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IMPROVED MULTILEVEL optimization APPROACH FOR THE DESIGN OF COMPLEX ENGINEERING SYSTEMS

AIAA JOURNAL 1988年第3期26卷 353-360页

作者： BARTHELEMY, JFM RILEY, MF VIRGINIA POLYTECH INST & STATE UNIV BLACKSBURGVA 24061 PRC KENTRON HAMPTONVA

Multilevel optimization methods are being considered for the design of complex systems on distributed networks of computers or even parallel processors. An obstacle to the use of multilevel methods is that they can be computationally expensive because of the cycling necessary to account for the coupling between the subproblems. This research effort aims at increasing the efficiency of multilevel optimization by adapting two techniques widely used in one-level optimization: constraint approximation and temporary constraint deletion. These improvements are tested on 3,10, and 52 bar planar trusses. The results show that for larger problems (approximately 100 variables and larger), the cost of analysis dominates the total cost so that multilevel optimization is no more expensive than one-level optimization. If parallel processing is used or the analysis process itself is decomposed, then multilevel optimization stands to become more economical than one-level optimization. © 1988 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Planar Truss Cost Analysis Nonlinear Programming Finite Element Modeling Sensitivity Analysis Strength of Materials Young's Modulus Polynomial Interpolation optimization algorithm Distributed Processing

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BIRTH OF A SALESMAN

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1988年第5期11卷 415-420页

作者： SHAW, JJ JAMES, RM GRUNBERG, DB ALPHATECH INC MKT RES & DEVBURLINGTONMA 01803

The AIAA Artificial Intelligence Design Challenge is eccentric and intriguing, combining features from traveling salesman and stochastic optimization problems together with several side constraints thrown in for additional appeal. The challenge is to devise a solution algorithm that will reliably find optimal (or near optimal) solutions and can be extended to more general problems. We present our algorithm for this challenge in this paper. The fundamental algorithm for finding near-optimal solutions is disarmingly simple and can be made quite efficient through the introduction of several bounds on the problem. The reader will quickly discover that these bounds do not require a deep understanding of traveling salesman algorithms and should enjoy devising additional bounds to add to the potpourri. © 1988 American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

关键词： algorithm Performance Artificial Intelligence Stochastic optimization optimization algorithm Greedy algorithm Gas Dynamics Kinetic Theory of Gases Aerodynamics Planetary Atmospheres Search algorithm

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STIFFNESS TAILORING FOR IMPROVED COMPRESSIVE STRENGTH OF COMPOSITE PLATES WITH HOLES

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AIAA JOURNAL 1988年第1期26卷 72-77页

作者： HAFTKA, RT STARNES, JH NASA LANGLEY RES CTRDIV STRUCT & DYNAMSTRUCT MECH BRANCHHAMPTONVA 23665

A structural optimization procedure is used to obtain minimum-mass designs of compression-loaded composite plates with holes by tailoring the plate cross-sectional stiffnesses. The plate cross sections consist of two different balanced symmetric laminates with 0, ±45, and 90 deg plies. The plate inner laminate contains a hole and is designed from a softer material system with a higher failure strain than the plate outer laminate. Allgraphite- epoxy plates and hybrid graphite/glass-epoxy plates were studied. Results for designs with different percentages of 0 and ±45 deg plies in the outer laminate are compared with results for the optimum designs. Results for designs with uniform cross-sectional stiffnesses are also compared with the results for tailored crosssectional stiffness designs. Specimens of each design were tested to verify the analytical predictions. The results show that cross-sectional stiffness tailoring can increase the ratio of compressive strength to mass of compression-loaded laminated plates with holes. It is shown that removing 0 deg plies from the hole region both increases the compression strength and decreases the mass of graphite-epoxy plates. © 1988 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Compression Strength Stiffness Structural optimization Finite Element Analysis Glass Fiber Stress Concentration Material Properties Strength of Materials optimization algorithm Electrical Resistance

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IMPROVED EXPONENTIAL TIME-SERIES APPROXIMATION OF UNSTEADY AERODYNAMIC OPERATORS

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JOURNAL OF AIRCRAFT 1988年第2期25卷 121-127页

