International Journal of Aerospace Engineering The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Ligament and Droplet Generation by Oil Film on a Rotating Disk Mon, 12 Oct 2015 11:39:31 +0000 The lubrication and heat transfer designs of bearing chamber depend on an understanding of oil/air two-phase flow. As initial and boundary conditions, the characteristics of ligament and droplet generation by oil film on rotating parts have significant influence on the feasibility of oil/air two-phase flow analysis. An integrated model to predict the oil film flow, ligament number, and droplet Sauter mean diameter (SMD) of a rotating disk, which is an abstraction of the droplet generation sources in a bearing chamber, is developed based on the oil film force balance analysis and wave theory. The oil film thickness and velocity, ligaments number, and droplet SMD are calculated as functions of the rotating disk radius, rotational speed and oil volume flow rate and oil properties. The theoretical results show that the oil film thickness and SMD are decreased with an increasing rotational speed, while the radial, transverse velocities, and ligament number are increased. The oil film thickness, radial velocity, and SMD are increased with an increasing oil flow rate, but the transverse velocity and ligament number are decreased. A test facility is built for the investigation into the ligament number of a rotating disk, and the measurement of ligament number is carried out by means of a high speed photography. Hengchao Sun, Guoding Chen, Li’na Wang, and Fei Wang Copyright © 2015 Hengchao Sun et al. All rights reserved. A Three-Dimensional Cooperative Guidance Law of Multimissile System Sun, 04 Oct 2015 13:36:15 +0000 In order to conduct saturation attacks on a static target, the cooperative guidance problem of multimissile system is researched. A three-dimensional guidance model is built using vector calculation and the classic proportional navigation guidance (PNG) law is extended to three dimensions. Based on this guidance law, a distributed cooperative guidance strategy is proposed and a consensus protocol is designed to coordinate the time-to-go commands of all missiles. Then an expert system, which contains two extreme learning machines (ELM), is developed to regulate the local proportional coefficient of each missile according to the command. All missiles can arrive at the target simultaneously under the assumption that the multimissile network is connected. A simulation scenario is given to demonstrate the validity of the proposed method. Xing Wei, Yongji Wang, Shuai Dong, and Lei Liu Copyright © 2015 Xing Wei et al. All rights reserved. A Numerical Method for Blast Shock Wave Analysis of Missile Launch from Aircraft Wed, 30 Sep 2015 14:34:30 +0000 An efficient empirical approach was developed to accurately represent the blast shock wave loading resulting from the launch of a missile from a military aircraft to be used in numerical analyses. Based on experimental test series of missile launches in laboratory environment and from a helicopter, equations were derived to predict the time- and position-dependent overpressure. The method was finally applied and validated in a structural analysis of a helicopter tail boom under missile launch shock wave loading. Sebastian Heimbs, Josef Ritzer, and Johannes Markmiller Copyright © 2015 Sebastian Heimbs et al. All rights reserved. A Comprehensive Probabilistic Framework to Learn Air Data from Surface Pressure Measurements Mon, 28 Sep 2015 12:28:19 +0000 Use of probabilistic techniques has been demonstrated to learn air data parameters from surface pressure measurements. Integration of numerical models with wind tunnel data and sequential experiment design of wind tunnel runs has been demonstrated in the calibration of a flush air data sensing anemometer system. Development and implementation of a metamodeling method, Sequential Function Approximation (SFA), are presented which lies at the core of the discussed probabilistic framework. SFA is presented as a tool capable of nonlinear statistical inference, uncertainty reduction by fusion of data with physical models of variable fidelity, and sequential experiment design. This work presents the development and application of these tools in the calibration of FADS for a Runway Assisted Landing Site (RALS) control tower. However, the multidisciplinary nature of this work is general in nature and is potentially applicable to a variety of mechanical and aerospace engineering problems. Ankur Srivastava and Andrew J. Meade Copyright © 2015 Ankur Srivastava and Andrew J. Meade. All rights reserved. Study on the Effect of Air Throttling on Flame Stabilization of an Ethylene Fueled Scramjet Combustor Thu, 17 Sep 2015 