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Aerospace, Volume 5, Issue 2 (June 2018)

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Editorial

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Open AccessEditorial Aerospace Mission Outcome: Predictive Modeling
Aerospace 2018, 5(2), 56; https://doi.org/10.3390/aerospace5020056 (registering DOI)
Received: 14 May 2018 / Revised: 14 May 2018 / Accepted: 19 May 2018 / Published: 22 May 2018
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(This article belongs to the Special Issue Challenges in Reliability Analysis of Aerospace Electronics)

Research

Jump to: Editorial, Review, Other

Open AccessArticle Influence of Fluid–Thermal–Structural Interaction on Boundary Layer Flow in Rectangular Supersonic Nozzles
Received: 30 December 2017 / Revised: 17 March 2018 / Accepted: 17 March 2018 / Published: 27 March 2018
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Abstract
The aim of this work is to highlight the significance of Fluid–Thermal–Structural Interaction (FTSI) as a diagnosis of existing designs, and as a means of preliminary investigation to ensure the feasibility of new designs before conducting experimental and field tests. The novelty of
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The aim of this work is to highlight the significance of Fluid–Thermal–Structural Interaction (FTSI) as a diagnosis of existing designs, and as a means of preliminary investigation to ensure the feasibility of new designs before conducting experimental and field tests. The novelty of this work lies in the multi-physics simulations, which are, for the first time, performed on rectangular nozzles. An existing experimental supersonic rectangular converging/diverging nozzle geometry is considered for multi-physics 3D simulations. A design that has been improved by eliminating the sharp throat is further investigated to evaluate its structural integrity at design Nozzle Pressure Ratio (NPR 3.67) and off-design (NPR 4.5) conditions. Static structural analysis is performed by unidirectional coupling of pressure loads from steady 3D Computational Fluid Dynamics (CFD) and thermal loads from steady thermal conduction simulations, such that the simulations represent the experimental set up. Structural deformation in the existing design is far less than the boundary layer thickness, because the impact of Shock wave Boundary Layer Interaction (SBLI) is not as severe. FTSI demonstrates that the discharge coefficient of the improved design is 0.99, and its structural integrity remains intact at off-design conditions. This proves the feasibility of the improved design. Although FTSI influence is shown for a nozzle, the approach can be applied to any product design cycle, or as a prelude to building prototypes. Full article
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Open AccessArticle Influence of Nozzle Exit Conditions on the Near-Field Development of High Subsonic and Underexpanded Axisymmetric Jets
Received: 19 February 2018 / Revised: 17 March 2018 / Accepted: 19 March 2018 / Published: 29 March 2018
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Abstract
Detailed knowledge of jet plume development in the near-field (the first 10–15 nozzle exit diameters for a round jet) is important in aero-engine propulsion system design, e.g., for jet noise and plume infrared (IR) signature assessment. Nozzle exit Mach numbers are often high
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Detailed knowledge of jet plume development in the near-field (the first 10–15 nozzle exit diameters for a round jet) is important in aero-engine propulsion system design, e.g., for jet noise and plume infrared (IR) signature assessment. Nozzle exit Mach numbers are often high subsonic but improperly expanded (e.g., shock-containing) plumes also occur; high Reynolds numbers (O (106)) are typical. The near-field is obviously influenced by nozzle exit conditions (velocity/turbulence profiles) so knowledge of exit boundary layer characteristics is desirable. Therefore, an experimental study was carried out to provide detailed data on nozzle inlet and exit conditions and near-field development for convergent round nozzles operated at Nozzle Pressure Ratios (NPRs) corresponding to high subsonic and supersonic (underexpanded) jet plumes. Both pneumatic probe and Laser Doppler Anemometry (LDA) measurements were made. The data revealed that internal nozzle acceleration led to a dramatic reduction in wall boundary layer thickness and a more laminar-like profile shape. The addition of a parallel wall extension to the end of the nozzle allowed the boundary layer to return to a turbulent state, increasing its thickness, and removing vena contracta effects. Differences in nozzle exit boundary layers exerted a noticeable influence but only in the first few diameters of plume development. The addition of the exit extension removed the vena contracta effects of the convergence only design. At underexpanded NPRs, this change to nozzle geometry modified the shock cell pattern and shortened the potential core length of the jet. Full article
(This article belongs to the Special Issue Under-Expanded Jets)
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Open AccessArticle Mechanical and Non-Destructive Study of CFRP Adhesive Bonds Subjected to Pre-Bond Thermal Treatment and De-Icing Fluid Contamination
Received: 27 February 2018 / Revised: 23 March 2018 / Accepted: 28 March 2018 / Published: 2 April 2018
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Abstract
Composite materials are commonly used in many branches of industry. One of the effective methods to join the carbon fibre reinforced polymer (CFRP) parts includes the use of adhesives. There is a search on effective methods for quality assurance of bonded parts. In
