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  Subjects -> AERONAUTICS AND SPACE FLIGHT (Total: 124 journals)
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CEAS Aeronautical Journal
Journal Prestige (SJR): 0.248
Citation Impact (citeScore): 1
Number of Followers: 29  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1869-5582 - ISSN (Online) 1869-5590
Published by Springer-Verlag Homepage  [2468 journals]
  • A contribution to the investigation of acoustic interferences in aircraft
           distributed propulsion

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      Abstract: Abstract The objective of this work is to better understand the acoustic interferences created by distributed propulsion engines based on an approach that combines RANS simulation results for the aerodynamic prediction and analytical models to calculate acoustics. A multi-propeller configuration without wing is considered for this investigation. The propeller geometry and the operating conditions are realistic for a regional transport airplane. In the first part of the paper, the results obtained by two different and independent prediction methods are compared. One method is well-established and serves as validation for the second, low-order method, which is better suited for design-to-noise applications since it requires less details as input and is computationally faster by several orders of magnitude. The good agreement between both methods, obtained for a single propeller as well as for the distributed propeller configuration, is exploited in the second part of the paper to investigate the role of acoustic interferences. Taking acoustic interferences into account drastically affects the directivity of the tonal emission. Compared to the results obtained by considering the propellers as if they were uncorrelated, the far-field sound pressure levels can be significantly lower at the radiation nodes or amplified up to the theoretical limit of 9 dB calculated for eight propellers. The directivity patterns depend on the relative initial angular positions of the propellers. When these positions are randomly varied according to the uniform probability density distribution model, the mean result (expectation) is the same as if the propellers were considered as uncorrelated. Finally, the results show that the probability that the acoustic level is lower than the mean value is higher than 50% because of the positive skewness of the probability distribution of the resulting pressure amplitude. Even though the propeller–propeller and propeller–wing interactions were not considered, the essence of the findings is expected to remain valid for more complex configurations because those interactions are rotor phase-locked.
      PubDate: 2023-09-20
       
  • Experimental investigation of UAV rotor aeroacoustics and aerodynamics
           with computational cross-validation

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      Abstract: Abstract The study provided a base of comparison of known computational techniques with different fidelity levels for performance and noise prediction of a single, fixed-pitch UAV rotor operating with varying flight parameters. The range of aerodynamic tools included blade element theory, potential flow methods (UPM, RAMSYS), lifting-line method (PUMA) and Navier–Stokes solver (FLOWer). Obtained loading distributions served as input for aeroacoustic codes delivering noise estimation for the blade passing frequency on a plane below the rotor. The resulting forces and noise levels showed satisfactory agreement with experimental data; however, differences in accuracy could be noticed depending on the computational method applied. The wake influence on the results was estimated based on vortex trajectories from simulations and those visible in background-oriented schlieren (BOS) pictures. The analysis of scattering effects showed that influence of ground and rotor platform on aeroacoustic results was observable even for low frequencies.
      PubDate: 2023-09-19
       
  • Conceptual design of a distributed electric anti-torque system for
           enhanced helicopter safety and performance

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      Abstract: Abstract The flexibility offered by distributed electric propulsion (DEP) has triggered in the recent years a variety of new aircraft concepts, showing a way to improve the overall efficiency, capabilities and robustness of the future air vehicles. In comparison, the conventional helicopter tail rotor, with its vulnerable and complex installation, looks like an example of system application ready to take advantage of DEP, both in terms of redundancy and simplification of the flight control chain. This article discusses the conceptual design of a distributed electric anti-torque system, starting from a reference usage spectrum and a theoretical architecture example. The goal is to optimize the key electrical components for steady-state operations and to verify the dynamic behaviour in healthy and degraded conditions. In addition, the resources introduced with the tail rotor electrification are considered to improve the aircraft performance in hot and high conditions. Following an introduction to the safety requirements and the electrical technology state-of-the-art, all the main components are modelled and combined into a single dynamic network. Simulation results from different testing scenarios are then reviewed (in the mechanical, thermal and electrical domain) to show compliance with the minimum acceptance criteria. Finally, the article discusses the advantages and disadvantages of a distributed versus concentrated electrical solution.
      PubDate: 2023-09-14
       
