Current Search:   Nazzal, Dima (x)

View All Items

  • CSV Spreadsheet
(1 - 8 of 8)
Specification and Runtime Checking of Timing Constraints in Safety Critical Java
Title
Specification and Runtime Checking of Timing Constraints in Safety Critical Java.
Creator
Haddad, Ghaith, Leavens, Gary, Turgut, Damla, Boloni, Ladislau, Nazzal, Dima, University of Central Florida
Abstract / Description
The Java platform is becoming a vital tool for developing real-time and safety-critical systems. Design patterns and the availability of Java libraries, both provide solutions to many known problems. Furthermore, the object-oriented nature of Java simplifies modular development of real-time systems. However, limitations of Java as a programming language for real-time systems are a notable obstacle to producing safe real-time systems. These limitations are found in the unpredictable execution...
Show moreThe Java platform is becoming a vital tool for developing real-time and safety-critical systems. Design patterns and the availability of Java libraries, both provide solutions to many known problems. Furthermore, the object-oriented nature of Java simplifies modular development of real-time systems. However, limitations of Java as a programming language for real-time systems are a notable obstacle to producing safe real-time systems. These limitations are found in the unpredictable execution model of the language, due to Java's garbage collector, and the lack of support for non-functional specification and verification tools. In this dissertation I introduce SafeJML, a specification language for support of functional and non-functional specifications, based on an implementation of a safety-critical Java platform and the Java Modeling Language (JML). This dissertation concentrates on techniques that enable specification and dynamic checking of timing constraints for some important Java features, including methods and subtyping. SafeJML and these dynamic checking techniques allow modular specification and checking of safety-critical systems, including those that use object-orientation and design patterns. Such coding techniques could have maintenance benefits for real-time and safety-critical software.
Show less
Date Issued
2012
Identifier
CFE0004542, ucf:49224
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004542
MULTIOBJECTIVE DESIGN OPTIMIZATION OF GAS TURBINE BLADE WITH EMPHASIS ON INTERNAL COOLING
Title
MULTIOBJECTIVE DESIGN OPTIMIZATION OF GAS TURBINE BLADE WITH EMPHASIS ON INTERNAL COOLING.
Creator
Nagaiah, Narasimha, Geiger, Christopher, Nazzal, Dima, Reilly, Charles, Kapat, Jayanta, University of Central Florida
Abstract / Description
In the design of mechanical components, numerical simulations and experimental methods are commonly used for design creation (or modification) and design optimization. However, a major challenge of using simulation and experimental methods is that they are time-consuming and often cost-prohibitive for the designer. In addition, the simultaneous interactions between aerodynamic, thermodynamic and mechanical integrity objectives for a particular component or set of components are difficult to...
Show moreIn the design of mechanical components, numerical simulations and experimental methods are commonly used for design creation (or modification) and design optimization. However, a major challenge of using simulation and experimental methods is that they are time-consuming and often cost-prohibitive for the designer. In addition, the simultaneous interactions between aerodynamic, thermodynamic and mechanical integrity objectives for a particular component or set of components are difficult to accurately characterize, even with the existing simulation tools and experimental methods. The current research and practice of using numerical simulations and experimental methods do little to address the simultaneous (")satisficing(") of multiple and often conflicting design objectives that influence the performance and geometry of a component. This is particularly the case for gas turbine systems that involve a large number of complex components with complicated geometries.Numerous experimental and numerical studies have demonstrated success in generating effective designs for mechanical components; however, their focus has been primarily on optimizing a single design objective based on a limited set of design variables and associated values. In this research, a multiobjective design optimization framework to solve a set of user-specified design objective functions for mechanical components is proposed. The framework integrates a numerical simulation and a nature-inspired optimization procedure that iteratively perturbs a set of design variables eventually converging to a set of tradeoff design solutions. In this research, a gas turbine engine system is used as the test application for the proposed framework. More specifically, the optimization of the gas turbine blade internal cooling channel configuration is performed. This test application is quite relevant as gas turbine engines serve a critical role in the design of the next-generation power generation facilities around the world. Furthermore, turbine blades require better cooling techniques to increase their cooling effectiveness to cope with the increase in engine operating temperatures extending the useful life of the blades.The performance of the proposed framework is evaluated via a computational study, where a set of common, real-world design objectives and a set of design variables that directly influence the set of objectives are considered. Specifically, three objectives are considered in this study: (1) cooling channel heat transfer coefficient, which measures the rate of heat transfer and the goal is to maximize this value; (2) cooling channel air pressure drop, where the goal is to minimize this value; and (3) cooling channel geometry, specifically the cooling channel cavity area, where the goal is to maximize this value. These objectives, which are conflicting, directly influence the cooling effectiveness of a gas turbine blade and the material usage in its design. The computational results show the proposed optimization framework is able to generate, evaluate and identify thousands of competitive tradeoff designs in a fraction of the time that it would take designers using the traditional simulation tools and experimental methods commonly used for mechanical component design generation. This is a significant step beyond the current research and applications of design optimization to gas turbine blades, specifically, and to mechanical components, in general.
