This article discusses a new technique for improving convergence In optimization problems by pruning the search space of weak variables. Such variables are identified by learning from a database of existing designs us...
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This article discusses a new technique for improving convergence In optimization problems by pruning the search space of weak variables. Such variables are identified by learning from a database of existing designs using neural networks. By using clustering techniques, different sets of weak variables are identified in different regions of the design space. Parameter sensitivity information obtained in the process of identifying weak variables provides accurate heuristics for formulating design rules. The impact of this methodology on obtaining converged designs has been investigated far turbine design problems. Results from a three-stage power turbine and an aircraft engine turbine design are presented in this article.
This paper discusses basic problem formulation, and solution procedures for solving a particular large-scale two-dimensional cutting stock problem at a furniture factory. In recent years there has been an explosion of...
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This paper discusses basic problem formulation, and solution procedures for solving a particular large-scale two-dimensional cutting stock problem at a furniture factory. In recent years there has been an explosion of interests in this application area. The cutting stock problems are met in many branches of industry. There is a large economical incentive to find more effective solution procedures, and it is easy to compare alternative solution procedures and to identify potential benefits of using a proposed procedure. The paper concentrates on the case in which both stock and ordered sizes are rectangular. We present a mathematical model of the problem, propose an optimization algorithm and describe its basic properties. The mathematical model of the optimization problem relies on the Gilmore and Gomory approach. To decrease the total computing time we propose an interactive procedure based on the forecasting of the criterion functions values.
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 SE...
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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.
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 continuati...
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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)
Integral equations, including the lifting surface integral equation, are numerically solved using modifications to the constant-vorticity panel method of Tuck.
Integral equations, including the lifting surface integral equation, are numerically solved using modifications to the constant-vorticity panel method of Tuck.
The problem is suggested of finding an optimal entry angle so that an aeroassisted orbit transfer vehicle does not need to pull down or pull up for a given orbital plane change. An explicit guidance law is presented o...
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The problem is suggested of finding an optimal entry angle so that an aeroassisted orbit transfer vehicle does not need to pull down or pull up for a given orbital plane change. An explicit guidance law is presented of a reentry aeroassisted orbital vehicle which enters the atmosphere with a prescribed entry angle and keeps the bank angle at 90 deg until exit. The entry angle is a function of the entry speed and the exit speed. The lift control in the atmosphere can be divided into two phases. In the first phase, the vehicle descends and keeps the normalized lift coefficient constant. During ascent, the normalized lift coefficient decreases proportionally to the increase in height. A comparison is made for the orbital plane change between the optimal aeroassisted trajectory and the trajectory realized by the explicit guidance. The proposed guidance scheme is simple to implement and produces nearly optimal plane change. (AIAA)
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...
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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.
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...
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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)
Analytical expressions are developed for computing eigenvector derivatives, specialized for the case of mechanical second-order dynamic systems. Both exact and approximate formulations are developed using a modal expa...
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Analytical expressions are developed for computing eigenvector derivatives, specialized for the case of mechanical second-order dynamic systems. Both exact and approximate formulations are developed using a modal expansion approach. The new exact formulations are found to be numerically accurate and to require significantly less computing time than the corresponding generalized formulations. An improved approximate method is also introduced for computing a truncated set of eigenvector derivatives for large structural systems. Numerical ex amples are included to evaluate the effectiveness of the approximate formulations, and they are found to be very efficient in the cases studied.
This paper deals with the proposal of a new genetic algorithm based optimization algorithm referred to as the constructive algorithm and its application to the discrete shape design of the strongest column with maximu...
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This paper deals with the proposal of a new genetic algorithm based optimization algorithm referred to as the constructive algorithm and its application to the discrete shape design of the strongest column with maximum buckling load of the first mode under constraint of constant weight. The buckling load analysis is performed by the finite element method. Introducing a set of system parameters concerned with the bending rigidity of each finite element, the problem is reduced to that of finding the best set of the system parameters from the great number of sets satisfying the constraint. The basic idea of the constructive algorithm is as follows. One individual is generated in which a set of system parameters is encoded. Then a set of strings with an updating rule of the system parameter set is generated. The strings are then stored to computer memory with fitness values based on a certain rule and the evolutionary operation of standard genetic algorithms is applied to the strings. To demonstrate the efficiency of the constructive algorithm numerical calculations were performed. It was shown that the constructive algorithm exhibits high performance in finding the best shape from the great number of shapes satisfying the constraint.
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