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Symbolic computation to estimate two-sided boundary conditions in two-dimensional conduction problems

JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 1997年第3期11卷 472-476页

作者： Yang, CY National Kaohsiung Inst. of Technology Taiwan

A method using symbolic computation is proposed to determine the boundary conditions in two-dimensional inverse heat conduction problems, The method uses symbols to represent the unknown boundaries and then executes the finite difference method to calculate the temperature field, The calculated results are expressed explicitly as functions of the undetermined boundaries, Then, a direct comparison between the output symbolic temperature and the measurement temperature are made to construct a set of Linear equations, Thus, the linear least-squares method is adopted to solve the linear equations, Finally, the unknown boundary conditions are determined, Results from the examples confirm that the proposed method is applicable in solving the multidimensional inverse heat conduction problems, In the example problems, three kinds of measuring methods are adopted to estimate the surface temperature, The result shows that only three measuring points are needed to estimate the surface temperature when measurement errors are neglected, When measurement errors are considered, seven measuring points are required to increase the congruence of the estimated results to the exact solutions.

关键词： Inverse Heat Conduction Inverse Problems Thermal Properties Heat Transfer Conjugate Gradient Method Boundary Element Method Finite Difference Method optimization algorithm Adiabatic Conditions Thermal Conductivity

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Cascade optimization strategy for aircraft and air-breathing propulsion system concepts

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JOURNAL OF AIRCRAFT 1997年第1期34卷 136-139页

作者： Patnaik, SN Lavelle, TM Hopkins, DA NASA LEWIS RES CTRAEROPROP ANAL OFFCLEVELANDOH 44135 NASA LEWIS RES CTRSTRUCT & ACOUST BRANCHCLEVELANDOH 44135 NASA LEWIS RES CTRCOMPUTAT SCI BRANCHCLEVELANDOH 44135

Flight optimization system (FLOPS) and the NASA engine performance program analyzer (NEPP) used in the design optimization for aircraft and air-breathing propulsion engine concepts. The FLOPS code was incorporated into the code COMETBOARDS which successfully solved both subsonic and supersonic aircraft problems. Also, NEPP and COMETBOARDS in combination successfully optimized a number of subsonic and supersonic engine design. Aircrafts and engines includes cascade optimizing strategy, constraint and design formulations, and global scaling strategy as the key features and unique strengths of COMETBOARDS.

关键词： Supersonic Aircraft Air Breathing Propulsion System Overall Pressure Ratio Aspect Ratio Aerodynamics Turbine Inlet Temperature optimization algorithm Nonlinear Programming Takeoff and Landing NASA Lewis Research Center

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Comparison of design optimization formulations for minimization of noise transmission in a cylinder

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JOURNAL OF AIRCRAFT 1997年第2期34卷 236-243页

作者： Crane, SP Cunefare, KA Engelstad, SP Powell, EA LOCKHEED MARTIN AERONAUT SYST CO MARIETTA GA 30063 USA

A computational design tool was developed to perform a constrained optimization of the acoustic environment within a vibrating cylinder, incorporating finite element and boundary element methods, This paper presents a comparison of the relative performance and results obtained through the use of four different objective function and constraint formulations within the optimization tool: 1) minimize the sum of the squared acoustic pressures at a number of points within the cylinder, 2) minimize the weight of the structure with a constraint on the sum of the acoustic pressures, 3) minimize the sum Of the acoustic pressures with a constraint on weight, and 4) minimize weight and summed pressures simultaneously, All four formulations were subject to upper and lower bounds on the design variables, the structural shell element thicknesses. All analyses were performed at a single excitation frequency. These formulations were implemented within the design tool and compared based on their overall pressure and weight reduction and computational efficiency. Two different cylinder models were used to evaluate the optimization formulations, It was found that the third formulation was the most stable and effective, In addition, a nearly Linear relationship was observed between the relative optimal decibel noise level within the cylinder and the optimal cylinder weight.

