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The computational budget for designing and optimizing engineering systems has been tightened by the growth in the number of technology alternatives to satisfy the increasingly demanding goals in modern systems and the use of sophisticated, but also computationally burdensome, simulation tools to quantitatively choose the best technology alternative more accurately. This paper develops a new Gaussian process metamodel, which leverages trends in engineering objectives that are similar across derivative concepts, as opposed to current approximation methods that handle concepts independently. This metamodel is based on a muitifidelity approach that enhances a new concept prediction with observations of a previous concept with similar trends. The influence of the sizes of the new and the old concept training sets in the performance of the proposed metamodel is explored in this paper. The proposed multifidelity metamodel is tested against traditional independent surrogates in approximating the engine shaft horsepower of a UH-60A modification with a Fenestron tail, where observations from the UH-60A with a conventional tail are available. The proposed metamodels are up to two times as accurate as independent concept modeling for small new concept training sets; then, a multiobjective efficient global optimization algorithm is applied to the proposed metamodel to search for minimal UH-60A power consumption in hover and cruise. This results in Pareto-optimal solutions that are 10% more efficient than the UH-60A baseline. [ABSTRACT FROM AUTHOR]

Nonlinearities can be present in an aeroelastic system because of some aerodynamic factors that occur in transonic flight regimes or at a large angle of attack. The sources are shock wave motions and separated flows. Complex aeroelastic problems due to the aerodynamic nonlinearity can be studied using high-fidelity computational fluid dynamics (CFD) codes. However, the computational cost may be very high. Hence, this kind of problem is conveniently solved using the reduced-order model (ROM) for unsteady aerodynamic analysis. Many studies have been done using reduced-order modeling for aeroelastic analysis. However, most of the reduced-order aerodynamic models are dynamic linear models and have loads proportional to the structural motions. In the current paper, a nonlinear unsteady reduced-order aerodynamic model is constructed using the radial basis function neural network model. This kind of ROM is used to analyze the limit cycle oscillation (LCO) for two linear structural models with large shock motions in transonic flow. Unlike the input signals in the traditional design method, the signals of the self-excited vibration of the aeroelastic system are designed as the input signals in the current paper. Coupling the structural equations of motion and nonlinear aerodynamic ROM, the system responses are determined by time marching the governing equations using a hybrid linear multistep algorithm. Then, the LCO change with velocities (dynamic pressure) was analyzed. The two transonic aeroelastic examples show that both the structural responses and the LCO characteristics simulated using the nonlinear ROM agree well with those obtained using the direct CFD method. Moreover, the computational efficiency of the nonlinear ROM-based method is improved by one to two orders of magnitude compared with that of the direct CFD method. [ABSTRACT FROM AUTHOR]

The main goal of this paper is to analyze different methodologies and to quantitatively compare a set of algorithms for multi-objective global optimization, as an initial step toward a multidisciplinary design optimization framework for space transportation systems. Through a comparative analysis based on mathematical benchmarks, hierarchies among several stochastic techniques are proposed. This leads to the identification of two algorithms as the most promising for multidisciplinary design optimization applications: the nondominated sorting genetic algorithm-II (NSGA-II) and an improved version of particle swarm optimization. Then a significant advantage of the latter is highlighted on the problem of trajectory optimization for expendable launch vehicles. In this applicative scenario, the paper also aims at proving the capability of global methods to correctly assess the performance of expendable launch vehicles. Environmental, dynamical, and guidance models for the optimization of ascent trajectories are therefore introduced. Results for seven performance optimization test cases show that global techniques provide comparable payload masses with respect to traditional gradient-based methods. In addition to the trajectory models, historical linear regressions simulating an expendable launch vehicle's design cycle are described. The focus is in this case on the definition of a simple model as a test bench for the verification of the effectiveness of global methods on multidisciplinary design optimization problems, rather than on the quality of the design results. Three widely different expendable launch vehicle design optimization problems are successfully solved by applying the improved particle swarm optimization algorithm. This demonstrates the suitability of the developed global optimization architecture and algorithms for search-space exploration in multidisciplinary design optimization, paving the way for more detailed modeling and more realistic applications. [ABSTRACT FROM AUTHOR]

The study of a multidomain coupling algorithm of numerical methods applied to direct acoustic waves simulation is the focus of this paper. The idea is to be able to use meshing techniques and numerical methods of different natures, depending on the domain area, in order to meet the local requirements of the computation. Here, the linearized Euler equations are solved by carrying out a coupling between a discontinuous Galerkin method running on an unstructured mesh and a finite difference method running on a Cartesian grid. The aim is to take into account complex geometries by running a discontinuous Galerkin method and run a finite difference method away from the obstacles to reduce computational costs, in this paper, two different discontinuous Galerkin/finite difference coupling algorithms are presented, and some associated validation results in terms of precision and stability are discussed. An application of a hybrid solver in the framework of an acoustic benchmark dedicated to complex geometries is also presented. [ABSTRACT FROM AUTHOR]

This research work is inspired by the fact that a mini aerial vehicle with low-aspect-ratio wings (aspect ratio less than 2) has nonlinear lift curves and does not stall sharply, as compared with high-aspect-ratio wings. This paper presents a data fusion algorithm for estimating the aerodynamic angles in a mini aerial vehicle that has low-aspect-ratio wings. The true states of the aircraft motion are generated using a flight simulation program, and a zero-mean white noise is added to a few of these states for sensor simulation. Using the simulated sensors, in the first stage, Euler angles are estimated using an extended Kalman filter algorithm. The estimated Euler angles are further used with accelerometer, angular rates, magnetometer measurements, and the airspeed V for estimation of aerodynamic angles at higher angles of attack. This paper also proposes a novel pseudoestimation technique and also discusses three different schemes of estimation of angle of attack and sideslip angle. Effect of drift in gyro measurements in the angle-of-attack and sideslip-angle estimation is studied. When sensor bias/drift is present, it was observed that there is a bias of more than 10 deg present in the estimated aerodynamic angles. A new modification is proposed in which the pseudoestimation of angle of attack and sideslip angle is used as measurement in the second-stage extended Kalman filter. This reduces the estimation bias and the mean error in both angle of attack and sideslip angle, and it is below 1 deg. [ABSTRACT FROM AUTHOR]