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Composite materials are commonly used in many branches of industry. One of the effective methods to join the carbon fibre reinforced polymer (CFRP) parts includes the use of adhesives. There is a search on effective methods for quality assurance of bonded parts. In the research here reported the influence of surface pre-bond modification on the adhesive bonds of CFRP plates has been analyzed. Adherends surface modifications, to include defects affecting the bonding quality, were obtained through surface thermal treatment, surface contamination with de-icing fluid and a combination of both the previously described treatments. Characterization of bonded joints was performed by means of mechanical testing, ultrasounds and electromechanical impedance (EMI) measurements. The study here proposed has also the aim to evaluate the ability of different destructive and non-destructive techniques to assess the quality of the bonds. While mechanical tests were strongly affected by the surface modifications, results obtained ultrasound and EMI test have demonstrate only a limited ability of these techniques to differentiate between the different samples. In fact, ultrasounds did not show any changes in the bondline, due to pre-bond modifications. However, this technique was able to detect delamination in CFRP for one of the samples thermally treated at 280 °C. Electromechanical impedance (EMI) measurements showed similar behavior as mechanical tests for samples thermally treated at 260 °C and 280 °C, and for the sample whose surface modification was made with a combination of thermally and de-icing fluid treatments. Full article
(This article belongs to the Special Issue Selected Papers from IWSHM 2017)
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Open AccessArticle Maintenance Model of Digital Avionics
Received: 20 February 2018 / Revised: 24 March 2018 / Accepted: 29 March 2018 / Published: 2 April 2018
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Abstract
The cost of avionics maintenance is extremely high for modern aircraft. It can be as high as 30% of the aircraft maintenance cost. A great impact on the cost of avionics maintenance is provided by a high level of No Fault Found events
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The cost of avionics maintenance is extremely high for modern aircraft. It can be as high as 30% of the aircraft maintenance cost. A great impact on the cost of avionics maintenance is provided by a high level of No Fault Found events (NFF). Intermittent faults are the leading cause of the NFF appearance in avionics. The NFF rate for avionics systems is between 20% and 50%. The practice of avionics operation and maintenance confirms the relevance of assessing the impact of intermittent faults on the maintenance cost and the choice of such option of the maintenance management, in which the negative impact of the intermittent faults is minimized. In this paper, a new mathematical model of digital avionics maintenance is developed. Key maintenance effectiveness indicators are selected. General mathematical expressions are obtained for the average availability, mean time between unscheduled removals (MTBUR), and expected maintenance cost of single unit and redundant avionics systems, which are subject to permanent failures and intermittent faults. The dependence of the maintenance effectiveness indicators on the rate of permanent failures and intermittent faults is investigated for the case of exponential distribution of time to failures and faults. The dependence of average availability on the number of spare units in the airline’s warehouse is also analyzed. On the base of the proposed maintenance model, different options of avionics maintenance management are considered. Numerical examples illustrate how to reduce the expected maintenance cost of avionics systems. Full article
(This article belongs to the Special Issue Challenges in Reliability Analysis of Aerospace Electronics)
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Open AccessArticle Transducer Placement Option of Lamb Wave SHM System for Hotspot Damage Monitoring
Received: 27 February 2018 / Revised: 24 March 2018 / Accepted: 28 March 2018 / Published: 4 April 2018
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Abstract
In this paper, we investigated transducer placement strategies for detecting cracks in primary aircraft structures using ultrasonic Structural Health Monitoring (SHM). The approach developed is for an expected damage location based on fracture mechanics, for example fatigue crack growth in a high stress
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In this paper, we investigated transducer placement strategies for detecting cracks in primary aircraft structures using ultrasonic Structural Health Monitoring (SHM). The approach developed is for an expected damage location based on fracture mechanics, for example fatigue crack growth in a high stress location. To assess the performance of the developed approach, finite-element (FE) modelling of a damage-tolerant aluminum fuselage has been performed by introducing an artificial crack at a rivet hole into the structural FE model and assessing its influence on the Lamb wave propagation, compared to a baseline measurement simulation. The efficient practical sensor position was determined from the largest change in area that is covered by reflected and missing wave scatter using an additive color model. Blob detection algorithms were employed to determine the boundaries of this area and to calculate the blob centroid. To demonstrate that the technique can be generalized, the results from different crack lengths and from tilted crack are also presented. Full article
(This article belongs to the Special Issue Selected Papers from IWSHM 2017)
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Open AccessArticle Damage Detection in a Composite T-Joint Using Guided Lamb Waves
Received: 22 February 2018 / Revised: 3 April 2018 / Accepted: 5 April 2018 / Published: 9 April 2018
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Abstract