关键词： Boundary Element Method Sound Pressure Level Aircraft Structures MDO optimization algorithm Structural Element Structural Modeling Aircraft Cabin Young's Modulus Structural optimization

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Control and flight performance of tethered satellite small expendable deployment system-II

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1996年第5期19卷 1148-1156页

作者： Lorenzini, EC Bortolami, SB Rupp, CC Angrilli, E NASA GEORGE C MARSHALL SPACE FLIGHT CTRSPACE SCI & APPLICAT SYST OFFHUNTSVILLEAL 35812 UNIV PADUA DEPT ENGN MECHI-35100 PADUAITALY

The second mission of the small expendable deployment system (SEDS-II) followed the successful mission of SEDS-I, which deployed freely a small instrumented probe on a 20-km tether. Unlike SEDS-I, the deployment of SEDS-II was controlled to provide a small libration amplitude and tether velocity at the end of deployment, The preflight goal for SEDS-II was a maximum libration of less than 10 deg and a final velocity of less than 1 m/s. The control problem was made difficult by the limited capabilities of the SEDS sensors and onboard computer and the large uncertainties inherent in the response of the actuator (brake) and the plant (deployer). The nonlinear, nonautonomous control problem is divided in two parts by using a numerically formulated feedback linearization, i.e., by devising 1) a nonlinear control (reference) trajectory and 2) a linear control about the reference trajectory. An ad hoc feedback law that forces the perturbed system to follow the reference trajectory is derived by using a linearized variational model. The controller is then tested, through computer simulations, for large deviations of the model parameters on the nonlinear model. The relevant flight data are also presented and compared to the reference values to demonstrate the validity and robustness of the control law, which provided a maximum libration amplitude of less than 4 deg and a final tether velocity of less than 0.02 m/s.

关键词： Satellites Flight Performance Feedback Linearization Actuators Flight Software Onboard Sensors Nonlinear Control Linear Time Invariant Friction Coefficient optimization algorithm

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Determination of equilibrium points for an aircraft dynamic model

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1996年第6期19卷 1392-1394页

作者： Avanzini, G deMatteis, G POLITECN TORINO DEPT AEROSP ENGN I-10129 TURIN ITALY

A technique is presented for the determination of the equilibrium points of the aircraft equations of motion. In particular, the goal is to develop a method for the evaluation of the starting points for the continuation algorithms that are used in bifurcation analyses of the nonlinear dynamics of high-performance aircraft to trace the steady states of the system as certain parameters, called continuation parameters, are varied. As a limitation, the method developed only applies to aircraft models where the aerodynamic coefficients depend linearly on the angular velocity components. (AIAA)

关键词： High Performance Aircraft Aerodynamic Angle Aerodynamic Force Coefficients Ailerons Leading Edge Flap Zero Gravity Nonlinear Programming Sideslip Angle optimization algorithm Mean Aerodynamic Chord

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Optimal rectangular end plates

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JOURNAL OF AIRCRAFT 1996年第3期33卷 623-625页

作者： Standingford, DWF Tuck, EO University of Adelaide Adelaide 5005 Australia

Integral equations, including the lifting surface integral equation, are numerically solved using modifications to the constant-vorticity panel method of Tuck.

关键词： Lift Coefficient Rectangular Wing Aerodynamic Design Thickness to Chord Ratio Vorticity Tsai Wu Failure Criterion optimization algorithm Vortex Lattice Method Two Dimensional Flow Cruise Altitude

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MODE TRACKING ISSUES IN STRUCTURAL optimization

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AIAA JOURNAL 1995年第10期33卷 1926-1933页

作者： ELDRED, MS VENKAYYA, VB ANDERSON, WJ UNIV MICHIGAN ANN ARBORMI 48109 USA AEROFLIGHTDYNAM DIRECTORATEWRIGHT PATTERSON AFBOH 45433