  • Numerical investigation of a Coandă-based fluidic thrust vectoring
           system for subsonic nozzles

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      Abstract: Abstract The numerical investigation of a novel subsonic thrust concept for fluidic thrust vectoring (FTV) of jet engines is the subject of this publication. FTV possibly offers advantages over conventional mechanical thrust vector control such as decreased complexity, mass and maintenance costs. The operating principle of the FTV nozzles under investigation at the Institute of Jet Propulsion is based on the Coandă effect. The applied concept of thrust vectoring uses dedicated secondary flow channels which are mounted in parallel around the nozzle inner cone or the nozzle wall. If required, bleed air, provided by extraction from the engine compressor or from an external source, is injected at a specific nozzle pressure ratio at the nozzle throat \(A_8\) through these secondary ducts, resulting in the redirection of the secondary jet towards the convex Coandă surface. The interaction between the primary mass flow and the secondary jet leads to a redirection of the primary exhaust mass flow of the engine and thus to a vectoring of the exhaust flow. In this paper, the influence of different nozzle geometric parameters and different operating points are investigated within an extensive parametric study applied to a convergent two-dimensional thrust vectoring nozzle using computational fluid dynamics tools. Thrust vector deflection of up to \({20}^{\circ }\) at a maximum secondary to primary mass flow ratio of \(10 \%\) is achieved. Reducing this mass flow rate to \(5 \%\) still yields vectoring angles of up to \({15}^{\circ }\) whereby similar deflection angles compared to conventional mechanical thrust vectoring systems are achievable.
      PubDate: 2023-09-05
       
  • Experimental and numerical analysis of the aerodynamics and vortex
           interactions on multi-swept delta wings

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      Abstract: Abstract The flow field around a generic multi-swept delta wing configuration is investigated under transonic flow conditions, both experimentally and numerically. A special focus is on the analysis of vortex/vortex and vortex/shock interactions at moderate angles of attack. In the present study, the Mach number is varied between \(\textrm{Ma} = {0.50}\) and \(\textrm{Ma} = {1.41}\) and the angle of attack is varied between \(\alpha = 8^\circ\) and \(\alpha = 28^\circ\) . Numerical results are validated using experimental surface pressure data from pressure taps, as well as forces and moments based on strain gauge measurements. For selected cases, velocity field data from particle image velocimetry (PIV) measurements are available as well. Over a broad range of angle of attack and Mach number, strong vortex/vortex interactions, including vortex braiding and vortex merging, occur. The location of vortex merging is moving downstream with increasing angle of attack and increasing Mach number. Additionally, at \(\textrm{Ma} = {0.85}\) , vortex/shock interaction occurs above the wing. For moderate angles of attack, shock-induced vortex breakdown is observed.
      PubDate: 2023-08-26
       
  • High-resolution vibroacoustic characterization of DLR’s Falcon
           2000LX ISTAR aircraft

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      Abstract: Abstract In the framework of CleanSky2’s Airframe project DA9, engine tonal noise is a cooperation between Dassault Aviation and DLR. The project aims to enhance the understanding and mitigation of engine-related tonal noise in the aircraft cabin. The presented work was done to get an in-depth understanding of the vibroacoustic behavior of DLR’s Falcon 2000LX ISTAR aircraft. A two and a half weeks long vibroacoustic ground test was conducted utilizing artificial shaker excitation and operational engine excitation. The responses were measured using a roving grid of accelerometers at more than 1200 positions, meaning a subset of about 250 sensors were installed at every given time and then moved along the fuselage in a predetermined way to get a high-resolution measurement of aircrafts fuselage. The accelerometer data were than processed to show operational deflections shapes and calculate experimental structural intensity vector fields to analyze the energy transfer through the structure for optimized placement of active or passive counter measures. Specifically, the transport of tonal frequencies generated by the engines was analyzed.
      PubDate: 2023-08-24
       
