International Journal of Aerospace Engineering The latest articles from Hindawi © 2017 , Hindawi Limited . All rights reserved. Modified Regression Rate Formula of PMMA Combustion by a Single Plane Impinging Jet Tue, 21 Feb 2017 00:00:00 +0000 A modified regression rate formula for the uppermost stage of CAMUI-type hybrid rocket motor is proposed in this study. Assuming a quasi-steady, one-dimensional, an energy balance against a control volume near the fuel surface is considered. Accordingly, the regression rate formula which can calculate the local regression rate by the quenching distance between the flame and the regression surface is derived. An experimental setup which simulates the combustion phenomenon involved in the uppermost stage of a CAMUI-type hybrid rocket motor was constructed and the burning tests with various flow velocities and impinging distances were performed. A PMMA slab of 20 mm height, 60 mm width, and 20 mm thickness was chosen as a sample specimen and pure oxygen and O2/N2 mixture (50/50 vol.%) were employed as the oxidizers. The time-averaged regression rate along the fuel surface was measured by a laser displacement sensor. The quenching distance during the combustion event was also identified from the observation. The comparison between the purely experimental and calculated values showed good agreement, although a large systematic error was expected due to the difficulty in accurately identifying the quenching distance. Tsuneyoshi Matsuoka, Kyohei Kamei, Yuji Nakamura, and Harunori Nagata Copyright © 2017 Tsuneyoshi Matsuoka et al. All rights reserved. Triple-Frequency GPS Precise Point Positioning Ambiguity Resolution Using Dual-Frequency Based IGS Precise Clock Products Tue, 21 Feb 2017 00:00:00 +0000 With the availability of the third civil signal in the Global Positioning System, triple-frequency Precise Point Positioning ambiguity resolution methods have drawn increasing attention due to significantly reduced convergence time. However, the corresponding triple-frequency based precise clock products are not widely available and adopted by applications. Currently, most precise products are generated based on ionosphere-free combination of dual-frequency L1/L2 signals, which however are not consistent with the triple-frequency ionosphere-free carrier-phase measurements, resulting in inaccurate positioning and unstable float ambiguities. In this study, a GPS triple-frequency PPP ambiguity resolution method is developed using the widely used dual-frequency based clock products. In this method, the interfrequency clock biases between the triple-frequency and dual-frequency ionosphere-free carrier-phase measurements are first estimated and then applied to triple-frequency ionosphere-free carrier-phase measurements to obtain stable float ambiguities. After this, the wide-lane L2/L5 and wide-lane L1/L2 integer property of ambiguities are recovered by estimating the satellite fractional cycle biases. A test using a sparse network is conducted to verify the effectiveness of the method. The results show that the ambiguity resolution can be achieved in minutes even tens of seconds and the positioning accuracy is in decimeter level. Fei Liu and Yang Gao Copyright © 2017 Fei Liu and Yang Gao. All rights reserved. Survey on Flight Control Technology for Large-Scale Helicopter Mon, 20 Feb 2017 14:15:27 +0000 A literature review of flight control technology is presented for large-scale helicopter. Challenges of large-scale helicopter flight control system (FCS) design are illustrated. Following this, various flight control methodologies are described with respect to their engineering implementation and theoretical developments, whose advantages and disadvantages are also analyzed. Then, the challenging research issues on flight control technology are identified, and future directions are highlighted. Jinshuo Hu and Hongbin Gu Copyright © 2017 Jinshuo Hu and Hongbin Gu. All rights reserved. Experimental Investigation on the Feasibility of Using a Fresnel Lens as a Solar-Energy Collection System for Enhancing On-Orbit Power Generation Performance Mon, 20 Feb 2017 06:53:01 +0000 Cube satellites have a limitation for generating power because of their cubic structure and extremely small size. In addition, the incidence angle between the sun and the solar panels continuously varies owing to the revolution and rotation of the satellite according to the attitude control strategy. This angle is an important parameter for determining the power generation performance of the cube satellite. In this study, we performed an experimental feasibility study that uses a Fresnel lens as a solar-energy collection system for cube satellite applications, so that the power generation efficiency can be enhanced under the worst incidence angle condition between the sun and solar panels by concentrating and redirecting solar energy onto the solar panels with a commercial Fresnel lens. To verify the effectiveness of the proposed system, we conducted a power-measurement test using a solar simulator and Fresnel lenses at various angles to the light