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Theses and Dissertations

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Full-Text Articles in Engineering

Aircraft Maintenance Performance: The Effects Of The Functional Decentralization Of On-Equipment Maintenance, Mark A. Commenator Mar 2001

Aircraft Maintenance Performance: The Effects Of The Functional Decentralization Of On-Equipment Maintenance, Mark A. Commenator

Theses and Dissertations

The Air Force has implemented various aircraft maintenance organizational structures. The implementation of the Objective Wing in the early 1990s was the latest occurrence of reorganization. This research looks at the effect of the type of aircraft maintenance organizational structure on aircraft maintenance performance. The type of organizational structure was defined by the functional centralization of the on-equipment maintenance. Aircraft maintenance performance was measured using TNMCM rates, fix rates, repeat/recur rates, man-hours per flying hour, and scheduling effectiveness rates. Three F-15 wings and three F-16 wings were selected to compare the changes in aircraft maintenance performance and to determine if …

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Environmental Disturbance Modeling For Large Inflatable Space Structures, Donald J. Davis Mar 2001

Environmental Disturbance Modeling For Large Inflatable Space Structures, Donald J. Davis

Theses and Dissertations

Tightening space budgets and stagnating spacelift capabilities are driving the Air Force and other space agencies to focus on inflatable technology as a reliable, inexpensive means of deploying large structures in orbit. Recent improvements in rigidization techniques make the use these inflatable structures feasible for a growing number of missions. For many of these missions, the primary design requirement is dimensional accuracy of the structure. Finite element analysis offers a means of predicting structural behavior in orbit. The analysis requires knowledge of external loads. This thesis examines the environmental disturbances which act upon large, orbiting structures. Calculations are made on …

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Numerical Study Of Optical Delay In Semiconductor Multilayer Distributed Bragg Reflector And Tunable Microcavity Structures, Michael I. K. Etan Mar 2001

Numerical Study Of Optical Delay In Semiconductor Multilayer Distributed Bragg Reflector And Tunable Microcavity Structures, Michael I. K. Etan

Theses and Dissertations

The Air Force has a growing need for the greater bandwidth, speed, and flexibility offered by optical communication links. Future space systems and airborne platforms will most likely use optical signals for efficient power transmission and to minimize the possibility of spoofing and eavesdropping. Tunable optical delays play an important role in the implementation of free space optical communication links. The primary challenge in implementing these systems is the active maintenance of coherent wave fronts across the system's optical aperture. For space applications, this aperture may he hundreds of meters in diameter. Spatial segmentation of a large aperture into smaller …

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Characterization And Validation Of The Gp-3 Experimental Radar System, Benjamin L. Crossley Mar 2001

Characterization And Validation Of The Gp-3 Experimental Radar System, Benjamin L. Crossley

Theses and Dissertations

The experimental GP-3 radar system was originally designed and built under contract for the Air Force Research Laboratory (AFRL). AFRL sought AFIT's support in characterizing the as delivered' performance of the GP-3. This research effort focused exclusively on software modifications and hardware validations related to the GP-3 post-processing mode. As modified, tested, and validated, the GP-3's post-processing mode is now fully operational. The GP-3 is capable of transmitting and receiving bandlimited (3.5 MHz) waveforms at X-Band frequencies. System characterization tests included, noise performance and frequency response. System noise performance characterization permitted establishment of the receiver 'noise floor' and enabled determination …

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Aircrew Ionizing Doses From Nuclear Weapon Bursts, Fred E. Garcia Ii Mar 2001

Aircrew Ionizing Doses From Nuclear Weapon Bursts, Fred E. Garcia Ii

Theses and Dissertations

Total radioactive doses to aircrew members have been calculated in the past using different methods. The methodologies include smearing models, disk-tosser codes, and puff models. This study uses output data from the Hazard Prediction and Assessment Capability (HPAC) code as input into a FORTRAN program written by the author to calculate total dose to aircrew members through sky-shine and cabin ingestion. A description of the input parameters and new project setup in the Nuclear Weapon (NWPN) module within HPAC is given. The various aspects of controlling the project and plotting the data are also described. This information is presented essentially …

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Broadband Application Of High Impedance Ground Planes, Keven J. Golla Mar 2001

Broadband Application Of High Impedance Ground Planes, Keven J. Golla

Theses and Dissertations

Electrical conductors have long been the only materials available to antenna designers for reflecting structures. However, recently reported high impedance ground plane (HIGP) structures offer an alternative by creating image currents and reflections, within a limited frequency stop-band, that are in-phase with a source rather than out-of-phase as for a perfect electric conducting (PEC) surface. Also, the high impedance structures suppress surface waves while surface waves propagate on PEC surfaces. This research explores broadband antenna applications for HIGP structures. A broadband surface mount antenna is applied to both a homogeneous narrowband HIGP and a spatially varying broadband HIGP design. Measurements …

