flying in close proximity to densely populated areas – individual operations can lead to unacceptable levels of nuisance, which require a specific approach in the development of noise abatement procedures. Therefore, in this research the European Clean Helicopter Optimization (ECHO) software suite has been developed which provides an efficient and sufficiently accurate means to numerically optimize site-specific helicopter approach trajectories, focusing specifically (but not exclusively) on noise mitigation in the surrounding communities. To provide a step change in helicopter optimization frameworks, the ECHO suite has been developed with a strong emphasis on computational efficiency. For this purpose, an advanced optimization methodology based on optimal control theory has been selected. In this method, the infinite-dimensional optimal control problem is discretized, and the time, state and control variables at the discretization point are treated as the variables of a large-scale Non-Linear Programming (NLP) problem. The method – more specifically a direct solution method based on pseudospectral collocation using Radau quadrature – has been chosen as it offers the best trade-off between accuracy and computational efficiency for three main reasons. Firstly, the use of a direct solution method to solve the optimal control problem requires significantly less complex problem setups, and as such results in a more flexible and versatile optimization suite. In addition, the selected methodology allows for a relatively easy imposition of constraints on both the state and control variables, and the use of collocation based on Gaussian quadrature reduces the overall problem size for a given level of accuracy. Finally, the specific use of Radau quadrature has been shown to provide good convergence behavior, specifically in open ended trajectory optimization problems such as considered in this study. To model the free motion of a helicopter an eight Degrees-of-Freedom (DoF) helicopter flight dynamics model with quasi-steady inflow angles for both the main and tail rotor has been integrated in ECHO. The model ensures that the motion of the helicopter is simulated sufficiently accurate, and ensures that the required input parameters to determine the helicopter source noise are directly available. The model has been adapted to simulate operations in non-standard atmospheric conditions including stationary wind fields. In addition, a fuel and gaseous emissions model has been integrated in the flight dynamics model to determine the total fuel burn and total emission of nitrogen oxides based on the required engine power. This allows for the optimization of trajectories with respect to fuel and NOx emissions. Although the model is a generic flight dynamics model, to test the capabilities of the suite a set of parameters representing a Messerschmitt-Bölkow-Blohm (MBB) Bo-105 has been used. These include a set of generic limits and constraints related to passenger comfort and the helicopter's flight envelope. To allow assessment of and hence optimization with respect to the noise impact on the ground, the ECHO suite contains a helicopter noise model consisting of three main components. The first component determines the source noise levels emitted by the helicopter. To model this, a database of source noise levels for different frequencies and different flight conditions is available, projected on a hemisphere centered around the helicopter's main rotor hub. The database has been derived aeroacoustically based on the disc-tilt angles and the advance ratio following from the flight dynamics model. Source noise levels corresponding to the actual flight conditions encountered in the optimization process are found through interpolation between the hemispheres. The second step in determining the noise exposure on the ground is the assessment of the propagation loss between source and receiver. An efficient model to determine the propagation loss was developed specifically for integration in the ECHO suite to comply with the continuity requirements following from the selected optimization methodology and to maintain relatively short execution times. The propagation model uses a geometrical approach to ray-tracing to determine the path of sound rays traveling from the source to the receiver. This approach allows for a significantly lower number of integration steps – and hence shorter runtimes – with sufficient accuracy for the atmospheric conditions considered in this research. The propagation model integrated in ECHO accounts for spreading loss, ground effect and atmospheric absorption, and includes a model to approximate the noise penetrating the shadow zone to ensure continuity in all observer locations and hence in the objective function. The final component of the helicopter noise model determines the total noise impact on the ground in order to allow for the optimization of noise abatement trajectories. A number of generic and site-specific noise impact assessment criteria is available in ECHO to quantify the total noise impact in the area surrounding the trajectory. To exemplify the capabilities of the ECHO suite a number of case studies with increasing complexity and different optimization criteria is presented. The first scenario, a relatively simple two-dimensional approach, shows that in order to minimize the noise Sound Exposure Level (SEL) footprint areas in general flight at low altitude and high airspeeds are preferred. Apart from the relatively low source noise levels at high airspeeds, also the total exposure time is reduced, reducing the SEL values. Furthermore, the presence of shadow zones and the dissipation of sound energy by the ground surface results in lower noise levels astride the helicopter's trajectory when flying at low altitudes. Consequently, SEL contours remain relatively narrow, and hence the generic noise footprint becomes smaller. In the second case study a more complex three-dimensional trajectory is optimized in a densely populated area. In addition, for this scenario the site-specific awakenings criterion was used in the objective function, and different atmospheric and ground surface conditions were assessed. Similar to the conclusions drawn from the first scenario, again low altitude flight at high airspeeds reduce the SEL values on which the awakenings criterion is partly dependent. In addition, the use of a site-specific noise criterion and a three-dimensional flight path allows the