Abstract: Abstract In this paper, we present control and parameter estimation strategies with theoretical guarantees to turn a hex-rotor unmanned aerial vehicle (UAV) into a microgravity enabling platform. We make the UAV to maintain a constant acceleration equal to free-fall acceleration for it and any payload on-board to experience microgravity. Towards this, we derive a feedback linearisation-based acceleration control law exploiting the differential flatness property of our system. The proposed control law requires the estimates of the system parameters. Therefore, ancillary to this control law, we propose a parameter estimation scheme and prove that the proposed control law along with the parameter estimation scheme ensures convergence of acceleration to the desired value under certain conditions. We also characterize these conditions that guarantee convergence. The flight tests that we have performed employing the proposed control and parameter estimation schemes gave microgravity levels of the order of \(10^{-3}g\) for 1.6 s. To our knowledge, our hex-rotor UAV is the first multi-rotor UAV to achieve microgravity, and the first UAV—fixed-wing or rotary—to attain and maintain such levels of microgravity. PubDate: 2019-10-09

Abstract: Abstract Supercooled large droplet (SLD), which can cause run-back ridged ice, will affect the aerodynamic performance of aircraft and poses a serious threat to aircraft safety. However, there is little knowledge about the abnormal run-back icing mechanism, which is vital for the development of aircraft anti-icing technologies. The flow and freezing of supercooled droplet impinging on inclined surface can help us better understand the run-back icing of SLD, especially the coupling of water flow and phase change in the freezing process. This paper experimentally investigates the freezing behavior of supercooled water droplet impinging on inclined surface. By observing the processes of water flow, ice formation and growth with a high-speed camera, the overflow distance and the freezing time are recorded with different temperatures. Different from previous discoveries that droplet freezes as the form of two smaller droplets on an inclined surface, we found two new frozen morphologies under the condition of short nucleation time: ellipse and slender strip, when the supercooling is high and low, respectively. The overflow distance and freezing time will increase with the decrease of ice growth rate, when supercooling decreases. And the freezing time will increase dramatically when the supercooling is low enough. Finally, the mechanism of run-back freezing of droplet based on the nucleation and icing evolution is discussed. Droplet impact on the inclined surface will result in large overflow distance when it nucleates after its retraction stage. PubDate: 2019-10-09

Abstract: Abstract Angular velocity plays a critical role in determining the outcome of a close-range aerial engagement between two identical fighter aircraft pitching at full deflection. In a zero gravity environment, a pursuer may exploit its ability to roll to increase its relative angular velocity against a pitching opponent. In this paper, we present a repeatable maneuver for an unmanned fighter aircraft that increases its relative angular velocity. Additionally, we provide maneuvers for aligning an aircraft’s trajectory with a desired target trajectory. PubDate: 2019-08-30

Abstract: Abstract The manuscript discusses issues related to the use of mathematical modeling to substantiate the reliability and safety of the Superjet-100 aircraft during the emergency landing. The problem of the passenger airplane airframe dynamic deformation in the landing with partially removed and released the landing gear under given initial conditions of touching the runway of the airfield. Confirmation of the adequacy and reliability of modeling and the accuracy of numerical results are considered. PubDate: 2019-08-07

Abstract: Abstract A review on state of the art of kinematic analysis and dynamic stable control of space flexible manipulators (SFMs) is presented. Specially, SFM as a significant assembled part of autonomous space robotics (ASRs) play an important role in precision-positioning and accurateness-controlling for space engineering application since this lightweight structure possesses a high-efficient payload-to-arm weight ratio. Further, the existing studies of kinematic analysis and dynamic stable control of SFMs are critically examined to ascertain the trends of research and to identify unsolved problems through comparing with different methods. Motivated by the current research results of the two aspects, some suggestions for future research are given concisely in our published literature: (1) a fast eliminate solution algorithm of forward kinematics is presented. (2) Two observer-based control methods are suggested after dynamic modeling of SFMs. (3) How to choose a suitable closed-loop strategy to describe system dynamic features is discussed in a comparison study of the two proposed observer-based control methods. PubDate: 2019-08-01