source. In addition, we predicted the on-orbit power-generation enhancement achieved by employing the solar-energy collection system with various attitude control strategies. Tae-Yong Park, Joo-Yong Jung, and Hyun-Ung Oh Copyright © 2017 Tae-Yong Park et al. All rights reserved. Networked Cascade Control System Design for Turboshaft Engines with Random Packet Dropouts Thu, 16 Feb 2017 12:51:28 +0000 The distributed control architecture becomes more and more important in future gas turbine engine control systems, in which the sensors and actuators will be connected to the controllers via a network. Therefore, the control problem of network-enabled high-performance distributed engine control (DEC) has come to play an important role in modern gas turbine control systems, while, due to the properties of the network, the packet dropouts must be considered. This study introduces a distributed control system architecture based on a networked cascade control system (NCCS). Typical turboshaft engine distributed controllers are designed based on the NCCS framework with state feedback under random packet dropouts. The sufficient robust stable conditions are derived via the Lyapunov stability theory and linear matrix inequality approach. Simulations illustrate the effectiveness of the presented method. Xiaofeng Liu and Xu Sun Copyright © 2017 Xiaofeng Liu and Xu Sun. All rights reserved. Bifurcation Analysis with Aerodynamic-Structure Uncertainties by the Nonintrusive PCE Method Thu, 16 Feb 2017 00:00:00 +0000 An aeroelastic model for airfoil with a third-order stiffness in both pitch and plunge degree of freedom (DOF) and the modified Leishman–Beddoes (LB) model were built and validated. The nonintrusive polynomial chaos expansion (PCE) based on tensor product is applied to quantify the uncertainty of aerodynamic and structure parameters on the aerodynamic force and aeroelastic behavior. The uncertain limit cycle oscillation (LCO) and bifurcation are simulated in the time domain with the stochastic PCE method. Bifurcation diagrams with uncertainties were quantified. The Monte Carlo simulation (MCS) is also applied for comparison. From the current work, it can be concluded that the nonintrusive polynomial chaos expansion can give an acceptable accuracy and have a much higher calculation efficiency than MCS. For aerodynamic model, uncertainties of aerodynamic parameters affect the aerodynamic force significantly at the stage from separation to stall at upstroke and at the stage from stall to reattach at return. For aeroelastic model, both uncertainties of aerodynamic parameters and structure parameters impact bifurcation position. Structure uncertainty of parameters is more sensitive for bifurcation. When the nonlinear stall flutter and bifurcation are concerned, more attention should be paid to the separation process of aerodynamics and parameters about pitch DOF in structure. Linpeng Wang, Yuting Dai, and Chao Yang Copyright © 2017 Linpeng Wang et al. All rights reserved. Edge Detection in UAV Remote Sensing Images Using the Method Integrating Zernike Moments with Clustering Algorithms Wed, 15 Feb 2017 11:22:28 +0000 Due to the unmanned aerial vehicle remote sensing images (UAVRSI) within rich texture details of ground objects and obvious phenomenon, the same objects with different spectra, it is difficult to effectively acquire the edge information using traditional edge detection operator. To solve this problem, an edge detection method of UAVRSI by combining Zernike moments with clustering algorithms is proposed in this study. To begin with, two typical clustering algorithms, namely, fuzzy -means (FCM) and -means algorithms, are used to cluster the original remote sensing images so as to form homogeneous regions in ground objects. Then, Zernike moments are applied to carry out edge detection on the remote sensing images clustered. Finally, visual comparison and sensitivity methods are adopted to evaluate the accuracy of the edge information detected. Afterwards, two groups of experimental data are selected to verify the proposed method. Results show that the proposed method effectively improves the accuracy of edge information extracted from remote sensing images. Liang Huang, Xueqin Yu, and Xiaoqing Zuo Copyright © 2017 Liang Huang et al. All rights reserved. Autonomous Rendezvous and Docking with Nonfull Field of View for Tethered Space Robot Mon, 13 Feb 2017 00:00:00 +0000 In the ultra-close approaching phase of tethered space robot, a highly stable self-attitude control is essential. However, due to the field of view limitation of cameras, typical point features are difficult to extract, where commonly adopted position-based visual servoing cannot be valid anymore. To provide robot’s relative position and attitude with the target, we propose a monocular visual servoing control method using only the edge lines of satellite brackets. Firstly, real time detection of edge lines is achieved based on image gradient and region growing. Then, we build an edge line based model to estimate the relative position and attitude between the robot and the