Show less
Date Issued
2012
Identifier
CFE0004495, ucf:49282
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004495
Shop Scheduling in the Presence of Batching, Sequence-Dependent Setups and Incompatible Job Families Minimizing Earliness and Tardiness Penalties
Title
Shop Scheduling in the Presence of Batching, Sequence-Dependent Setups and Incompatible Job Families Minimizing Earliness and Tardiness Penalties.
Creator
Buchanan, Patricia, Geiger, Christopher, Mollaghasemi, Mansooreh, Pazour, Jennifer, Nazzal, Dima, University of Central Florida
Abstract / Description
The motivation of this research investigation stems from a particular job shop production environment at a large international communications and information technology company in which electro-mechanical assemblies (EMAs) are produced. The production environment of the EMAs includes the continuous arrivals of the EMAs (generally called jobs), with distinct due dates, degrees of importance and routing sequences through the production workstations, to the job shop. Jobs are processed in...
Show moreThe motivation of this research investigation stems from a particular job shop production environment at a large international communications and information technology company in which electro-mechanical assemblies (EMAs) are produced. The production environment of the EMAs includes the continuous arrivals of the EMAs (generally called jobs), with distinct due dates, degrees of importance and routing sequences through the production workstations, to the job shop. Jobs are processed in batches at the workstations, and there are incompatible families of jobs, where jobs from different product families cannot be processed together in the same batch. In addition, there are sequence-dependent setups between batches at the workstations. Most importantly, it is imperative that all product deliveries arrive on time to their customers (internal and external) within their respective delivery time windows. Delivery is allowed outside a time window, but at the expense of a penalty. Completing a job and delivering the job before the start of its respective time window results in a penalty, i.e., inventory holding cost. Delivering a job after its respective time window also results in a penalty, i.e., delay cost or emergency shipping cost. This presents a unique scheduling problem where an earliness-tardiness composite objective is considered.This research approaches this scheduling problem by decomposing this complex job shop scheduling environment into bottleneck and non-bottleneck resources, with the primary focus on effectively scheduling the bottleneck resource. Specifically, the problem of scheduling jobs with unique due dates on a single workstation under the conditions of batching, sequence-dependent setups, incompatible job families in order to minimize weighted earliness and tardiness is formulated as an integer linear program. This scheduling problem, even in its simplest form, is NP-Hard, where no polynomial-time algorithm exists to solve this problem to optimality, especially as the number of jobs increases. As a result, the computational time to arrive at optimal solutions is not of practical use in industrial settings, where production scheduling decisions need to be made quickly. Therefore, this research explores and proposes new heuristic algorithms to solve this unique scheduling problem. The heuristics use order review and release strategies in combination with priority dispatching rules, which is a popular and more commonly-used class of scheduling algorithms in real-world industrial settings. A computational study is conducted to assess the quality of the solutions generated by the proposed heuristics. The computational results show that, in general, the proposed heuristics produce solutions that are competitive to the optimal solutions, yet in a fraction of the time. The results also show that the proposed heuristics are superior in quality to a set of benchmark algorithms within this same class of heuristics.
Show less
Date Issued
2014
Identifier
CFE0005139, ucf:50717
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005139
Inventory Management Problem for Cold Items with Environmental and Financial Considerations
Title
Inventory Management Problem for Cold Items with Environmental and Financial Considerations.
Creator
Hajiaghabozorgi, Ali, Pazour, Jennifer, Karwowski, Waldemar, Zheng, Qipeng, Nazzal, Dima, University of Central Florida
Abstract / Description
The overarching theme of this dissertation is analytically analyzing the cold supply chain from a financial and environmental perspective. Specifically, we develop inventory policy models in the cold supply chain that consider holding and transportation unit capacities. The models provide insights for the decision maker on the tradeoff between setting order quantities based on the cost or the emission function.In Chapter 2, we review two major bodies of literature: 1) supply chain design, and...