作者： PETERSON, LD CRAWLEY, EF Massachusetts Institute of Technology Cambridge Massachusetts

A procedure has been developed for approximating unsteady aerodynamic operators as truncated exponential series in the time domain. The approximation is accomplished using a least squares minimization fit to aerodynamic data in the frequency domain. The procedure extends previous methods by including the pole locations as unknown parameters of the least squares minimization. In addition, the error associated with both the real and imaginary parts of the Fourier transform of the approximation is minimized. A Newton-Raphson search algorithm is used to find the minimum of the weighted square error in the parameter space of the approximation while constraining the poles to be in the left half-plane. By freely varying the poles of the approximation during the numerical least squares minimization, the representation of the unsteady aerodynamics is improved and is comparable to existing higher-order Fade approximations. Hence, the method offers the aeroelastic designer a more direct method of finding approximate aerodynamic states. However, because the minima of the square error in the cost function found are not necessarily global and depend on the number of poles in the approximation, the initial trial minimum, and the details of the cost minimization algorithm, the poles found in the search do not necessarily correspond to the theoretical poles of the aerodynamic transfer function. Example exponential time series approximations of the Theodorsen function are presented and compared with a Fade approximation and other exponential time series approximations. © American Institute of Aeronautics and Astronautics, Inc., 1985. All rights reserved.

关键词： Frequency Domain Search algorithm Unsteady Aerodynamics Aerodynamic Force Nonlinear Programming Aeroelastic Analysis optimization algorithm Computing

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STRUCTURAL SIZING BY GENERALIZED, MULTILEVEL optimization

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AIAA JOURNAL 1987年第1期25卷 139-145页

作者： SOBIESZCZANSKISOBIESKI, J JAMES, BB RILEY, MF KENTRON INT INC DIV AEROSP TECHNOLADV COMP METHODS UNITHAMPTONVA

Developments of a general multilevel optimization capability and results for a three-level structural optimization are described. The latter is considered a major stage in the method development because the addition of more levels beyond three does not introduce any new qualitative elements. Therefore, a three-level implementation is, qualitatively, the equivalent to a multilevel implementation. The method partitions a structure into a number of substructuring levels where each substructure corresponds to a subsystem. The method is illustrated by a portal framework that decomposes into individual beams. Each beam is a box that can be further decomposed into stiffened plates. Consequently, substructuring for this example spans three levels: the bottom level of finite elements representing the plates, an intermediate level of beams treated as substructures, and the top level for the assembled structure. This example is an extension of a previously presented case that was limited to two levels. © 1987 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Finite Element Analysis Structural optimization Engineer's Beam Theory optimization algorithm Sensitivity Analysis Aerospace Technology Distributed Computing Black Box Structural Sensitivity Analysis NASA Langley Research Center

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SPACE FRAME optimization SUBJECT TO FREQUENCY CONSTRAINTS

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AIAA JOURNAL 1987年第10期25卷 1396-1404页

作者： WOO, TH TRW Space and Technology Group Redondo Beach California

An efficient structural optimization methodology is presented for the design of minimum-weight space frames subject to multiple natural frequency constraints. A powerful class of generalized hybrid constraint approximations that require only the first-order constraint function derivatives has been developed to overcome the inherent nonlinearity of the frequency constraint. The generalized hybrid constraint functions are shown to be relatively conservative, separable, and convex in the region bounded by the move limits based on the formula described in this paper. The optimization methodology is implemented in an automated structural optimization system, which has been applied to solve a variety of space frame optimization problems. Numerical results obtained for three example problems indicate that the optimization methodology requires fewer than 10 complete normal modes analyses to generate a near-optimum solution. © 1987 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Structural optimization Sensitivity Analysis Finite Element Analysis Structural Analysis Trusses Cantilever Beam Helicopters Nonlinear Programming optimization algorithm Membrane Structures

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optimization OF GEOMETRY DESCRIBED BY CURVES

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COMPUTER-AIDED DESIGN 1987年第5期19卷 251-256页

