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The total cost of ownership of a naval ship is largely influenced by decisions made during concept design. In recent years the US Navy has undertaken numerous initiatives to reduce total ownership cost. This has prompted particular interest in reducing manning, as this is the largest single expenditure in total ownership cost. Normally ships are designed and then a study is performed to determine their required manning, but manning has a significant design impact and designs can either be too small to accommodate necessary manning or too large and costly if manning is overestimated. Manpower analysis implemented early in the design process and included in design synthesis could significantly minimize total ownership cost while optimizing ship design performance. The Department of Aerospace and Ocean Engineering at Virginia Tech has developed a Multi-Objective Genetic Optimization process to aid in ship concept exploration. This thesis describes a manning model created to be incorporated into this ship synthesis and optimization. DDG-51 guided missile destroyer manning is used as a baseline for a guided missile destroyer (DDGx) concept exploration. ISMAT (Integrated Simulation Manning Analysis Tool) discrete event manning tool is used to decompose complex ship operations into functions and tasks to build scenarios and assign crewmembers to accomplish maintenance and ship operations and ultimately calculate manning requirements as a function of ship mission, system, size, automation and maintenance strategy. The manning model results are then linked to the ship synthesis model and design optimization to determine an estimated crew number for a particular ship design. This thesis demonstrates that a manning estimation tool can effectively be linked to a naval ship concept exploration process and have a significant impact on selected designs. / Master of Science

Accurate flow path modeling of scramjet engines is a key step in the development of an airframe integrated engine for hypersonic vehicles. A scramjet system model architecture is proposed and implemented using three different engine components: the isolator, combustor, and nozzle. For each component a set of intensive properties are iterated to match prescribed conditions, namely the mass flow. These low-fidelity one-dimensional models of hypersonic propulsion systems are used in tandem with Sandia Labs' Dakota optimization toolbox with the goal of accelerating the design and prototyping process. Simulations were created for the various components of the propulsion system and tied together to provide information for the entire flow-path of the engine given an inlet state. The isolator model incorporated methods to compute the intensive properties such as temperature and pressure of the flow path whether a shock-train exists internally as a dual-mode ramjet or if the engine is operating as a pure scramjet with a shock free isolator. A Fanno flow-like model was implemented to determine the friction losses in the isolator and a relation is iterated upon to determine the strength and length of the shock train. Two combustor models were created, the first of which uses equilibrium chemistry to estimate the state of the flow throughout the combustor and nozzle. Going one step further, the second model uses a set of canonical reactors to capture the non-equilibrium effects that may exist in the combustor/nozzle. The equilibrium combustor model was created to provide faster calculations in early iterations, and the reactor model was created to provide more realistic data despite its longer computational time. The full engine model was then compared and validated with experimental data from a scramjet combustor rig. The model is then paired with an optimization toolbox to yield a preliminary engine design for a provided design space, using a finite element analysis to ensure a feasible design. The implemented finite element analysis uses a coarse mesh with simple geometry to reduce computational time while still yielding sufficiently accurate results. The results of the optimization are then available as the starting point for higher fidelity analyses such as 2-D or 3-D computational fluid dynamics. / Master of Science / Ramjets and scramjets are the key to sustained flight at speeds above five times the speed of sound. These propulsion systems pose a challenging simulation environment due to the wide range of flow seen by the system structure. A scramjet simulation model is formulated using a series of combustion models with the goal of accurately modelling the combustion processes throughout the engine. The combustor model is paired with an isolator model and the engine model is compared against previous studies. A structural analysis model is then paired with the engine simulation, and the combined model is used within an optimizer to find an optimum design.

SNCF is a large-sized railway transportation company that needs to be operated 365 days a year and 24 hours a day. In order to schedule a certain category of workers in train stations and selling points, rosters are designed to cover a cyclical demand. However, the highly combinatorial nature of the rostering problem makes it very difficult to solve manually, and experts spend a huge amount of time to derive implementable solutions that improve a number of preference criteria. This thesis presents two formulations based on mixed-integer programming to adress the cyclical rostering problem. The first one uses variables to express the nature of each day of the roster, whereas the second one uses patterns corresponding to feasible blocks of seven days and assigns them to each week of the roster. Different strategies relative to the management of some preference criteria are compared, some of them leading to significant reductions in computational times. Cuts are finally introduced to improve the bounds obtained by the linear relaxation of the mixed-integer programs. The impact of these cuts on computational times depends much on the problem. / Master of Science