target. Finally, we design a visual servoing controller combined with PD controller. Experimental results demonstrate that our algorithm can extract edge lines stably and adjust the robot’s attitude to satisfy the grasping requirements. Panfeng Huang, Lu Chen, Bin Zhang, Zhongjie Meng, and Zhengxiong Liu Copyright © 2017 Panfeng Huang et al. All rights reserved. Learning Control of Fixed-Wing Unmanned Aerial Vehicles Using Fuzzy Neural Networks Thu, 09 Feb 2017 00:00:00 +0000 A learning control strategy is preferred for the control and guidance of a fixed-wing unmanned aerial vehicle to deal with lack of modeling and flight uncertainties. For learning the plant model as well as changing working conditions online, a fuzzy neural network (FNN) is used in parallel with a conventional P (proportional) controller. Among the learning algorithms in the literature, a derivative-free one, sliding mode control (SMC) theory-based learning algorithm, is preferred as it has been proved to be computationally efficient in real-time applications. Its proven robustness and finite time converging nature make the learning algorithm appropriate for controlling an unmanned aerial vehicle as the computational power is always limited in unmanned aerial vehicles (UAVs). The parameter update rules and stability conditions of the learning are derived, and the proof of the stability of the learning algorithm is shown by using a candidate Lyapunov function. Intensive simulations are performed to illustrate the applicability of the proposed controller which includes the tracking of a three-dimensional trajectory by the UAV subject to time-varying wind conditions. The simulation results show the efficiency of the proposed control algorithm, especially in real-time control systems because of its computational efficiency. Erdal Kayacan, Mojtaba Ahmadieh Khanesar, Jaime Rubio-Hervas, and Mahmut Reyhanoglu Copyright © 2017 Erdal Kayacan et al. All rights reserved. Airborne Position and Orientation System for Aerial Remote Sensing Thu, 09 Feb 2017 00:00:00 +0000 The airborne Position Orientation System (POS) can accurately measure space-time reference information and plays a vital role in aerial remote sensing system. It may be applied in a direct georeference system for optical camera and a motion imaging system for Synthetic Aperture Radar (SAR), which further advances efficiency and quality of imaging sensors. In this paper, the operation principle and components of airborne POS are introduced. Some key technologies of airborne POS are summarized. They include the error calibration and compensation, initial alignment, lever arm error modeling, time synchronization, and integrated estimation method. A high precision airborne POS has been developed and applied to a variety of aerial remote sensing systems. Jianli Li, Jiancheng Fang, Zhaoxing Lu, and Lijian Bai Copyright © 2017 Jianli Li et al. All rights reserved. A Novel Technique to Compute the Revisit Time of Satellites and Its Application in Remote Sensing Satellite Optimization Design Tue, 31 Jan 2017 14:09:52 +0000 This paper proposes a novel technique to compute the revisit time of satellites within repeat ground tracks. Different from the repeat cycle which only depends on the orbit, the revisit time is relevant to the payload of the satellite as well, such as the tilt angle and swath width. The technique is discussed using the Bezout equation and takes the gravitational second zonal harmonic into consideration. The concept of subcycles is defined in a general way and the general concept of “small” offset is replaced by a multiple of the minimum interval on equator when analyzing the revisit time of remote sensing satellites. This technique requires simple calculations with high efficiency. At last, this technique is used to design remote sensing satellites with desired revisit time and minimum tilt angle. When the side-lap, the range of altitude, and desired revisit time are determined, a lot of orbit solutions which meet the mission requirements will be obtained fast. Among all solutions, designers can quickly find out the optimal orbits. Through various case studies, the calculation technique is successfully demonstrated. Xin Luo, Maocai Wang, Guangming Dai, and Xiaoyu Chen Copyright © 2017 Xin Luo et al. All rights reserved. Efficient Method for Aeroelastic Tailoring of Composite Wing to Minimize Gust Response Thu, 26 Jan 2017 00:00:00 +0000 Aeroelastic tailoring of laminated composite structure demands relatively high computational time especially for dynamic problem. This paper presents an efficient method for aeroelastic dynamic response analysis with significantly reduced computational time. In this method, a relationship is established between the maximum aeroelastic response and quasi-steady deflection of a wing subject to a dynamic loading. Based on this relationship, the time consuming dynamic response can be approximated by a quasi-steady deflection analysis in a large proportion of the optimization process. This method has been applied to the aeroelastic tailoring of a composite wing of a tailless