作者： WESTBERG, SKE LINKOPING UNIV DEPT MEDDIV MECH ENGN DESIGNS-58183 LINKOPINGSWEDEN

In CAD, the shape of a design is often described by an interpolating curve. In this paper, an automated method for finding the optimal geometry of such a curve is used to study the blade geometry of vertical axis wind turbines. To minimize bending moments due to centrifugal loads during rotation the blades are often curved in the shape of the troposkien (Greek for ‘turning rope’). From a fabrication point of view a simpler shape is preferred. An optimal number of interpolating points along the curve are used as design variables and their movements controlled by an optimization algorithm. During the optimization, the shape of the curve is successively recomputed and current objective and constraint functions are analysed. Stresses along the beam are computed using the finite element method by regarding the curve as a plane elastic beam.

关键词： computer-aided design optimization algorithm troposkien blade geometry

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TIME-INVARIANT CONTROLLERS FOR TARGET TRACKING

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1987年第4期10卷 330-337页

作者： GARDNER, BE CANNON, RH BRYSON, AE STANFORD UNIV DEPT AERONAUT & ASTRONAUTSTANFORDCA 94305

A method is described for designing time-invariant controllers to minimize root-mean-square target-tracking errors with root-mean-square control constraints in the presence of random initial conditions, target motions, and sensor errors. The maximum control responses usually occur during the initial transient period before the statistical steady state is reached. Hence we determine the controller parameters by minimizing a quadratic performance index that has separate weights on the transient and steady-state components of the control and tracking error. The designer makes tradeoffs between maximum control responses and steady-state tracking errors by varying the weights in this performance index. Two examples are given. The first is relatively simple to demonstrate the ideas, while the second is more complex, involving the recovery of a remotely piloted vehicle in a net on a rolling, pitching ship. The controller designs exhibit an improved performance over designs based on the minimization of the conventional performance index associated with linear quadratic Gaussian and parameter optimization methods. © 1987 American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

关键词： Linear Quadratic Gaussian Sensors Closed Loop System Ailerons Bank Angle Autopilot Heading Angle optimization algorithm Single Input Single Output Search algorithm

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HYPERVELOCITY GLIDING MANEUVERS

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JOURNAL OF AIRCRAFT 1987年第8期24卷 572-574页

作者： TAUBER, ME NASA Ames Research Center Moffett Field California

The ability to maneuver within the atmosphere during orbital return is a major advantage of high-lift vehicles. For example, a maximum lift/drag ratio of nearly 2 affords the Space Shuttle orbiter a choice of several landing sites. In addition, the Shuttle can be rolled during entry while still maintaining a shallow glide trajectory. This roll maneuver during entry reduces the descent time and, therefore, the total heat input, although the heating rate is increased. One typical measure of maneuvering capability is the maximum lateral range that a vehicle can achieve;the solution to this problem was originally given. Another important maneuver consists of performing turns that change the vehicle's heading. This paper contains a brief analysis of turning maneuvers during gliding flight, including lateral distances traversed, at velocities up to circular satellite speed.

关键词： Aerodynamic Force Lift Drag Ratio Satellites Yaw Control Flight Altitude Earth NASA Ames Research Center optimization algorithm Space Shuttle Orbiter Mathematical Models

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COMPUTATIONAL METHOD FOR optimization OF STRUCTURAL SHAPES

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AIAA JOURNAL 1986年第6期24卷 1005-1012页

作者： HOU, JW CHEN, JL SHEEN, JS Old Dominion University Norfolk Virginia

In the direct method of shape optimum design, mesh regridding is a necessary step in avoiding the distortion of finite element grids. The effect of internal-nodal movements on the shape design sensitivity associated with the regridding process has been carefully examined in this paper. It shows that to maintain computational accuracy, the effects of internal-nodal movement should be considered in shape design sensitivity analysis. To take the internal-nodal movement into account, the numerical accuracy of the speed method is investigated. A new approach, which constructs the velocity field over the element domain, is presented. Although it takes more computational time, the new approach does improve the accuracy of shape design sensitivity. © 1986 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Computational Methods Sensitivity Analysis Finite Element Analysis Material Derivatives Triangular Element Shape optimization optimization algorithm Boundary Element Method Stress Distribution Young's Modulus

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