15:22:42 +0000 The effect of air throttling on flame stabilization of an ethylene fueled scramjet combustor was investigated by numerical simulation and experiments in this paper. The results were obtained under the inflow condition with Mach number of 2.0, total temperature of 900 K, total pressure of 0.8 MPa, and total equivalence ratio of 0.5. The shock train generated by air throttling had a big effect on the flow structure of the scramjet combustor. Compared with the combustor without air throttling, the flow field with air throttling had a lower velocity and higher pressure, temperature, and vortices intensity. Air throttling was an effective way to achieve flame stabilization; the combustion in the combustor without air throttling was nearly blowout. In the experiment, the combustion was nearly blowout with air throttling location of 745 mm, and the fuel/air mixture in the combustor with air throttling location of 875 mm was burned intensively. It was important to choose the location and time sequence of air throttling for fuel ignition and flame stabilization. The numerical simulation results agreed well with experimental measurements. Ye Tian, Shunhua Yang, and Jialing Le Copyright © 2015 Ye Tian et al. All rights reserved. Designing Backstepping Control System for Hypersonic Vehicle Based on Feedback Linearization Mon, 17 Aug 2015 13:52:39 +0000 A hypersonic vehicle uses the airbreathing scramjet engine and the airframe and engine integrated design. Therefore, there is a strong cross-coupling effect among its aerodynamic force, thrust, structure, and control. The nonlinearity and uncertainty of the model cause difficulties in control system design. Considering the nonlinearity, coupling characteristics, and aerodynamic parametric uncertainty of its longitudinal dynamic model, we design the control law for its altitude system and velocity system based on the adaptive backstepping control method. Because of the feedback linearization method, we introduce the constraints of the flight vehicle’s actuator into the design, obtaining the robust adaptive control system constrained by the actuator of the flight vehicle. To avoid the high-order derivation problem of the feedback linearization method and the derivation of the virtual control volume in adaptive backstepping control method, we use the arbitrary-order robust exact differentiator to solve the high-order derivatives in feedback linearization and utilize the command filter to obtain the virtual control volume and its derivatives. The simulation results show that the robust adaptive control system we designed can achieve the error-free tracking of altitude and velocity command. It can well overcome the influence of structural parameters, aerodynamic parametric uncertainty, and disturbances; meanwhile, the control command can satisfy the constraints of the actuator. Jianli Wei and Huan Chen Copyright © 2015 Jianli Wei and Huan Chen. All rights reserved. Guidance and Control Design for a Class of Spin-Stabilized Projectiles with a Two-Dimensional Trajectory Correction Fuze Tue, 11 Aug 2015 09:49:44 +0000 A guidance and control strategy for a class of 2D trajectory correction fuze with fixed canards is developed in this paper. Firstly, correction control mechanism is researched through studying the deviation motion, the key point of which is the dynamic equilibrium angle. Phase lag of swerve response is the dominating factor for correction control, and formula is deduced with the Mach number as argument. Secondly, impact point deviation prediction based on perturbation theory is proposed, and the numerical solution and application method are introduced. Finally, guidance and control strategy is developed, and simulations to validate the strategy are conducted. Yi Wang, Wei-dong Song, Dan Fang, and Qing-wei Guo Copyright © 2015 Yi Wang et al. All rights reserved. Robust Predictive Functional Control for Flight Vehicles Based on Nonlinear Disturbance Observer Thu, 30 Jul 2015 17:07:24 +0000 A novel robust predictive functional control based on nonlinear disturbance observer is investigated in order to address the control system design for flight vehicles with significant uncertainties, external disturbances, and measurement noise. Firstly, the nonlinear longitudinal dynamics of the flight vehicle are transformed into linear-like state-space equations with state-dependent coefficient matrices. And then the lumped disturbances are considered in the linear structure predictive model of the predictive functional control to increase the precision of the predictive output and resolve the intractable mismatched disturbance problem. As the lumped disturbances cannot be derived or measured directly, the nonlinear disturbance observer is applied to estimate