Yes / Multi-Stage Flash (MSF) desalination process has been used for decades for making fresh water from seawater and is the largest sector in desalination industries. In this work, dynamic optimisation of MSF desalination is carried out using powerful and robust dynamic simulation and optimisation software called gPROMS model builder. For a fixed freshwater demand, a number of optimal combinations of the factors such as heat transfer area, brine flow rate, cooling water flow rate, steam flow in brine heater, Top Brine Temperature, the number of stages, etc. are determined with the objective of maximising the performance ratio of the process (defined as the amount of fresh water produced per unit of energy input) considering the seasonal variations. An attempt has been made to develop an operational schedule for a particular day using dynamic optimisation.

This study was conducted to investigate whether hamstring muscle activation rate could potentially serve as an indicator for slip-induced falls, particularly for older adults. Kinematics (heel contact velocity, walking velocity, slip distance, and step length), kinetics (friction demand), and electromyography (EMG) while walking over a slippery surface were collected and examined in the study. Normalized EMG data were examined in term of activation rate and compared to heel contact velocity. Twenty-eight subjects from two age groups (14 young and 14 elderly) walked across a track with embedded force platforms while wearing a fall arresting harness attached to an arresting rig for safety. In order to obtain realistic unexpected slip-induced fall data, the slippery surface was hidden from the subjects and unexpectedly introduced. The primary objective of the study was to evaluate if hamstring activation rate could be a valid indicator for the initiation of slip-induced falls. The results suggested that hamstring activation rate in younger adults was higher than older adults, whereas, younger adults’ heel contact velocity was not different from older adults. These results suggested that heel contact velocity in younger adults was sufficiently reduced before the heel contact phase of the gait cycle. This could be due to the outcome of higher hamstring activation rate in younger adults in comparison to older adults. However, an equal number of falls in two age groups, in spite of older adults’ slower walking velocity, lower RCOF, shorter slip distance, and slower peak sliding heel velocity, suggested that the recovery phase of the slip-induced fall accidents should be studied further. / Master of Science

In many situations, different consumers have different degrees of willingness to wait to get delivery of a product. So, consumers can be segregated based upon the demand lead time they are providing. In this paper, two types of consumers have been considered. The first category needs immediate delivery of the product, so there is no demand lead time; whereas for the other category, demand lead time is positive. A manufacturer, which produces the items using a base stock policy, can benefit from the advance demand information that the second category of consumers are providing. Early fulfillment for a particular order means fulfilling the order before the demand lead time. In this research, it is shown that a restrictive early fulfillment policy can help the firm to reduce the chances of order loss. A production control approach for restrictive early fulfillment is discussed and the factors that may affect the early fulfillment policy are examined. / Master of Science

High renewable energy penetration is a goal for many countries to increase energy security and reduce carbon emissions from conventional power plants. Wind energy is one of leading sources among different renewable resources. However, high wind energy penetration in the system brings new challenges to the electric power system due to its variable and stochastic nature, and non-correlation between wind and load profiles. The term non-correlation is used in this research refers to the fact that wind or any other renewable generation, which is nature driven, does not follow the load like conventional power plants. Wind spill is a challenge to utilities with high wind energy penetration levels. This occurs from situations mentioned above and the fact that wind generation sometimes exceeds the servable load minus must-run generation. In these cases there is no option but to curtail non-usable wind generation. This dissertation presents grid-scale energy storage and demand response options as an optimization problem to minimize spilled wind energy. Even after managing this spilled wind energy, there is still a challenge in a system with high wind energy penetration coming from wind power forecast error. Wind power forecast error is handled by having more back-up energy and spilling the non-usable wind power. This research offers a way to use the grid-scale energy storage units to mitigate impacts of wind power forecast error by. A signal processing method is proposed to decompose the fluctuating wind power forecast error signal, based on the fact that each energy storage or conventional unit is more efficient to operate within specific cycling regimes. Finally, an algorithm is proposed schedule energy storage for mitigating both impacts. / Ph. D.

