This paper considers stability optimization of undamped cantilevered columns subjected to the simultaneous action of a conservative ('dead') load and a nonconservative ('follower') load at their free e...
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This paper considers stability optimization of undamped cantilevered columns subjected to the simultaneous action of a conservative ('dead') load and a nonconservative ('follower') load at their free ends. The load combination is characterized by a 'nonconservativeness parameter' eta, where eta = 0 corresponds to a purely conservative load (an Euler column) and eta = 1 to a pure follower load (Beck's column). The optimization problem is considered in the form of volume minimization by constant critical load and is solved numerically by using finite elements and sequentiallinear optimization. It is shown that the minimum volume design for constant critical load is equivalent to the maximum critical load design for constant volume;for any design and any load combination, critical load/(volume of column)(2) = constant. Optimum designs are determined for eta = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0. For the uniform column, stability is lost by divergence for eta < 0.5 and by flutter for eta > 0.5. For the optimal columns, divergence occurs only in the case eta = 0.0;for the other eta-values considered, stability is lost by flutter. The largest benefit of optimization is obtained in the case eta = 0.4;here the critical load for the optimal column is more than ten times larger than for the uniform column. The stability of the optimal columns for other types of loads than the design-load is thoroughly investigated and illustrated by diagrams. (C) 2000 Elsevier Science Ltd. All rights reserved.
作者：
Celi, RUniv Maryland
Alfred Gessow Rotorcraft Ctr Dept Aerosp Engn College Pk MD 20742 USA
An inverse simulation methodology based on numerical optimization is presented. The methodology is applied to a simplified version of the slalom maneuver in the ADS-33D helicopter handling qualities specification. The...
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An inverse simulation methodology based on numerical optimization is presented. The methodology is applied to a simplified version of the slalom maneuver in the ADS-33D helicopter handling qualities specification. The inverse simulation is formulated as an optimization problem with trajectory. and dynamic constraints, pilot inputs as design variables, and an objective function that depends on the specific problem being solved. A maximum speed solution is described. The results show that numerical optimization is a reliable and flexible tool for inverse simulation, both when the required trajectory is prescribed explicitly and when it is defined indirectly through geometric and dynamic constraints. When the trajectory is defined indirectly, there is not a single acceptable trajectory but rather an entire family with noticeable differences in the helicopter dynamics and in the required pilot inputs. Even when the trajectory is prescribed explicitly, multiple solutions exist. For handling qualities studies, the multiple solutions may provide an indication of tbe amount of scatter in pilot ratings to be expected for a given aircraft and a given maneuver. However, if the inverse simulation is used for simulation validation, then additional constraints may have to be placed on the solution to make it unique.
In the past few Sears there has been interest in using response surface techniques to create surrogates to computer simulations. Response surface techniques allow detection and correction of errors as well as filterin...
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In the past few Sears there has been interest in using response surface techniques to create surrogates to computer simulations. Response surface techniques allow detection and correction of errors as well as filtering out numerical noise, but these techniques introduce additional modeling errors. Methods of reducing both noise and modeling errors are explored. It is also demonstrated that repairing designs with large errors is preferable to eliminating these designs from consideration. Response surface approximations for a high-speed civil transport wing weight equation created from the results of a large number of structural optimizations are used for demonstration. It is shown that the statistical tools available for response surface techniques are effective for error detection and for filtering out noise. Once the noise is reduced, modeling errors can also be reduced by increasing the order of the approximation.
The critical buckling loads of unsymmetrically laminated rectangular plates with a given material system and subjected to combined lateral and inplane loads are maximized with respect to fiber orientations by using a ...
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The critical buckling loads of unsymmetrically laminated rectangular plates with a given material system and subjected to combined lateral and inplane loads are maximized with respect to fiber orientations by using a sequential linear programming method together with a simple move-limit strategy. Significant influence of plate aspect ratios, central circular cutouts, lateral loads and end conditions on the optimal fiber orientations and the associated optimal buckling loads of unsymmetrically laminated plates has been shown through this investigation.
This paper proposes a two-stage optimization algorithm for topology optimization based on the homogenization method. The multistage approach aims to increase the stability and overall efficiency of homogenization-base...