the lumped disturbances, which are then introduced to the predictive functional control to replace the unknown actual lumped disturbances. Consequently, the robust predictive functional control for the flight vehicle is proposed. Compared with the existing designs, the effectiveness and robustness of the proposed flight control are illustrated and validated in various simulation conditions. Yinhui Zhang, Huabo Yang, Zhenyu Jiang, Fan Hu, and Weihua Zhang Copyright © 2015 Yinhui Zhang et al. All rights reserved. Multidisciplinary Design Optimization and Analysis of Hydrazine Monopropellant Propulsion System Tue, 28 Jul 2015 08:46:10 +0000 Monopropellant propulsion systems are widely used especially for low cost attitude control or orbit correction (orbit maintenance). To optimize the total propulsion system, subsystems should be optimized. Chemical decomposition, aerothermodynamics, and structure disciplines demand different optimum condition such as tank pressure, catalyst bed length and diameter, catalyst bed pressure, and nozzle geometry. Subsystem conflicts can be solved by multidisciplinary design optimization (MDO) technique with simultaneous optimization of all subsystems with respect to any criteria and limitations. In this paper, monopropellant propulsion system design algorithm is presented and the results of the proposed algorithm are validated. Then, multidisciplinary design optimization of hydrazine propulsion system is proposed. The goal of optimization can be selected as minimizing the total mass (including propellant), minimizing the propellant mass (maximizing the Isp), or minimizing the dry mass. Minimum total mass, minimum propellant mass, and minimum dry mass are derived using MDO technique. It is shown that minimum total mass, minimum dry mass, and minimum propellant mass take place in different conditions. The optimum parameters include bed-loading, inlet pressure, mass flow, nozzle geometry, catalyst bed length and diameter, propellant tank mass, specific impulse (Isp), and feeding mass which are derived using genetic algorithm (GA). Amirhossein Adami, Mahdi Mortazavi, Mehran Nosratollahi, Mohammadreza Taheri, and Jalal Sajadi Copyright © 2015 Amirhossein Adami et al. All rights reserved. Research on Dynamic Reliability of a Jet Pipe Servo Valve Based on Generalized Stochastic Petri Nets Wed, 22 Jul 2015 10:17:45 +0000 The jet pipe servo valve is widely used in the military fields of aviation and ship, whose reliability has obvious randomness and dynamic. However, existing methods are either having complicated theory or analyzing static reliability. Based on the generalized stochastic petri nets (GSPN) theory and the collected basic failure modes and failure rate data of jet pipe servo valve, this paper proposes a novel modeling and simulating method for system’s dynamic behavior analysis. In this method, the dynamic reliability model considering failure’s random and repair is established and is simulated using GSPN software. Then, the steady state probability of servo valve is calculated, which is compared with the value calculated by Markov method. Finally, the dynamic reliability parameters of jet pipe servo valve are calculated using collected failure rate data and different repair rate data. Results show the probability that the maximum error between methods of GSPN and Markov is 2.07%, the optimal repair rate set is less than 1.71µi, and also the dynamic reliability parameters become better with increasing simulation time because of failure’s recovery. Therefore, research methods and results based on GSPN are concise and realistic, which can be used for failure’s qualitative forecast and dynamic reliability’s quantitative calculation of similar complicated system. Yuanbo Chu, Zhaohui Yuan, and Jia Chen Copyright © 2015 Yuanbo Chu et al. All rights reserved. Chaotic Artificial Bee Colony Algorithm for System Identification of a Small-Scale Unmanned Helicopter Tue, 21 Jul 2015 08:24:13 +0000 The purpose of this paper is devoted to developing a chaotic artificial bee colony algorithm (CABC) for the system identification of a small-scale unmanned helicopter state-space model in hover condition. In order to avoid the premature of traditional artificial bee colony algorithm (ABC), which is stuck in local optimum and can not reach the global optimum, a novel chaotic operator with the characteristics of ergodicity and irregularity was introduced to enhance its performance. With input-output data collected from actual flight experiments, the identification results showed the superiority of CABC over the ABC and the genetic algorithm (GA). Simulations are presented to demonstrate the effectiveness of our proposed algorithm and the accuracy of the identified helicopter model. Li