International Journal of Aerospace Engineering The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . 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. Steepest-Ascent Revisited: Unconstrained Missile Trajectory Mon, 15 Sep 2014 00:00:00 +0000 A Steepest-Ascent numerical procedure for offline trajectory optimization of a surface-to-surface missile attacking a stationary target is presented. A detailed numerical solution, starting from building the mathematical formulation till generating an offline angle of attack control history, is illustrated. A novel approach for guessing a nominal control program is conducted. The formulation entails nonlinear 2-DOF missile flight dynamics with mixed boundary conditions. The technique of changing of variables is adopted to convert the free-final-time optimization problem to a fixed-final-time one. The influences of the optimization algorithm controlling parameters are investigated. A new form of the weighting matrix is proposed. A novel technique of relaxation factors for eliminating the terminal states violation is described. Finally, a comparison between the obtained control history and the one obtained by a nonlinear optimal control package “GPOPS” is presented. The results indicate that the use of Steepest-Ascent method, to a great extent, is comparable in accuracy and iteration time to the pseudospectral optimization package “GPOPS.” This paper, to a great extent, is a detailed procedure for the method of Steepest-Ascent analyzed and verified by the authors from many undetailed sources to disclosure of the main problems faced by user of Steepest-Ascent. Elsayed M. Khalil, Hao Zhou, and Wanchun Chen Copyright © 2014 Elsayed M. Khalil et al. All rights reserved. Nonlinear Finite-Horizon Regulation and Tracking for Systems with Incomplete State Information Using Differential State Dependent Riccati Equation Wed, 10 Sep 2014 07:25:04 +0000 This paper presents an efficient online technique used for finite-horizon, nonlinear, stochastic, regulator, and tracking problems. This can be accomplished by the integration of the differential SDRE filter algorithm and the finite-horizon state dependent Riccati equation (SDRE) technique. Unlike the previous methods which deal with the linearized system, this technique provides finite-horizon estimation and control of the nonlinear stochastic systems. Further, the proposed technique is effective for a wide range of operating points. Simulation results of a missile guidance system are presented to illustrate the effectiveness of the proposed technique. Ahmed Khamis, D. Subbaram Naidu, and Ahmed M. Kamel Copyright © 2014 Ahmed Khamis et al. All rights reserved. Shape Optimization of NREL S809 Airfoil for Wind Turbine Blades Using a Multiobjective Genetic Algorithm Tue, 09 Sep 2014 10:21:41 +0000 The goal of this paper is to employ a multiobjective genetic algorithm (MOGA) to optimize the shape of a well-known wind turbine airfoil S809 to improve its lift and drag characteristics, in particular to achieve two objectives, that is, to increase its lift and its lift to drag ratio. The commercially available software FLUENT is employed to calculate the flow field on an adaptive structured mesh using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a two-equation SST turbulence model. The results show significant improvement in both lift coefficient and lift to drag ratio of the optimized airfoil compared to the original S809 airfoil. In addition, MOGA results are in close agreement with those obtained by the adjoint-based optimization technique. Yilei He and Ramesh K. Agarwal Copyright © 2014 Yilei He and Ramesh K. Agarwal. All rights reserved. A Miniature Integrated Navigation System for Rotary-Wing Unmanned Aerial Vehicles Thu, 28 Aug 2014 11:33:15 +0000 This paper presents the development of a low cost miniature navigation system for autonomous flying rotary-wing unmanned aerial vehicles (UAVs). The system incorporates measurements from a low cost single point GPS and a triaxial solid state inertial/magnetic sensor unit. The navigation algorithm is composed of three modules running on a microcontroller: the sensor calibration module, the attitude estimator, and the velocity and position estimator. The sensor calibration module relies on a recursive least square based ellipsoid hypothesis calibration algorithm to estimate biases and scale factors of accelerometers and magnetometers without any additional calibration equipment. The attitude estimator is a low computational linear attitude fusion algorithm that effectively incorporates high frequency components of gyros and low frequency components of accelerometers and magnetometers to guarantee both accuracy and bandwidth of attitude estimation. The velocity and position estimator uses two cascaded complementary filters which fuse translational acceleration, GPS velocity, and position to improve the bandwidth of velocity and position. The designed navigation system is feasible for miniature UAVs due to its low cost, simplicity, miniaturization, and guaranteed estimation errors. Both ground tests and autonomous flight