Rex K. Kincaid

Good solutions to discrete noxious location problems via metaheuristics

An implementation of simulated annealing and tabu search is described for discrete versions of two noxious facility location problems —p-dispersion andp-defense-sum. A series of computational experiments leading to good choices of the parameters that drive simulated annealing and tabu search are presented for a 33-node data set. Using these parameter settings, the performance of simulated annealing and tabu search are compared to a semi-greedy heuristic for thirty randomly generated 25-node data sets.

Minimizing distortion and internal forces in truss structures by simulated annealing

Inaccuracies in the length of members and the diameters of joints of large space structures may produce unacceptable levels of surface distortion and internal forces. We formulate two discrete optimization problems, one to minimize surface distortion (DRMS) and the other to minimize internal forces (FRMS). Both of these problems are based on the influence matrices generated by a small deformation linear analysis. Good solutions are obtained for DRMS and FRMS through the use of a simulated annealing heuristic. Results based on two biobjective (DRMS and FRMS) optimization models are discussed

Reactive Tabu Search and Sensor Selection in Active Structural Acoustic Control Problems

A Reactive Tabu Search (RTS) is examined. In addition to a dynamic tabu tenure RTS also detects when the search has entered an unproductive area and restarts RTS based on distinctive features of the unproductive area. We explore the effectiveness of RTS over a static tabu list (of a kind used in many implementations) for a two variable unconstrained discrete optimization model with 9 nearly identical minima and 513 other local minima. One of the key features of this problem is that the two-dimensional domain allows us to provide graphical descriptions of the performance of RTS. We then apply RTS to a sensor selection problem in active structural acoustic control. The objective in this problem is to select a set of 8 sensors out of 462 potential sensor locations so that the noise measured at the 8 chosen sensors is as close as possible to the noise measured at all 462. Computational experiments for data taken from a laboratory test article at NASA Langley Research Center are provided.

Minimum Kolmogorov–Smirnov test statistic parameter estimates

We present and implement an algorithm for computing the parameter estimates in a univariate probability model for a continuous random variable that minimizes the Kolmogorov–Smirnov test statistic. The algorithm uses an evolutionary optimization technique to solve for the estimates. Several simulation experiments demonstrate the effectiveness of this approach.

D-optimal designs for sensor and actuator locations

Active control of noise and vibration is now possible in automobiles, aircraft, and many other devices. Where to place actuators, to control noise and vibration, and sensors, to measure the performance of the actuators, is a central question. Given a truss structure, we seek the k most effective locations to control and/or sense vibrations. A discrete D-optimal design has been proposed as a solution to this location problem. We develop a simple static tabu search and test its performance on an 80 node truss structure built at NASA-Langley Research Center. We show that our tabu search approach dominates the traditional approaches to finding D-optimal designs.

Quelling Cabin Noise in Turboprop Aircraft via Active Control

Cabin noise in turboprop aircraft causes passenger discomfort, airframe fatigue, and employee scheduling constraints due to OSHA standards for exposure to high levels of noise. The noise levels in the cabins of turboprop aircraft are typically 10 to 30 decibels louder than commercial jet noise levels. However, unlike jet noise the turboprop noise spectrum is dominated by a few low frequency tones. Active structural acoustic control is a method in which the control inputs (used to reduce interior noise) are applied directly to a vibrating structural acoustic system. The control concept modeled in this work is the application of in-plane force inputs to piezoceramic patches bonded to the wall of a vibrating cylinder. The goal is to determine the force inputs and locations for the piezoceramic actuators so that (1) the interior noise is effectively damped; (2) the level of vibration of the cylinder shell is not increased; and (3) the power requirements needed to drive the actuators are not excessive. Computational experiments for data taken from a computer generated model and from a laboratory test article at NASA Langley Research Center are provided.

A look-ahead heuristic for scheduling jobs with release dates on a single machine

Abstract The paper explores how limited look-ahead improves the performance of on-line heuristics. In particular, we consider the NP-complete single machine scheduling of independent jobs with release dates to minimize the total completion time. We present an on-line with look-ahead algorithm which foresees the next in-coming job. We study its worst-case behavior and prove that it outperforms most on-line and off-line heuristics.

Toward Optimal Transport Networks

Strictly evolutionary approaches to improving the air transport system ‐ a highly complex network of interacting systems ‐ no longer suce in the face of demand that is projected to double or triple in the near future. Thus evolutionary approaches should be augmented with active design methods. The ability to actively design, optimize and control a system presupposes the existence of predictive modeling and reasonably well-defined functional dependences between the controllable variables of the system and objective and constraint functions for optimization. Following recent advances in the studies of the eects of network topology structure on dynamics, we investigate the performance of dynamic processes on transport networks as a function of the first nontrivial eigenvalue of the network’s Laplacian, which, in turn, is a function of the network’s connectivity and modularity. The last two characteristics can be controlled and tuned via optimization. We consider design optimization problem formulations. We have developed a flexible simulation of network topology coupled with flows on the network for use as a platform for computational experiments.

The location of central structures in trees

Abstract A nonlinear version of the path center location problem is analyzed. We introduce a closely related problem called the subtree location problem. Variants in which the endpoints of the central structure to be located may or may not be restricted to the vertex set are also studied. We give theoretical results for the nonlinear cases when the underlying structure is a tree with edges of varying length and linear time algorithms for the unweighted vertex case. The linear time algorithms have their basis in an efficient data structures for representing trees.

Using tabu search to determine the number of kanbans and lotsizes in a generic kanban system

A generic kanban system designed for non-repetitive manufacturing environments is described. The purpose of this paper is to determine the number of kanbans and lotsizes to maximize system performance. System objectives include minimizing cycle time, operation costs and capital losses. A scalar multi-attribute utility function is constructed and a tabu search algorithm is proposed to search for the optimal utility value. Simulation is used to generate objective function values for each system setup. Four different variations of tabu search are employed. It is shown that a random sampling of the neighborhood provides good results with the shortest computation time. The tabu search algorithm proposed performs much better than a local search. The results are then compared to those from a modified simulated annealing algorithm. Due to the planar nature of the objective function, it is shown that tabu search can provide excellent results, yet a simulated annealing approach provides the same results with better computation time.