Though the field of hypersonic vehicle design is thriving again, few studies to date demonstrate the technology through a mission in which multiple flight conditions and constraints are encountered. This is likely due to the highly integrated and sensitive nature of hypersonic vehicle components. Consequently, a formal Mach 6 through Mach 10 flight envelope is explored which includes cruise, acceleration/climb, deceleration/descend and turn mission segments. An exergy approach to the vehicle synthesis/design, in which trade-offs between dissimilar technologies are observed, is proposed and measured against traditional methods of assessing highly integrated systems. A quasi one-dimensional hypersonic vehicle system simulation program was constructed. Composed of two sub-systems, propulsion and airframe, mechanisms for loss are computed from such irreversible processes as shocks, friction, heat transfer, mixing, and incomplete combustion. The propulsion sub-system consists of inlet, combustor, and nozzle, while the airframe provides trim and force accounting measures. An energy addition mechanism, based on the potential of MHD technology, is utilized to maintain a shock-on-lip inlet operating condition. Thirteen decision variables (seven design and six operational) were chosen to govern the vehicle geometry and performance. A genetic algorithm was used to evaluate the optimal vehicle synthesis/design for three separate objective functions, i.e the optimizations involved the maximization of thrust efficiency, the minimization of fuel mass consumption, and the minimization of exergy destruction plus fuel exergy loss. The principal results found the minimum fuel consumption and minimum exergy destruction measures equivalent, both meeting the constraints of the mission while using 11% less fuel than the thrust efficiency measure. Optimizing the vehicle for the single most constrained mission segment yielded a vehicle capable of flying the entire mission but with fuel consumption and exergy destruction plus fuel loss values greater than the above mentioned integrated vehicle solutions. In essence, the mission-level analysis provided much insight into the dynamics of mission-level hypersonic flight and demonstrated the usefulness of an exergy destruction minimization measure for highly integrated synthesis/design. / Master of Science

This thesis work presents detailed results of the application of exergy-based methods to highly dynamic, integrated aerospace systems such as hypersonic vehicle concepts. In particular, an exergy-based methodology is compared to a more traditional based measure by applying both to the synthesis/design and operational optimization of a hypersonic vehicle configuration comprised of an airframe sub-system and a propulsion sub-system consisting of inlet, combustor, and nozzle components. A number of key design and operational decision variables are identified as those which govern the hypersonic vehicle flow physics and thermodynamics and detailed one-dimensional models of each component and sub-system are developed. Rates of exergy loss as well as exergy destruction resulting from irreversible loss mechanisms are determined in each of the hypersonic vehicle sub-systems and their respective components. Multiple optimizations are performed for both the propulsion sub-system only and for the entire hypersonic vehicle system for single mission segments and for a partial, three-segment mission. Three different objective functions are utilized in these optimizations with the specific goal of comparing exergy methods to a standard vehicle performance measure, namely, the vehicle overall efficiency. Results of these optimizations show that the exergy method presented here performs well when compared to the standard performance measure and, in a number of cases, leads to more optimal syntheses/designs in terms of the fuel mass flow rate required for a given task (e.g., for a fixed-thrust requirement or a given mission). In addition to the various vehicle design optimizations, operational optimizations are conducted to examine the advantage if any of energy exchange to maintain shock-on-lip for both design and off-design conditions. Parametric studies of the hypersonic vehicle sub-systems and components are also conducted and provide further insights into the impacts that the design and operational decision variables and flow properties have on the rates of exergy destruction. / Master of Science