In order to improve the design and to control satisfactorily the operation of the modern sewage disposal and industrial waste treatment plants, a great deal of work remains to be done by competent sanitary engineers, biologists, and chemists. It is the general belief that the stabilization of organic wastes is a biological phenomena. This indicates that a concentrated study of the organisms that are responsible for such stabilization should be undertaken and the part that each organism contributes should be evaluated The lack of specific knowledge has resulted in "rule of thumb" methods of design and control. A considerable amount of work on the biology of sewage disposal has been done by the New Jersey Experiment Station (4)(5)(8); by C.T. Butterfield and Elsie Wattie of the U.S. Public Health Services (10) (13) and by others, but a concentrated effort is still needed. James B. Lackey (1), has done an excellent job in summing up the work accomplished to date in the field of sanitary biology in his article “Sewage Treatment Biology”. In this article, Dr. Lackey lists four things that must be known before a clear picture can be presented on the subject of sewage and waste treatment. These points are as follows: (1) More precise information on the species of each group of organisms working in treatment plants. (2) The relative abundance of each so that no important (numerically or volumetrically) organism is neglected. (3) The range-not optimum- of environmental conditions under which the organism works. (4) The work accomplished by the organisms - whether a small segment of the stabilizing process, or a large one. Gerald A. Rohlick (2), in discussing Lackey’s article, places special emphasis on additional experimental work that should be done on the activities of protozoa and higher forms of life. The editors of Savage Works Journal (3) have summed up the problem in the following statement, “When we can answer completely the what, how, who, when and why of the organisms that populate our digestors, aerators and trickling filters, we shall simultaneously solve the problems of treatment plant design and operation that are of present concern”. In an effort to contribute something to the fund of knowledge of sanitary biology, the author undertook an investigation based on the for needs suggested by Lackey. The investigation is divided into three major parts: (l) A preliminary investigation; (2) the construction of a pure culture testing apparatus; and (3) the testing of a pure culture of organisms. The complete investigation is confined to studies of the organisms found in the aerobic phase of treatment, the precise source being the trickling filter at the Virginia Polytechnic Institute sewage disposal plant. This confinement of purpose was to allow the investigator to conduct a concentrated study of a single phase of treatment. The preliminary investigation consisted of taking frequent samples from the trickling filter and examining them under the microscope. The predominate organisms were noted and the development of pure cultures of each was attempted. The construction of a pure culture filter consisted of an attempt to duplicate in the laboratory as nearly as conditions would allow, the actual conditions that exist in the trickling filter at the plant, while at the same time observing pure culture requirements and techniques. The testing of the organisms consisted of measuring the amount of purification exerted by the organism on a synthetic sewage as it passed through the filter. The results of this investigation should answer two questions: First, can a pure culture apparatus be constructed and operated with such success that it can be used as a standard device for determining in the laboratory the degree of purification exhibited by organisms in pure culture, and Second, is it possible for a pure culture of organism to carry on the purification process. The answer to the second question will, of course, depend on a positive answer to the first question. / Master of Science