  • Nonlinear system identification of a UAV model with distributed
           aerodynamics and flexible structure

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      Abstract: Abstract This paper presents the nonlinear system identification of a slightly flexible 25 kg fixed-wing UAV in the time-domain using a computationally efficient distributed aerodynamics model and a linear structural dynamics representation. The equations of motion are formed by making use of the free vibration modes of the structure and the mean axes formulation. The structural modes and mode shapes are determined from ground vibration tests. The distributed aerodynamics, accounting for elastic deformations, are modeled using a quasi-steady stability and control derivative approach and by applying strip theory. Initial distributions for the derivatives are obtained from vortex-lattice-method calculations. For matching the model response to the measured response, parameters for scaling the initial derivative distributions are introduced. The flexible model is subsequently identified based on flight test data using the output error method in the time-domain and maximum-likelihood estimation. A good overall identification result is achieved with a close match of the fast aircraft dynamics. Finally, an evaluation is given on the suitability of the identified model for real-time simulation, loads’ estimation, and active load control law design.
      PubDate: 2023-07-25
       
  • Effects of an enhanced fibre–matrix adhesion on the fatigue behaviour of
           composite materials under very high cycle fatigue

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      Abstract: Abstract The fatigue behaviour of two glass fibre-reinforced epoxy composite materials with a cross-ply layup is investigated in the very high cycle fatigue (VHCF) regime with up to \(10^8\) load cycles. In addition to the influence on the fatigue lifetime, different materials can also cause a different damage phenomenology. One reference fibre (OC111A) and one fibre with increased fibre–matrix adhesion (SE2020) are tested. The experimental and numerical investigations show that the damage threshold is shifted to higher loads with increased fibre–matrix adhesion, but the damage mode of delaminations becomes more important.
      PubDate: 2023-07-07
      DOI: 10.1007/s13272-023-00673-y
       
  • A multi-model and multi-objective approach to the design of helicopter
           flight control laws

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      Abstract: Abstract This study addresses the design of a full-authority Attitude Command-Attitude Hold flight control system for the Bo-105 helicopter. A single sixth-order dynamic controller replaces the PID-based arrangement that usually forms the core of rotorcraft flight control systems. The proposed design methodology combines multi-model and multi-objective approaches within the framework of structured \(H_\infty\) software tools. Owing to the multi-model approach, only two sets of gains are sufficient to cover the entire speed range between hover and maximum velocity. In addition, \(\mu\) -analysis tools can be used in conjunction with this approach to improve robustness against parametric uncertainties. Simultaneously, the multi-objective approach facilitates the design process and establishes connections between the tuning parameters and handling qualities. The performance of the resulting flight control system is investigated in this study, and evaluated against the attitude quickness, bandwidth and inter-axis coupling criteria, as defined by ADS-33. The resulting design achieves Level 1 performance in most cases. Besides, the merits and limitations of the proposed methodology are discussed in this paper.
      PubDate: 2023-07-06
      DOI: 10.1007/s13272-023-00675-w
       
  • Robust gain-scheduled autopilot design with anti-windup compensation for a
           guided projectile

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      Abstract: Abstract This article deals with the control design of a dual-spin projectile concept, characterized by highly nonlinear parameter-dependent and coupled dynamics, and subject to uncertainties and actuator saturations. An open-loop nonlinear model stemming from flight mechanics is first developed. It is subsequently linearized and decomposed into a linear parameter-varying system for the roll channel, and a quasi-linear parameter-varying system for the pitch/yaw channels. The obtained models are then used to design gain-scheduled \(\mathcal {H}_\infty\) baseline autopilots, which do not take the saturations into account. As a major contribution of this paper, the saturation nonlinearities are addressed in a second step through anti-windup augmentation. Three anti-windup schemes are proposed, which are evaluated and compared through time-domain simulations and integral quadratic constraints analysis. Finally, complete guided flight scenarios involving a wind disturbance, perturbed launch conditions, or aerodynamic uncertainties, are analyzed by means of nonlinear Monte Carlo simulations to evaluate the improvements brought by the proposed anti-windup compensators.
      PubDate: 2023-07-05
      DOI: 10.1007/s13272-023-00668-9
       
