International Journal of Aerospace Engineering The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . 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. Theoretical and Numerical Studies of Dynamic Scaling of a Six-Degree-of-Freedom Laser Propulsion Vehicle Sun, 08 Mar 2015 06:54:00 +0000 To estimate the flight reactions of a full-scale vehicle from reduced-scale tests, we constructed a scaling theory for the vehicle size, input energy, moment of inertia, and pulse frequency needed to maintain dynamic equivalence between a laboratory-scale and full-scale launch of a laser propulsion vehicle. The dynamic scaling law for a single pulse was constructed using translational and angular equations of motion. The analytical scaling was confirmed for a single-pulse incident using a fluid-orbit coupling simulator for the interaction between the blast wave and the vehicle. Motion equivalence was maintained for multiple pulses by adjusting the repetition frequency of the pulse incident to correct for the effect of aerodynamic drag during the free flight of the pulse-to-pulse interval. The flight of a full-scale vehicle can be estimated for single- and multiple-pulse operations from the flight data for a small-scale vehicle using the proposed scaling theory, which provides correlations between the characteristics of small-scale and large-scale flight systems. Small-scale tests were shown to be useful in estimating the flight of a full-scale vehicle using dynamic scaling theory. Masayuki Takahashi and Naofumi Ohnishi Copyright © 2015 Masayuki Takahashi and Naofumi Ohnishi. All rights reserved. Degree Distribution of Arbitrary AANET Sat, 28 Feb 2015 06:52:40 +0000 Taking the safe distance between two adjacent planes in the same airline into account, we give a model for the multiairline aeronautical ad hoc network (AANET). Based on our model, we analyze the plane’s degree distribution of any arbitrary AANET. Then, the expressions of the degree distributions of one single plane and the whole networks are both worked out and verified by the simulations, in which we generate several random AANETs. Since our model is a reasonable abstraction of the real situation, the theoretical result we get is very close to the result of the real networks, which is also shown in the simulations. Xue Liu, Xiaoping Zeng, Zhiming Wang, Li Chen, and Yuemei Jin Copyright © 2015 Xue Liu et al. All rights reserved. Assessments of - Turbulence Model Based on Menter’s Modification to Rotta’s Two-Equation Model Thu, 26 Feb 2015 06:53:21 +0000 The main objective of this paper is to construct a turbulence model with a more reliable second equation simulating length scale. In the present paper, we assess the length scale equation based on Menter’s modification to Rotta’s two-equation model. Rotta shows that a reliable second equation can be formed in an exact transport equation from the turbulent length scale and kinetic energy. Rotta’s equation is well suited for a term-by-term modeling and shows some interesting features compared to other approaches. The most important difference is that the formulation leads to a natural inclusion of higher order velocity derivatives into the source terms of the scale equation, which has the potential to enhance the capability of Reynolds-averaged Navier-Stokes to simulate unsteady flows. The model is implemented in the CFD solver with complete formulation, usage methodology, and validation examples to demonstrate its capabilities. The detailed studies include grid convergence. Near-wall and shear flows cases are documented and compared with experimental and large eddy simulation data. The results from this formulation are as good or better than the well-known shear stress turbulence model and much better than - results. Overall, the study provides useful insights into the model capability in predicting attached and separated flows. Khaled S. Abdol-Hamid Copyright © 2015 All rights reserved. LARES: A New Satellite Specifically Designed for Testing General Relativity Thu, 19 Feb 2015 16:03:08 +0000 It is estimated that today several hundred operational satellites are orbiting Earth while many more either have already reentered the atmosphere or are no longer operational. On the 13th of February 2012 one more satellite of the Italian Space Agency has been successfully launched. The main difference with respect to all other satellites is its extremely high density that makes LARES not only the densest satellite but also the densest known orbiting object in the solar system. That implies that the nongravitational perturbations on its surface will have the smallest effects on its orbit. Those design characteristics are required to perform an accurate test