Low velocity impact induces barely visible damage in the form of matrix cracking or delamination that can grow under hydro-thermo-mechanical loading and possibly lead to catastrophic failure if not detected at an early stage. A network of piezoelectric transducers can be used to
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Low velocity impact induces barely visible damage in the form of matrix cracking or delamination that can grow under hydro-thermo-mechanical loading and possibly lead to catastrophic failure if not detected at an early stage. A network of piezoelectric transducers can be used to monitor a structure over time for life prognosis through generation and sensing of guided ultrasonic waves. The aim of this study is to design and develop such a sensing method for damage assessment in a composite T-joint subjected to mechanical impacts. In this context, monitoring of Lamb waves in a carbon fibre reinforced polymer (CFRP) T-joint has been completed where dispersion and tuning curves have been obtained. Guided waves are transmitted into the structure through different specified pairs of surface-bonded lead-zirconate-titanate (PZT) transducers in a pitch–catch active structural health monitoring (SHM) approach. With these experiments, Lamb wave fundamental modes (A0 and S0) are identified for monitoring impact damage by signal comparison with a prior obtained baseline. Detecting 4J and 10J inner impacts within the central region of the specimen is challenging when using conventional non-destructive techniques (NDT) because of the complex geometry and interference with the web. Signals are compared for the same selected sensing path; and amplitude differences have been observed in tuning curves after the 10J impact, which implies the occurrence of a structural change related to the impact. Full article
(This article belongs to the Special Issue Selected Papers from IWSHM 2017)
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Open AccessArticle AEROM: NASA’s Unsteady Aerodynamic and Aeroelastic Reduced-Order Modeling Software
Received: 3 November 2017 / Revised: 8 March 2018 / Accepted: 6 April 2018 / Published: 10 April 2018
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Abstract
The origins, development, implementation, and application of AEROM, NASA’s patented reduced-order modeling (ROM) software, are presented. Using the NASA FUN3D computational fluid dynamic (CFD) code, full and ROM aeroelastic solutions are computed at several Mach numbers and presented in the form of root
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The origins, development, implementation, and application of AEROM, NASA’s patented reduced-order modeling (ROM) software, are presented. Using the NASA FUN3D computational fluid dynamic (CFD) code, full and ROM aeroelastic solutions are computed at several Mach numbers and presented in the form of root locus plots. The use of root locus plots will help reveal the aeroelastic root migrations with increasing dynamic pressure. The method and software have been applied successfully to several configurations including the Lockheed-Martin N+2 supersonic configuration and the Royal Institute of Technology (KTH, Sweden) generic wind-tunnel model, among others. The software has been released to various organizations with applications that include CFD-based aeroelastic analyses and the rapid modeling of high-fidelity dynamic stability derivatives. We present recent results obtained from the application of the method to the AGARD 445.6 wing that reveal several interesting insights. Full article
(This article belongs to the Special Issue Computational Aerodynamic Modeling of Aerospace Vehicles)
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Open AccessArticle Flight Load Assessment for Light Aircraft Landing Trajectories in Windy Atmosphere and Near Wind Farms
Received: 16 February 2018 / Revised: 4 April 2018 / Accepted: 5 April 2018 / Published: 10 April 2018
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Abstract
This work focuses on the wake encounter problem occurring when a light, or very light, aircraft flies through or nearby a wind turbine wake. The dependency of the aircraft normal load factor on the distance from the turbine rotor in various flight and
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This work focuses on the wake encounter problem occurring when a light, or very light, aircraft flies through or nearby a wind turbine wake. The dependency of the aircraft normal load factor on the distance from the turbine rotor in various flight and environmental conditions is quantified. For this research, a framework of software applications has been developed for generating and controlling a population of flight simulation scenarios in presence of assigned wind and turbulence fields. The JSBSim flight dynamics model makes use of several autopilot systems for simulating a realistic pilot behavior during navigation. The wind distribution, calculated with OpenFOAM, is a separate input for the dynamic model and is considered frozen during each flight simulation. The aircraft normal load factor during wake encounters is monitored at different distances from the rotor, aircraft speeds, rates of descent and crossing angles. Based on these figures, some preliminary guidelines and recommendations on safe encounter distances are provided for general aviation aircraft, with considerations on pilot comfort and flight safety. These are needed, for instance, when an accident risk assessment study is required for flight in proximity of aeolic parks. A link to the GitHub code repository is provided. Full article
(This article belongs to the collection Feature Papers in Aerospace)
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Open AccessArticle Simulation and Modeling of Rigid Aircraft Aerodynamic Responses to Arbitrary Gust Distributions
Received: 19 March 2018 / Revised: 9 April 2018 / Accepted: 14 April 2018 / Published: 18 April 2018