Abstract: Abstract For low-cost unmanned aerial vehicles, it is practically important to estimate flight height using the measurements from low-cost accelerometer and barometer sensors. In this paper, we propose a simple two-step strategy to fuse the measurements from the two sensors. In the first step, two different filters, moving average filter and Kalman filter, are adopted to pre-process the measurements from accelerometer and barometer, respectively. In the second step, a properly designed complementary filter is employed for high-precision height estimation. Several experimental comparison results on a small-size quadrotor demonstrate the effectiveness of the strategy. The strategy is further combined with a simple height controller to yield a height feedback-control scheme. The closed-loop experimental results show that 8-cm and 20-cm control accuracies are achieved for 5-m- and 10-m-height tracking tasks, respectively. PubDate: 2019-08-01

Abstract: Abstract When aircraft flying at a high speed, the density and reflective index of atmosphere around it become uneven. Thus images or videos observed from the observation window on the aircraft are usually blur or quivering, which is called the aero-optical effect. To recover the images from poor quality, it is necessary to learn about the wavefront distortion of the light, described as optical path difference (OPD). Among the existing methods, the method of computational fluid dynamics (CFD) simulation followed by ray tracing is very time consuming, and the method of real-time OPD measurement with OPD sensor has a certain lag for OPD with high frequency. In this paper, a reconstructible dimension reduction method based on dictionary learning is employed to map the high-dimensional OPD data into a low-dimensional space, and the OPD data are calculated when rays travel across the supersonic shear layer. All the parameters of training and test datasets remain the same except the convective Mach numbers (Mc number). According to the dimension reduction results of training sets, we find that OPD is obviously periodic and its distribution characteristics have a strong correlation with Mc number. By fitting the OPD data in the low-dimensional space, every point on the fitting curve can be reconstructed to the original high-dimensional space, which works as prediction. Compared with the truthful data, the average similarity coefficient of the prediction for the test datasets is up to 83%, which means that the prediction result is credible. PubDate: 2019-08-01

Abstract: Abstract Avionics system integration is a prominent trend in research and development of civil airplane. It can improve task effectiveness, function efficiency, and resource utilization of system. Information fusion, which includes function information fusion, processing information fusion, and sensor input fusion, is a core process of avionics system integration. Some researches about the impact of information fusion on system safety are done in avionics system which is shown as follows: (1) the concept of Mishap Dilution, Mishap Implication and Mishap Confusion (MD–MI–MC) is first defined in function information fusion of avionics system. (2) The model of multi-source MD–MI–MC is established based on hazard theory. (3) The function fusion of Automatic-Dependent Surveillance–Broadcast (ADS–B) and Traffic Collision Avoidance System (TCAS) is used as a typical example to analyze fusion system during the aircraft climbing or landing state. In this paper, the concept and model of multi-source MD–MI–MC are proposed for safety analysis of integrated avionics system. A fusion model with a variable sampling Variational Bayesian–Interacting Multiple Model (VSVB–IMM) algorithm is used to analyze. At last, a set of theory system and evaluation standards including the positive and negative earning analyses are built based on the presented MD–MI–MC theory and mechanism of integrated avionics. PubDate: 2019-08-01

Abstract: Abstract Current trends in increasing fuel efficiency and improving aircrafts flight characteristics place engineers before task of reducing the weight of onboard systems and decreasing power consumption with preserving required degree of reliability. In part of aircraft control system, the main stream is the actuators usage with power supply. In this article, three architecture options of the power part of the aircraft control system with different electrification levels are considered. The considered options of the power part of the control system are estimated by three criteria: reliability, mass, power consumption. The selected criteria allow for the preliminary conclusion about the prospects one or another aircraft control system architecture. PubDate: 2019-08-01