This paper concerns optimal longitudinal trajectories and guidance strategies of a reusable launch vehicle during the terminal-area energy-management phase. During this phase, it is important to know the limits of the vehicle capabilities and the best strategy for a flight in the vertical plane. This paper describes optimal trajectories using a genetic algorithm and guidance strategies for both maximum-range and maximum-dive flights. The optimal trajectories show an increased maximum range up to 6%, compared with the trajectories using an angle of attack for maximum lift-to-drag ratio. A turning flight has an influence on the optimal trajectories and optimal turns are flown at a lower velocity. Based on the calculation of optimal trajectories and an energy-state approximation analysis, a longitudinal guidance law is designed, using robust design to approximate the optimal trajectories. Offnominal conditions, in terms of a change in initial altitude and velocity, also have an influence on the optimal trajectories. Maximum-range trajectories for different initial states define the minimum-energy boundary in the energy space. [ABSTRACT FROM AUTHOR]

The use of adaptive wing/aerofoil designs is being considered, as they are promising techniques in aeronautic/ aerospace since they can reduce aircraft emissions and improve aerodynamic performance of manned or unmanned aircraft. This paper investigates the robust design and optimization for one type of adaptive techniques: active flow control bump at transonic flow conditions on a natural laminar flow aerofoil. The concept of using shock control bump is to control supersonic flow on the suction/pressure side of natural laminar flow aerofoil that leads to delaying shock occurrence (weakening its strength) or boundary-layer separation. Such an active flow control technique reduces total drag at transonic speeds due to reduction of wave drag. The location of boundary-layer transition can influence the position and structure of the supersonic shock on the suction/pressure side of aerofoil. The boundary-layer transition position is considered as an uncertainty design parameter in aerodynamic design due to the many factors, such as surface contamination or surface erosion. This paper studies the shock-control-bump shape design optimization using robust evolutionary algorithms with uncertainty in boundary-layer transition locations. The optimization method is based on a canonical evolution strategy and incorporates the concepts of hierarchical topology, parallel computing, and asynchronous evaluation. Two test cases are conducted: the first test assumes the boundary-layer transition position is at 45 % of chord from the leading edge, and the second test considers robust design optimization for the shock control bump at the variability of boundary-layer transition positions. The numerical result shows that the optimization method coupled to uncertainty design techniques produces Pareto optimal shock-control-bump shapes, which have low sensitivity and high aerodynamic performance while having significant total drag reduction. [ABSTRACT FROM AUTHOR]

Algorithms for resolving air traffic conflicts are tested on archived tracking data from 102 actual operational errors (violations of minimum required separation due to controller error). The algorithms compute horizontal or vertical resolution maneuvers for tactical conflicts in which the minimum required separation is predicted to be lost within approximately two min. The horizontal maneuvers are issued as heading vectors, and the vertical maneuvers are issued as standard altitude clearances. Algorithms for the vertical resolutions were presented in an earlier paper, and algorithms for the horizontal resolutions are described in this paper. Simulation results show that these resolution algorithms could have prevented most of the archived operational errors. In some cases, the controller failed to enter an altitude amendment consistent with the voice clearance, and in eight such cases the conflict was not detected early enough to be resolved in the simulation. The correct altitude amendments were added to the recorded data for those cases (to simulate the correct entry by the controller), and successful resolution was then achieved for all cases. [ABSTRACT FROM AUTHOR]

Finite volume discretizations on unstructured grids that are more than second-order-accurate have not yet gained wide acceptance. This is due to the high computational cost and memory requirements of the proposed schemes and the technical difficulties in achieving a high-order-accurate solution. It is especially true when considering flows in complex geometries. In this paper, a third-order cell-centered finite volume discretization is detailed that is based on quadratic data recovery, which is computationally efficient and has optimal memory requirements. The density-based flow-solver discretization and solution algorithm are described briefly, followed by a detailed presentation of the least-squares-based multistep quadratic data-reconstruction methodology proposed here. The paper is concluded with numerical examples to verify the accuracy and numerical efficiency of this high-order finite volume discretization. [ABSTRACT FROM AUTHOR]

This paper analyzes the performance of some global search algorithms on a number of space trajectory design problems. A rigorous testing procedure is introduced to measure the ability of an algorithm to identify the set of &epsilon-optimal solutions. From the analysis of the test results, a novel algorithm is derived. The development of the novel algorithm starts from the redefinition of some evolutionary heuristics in the form of a discrete dynamical system. The convergence properties of this discrete dynamical system are used to derive a hybrid evolutionary algorithm that displays very good performance on the particular class of problems presented in this paper. [ABSTRACT FROM AUTHOR]

Because of their small size and flight regime, coupling of aerodynamics, structural dynamics, and flight dynamics are critical for micro aerial vehicles. This paper presents a computational framework for simulating structural models of varied fidelity and a Navier-Stokes solver, aimed at simulating flapping and flexible wings. The structural model uses either 1) the in-house developed UM/NLABS, which decomposes the equations of 3-D elasticity into cross-sectional and spanwise analyses for slender wings, or 2) MSC.Marc, which is a commercial finite-element solver capable of modeling geometrically nonlinear structures of arbitrary geometry. The flow solver employs a well-tested pressure-based algorithm implemented in STREAM. A NACA0012 cross-sectional rectangular wing of aspect ratio 3, chord Reynolds number of 3 x 104, and reduced frequency varying from 0.4 to 1.82, with prescribed pure plunge motion is investigated. Both rigid and flexible wing results are presented, and good agreement between experiment and computation are shown regarding tip displacement and thrust coefficient. Issues related to coupling strategies, fluid physics associated with rigid and flexible wings, and implications of fluid density on aerodynamic loading are also explored in this paper. [ABSTRACT FROM AUTHOR]