aircraft for minimum gust response. The results have shown that 20%–36% gust response reduction has been achieved for this case. The computational time of the optimization process has been reduced by 90% at the cost of accuracy reduction of 2~4% comparing with the traditional dynamic response analysis. Yang Yu, Zhengjie Wang, and Shijun Guo Copyright © 2017 Yang Yu et al. All rights reserved. Time and Covariance Threshold Triggered Optimal Uncooperative Rendezvous Using Angles-Only Navigation Tue, 24 Jan 2017 08:30:30 +0000 A time and covariance threshold triggered optimal maneuver planning method is proposed for orbital rendezvous using angles-only navigation (AON). In the context of Yamanaka-Ankersen orbital relative motion equations, the square root unscented Kalman filter (SRUKF) AON algorithm is developed to compute the relative state estimations from a low-volume/mass, power saving, and low-cost optical/infrared camera’s observations. Multi-impulsive Hill guidance law is employed in closed-loop linear covariance analysis model, based on which the quantitative relative position robustness and relative velocity robustness index are defined. By balancing fuel consumption, relative position robustness, and relative velocity robustness, we developed a time and covariance threshold triggered two-level optimal maneuver planning method, showing how these results correlate to past methods and missions and how they could potentially influence future ones. Numerical simulation proved that it is feasible to control the spacecraft with a two-line element- (TLE-) level uncertain, 34.6% of range, initial relative state to a 100 m v-bar relative station keeping point, at where the trajectory dispersion reduces to 3.5% of range, under a 30% data gap per revolution on account of the eclipse. Comparing with the traditional time triggered maneuver planning method, the final relative position accuracy is improved by one order and the relative trajectory robustness and collision probability are obviously improved and reduced, respectively. Yue You, Hua Wang, Christophe Paccolat, Volker Gass, Jean-Philippe Thiran, and Jiu Ren Li Copyright © 2017 Yue You et al. All rights reserved. Study of the Effect of Centrifugal Force on Rotor Blade Icing Process Mon, 23 Jan 2017 00:00:00 +0000 In view of the rotor icing problems, the influence of centrifugal force on rotor blade icing is investigated. A numerical simulation method of three-dimensional rotor blade icing is presented. Body-fitted grids around the rotor blade are generated using overlapping grid technology and rotor flow field characteristics are obtained by solving N-S equations. According to Eulerian two-phase flow, the droplet trajectories are calculated and droplet impingement characteristics are obtained. The mass and energy conservation equations of ice accretion model are established and a new calculation method of runback water mass based on shear stress and centrifugal force is proposed to simulate water flow and ice shape. The calculation results are compared with available experimental results in order to verify the correctness of the numerical simulation method. The influence of centrifugal force on rotor icing is calculated. The results show that the flow direction and distribution of liquid water on rotor surfaces change under the action of centrifugal force, which lead to the increasing of icing at the stagnation point and the decreasing of icing on both frozen limitations. Zhengzhi Wang and Chunling Zhu Copyright © 2017 Zhengzhi Wang and Chunling Zhu. All rights reserved. CFD Simulations of a Finned Projectile with Microflaps for Flow Control Thu, 19 Jan 2017 00:00:00 +0000 This research describes a computational study undertaken to determine the effect of a flow control mechanism and its associated aerodynamics for a finned projectile. The flow control system consists of small microflaps located between the rear fins of the projectile. These small microflaps alter the flow field in the aft finned region of the projectile, create asymmetric pressure distributions, and thus produce aerodynamic control forces and moments. A number of different geometric parameters, microflap locations, and the number of microflaps were varied in an attempt to maximize the control authority generated by the flaps. Steady-state Navier-Stokes computations were performed to obtain the control aerodynamic forces and moments associated with the microflaps. These results were used to optimize the control authority at a supersonic speed, . Computed results showed not only the microflaps to be effective at this speed, but also configurations with 6 and 8 microflaps were found to generate 25%–50% more control force than a baseline 4-flap configuration. These results led to a new optimized 8-flap configuration that was further investigated for a range of Mach numbers from to and was found to be a viable configuration effective in providing control at all of these speeds. Jubaraj Sahu Copyright © 2017 Jubaraj Sahu. All rights reserved. Architecture Level Safety Analyses for Safety-Critical Systems Sun, 15 Jan 2017 00:00:00 +0000 The dependency of complex embedded Safety-Critical Systems across Avionics and Aerospace domains on their underlying software and hardware components has gradually increased with progression in time. Such application domain systems are developed based on a complex integrated architecture, which is modular in nature. Engineering practices assured with system safety standards to manage the failure, faulty, and unsafe operational conditions are very much necessary. System safety analyses involve the analysis of complex software architecture of the system, a major aspect in leading to fatal consequences in the behaviour of Safety-Critical Systems, and provide high reliability and dependability factors during their development. In this paper, we propose an architecture fault modeling and the safety analyses approach that will aid in identifying and eliminating the design flaws. The formal foundations of SAE Architecture Analysis & Design Language (AADL) augmented with the Error Model Annex (EMV) are discussed. The fault propagation, failure behaviour, and the composite behaviour of the design flaws/failures are considered for architecture safety analysis. The illustration of the proposed approach is validated by implementing the Speed Control Unit of Power-Boat Autopilot (PBA) system. The Error Model Annex (EMV) is guided with the pattern of consideration and inclusion of probable failure scenarios and propagation of fault conditions in the Speed Control Unit of Power-Boat Autopilot (PBA). This helps in validating the system architecture with the detection of the error event in the model and its impact in the operational environment. This also provides an insight of the certification impact that these exceptional conditions pose at various criticality levels and design assurance levels and its implications in verifying and validating the designs. K. S. Kushal, Manju Nanda, and J. Jayanthi Copyright © 2017 K. S. Kushal et al. All rights reserved. Novel Fractional Order Calculus Extended PN for Maneuvering Targets Thu, 12 Jan 2017 09:51:43 +0000 Based on the theory of fractional order calculus (FOC), a novel extended proportional guidance (EPN) law for intercepting the maneuvering target is proposed. In the first part, considering the memory function and filter characteristic of FOC, the novel extended PN guidance algorithm is developed based on the conventional PN after introducing the properties and operation rules of FOC. Further, with the help of FOC theory, the average load and ballistics characteristics of proposed guidance law are analyzed. Then, using the small offset kinematic model, the robustness of the new guidance law against autopilot parameters is studied theoretically by analyzing the sensitivity of the closed loop guidance system. At last, representative numerical results show that the designed guidance law obtains a better performance than the traditional PN for maneuvering target. Jikun Ye, Humin Lei, and Jiong Li Copyright © 2017 Jikun Ye et al. All rights reserved. Flight Loads Prediction of High Aspect Ratio Wing Aircraft Using Multibody Dynamics Tue, 27 Dec 2016 06:46:01 +0000 A framework based on multibody dynamics has been developed for the static and dynamic aeroelastic analyses of flexible high aspect ratio wing aircraft subject to structural geometric nonlinearities. Multibody dynamics allows kinematic nonlinearities and nonlinear relationships in the forces definition and is an efficient and promising methodology to model high aspect ratio wings, which are known to be prone to structural nonlinear effects because of the high deflections in flight. The multibody dynamics framework developed employs quasi-steady aerodynamics strip theory and discretizes the wing as a series of rigid bodies interconnected by beam elements, representative of the stiffness distribution, which can undergo arbitrarily large displacements and rotations. The method is applied to a flexible high aspect ratio wing commercial aircraft and both trim and gust response analyses are performed in order to calculate flight loads. These results are then compared to those obtained with the standard linear aeroelastic approach provided by the Finite Element Solver Nastran. Nonlinear effects come into play mainly because of the need of taking into account the large deflections of the wing for flight loads computation and of considering the aerodynamic forces as follower forces. Michele Castellani, Jonathan E. Cooper, and Yves Lemmens Copyright © 2016 Michele Castellani et al. All rights reserved. Quantification of Limit Cycle Oscillations in Nonlinear Aeroelastic Systems with Stochastic Parameters Tue, 20 Dec 2016 11:12:41 +0000 This paper presents an analytical feature for limit cycle oscillation (LCO) in the nonlinear aeroelastic system of an airfoil, with major emphasis on its applications in LCO quantification. The nonlinear stiffness is modeled as the product of the th power of vibration displacement and the th power of velocity, with its coefficient as a stochastic parameter. One interesting finding is that the LCO amplitude is directly