Browsing by Author "Miller, David M."

Now showing 1 - 5 of 5
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    A decision problem involving the introduction of RTOL aircraft into commercial air transportation systems
    Schmitt, Gary Allen (Virginia Tech, 1976-06-05)
    This study is concerned with determining the feasibility of introducing a reduced takeoff and landing (RTOL) aircraft into the national aviation system. In considering this problem, a multiple criteria decision model based on the responses of airline executives was developed to describe the RTOL utilization problem. The exact problem that is considered in this thesis is, for a given set of itineraries, determine the itineraries for which aircraft (RTOL or CTOL, conventional takeoff and landing) are to be assigned such that the amount of fuel used, delay and noise levels are to be minimized. These assignments are subject to aircraft, airport, system and budgetary constraints. A decision-making procedure was formulated to solve the decision problem utilizing an interactive, multicriteria programming procedure. This procedure was developed to consider the use of 0-l decision variables. Two example problems are presented. The air transportation systems considered in the examples include (a) six airports in New York State and (b) five major airport hub areas in the north-eastern section of the United States.
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    Externally Bonded FBG Strain Sensors Structural Health Monitoring of Marine Hydrokinetic Structures
    Schuster, Michael; Fritz, Nathan; McEntee, Jarlath; Graver, Tom; Rumsey, Mark; Hernandez-Sanchez, Bernadette; Miller, David M.; Johnson, Erik (2014-04)
    To reduce operations and maintenance costs, mitigate failures, and improve capacity factor, structural health‐monitoring systems can provide key information to improve management of marine hydrokinetic devices. While present systems include instrumentation to measure power output, few adequately monitor mechanical load and structural response, which are equally important for determining device performance and integrity. Fiber optic fiber Bragg grating (FBG) sensors could prove to be a reliable and unobtrusive measurement tool for marine power; however, externally adhered FBGs have not been extensively studied on submerged, dynamic structures. Thus investigations on thebBond integrity between sensor and structure of a kinetic system, FBG strain sensors were tested in dry and environmentally soaked conditions under both static and fatigue loads. Composite coupons were strained in a fatigue testing system and monitored. Dry results demonstrated very high correlation and response from the FBG sensors, up to coupon failure. The environmentally soaked samples and sensors were subject to many failure modes and verified the developer's recommendation to not externally adhere the FBG strain sensors without additional mechanical and environmental protections.
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    Probabilistic formulations of some facility location problems
    Aly, Adel Ahmed (Virginia Tech, 1975-01-07)
    The area of facilities location covers a wide variety of problems involving both public and private sector applications. To date, the study of location problems has been restricted primarily to deterministic formulations of the problem. The present research effort investigates the effect of random variation on the location decision. Three location problems are considered: the single facility location problem, the multifacility location problem, and the emergency service location problem. The first two problems treated are defined as the generalized Weber problem, where the concern is to locate one or more new facilities in the plane relative to several existing facilities such that the expected total cost of item movements is minimized. The total cost function is considered to be a linear function of either the expected rectilinear or the Euclidean distance, as well as a quadratic function of the expected Euclidean distance. In the generalized Weber problem the locations of the existing facilities and the item movement between facilities are considered to be random variables. Two expected total cost formulations are presented; the first involves the product of the random variables, weight and distance; the second involves the random sum of each individual distance traveled. For each formulation, possible applications are discussed, theoretical properties are developed, and a solution procedure is provided. Each algorithm is programmed and optimal solutions are obtained for several example problems. A comparison between the probabilistic and deterministic solutions is provided. Both discretely and continuously distributed random variables are treated; however, for the case of continuously distributed random variables, the normal distribution is emphasized. Both constrained and unconstrained formulations are considered. In formulating the emergency service facilities location problems which are studied, random variation is assumed to be present due to the assumption that the location of an incident is a random variable occurring uniformly over a given region. Both discrete space and continuous space formulations are considered. For the discrete case, a covering criterion is employed and the deterministic equivalent problem is solved as a set cover problem. For the continuous case, the problem is solved as a location-allocation problem. In all formulations, the rectilinear norm is used to measure the distance traveled. An example is solved for each case to illustrate the impact of probabilistic aspects on the location decision.
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    Probabilistic formulations of some facility location problems in discrete space
    Chapman, Stephen Clay (Virginia Tech, 1975-05-04)
    The first formulation to be examined is a probabilistic version of the set covering problem. The problem can be stated as follows: determine the locations of the minimum number of facilities among a discrete set of feasible location sites in order to assure that the probability each customer is covered by some facility is no less than a specified value. The second problem treated involves the location of a given number of facilities among a discrete set of feasible location sites in order to maximize the minimum probability that a customer is covered by some facility. This problem is a probabilistic formulation of a special case of the discrete space, minimax location problem known as the p-center problem. Thus, the first and second problems can be considered to be complementary problems. Frequently, several measures of overall system effectiveness must be considered simultaneously. This is particularly the case in many public sector location problems. Thus, the third problem treated in the dissertation considers the case in which several objectives are to be optimized collectively. The problem is formulated as a goal programming problem in which the objectives are ranked ordinally. The problems discussed above are formulated probabilistically under the assumption of a discrete solution space. This approach was taken in order to account explicitly for the random variation inherent in the systems of inte~est. Example problems are employed throughout the research to assist in the explanation of each formulation. The emphasis in the research is placed upon a sound formulation of each problem, reduction of the problem to an equivalent but computationally more efficient formulation, and the application of an appropriate procedure in solving each problem. Sensitivity analyses are conducted in order to provide further insight into the specific cause-effect relationships.
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    Social security as an investment:a Monte Carlo investigation
    Nguyen, Han Quang (Virginia Tech, 1975)
    This study addresses the problem of assessing the value of Social Security as an investment for an individual with given characteristics. The characteristics considered are age, sex, race, marital status, and salary earning history. The problem formulation takes into account the uncertainties of human life, i.e., the probabilistic characteristics of the events that an individual may experience and may affect his tax payments and the benefits he will receive. These events are the birth of a child, death, marriage, divorce, retirement, and disability onset. The measurements used are the individual expected rate of return and the overall population rate of return. The former is expected to be more important to an individual, while the latter is more significant to the Social Security Administration. The difficulties inherent in an analytic solution procedure to obtain numerical values for these rates are shown. Using actual demographic and social security data, the use of the model is illustrated through case studies. The four cases examined, although hypothetical, represent large segments of the United States population. Additional analyses are performed to assess the value of separate components of the total benefits, including secondary, retirement, and disability-survivor benefits. The effect on the rates of return of the two factors, salary level and age of the individual’s examined. A sensitivity analysis for five types of input data, birth, death, marriage, divorce, and disability, is included.