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Mesh deformation strategy optimized by the adjoint method on unstructured meshes

AIAA JOURNAL 2007年第12期45卷 2885-2896页

作者： Yang, Zhi Mavriplis, Dirnitri J. Univ Wyoming Dept Mech Engn Laramie WY 82071 USA

An adjoint-based optimization procedure is proposed for improving the robustness and extending the range of linear-elasticity-based mesh deformation techniques. Using the values of the modulus of elasticity E defined in each mesh cell as the design variables, the procedure seeks to determine an optimum distribution of E throughout the mesh, to minimize a global objective function that reflects the skewness or lack of quality of the deformed mesh. The technique is applied to highly stretched mixed element meshes in two and three dimensions on complex geometries and is shown to be capable of recovering a valid mesh in a small number of optimization cycles for cases in which the nonoptimized linear-elasticity approach fails. However, the solution of the optimization problem remains relatively costly in terms of CPU time, compared with a nonoptimized mesh deformation calculation, making this technique best suited for precomputing improved E distributions before the simulation or for use as a plug-in module to be invoked in cases in which the nonoptimized procedure fails.

关键词： Linear Elasticity Poisson's Ratio optimization algorithm Stiffness Matrices Steepest Descent Method Multigrid algorithm Landing Gear Computing Shape optimization Trailing Edge Flap

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Optimal multi-objective linearized impulsive rendezvous

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2007年第2期30卷 383-389页

作者： Luo, Ya-Zhong Tang, Guo-Jin Lei, Yong-Jun Natl Univ Def Technol Coll Aerosp & Mat Engn Dept Aerosp Sci & Technol Changsha 410073 Peoples R China

The multi-objective optimization of linearized impulsive rendezvous is investigated in this paper and this optimization includes the minimum characteristic velocity, the minimum time of flight, and the maximum safety performance index, of which the trajectory safety performance index is defined as the minimum relative distance between a chaser and a target in the chaser's free-flying path. A theoretical model for calculating this safety performance index is provided. The three-objective optimization model is proposed based on the Clohessy-Wiltshire system. wherein a generalized inverse matrix solution for linear equations is applied to avoid handling the terminal equality constraints. The multi-objective nondominated sorting genetic algorithm is employed to obtain the Pareto solution set. The proposed approach is evaluated using the -V-bar homing and +V-bar homing rendezvous missions. It is shown that tradeoffs between time of flight, fuel cost, and passive trajectory safety for rendezvous trajectory is quickly demonstrated by the approach. By identifying multiple solutions, the approach can produce a variety of missions to meet different needs.

关键词： Multi Objective Genetic algorithm Characteristic Velocity Target Spacecraft Earth optimization algorithm Spacecraft Rendezvous Newton Raphson Method

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Two-dimensional optical splitters with polymer optical fibre arrays

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JOURNAL OF OPTICS A-PURE AND APPLIED OPTICS 2007年第7期9卷 723-727页

作者： Wen, Fung Jacky Chung, Po Sheun City Univ Hong Kong Dept Elect Engn Kowloon Hong Kong Peoples R China

A novel approach for optical beam distribution into two-dimensional (2D) fibre arrays using 2D Dammann gratings is investigated. We report for the first time experimental results of a 2D optical power distribution into 2 x 2 polymer optical fibre arrays using a Dammann grating. This paper focuses on the design and fabrication of the diffractive optical element (DOE) along with investigating the coupling performance of the system. This grating may be applicable to a fibre to the home (FTTH) network as it can support sufficient channels with good output uniformity together with low polarization-dependent loss (PDL). Using an appropriate optimization algorithm, the optimum profile for the Dammann gratings can be calculated. The gratings are then fabricated on indium-doped tin oxide (ITO) glass using electron-beam lithography. This method shows that it can achieve low PDL and good uniformity together with acceptable insertion loss.