Abstract: Abstract The control problem for linearised three-dimensional perturbations about a nominal laminar boundary layer over a flat plate (the Blasius profile) is considered. With a view to preventing the laminar to turbulent transition, appropriate inputs, outputs, and feedback controllers are synthesised that can be used to stabilise the system. The linearised Navier–Stokes equations are reduced to the Orr–Sommerfeld and Squire equations with wall-normal velocity actuation entering through the boundary conditions on the wall. An analysis of the work-energy balance is used to identify an appropriate sensor output that leads to a passive system for certain values of the streamwise and spanwise wavenumbers. Even when the system is unstable, it is demonstrated that strictly positive real feedback can stabilise this system using the special output. PubDate: 2019-08-01

Abstract: Abstract By detecting the severe meteorological situations on flight route, airborne weather radar (WXR) can ensure the safety of the aircraft and on-board personnel. Among these critical weather conditions, atmospheric turbulence is one of the main factors that affect flight safety. Atmospheric turbulence detection method that the current WXR adopts mainly is the pulse pair processing (PPP) method, which estimates Doppler spectrum width of weather target echo and compares it with a threshold to determine whether this weather target is turbulence or not. PPP method is simple and easy to implement, but the performance of this method under the condition of low signal-to-noise ratio (SNR) is poor. In this paper, we propose a new turbulence detection method based on the principal component analysis (PCA) approach. This new method uses PCA approach to preprocess the weather target echo and divides it into two parts: the principal component part as signal and the rest part as noise, so as to realize the de-noising function of PCA approach, and it is then combined with PPP method to estimate the spectrum width. Due to the good de-noising performance of PCA approach, this new method improves the detection performance of traditional PPP method especially under the condition of low SNR. PubDate: 2019-08-01

Abstract: Abstract The reduction of the aircraft weight is a great challenge for constructors, allowing them to cut down on fuel consumption and to increase the load carrying. This can be achieved by improving the properties of materials of aircraft parts. One of the most massive parts is the wing itself. In fact, according to a recent review of Aircraft Wing Mass Estimation Methods made by Dababneha and Kipouros (Aerosp Sci Technol, https://doi.org/10.1016/j.ast.2017.11.006, 2017) an aircraft wing could reach 8811 kg (Megson in Aircraft structure for engineering students, 3rd edn. Arnold, London, (1999) for an Airbus A320-200 and even 39,914 kg (Anderson in Fundamentals of aerodynamic, 3rd edn. McGraw-Hill, Boston, 1999) for a Boeing 747-100 since it is a long-range aircraft. Thus, it seems very interesting to act upon the material choice of wing components but without harming structure stiffness. In fact, composite integration has a direct impact on the stress and the weight of the wing which matters a lot in the conception of an aircraft wing. Such a complex problem requires indeed a multidisciplinary approach based on aerodynamics and structural analysis of both composite material and aluminum alloy. Solving this problem could be of great interest for both industrialists and researchers since it would lighten the path towards full composite wing integration. In this work, we propose a double-approach numerical method to study the effect of different composite materials integrated into aircraft wing skin stiffeners. By this way, this investigation aims to show the improvement given by composite materials to the structure and the achieved mass reduction after cautious integration, taking into consideration the stiffness of structure after load application. It also gives a method based on the best yield on weight ratio to compare the different possibilities of integrations to choose the most relevant material, its stacking and fibers orientations. For that, we relied on both analytical calculation and finite element analysis. A Matlab code was developed to determine structure response to loading such as longitudinal and shear stress and to estimate the global structure’s weight for different materials. We started by working on a wing made from the aluminum alloy AA2024 and then we integrated various composite materials like Glass fiber, S-glass/epoxy, and hm graphite/epoxy. Also, an investigation of the variability of stacking sequences and plies orientations was undertaken. As a result, we obtained a clear assessment of the potential of each material. We finally created, inspired by the Airbus technical data, an accurate finite-element model of an aircraft’s wing that served to study the structural resistance with Abaqus. Coherent results for the selected composite material and for its ply’s stacking and orientation were found. PubDate: 2019-06-04