Ding, Hongtao Wu, and Yu Yao Copyright © 2015 Li Ding et al. All rights reserved. Ionospheric Delay Handling for Relative Navigation by Carrier-Phase Differential GPS Thu, 16 Jul 2015 10:20:15 +0000 The paper investigates different solutions for ionospheric delay handling in high accuracy long baseline relative positioning by Carrier-Phase Differential GPS (CDGPS). Standard literature approaches are reviewed and the relevant limitations are discussed. Hence, a completely ionosphere-free approach is proposed, in which the differential ionospheric delays are cancelled out by combination of dual frequency GPS measurements. The performance of this approach is quantified over real-world spaceborne GPS data made available by the Gravity Recovery and Climate Experiment (GRACE) mission and compared to the standard solution. A. Renga, U. Tancredi, and M. Grassi Copyright © 2015 A. Renga et al. All rights reserved. Prediction of Pressing Quality for Press-Fit Assembly Based on Press-Fit Curve and Maximum Press-Mounting Force Wed, 15 Jul 2015 09:13:34 +0000 In order to predict pressing quality of precision press-fit assembly, press-fit curves and maximum press-mounting force of press-fit assemblies were investigated by finite element analysis (FEA). The analysis was based on a 3D Solidworks model using the real dimensions of the microparts and the subsequent FEA model that was built using ANSYS Workbench. The press-fit process could thus be simulated on the basis of static structure analysis. To verify the FEA results, experiments were carried out using a press-mounting apparatus. The results show that the press-fit curves obtained by FEA agree closely with the curves obtained using the experimental method. In addition, the maximum press-mounting force calculated by FEA agrees with that obtained by the experimental method, with the maximum deviation being 4.6%, a value that can be tolerated. The comparison shows that the press-fit curve and max press-mounting force calculated by FEA can be used for predicting the pressing quality during precision press-fit assembly. Bo You, Zhifeng Lou, Yi Luo, Yang Xu, and Xiaodong Wang Copyright © 2015 Bo You et al. All rights reserved. The Simultaneous Interpolation of Target Radar Cross Section in Both the Spatial and Frequency Domains by Means of Legendre Wavelets Model-Based Parameter Estimation Sun, 12 Jul 2015 08:30:00 +0000 The understanding of the target radar cross section (RCS) is significant for target identification and for radar designing and optimization. In this paper, a numerical algorithm for calculating target RCS is presented which is based on Legendre wavelet model-based parameter estimation (LW-MBPE). The Padé rational function fitting model applied for MBPE in the frequency domain is enhanced to include spatial dependence on the numerator and denominator coefficients. This allows the function to interpolate target RCS in both the frequency and spatial domains simultaneously. The combination of Legendre wavelets guarantees the convergence of the algorithm. The method is convergent by increasing the sampling frequency and spatial points. Numerical results are provided to demonstrate the validity and applicability of the new technique. Yongqiang Yang, Yunpeng Ma, and Lifeng Wang Copyright © 2015 Yongqiang Yang et al. All rights reserved. GPS Based Reduced-Dynamic Orbit Determination for Low Earth Orbiters with Ambiguity Fixing Tue, 07 Jul 2015 06:48:33 +0000 With the ever-increasing number of satellites in Low Earth Orbit (LEO) for scientific missions, the precise determination of the position and velocity of the satellite is a necessity. GPS (Global Positioning System) based reduced-dynamic orbit determination (RPOD) method is commonly used in the post processing with high precision. This paper presents a sequential RPOD strategy for LEO satellite in the framework of Extended Kalman Filter (EKF). Precise Point Positioning (PPP) technique is used to process the GPS observations, with carrier phase ambiguity resolution using Integer Phase Clocks (IPCs) products. A set of GRACE (Gravity Recovery And Climate Experiment) mission data is used to test and validate the RPOD performance. Results indicate that orbit determination accuracy could be improved by 15% in terms of 3D RMS error in comparison with traditional RPOD method with float ambiguity solutions. Yang Yang, Xiaokui Yue, and Jianping Yuan Copyright © 2015 Yang Yang et al. All rights reserved. A New Adaptive Square-Root Unscented Kalman Filter for Nonlinear Systems with Additive Noise Mon, 06 Jul 2015 05:45:04 +0000 The Kalman filter (KF), extended KF, and unscented KF all lack a self-adaptive capacity to deal with system noise. This paper describes a new adaptive filtering approach for nonlinear