The presence of substitution among multiple similar products plays an important role in inventory management. It has been observed in the literature that incorporating the impact of substitution among products can substantially improve the profit and reduce the understock or overstock risk. This thesis focuses on exploring and exploiting the impact of substitution on inventory management problems by theoretically analyzing mathematical models and developing efficient solution approaches. To that end, we address four problems. In the first problem, we study different pricing strategies and the role of substitution for new and remanufactured products. Our work presents a two-stage model for an original equipment manufacturer (OEM) in this regard. A closed-form one-to-one mapping of product designs onto the optimal product strategies is developed, which provides useful information for the retailer. Our second problem is a multi-product newsvendor problem with customer-driven demand substitution. We completely characterize the optimal order policy when the demand is known and reformulate this nonconvex problem as a binary quadratic program. When the demand is stochastic, we formulate the problem as a two-stage stochastic program with mixed integer recourse, derive several necessary optimality conditions, prove the submodularity of the profit function, develop polynomial-time approximation algorithms, and show their performance guarantees. Our numerical investigation demonstrates the effectiveness of the proposed algorithms and, furthermore, reveals several useful findings and managerial insights. In the third problem, we study a robust multi-product newsvendor model with substitution (R-MNMS), where both demand and substitution rates are uncertain and are subject to cardinality-constrained uncertainty set. We show that for given order quantities, computing the worst-case total profit, in general, is NP-hard, and therefore, address three special cases for which we provide closed-form solutions. In practice, placing an order might incur a fixed cost. Motivated by this fact, our fourth problem extends the R-MNMS by incorporating fixed cost (denoted as R-MNMSF) and develop efficient approaches for its solution. In particular, we propose an exact branch-and-cut algorithm to solve small- or medium-sized problem instances of the R-MNMSF, and for large-scale problem instances, we develop an approximation algorithm. We further study the effects of the fixed cost and show how to tune the parameters of the uncertainty set. / Doctor of Philosophy / In a multi-product supply chain, the substitution of products arises if a customer's first-choice product is out-of-stock, and she/he have to turn to buy another similar product. It has been shown in the literature that the presence of product substitution reduces the assortment size, and thus, brings in more profit. %and reduce the inventory level. However, how to quantitatively study and analyze substitution effects has not been addressed in the literature. This thesis fills this gap by developing and analyzing the profit model, and therefore, providing judicious decisions for the retailer to make in order to maximize their profit. In our first problem, we consider substitution between new products and remanufactured products. We provide closed-form solutions, and a mapping that can help the retailer in choosing optimal prices and end-of-life options given a certain product design. In our second problem, we study multi-product newsvendor model with substitution. We first show that, when the probability distribution of customers' demand is known, we can tightly approximate the proposed model as a stochastic integer program under discrete support. Next, we provide effective solution approaches to solve the multi-product newsvendor model with substitution. In practice, typically, there is a limited information available on the customers' demand or substitution rates, and therefore, for our third problem, we study a robust model with a cardinality uncertainty set to account for these stochastic demand and substitution rates. We give closed-form solutions for the following three special cases: (1) there are only two products, (2) there is no substitution among different products, and (3) the budget of uncertainty is equal to the number of products. Finally, similar to many inventory management problems, we include a fixed cost in the robust model and develop efficient approaches for its solution. The numerical study demonstrates the effectiveness of the proposed methods and the robustness of our model. We further illustrate the effects of the fixed cost and how to tune the parameters of the uncertainty set.

In a world where calls for climate action grow louder by the day, the role of renewable energy and energy efficient generation sources has become extremely important. One such energy efficient resource that can increase the penetration of renewable energy into the grid is the Combined Heat and Power technology. Combined Heat and Power (CHP) plants produce useful thermal and electrical power output from a single input fuel source and are widely used in the industrial and commercial sectors for reliable on-site power production. However, several unfavorable policies combined with inconsistent regulations have discouraged investments in this technology and reduced participation of such facilities in grid operations. The potential benefits that could be offered by this technology are numerous - improving grid resiliency during emergencies, deferring transmission system updates and reducing toxic emissions, to name a few. With increased share of renewable energy sources in the generation mix, there is a pressing need for reliable base generation that can meet the grid requirements without contributing negatively to the environment. Since CHP units are good candidates to help achieve this two-fold requirement, it is important to understand the present barriers to their deployment and grid involvement. In this thesis work, we explore some of these challenges and propose suitable grid integration technology as well as market participation approaches for better involvement of distributed CHP units in the industrial and commercial sectors. / Master of Science / Combined Heat and Power is a generation technology which uses a single fuel source to produce two useful outputs - electric power and thermal energy - by capturing and reusing the exhaust steam by-product. These generating units have much higher efficiencies than conventional power plants, lower fuel emissions and have been a popular choice among several industries and commercial buildings with a need for uninterrupted heat and power. With increasing calls for climate action and large scale deployment of renewable based energy generation sources, there is a higher need for reliable base-line generation which can handle the fluctuations and uncertainty of such renewables. This need can be met by CHP units owing to their geographic distribution and their high operating duration. CHPs also provide a myriad of other benefits for the grid operators and environmental benefits, compared to the conventional generators. However, unfavorable and inconsistent regulatory procedures have discouraged these facility owners from actively engaging in providing grid services. Therefore, it is imperative to look into some of the existing policies and understand where the changes and incentives need to be made. In this work, we look into methods that can ease CHP integration from a technological and an economic point of view, with the aim of encouraging grid operators and CHP owners to be more active participants.