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Vibration Suppression Of A Rotationally Periodic Structure Using An Adaptive/Ppf Control Law, Mark J. Keller Mar 2001

Vibration Suppression Of A Rotationally Periodic Structure Using An Adaptive/Ppf Control Law, Mark J. Keller

Theses and Dissertations

For a compressor disk, effective vibration suppression requires broadband control, and the elimination of inter-blade coupling forces. Previous researchers achieved this using an active/passive piezoelectric shunt network. Unfortunately, optimal tuning of the shunt requires prior knowledge of the coupling strength, which is not well defined. This thesis uses an adaptive parameter estimator to eliminate the inter-blade coupling forces. In addition, the passive shunt is replaced with an analogous positive position feedback method. The resulting control law was used on a simulated four and eight bladed system. While substantial reductions in system response were achieved for the Adaptive/PPF control technique, the …

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Weapon System Environmental Life Cycle Cost Methodologies And Models, William H. Kale Iii Mar 2001

Weapon System Environmental Life Cycle Cost Methodologies And Models, William H. Kale Iii

Theses and Dissertations

Major Defense Acquisition Programs (MDAP) cost billions of dollars and have 30 to 50 year life spans. Numerous (federal, state, etc.) laws, Environmental Protection Agency regulations, and Executive Orders have driven DoD to develop and implement significant environmental policies within the past ten to fifteen years. Congressional mandate now requires each MDAP to evaluate its environmental life cycle cost (ELCC) to minimize these costs. This research focuses on the current methodologies and models used to predict and calculate the ELCC of a MDAP. This thesis analyzed the difficulties associated with using ELCC methodologies and models and examined several case studies …

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Differences In Civil Engineer Perceptions Of Change Based On Prior Training And Experience, Steven W. Lo Mar 2001

Differences In Civil Engineer Perceptions Of Change Based On Prior Training And Experience, Steven W. Lo

Theses and Dissertations

The Department of Defense (DoD) and the United States Air Force (USAF) have moved toward an aggressive stance to competitively source and privatize (CS&P) support functions as much as possible. This move is intended to shrink support costs and redirect the savings to force and equipment modernization. In addition, the USAF hopes to realize improved services, gain access to technology, share risks with contractors, and allow its forces to focus on the core competencies. In order to implement OS&P, the USAF communicates information through two major pathways, passive and active. Passive communication is similar to traditional classroom learning where information …

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A Methodology For Simulating The Joint Strike Fighter's Prognostics And Health Management System, Michael E. Malley Mar 2001

A Methodology For Simulating The Joint Strike Fighter's Prognostics And Health Management System, Michael E. Malley

Theses and Dissertations

The Autonomic Logistics System Simulation (ALSim) model was developed to provide decision makers a tool to make informed decisions regarding the Joint Strike Fighter's (JSF) Autonomic Logistics System (ALS). The ALS provides real-time maintenance information to ground maintenance crews, supply depots, and air planners to efficiently manage the availability of JSF aircraft. This thesis effort focuses on developing a methodology to model the Prognostics and Health Management (PHM) component of ALS. The PHM component of JSF monitors the aircraft status. To develop a PHM methodology to use in ALSim a neural network approach is used. Notional JSF prognostic signals were …

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Forecasting Readiness: Using Regression To Predict The Mission Capability Of Air Force F-16 Fighter Aircraft, Steven A. Oliver Mar 2001

Forecasting Readiness: Using Regression To Predict The Mission Capability Of Air Force F-16 Fighter Aircraft, Steven A. Oliver

Theses and Dissertations

According to many, the readiness of America's forces deteriorated in the 1990s. In the Air Force, the combat readiness of its fighter aircraft has declined. One of its indicators of combat readiness, the mission capable rate, is used to identify the percentage of aircraft unable to perform their missions. From FY94-FY98, the aggregate total not mission capable rate for maintenance steadily increased from 14% to 18.2% while total not mission capable rate for supply increased from 5.5% to 17.5% between FY86 and FY00. The USAF uses the funding/Availability Multi-Method Allocator for Spares model to forecast these rates for its aircraft. …

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Determining The Value Of Groundwater Contamination Source Removal: A Methodology, Benjamin C. Recker Mar 2001

Determining The Value Of Groundwater Contamination Source Removal: A Methodology, Benjamin C. Recker