  • Numerical studies on small rotor configurations with validation using
           acoustic wind tunnel data

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      Abstract: Abstract This paper addresses the acoustic and aerodynamic characteristics of small rotor configurations, including the influence of the rotor–rotor interactions. For this purpose, a Rotor/Rotor/Pylon configuration is chosen for both the test and numerical simulations. The wind tunnel experiments on various rotor configuration were performed in DLR’s Acoustic Wind Tunnel Braunschweig (AWB). The experiments involve isolated rotors, and rotors in tandem and coaxial configuration in hover and forward flight. For numerical simulations, an unsteady free wake 3D panel method (UPM) is used to account for aerodynamic non-linear effects associated with the mutual interference among the Rotor/Rotor/Pylon configurations. The effect of the pylon is simulated using potential theory in form of a panelized body. Finally, the sound propagation into the far field is calculated with DLR’s FW–H code APSIM, using UPM blade surface pressure as input. The validation effort is supported by CFD TAU steady simulations on selected hover test cases. The experiments and numerical results indicate that the noise at the blade passing frequency (BPF) and its higher harmonics is the dominant source of the noise for the present rotor selection. The extra subharmonics between two BPFs appearing in the results are caused by the small geometric discrepancy between the blades as well as the motor noise. Broadband noise is also observed in the experiment, but its contribution to the overall sound pressure is very small and can be neglected. The simulation of the acoustic scattering from the rotor support system for the isolated rotor cases indicated an influence about 1–3 dB on the overall sound pressure of the polar microphones. In both the coaxial and the tandem configuration, the acoustic interferences are particularly well visible in the numerical simulations and cause a more complex noise directivity. There is almost no change in time-averaged inflow by applying phase angles. In the coaxial condition, in hover, the phase delay between rotors does not change the maximum noise level. In forward flight, the phase delay can influence the maximum level of the noise radiation. In both coaxial and tandem configuration, the position of the downstream rotor is key for the noise radiation, and therefore, avoiding the interaction with upstream wake can reduce the noise radiation.
      PubDate: 2023-06-30
      DOI: 10.1007/s13272-023-00671-0
       
  • Identifying challenges in maintenance planning for on-demand UAM fleets
           using agent-based simulations

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      Abstract: Abstract The novel aircraft architectures for Urban Air Mobility (UAM), combined with pure on-demand operations, mean a significant change in aircraft operation and maintenance compared to traditional airliners. Future flight missions and related variables such as the aircraft position or utilisation are unknown for on-demand operation. Consequently, existing methods to optimise aircraft assignment and maintenance planning cannot be transferred. This study examines the behaviour of an aircraft fleet in an on-demand UAM transport system regarding the interlinking between operation and maintenance. Initially, a potential maintenance schedule for UAM vehicles is deduced. A transport and maintenance simulation is introduced where aircraft are modelled as agents servicing a simple network. As aircraft reach their maintenance intervals, they transfer to one of the maintenance bases and compete for that resource. Since that competition can result in avoidable waiting times, the maintenance costs are extended by running costs for the bases and opportunity costs for missed revenue during these waiting periods. Opportunity costs are cost drivers. To reduce the waiting times, two operational approaches are examined: Extending the opening hours of the maintenance facilities and checking the aircraft earlier to reduce simultaneous maintenance demand. While an extension of operating hours reduces the overall maintenance costs, the adjustment of tasks is more effective to lower waiting times. Thus, an improved system needs to use a combined approach. That combination results in overall maintenance costs of approximately $ 58 per flight hour of which about seven percent account for the opportunity costs.
      PubDate: 2023-06-27
      DOI: 10.1007/s13272-023-00665-y
       
  • Modelling of aircraft trajectories for emergency landing using kinematoid
           chains