关键词： diffractive optical element optimization algorithm optical splitter optical coupling

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Feedback-based steering law for control moment gyros

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2007年第3期30卷 848-855页

作者： Pechev, Alexandre N. Univ Surrey Surrey Space Ctr Guildford GU2 7XH Surrey England

A new approach for solving the singularity avoidance problem is presented, based on the observation that the gimbal rates can be derived by minimizing (in a feedback loop) the difference between the demanded torque and the control moment gyro output torque. The derivations are approached from a control prospective, but the final solution results in a structure very similar to the classical singularity robust steering law. Some differences, however, need to be acknowledged. Because the gimbal rates are related to the demanded torque through the control sensitivity function, the solutions are generated in a feedback loop, and thus the algorithm does not require computations of matrix inversion and matrix determinant. The steering law has a dynamic structure, and a relationship is established between the torque error and the gimbal-rate capacity of the actuator. Th new steering law also breaks the symmetry in the computation in the gimbal rates, and thus the gimbal trajectories avoid the internal singularities, rather than passing through them. Consequently, the full control moment gyro momentum space is used. Examples with some typical maneuvers are presented to justify this numerically. For the derivation of the steering law, empty set infinity theory is used, and an efficient adaptation algorithm is developed to account for the dependence of the Jacobian on the gimbal angles. Derivation and,implementation steps are presented with numerical examples.

关键词： Steering Law Control Moment Gyroscope Actuators Feedback Control Transient Response International Space Station Riccati Equations Quaternions optimization algorithm Mir Space Station

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Efficient approach for multipoint aerodynamic wing design of business jet aircraft

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AIAA JOURNAL 2007年第11期45卷 2612-2621页

作者： Epstein, Boris Peigin, Sergey Acad Coll Tel Aviv Yaffo Dept Comp Sci IL-64044 Tel Aviv Israel Israel Aircraft Ind Ltd Div Engn IL-70100 Ben Gurion Israel

An efficient computational-fluid-dynamics-driven approach to multipoint constrained aerodynamic wing design for business jet aircraft is proposed. This method significantly extends the capabilities of the optimization tool OPTIMAS, previously developed by the authors, for aerodynamic design of three-dimensional isolated wings. In the framework of the method, the total drag of an optimized aircraft configuration is minimized at fixed lift values subject to numerous geometrical and aerodynamical constraints. The optimum search is driven by genetic algorithms and is based on full Navier-Stokes computations supported by massive multilevel parallelization. The applications include a series of single- and multipoint aerodynamic design optimizations for a generic business jet. For the considered class of shape optimizations, significant drag reduction in on- and off-design conditions has been achieved.

关键词： Generic Business Jet Configuration Aerodynamic Characteristics CFD Aircraft Configurations Genetic algorithm Shape optimization Wing Body Configuration Aerodynamic Performance High Aspect Ratio optimization algorithm

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Inverse problem for estimation of loads and constraints from structural response data

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AIAA JOURNAL 2007年第6期45卷 1199-1207页

作者： Padmanabhan, Sanjeev Kumar, Ashok V. Univ Florida Gainesville FL 32611 USA

An important source of uncertainty in finite element models used for static and fatigue analysis is due to inaccuracy in estimating both the magnitude and distribution of loads. Furthermore, it is often assumed in the models that the structure is rigidly supported even though there may be significant compliance at the support. It is often difficult to accurately estimate the compliance as well as the actual distribution of the load. Recent improvements in experimental techniques enable full-field strain measurement with relative ease for structural components. A method for using these measurements to compute the applied load and distribution, as well as compliances at the supported boundaries, is presented in this paper. Accurately determining the loads and boundary conditions can significantly improve the ability to predict fatigue life and the likely location of failure for structures.

关键词： Structural Response Inverse Problems Finite Element Analysis Fatigue Life Static Fatigue Maximum Shear Stresses Poisson's Ratio Aerodynamic Loads optimization algorithm Computing

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The Nukiyama curve in water spray cooling: Its derivation from temperature-time histories and its dependence on the quantities that characterize drop impact

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2007年第25-26期50卷 4948-4966页

作者： Ciofalo, Michele Caronia, Antonino Di Liberto, Massimiliano Puleo, Salvo Univ Palermo Dipartimento Ingn Nucl I-90128 Palermo Italy

Heat transfer from hot aluminium walls to cold water sprays was investigated. The method used was the transient two-side symmetric cooling of a planar aluminium target, previously heated to temperatures of up to 750 K, by twin sprays issuing from full-cone swirl spray nozzles of various gauge. The target's mid-plane temperature was recorded during the cooling transient by thin-foil K thermocouples and a high-frequency data acquisition system. In order to determine the wall temperature T-w, the wall heat flux q(w)" and the q(w)" - T-w heat W W transfer (Nukiyama) curve, two different approaches were used: the first was based on the solution of an inverse heat conduction problem, the second on a suitable parameterization of the Nukiyama curve and on the solution of a minimum problem. Relevant heat transfer quantities, such as the critical heat flux and the single-phase heat transfer coefficient, were obtained from each heat transfer curve. Their dependence on the main parameters characterizing the spray impact phenomenon (mass flow rate, drop velocity and drop diameter) was investigated on the basis of a preliminary hydrodynamic characterization study, and suitable correlations were proposed. (c) 2007 Elsevier Ltd. All rights reserved.