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Abstract
The stresses resulting from wind gusts can exceed the limit value and may cause large-scale structural deformation or even failure. All certified airplanes should therefore withstand the increased loads from gusts of considerable intensity. A large factor of safety will make the structure
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The stresses resulting from wind gusts can exceed the limit value and may cause large-scale structural deformation or even failure. All certified airplanes should therefore withstand the increased loads from gusts of considerable intensity. A large factor of safety will make the structure heavy and less economical. Thus, the need for accurate prediction of aerodynamic gust responses is motivated by both safety and economic concerns. This article presents the efforts to simulate and model air vehicle aerodynamic responses to various gust profiles. The computational methods developed and the research outcome will play an important role in the airplane’s structural design and certification. Cobalt is used as the flow solver to simulate aerodynamic responses to wind gusts. The code has a user-defined boundary condition capability that was tested for the first time in the present study to model any gust profile (intensity, direction, and duration) on any arbitrary configuration. Gust profiles considered include sharp edge, one minus cosine, a ramp, and a 1-cosine using tabulated data consisting of gust intensity values at discrete time instants. Test cases considered are a flat plate, a two-dimensional NACA0012 airfoil, and the high Reynolds number aero-structural dynamics (HIRENASD) configuration, which resembles a typical large passenger transport aircraft. Test cases are assumed to be rigid, and only longitudinal gust profiles are considered, though the developed codes can model any gust angle. Time-accurate simulation results show the aerodynamic responses to different gust profiles including transient solutions. Simulation results show that sharp edge responses of the flat plate agree well with the Küssner approximate function, but trends of other test cases do not match because of the thin airfoil assumptions made to derive the analytical function. Reduced order aerodynamic models are then created from the convolution integral of gust amplitude and the time-accurate responses to sharp-edge gusts. Convolution models are next used to predict aerodynamic responses to arbitrary gust profiles without the need of running time-accurate simulations for every gust shape. The results show very good agreement between developed models and simulation data. Full article
(This article belongs to the Special Issue Computational Aerodynamic Modeling of Aerospace Vehicles)
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Open AccessArticle Simulation-Based Virtual Cycle for Multi-Level Airport Analysis
Received: 11 February 2018 / Revised: 15 April 2018 / Accepted: 16 April 2018 / Published: 19 April 2018
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Abstract
The aeronautical industry is expanding after a period of economic turmoil. For this reason, a growing number of airports are facing capacity problems that can sometimes only be resolved by expanding infrastructure, with the inherent risks that such decisions create. In order to
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The aeronautical industry is expanding after a period of economic turmoil. For this reason, a growing number of airports are facing capacity problems that can sometimes only be resolved by expanding infrastructure, with the inherent risks that such decisions create. In order to deal with uncertainty at different levels, it is necessary to have relevant tools during an expansion project or during the planning phases of new infrastructure. This article presents a methodology that combines simulation approaches with different description levels that complement each other when applied to the development of a new airport. The methodology is illustrated with an example that uses two models for an expansion project of an airport in The Netherlands. One model focuses on the operation of the airport from a high-level position, while the second focuses on other technical aspects of the operation that challenge the feasibility of the proposed configuration of the apron. The results show that by applying the methodology, analytical power is enhanced and the risk of making the wrong decisions is reduced. We identified the limitations that the future facility will have and the impact of the physical characteristics of the traffic that will operate in the airport. The methodology can be used for tackling different problems and studying particular performance indicators to help decision-makers take more informed decisions. Full article
(This article belongs to the collection Air Transportation—Operations and Management)
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Open AccessArticle Uncertainty Evaluation in the Design of Structural Health Monitoring Systems for Damage Detection
Received: 28 February 2018 / Revised: 13 April 2018 / Accepted: 17 April 2018 / Published: 21 April 2018
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Abstract
The validation of structural health monitoring (SHM) systems for aircraft is complicated by the extent and number of factors that the SHM system must demonstrate for robust performance. Therefore, a time- and cost-efficient method for examining all of the sensitive factors must be