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      Abstract: Abstract Most methods that compute trajectories for un- or low-powered flight operate under simplifying assumptions such as constant curve radii and wind conditions. Likewise, changes of air density with altitude that lead to significant differences between equivalent airspeed (EAS) und true airspeed (TAS) are often not considered. Some approaches are based on Dubins paths, which are introduced in Dubins LE (Am J Math 79: 497, 1957). They combine three sections to form a trajectory, which is the shortest from a given start to an end position (In the original work, the position extended by the heading, is referred to as configuration. Since configuration has a different connotation in our context, we use the term state, which can contain other parameters in addition to the position and the heading, e.g. orientation, configuration of landing flaps, landing gear, etc.). A maximum distant landing spot can be reached this way. Often, the targeted landing spot is closer to the aircraft. If it is approached using a Dubins Path, the excess height must be dealt with. Here, we present a method addressing the problem directly, namely finding a trajectory which reduces the excess height over its entire length. Furthermore, it takes spatial and temporal changes of wind and air density into account. Several conditions influence the final shape of the trajectory. For example, avoidance of obstacles and predefined areas is easily achieved. Our method is motivated by kinematic chains, which are used in robotics and computer animation. We extend and modify this principle by incrementally transferring start and end states of the trajectory, modelled as state vectors, into each other. The resulting intermediate states form ends of chain links. To connect initial and final states through the resulting chain, we solve the inverse kinematic problem known from robotics. We extend it by several conditions, which are derived from the flight mechanical characteristics of the modeled aircraft on the one hand and from the desired properties of the trajectory on the other. Using practical examples, we will show the performance of this method, which we have efficiently implemented on off-the-shelf hardware. The method is suitable for systems that assist in the event of engine failures as well as for modeling planned un- or low-powered flights like continuous descent approaches or return flights of space gliders.
      PubDate: 2023-06-16
      DOI: 10.1007/s13272-023-00667-w
       
  • Rotorcraft source noise characterization via acoustic snapshot array:
           development and evaluation

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      Abstract: Abstract Historical development of acoustic hemispheres has required steady flight of a rotorcraft vehicle across a large linear array of microphones. The US Army, NASA, and Navy recently conducted a rotorcraft acoustics flight test in which multiple “snapshot” microphone arrays were used alongside a traditional linear microphone array. The snapshot arrays allow for a near instantaneous capture of rotorcraft acoustic emission directivities, without the need for steady flight. Development of the snapshot array is contained herein, and an evaluation of effectiveness of the array during adverse weather conditions. The snapshot arrays captured significant variation in acoustic emissions throughout a single run and between multiple runs of similar conditions. Hemispheres were created and modelled in land-use planning software and an investigation of A-weighted Sound Exposure Level (SEL [dBA]) was conducted. Sideline predictions of SEL compared well (within 0.1 dBA) between traditional and snapshot arrays, while centre line locations were less favourable with a difference of 1.6 dBA. A posteriori analysis was conducted and shown that a minimum of 51 microphones is likely necessary for snapshot arrays without requiring modification to land-use planning software. Future refinement is required, including development of a semi-empirical method to interpolate between measurement points, instead of the linear frequency weighting conventionally employed.
      PubDate: 2023-06-16
      DOI: 10.1007/s13272-023-00672-z
       
  • The single flapping rotor: detailed physical explanations

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      Abstract: Abstract A motor-driven helicopter rotor generates a reaction torque. This torque would accelerate the airframe of the helicopter about the yaw axis opposite to the rotor rotation if no measures are taken to compensate it. In the early days of helicopter development, a diversity of measures was considered: Henrich Focke has discussed these different measures. Not well known is a torque compensation measure which is restricted to only one main rotor, thus skipping the tail rotor or any additional rotor as well. This principle is worth looking into the details of the physical mechanism involved. The German scientist Prof. Hans-Georg Küssner of the AVA-Göttingen, Germany (Aerodynamic Research Institute with heads at this time: L. Prandtl and A. Betz) was the first to study the method successfully. He constructed a wind tunnel model and showed that the reaction torque could indeed be completely compensated. The present author has reviewed Küssner’s experimental data and could show that numerical calculations are in good correspondence with the measured results. In the present paper, the details of the method to compensate the reaction torque will be discussed. Corresponding numerical data will be presented taking into account Navier–Stokes calculations on rotor blade sections. Blade element theory will then be applied and combined with the Navier–Stokes data. Calculated forces and moments of a complete four-bladed helicopter rotor will be presented.
      PubDate: 2023-06-15
      DOI: 10.1007/s13272-023-00669-8
       