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This paper proposes a two-stage optimization algorithm for topology optimization based on the homogenization method. The multistage approach aims to increase the stability and overall efficiency of homogenization-based topology optimizations. The homogenization method employed in this study uses a material constraint, which seeks the optimal configuration with the least amount of compliance. In a two-stage approach, a finite element model with a large element size was employed in the first stage of the topology optimization. The purpose of using a smaller number of finite elements is to increase the chances of attaining a good topology while the associated computational cost is limited. At the end of the first optimization stage, the optimal topology obtained is subsequently used to construct an initial topology in a finite element model with a smaller element size. The second-stage topology optimization is thus performed with the goal of capturing a topology of good quality with detailed contour description. A number of smoothing strategies for converting the optimal topology into the initial topology in a finer FEM model space are entailed. The stability and effectiveness of the proposed two-stage topology optimization algorithm are illustrated by two structural design problems. (C) 1999 Elsevier Science Ltd. All rights reserved.
The dynamics and control for the specific application of a large orbiting flexible thin square plate are considered. The focus is on the utilization of a singular value decomposition (SVD) method to create a stable re...
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The dynamics and control for the specific application of a large orbiting flexible thin square plate are considered. The focus is on the utilization of a singular value decomposition (SVD) method to create a stable reduced-order system. By reviewing the system's singular value bounds in the frequency domain one can properly assess stability robustness parameters that are difficult to characterize effectively in a time-domain setting. This system's open-loop singular values were extremely close to zero, denoting singular system matrices. To alleviate this problem with matrix singularity, the SVD method was applied to transform the original systems. The reduction of actuators/sensors is done partially in the physical sense and partially in the mathematical space. Results show that when the SVD method transformation is applied stable controllable closed-loop system matrices can be designed.
The fundamental frequencies of fiber-reinforced laminated curved panels with a given material system are maximized with respect to fiber orientation by using a sequential linear programming method with a simple move-l...
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The fundamental frequencies of fiber-reinforced laminated curved panels with a given material system are maximized with respect to fiber orientation by using a sequential linear programming method with a simple move-limit strategy. The significant influences of panel thickness, curvature, aspect ratio, cutouts, and end conditions on the maximum fundamental frequencies and the associated optimal fiber orientations are demonstrated.
An integrated structural/control design for the vibration suppression of a composite plate with segmented piezoelectric (PZT) actuators is examined, The electric power used by the PZT materials becomes a very importan...
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An integrated structural/control design for the vibration suppression of a composite plate with segmented piezoelectric (PZT) actuators is examined, The electric power used by the PZT materials becomes a very important factor for real application to the control of flexible structures, The method to predict power required for the control is presented, and the power is used as a part of the objective functions, The structural weight, the state error energy, control energy, stability robustness, and the electric power required for vibration control are considered as the objective function. The locations of the PZT actuators are considered as control design variables, The ply orientation and thickness coefficients of the laminated composite plate are considered as structural design variables, The improved compromise multiobjective optimization by using a reduction factor of performance indices is applied to solve this optimization problem, The sequential linear programming method with move limits is used, The sensitivity analysis, which is required in the optimization process, is performed for the eigenstructure assignment control scheme and the performance indices with respect to the design parameters, The optimized results showed a significant amount of reduction in the structural weight as well as the control performance indices. The required electric power is also decreased.
We present a new algorithm for nonlinear minimax optimization which is well suited for large and sparse problems. The method is based on trust regions and sequential linear programming. On each iteration a linear mini...
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We present a new algorithm for nonlinear minimax optimization which is well suited for large and sparse problems. The method is based on trust regions and sequential linear programming. On each iteration a linear minimax problem is solved for a basic step. If necessary, this is followed by the determination of a minimum norm corrective step based on a first-order Taylor approximation. No Hessian information needs to be stored. Global convergence is proved. This new method has been extensively tested and compared with other methods, including two well known codes for nonlinearprogramming. The numerical tests indicate that in many cases the new method can find the solution in just as few iterations as methods based on approximate second-order information. The tests also show that for some problems the corrective steps give much faster convergence than for similar methods which do not employ such steps.
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