In this paper, we propose a methodology for the prediction and optimization of the ascent trajectory of a stratospheric balloon to target a specified three-dimensional area. The methodology relies mainly on the Analysis Code for High-Altitude Balloons, a simulation tool for the prediction of flight trajectory and thermal behavior of high-altitude, zero-pressure balloons, and on a statistical analysis for estimating the trajectory prediction errors. The paper also describes the algorithms used for balloon parameter optimization to obtain a flight trajectory that reaches a predefined target area without any ballast drop or gas venting control. The proposed methodology was successfully used during the first Dropped Transonic Flight Test of the Flying Test Bed 1 demonstrator accomplished on 24 February 2007 by the Italian Aerospace Research Center. The reported postflight analysis of all the test campaign demonstrates that the proposed methodology for trajectory prediction and optimization guarantees very satisfactory and reliable results for both the selection of the best day to perform such a mission and the definition of the correct balloon parameters to be used for targeting a predefined three-dimensional area. [ABSTRACT FROM AUTHOR]

This paper reports on the SIMPLE-like solution algorithm that significantly improves velocity-pressure coupling, leading to the accelerated convergence. The algorithm is applicable to both incompressible and compressible flows. It is implemented within the framework of a cell centered finite volume method using colocated storage of flow variables on unstructured grids. The convergence acceleration is an outcome of the novel treatment of the pressure correction equation that accounts for two commonly neglected terms appearing in a general pressure correction equation. These terms, namely, the neighbor and nonorthogonal corrections, represent velocity corrections from neighboring cells and the cell-face pressure correction gradient associated with the grid nonorthogonality, respectively. Reminiscent of the PISO method, both neighbor and nonorthogonal corrections are taken into account by performing two or more correction steps. However, the full inclusion of neighbor velocity corrections can prevent the solution convergence. Following an analogy between time marching and a steady-state iterative approach, this problem has been resolved by introducing a pseudounsteady term into discretized velocity correction equations. Using this term, the contribution of neighbor corrections is underrelaxed, enabling a satisfactory convergence rate. The algorithm is applied to several benchmark test cases, covering laminar and turbulent, as well as incompressible and compressible, flows. For all test cases, the convergence rate can be significantly improved by performing two or more pressure correction steps. An optimal number of pressure corrections exists for which a meaningful reduction of computing time is possible. [ABSTRACT FROM AUTHOR]

The paper presents the developments of novel mesh generation algorithms over complex glaze-ice shapes containing multicurvature ice-accretion geometries, such as single/double ice horns. The twofold approaches tackle surface geometry discretization as well as field mesh generation. First, an adaptive curvilinear curvature control algorithm is constructed, solving a one-dimensional elliptic partial differential equation with periodic source terms. This method controls the arc length grid spacing, so that high convex and concave curvature regions around ice horns are appropriately captured, and is shown to effectively treat the grid shock problem. Second, a novel blended method is developed by defining combinations of source terms with two-dimensional elliptic equations. The source terms include two common control functions, Sorenson and Spekreijse, and an additional third source term to improve orthogonality. This blended method is shown to be very effective for improving grid quality metrics for complex glaze-ice meshes with Reynolds-averaged Navier-Stokes resolution. The performance in terms of residual reduction per nonlinear iteration of several solution algorithms (point-Jacobi, Gauss-Seidel, alternating direction implicit, point, and line Successive Over-Relaxation) are discussed within the context of a full multigrid operator. Details are given on the various formulations used in the linearization process. It is shown that this performance of the solution algorithm depends on the type of control function used. Finally, the algorithms are validated on standard complex experimental ice shapes, demonstrating the applicability of the methods. [ABSTRACT FROM AUTHOR]

This paper focuses on the development of a surface mesh movement algorithm suitable for computer-aided-design-based aerodynamic shape optimization. The algorithm interrogates the computer-aided-design system via the vendor-neutral application programming interface Computational Analysis Programming Interface and uses the Computational Analysis Programming Interface's watertight triangulation of a modified computer-aided-design geometry to guide the movement of the structured surface mesh as the geometry changes during the optimization process. A mapping procedure is introduced that not only preserves the characteristics of the original surface mesh but also guarantees that the new mesh points are on the computer-aided-design geometry. The deformed surface mesh is then smoothed in the parametric space before it is transformed back into three-dimensional space. The procedure is efficient, in that all the processing is done in the parametric space, incurring minimal computational cost. The mesh movement tool is integrated into a three-dimensional shape-optimization framework, with a linear-elasticity volume-mesh movement algorithm, a Newton-Krylov flow solver for the Euler equations, and a discrete-adjoint gradient-based optimizer. The accuracy of the computed gradients is verified through a number of examples. [ABSTRACT FROM AUTHOR]

A computational-fluid-dynamics-driven robust and accurate method for aerodynamic shape optimization, previously developed by the authors, is further enhanced by extending it to automatic multipoint design of wingbody- nacelle configurations. The shape is optimized for minimum drag at fixed lift subject to numerous geometrical and aerodynamical constraints. The method, which is driven by genetic algorithms and full Navier-Stokes computations combined with reduced-order models approach, is supported by massive multilevel parallelization. The applications include single- and multipoint aerodynamic designs for a transport-type aircraft configuration. For the considered class of shape optimizations, significant drag reduction in on- and off-design conditions has been achieved. It was also shown that the optimizations, which start from markedly different initial shapes, ultimately converge to optimum shapes very close one to one another. The paper demonstrates how automated techniques based on the developed method have now matured and provide an industrial strength solution. [ABSTRACT FROM AUTHOR]

Numerical algorithms and solutions of generalized nonlinear lifting-line theory over an elliptical wing are examined, with emphasis on near/poststall flows. First, a thorough analysis on the circulation-based and angle-ofattack- based correction methods (Γ and α methods, respectively) highlights their respective numerical poststall characteristics. The stability of the method is demonstrated, producing single and multiple solutions in the pre- and poststall regions, respectively. Second, artificial dissipation added to the a method is shown to be an effective means of controlling the poststall flow region. Finally, a strongly coupled algorithm is presented, allowing to bypass the interpolation phase via the use of Legendre polynomials. The model sheds light on poststall flow behavior, in agreement with several papers studying formation of stall cell patterns. [ABSTRACT FROM AUTHOR]