systems with additive noise. Based on the square-root unscented KF (SRUKF), traditional Maybeck’s estimator is modified and extended to nonlinear systems. The square root of the process noise covariance matrix Q or that of the measurement noise covariance matrix R is estimated straightforwardly. Because positive semidefiniteness of Q or R is guaranteed, several shortcomings of traditional Maybeck’s algorithm are overcome. Thus, the stability and accuracy of the filter are greatly improved. In addition, based on three different nonlinear systems, a new adaptive filtering technique is described in detail. Specifically, simulation results are presented, where the new filter was applied to a highly nonlinear model (i.e., the univariate nonstationary growth model (UNGM)). The UNGM is compared with the standard SRUKF to demonstrate its superior filtering performance. The adaptive SRUKF (ASRUKF) algorithm can complete direct recursion and calculate the square roots of the variance matrixes of the system state and noise, which ensures the symmetry and nonnegative definiteness of the matrixes and greatly improves the accuracy, stability, and self-adaptability of the filter. Yong Zhou, Chao Zhang, Yufeng Zhang, and Juzhong Zhang Copyright © 2015 Yong Zhou et al. All rights reserved. Distributed Cooperative Search Control Method of Multiple UAVs for Moving Target Wed, 17 Jun 2015 09:54:00 +0000 To reduce the impact of uncertainties caused by unknown motion parameters on searching plan of moving targets and improve the efficiency of UAV’s searching, a novel distributed Multi-UAVs cooperative search control method for moving target is proposed in this paper. Based on detection results of onboard sensors, target probability map is updated using Bayesian theory. A Gaussian distribution of target transition probability density function is introduced to calculate prediction probability of moving target existence, and then target probability map can be further updated in real-time. A performance index function combining with target cost, environment cost, and cooperative cost is constructed, and the cooperative searching problem can be transformed into a central optimization problem. To improve computational efficiency, the distributed model predictive control method is presented, and thus the control command of each UAV can be obtained. The simulation results have verified that the proposed method can avoid the blindness of UAV searching better and improve overall efficiency of the team effectively. Chang-jian Ru, Xiao-ming Qi, and Xu-ning Guan Copyright © 2015 Chang-jian Ru et al. All rights reserved. Investigation of Flow Control for the Hypersonic Inlets via Counter Flow Wed, 17 Jun 2015 08:28:31 +0000 Experimental results show that there exist two flow fields in the hypersonic inlets when the forebody waves interact with the lip boundary, which is similar to the shock reflection ion hysteresis phenomenon. In order to improve the performance of the flow field, counterflow is applied to control the shock reflection configuration in the hypersonic inlets. For better understanding of the internal mechanism, inviscid numerical simulation is conducted. And the results demonstrate that it is feasible to realize the transition between the regular reflection configuration and the Mach reflection ion configuration in the hypersonic inlets. That is because the von Neumann criterion and detached criterion play a dominant role, respectively, in these transitions. In addition, the evolution process of Mach reflection ion in the hypersonic inlets can be divided into three stages: transmission of waves, emergence of Mach stem, and stabilization of flow field. Xiaoqiang Fan and Yuan Tao Copyright © 2015 Xiaoqiang Fan and Yuan Tao. All rights reserved. ARMA Prediction of SBAS Ephemeris and Clock Corrections for Low Earth Orbiting Satellites Tue, 16 Jun 2015 08:49:28 +0000 For low earth orbit (LEO) satellite GPS receivers, space-based augmentation system (SBAS) ephemeris/clock corrections can be applied to improve positioning accuracy in real time. The SBAS correction is only available within its service area, and the prediction of the SBAS corrections during the outage period can extend the coverage area. Two time series forecasting models, autoregressive moving average (ARMA) and autoregressive (AR), are proposed to predict the corrections outside the service area. A simulated GPS satellite visibility condition is applied to the WAAS correction data, and the prediction accuracy degradation, along with the time, is investigated. Prediction results using the SBAS rate of change information are compared, and the ARMA method yields a better accuracy than the rate method. The error reductions of the ephemeris and clock by the