Steven T. Hackman

Fast, effective algorithms for simple assembly line balancing problems

A simple, fast and effective heuristic for the Simple Assembly Line Balancing Type I problem (minimizing the number of workstations) is proposed. A fast and effective branch-and-bound algorithm, which incorporates this heuristic for use in bounding, is developed. The algorithm introduces heuristic fathoming as a technique for reducing the size of the branch-and-bound tree. Methods to solve the Simple Assembly Line Balancing Type II problem (maximizing the production rate) are also described. Upper bounds on all heuristics for both problems are provided.

Allocating Items to an Automated Storage and Retrieval System

Abstract To reduce material handling costs, distribution centers purchase automated storage and retrieval systems (AS/RS). It is often the case that the capacity of the AS/RS is insufficient to store all items. The distribution center must then decide which items to assign to the AS/RS and in what quantities they will be stored. In this paper, we develop a heuristic procedure to solve this problem. A priori and a posteriori tests of the data for the optimality of this heuristic procedure are provided. The proposed procedure is testedwith data gathered fr oma naval supply center.

Benchmarking Warehousing and Distribution Operations: An Input-Output Approach

We developan input-output model of a warehouse system to assess operationalefficiency. Our model simultaneously accounts for all of thecritical resources (labor, space, storage and handling equipment)and the different workload requirements (broken case, full caseand pallet picking, storage and order accumulation) of a warehouse.We collected extensive data on 57 warehouse and distributionfacilities from a variety of industries, including auto parts,dental and office supplies, electronics, fine papers, hardware,health care, industrial packaging, mail order apparel, officemachines, photographic supplies, and wholesale drugs, and usedthe model to assess and compare their efficiencies. We offer3 conclusions based on a statistical analysis of the operatingefficiencies obtained from several models: Smaller warehouses tend to be more efficient than larger warehouses.Warehouses using lower levels of automation tend to be moreefficient. This association is more pronounced in small firms.Unionization is not negatively associated with efficiencyand in fact may actually contribute to higher efficiency.

Allocating space in a forward pick area of a distribution center for small parts

The forward pick area of a distribution center is a cache of conveniently located products from which order pickers can quickly draw, but which must be replenished from bulk or reserve storage. The quantities stored forward determine the amount of work required to sustain the forward pick area. Two stocking strategies that are commonly used in industry are analyzed and compared with the optimal stocking strategy for small parts.

An aggregate model of project-oriented production

A production system is studied in which thousands of activities are carried out concurrently subject to precedence constraints and limitations on resources such as skilled labor and equipment. Ideally, management proposes a set of milestone dates, obtains an analysis of which milestones cannot be met, and determines which resources are underused or overused. This process continues interactively until milestones consistent with managements objectives are obtained. The authors derive, from elementary principles and basic assumptions (axioms), a continuous-time model of project execution of an aggregate level of detail. The model is approximated using a set of linear inequalities. This data structure can be manipulated easily and quickly by methods of linear programming to perform the required analysis. >

Investment Under Uncertainty, Heterogeneous Beliefs and Agency Conflicts

We develop a structural model to investigate the effects of asymmetric beliefs and agency conflicts on dynamic principal--agent relationships. Optimism has a first-order effect on incentives, investments, and output, which could reconcile the private equity puzzle. Asymmetric beliefs cause optimal contracts to have features consistent with observed venture capital and research and development (R&D) contracts. We derive testable implications for the effects of project characteristics on contractual features. We calibrate our model to data on pharmaceutical R&D projects and show that optimism indeed significantly influences project values. Permanent and transitory components of risk have opposing effects on project values and durations. The Author 2009. Published by Oxford University Press on behalf of The Society for Financial Studies. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org, Oxford University Press.

Explicit Representation of the Two-Dimensional Section of a Production Possibility Set

Technical and scale efficiencies of Data Envelope Analysis are associated with a two dimensionalsection (a convex set) representing the amounts by which the input and output vectors of a reference decision making unit, may be scaled and still lie in the production possibility set. We describe a simple algorithm, closely resembling the simplex algorithm of linear programming, to traverse the boundary of this set. Given the output of our algorithm, the scalar efficiency measures and return-to-scale characterization are trivially determined. Moreover, the set may be graphically displayed for any problem in any number of dimensions with only a minimum of additional computing effort.

Projectively-convex sets and functions

Abstract We introduce a generalization of convexity called projective-convexity (or P-convexity) which extends models for consumer preference and consumer budgeting. We prove a separation theorem for projectively-convex sets, establish a duality theorem for projectively-concave technologies, and briefly analyse extremal properties of projectively-concave functions.

A committed delivery strategy with fixed frequency and quantity

Abstract We analyze a supply chain environment in which a distributor facing price-sensitive demand has the opportunity to contractually commit to a delivery quantity at regular intervals over a finite horizon in exchange for a per-unit cost reduction for units acquired via committed delivery. Supplemental orders needed to meet demand are purchased at an additional unit cost. For normally distributed demand, we use a simulation-based approximation to develop models yielding closed-form solutions for the optimal order quantity and resell price for the distributor. Inventory, ordering and pricing implications for this “committed delivery strategy” are investigated.

Back-of-the-Envelope Miniload Throughput Bounds and Approximations

We derive simple formulas bounding and approximating the throughput of an end-of-aisle miniload system with exponentially distributed pick times and either uniform or turnover-based storage. For typical configurations, the worst-case relative error for the bounds is less than 4%. We use our bounds to show that, for all practical purposes, regardless of the configuration, the picker utilization determines the storage/retrieval machine utilization, and vice versa. Thus, a system designer cannot hope to independently achieve separate goals for the utilization rates.