This paper describes a vision-based relative navigation and control strategy for inspecting an unknown, noncooperative, and possibly spinning object in space using a visual-inertial system that is designed to minimize the computational requirements while maintaining a safe relative distance. The proposed spacecraft inspection system relies solely on a calibrated stereo camera and a three-axis gyroscope to maintain a safe inspection distance while following a circular trajectory around the object. The navigation system is based on image processing algorithms, which extract the relative position and velocity between the inspector and the object, and a simple control approach is used to ensure that the desired range and bearing are maintained throughout the inspection maneuver. The hardware implementation details of the system are provided. Computer simulation results and experiments conducted aboard the International Space Station during Expedition 34 are reported to demonstrate the performance and applicability of the proposed hardware, and related navigation and control systems to inspect an unknown spacecraft. [ABSTRACT FROM AUTHOR]

The particle swarm optimization technique is a population-based stochastic method developed in recent years and successfully applied in several fields of research. The particle swarm optimization methodology aims at taking advantage of the mechanism of information sharing that affects the overall behavior of a swarm, with the intent of determining the optimal values of the unknown parameters of the problem under consideration. This research applies the technique to determining optimal continuous-thrust rendezvous trajectories in a rotating Euler-Hill frame. Five distinct applications, both in two dimensions and in three dimensions, are considered. Hamiltonian methods are employed to translate the related optimal control problems into parameter optimization problems. The transversality condition, which is an analytical condition that arises from the calculus of variations, is proven to be ignorable for these problems, and this property greatly simplifies the solution process. For each of the five applications considered in the paper, despite its simplicity, the swarming algorithm successfully finds the optimal control law corresponding to the minimum-time trajectory with great accuracy. [ABSTRACT FROM AUTHOR]

Predicted ice shapes obtained with a fully automated multi-stepping procedure implemented in the ice prediction code ICECREMO2 are discussed in this paper. Several multi-step algorithms are used to generate ice layers on cylinders in rime and glaze ice conditions. Although all multi-step algorithms produce acceptable rime ice results, a multi-step approach based on an ice height criterion appears as the most efficient method for glaze ice predictions. The outcome is compared with results obtained for a NACA0012 airfoil geometry. The influence of the un-iced substrate shape is investigated, general restart criteria for multi-step height-based icing codes are presented and discussed. [ABSTRACT FROM AUTHOR]

The space community has recognized the problem of sustaining current space operations and has responded by supporting research and development in technologies to reduce cost and schedule without sacrificing performance. One solution is maneuverable satellites. There are very few studies on maneuvering satellites in low-Earth orbit from a ground-track perspective. Operational responsiveness is achievable by changing the ground track and thereby a geographical target location. The existing paradigm on maneuvering is that it is cost-prohibitive, thus orbit-changing maneuvers are done sparingly. This paper presents methodology to quantify reachability of a satellite with chemical and electric propulsion based on initial orbit, A V, and available maneuvering time. Initial orbit parameters are examined to determine which would yield the greatest benefit from maneuvering and the analysis shows that initial orbit orientation has no effect. These maneuvers are highly predictable and equations are formulated to become part of an algorithm that allows overflight of user-specified ground targets. In sacrificing timeliness with electric propulsion the system gains repeatability over chemical propulsion. Existing technology could maneuver a satellite significantly to change its ground track in a relatively short period of time and within standard propellant budgets. [ABSTRACT FROM AUTHOR]

The interaction of vortical structures with a solid wall is studied numerically in this paper. The incompressible Navier--Stokes equations in their primitive variable formulation are solved on a staggered Cartesian grid using the fractional-step algorithm. The convective terms are marched in time using the Adams--Bashforth or Runge--Kutta schemes, while the viscous terms are treated implicitly using the trapezoidal scheme. An upwind reconstruction of the convective fluxes in their conservative form is proposed and compared against the nonconservative flux formulation, as differences are expected due to nonzero velocity divergence in the numerical solution. The performance of the algorithm is assessed on the convection of an isolated vortex. The algorithm is verified on benchmark incompressible flows and flows involving the convection, mutual interaction, and wall impingement of vortical structures. An attempt is made to simulate the impingement of two and multiple vortex rings against a solid wall to understand the effect of mutual interactions on the interactions with a solid wall. The effects of Reynolds number and initial separation between the rings are studied. These parameters are observed to affect the behavior of the vortical structures, thus affecting the formation and ejection of secondary vortices. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) based on the Navier-Stokes equations is by far the most useful predictive method available today for helicopter analysis and design. The main drawback of CFD, and perhaps the reason for its slow acceptance by design offices of helicopter manufacturers, is apparently due to the substantial requirements of CPU time and the relatively slow turnaround times in comparison to lower-order methods. However, progress with CFD algorithms and parallel computing has allowed CFD analyses to be used more routinely. Typical applications include computations of aerofoil data that feed rotor performance codes and analyses of rotors in hovering flight. The computation of unsteady flow cases is, however, still challenging. This paper presents alternative ways of tackling unsteady flow problems pertinent to rotorcraft using methods that aim to reduce the time-marching unsteady computations to more manageable steady-state solutions. The techniques investigated so far by the CFD laboratory of Liverpool include time-linearized and harmonic-balance methods. The details of the methods are presented along with their implementation in the framework of the helicopter multiblock CFD solver. Results were obtained for several flow cases, ranging from pitching/translating aerofoils to complete rotors. The results highlight some of the limitations of the time-linearized method and the potential of the harmonic-balance technique. It was found that the time-linearized method can provide adequate results for cases where the unsteady flow is a rather small perturbation of a known mean. The harmonic-balance method proved to have a larger range of applicability and provided adequate results for the analysis of unsteady flows. The required CPU time was reduced, and the required core computer memory was increased. Overall, the harmonic-balance method appears to be a possible alternative to time-marching CFD for a wide range of problems. [ABSTRACT FROM AUTHOR]