Theses and Dissertations

Subsurface contamination by industrial chemicals is one of the most prevalent and costly environmental problems facing the United States government. This contamination problem must be managed to protect human health and the environment. Two basic strategies are used to deal with subsurface contamination: source removal and contaminant containment. While much cost and performance data are available for individual technologies associated with each of these strategies, there have been very few studies that have examined the benefits of implementing source removal technologies in order to reduce contaminant containment (and hopefully total) costs. This study examines the tradeoff between extent of source …

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Modeling Chlorinated Ethene Removal In The Methanogenic Zone Of Constructed Wetlands: A System Dynamics Approach, Randall L. Roberts Mar 2001

Modeling Chlorinated Ethene Removal In The Methanogenic Zone Of Constructed Wetlands: A System Dynamics Approach, Randall L. Roberts

Theses and Dissertations

The purpose of this study is to gain understanding of the dynamics of the processes that degrade Perchloroethene (PCE) to ethene, within the confines of the methanogenic zone of a constructed wetland. A system dynamics modeling approach is used. This model is focused on determining conditions that will enhance contaminant degradation. The chemical and biological processes within the methanogenic zone of a wetland system are extremely complex and dynamic processes. The model is broken up into three simultaneous processes: dechlorination, methanogenesis, and fermentation. The system behavior of the methanogenic zone can be adequately described by the classical formulations of representative …

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Identification Of Critical Roles Of Program Managers And Contracting Officers, Daniel R. Shingledecker Mar 2001

Identification Of Critical Roles Of Program Managers And Contracting Officers, Daniel R. Shingledecker

Theses and Dissertations

The purpose of this research was to identify current disagreement among acquisition professionals in regards to their role and authority; and to identify benefits and risks associated with combining program management and contracting officer roles into a single position. The research questions were answered through a literature review and use of the Delphi technique. The literature review indicated that the DoD has been operating with multiple conflicting perceptions of authority among its key acquisition professionals. The literature also identified the need for complex organizations, such as DoD acquisition offices, to pair high levels of responsibility with equally high levels of …

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A Force Structuring Model For A Moderately-Sized Nato Country, Hakan Bal Mar 2001

A Force Structuring Model For A Moderately-Sized Nato Country, Hakan Bal

Theses and Dissertations

The purpose of this research is to develop a mathematical model which will aid the decision-makers of a moderately-sized NATO country to develop their future force structure composition. As the number of alternatives grows, and as the consequences become more important and more uncertain, the force structuring decision becomes increasingly difficult. The valuable lessons of past experience cannot be ignored. However, when one considers the high rotation rates of most countries' air forces, the rapid change in technology and the vast array of options available, even the most experienced leaders need some assistance. Hence, decision support tools are needed to …

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Life-Cycle Cost Analysis: A Computer Aided Tool For The Egyptian Construction Industry, Ahmed Mohamed Ahmed Ibrahim Jan 2001

Life-Cycle Cost Analysis: A Computer Aided Tool For The Egyptian Construction Industry, Ahmed Mohamed Ahmed Ibrahim

Theses and Dissertations

The construction industry can be considered as an indication of economical status of any country.

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Computer-Based Methods For Constructing Two-Level Fractional-Factorial Experimental Designs With A Requirement Set, Steven L. Forsythe Dec 2000

Computer-Based Methods For Constructing Two-Level Fractional-Factorial Experimental Designs With A Requirement Set, Steven L. Forsythe

Theses and Dissertations

This dissertation developed four methodologies for computer-aided experimental design of two-level fractional factorial designs with requirement sets (DOE/RS). The requirement sets identify all the experimental factors and the appropriate interaction terms to be evaluated in the experiment. Taguchi graphs and similar manual methods provide techniques for solving the DOE/RS problem. Unfortunately, these methods are limited because they become difficult to use as the number of factors or interaction terms exceeds ten. This research showed that the DOE/RS problem belongs to a class of difficult-to-solve problems known as NP-Complete. It is the combinatorial nature of NP-Complete problems that causes them to …

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Estimating Budget Relationships With A Leontief Input-Output Model, Guenever L. R. Shariff Dec 2000

Estimating Budget Relationships With A Leontief Input-Output Model, Guenever L. R. Shariff

Theses and Dissertations

Forty years ago, the Office of the Secretary of Defense proposed using the Leontief input-output model to assess tradeoffs in the Department of Defense's (DoD) budget. We demonstrate that the Leontief input-output model can assess tradeoffs in the Air Force's budget. To increase one part of the Air Force's budget, we need to know the interrelationships between that budget area and the other areas. In this research, we look at different methods of how the functional areas might interact. We demonstrate our methodology on two data sets - DoD and the Air Force aggregate budget data. By looking at how …