of frame dragging and specifically a test of Lense-Thirring effect, predicted by General Relativity. LARES satellite, although passive, with 92 laser retroreflectors on its surface, was a real engineering challenge in terms of both manufacturing and testing. Data acquisition and processing are in progress. The paper will describe the scientific objectives, the status of the experiment, the special feature of the satellite and separation system including some manufacturing issues, and the special tests performed on its retroreflectors. Antonio Paolozzi, Ignazio Ciufolini, Claudio Paris, and Giampiero Sindoni Copyright © 2015 Antonio Paolozzi et al. All rights reserved. Autopilot Design Method for the Blended Missile Based on Model Predictive Control Sun, 08 Feb 2015 14:23:21 +0000 This paper develops a novel autopilot design method for blended missiles with aerodynamic control surfaces and lateral jets. Firstly, the nonlinear model of blended missiles is reduced into a piecewise affine (PWA) model according to the aerodynamics properties. Secondly, based on the equivalence between the PWA model and mixed logical dynamical (MLD) model, the MLD model of blended missiles is proposed taking into account the on-off constraints of lateral pulse jets. Thirdly, a hybrid model predictive control (MPC) method is employed to design autopilot. Finally, simulation results under different conditions are presented to show the effectiveness of the proposed method, which demonstrate that control allocation between aerodynamic control surfaces and lateral jets is realized by adjusting the weighting matrix in an index function. Baoqing Yang and Yuyu Zhao Copyright © 2015 Baoqing Yang and Yuyu Zhao. All rights reserved. Research on Aircraft Attack Angle Control Considering Servo-Loop Dynamics Mon, 26 Jan 2015 13:36:44 +0000 This paper presents a novel robust attack angle control approach, which can effectively suppress the impacts from system uncertainties and servo-loop dynamics. A second-order linear model of electromechanical servo loop is considered in the modeling and design processes. With regard to the block-structure models facing attack angle control, the multiple robust surfaces and dynamic surface control (DSC) approaches are both employed. By means of Lyapunov function method, the stability conditions of attack angle control systems are, respectively, given without/with considering the servo-loop dynamics in design process. Computer simulation results present that, compared with the attack angle control scheme which does not consider the servo-loop dynamics in design process, the proposed scheme can guarantee that the whole attack angle control system possesses the better comprehensive performances. Moreover, it is easy to be realized in engineering application. Xiaodong Liu, Yan Wang, Wanwei Huang, and Zongxia Jiao Copyright © 2015 Xiaodong Liu et al. All rights reserved. Modeling of the Diffusion Bond for SPF/DB Titanium Hollow Structures Tue, 20 Jan 2015 07:40:16 +0000 Diffusion-bonded titanium hollow warren structures have been successfully applied in aircraft engine components, such as fan blade, and OGV, while the optimal design of the hollow warren structure to improve its impact resistance, especially under bird-strike event, has been a challenge. In this work, a series of impact tests and numerical simulations are carried out to investigate the effect of key geometric features on the overall impact strength of a panel-shaped titanium hollow warren structure. Based on experimental and numerical studies, a quantitative relationship between diffusion bonding seam strength and the overall impact strength is developed. Meanwhile, key geometric factors affecting the resultant bonding seam strength for a typical manufacturing process are identified. This work provides useful references for the optimal design to increase impact resistance for aircraft engine hollow warren structure components. Xianghai Chai, Xiaoyun Zhang, Zhiqiang Wang, and Yesheng Liu Copyright © 2015 Xianghai Chai et al. All rights reserved. Sensitivity Analysis of Transonic Flow over J-78 Wings Thu, 08 Jan 2015 07:02:58 +0000 3D transonic flow over swept and unswept wings with an J-78 airfoil at spanwise sections is studied numerically at negative and vanishing angles of attack. Solutions of the unsteady Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume solver on unstructured meshes. The numerical simulation shows that adverse Mach numbers, at which the lift coefficient is highly sensitive to small perturbations, are larger than those obtained earlier for 2D flow. Due to the larger Mach numbers, there is an onset of self-exciting oscillations of shock waves on the wings. The