In response to the Fiscal Year 2006 National Defense Authorization Act, the US Navy conducted an evaluation of alternative propulsion methods for surface combatants and amphibious warfare ships. The study looked at current and future propulsion technology and propulsion alternatives for these three sizes of warships. In their analysis they developed 23 ship concepts, only 7 of which were variants of medium size surface combatants (MSC,21,000-26,000 MT). The report to Congress was based on a cost analysis and operational effectiveness analysis of these variants. The conclusions drawn were only based on the ship variants they developed and not on a representative sample of the feasible, non-dominated designs in the design space. This thesis revisits the Alternative Propulsion Study results for a MSC, which were constrained by the inability of the Navy's design tools to adequately search the full design space. This thesis will also assess automated methods to improve the APS approach, and examine a range of power generation alternatives using realistic operational profiles and requirements to develop a notional medium surface combatant (CGXBMD). It is essential to base conclusions on the non-dominated design space, and this new approach will use a multi-objective optimization to find non-dominated designs in the specified design space and use new visualization tools to assess the characteristics of these designs. This automated approach and new tools are evaluated in the context of the revisited study. / Master of Science

The naval ship concept design process often embraces novel concepts and technologies that carry with them an inherent risk of failure simply because their application is the first of its kind. Failure is recognized by gaps between actual and required measures of performance, exceeded budgets, and late deliveries. These risks can be defined and quantified as the product of the probability of an occurrence of failure and a measure of the consequence of that failure. Since the objective of engineering is to design and build things to meet requirements, within budget, and on schedule the first time, it is important to consider risk, along with cost and performance, in trade assessments and technology selections made during concept design. To this end, this thesis presents a simplified metric and methodology for measuring the risk of ship design concepts as part of a Multi-Objective Optimization tool for naval ship concept design. The purpose of this tool is to provide a consistent format and methodology for multi-objective decisions based on dissimilar objective attributes, specifically effectiveness, cost and risk. This approach provides a more efficient and robust method to search the design space for optimal concepts than the traditional "ad hoc" naval ship concept design process where selection and assessment are often based on experience, design lanes, rules-of-thumb and Imagineering. This thesis begins with the results of a literature and information search that investigates and describes risk, engineering systems safety, and state of the art risk analysis techniques currently in practice. Based on this background, a simplified metric and methodology is developed to calculate, quantify, and compare relative overall risk in a naval ship design optimization. To demonstrate this method, a naval ship risk register is developed for a notional ship design. This register identifies potential cost, performance, and schedule risk issues. Risk item descriptions are further defined as a function of the design parameters (DPs) considered for the notional ship. Risk Factors (RF) are calculated for each risk item based on the DP selection. Each RF is the product of a Probability of Failure Occurrence (PF) and Potential Consequence of Failure (CF). An Overall Measure of Risk (OMOR) function is developed to measure the level of overall risk for a single concept design based on DP selections. A ship design case study is performed incorporating the OMOR function and risk items into a ship synthesis model capable of calculating cost, performance, and effectiveness. This case study uses a Multi-Objective Genetic Optimization (MOGO) to identify and define a series of non-dominated cost-effectiveness frontiers for a range of risk (OMOR) values. This new method for ship design optimization provides a novel approach and consistent format for multi-objective decision-making based on three dissimilar objective attributes: effectiveness, cost, and risk. / Master of Science

This thesis work shows the advantages of applying exergy-based analysis and optimization methods to the synthesis/design and operation an Advanced Aircraft Fighter (AAF) with three subsystems: a Propulsion Subsystem (PS), an Environmental Control Subsystem (ECS), and an Airframe Subsys-tem - Aerodyanmics (AFS-A) is used to illustrate these advantages. Thermodynamic (both energy and exergy), aerodynamic, geometric, and physical models of the components comprising the subsystems are developed and their interactions defined. An exergy-based parametric study of the PS and its components is first performed in order to show the type of detailed information on internal system losses. This is followed by a series of constrained, system synthesis/design optimizations based on five different objective functions, which define energy-based and exergy-based measures of performance. A first set of optimizations involving four of the objectives (two energy-based and two exergy-based) are performed with only PS and ECS degrees of freedom. Losses for the AFS-A are not incorporated into the two exergy-based objectives. The results show that as expected all four objectives globally produce the same optimum vehicle.A second set of optimizations is then performed with AFS-A degrees of freedom and again with two energy- and exergy-based objectives. However, this time one of the exergy-based objectives incorporates AFS-A losses directly into the objective. The results are that this latter objective produces a significantly better optimum vehicle. Thus, an exergy-based approach is not only able to pinpoint where the greatest inefficiencies in the system occur but produces a superior optimum vehicle as well by accounting for irreversibility losses in subsystems (e.g., the AFS-A) only indirectly tied to fuel usage. / Master of Science