Within the context of optimization of the structural dynamics properties of finite element models, methodology is developed for the tracking of eigenpairs through changes in the structural eigenvalue problem. The goal is to eliminate difficulties caused by ''mode switching'' (i.e., frequency crossing), Out of several candidate methods, two methods for mode tracking are successful. The first method, the higher order eigenpair perturbation algorithm, is based on a perturbation expansion of the eigenproblem. It iteratively computes changes in the eigenpairs due to parameter perturbations with the important feature of maintaining the correspondence between the baseline and perturbed eigenpairs. The second method is a cross-orthogonality check method, which uses mass orthogonality to reestablish correspondence after a standard reanalysis. Modified eigenpair extraction routines (Lanezos, subspace iteration, inverse power) were unsuccessful in tracking modes. Applications of mode tracking technology that are presented are frequency-constrained optimization and optimization with mode shape constraints. Each application procedure is outlined and examples are given. Recommendations are made based on method efficiency and robustness in the example problems.

关键词： Structural optimization Finite Element Modeling Structural Dynamics Wing Box Nonlinear Programming Free Vibrations Singular Value Decomposition Aeroelastic Analysis Track algorithm optimization algorithm

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CONTROLLABILITY AND optimization IN AEROASSISTED ORBITAL TRANSFER

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1995年第4期18卷 911-913页

作者： ANDIARTI, R MOOG, CH SZYMANOWSKI, J WARSAW UNIV TECHNOL INST AUTOMAT CONTROLPL-00665 WARSAWPOLAND

The paper addresses the optimal control for the atmospheric flight phase of a spacecraft. From an analysis of the vehicle's controllability, it is shown that the acceptable domain of initialization for the adjoint vector ensuring the convergence of the solution increases when the flight is considered in the lower altitude, i.e., when the controllability increases. The optimal control should be applied to determine the reference trajectory only in the lower layers of the atmosphere. (AIAA)

关键词： Orbital Transfer Accelerometer Feedback Loop Transversality Condition Lift Forces Flight Path Angle Flight Trajectory Linear Time Invariant Earth optimization algorithm

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OPTIMAL PLACEMENT OF DAMPED STRUTS USING SIMULATED ANNEALING

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JOURNAL OF SPACECRAFT AND ROCKETS 1995年第4期32卷 653-661页

作者： HAMERNIK, TA GARCIA, E STECH, D VANDERBILT UNIV DEPT MECH ENGNSMART STRUCT LABNASHVILLETN 37235 USAF ACAD FRANK J SEILER RES LABCOLORADO SPRINGSCO 80840

Presented is the optimization of the placement of damped structural elements in a two-dimensional truss network. This work presents a modification of a heuristic optimization technique called simulated annealing, to improve the speed of convergence. Rather than setting the annealing temperature schedule a priori, it is modified according to the change in cost functional. For a single mode of vibration, a comparison is made between the simulated-annealing results and the true optimal locations, as determined by the modal strain locations. As expected, simulated annealing returns a near-optimal solution from a variety of initial configurations. Modal weighting factors are utilized to examine multiple modes, and again the modal strain locations are used for comparison.

关键词： Annealing Temperature Planar Truss Structural Response Vibration Suppression Finite Element Analysis optimization algorithm Structural System Ball Bearings Frequency Response Functions Adaptive Structures

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GENETIC-algorithm-BASED PROCEDURE FOR PRETEST ANALYSIS

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AIAA JOURNAL 1995年第7期33卷 1362-1364页

作者： FRANCHI, CG GALLIENI, D Politecnico di Milano Milan 20133 Italy

The features of genetic algorithm and their major advantages with respect to other analytical, heuristic, or stochastic optimization methods are pointed out. The algorithm is applied to solve a problem and has been proved to fulfill its properties: the optimal placement of sensors in pretest analysis. A proper objective function is defined to include both the requests of observability of the reduced system and of geometrical reconstruction of the measured mode shapes. The results, although obtained from simple examples, confirm all of the premises and are in accordance with physical experience.

关键词： Genetic algorithm Finite Element Modeling Modal Analysis Cantilever Annealing Computing Boundary Value Problems Stochastic optimization optimization algorithm Structural Dynamics

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