We consider a continuous time dynamic pricing model where a seller needs to sell a single item over a finite time horizon. Customers arrive in accordance with a Poisson process. Upon arrival, a customer either purchases the item if the posted price is lower than his/her reservation price, or leaves empty-handed. After purchasing the item, some customers, however, will return the item to the seller at an exponential rate for a full refund. We assume that a returned item is in mint condition and the seller can resell it to future customers. The objective of the seller is to dynamically adjust the price in order to maximize the expected total revenue when the sale horizon ends. We formulate the dynamic pricing problem as a dynamic programming model and derive the structural properties of the optimal policy and the optimal value function. For cases in which the customer's reservation price is exponentially distributed, we derive the optimal policy in a closed form. For general reservation price distribution, we consider an approximation of the original model by discretizing both time and the allowable price set. We then present an algorithm for numerically computing the optimal policy in this discrete time model. Numerical examples show that if the discrete price set is carefully chosen, the expected total revenue is nearly the same as that when the allowable price set is continuous. / Master of Science

Realistic mobility and cellular traffic modeling is key to various wireless networking applications and have a significant impact on network performance. Planning and design, network resource allocation and performance evaluation in cellular networks require realistic traffic modeling. We propose a Discrete Event Simulation framework, Diamond - (Discrete Event Simulation of Mobility and Spatio-Temporal Spectrum Demand) to model and analyze realistic activity based mobility and spectrum demand patterns. The framework can be used for spatio-temporal estimation of load, in deciding location of a new base station, contingency planning, and estimating the resilience of the existing infrastructure. The novelty of this framework lies in its ability to capture a variety of complex, realistic and dynamically changing events effectively. Our initial results show that the framework can be instrumental in contingency planning and dynamic spectrum allocation. / Master of Science

The financial and environmental effects of traffic congestion and automobile-centric air pollution continue to be problems that must be addressed within the United States. In response, travel demand management (TDM) has emerged as a potential way to reduce automobile-based travel in order to minimize these effects. TDM strategies are highly dependent on specific urban form characteristics such as bicycle lanes, sidewalks, or transit facilities. A current gap exists in the analytical tools available to transportation planners when evaluating TDM projects. The standard transportation models do not take into account urban form characteristics in a systematic way. These characteristics play an import role in an individual's selection of walking, bicycling, or transit based travel modes. This gap needs to be filled in order to evaluate TDM projects with the same decision-making rigor that is applied to road expansion projects. The purpose of this project is to develop an enhanced transportation mode choice model that presents a systematic approach for incorporating urban form characteristics. This approach determines which elements of urban form have the strongest influence on transportation mode choice behavior. This work is being done in conjunction with the Roanoke Valley Allegheny Metropolitan Planning Organization as a way to evaluate the potential of TDM projects in promoting non-automobile forms of travel within the Roanoke region. This approach to developing an enhanced transportation mode choice model is a step forward in address the gap between TDM strategies and the tools needed to evaluate them. / Master of Urban and Regional Planning