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The validation of structural health monitoring (SHM) systems for aircraft is complicated by the extent and number of factors that the SHM system must demonstrate for robust performance. Therefore, a time- and cost-efficient method for examining all of the sensitive factors must be conducted. In this paper, we demonstrate the utility of using the simulation modeling environment to determine the SHM sensitive factors that must be considered for subsequent experiments, in order to enable the SHM validation. We demonstrate this concept by examining the effect of SHM system configuration and flaw characteristics on the response of a signal from a known piezoelectric wafer active sensor (PWAS) in an aluminum plate, using simulation models of a particular hot spot. We derive the signal responses mathematically and through the statistical design of experiments, we determine the significant factors that affect the damage indices that are computed from the signal, using only half the number of runs that are normally required. We determine that the transmitter angle is the largest source of variation for the damage indices that are considered, followed by signal frequency and transmitter distance to the hot spot. These results demonstrate that the use of efficient statistical design and simulation may enable a cost- and time-efficient sequential approach to quantifying sensitive SHM factors and system validation. Full article
(This article belongs to the Special Issue Selected Papers from IWSHM 2017)
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Open AccessArticle The Public Safety Zones around Small and Medium Airports
Received: 27 March 2018 / Revised: 16 April 2018 / Accepted: 20 April 2018 / Published: 23 April 2018
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Abstract
Proper planning around airports safeguards the surrounding territory from risks of air accidents. Many countries have defined Public Safety Zones (PSZs) beyond the runway thresholds as a result of targeted risk assessment methods. Therefore, national aviation Authorities could limit building construction and industrial
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Proper planning around airports safeguards the surrounding territory from risks of air accidents. Many countries have defined Public Safety Zones (PSZs) beyond the runway thresholds as a result of targeted risk assessment methods. Therefore, national aviation Authorities could limit building construction and industrial development in order to contain the risk for dwellers to be involved in aircraft accidents. The number of people who live, work or congregate in these areas should be limited. The procedure to set Public Safety Zones is based on advanced technical analyses for major infrastructures. For smaller airports, simplified schemes are used, but, sometimes, they are not as effective when considering the actual safety conditions. This article aims to identify the shape and size of the Public Safety Zones for small and medium one-runway airports. The influence of the volume and mix of traffic on the PSZ geometry has been evaluated using the program named SARA (Sapienza Airport Risk Analysis); the results are correlated with the current Risk Plans generally adopted in Italy. According to the air traffic, the Risk Plans are characterized by a dynamic definition and fit the results obtained from risk assessment. Full article
(This article belongs to the collection Air Transportation—Operations and Management)
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Open AccessArticle Interfacing Sail Modules for Use with “Space Tugs”
Received: 28 February 2018 / Revised: 20 April 2018 / Accepted: 21 April 2018 / Published: 1 May 2018
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Abstract
The paper introduces and describes the recent and still ongoing development activities performed in Luxembourg for In-Orbit Attach Mechanisms for (Drag) Sails Modules to be operated from Space Tugs. After some preparatory work aiming at understanding the possible operational aspects and implications
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The paper introduces and describes the recent and still ongoing development activities performed in Luxembourg for In-Orbit Attach Mechanisms for (Drag) Sails Modules to be operated from Space Tugs. After some preparatory work aiming at understanding the possible operational aspects and implications of mating interfaces between these space systems, three possible designs of In-Orbit Attach Mechanisms have been proposed and completed for their 3D (Metal and Plastic) Printing, a new manufacturing technology assessed within this project. The Plastic-printed prototype underwent a series of automated tests in which a robotic arm, equipped with an advanced force sensor, replicated four docking scenarii in ideal and degraded modes. The observation of the forces and torque behaviors at and after impact allowed one to characterize the typical patterns for the various contacts but also, to identify a type of potentially dramatic impact for the safety of the docking and its equipment: in the case of the off-axis approach, “point” contacts shall be avoided, as they instantaneously transfer the total kinetic energy in a small area that could break. Full article
(This article belongs to the Special Issue Space Debris: Impact and Remediation)
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Open AccessArticle Energy-Dynamics Resulting in Turbulent and Acoustic Phenomena in an Underexpanded Jet
Received: 11 April 2018 / Revised: 23 April 2018 / Accepted: 25 April 2018 / Published: 1 May 2018
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Abstract
Underexpanded jets exhibit interactions between turbulent shear layers and shock-cell trains that yield complex phenomena that are absent in the more commonly studied perfectly expanded jets. We quantitatively analyze these mechanisms by considering the interplay between hydrodynamic (turbulence) and acoustic modes, using a