  • Energy optimal 3D flight path planning for unmanned aerial vehicle in
           urban environments

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      Abstract: Abstract This paper presents a general approach to compute energy optimal flight paths for unmanned aerial vehicle (UAV) in urban environments. To minimize the energy required, the flight path is optimized by exploiting local wind phenomena, i.e., upwind and tailwind areas from the airflow around buildings. A realistic wind field of a model urban environment typical for continental Europe is generated using PALM, a Large Eddy Simulation tool. The calculated wind field feeds into the flight path planning algorithm to minimize the energy required. A specifically tailored A-Star-Algorithm is used to optimize flight trajectories. The approach is demonstrated on a delivery UAV benchmark scenario. Energy optimal flight paths are compared to shortest way trajectories for 12 different scenarios. It is shown that energy can be saved significantly while flying in a city using knowledge of the current wind field.
      PubDate: 2023-06-15
      DOI: 10.1007/s13272-023-00666-x
       
  • Development of a medium/long-haul reference aircraft

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      Abstract: Abstract For the evaluation of future aircraft architectures or novel technologies, a well-understood and sound reference to compare to is essential to prove the impact of intended changes. A reference aircraft serves as a basis for calibration of the aircraft and is used as a starting point for subsequent investigations, sensitivity studies or optimizations. The prime need for such a reference arose from the European Clean-Sky-2 project HLFC-Win (Hybrid Laminar Flow Control—Wing), where no industrial reference data for a conventional aircraft were available. The project investigates a HLFC system integrated into the wing aiming to reduce the wing drag and consequently reducing the fuel consumption. Therefore, this paper presents the D300-XRF1 designed by DLR, which is based on the AIRBUS research aircraft XRF1 (eXternal Research Forum). It is intended to be used as a reference aircraft database representing aircraft for medium- and long-range missions. A variable fidelity multidisciplinary design analysis and optimization (MDAO) aircraft design environment is set up to provide a consistent estimate of the geometry, mass breakdown, propulsion system, aerodynamics and aircraft performance. A conceptual aircraft design tool is utilized in the aircraft design environment to initialize the process, and higher-fidelity modules are used to enhance the results. The presented results describe the overall aircraft characteristics of the D300-XRF1 based on 2010 entry into service technology level and is offered to be used as a reference within the aviation research community, hopefully reducing similar design efforts in other research projects.The aircraft operates at a design cruise Mach number of 0.83, has a design range of 5500 NM and transports a payload of 31.5 t (300 PAX at 105 kg/PAX). The D300-XRF1 serves as a consistent reference aircraft database and provides a holistic overview of the aircraft’s performance that has been presented to and approved by AIRBUS. Therefore, this reference aircraft design can be used for future studies and to assess new technologies on a sophisticated level.
      PubDate: 2023-05-18
      DOI: 10.1007/s13272-023-00662-1
       
  • A stochastic optimization approach for optimal Tail Assignment with
           knowledge-based predictive maintenance

