Success in the express-mail market hinges on paying attention to every parcel in the system. A key component is safe, efficient loading of aircraft. Federal Express, a perennial leader in the express business, has recently added the Airbus A300, a lighter aircraft, to its fleet. Because of the Airbus design, shear limits—shear being a measure of the downward forces exerted on the plane—are extremely sensitive to the loading, a problem not experienced in the heavier craft. We developed a heuristic for loading containers into positions on the aircraft to address loading preferences and maintain feasibility constraints.

We built a bid-line generator to help Federal Express perform what-if analyses of work rules during contract negotiations with ALPA, the bargaining unit for the company's pilots. The objectives were to minimize both the number of bid lines produced (a measure of required manning) and the amount of flying not assigned to bid lines (flying requirements that must be accommodated during subsequent phases of scheduling). The tool was useful in negotiations since it was automated and easily modified in-house to provide quick responses to bid line what-ifs. Using a two-step process, the tool produces a complete set of legal, flyable lines for an airplane fleet and identifies the remaining open (unscheduled) flying. First it uses simulated annealing to find as many good bid lines as possible; then it uses a greedy heuristic to complete as many more lines as possible.

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The importance of simulation methods and languages seems ever to increase, despite the continuing existence of skeptics in various quarters. It appears that methods, languages, and other support tools are increasing in quality at a faster pace than in the past. Theoretical bases for methodologies and languages are being determined that should inevitably lead to greater understanding and then to more efficient tools and methods.The available array of simulation languages must appear bewildering to one unfamiliar with the field. The &dquo;old stan-dards&dquo; for discrete event simulation such as GPSS, SIMSCRIPT, and GASP IV are still very much around, as are SLAM, SIMULA, and many others. For continuous simulation use, ACSL, CSSL IV, DARE, and many others are available. Also, there are languages for combined discrete/continuous simulation, including GASP IV, SLAM, and a version of SIMSCRIPT. Many new languages are being developed and marketed, and older languages are being updated. Language &dquo;cross-fertilization&dquo; is a perceivable trend, both in general purpose languages and simulation languages. We see FORTRAN, for example, gradually being revised to incorporate features considered important in other languages. Similarly, SIMSCRIPT 11.5 has recently been augmented to include the &dquo;process&dquo; orientation (i.e., world view), by GPSS. GPSS/H, marketed by Wolverine Software Corporation, is an enhanced version of GPSS including improved run-time performance (as compared to GPSS V), increased computational and input/output facilities, and direct invocation of external procedures. SLAM incorporates both the &dquo;event scheduling&dquo; and &dquo;process&dquo; orientations, and supports combined discrete/continuous simulation. ACSL, basically a continuous simulation language, has been augmented to support inclusion of discrete event components. It is worth noting that SIMULA has had significant impacts on general purpose languages, especially in the &dquo;abstract data type&dquo; mechanism (first realized in SIMULA's &dquo;class&dquo; concept). Additionally, significant activities are underway concerning the use of strongly typed languages for simulation (especially, Ada and Pascal); we will likely see significant future impacts in this area.In addition to strongly typed languages, other activities in the software field are having beneficial effects in better approaches to requirements determination, design, development, and in testing, verification, and validation. The concept of integrated programming environments, involving a knowledge base that spans all aspects of software system requirements determination, design, develpment, and testing, along with a set of effective software support tools, is beginning to have its realization in simulation applications.Pritsker and Associates' support tools such as SDL and SIM-CHART, are notable examples of such simulation-specific tools. Integration of a full complement of tools, including support for model preparation, input data preparation, interactive run-t...

Increased demand for wood and wood products coupled with changes in timber harvesting systems in the Southeastern United States from a labor-intensive to a more costly, almost totally mechanized operation requires optimal use of harvesting equipment. Simulation can provide an inexpensive tool for evaluating harvesting procedures or use of new equipment.Existing harvesting simulation models were evaluated and found to be insufficiently documented and difficult for one lacking computer experience to use.No consensus of what constitutes the essential elements of a model exists.This paper presents the design criteria for a new second-generation model that will be modular, useroriented, and uniform in the level of detail it provides.