swept wing exhibits a higher sensitivity to variations of the Mach number than the unswept one. Alexander Kuzmin Copyright © 2015 Alexander Kuzmin. All rights reserved. Nonlinear Vibrations of FGM Cylindrical Panel with Simply Supported Edges in Air Flow Tue, 06 Jan 2015 12:48:21 +0000 Chaotic and periodic motions of an FGM cylindrical panel in hypersonic flow are investigated. The cylindrical panel is also subjected to in-plane external loads and a linear temperature variation in the thickness direction. The temperature dependent material properties of panel which are assumed to be changed through the thickness direction only can be determined by a simple power distribution in terms of the volume fractions. With Hamilton’s principle for an elastic body, a nonlinear dynamical model based on Reddy’s first-order shear deformation shell theory and von Karman type geometric nonlinear relationship is derived in the form of partial equations. A third-order piston theory is adopted to evaluate the hypersonic aerodynamic load. Here, Galerkin’s method is employed to discretize this continuous nonlinear dynamic system to ordinary differential governing equations involving two degrees of freedom. The chaotic and periodic response are studied by the direct numerical simulation method for influences of different Mach number and the value of in-plane load. The bifurcations, Poincare section, waveform, and phase plots are presented. Y. X. Hao, W. Zhang, S. B. Li, and J. H. Zhang Copyright © 2015 Y. X. Hao et al. All rights reserved. Mechanical Behaviour of Inconel 718 Thin-Walled Laser Welded Components for Aircraft Engines Wed, 31 Dec 2014 00:10:32 +0000 Nickel alloys are very important in many aerospace applications, especially to manufacture gas turbines and aero engine components, where high strength and temperature resistance are necessary. These kinds of alloys have to be welded with high energy density processes, in order to preserve their high mechanical properties. In this work, CO2 laser overlap joints between Inconel 718 sheets of limited thickness in the absence of postweld heat treatment were made. The main application of this kind of joint is the manufacturing of a helicopter engine component. In particular the aim was to obtain a specific cross section geometry, necessary to overcome the mechanical stresses found in these working conditions without failure. Static and dynamic tests were performed to assess the welds and the parent material fatigue life behaviour. Furthermore, the life trend was identified. This research pointed out that a full joint shape control is possible by choosing proper welding parameters and that the laser beam process allows the maintenance of high tensile strength and ductility of Inconel 718 but caused many liquation microcracks in the heat affected zone (HAZ). In spite of these microcracks, the fatigue behaviour of the overlap welds complies with the technical specifications required by the application. Enrico Lertora, Chiara Mandolfino, and Carla Gambaro Copyright © 2014 Enrico Lertora et al. All rights reserved. A Novel Complementary Method for the Point-Scan Nondestructive Tests Based on Lamb Waves Tue, 25 Nov 2014 12:50:16 +0000 This study presents a novel area-scan damage identification method based on Lamb waves which can be used as a complementary method for point-scan nondestructive techniques. The proposed technique is able to identify the most probable locations of damages prior to point-scan test which lead to decreasing the time and cost of inspection. The test-piece surface was partitioned with some smaller areas and the damage probability presence of each area was evaluated. mode of Lamb wave was generated and collected using a mobile handmade transducer set at each area. Subsequently, a damage presence probability index (DPPI) based on the energy of captured responses was defined for each area. The area with the highest DPPI value highlights the most probable locations of damages in test-piece. Point-scan nondestructive methods can then be used once these areas are found to identify the damage in detail. The approach was validated by predicting the most probable locations of representative damages including through-thickness hole and crack in aluminum plates. The obtained experimental results demonstrated the high potential of developed method in defining the most probable locations of damages in structures. Rahim Gorgin, Zhanjun Wu, and Yuebin Zheng Copyright © 2014 Rahim Gorgin et al. All rights reserved. Optimum Disposition of Metal Particles in the Propellant Grain Wed, 12 Nov 2014 07:30:41 +0000 Using the dispersed metal in solid propellants to increase the temperature of combustion products leads to