proportional to the th power of the coefficient, whereas the frequency is independent of the coefficient. Based on this feature, the statistics and distribution functions of the LCO amplitude are obtained semianalytically, which are validated by Monte Carlo simulations. In addition, we discuss the possible influences of the nonlinear stiffness on flutter suppression of the airfoil subjected to Gaussian white noises. Surprisingly, increasing the nonlinear stiffness alone does not necessarily reduce the vibration amplitude as expected. Instead, it may sometimes induce disastrous subcritical LCOs with much higher vibration amplitudes. C. C. Cui, J. K. Liu, and Y. M. Chen Copyright © 2016 C. C. Cui et al. All rights reserved. Squeeze Film Dampers Executing Small Amplitude Circular-Centered Orbits in High-Speed Turbomachinery Sun, 18 Dec 2016 11:15:09 +0000 This work represents a pressure distribution model for finite length squeeze film dampers (SFDs) executing small amplitude circular-centered orbits (CCOs) with application in high-speed turbomachinery design. The proposed pressure distribution model only accounts for unsteady (temporal) inertia terms, since based on order of magnitude analysis, for small amplitude motions of the journal center, the effect of convective inertia is negligible relative to unsteady (temporal) inertia. In this work, the continuity equation and the momentum transport equations for incompressible lubricants are reduced by assuming that the shapes of the fluid velocity profiles are not strongly influenced by the inertia forces, obtaining an extended form of Reynolds equation for the hydrodynamic pressure distribution that accounts for fluid inertia effects. Furthermore, a numerical procedure is represented to discretize the model equations by applying finite difference approximation (FDA) and to numerically determine the pressure distribution and fluid film reaction forces in SFDs with significant accuracy. Finally, the proposed model is incorporated into a simulation model and the results are compared against existing SFD models. Based on the simulation results, the pressure distribution and fluid film reaction forces are significantly influenced by fluid inertia effects even at small and moderate Reynolds numbers. Sina Hamzehlouia and Kamran Behdinan Copyright © 2016 Sina Hamzehlouia and Kamran Behdinan. All rights reserved. Study on Helicopter Antitorque Device Based on Cross-Flow Fan Technology Thu, 15 Dec 2016 12:41:33 +0000 In order to improve low-altitude flight security of single-rotor helicopter, an experimental model of a helicopter antitorque device is developed for wind tunnel test. The model is based on the flow control technology of the cross-flow fan (CFF). Wind tunnel tests show that the model can produce side force. It is concluded that the influence of the CFF rotating speed, the rotor collective pitch, and the forward flight speed on the side force of the model is great. At the same time, the numerical simulation calculation method of the model has been established. Good agreement between experimental and numerical side force and power shows that results of numerical solution are reliable. Therefore, the results in actual helicopter obtained from Computational Fluid Dynamics (CFD) solution are acceptable. This proves that this antitorque device can be used for a helicopter. Du Siliang, Tang Zhengfei, Xu Pei, and Ji Mengjiang Copyright © 2016 Du Siliang et al. All rights reserved. Feedback Control of Flow Separation Using Plasma Actuator and FBG Sensor Wed, 14 Dec 2016 10:58:01 +0000 A feedback control system for mitigating flow separation was developed by using a string-type dielectric-barrier-discharge (DBD) plasma actuator and a fiber Bragg grating (FBG) sensor. Tangential jets were induced from the string-type DBD plasma actuator, which was located at 5% chord from the leading edge of an NACA0024 airfoil. The FBG sensor was attached to the interior surface near the root of the cantilever beam modeled on the pressure surface of the airfoil. The strain at the cantilever root was reflected in the form of Bragg wavelengths () detected by the FBG sensor when the cantilever tip was vibrated by the flow near the trailing edge of the airfoil. It was found that calculating running standard deviations in the Bragg wavelength () detected by the sensor was valuable for judging flow separation in real time. The feedback control of flow separation on the NACA0024 airfoil was successfully demonstrated by setting with periodic flow separations generated in a wind tunnel by oscillating a side wall of the test section with frequency  Hz. It was confirmed that the appearance probability of flow separation tends to decrease with a decrease in the duration for calculating and with an increase in the duration of jet injection. Takehiko Segawa, Daiki Suzuki, Takayasu Fujino, Timothy Jukes, and Takayuki Matsunuma Copyright © 2016 Takehiko Segawa et al. All rights reserved. Effects of Freestream Turbulence on Cavity Tone and Sound Source Mon, 12 Dec 2016 08:04:05 +0000 To clarify the effects of freestream turbulence on