Show moreThe overarching theme of this dissertation is analytically analyzing the cold supply chain from a financial and environmental perspective. Specifically, we develop inventory policy models in the cold supply chain that consider holding and transportation unit capacities. The models provide insights for the decision maker on the tradeoff between setting order quantities based on the cost or the emission function.In Chapter 2, we review two major bodies of literature: 1) supply chain design, and 2) sustainability in supply chain design. We benefit from this literature review to map the current body of research on traditional supply chain for further comparison with the cold supply chain. Sustainability in supply chain network design is often measured by the carbon footprint; other sustainability metrics such as water footprint and sustainable energy are not included. Literature on supply chain design can be further broken down into its three major components: 1) facility location/allocation, 2) inventory management, and 3) facility location/allocation combined with inventory management. In Chapter 3, we study and present an overview of the cold chain. In accordance to the three levels of supply chain management decision making, the study is divided into the following three sections: (1) strategic level, (2) tactical level, and (3) operational level. Specifically, we capture how these decisions will impact the three main components of sustainability: economic, environmental, and social components. In addition, we explain how these components are different in the cold chain, in comparison to the traditional supply chain, and why such unique differences are worth studying. The intent of this chapter is to provide an overview of cold chains and to identify open areas for research. Examples from industrial cases, in addition to data and information from white papers, reports and research articles are provided.In Chapter 4, the cold item inventory problem is formulated as a single-period model that considers both financial and emissions functions. A new formulation for holding and transportation cost and emission is proposed by considering unit capacity for holding and transportation. This model applies to cold items that need to be stored at a certain, non-ambient temperature. Holding cold items in a warehouse is usually done by dividing the warehouse into a set of cold freezer units inside rather than refrigerating the entire warehouse. The advantage of such a design is that individual freezer units can be turned off to save cost and energy, when they are not needed. As a result, there is a fixed (setup) cost for holding a group of items, which results in a step function to represent the fixed cost of turning on the freezer units, in addition to the variable cost of holding items based on the number of units held in inventory. Three main goals of studying this problem are: 1) deriving the mathematical structure and modeling the holding and transportation costs and environmental functions in cold chains, 2) proposing exact solution procedures to solve the math models, and 3) analyzing the tradeoffs involved in making inventory decisions based on minimizing emissions vs. minimizing cost in cold chains.This problem demonstrates the tradeoff between the cost and the emission functions in an important supply chain decision. Also, the analytical models and solution approaches provide the decision maker with analytical tools for making better decisions.In Chapter 5, we expand the developed model from Chapter 4 to include multiple types of products. We consider a group of products that share capacities as a family of products. According to the problem formulation, we have two types of decision variables: (1) determining if a product is a member of a family or not, and (2) how much to order and how frequently to order for products within each family. We propose a solution procedure in accordance with the decision variable types: (1) a procedure for grouping (partitioning) the products into different families, and (2) a procedure to solve the inventory problem for each family. A set of experiments are designed to answer a number of research questions, and brings more understandings of the developed models and solutions algorithms.Finally, the conclusions of this dissertation and suggestions for future research topics are presented in Chapter 6.
Show less
Date Issued
2014
Identifier
CFE0005501, ucf:50365
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005501
A Model to Integrate Sustainability into the User-Centered Design Process
Title
A Model to Integrate Sustainability into the User-Centered Design Process.
Creator
Brown, Adrienne, Crumpton-Young, Lesia, Mccauley Bush, Pamela, Nazzal, Dima, University of Central Florida
Abstract / Description
With concerns for the environment becoming more prevalent in business and the government, it is increasingly important to re-evaluate and update processes to include sustainability considerations early in the design process. In response to this charge, this research effort was designed to integrate sustainability factors into the user-centered design process. The results of this research highlight the benefits of sustainability requirement planning, as well as those derived from integrating...
Show moreWith concerns for the environment becoming more prevalent in business and the government, it is increasingly important to re-evaluate and update processes to include sustainability considerations early in the design process. In response to this charge, this research effort was designed to integrate sustainability factors into the user-centered design process. The results of this research highlight the benefits of sustainability requirement planning, as well as those derived from integrating sustainability into the current user-centered design model.
Show less
Date Issued
2011
Identifier
CFE0004091, ucf:49132
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004091
Multi-Vehicle Dispatching and Routing with Time Window Constraints and Limited Dock Capacity
Title
Multi-Vehicle Dispatching and Routing with Time Window Constraints and Limited Dock Capacity.
Creator
El-Nashar, Ahmed, Nazzal, Dima, Sepulveda, Jose, Geiger, Christopher, Hosni, Yasser, University of Central Florida
Abstract / Description
The Vehicle Routing Problem with Time Windows (VRPTW) is an important and computationally hard optimization problem frequently encountered in Scheduling and logistics. The Vehicle Routing Problem (VRP) can be described as the problem of designing the most efficient and economical routes from one depot to a set of customers using a limited number of vehicles. This research addresses the VRPTW under the following additional complicating features that are often encountered in practical problems...