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Underexpanded jets exhibit interactions between turbulent shear layers and shock-cell trains that yield complex phenomena that are absent in the more commonly studied perfectly expanded jets. We quantitatively analyze these mechanisms by considering the interplay between hydrodynamic (turbulence) and acoustic modes, using a validated large-eddy simulation. Using momentum potential theory (MPT) to achieve energy segregation, the following observations are made. The sharp gradients in fluctuations introduced by the shock-cell structure are captured mostly in the hydrodynamic mode, whose amplitude is an order of magnitude larger than the acoustic mode. The acoustic mode has a relatively smoother distribution, exhibiting a compact wavepacket form. Proper orthogonal decomposition (POD) identifies the third-to-sixth cells as the most dynamic structures. The imprint of shock cells is discernible in the nearfield of the acoustic mode, primarily along the sideline direction. Energy interactions that feed the acoustic mode remain compact in nature, facilitating a simple propagation technique for farfield noise prediction. The farfield sound spectra show peak directivity at 30 to the downstream axis. The POD modes of the acoustic component also identify two main energetic components in the wavepacket: one representative of the periodic internal structure and the other of intermittent downstream lobes. The latter component occurs at exactly the same frequency as, and displays high correlation with, the farfield peak noise spectra, making the acoustic mode a better predictor of the dynamics than velocity fluctuations. Full article
(This article belongs to the Special Issue Under-Expanded Jets)
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Open AccessArticle Single-Sensor Acoustic Emission Source Localization in Plate-Like Structures Using Deep Learning
Received: 27 March 2018 / Revised: 19 April 2018 / Accepted: 19 April 2018 / Published: 1 May 2018
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Abstract
This paper introduces two deep learning approaches to localize acoustic emissions (AE) sources within metallic plates with geometric features, such as rivet-connected stiffeners. In particular, a stack of autoencoders and a convolutional neural network are used. The idea is to leverage the reflection
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This paper introduces two deep learning approaches to localize acoustic emissions (AE) sources within metallic plates with geometric features, such as rivet-connected stiffeners. In particular, a stack of autoencoders and a convolutional neural network are used. The idea is to leverage the reflection and reverberation patterns of AE waveforms as well as their dispersive and multimodal characteristics to localize their sources with only one sensor. Specifically, this paper divides the structure into multiple zones and finds the zone in which each source occurs. To train, validate, and test the deep learning networks, fatigue cracks were experimentally simulated by Hsu–Nielsen pencil lead break tests. The pencil lead breaks were carried out on the surface and at the edges of the plate. The results show that both deep learning networks can learn to map AE signals to their sources. These results demonstrate that the reverberation patterns of AE sources contain pertinent information to the location of their sources. Full article
(This article belongs to the Special Issue Selected Papers from IWSHM 2017)
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Open AccessArticle Prediction of Heat Transfer in a Jet Cooled Aircraft Engine Compressor Cone Based on Statistical Methods
Received: 17 February 2018 / Revised: 12 April 2018 / Accepted: 16 April 2018 / Published: 1 May 2018
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Abstract
The paper presents the setup and analysis of an experimental study on heat transfer of a jet cooled compressor rear cone with adjacent conical housing. The main goal of the paper is to describe the systematic derivation of empirical correlations for global Nusselt
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The paper presents the setup and analysis of an experimental study on heat transfer of a jet cooled compressor rear cone with adjacent conical housing. The main goal of the paper is to describe the systematic derivation of empirical correlations for global Nusselt numbers to be used in the design process of a jet engine secondary air system. Based on the relevant similarity parameters obtained from literature, operating points are deduced leading to a full factorial design experiment to identify all effects and interactions. The varied similarity parameters are the circumferential Reynolds number, the non-dimensional mass flow, the non-dimensional spacing between rotor and stator, and the jet incidence angle. The range of the varied similarity parameters covers engine oriented operating conditions and is therefore suitable to predict Nusselt numbers in the actual engine component. In order to estimate measurement uncertainties, a simplified model of the test specimen, consisting of a convectively cooled flat plate, has been derived. Uncertainties of the measured quantities and derived properties are discussed by means of a linear propagation of uncertainties. A sensitivity study shows the effects of the input parameters and their interactions on the global Nusselt number. Subsequently, an empirical correlation for the global Nusselt numbers is derived using a multivariate non-linear regression. The quality of the empirical correlation is assessed by means of statistical hypotheses and by a comparison between measured and predicted data. The predicted values show excellent agreement with experimental data. In a wide range, accuracies of 15% can be reached when predicting global Nusselt numbers. Furthermore, the results of the sensitivity study show that pre-swirled cooling air does not have a positive effect on heat transfer. Full article
(This article belongs to the Special Issue Secondary Air Systems in Gas Turbine Engines)
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Open AccessArticle A Dual Mode Propulsion System for Small Satellite Applications