ARMA method over the rate method are 37.8% and 38.5%, respectively. The AR method shows a slightly better orbit accuracy than the rate method, but its clock accuracy is even worse than the rate method. If the SBAS correction is sufficiently accurate comparing with the required ephemeris accuracy of a real-time navigation filter, then the predicted SBAS correction may improve orbit determination accuracy. Jeongrae Kim and Mingyu Kim Copyright © 2015 Jeongrae Kim and Mingyu Kim. All rights reserved. Helicopter Vibratory Loads Alleviation through Combined Action of Trailing-Edge Flap and Variable-Stiffness Devices Thu, 04 Jun 2015 11:37:58 +0000 The aim of this paper is the assessment of the capability of controllers based on the combined actuation of flaps and variable-stiffness devices to alleviate helicopter main rotor vibratory hub loads. Trailing-edge flaps are positioned at the rotor blade tip region, whereas variable-stiffness devices are located at the pitch link and at the blade root. Control laws are derived by an optimal control procedure based on the best trade-off between control effectiveness and control effort, under the constraint of satisfaction of the equations governing rotor blade aeroelastic response. The numerical investigation concerns the analysis of performance and robustness of the control techniques developed, through application to a four-bladed helicopter rotor in level flight. The identification of the most efficient control configuration is also attempted. Massimo Gennaretti, Giovanni Bernardini, Jacopo Serafini, and Marco Molica Colella Copyright © 2015 Massimo Gennaretti et al. All rights reserved. Stress Distribution on Sandwich Structure with Triangular Grid Cores Suffered from Bending Load Sun, 31 May 2015 12:02:14 +0000 Triangular grid reinforced by carbon fiber/epoxy (CF/EP) was designed and manufactured. The sandwich structure was prepared by gluing the core and composite skins. The mechanical properties of the sandwich structure were investigated by the finite element analysis (FEA) and three-point bending methods. The calculated bending stiffness and core shear stress were compared to the characteristics of a honeycomb sandwich structure. The results indicated that the triangular core ultimately failed under a bending load of 11000 N; the principal stress concentration was located at the loading region; and the cracks occurred on the interface top skin and triangular core. In addition, the ultimate stress bearing of the sandwich structure was 8828 N. The experimental results showed that the carbon fiber reinforced triangular grid was much stiffer and stronger than the honeycomb structure. Cui Xu, Huang Yanjiao, Wang Shou, Lu Chun, and Fang Luping Copyright © 2015 Cui Xu et al. All rights reserved. An EBSPK-/MPPSK-Modem Based Transceiver for Radar-Communications Tue, 05 May 2015 09:32:11 +0000 A joint communication and ranging system would constitute a unique platform for future weapon platform or intelligent transportation system to affect the essential tasks of Identification Friend or Foe (IFF) system and location sharing services, in terms of both spectrum efficiency and cost effectiveness. In this paper, the design of efficient modulation system which is suitable for simultaneously performing both data transmission and range measurement is proposed. The approach is based on extended binary phase shift keying (EBPSK) or -ary Position Phase Shift Keying (MPPSK) modulated waveforms utilized in digital communication. In particular, requirements that allow for employing such signals for range measurements are investigated. Also, Constant False Alarm Rate (CFAR) target detection performances of the new proposed system are discussed when target velocity and time delay take different values. Moreover, Doppler tolerance range of impacting filter for demodulating EBPSK/MPPSK pulse signal at 10 GHz is considered. In addition to theoretical considerations, the paper presents simulations and measurement results of the new systems, demonstrating the high spectral utilization of integrated communication and ranging applications. Yu Yao and Lenan Wu Copyright © 2015 Yu Yao and Lenan Wu. All rights reserved. Cartesian Mesh Linearized Euler Equations Solver for Aeroacoustic Problems around Full Aircraft Thu, 30 Apr 2015 14:19:09 +0000 The linearized Euler equations (LEEs) solver for aeroacoustic problems has been developed on block-structured Cartesian mesh to address complex geometry. Taking advantage of the benefits of Cartesian mesh, we employ high-order schemes for spatial derivatives and for time integration. On the other hand, the difficulty of accommodating curved wall boundaries is addressed by the immersed boundary method. The resulting LEEs solver is robust to