In this paper, an improved ant colony optimization (ACO) algorithm and the finite element analysis (FEA) method are employed in the topology optimization for the forward mount of a pylon. Aiming at the basic ACO algorithm's shortcomings, which hold slow convergence rate at the ending and easily plunge into the local optimum, a new ACO algorithm is proposed by using the strategy of weighting factors and resetting pheromone when the algorithm falls into local optimization. Finally, the Patran command language is used to combine the improved ACO algorithm and MSC.Patran/Nastran to realize the information exchanging between the ACO algorithm and the finite element method. The stiffest structure with a certain amount of materials will be found according to the average stress of every element. The optimized solutions and the static test of the forward mount of a pylon prove that the study is not only theoretically significant but also practically valuable. [ABSTRACT FROM AUTHOR]

One important issue to be handled online during flight testing is flutter monitoring, here addressed as a detection problem. From subspace detection algorithms proposed for vibration-based monitoring, several online flutter monitoring algorithms have been designed by the authors. They are based on a recursive version of the subspace-based residual and on an hypothesis test for detecting changes in a specific instability indicator with respect to a fixed-reference modal parameter (identified on a safe structure). However, the flutter onset time provided by those algorithms turns out to be too conservative. In this paper, a moving-reference approach is proposed to overcome that issue. Two adaptive flutter-monitoring algorithms are proposed that update the reference modal state during the online test. The usefulness of the proposed approach is discussed based on experimental results obtained on simulation data provided by two academic and industry-relevant simulated aircraft models. [ABSTRACT FROM AUTHOR]

This paper presents a provably convergent multifidelity optimization algorithm for unconstrained problems that does not require high-fidelity gradients. The method uses a radial basis function interpolation to capture the error between a high-fidelity function and a low-fidelity function. The error interpolation is added to the low-fidefity function to create a surrogate model of the high-fidelity function in the neighborhood of a trust region. When appropriately distributed spatial calibration points are used, the low-fidelity function and radial basis function interpolation generate a fully linear model. This condition is sufficient to prove convergence in a trust region framework. In the case when there are multiple lower-fidelity models, the predictions of all calibrated lower-fidelity models can be combined with a maximum likelihood estimator constructed using kriging variance estimates from the radial basis function models. This procedure allows for flexibility in sampling lower-fidelity functions, does not alter the convergence proof of the optimization algorithm, and is shown to be robust to poor low-fidelity information. The algorithm is compared with a single-fidelity quasi-Newton algorithm and two first-order consistent multifidelity trust region algorithms. For simple functions the quasi-Newton algorithm uses slightly fewer high-fidelity function evaluations; however, for more complex supersonic airfoil design problems it uses significantly more. In all cases tested, our radial basis function calibration approach uses fewer high-fidelity function evaluations when compared with first-order consistent trust region schemes. [ABSTRACT FROM AUTHOR]

Based on the measured vibration information, a method for detecting reduction in stiffness parameters of a structure using generalized flexibility matrix and changes in natural frequencies is presented in this paper. For incomplete measured data of the first mode shape, dynamic expansion of mode shape is introduced. The generalized flexibility matrix is approximately constructed by using the measured first frequency and the extended mode shape only, and it is further used to detect the possible damaged elements. An iterative algorithm using the changes of the first several natural frequencies only is subsequently used to update the damage extent of these possible damaged elements, while the number of damage-extent parameters to be determined in the algorithm is remarkably reduced. Finally, two numerical examples concerning a two-span beam and a two-story frame are used to illustrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes an en route speed reduction to complement current ground delay practices in air traffic flow management. Given a nominal cruise speed, there exists a bounded range of speeds that allows aircraft to fly slower with the same or lower fuel consumption than the nominal flight. Therefore, flight times are increased and delay can be partially performed in the air, at no extra fuel cost for the operator. This concept has been analyzed in an initial feasibility study, computing the maximum amount of delay that can be performed in the air in some representative flights. The impact on fuel consumption has been analyzed, and two scenarios are proposed: the flight fuel remains the same as in the nominal flight, and some extra fuel allowance is permitted in order to face uncertainties. Results show significant values of airborne delay that may be useful in many situations, with the exception of short hauls where airborne delay may be too short. If cruise altitude is changed, the amount of airborne delay increases, since changes in cruise speed modify the optimal flight altitudes. From the analyzed flights, a linear dependency is found relating the airborne delay with the amount of extra fuel allowance. [ABSTRACT FROM AUTHOR]

This paper presents a discretization method for the development of a modular morphing wing. The proposed method determines the number of morphing wing modules and the respective spacing required to emulate a known wing shape and satisfy a corresponding flight requirement. This method consists of two steps. The first step is geometry discretization, in this step, curvature and twist distribution from the reference wing shape quarter chord line are extracted and used to determine the spacing of the discretized wing modules. This is achieved by clustering more tightly spaced morphing wing modules in areas of large total curvature, and fewer longer wing modules in areas of small total curvature. By doing so, geometric congruency between the reference and discretized wings is maintained. The second step is performance evaluation. In this step, an aerodynamic performance index (such as the lift-to-drag ratio) for a given flight regime is used to evaluate the effectiveness of each modular morphing wing configuration. Optimal morphing wing modules are determined until an acceptable flight performance is achieved by the discretized wing. The effectiveness of the proposed discretization algorithm is demonstrated through a case study by determining an optimal number of modules for a modular morphing wing. [ABSTRACT FROM AUTHOR]