cavity tones, flow and acoustic fields were directly predicted for cavity flows with various intensities of freestream turbulence. The freestream Mach number was 0.09 and the Reynolds number based on the cavity length was 4.0 × 104. The depth-to-length ratio of the cavity, , was 0.5 and 2.5, where the acoustic resonance of a depth-mode occurs for = 2.5. The incoming boundary layer was laminar. The results for the intensity of freestream turbulence of Tu = 2.3% revealed that the reduced level of cavity tones in a cavity flow with acoustic resonance was greater than that without acoustic resonance . To clarify the reason for this, the sound source based on Lighthill’s acoustic analogy was computed, and the contributions of the intensity and spanwise coherence of the sound source to the reduction of the cavity tone were estimated. As a result, the effects of the reduction of spanwise coherence on the cavity tone were greater in the cavity flow with acoustic resonance than in that without resonance, while the effects of the intensity were comparable for both flows. Hiroshi Yokoyama, Hiroshi Odawara, and Akiyoshi Iida Copyright © 2016 Hiroshi Yokoyama et al. All rights reserved. Application of Latitude Stripe Division in Satellite Constellation Coverage to Ground Tue, 29 Nov 2016 09:37:20 +0000 Grid point technique is a classical method in computing satellite constellation coverage to the ground regions. Aiming at improving the low computational efficiency of the conventional method, a method using latitude stripe division is proposed, which has high efficiency, and we name it latitude stripe method. After dividing the target region into several latitude stripes, the coverage status of each latitude stripe is computed by means of the spherical geometry relationship in the first orbital period. The longitude coverage intervals in the remaining orbital periods are computed by sliding the coverage status in the first orbital period. Based on this method, the instantaneous and cumulative coverage in simulation time can be calculated more efficiently. As well, the relationship between the cumulative coverage and altitude can be computed fast by this method, which could be used in the optimized design of repeating sun-synchronous orbits. The comparison between the conventional grid point method and the latitude stripe method shows that the latitude stripe method has high efficiency and accuracy. Through various case studies, the optimization in repeating sun-synchronous orbits design is successfully represented. Maocai Wang, Xin Luo, Guangming Dai, and Xiaoyu Chen Copyright © 2016 Maocai Wang et al. All rights reserved. A Novel Concept for Guidance and Control of Spacecraft Orbital Maneuvers Tue, 29 Nov 2016 08:54:49 +0000 The purpose of this paper is the design of guidance and control algorithms for orbital space maneuvers. A 6-dof orbital simulator, based on Clohessy-Wiltshire-Hill equations, is developed in C language, considering cold gas reaction thrusters and reaction wheels as actuation system. The computational limitations of on-board computers are also included. A combination of guidance and control algorithms for an orbital maneuver is proposed: (i) a suitably designed Zero-Effort-Miss/Zero-Effort-Velocity (ZEM/ZEV) algorithm is adopted for the guidance and (ii) a linear quadratic regulator (LQR) is used for the attitude control. The proposed approach is verified for different cases, including external environment disturbances and errors on the actuation system. Matteo Dentis, Elisa Capello, and Giorgio Guglieri Copyright © 2016 Matteo Dentis et al. All rights reserved. Preliminary Study on Aerodynamic Control of High-Angle-of-Attack Slender Body Using Blowing from Penetrating Flow Channels Sun, 27 Nov 2016 12:31:30 +0000 The objective of this study is to experimentally verify a new aerodynamic control concept of a high-angle-of-attack slender body. In the concept, penetrating flow channels are installed to the apex of the slender body. The blowing or suction is generated at the channel exits in response to the surface pressure distribution. First, the effects of the flow channels on the aerodynamic characteristics are experimentally investigated in a low-speed wind tunnel. The result shows the Suction-Blowing type channel is the most effective because its control effect does not reduce even in higher mainstream flow velocity. The peak value of the side force and yawing moment can be reduced by up to 64% and 49%, respectively. In addition, visualization of the surface flow pattern by the oil flow method shows that the Suction-Blowing type channel makes not only the primary separation line on the body side but also the secondary separation line on the body back become symmetric. Ayane Sato, Hiroyuki Nishida, and Satoshi Nonaka Copyright © 2016 Ayane Sato et al. All rights reserved. Three-Dimensional Integrated Guidance and Control for Near Space Interceptor Based on Robust Adaptive Backstepping Approach Thu, 24 Nov 2016 13:03:16 +0000 This study presents a novel integrated guidance and control method for near space interceptor, considering