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Covalidation Of Dissimilarly Structured Models, Samuel A. Wright Dec 2000

Covalidation Of Dissimilarly Structured Models, Samuel A. Wright

Theses and Dissertations

A methodology is presented which allows comparison between models constructed under different modeling paradigms. Consider the following situation: Two models are constructed to study different aspects of the same system. One model simulates a fleet of aircraft moving a given combination of cargo and passengers from an onload point to an offload point. A second model is a linear programming model that optimizes the aircraft and route selection required for the same scenario. We develop a methodology to structure the comparison between large-scale models such as these. Models that compare favorably using this methodology are deemed covalid. Models that perform …

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Simulation And Analysis Of Wing Rock Physics For A Generic Fighter Model With Three Degrees-Of-Freedom, Ahmed Saad Aug 2000

Simulation And Analysis Of Wing Rock Physics For A Generic Fighter Model With Three Degrees-Of-Freedom, Ahmed Saad

Theses and Dissertations

Modern fighter designs have been associated with lateral self-excited oscillations own as "Wing Rock". Simulations of wing rock by flow visualization utilities have been encouraged to develop a complete understanding of the fluid mechanism that drives the motion as well as for prediction purposes. Previous wind/water tunnel simulations have been limited to a single degree-of freedom (DoF) in roll. In this study, for the first time, wing rock is computationally simulated in three DoF: roll, sideslip, and vertical motion to study the effect of adding file sideslip and vertical motion. The results are for a generic fighter model consisting of …

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Three-Dimensional Dynamic Stress Analysis Of Sandwich Panels, Victor Y. Perel Jul 2000

Three-Dimensional Dynamic Stress Analysis Of Sandwich Panels, Victor Y. Perel

Theses and Dissertations

A layerwise geometrically nonlinear theory for a thick sandwich plate was developed by introducing assumptions on a variation of transverse strains in the thickness direction of the faces and the core of the plate. An effect of transverse extensibility or compressibility of the core and the face sheets is taken into account, and the terms associated with transverse shear strain of the face sheets and the core are included into the expression for the strain energy. Displacements, obtained by integration of the strain-displacement relations, depend nonlinearly on a coordinate in the thickness direction, and are continuous at the boundaries between …

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Turbo Codes For Wireless Mobile Communication Systems Applications, Moataz M. Salah Jun 2000

Turbo Codes For Wireless Mobile Communication Systems Applications, Moataz M. Salah

Theses and Dissertations

Research in coding theory has seen many proposals aimed at the construction of powerful codes using block and convolutional codes. Recently, a new forward error control code, known as turbo code, was introduced. This new code yields very good performance (near the Shannon limit) with relatively simple component codes and large interleavers in combination with an iterative decoding process. Among the most important applications of turbo codes are wireless mobile communication systems. A significant performance metric for this application is the minimization of end-to-end delay. In this dissertation, different ways to enhance the performance of turbo codes with short frames …

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Obtaining Objective Measurements Of Reaction Times To Auditory Alarms, Andrew George Neubauer May 2000

Obtaining Objective Measurements Of Reaction Times To Auditory Alarms, Andrew George Neubauer

Theses and Dissertations

Several pulse parameters that were believed to affect response time to auditory alarms were investigated in a factorial experiment. 18 subjects, (14 male, 4 female), participated in an experiment where the effects of inter-pulse interval (125, 250, and 500 milliseconds) and pulse format (sine, sawtooth, and square waves) on both selfreported ratings of workload and reaction time to alarms (auditory and visual) were explored. The results show that alarms with a shorter inter-pulse interval produced the fastest reaction times. Subjective preferences were rated as equal. Accuracy was equal across groups as measured by amount of errors in responding to auditory …

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Modeling And Simulation Of Communication Systems In Opnet, David M. Banker Mar 2000

Modeling And Simulation Of Communication Systems In Opnet, David M. Banker

Theses and Dissertations

This research aims to present accurate computer models of a communication link and a Super High Frequency (SHF) radio communication system. Network Warfare Simulation (NETWARS) is a J-6 initiative aimed at modeling all communication traffic in the Department of Defense (DoD) for testing and analysis of specific real world scenarios. The AN/TSC-94 is a SHF radio system with satellite communication capabilities. The AN/TSC-94 incorporates a Direct Sequence Spread Spectrum (DSSS) radio link for certain Anti-Jam (AJ) features. A DSSS spreads' signal power over a large bandwidth, reducing power previously concentrated within the original system bandwidth. The simulations were performed using …

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Robust Multi-Scenario Optimization Of An Air Expeditionary Force Force Structure Applying Genetic Algorithms To The Combat Forces Assessment Model, Barry D. Bennett Jr. Mar 2000

Robust Multi-Scenario Optimization Of An Air Expeditionary Force Force Structure Applying Genetic Algorithms To The Combat Forces Assessment Model, Barry D. Bennett Jr.