tests of miniature unmanned helicopter and quadrotor have shown the effectiveness of the proposed system, demonstrating its promise in UAV systems. Yu Xu, Wenda Sun, and Ping Li Copyright © 2014 Yu Xu et al. All rights reserved. On the Effects of Modeling As-Manufactured Geometry: Toward Digital Twin Wed, 27 Aug 2014 08:11:17 +0000 A simple, nonstandardized material test specimen, which fails along one of two different likely crack paths, is considered herein. The result of deviations in geometry on the order of tenths of a millimeter, this ambiguity in crack path motivates the consideration of as-manufactured component geometry in the design, assessment, and certification of structural systems. Herein, finite element models of as-manufactured specimens are generated and subsequently analyzed to resolve the crack-path ambiguity. The consequence and benefit of such a “personalized” methodology is the prediction of a crack path for each specimen based on its as-manufactured geometry, rather than a distribution of possible specimen geometries or nominal geometry. The consideration of as-manufactured characteristics is central to the Digital Twin concept. Therefore, this work is also intended to motivate its development. Albert Cerrone, Jacob Hochhalter, Gerd Heber, and Anthony Ingraffea Copyright © 2014 Albert Cerrone et al. All rights reserved. Thermochemical Analysis of Hypergolic Propellants Based on Triethylaluminum/Nitrous Oxide Wed, 27 Aug 2014 00:00:00 +0000 The vacuum specific impulse, density vacuum specific impulse, and solid exhaust products were examined for several propellant formulations based on the pyrophoric material triethylaluminum (TEA) using CEA thermodynamics code. Evaluation of TEA neat and mixed with hydrocarbon fuels with LOX, N2O, N2O4, liquefied air, and HNO3 were performed at stoichiometry. The vacuum specific impulse of neat TEA with N2O is comparable to that of nitric acid with the same, but the N2O formulation will produce slightly less solid products during combustion. Additionally, N2O-TEA propellants have vacuum specific impulses and density vacuum specific impulses within 92.9% and 86.7% of traditional hydrazine propellant formulations under stoichiometric conditions. Stephen M. Davis and Nadir Yilmaz Copyright © 2014 Stephen M. Davis and Nadir Yilmaz. All rights reserved. External Aerodynamics Simulations in a Rotating Frame of Reference Mon, 14 Jul 2014 11:32:02 +0000 This paper presents the development of a tool integrated in the UNS3D code, proprietary of Alenia Aermacchi, for the simulation of external aerodynamic flow in a rotating reference frame, with the main objective of predicting propeller-aircraft integration effects. The equations in a rotating frame of reference have been formulated in terms of the absolute velocity components; in this way, the artificial dissipation needed for convergence is lessened, as the Coriolis source term is only introduced in the momentum equation. An Explicit Algebraic Reynolds Stress turbulence model is used. The first assessment of effectiveness of this method is made computing stability derivatives of a NACA 0012 airfoil. Finally, steady Navier-Stokes and Euler simulations of a four-blade single-rotating propeller are presented, demonstrating the efficiency of the chosen approach in terms of computational cost. Filomena Cariglino, Nicola Ceresola, and Renzo Arina Copyright © 2014 Filomena Cariglino et al. All rights reserved. Active Vibration Control of Plate Partly Treated with ACLD Using Hybrid Control Mon, 14 Jul 2014 10:05:23 +0000 A finite element model of plate partly treated with ACLD treatments is developed based on the constitutive equations of elastic, piezoelectric, viscoelastic materials and Hamilton’s principle. The Golla-Hughes-Mctavish (GHM) method is employed to describe the frequency-dependent characteristics of viscoelastic material (VEM). A model reduction is completed by using iterative dynamic condensation and balance model reduction method to design an effective control system. The emphasis is concerned on hybrid (combined feedback/feedforward) control system to attenuate the vibration of plates with ACLD treatments. The optimal linear quadratic Gaussian (LQG) controller is considered as a feedback channel and the adaptive filtered-reference LMS (FxLMS) controller is used as a feedforward channel. They can be utilized individually or in a hybrid way to suppress the vibration of plate/ACLD system. The results show that the hybrid controller which combines feedback/feedforward together can reduce the displacement amplitude of plate/ACLD system subjected to a complicated disturbance substantially without requiring more control effort. Furthermore, the hybrid controller has more rapid and stable convergence rate than the adaptive feedforward FxLMS controller. Meanwhile, perfect robustness to phase error of the cancellation path in feedforward controller and the weight matrices in feedback LQG controller is demonstrated in proposed hybrid controller. Therefore, its application in structural engineering can be highly appreciated. Dongdong Zhang and Ling