Stacking-sequence optimization of laminated composite structures is a combinatorial problem involving discrete variables when ply angles are used as design variables. Such an optimization problem can be solved using genetic algorithms coupled with response surface methods to reduce the computational cost. Alternatively, the optimization problem can be formulated using lamination parameters as design variables, allowing efficient gradient-based optimization methods to be used. Nevertheless, practical stacking sequences have to be reconstructed in a second step, which can be problematic. A synthesis of the two-step approach and the response surface approach to composite design is proposed in this paper. The synthesis is effected by constructing a new multipoint structural approximation scheme based on an innovative use of the classical Shepard's method applied in the space of laminate stiffness. A distance measure in the stiffness space is proposed to adapt the method to composite design. The response surface genetic algorithm optimization is performed starting from a continuous optimum defined by prior continuous optimization. The method is first applied to single-laminate design example problems to demonstrate its efficiency and accuracy compared with known methods. The capacity of the optimization strategy to solve more complex problems is then demonstrated using two patch design examples. [ABSTRACT FROM AUTHOR]

The research and development efforts outlined in this paper address the aerodynamic design of micro air vehicles that are capable of vertical takeoff and landing, as well as hovering. The effect of a propulsive slipstream on a wing's quasi-steady aerodynamics is investigated as an early step toward improving existing vertical takeoff and landing designs and control algorithms. Wind-tunnel testing was conducted on a propulsion system with contrarotating propellers, a wing, and the combined wing and propulsion system. Aerodynamic coefficient definitions are discussed with regard to vertical takeoff and landing micro air vehicles, and modified definitions are presented. [ABSTRACT FROM AUTHOR]

Two approaches are examined for finding the best stacking sequence of laminated composite wing structures with blending and manufacturing constraints: smeared-stiffness-based method and lamination-parameter-based method. In the first method, the material volume is the objective function at the global level, and the stack shuffling to satisfy blending and manufacturing constraints is performed at the local level. The other method introduced in this paper is to use lamination parameters and numbers of plies of the predefined angles (0, 90, 45, and -45 deg) as design variables with buckling, strain, and ply percentage constraints while minimizing the material volume in the top-level optimization run. Given lamination parameters from the top-level optimization as targets for the local level, an optimal stacking sequence is determined to satisfy the global blending requirements. On a benchmark problem of an 18-panel wing box, the results from these two approaches are compared to published results to demonstrate their potential. [ABSTRACT FROM AUTHOR]

This paper presents an unsteady discrete adjoint algorithm for high-order implicit discontinuous Galerkin discretizations in time-dependent inviscid flow problems. The major function of the adjoint approach is to obtain the sensitivity information in a time-dependent functional output, which in turn is used to drive an unsteady shape-optimization process to deliver a minimum of the objective functional. A gradient-based optimization strategy is investigated, in which the sensitivity derivatives of the objective functional with respect to input variables are formulated in the context of high-order discontinuous Galerkin discretizations, while special emphasis is given to the variations and linearizations of curvilinear boundary elements. Implicit temporal discretizations consisting of a second-order backward Euler scheme and a fourth-order implicit Runge-Kutta scheme are considered exclusively in this work, where the corresponding adjoint problem is required to be solved in a backward time-integration manner due to the associated transpose operation. Two numerical examples for the unsteady shape design techniques are presented to verify the derived sensitivity formulations and to demonstrate the performance of the adjoint approach; the first involves an inverse shape-optimization case by matching a time-dependent target pressure profile for a two-dimensional periodic vortical gust impinging on a RAE-2822 airfoil, and the second considers minimization of the acoustic noise produced by subsonic flow over a NACA0012 airfoil with a 0.03c thick blunt trailing edge. [ABSTRACT FROM AUTHOR]

Aeroelastic systems may exhibit vibrations that are induced by a forced periodic motion of their elements. For example, the forced periodic motion of an aileron on a deformable wing produces vibrations of this wing. Accurate numerical simulation of such problems is usually based on a time-marching scheme and a code-coupling strategy. Such computations are costly, since before the periodic-vibration cycles, a long transient has to be computed. A technique called time-harmonic balance has been developed in the field of computational fluid dynamics to accelerate the computation of unsteady periodic flows. This technique allows the periodic state of these flows to be computed directly without computing their transients. In this paper the time-harmonic-balance strategy is applied to an aeroelastic solver consisting of two coupled codes. The time-harmonic-balance technique allows the resulting aeroelastic solver to compute the periodic-vibration cycles caused by a periodic forced motion directly, without computing the long transients. The time-harmonic-balance-based aeroelastic solver is analyzed and validated on a two-dimensional aeroelastic pitch-plunge airfoil undergoing a forced pitching. Furthermore, application to an industrial case is considered, where the flexibility of an aircraft wing is taken into account in the computation of unsteady aerodynamic forces caused by an oscillating aileron. [ABSTRACT FROM AUTHOR]

The present paper reports on the interaction of a hot side jet in a supersonic freestream and compares the effects with results from cold-gas jet investigations. With high-speed schlieren videos, a significant enlargement of the separation area has been ascertained upstream from the hot-gas jet and quantitatively confirmed with wall pressure measurements. The schlieren videos also show a strong oscillation of the separation and bow shock. By using an algorithm that analyzes the similarity of neighboring images, the oscillation frequency of the separation and bow shock has been measured to be 11.3 kHz. As a consequence of the dominant shocks in the area in front of the jet, the hot jet plume is screened off strongly from the freestream, thus resulting in an upstream inclination. Finally, high-speed videos have revealed large-scale structures in the hot-gas jet and their convection velocities have been analyzed. According to the shocks, the large-scale structures oscillate at 11.3 kHz. Jet oscillation is thus excited by the interaction of the hot-gas jet with the freestream and not by resonances from the combustion chamber. [ABSTRACT FROM AUTHOR]

In this paper an efficient general algorithm to calculate the Hessian of a steady or unsteady functional of interest in the context of computational fluid dynamics is outlined, verified, and applied to an aerodynamic optimization and to an extrapolation example. The successful extrapolation is then applied to approximate Monte Carlo simulations for artificial geometric uncertainty analysis. The presented optimization and extrapolation examples demonstrate that the combination of automatic differentiation and an adjoint method to calculate the Hessian of a steady or unsteady objective function, and thereby obtaining second-order information, can be an efficient tool for optimization and uncertainty quantification. [ABSTRACT FROM AUTHOR]