complex geometry and numerically efficient in a parallel environment. The accuracy and effectiveness of the present solver are validated by one-dimensional and three-dimensional test cases. Acoustic scattering around a sphere and noise propagation from the JT15D nacelle are computed. The results show good agreement with analytical, computational, and experimental results. Finally, noise propagation around fuselage-wing-nacelle configurations is computed as a practical example. The results show that the sound pressure level below the over-the-wing nacelle (OWN) configuration is much lower than that of the conventional DLR-F6 aircraft configuration due to the shielding effect of the OWN configuration. Yuma Fukushima, Daisuke Sasaki, and Kazuhiro Nakahashi Copyright © 2015 Yuma Fukushima et al. All rights reserved. Firing Control Optimization of Impulse Thrusters for Trajectory Correction Projectiles Mon, 27 Apr 2015 06:50:55 +0000 This paper presents an optimum control scheme of firing time and firing phase angle by taking impact point deviation as optimum objective function which takes account of the difference of longitudinal and horizontal correction efficiency, firing delay, roll rate, flight stability, and so forth. Simulations indicate that this control scheme can assure lateral impulse thrusters are activated at time and phase angle when the correction efficiency is higher. Further simulations show that the impact point dispersion is mainly influenced by the total impulse deployed, and the impulse, number, and firing interval need to be optimized to reduce the impact point dispersion of rockets. Live firing experiments with two trajectory correction rockets indicate that the firing control scheme works effectively. Min Gao, Yongwei Zhang, and Suochang Yang Copyright © 2015 Min Gao et al. All rights reserved. Load-Sharing Characteristics of Power-Split Transmission System Based on Deformation Compatibility and Loaded Tooth Contact Analysis Sun, 12 Apr 2015 14:20:39 +0000 In order to implement the uniform load distribution of the power-split transmission system, a pseudostatic model is built. Based on the loaded tooth contact analysis (LTCA) technique, the actual meshing process of each gear pair is simulated and the fitting curve of time-varying mesh stiffness is obtained. And then, the torsional angle deformation compatibility conditions are proposed according to the closed-loop characteristic of power flow, which will be combined with the torque equilibrium conditions and elastic support conditions to calculate the transfer torque of each gear pair. Finally, the load-sharing coefficient of the power-split transmission system is obtained, and the influences of the installation errors are analyzed. The results show that the above-mentioned installation errors comprehensively influence the load-sharing characteristics, and the reduction of only one error could not effectively achieve perfect load-sharing characteristics. Allowing for the spline clearance floating and constrained by the radial spacing ring, the influence of the floating pinion is analyzed. It shows that the floating pinion can improve the load-sharing characteristics. Through the comparison between the theoretical and related experimental data, the reasonability and feasibility of the above-proposed method and model are verified. Hao Dong, Ling-ling Duan, Jun-an Zhang, and Zhou Fang Copyright © 2015 Hao Dong et al. All rights reserved. Numerical Simulation of Reactive Flows in Overexpanded Supersonic Nozzle with Film Cooling Sun, 05 Apr 2015 08:34:05 +0000 Reignition phenomena occurring in a supersonic nozzle flow may present a crucial safety issue for rocket propulsion systems. These phenomena concern mainly rocket engines which use H2 gas (GH2) in the film cooling device, particularly when the nozzle operates under over expanded flow conditions at sea level or at low altitudes. Consequently, the induced wall thermal loads can lead to the nozzle geometry alteration, which in turn, leads to the appearance of strong side loads that may be detrimental to the rocket engine structural integrity. It is therefore necessary to understand both aerodynamic and chemical mechanisms that are at the origin of these processes. This paper is a numerical contribution which reports results from CFD analysis carried out for supersonic reactive flows in a planar nozzle cooled with GH2 film. Like the experimental observations, CFD simulations showed their ability to highlight these phenomena for the same nozzle flow conditions. Induced thermal load are also analyzed in terms of cooling efficiency and the results already give an idea on their magnitude. It was also shown that slightly increasing the film injection pressure can avoid the reignition