the coupling among different channels of the missile dynamics, which makes the most of the overall performance of guidance and control system. Initially, three-dimensional integrated guidance and control model is employed by combining the interceptor-target relative motion model with the nonlinear dynamics of the interceptor, which establishes a direct relationship between the interceptor-target relative motion and the deflections of aerodynamic fins. Subsequently, regarding the acceleration of the target as bounded uncertainty of the system, an integrated guidance and control algorithm is designed based on robust adaptive backstepping method, with the upper bound of the uncertainties unknown. Moreover, a nonlinear tracking differentiator is introduced to reduce the “compute explosion” caused by backstepping method. It is proved that tracking errors of the state and the upper bound of the uncertainties converge to the neighborhoods of the origin exponentially. Finally, simulations results show that, compared to the conventional guidance and control design, the algorithm proposed in this paper has greater advantages in miss distance, required normal overload, and flight stability, especially when attacking high-maneuvering targets. Changsheng Gao, Chunwang Jiang, Yan Zhang, and Wuxing Jing Copyright © 2016 Changsheng Gao et al. All rights reserved. A Bayesian Classifier for X-Ray Pulsars Recognition Thu, 24 Nov 2016 05:44:38 +0000 Recognition for X-ray pulsars is important for the problem of spacecraft’s attitude determination by X-ray Pulsar Navigation (XPNAV). By using the nonhomogeneous Poisson model of the received photons and the minimum recognition error criterion, a classifier based on the Bayesian theorem is proposed. For X-ray pulsars recognition with unknown Doppler frequency and initial phase, the features of every X-ray pulsar are extracted and the unknown parameters are estimated using the Maximum Likelihood (ML) method. Besides that, a method to recognize unknown X-ray pulsars or X-ray disturbances is proposed. Simulation results certificate the validity of the proposed Bayesian classifier. Hao Liang, Yafeng Zhan, and Chaowei Duan Copyright © 2016 Hao Liang et al. All rights reserved. Online Fault-Tolerant Onboard Aeroengine Model Tuning Structure Sun, 20 Nov 2016 07:36:47 +0000 Online onboard aeroengine models (OBEMs) have been widely used in health management, fault diagnostics, and fault-tolerant control. A mismatch between the OBEM and the actual engine may be caused by a variety of factors such as health degradation or sensor fault and may influence the effectiveness of the systems mentioned above. However, mismatch caused by unpredictable sensor fault is hardly distinguished from that caused by health degradation through the tuning process. A fault-tolerant OBEM tuning structure is provided to perform the online tuning function when health degradation and sensor fault coexist. This system includes three parts that include improved fault diagnostics and isolation (IFDI), a fault-tolerant OBEM tuning system (FTOTS), and a channel switching module. IFDI is used to distinguish the cause of mismatch and provide fault information, a FTOTS is used to complete an online tuning process based on information obtained from the IFDI, and the channel switching module is used to switch the working process from the IFDI to the FTOTS. Several simulation results show that this system is able to distinguish the causes of mismatch and complete online tuning in the case of sensor faults. Shuiting Ding, Ye Yuan, Naiyu Xue, and Xiaofeng Liu Copyright © 2016 Shuiting Ding et al. All rights reserved. Detecting Silent Data Corruptions in Aerospace-Based Computing Using Program Invariants Tue, 15 Nov 2016 12:06:34 +0000 Soft error caused by single event upset has been a severe challenge to aerospace-based computing. Silent data corruption (SDC) is one of the results incurred by soft error. SDC occurs when a program generates erroneous output with no indications. SDC is the most insidious type of results and very difficult to detect. To address this problem, we design and implement an invariant-based system called Radish. Invariants describe certain properties of a program; for example, the value of a variable equals a constant. Radish first extracts invariants at key program points and converts invariants into assertions. It then hardens the program by inserting the assertions into the source code. When a soft error occurs, assertions will be found to be false at run time and warn the users of soft error. To increase the coverage of SDC, we further propose an extension of Radish, named Radish_D, which applies software-based instruction duplication mechanism to protect the uncovered code sections. Experiments using architectural fault injections show that Radish achieves high SDC coverage with very low overhead. Furthermore, Radish_D provides higher SDC coverage than that of either Radish or pure instruction duplication. Junchi Ma, Dengyun Yu, Yun Wang, Zhenbo Cai, Qingxiang Zhang, and Cheng Hu Copyright © 2016 Junchi Ma et al. All rights reserved.