This paper develops a methodology for the optimum layout design of sensor arrays of structural health monitoring systems under uncertainty. This includes finite element analysis under transient mechanical and thermal loads and incorporation of uncertainty quantification methods. The finite element model is validated with experimental data, accounting for uncertainties in experimental measurements and model predictions. The structural health monitoring sensors need to be placed optimally in order to detect with high reliability any structural damage before it turns critical. The proposed methodology achieves this objective by combining probabilistic finite element analysis, structural damage detection algorithms, and reliability-based optimization concepts. [ABSTRACT FROM AUTHOR]

This paper deals with aerodynamic shape optimization using a high-fidelity solver. Because of the computational cost needed to solve the Reynolds-averaged Navier-Stokes equations, the performance of the shape must be improved using very few objective function evaluations, despite the high number of design variables. In our framework, the reference algorithm is a quasi-Newton gradient optimizer. An adjoint method inexpensively computes the sensitivities of the functions, with respect to design variables, to build the gradient of the objective function. As usual, aerodynamic functions show numerous local optima when the shape varies, and a more global optimizer is expected to be beneficial. Consequently, a kriging-based optimizer is set up and described. It uses all original sampling refinement process that adds up to three points per iteration by using a balancing between function minimization and error minimization. To efficiently apply this algorithm to high-dimensional problems, the same sampling process is reused to form a cokriging (gradient-enhanced model) based optimizer. A comparative study is then described on two drag-minimization problems depending on 6 and 45 design variables. This study was conducted using an original set of performance criteria, characterizing the strength and weakness of each optimizer in terms of improvement, cost, exploration, and exploitation. [ABSTRACT FROM AUTHOR]

This paper presents the development and evaluation of a computational fluid dynamics based methodology to predict the aerodynamic forces produced by a flexible flapping wing. The computational fluid dynamics analysis code solves the compressible Reynolds-averaged form of the Navier-Stokes equations on structured curvilinear grids. A grid deformation algorithm is devised that deforms the body-conforming volume grid at each time step consistent with the measured wing motions. This algorithm is based on geometric considerations and is both computationally efficient and capable of handling very large deformations. This methodology is validated using experimental data obtained from a test on an ornithopter with flexible wings. Test data include measurements of the wing surface deformations as well as the generated forces in the horizontal and vertical directions. Correlation with test data shows good agreement with measured vertical force and satisfactory agreement with measured horizontal force at low flapping frequencies. However, the prediction accuracy degrades with an increase in flapping frequency. Evidence of resonance in the vehicle system was detected from the analysis of the experimental data. Unmodeled inertial effects from the vehicle body and support mounts may be one of the contributors to disagreement between the data and analysis. [ABSTRACT FROM AUTHOR]

This paper presents a fast tool that can be used during the preliminary design of isotropic and composite stiffened panels subjected to axial compression. It consists of two modules, one for the analysis and one for the optimization. The analysis is performed by implementing an analytical formulation to obtain the linearized buckling load and to study the nonlinear postbuckling field. In particular, closed-form solutions are derived for the linearized local and global buckling loads, and a semi-analytical procedure is implemented for the study of the nonlinear local postbuckling field. The optimization is based on genetic algorithms and allows taking into account buckling and postbuckling requirements with reduced computational time. Two examples regarding the minimum weight optimization of an isotropic panel and a composite panel are discussed and verified by means of finite element eigenvalue and nonlinear analyses. The total time required for the analysis and the optimization is of the order of a few minutes, and the difference between the analytical and numerical results is below 9% for the buckling load and below 3% for the postbuckling stiffness. [ABSTRACT FROM AUTHOR]

The Global Positioning System has great potential for the development of new collision avoidance systems and is being considered for the next-generation traffic alert and collision avoidance system. The navigation states estimated by Global Positioning System code information can be broadcast to nearby airplanes via the current traffic alert and collision avoidance system equipment. In this paper, the problem of aircraft collision detection system using Global Positioning System carrier-phase information is addressed. A new approach to the carrier-phase-based relative position estimation problem is proposed that uses particle filters in which the samples are drawn from Cartesian position space coordinates. The particle filters with position samples makes the Global Positioning System carrier-phase-based position estimation algorithm robust and practical in that the algorithm is not sensitive to changes of Global Positioning System satellites and cycle slips. The same algorithm can be used to estimate the vehicle attitude if multiple Global Positioning System antennas are used. For a reliable and enhanced collision avoidance system, three-dimensional trajectories are projected using relative position, velocity, and attitude estimates. It is shown that the performance of the Global Positioning System carrier-phase-based collision-detecting algorithm meets the accuracy requirements for a precise approach of flight with significantly less collision false alarms and no miss alarms. [ABSTRACT FROM AUTHOR]

This paper presents a practical methodology for static aeroelastic analysis and aeroelastic optimization via coupling of high-fidelity commercial codes. A finite-volume-based flow solver FLUENT is used to solve three-dimensional Euler equations, Gambit is used to generate mesh in the fluid domain, and CATIA is used to model parametric solid geometry. Abaqus, a structural finite element method solver, is used to compute the structural response of the aeroelastic system. The mesh-based parallel-code coupling interface MpCCI is used to exchange the pressure and displacement information between FLUENT and Abaqus to perform a loosely coupled aeroelastic analysis by a staggered algorithm, and modeFRONTIER software is used as the optimization driver for scheduling a nondominated sorting genetic algorithm initiated with design of experiments. First, an AGARD 445.6 wing configuration is optimized with objectives of maximum lift/drag ratio and minimum weight. Optimization variables are chosen as sweep angle at the quarter-chord and the taper ratio of the wing. Second, a more realistic wing model, ARW-2, is optimized for thickness values of the inner ribs and spars. Aeroelastic analysis produce consistent results with experimental data, and the applied optimization methodology results in Pareto-optimal solutions. [ABSTRACT FROM AUTHOR]