Abstract: Abstract Microelectromechanical systems’ (MEMS) inertial measurement unit (IMU) is widely used in many scenarios for its small size, low weight, and low-power consumptions. However, it possesses relatively low positioning accuracy compared with other high-grade IMUs, as errors accumulate quickly over time. This paper mainly focuses on the error characteristics of the gyro part of MEMS IMU by analyzing different kinds of error parameters. As there is no published standard for MEMS gyro error characterization, three dominant error parameters are selected and investigated, namely, scale factor, in-run bias stability, and angular random walk. In addition, Allan variance analysis is deployed as an important part of the scheme with relative results presented in this paper. Not only is theoretical analysis presented, but experimental verification is also carried out correspondingly with an ADIS16490 MEMS IMU. By comparison, we find that the results of in-run bias stability exceed the given features by up to ten times, while the rest of the results agree quite well with the given features. Possible reasons for the exceeding part are given. Calibration testing results not only provide concrete characterization for MEMS gyro errors, but also enhance the importance of overall calibration of MEMS IMU before use. PubDate: 2019-06-04

Abstract: Abstract To phased microphone array for sound source localization, algorithm with both high computational efficiency and high precision is a persistent pursuit until now. In this paper, convolutional neural network (CNN) a kind of deep learning is preliminarily applied as a new algorithm. The input of CNN is only cross-spectral matrix, while the output of CNN is source distribution. With regard to computing speed in applications, CNN once trained is as fast as conventional beamforming, and is significantly faster than the most famous deconvolution algorithm DAMAS. With regard to measurement accuracy in applications, at high frequency, CNN can reconstruct the sound localizations with up to 100% test accuracy, although sidelobes may appear in some situations. In addition, CNN has a spatial resolution nearly as that of DAMAS and better than that of the conventional beamforming. CNN test accuracy decreases with frequency decreasing; however, in most incorrect samples, CNN results are not far away from the correct results. This exciting result means that CNN perfectly finds source distribution directly from cross-spectral matrix without given propagation function and microphone positions in advance, and thus, CNN deserves to be further explored as a new algorithm. PubDate: 2019-05-14

Abstract: Abstract In the present study, asymmetric supersonic expansion flow produced by an annular conical supersonic nozzle has been studied under static conditions. To understand the details of Reynolds number influence on the backpressure-induced shock–boundary layer interaction, a computational program has been carried out. Particular attention has been paid to the shock physics and characteristics of shock–shock and shock–boundary layer interaction change in the flow field when applied to engines operating in different ambient pressure environments. The identification of this Reynolds number correlated flow behavior changes is important for low supersonic expansion flow in engines, as it is directly attributed to the limits of off-design capability on launcher performance. The obtained results show that Reynolds number has significant influence on flow pattern at low pressure ratio, PR, conditions. When PR grows from 2.00 to 2.10, the most prominent phenomenon is that the separation point on the upper wall keeps moving downstream while the one on the lower wall keeps still. This special flow pattern results in a gradual transition from a Mach reflection to the regular reflection. However, for results at higher pressure ratios than 2.57, the comparison between the predicted shock patterns at the three ambient conditions shows a close one for these higher PR regimes. This suggests that the Reynolds number effect is going to weaken at a higher Mach number flow regime when the flow Reynolds number increases with an increase of the pressure ratio as well as the expansion flow Mach number. PubDate: 2019-04-17

Abstract: Abstract Increasing the environmental sustainability of aviation is a key design goal for commercial aircraft for the foreseeable future. From the perspective of structural engineering, this is accomplished through reducing the mass of aircraft components and structures. Advanced manufacturing techniques offer new avenues for design, enabling more complex structures which can have highly tailored properties. One advanced manufacturing concept is the use of 3D printed polymer preforms that are coated with nanocrystalline metal through electrodeposition. This enables the use of high-performance materials in virtually any geometry. To exploit this manufacturing approach, it is incumbent to have well-established mechanical models of the behavior of such hybrid structures. In particular, hybrid polymer–nanometal structures tend to fail due to compressive instabilities. This paper describes a model of local shell buckling, a typical compressive instability, as it applies to hybrid polymer–nanometal structures. The analysis depends upon the Southwell stress function model for radially loaded solids of rotation, and couples this with the Timoshenko analysis of local shell buckling. This combination is applicable to a range of practical configurations for truss-like hybrid structures. PubDate: 2019-02-05