Received: 6 February 2018 / Revised: 11 April 2018 / Accepted: 26 April 2018 / Published: 2 May 2018
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Abstract
This study focused on the development of a chemical micropropulsion system suitable for primary propulsion and/or attitude control for a nanosatellite. Due to the limitations and expense of current micropropulsion technologies, few nanosatellites with propulsion have been launched to date; however, the availability
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This study focused on the development of a chemical micropropulsion system suitable for primary propulsion and/or attitude control for a nanosatellite. Due to the limitations and expense of current micropropulsion technologies, few nanosatellites with propulsion have been launched to date; however, the availability of such a propulsion system would allow for new nanosatellite mission concepts, such as deep space exploration, maneuvering in low gravity environments and formation flying. This work describes the design of “dual mode” monopropellant/bipropellant microthruster prototype that employs a novel homogeneous catalysis scheme. Results from prototype testing are reported that validate the concept. The micropropulsion system is designed to be fabricated using a combination of additively-manufactured and commercial off the shelf (COTS) parts along with non-toxic fuels, thus making it a low-cost and environmentally-friendly option for future nanosatellite missions. Full article
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Open AccessArticle Simulation of Random Events for Air Traffic Applications
Received: 23 March 2018 / Revised: 27 April 2018 / Accepted: 28 April 2018 / Published: 3 May 2018
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Abstract
Resilience to uncertainties must be ensured in air traffic management. Unexpected events can either be disruptive, like thunderstorms or the famous volcano ash cloud resulting from the Eyjafjallajökull eruption in Iceland, or simply due to imprecise measurements or incomplete knowledge of the environment.
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Resilience to uncertainties must be ensured in air traffic management. Unexpected events can either be disruptive, like thunderstorms or the famous volcano ash cloud resulting from the Eyjafjallajökull eruption in Iceland, or simply due to imprecise measurements or incomplete knowledge of the environment. While human operators are able to cope with such situations, it is generally not the case for automated decision support tools. Important examples originate from the numerous attempts made to design algorithms able to solve conflicts between aircraft occurring during flights. The STARGATE (STochastic AppRoach for naviGATion functions in uncertain Environment) project was initiated in order to study the feasibility of inherently robust automated planning algorithms that will not fail when submitted to random perturbations. A mandatory first step is the ability to simulate the usual stochastic phenomenons impairing the system: delays due to airport platforms or air traffic control (ATC) and uncertainties on the wind velocity. The work presented here will detail algorithms suitable for the simulation task. Full article
(This article belongs to the collection Air Transportation—Operations and Management)
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Open AccessArticle Faster Command Input Using the Multimodal Controller Working Position “TriControl”
Received: 6 April 2018 / Revised: 27 April 2018 / Accepted: 4 May 2018 / Published: 8 May 2018
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Abstract
TriControl is a controller working position (CWP) prototype developed by German Aerospace Center (DLR) to enable more natural, efficient, and faster command inputs. The prototype integrates three input modalities: speech recognition, eye tracking, and multi-touch sensing. Air traffic controllers may use all three
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TriControl is a controller working position (CWP) prototype developed by German Aerospace Center (DLR) to enable more natural, efficient, and faster command inputs. The prototype integrates three input modalities: speech recognition, eye tracking, and multi-touch sensing. Air traffic controllers may use all three modalities simultaneously to build commands that will be forwarded to the pilot and to the air traffic management (ATM) system. This paper evaluates possible speed improvements of TriControl compared to conventional systems involving voice transmission and manual data entry. 26 air traffic controllers participated in one of two air traffic control simulation sub-studies, one with each input system. Results show potential of a 15% speed gain for multimodal controller command input in contrast to conventional inputs. Thus, the use and combination of modern human machine interface (HMI) technologies at the CWP can increase controller productivity. Full article
(This article belongs to the collection Air Transportation—Operations and Management)
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Open AccessArticle The Legal Framework for Space Debris Remediation as a Tool for Sustainability in Outer Space
Received: 28 February 2018 / Revised: 18 April 2018 / Accepted: 2 May 2018 / Published: 9 May 2018
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Abstract
The growth of orbital space debris is both a consequence of and a potential hindrance to space activities. The risks posed by space debris propagation in the most used orbital regions highlight the need to adequately address the challenges posed to the sustainability