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      Abstract: Abstract Recent developments in the field of data analysis offer enormous potential to derive predictions of future aircraft maintenance necessities from observable aircraft attributes. This procedure is called Predictive Maintenance. The Predictive Maintenance generates considerable business benefits compared to alternatives like reactive or preventive maintenance for various reasons. Nevertheless, recognizing a maintenance necessity is only the first step, since the execution of the maintenance action has to fit into the airlines operational schedule. An essential step to realize financial benefits is to integrate Predictive Maintenance into the airlines optimization processes. To contribute to this task, we expand a well-known Tail Assignment model for the assignment of a potentially heterogeneous fleet of aircraft to a schedule of flights by a number of part failure scenarios. This results in a stochastic mixed integer linear optimization program, for which an optimization algorithm with solution guarantees is developed. This optimization algorithm is based on Benders Decomposition, which is concretized for the Tail Assignment problem and optimized for this task. Using this algorithm, a large proportion of the recovery costs for almost all instances tested is saved. The algorithm solves all instances in a reasonable amount of time. The algorithm uses a state-of-the-art mixed-integer linear solver, implementing a decomposition-based solution procedure for stochastic programs, called the L-shaped method. To demonstrate the potential of the approach, we benchmark our results using four strategies, motivated by commonly used preventive, reactive and passive approaches. Our approach leads to considerable cost savings when compared to each of the four benchmark approaches. The algorithms are tested on a set of instances with up to 80 flights based on a pre-pandemic schedule of a larger German airline. To the best of our knowledge, this article presents the first attempt to implement an exact optimization approach integrating malfunction predictions of the form presented into a Tail Assignment model.
      PubDate: 2023-05-13
      DOI: 10.1007/s13272-023-00663-0
       
  • Permanently updated 3D-model of actual geometries of research environments

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      Abstract: Abstract This report describes the approach to create permanently updated 3D models of research aircraft and laboratory facilities. Therefore, optical metrology scans the research environment in its raw or as-delivered condition. The result is a virtual model of the actual geometry and, in comparison to reference data (e.g. CAD-data), the smallest inaccuracies can be identified and analyzed. The exact position of non-rigid components, like riser ducts, electronics or isolation, can be determined in the models. Further changes to the layout of these facilities are permanently digitized and added to the virtual model of the environment. This can be a new recording of the entire facility or of individual areas that are affected by the changes. The individual, newly recorded models are then integrated into the existing model. This creates an always up-to-date 3D model of the research environment, which is added to its digital twin and can be observed there. In combination with CAD data, future conversion and installation measures are planned in advance and analyzed virtually in relation to the up-to-date geometry and installation space data. In addition, the virtual models of the aircraft cabins can be used to support the lengthy approval and certification process at an early stage.
      PubDate: 2023-05-09
      DOI: 10.1007/s13272-023-00661-2
       
  • Adjoint high-dimensional aircraft shape optimization using a CAD-ROM
           parameterization

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      Abstract: Abstract A gradient-based aeroelastic shape optimization framework making use of a reduced order model to substitute a parameterization based on computer-aided design software is presented. This parameterization concept is not novel in principle, but it is embedded here in a complex high-fidelity optimization process and proven for a high-dimensional design space. The design software is used initially to generate a parametric model of a three-dimensional transport aircraft configuration. To streamline the actual optimization process, the computer-aided design model is replaced with a parametric reduced order model based on proper orthogonal decomposition that is capable of predicting discrete surface displacement fields as a function of the design parameters. During the optimization, surface displacements are computed according to the current design parameters and applied on the baseline shape. In every optimization step, the aircraft's steady-state equilibrium of forces and moments are satisfied by a trimming algorithm and the Reynolds-averaged Navier–Stokes solver TAU is coupled with a linear structural finite-element method model. Gradients are computed analytically using geometric sensitivities provided by the reduced order model and by applying the adjoint method to the flow solver and the mesh deformation tool. The workflow is embedded within FlowSimulator, a multiphysics environment for high performance computing. The optimization process is demonstrated for a high-dimensional wing parameterization with 126 degrees of freedom. The aircraft cruise drag could be significantly reduced by 6% on a series of three continuously refined meshes for the aerodynamic analysis. For an accurate representation of the optimal shape by the computer-aided design software after the optimization, the approximation error introduced by the reduced order modelling approach must be sufficiently small. Therefore, the accuracy of the predictions was analyzed. The results identify the main source of the geometric error and quantify their effect on the drag reduction gained by the optimization. We dedicate this article to the memory of our colleague and friend Arno Ronzheimer, whose devotion to CAD modeling was unsurpassed.
      PubDate: 2023-04-24
      DOI: 10.1007/s13272-023-00660-3
       
 
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