关键词： spray cooling induction heating inverse problem optimization algorithm

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Optimal multi-objective nonlinear impulsive rendezvous

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2007年第4期30卷 994-1002页

作者： Luo, Ya-Zhong Lei, Yong-Jun Tang, Guo-Jin Natl Univ Def Technol Coll Aerosp & Mat Engn Changsha 410073 Peoples R China

The multi-objective optimization of unperturbed two-body impulsive rendezvous is investigated in this paper. In addition to the total characteristic velocity and the time of rendezvous flight, the minimum relative distance between the chaser and the target in the chaser's free-flying path is proposed as another design performance index. The feasible iteration optimization model of three-objective impulsive rendezvous with path constraints including trajectory safety and field of view constraints is established using a Lambert algorithm. The multi-objective nondominated sorting genetic algorithm is employed to obtain the Pareto solution set. The -V-bar and +V-bar homing rendezvous missions are examined by the proposed approach. It is shown that tradeoffs between time of flight, propellant cost and passive trajectory safety, and several inherent principles of the rendezvous trajectory are demonstrated by this approach.

关键词： Propellant Multi Objective Genetic algorithm Lambert algorithm Characteristic Velocity Numerical optimization optimization algorithm Target Spacecraft Path Constrained Rendezvous Perigee Earth

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Sensitivity-analysis method for inverse simulation application

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2007年第1期30卷 114-121页

作者： Lu, Linghai Murray-Smith, David J. Thomson, D. G. Univ Glasgow Dept Elect & Elect Engn Glasgow G12 8LT Lanark Scotland Univ Glasgow Dept Aerosp Engn Glasgow G12 8QQ Lanark Scotland

An important criticism of traditional methods of inverse simulation that are based on the Newton-Raphson algorithm is that they suffer from numerical problems. In this paper these problems are discussed and a new method based on sensitivity-analysis theory is developed and evaluated. The Jacobian matrix may be calculated by solving a sensitivity equation and this has advantages over the approximation methods that are usually applied when the derivatives of output variables with respect to inputs cannot be found analytically. The methodology also overcomes problems of input-output redundancy that arise in the traditional approaches to inverse simulation. The sensitivity-analysis approach makes full use of information within the time interval over which key quantities are compared, such as the difference between calculated values and the given ideal maneuver after each integration step. Applications to nonlinear HS125 aircraft and Lynx helicopter models show that, for this sensitivity-analysis method, more stable and accurate results are obtained than from use of the traditional Newton-Raphson approach.

关键词： Sensitivity Analysis Helicopters Fixed Wing Aircraft Mathematical Models Numerical Stability Momentum Theory Business Jet Elevator Fuselages optimization algorithm

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Computing strategies for achieving acceptability: A Monte Carlo approach

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STOCHASTIC PROCESSES AND THEIR APPLICATIONS 2007年第11期117卷 1587-1605页

作者： Pal, Soumik Cornell Univ Dept Math Ithaca NY 14853 USA Cornell Univ ORIE Ithaca NY 14853 USA Columbia Univ Dept Stat New York NY 10027 USA

We consider a trader who wants to direct his or her portfolio towards a set of acceptable wealths given by a convex risk measure. We propose a Monte Carlo algorithm, whose inputs are the joint law of stock prices and the convex risk measure, and whose outputs are the numerical values of initial capital requirement and the functional form of a trading strategy for achieving acceptability. We also prove optimality of the capital obtained. Explicit theoretical evaluations of hedging strategies are extremely difficult, and we avoid the problem by resorting to such computational methods. The main idea is to utilize the finite Vapnik-Cervonenkis dimension of a class of possible strategies. (C) 2007 Elsevier B.V. All rights reserved.

关键词： measures of risk VC dimension portfolio optimization Neyman-Pearson lemma optimization algorithm

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