such a problem as the specific impulse loss due to the incomplete combustion of metal particles in the exhaust products. A redistribution of metal loaded into the propellant grain is one of the methods to decrease the specific impulse loss. This paper reports on the ways to obtain the optimum metal particle disposition for the case-bounded propellant grain of tube cross-sectional type. Three different approaches to analyze the metal combustion efficiency are discussed. The influence of the dynamic nonequilibrium of two-phase flow on the optimum metal particles disposition in the propellant grain of tube cross-sectional type is investigated. Leonid L. Minkov, Ernst R. Shrager, and Elizaveta V. Pikushchak Copyright © 2014 Leonid L. Minkov et al. All rights reserved. Experiment and Theoretical Analysis Study of ETFE Inflatable Tubes Tue, 11 Nov 2014 11:49:41 +0000 The load bearing capacity of an ETFE (ethylene-tetra-fluoro-ethylene) inflatable tube is tested in this paper, and a comparative study of two wrinkling theories, the bifurcation theory and the tension field theory, is carried out for wrinkling analysis of the ETFE inflatable tube. Results obtained from the bifurcation theory and experiment reveal the limitations of tension field theory on the wrinkling analysis. The load-displacement curves of inflatable beams under bending load are obtained and compared with the experimental results; curves obtained using the bifurcation theory show coincidence with experimental curves, but the curves obtained using the tension field theory have noticeable deviations between calculated and experimental results. YanLi He and WuJun Chen Copyright © 2014 YanLi He and WuJun Chen. All rights reserved. Active Control Optimization for Minimizing the Dynamic Response of Functionally Graded Plate Mon, 27 Oct 2014 11:11:24 +0000 A control optimization problem for functionally graded (FG) plates is presented using a first-order shear deformation plate theory including through-the-thickness normal strain effect. The aim of the optimization is to minimize the vibrational response of FG plate with constraints on the control energy used in the damping process. An active control optimization is presented to determine the optimal level of a closed loop control function. Plate thickness and a homogeneity parameter of FG plates are used as design variables. Numerical results for the optimal control force and the total energy for a simply supported FG plate are given. The influence of through-the-thickness normal strain effect on the accuracy of the obtained results is illustrated. The effectiveness of the present control and design procedure is examined. M. E. Fares, M. Kh. Elmarghany, and Doaa Atta Copyright © 2014 M. E. Fares et al. All rights reserved. Influence of Root Rotation on Delamination Fracture Toughness of Composites Mon, 20 Oct 2014 00:00:00 +0000 Large deviations have been observed while analysing composite double cantilever beam (DCB) specimens assuming each cracked half as a simple cantilever beam. This paper examines the effect of rotational spring stiffness on the critical fracture energy considering nonzero slope at the crack-tip of the DCB specimen by modelling each cracked half as the spring-hinged cantilever beam. The critical load estimates of DCB specimens from are found to be in good agreement with in-house and existing test results of different composite material systems. V. Alfred Franklin, T. Christopher, and B. Nageswara Rao Copyright © 2014 V. Alfred Franklin et al. All rights reserved. Modeling Techniques for a Computational Efficient Dynamic Turbofan Engine Model Sun, 12 Oct 2014 09:18:16 +0000 A transient two-stream engine model has been developed. Individual component models developed exclusively in MATLAB/Simulink including the fan, high pressure compressor, combustor, high pressure turbine, low pressure turbine, plenum volumes, and exit nozzle have been combined to investigate the behavior of a turbofan two-stream engine. Special attention has been paid to the development of transient capabilities throughout the model, increasing physics model, eliminating algebraic constraints, and reducing simulation time through enabling the use of advanced numerical solvers. The lessening of computation time is paramount for conducting future aircraft system-level design trade studies and optimization. The new engine model is simulated for a fuel perturbation and a specified mission while tracking critical parameters. These results, as well as the simulation times, are presented. The new approach significantly reduces the simulation time. Rory A. Roberts and Scott M. Eastbourn Copyright © 2014 Rory A. Roberts and Scott M. Eastbourn. All rights reserved.