Theses and Dissertations

The United States Air Force is increasingly facing more diverse threat situations while existing force structure levels are being reduced and proposed compositions are being severely scrutinized for relevance, affordability, and effectiveness. Military planners are struggling with the question of how to generate a single force structure that can adequately respond to a multitude of threat scenarios in an uncertain future while at the same time being tasked to prove just how effective their choice will be. In the past, modeling has been effective in showing how a force can respond to a single threat scenario but a new modeling …

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Investigation Of Ge2Te2Sb5 Chalcogenide Thin Film For Use As An Analog Memory, Travis F. Blake Mar 2000

Investigation Of Ge2Te2Sb5 Chalcogenide Thin Film For Use As An Analog Memory, Travis F. Blake

Theses and Dissertations

This work investigates the feasibility of using Ge2Te2Sb5 chalcogenide films for analog memory. Thick film chalcogenide memory devices provided by Ovonyx, Inc. are characterized to determine how well the devices meet the repeatability, stability and predictability criteria needed to accurately store analog data values. Chalcogenide memory devices take advantage of the phase-shifting nature of chalcogenide materials to store the analog data as a resistance level. An automated test system was developed to characterize the material and the prototype devices with the goal to determine the 1) non-destructive readability of the device at different resistance values; …

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Finite Element Analysis Of A Composite Cylindrical Shell With A Cutout Under A Fatigue Load, Joshua T. Boatwright Mar 2000

Finite Element Analysis Of A Composite Cylindrical Shell With A Cutout Under A Fatigue Load, Joshua T. Boatwright

Theses and Dissertations

A higher-order shell theory is used to analyze compressive and tensile loads on a graphite/epoxy laminated cylinder containing a square cutout. The Hashin failure criterion is used to determine failure in the fiber, matrix, or lamination. Once failure occurs, the appropriate stiffness terms are reduced. This failure causes a redistribution of stress, leading to further failure. In order to account for the loss of residual strength due to cyclic loading, the stiffness matrix is further reduced at each new increment of load or displacement. The objective is not to determine the S-N curve for the material, but rather to determine …

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A Tabu Search For Scheduling And Rescheduling Combat Aircraft, Kevin M. Calhoun Mar 2000

A Tabu Search For Scheduling And Rescheduling Combat Aircraft, Kevin M. Calhoun

Theses and Dissertations

Scheduling an air campaign is time and labor intensive. Exacerbating the problem, combat planners use manual methods to accomplish much of this daunting but critical task. While some work has been done to automate the process, the approaches used generate schedules that must undergo major modifications before they are "flyable." Planners, therefore, distrust the results and use the automated features of the software sparingly. Additional problems arise due to the lag time between the publication of the Air Tasking Order (ATO) and the start of the ATO day. During this time, conditions change in the dynamic battlespace (aircraft break, runways …

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A Methodology For Integrating Tools In A Web-Based Environment, Musa Serdar Arslan Mar 2000

A Methodology For Integrating Tools In A Web-Based Environment, Musa Serdar Arslan

Theses and Dissertations

Web-based technologies are evolving very rapidly. New technologies are introduced very frequently in the realm of the Web and Internet. This evolution also affects database management systems (DBMSs). Almost all DBMS vendors are making their systems "Web-enabled." The Internet and the World Wide Web are getting more important and bigger than ever. Because of the increase in the importance of the Internet and the Web, migrating old applications and tools to a web-based environment is becoming more important. When migrating old applications or tools to the web-based environment, integration of tools becomes an important issue. In this research, a step-by-step …

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The Distributor’S Three-Dimensional Pallet-Packing Problem: A Mathematical Formulation And Heuristic Solution Approach, Brian P. Ballew Mar 2000

The Distributor’S Three-Dimensional Pallet-Packing Problem: A Mathematical Formulation And Heuristic Solution Approach, Brian P. Ballew

Theses and Dissertations

It is through practice and experience Air Force loadmasters are able to pack the Air Force standard HCU-6/E (463L) pallets efficiently. Although the loadmasters perform their jobs exceptionally well, the Air Force is in search of a model that will more efficiently pack the pallets. We have developed a mathematical formulation of the three-dimensional pallet-packing problem which minimizes the amount of unused space on a pallet. The formulation ensures each box is packed with the correct volume and dimensions, and ensures the volume of all the boxes packed is less than the available pallet volume. Additionally, the formulation ensures that …

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