helicopter not only to reduce the noise levels astride or below the trajectory, but also to avoid densely populated areas. In the cases where wind from different directions and different strengths were considered, it was found that even though the effect of wind on the total number of awakenings was significant, the effect on the relative improvements to be gained through optimization was small when compared to optimization in standard atmospheric conditions. The effect on the total number of awakenings can be attributed mainly to changes in ground speed on the one hand, and the positioning of the helicopter such that significant parts of the population are inside the shadow zone on the other. In cold atmospheric conditions the atmospheric absorption loss increases, resulting in a generally higher flight profile in order to increase the slant range between source and receiver. The opposite is true in case softer ground surfaces (such as e.g. snow) are modeled. The soft ground surface leads to an increased dissipation of sound energy on the ground, and hence to a larger lateral attenuation leading to a stronger preference for low altitude flight. Finally, the third case study was set up to assess the effect of different site-specific noise optimization criteria on a complex three-dimensional arrival trajectory. The third scenario further supported the findings with respect to noise abatement found in the first two case studies, and additionally showed that the different site-specific criteria do not lead to significant changes in the helicopter trajectory when minimizing the total noise impact. In addition to the main conclusions from the case studies regarding noise abatement, with respect to the efficiency of the ECHO suite – one of the main objectives of the software, the case studies have shown that the suite is capable of optimizing helicopter trajectories with a complex set of constraints imposed with relatively short runtimes, depending highly on the overall problem size and problem complexity. From the development and the analysis of the capabilities of the ECHO suite it can be concluded that the objective of providing an efficient means to optimize helicopter trajectories with respect to different environmental and economic criteria has been met. Although the objectives with respect to total problem runtimes were not met in all cases, further development of the suite has seen a further step change in the overall efficiency, showing the potential to indeed meet the challenging requirements. Although the case studies have shown the potential of the suite, and ECHO meets the accuracy requirements to indeed prove to be a step change with respect to state of the art research, further improvements were identified. Especially the source noise model requires an expansion of the database to allow modeling of flight conditions other than steady forward level or descending flight at different airspeeds. This, in combination with the modeling of noise other than the main rotor would allow for a more accurate assessment of the noise impact for a wider range of flight conditions. Furthermore, the capabilities of the ECHO suite should be assessed for different helicopter classes, and in more realistic case studies, better accounting for all operational constraints encountered in real-world operations. Finally, although the ECHO suite has been developed specifically for the optimization of conventional helicopter trajectories, the flight dynamics, noise modeling and model integration in general could easily be adapted for the optimization of novel helicopter concepts or fixed-wing aircraft trajectories, further extending the research scope of the suite.Air Transport & OperationsAerospace Engineerin
Evaluation of Intermediate Stop Operations in Long-haul Flights
No full textAbstractRecent crises - both economic and geopolitical - and the rise of new competitors in the form of low-cost carriers and Middle East carriers have put a heavy strain on the profitability of traditional legacy airlines worldwide. Many airlines are struggling to survive and are looking for ways to cut their operational costs.Continuously increasing fuel prices further contribute to the financial difficulties, and although airlines (and aircraft manufacturers alike) have put a significant effort on reducing the operational fuel consumption, fuel still accounts for approximately 35% of airlines’ operating expenses. Therefore many airlines seek new ways to further reduce the operational costs through improved fuel efficiency.One of the less self-evident methods to potentially significantly reduce the total operational fuel consumption is the introduction of intermediate refueling stops. Previous studies have already shown that operating existing aircraft on a long-haul flight with one or two intermediate stops can lead to potential fuel savings varying from 5% to 25% by reducing the additional fuel burn on long-haul flights referred to as transport loss. On the other hand, the concept of intermediate stop operations will also affect the operational costs through higher landing fees, an increased required maintenance effort, a longer total flight time and different crew costs. As previous studies have not addressed the additional costs or benefits of intermediate stop operations, this study aims to identify the total potential of the concept.For this purpose, a software tool was developed to analyze individual long-haul origin-destination pairs to identify the optimal operation: either direct or including an intermediate stop. Within the tool crew cost, maintenance cost and local fuel prices are determined for simulated flights according to typical operating procedures. A Dijkstra's algorithm then selects the most suitable and cost-efficient airport from a large database if an intermediate stop proves a viable option for the city-pair.A number of case studies has shown that although in all cases intermediate stops proved beneficial to reduce the total fuel burn, reducing the total operating cost depended highly on city-pair specific conditions, mainly the local fuel prices, changed crew-composition and wind direction. Still, the case studies do indicate that the concept of intermediate stop operations may offer significant cost reductions for many typical long-haul flights across the world, and could prove a viable concept to gain a competitive advantage for specific airlines and routes
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