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The growth of orbital space debris is both a consequence of and a potential hindrance to space activities. The risks posed by space debris propagation in the most used orbital regions highlight the need to adequately address the challenges posed to the sustainability in outer space. The preservation of the access to and usability of outer space in the long-term requires that action is taken which has to be the result of both mitigation and remediation measures for existing and future space missions. As the enforcement of such technical measures will depend on adequate regulation, they need to be approached also from a legal perspective. The deficiencies in law for space debris remediation mechanisms originate from the fact that although technical concepts have been developed, the legal framework for space activities does not impose any legal obligations for debris removal and on-orbit servicing. Nevertheless, an overview of the relevant legal framework shows that there is a legal basis for the protection of the outer space environment which can, as has already been the case with space debris mitigation guidelines, be substantiated in more concrete terms by the formulation of voluntary, non-binding instruments and included in national legislation. Full article
(This article belongs to the Special Issue Space Debris: Impact and Remediation)

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Open AccessReview Hybrid Propulsion Systems for Remotely Piloted Aircraft Systems
Received: 31 December 2017 / Revised: 19 March 2018 / Accepted: 20 March 2018 / Published: 29 March 2018
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Abstract
The development of more efficient propulsion systems for aerospace vehicles is essential to achieve key objectives. These objectives are to increase efficiency while reducing the amount of carbon-based emissions. Hybrid electric propulsion (HEP) is an ideal means to maintain the energy density of
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The development of more efficient propulsion systems for aerospace vehicles is essential to achieve key objectives. These objectives are to increase efficiency while reducing the amount of carbon-based emissions. Hybrid electric propulsion (HEP) is an ideal means to maintain the energy density of hydrocarbon-based fuels and utilize energy-efficient electric machines. A system that integrates different propulsion systems into a single system, with one being electric, is termed an HEP system. HEP systems have been studied previously and introduced into Land, Water, and Aerial Vehicles. This work presents research into the use of HEP systems in Remotely Piloted Aircraft Systems (RPAS). The systems discussed in this paper are Internal Combustion Engine (ICE)–Electric Hybrid systems, ICE–Photovoltaic (PV) Hybrid systems, and Fuel-Cell Hybrid systems. The improved performance characteristics in terms of fuel consumption and endurance are discussed. Full article
(This article belongs to the Special Issue Aeroengine)
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Open AccessReview Survey of the Current Activities in the Field of Modeling the Space Debris Environment at TU Braunschweig
Received: 28 February 2018 / Revised: 22 March 2018 / Accepted: 27 March 2018 / Published: 2 April 2018
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Abstract
The Institute of Space Systems at Technische Universität Braunschweig has long-term experience in the field of space debris modeling. This article reviews the current state of ongoing research in this area. Extensive activities are currently underway to update the European space debris model
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The Institute of Space Systems at Technische Universität Braunschweig has long-term experience in the field of space debris modeling. This article reviews the current state of ongoing research in this area. Extensive activities are currently underway to update the European space debris model MASTER. In addition to updating the historical population, the future evolution of the space debris environment is also being investigated. The competencies developed within these activities are used to address current problems with regard to the possibility of an increasing number of catastrophic collisions. Related research areas include, for example, research in the field of orbit determination and the simulation of sensor systems for the acquisition and cataloging of orbital objects. In particular, the ability to provide simulated measurement data for object populations in almost all size ranges is an important prerequisite for these investigations. Some selected results on the distribution of space debris on Earth orbit are presented in terms of spatial density. Furthermore, specific fragmentation events will be discussed. Full article
(This article belongs to the Special Issue Space Debris: Impact and Remediation)
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Other

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Open AccessProject Report Aircraft Geometry and Meshing with Common Language Schema CPACS for Variable-Fidelity MDO Applications
Received: 1 March 2018 / Revised: 16 April 2018 / Accepted: 19 April 2018 / Published: 24 April 2018
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Abstract
This paper discusses multi-fidelity aircraft geometry modeling and meshing with the common language schema CPACS. The CPACS interfaces are described, and examples of variable fidelity aerodynamic analysis results applied to the reference aircraft are presented. Finally, we discuss three control surface deflection models
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This paper discusses multi-fidelity aircraft geometry modeling and meshing with the common language schema CPACS. The CPACS interfaces are described, and examples of variable fidelity aerodynamic analysis results applied to the reference aircraft are presented. Finally, we discuss three control surface deflection models for Euler computation. Full article
(This article belongs to the Special Issue Computational Aerodynamic Modeling of Aerospace Vehicles)
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