Zheng Copyright © 2014 Dongdong Zhang and Ling Zheng. All rights reserved. A Numerical Study on a Vertical-Axis Wind Turbine with Inclined Arms Mon, 30 Jun 2014 10:31:02 +0000 This work focuses on a particular type of vertical-axis wind turbine, in which a number of inclined arms with airfoil-shaped cross-sections are mounted to connect the principal blades to their hub. While the majority of the known studies on vertical-axis turbines is devoted to the role of principal blades, in most of the cases without taking into account other parts of the wind turbine, the objective of this work is to investigate the effect of uncommon arm geometries, such as the inclined arms. The inclined arms are known to have a potentially beneficial role in the power extraction from the wind current but, due to the complexity of the phenomena, the investigation on aerodynamics of this type of turbine is often impossible through analytical models, such as blade-element momentum theory. It turns out that adequate studies can only be carried out by wind tunnel experiments or CFD simulations. This work presents a methodical CFD study on how inclined arms can be used on a selected wind turbine configuration to harvest additional power from the wind. The turbine configuration, geometry, and some fundamental definitions are introduced first. Then an in-depth CFD analysis is presented and discussed. Agostino De Marco, Domenico P. Coiro, Domenico Cucco, and Fabrizio Nicolosi Copyright © 2014 Agostino De Marco et al. All rights reserved. Use of Active Learning to Design Wind Tunnel Runs for Unsteady Cavity Pressure Measurements Thu, 19 Jun 2014 09:11:12 +0000 Wind tunnel tests to measure unsteady cavity flow pressure measurements can be expensive, lengthy, and tedious. In this work, the feasibility of an active machine learning technique to design wind tunnel runs using proxy data is tested. The proposed active learning scheme used scattered data approximation in conjunction with uncertainty sampling (US). We applied the proposed intelligent sampling strategy in characterizing cavity flow classes at subsonic and transonic speeds and demonstrated that the scheme has better classification accuracies, using fewer training points, than a passive Latin Hypercube Sampling (LHS) strategy. Ankur Srivastava and Andrew J. Meade Copyright © 2014 Ankur Srivastava and Andrew J. Meade. All rights reserved. Effects of Surface Coating Preparation and Sliding Modes on Titanium Oxide Coated Titanium Alloy for Aerospace Applications Tue, 06 May 2014 06:24:45 +0000 This paper investigates the mechanical response of a coated Ti-6Al-4V alloy surface under different sliding contact stress conditions. The surface was coated with an oxide ceramic material created through the use of a recently developed technique known as plasma electrolytic oxidation (PEO). During the PEO procedure, a composition of silicate and phosphate was used as the electrolyte. In order to evaluate the coating, pin-on-disk (POD) tribology tests and cyclic inclined sliding tests were used under dry room conditions. Furthermore, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were utilized to examine the morphology and composition of the coating surfaces. The results of the POD tests revealed that the PEO coating could have a low coefficient of friction and suggested that high silicon concentrations in the PEO coatings take away oxygen from stoichiometric Ti oxides to create lubricating oxides. In addition, cyclic inclined sliding tests showed that smaller pores on the surface of the coating could permit a higher coating cohesive strength and allow the coated Ti alloy surface to perform better under high inclined sliding forces. Bo Yuan Peng, Xueyuan Nie, and Ying Chen Copyright © 2014 Bo Yuan Peng et al. All rights reserved. Airloads Correlation of the UH-60A Rotor inside the 40- by 80-Foot Wind Tunnel Sun, 23 Mar 2014 09:17:01 +0000 The presented research validates the capability of a loosely coupled computational fluid dynamics (CFD) and comprehensive rotorcraft analysis (CRA) code to calculate the flowfield around a rotor and test stand mounted inside a wind tunnel. The CFD/CRA predictions for the Full-Scale UH-60A Airloads Rotor inside the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel at NASA Ames Research Center are compared with the latest measured airloads and performance data. The studied conditions include a speed sweep at constant lift up to an advance ratio of 0.4 and a thrust sweep at constant speed up to and including stall. For the speed sweep, wind tunnel modeling becomes important at advance ratios greater than 0.37 and test stand modeling becomes increasingly important as the advance ratio increases. For the thrust sweep, both the wind tunnel and test stand modeling become important as the rotor approaches stall. Despite the beneficial effects of modeling the wind tunnel and test stand, the new models do not completely resolve the current airload discrepancies between prediction and experiment. I-Chung Chang, Thomas R. Norman, and Ethan A. Romander Copyright © 2014 I-Chung Chang et al. All rights reserved.