Abstract: Abstract In this paper, we investigated the dynamic properties of origami structures composed of Miura unit cells with rigid facets and elastic hinges under three types of excitations: harmonic force, harmonic displacement and impact. Under the simple harmonic force or displacement excitations, different crease stiffness affects the vibration responses of Miura folded metamaterials. The single degree-of-freedom (DOF) models have one resonant peak, after which the vibration amplitude at the response end is lower than that of the excitation end. Increasing the crease stiffness can increase the resonant frequency. The multi-DOF model exhibits multiple resonant peaks under harmonic excitations, where the lowest resonant frequency has the highest peak. Increasing the number of layers can reduce the resonant frequency. When the multi-DOF model is subjected to impact load, the magnitude of the impact wave decays quickly after the impact and finally reaches a steady state with a low average strain magnitude. When the crease stiffness is increased, the propagation of the impact wave becomes faster, whereas the maximum strain magnitude becomes smaller. Introducing different damping coefficient to the crease has no influence on the propagation speed of the impact waves, but can accelerate the decay in the magnitude of the impact wave. PubDate: 2019-01-17

Abstract: Abstract Buckling problem is quite important for the engineering practice, mostly in cases of lightweight structures. The use of composites reduces the weight of the structure but gives problems in choice of reliable methods to model buckling and postbuckling behavior of details, especially if they contain thin-walled components. One of the problems is the choice of correct elastic properties of composite material for analysis. Elastic characteristics of composite material depend on the type of loading and uniaxial tension/compression test results in some cases demonstrate an essential difference. The buckling analysis usually assumes compression of the structure and the choice of elastic constants obtained in compression tests leads to more accurate results, but does not guarantee a good correlation with experiments in case of postbuckling analysis due to ignoring some regions with tension stress state. A possible way of material stress-state sensitivity consideration is usage of material models that take into account stiffness susceptibility to different types of loading. Further development of nonlinear elastic model in problems related to buckling and postbuckling analysis for composite materials up to failure is the introduction of material progressive degradation model to consider material properties reduction due to damage in conjunction with nonlinear elasticity. PubDate: 2018-12-06

Abstract: Abstract The paper describes a model for simulation of residual stresses and process-induced cracks in thermoplastic fibre-reinforced composites. The main aspect of the research is the modeling of phase transitions in thermoplastic matrix, taking into account changes in the matrix mechanical properties and shrinkage. An experimental comparison of modeling results for all mechanical characteristics at all stages of material phase transformation is provided. Equations for modeling of all key processes related to temperature cycle of a thermoplastic matrix solidification are provided together with corresponding material constants, using polyetheretherketone (PEEK) as an example. Approach to modeling of process-induced defects in thermoplastic matrix in dependence of crystallinity degree and different temperature conditions is proposed. PubDate: 2018-12-01

Abstract: Abstract This paper presents the structural design and optimization process of a morphing wing trailing edge (TE) flap. The flap consists of flexible upper and lower skins and various connections that constrains the relative motion between the upper and lower skins, and is actuated by an eccentric beam to which several discs of variable radii and setting angles with respect to the beam is rigidly attached. The focus of this work is to find the optimal parameters for the eccentric beam and the connections so that the upper and lower skins bend to the desired shapes and their deformation process is continuous. To achieve this goal, a computer design tool that makes synthetic use of MATLAB, Python and ABAQUS is developed. Specifically, the shape of the eccentric beam, the number, locations, shapes and orientations of the discs, and the number and locations of the connections are calculated according to the target shapes of the morphing flap in MATLAB. These parameters are passed to a Python script that automatically generates the finite element (FE) model of the morphing TE flap assembly for ABAQUS. The FE model is then simulated in ABAQUS and the needed results are extracted by the Python script and passed back to the main MATLAB code, in which a particle swarm optimization is used to find the set of parameters that lead to the optimal bent shape of the upper and lower skins. The results showed that the proposed design process is robust and able to achieve the desired morphed continuously shape of the TE flap. PubDate: 2018-12-01