phenomena by moving the separation shock towards the nozzle exit section. Mohamed Sellam and Amer Chpoun Copyright © 2015 Mohamed Sellam and Amer Chpoun. All rights reserved. Collaborative Deformation Design Using Control Integrated Analysis Methods for Hypersonic Waverider Mon, 30 Mar 2015 12:00:38 +0000 Hypersonic waveriders have a large flight envelope, leading to the difficulty in keeping overall flight stability for a fixed geometry. Accordingly, hypersonic waveriders can be considered to design as a morphing vehicle such that the flight range is expanded for waveriding stability. To this end, this paper investigates the collaborative deformation design using control integrated analysis methods for the hypersonic waverider. Firstly, a parametric model is applied to combine the shape deformation with the geometrical properties. Secondly, the morphing process with regard to the change in a single geometric parameter and the static and dynamic characteristics affected by this deformation are analyzed. Afterwards, the collaborative relations are discussed for the changes in the lower forebody angle and elevon area. Furthermore, a flight control law is designed to guarantee flight stability while implementing the collaborative deformation, and the morphing results are evaluated based on the control-oriented idea. Finally, a simulation example is used to verify the effectiveness of the proposed methods for the hypersonic waverider. Yanbin Liu and Yuping Lu Copyright © 2015 Yanbin Liu and Yuping Lu. All rights reserved. Hybrid Vortex Method for the Aerodynamic Analysis of Wind Turbine Mon, 30 Mar 2015 08:49:29 +0000 The hybrid vortex method, in which vortex panel method is combined with the viscous-vortex particle method (HPVP), was established to model the wind turbine aerodynamic and relevant numerical procedure program was developed to solve flow equations. The panel method was used to calculate the blade surface vortex sheets and the vortex particle method was employed to simulate the blade wake vortices. As a result of numerical calculations on the flow over a wind turbine, the HPVP method shows significant advantages in accuracy and less computation resource consuming. The validation of the aerodynamic parameters against Phase VI wind turbine experimental data is performed, which shows reasonable agreement. Hao Hu, Bo Gu, Hongtao Zhang, Xiancheng Song, and Wanli Zhao Copyright © 2015 Hao Hu et al. All rights reserved. A Novel Software Simulator Model Based on Active Hybrid Architecture Mon, 23 Mar 2015 12:44:53 +0000 The simulated training is an important issue for any type of missions such as aerial, ground, sea, or even space missions. In this paper, a new flexible aerial simulator based on active hybrid architecture is introduced. The simulator infrastructure is applicable to any type of training missions and research activities. This software-based simulator is tested on aerial missions to prove its applicability within time critical systems. The proposed active hybrid architecture is introduced via using the VB.NET and MATLAB in the same simulation loop. It exploits the remarkable computational power of MATLAB as a backbone aircraft model, and such mathematical model provides realistic dynamics to the trainee. Meanwhile, the Human-Machine Interface (HMI), the mission planning, the hardware interfacing, data logging, and MATLAB interfacing are developed using VB.NET. The proposed simulator is flexible enough to perform navigation and obstacle avoidance training missions. The active hybrid architecture is used during the simulated training, and also through postmission activities (like the generation of signals playback reports for evaluation purposes). The results show the ability of the proposed architecture to fulfill the aerial simulator demands and to provide a flexible infrastructure for different simulated mission requirements. Finally, a comparison with some existing simulators is introduced. Amr AbdElHamid and Peng Zong Copyright © 2015 Amr AbdElHamid and Peng Zong. All rights reserved. Approximate State Transition Matrix and Secular Orbit Model Tue, 10 Mar 2015 06:33:10 +0000 The state transition matrix (STM) is a part of the onboard orbit determination system. It is used to control the satellite’s orbital motion to a predefined reference orbit. Firstly in this paper a simple orbit model that captures the secular behavior of the orbital motion in the presence of all perturbation forces is derived. Next, an approximate STM to match the secular effects in the orbit due to oblate earth effect and later in the presence of all perturbation forces is derived. Numerical experiments are provided for illustration. M. P. Ramachandran Copyright © 2015 M. P. Ramachandran. All rights reserved.