In this paper, we present the design and development of the guidance, navigation, and control system of a small vertical-takeoff-and-landing unmanned air vehicle based on a 6 degrees-of-freedom nonlinear dynamic model. The vertical-takeoff-and-landing unmanned air vehicle is equipped with three propellers for vertical thrust, and thrust differential together with a set of yaw trim flaps are used for 3 degrees-of-freedom attitude and thrust control actuation. The focus is on the 6 degrees-of-freedom flight control algorithm design using the trajectory linearization control method, along with simulation verification and robustness tests. Hardware and software implementation of the flight controller and onboard navigation sensors are also briefly discussed. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to describe and demonstrate new capabilities in the two-dimensional implicit thermal response and ablation program. These expanded capabilities include grid options for flight and arcjet geometries, a sizing algorithm for the flight-type geometry, and an orthotropic thermal conductivity model: Applications to analysis of an orthotropic low-density carbon-phenolic material in arcjet and flight environments relevant to the Orion crew module are presented. For the arcjet environment, multidimensional conduction effects strongly influence the in-depth thermal response. For a lunar return flight environment, in the shoulder region of the crew module (where the radius of curvature is smallest), the thermal response is influenced by multidimensional conduction and by the orientation of the orthotropic material. [ABSTRACT FROM AUTHOR]

In this paper, a new damage detection technique able to identify the location of a breathing crack in an isotropic rod, relying only on real-time measurements, is proposed. The detection algorithm exploits the phase information associated with the superharmonic components produced, in the Fourier spectrum, by the nonlinear dynamic response of this kind of defect under the influence of an external dynamic excitation. The validity of the proposed algorithm for a weakly nonlinear system is supported by an analytical solution for a cracked beam obtained through the harmonic balance approach. A numerical investigation is conducted by means of a finite element model of an isotropic beam integrating nonlinear contact elements in the damaged area and solved for the steady-state response. Three different postprocessing approaches, incorporating the proposed damage detection algorithm, are formulated and compared to assess the capability of the current methodology. Results from the cracked beam model clearly show the generation of the superharmonics as a result of the nonlinear dynamic behavior of the breathing crack. The phase associated with the superharmonic components is then processed through the detection algorithm and the predicted location is compared with the actual position of the defect to assess the performances of the methodology. [ABSTRACT FROM AUTHOR]

This paper presents the work done in designing a morphing wing concept for a small experimental unmanned aerial vehicle to improve the vehicle's performance over its intended speed range. The wing is designed with a multidisciplinary design optimization tool, in which an aerodynamic shape optimization code coupled with a structural morphing model is used to obtain a set of optimal wing shapes for minimum drag at different flight speeds. The optimization procedure is described as well as the structural model. The aerodynamic shape optimization code, that uses a viscous two-dimensional panel method formulation coupled with a nonlinear lifting-line algorithm and a sequential quadratic programming optimization algorithm, is suitable for preliminary wing design optimization tasks. The morphing concept, based on changes in wing-planform shape and wing-section shape achieved by extending spars and telescopic ribs, is explained in detail. Comparisons between optimized fixed wing performance, optimal morphing wing performance, and the performance of the wing obtained from the coupled aerodynamic-structural solution are presented. Estimates for the performance enhancements achieved by the unmanned aerial vehicles when fitted with this new morphing wing are also presented. Some conclusions on this concept are addressed with comments on the benefits and drawbacks of the morphing mechanism design. [ABSTRACT FROM AUTHOR]

In this paper, we present a technique for generating solution adaptive meshes that uses feature-aligned surfaces embedded in the computational domain. A feature-detection algorithm is first employed to identify features of interest. Surfaces associated with these features are then meshed, and a volume mesh that respects these embedded surface meshes is then generated. This approach is promising because it provides a mechanism for controlling local grid quality as well as automatically aligning cell faces with the feature. For flows that include topologically and/or geometrically complex features, we describe a mesh refinement technique that can be used in tandem with the embedded surface meshes to provide a mechanism for refining throughout the computational domain. We include results from two cases to illustrate how the method works. [ABSTRACT FROM AUTHOR]

Safe, precise, and efficient lunar landings must detect and avoid hazardous boulders, craters, and slopes while identifying predeployed assets and managing fuel consumption. This paper describes an algorithm to designate landing points during lunar descent. Inputs to the algorithm are the lander footprint, divert A V costs, detected hazards, and identified points of interest. The algorithm is designed to accept any number of input cost functions and constraints, ensuring flexibility to a variety of missions. The input cost functions are weighted and input into a search algorithm that returns all feasible landing points on the map, prioritized by the weighted cost function. The output of the algorithm is a set of landing aim points. The algorithm provides onboard crew or autonomous robotic vehicles with landing point designation capabilities. [ABSTRACT FROM AUTHOR]

The ability to compute the weight and balance of a helicopter in flight under general conditions is an enabling technology for future condition based maintenance systems as well as advanced automatic flight control systems. This paper creates a real-time weight and balance estimation algorithm using an extended Kalman filter framework. To highlight estimation characteristics, the algorithm is exercised on the OH-6A helicopter in a variety of flight regimes. The algorithm is examined in hover and forward flight as well as situations where loads are dropped and picked up in flight. For sample scenarios considered, the algorithm quickly estimates station line and butt line mass center position (1 s) and more slowly converges on helicopter weight (10 s). To estimate the helicopter waterline, the algorithm requires modest flight maneuvering where a nonzero roll rate is present. The algorithm is also shown to be reasonably robust relative to sensor and model errors with increasing estimation error with increasing levels of model mismatch and sensor error. [ABSTRACT FROM AUTHOR]

The ability to perform autonomous mission planning is considered one of the key enabling technologies for uninhabited aerial systems. Subsequently, a big effort is made in the development of algorithms capable of computing safe and efficient routes in terms of distance, time, and fuel. In this paper an innovative 3-D planning algorithm is presented. The algorithm is based on considering the uninhabited aerial systems representation of real world systems as objects moving in a virtual environment (terrain, obstacles, and no fly zones), which replicates the airspace. Original obstacle avoidance strategies have been conceived to generate mission plans that are consistent with flight rules and with the vehicle performance constraints. Simulation test results show that efficient routes are computed in a few seconds. [ABSTRACT FROM AUTHOR]