Show moreThe Vehicle Routing Problem with Time Windows (VRPTW) is an important and computationally hard optimization problem frequently encountered in Scheduling and logistics. The Vehicle Routing Problem (VRP) can be described as the problem of designing the most efficient and economical routes from one depot to a set of customers using a limited number of vehicles. This research addresses the VRPTW under the following additional complicating features that are often encountered in practical problems:1. Customers have strict time windows for receiving a vehicle, i.e., vehicles are not allowed to arrive at the customer's location earlier than the lower limit of the specified time window, which is relaxed in previous research work.2. There is a limited number of loading/unloading docks for dispatching/receiving the vehicles at the depotThe main goal of this research is to propose a framework for solving the VRPTW with the constraints stated above by generating near-optimal routes for the vehicles so as to minimize the total traveling distance. First, the proposed framework clusters customers into groups based on their proximity to each other. Second, a Probabilistic Route Generation (PRG) algorithm is applied to each cluster to find the best route for visiting customers by each vehicle; multiple routes per vehicle are generated and each route is associated with a set of feasible dispatching times from the depot. Third, an assignment problem formulation determines the best dispatching time and route for each vehicle that minimizes the total traveling distance.iiiThe proposed algorithm is tested on a set of benchmark problems that were originally developed by Marius M. Solomon and the results indicate that the algorithm works well with about 1.14% average deviation from the best-known solutions. The benchmark problems are then modified by adjusting some of the customer time window limits, and adding the staggered vehicle dispatching constraint. For demonstration purposes, the proposed clustering and PRG algorithms are then applied to the modified benchmark problems.
Show less
Date Issued
2012
Identifier
CFE0004532, ucf:49233
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004532
Design of the layout of a manufacturing facility with a closed loop conveyor with shortcuts using queueing theory and genetic algorithms
Title
Design of the layout of a manufacturing facility with a closed loop conveyor with shortcuts using queueing theory and genetic algorithms.
Creator
Lasrado, Vernet, Nazzal, Dima, Mollaghasemi, Mansooreh, Reilly, Charles, Garibay, Ivan, Sivo, Stephen, Armacost, Robert, University of Central Florida
Abstract / Description
With the ongoing technology battles and price wars in today's competitive economy, every company is looking for an advantage over its peers. A particular choice of facility layout can have a significant impact on the ability of a company to maintain lower operational expenses under uncertain economic conditions. It is known that systems with less congestion have lower operational costs. Traditionally, manufacturing facility layout problem methods aim at minimizing the total distance traveled,...
Show moreWith the ongoing technology battles and price wars in today's competitive economy, every company is looking for an advantage over its peers. A particular choice of facility layout can have a significant impact on the ability of a company to maintain lower operational expenses under uncertain economic conditions. It is known that systems with less congestion have lower operational costs. Traditionally, manufacturing facility layout problem methods aim at minimizing the total distance traveled, the material handling cost, or the time in the system (based on distance traveled at a specific speed). The proposed methodology solves the looped layout design problem for a looped layout manufacturing facility with a looped conveyor material handling system with shortcuts using a system performance metric, i.e. the work in process (WIP) on the conveyor and at the input stations to the conveyor, as a factor in the minimizing function for the facility layout optimization problem which is solved heuristically using a permutation genetic algorithm. The proposed methodology also presents the case for determining the shortcut locations across the conveyor simultaneously (while determining the layout of the stations around the loop) versus the traditional method which determines the shortcuts sequentially (after the layout of the stations has been determined). The proposed methodology also presents an analytical estimate for the work in process at the input stations to the closed looped conveyor.It is contended that the proposed methodology (using the WIP as a factor in the minimizing function for the facility layout while simultaneously solving for the shortcuts) will yield a facility layout which is less congested than a facility layout generated by the traditional methods (using the total distance traveled as a factor of the minimizing function for the facility layout while sequentially solving for the shortcuts). The proposed methodology is tested on a virtual 300mm Semiconductor Wafer Fabrication Facility with a looped conveyor material handling system with shortcuts. The results show that the facility layouts generated by the proposed methodology have significantly less congestion than facility layouts generated by traditional methods. The validation of the developed analytical estimate of the work in process at the input stations reveals that the proposed methodology works extremely well for systems with Markovian Arrival Processes.
Show less
Date Issued
2011
Identifier
CFE0004125, ucf:49088
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004125
Defining a Stakeholder-Relative Model to Measure Academic Department Efficiency at Achieving Quality in Higher Education
Title
Defining a Stakeholder-Relative Model to Measure Academic Department Efficiency at Achieving Quality in Higher Education.
Creator
Robinson, Federica, Sepulveda, Jose, Reilly, Charles, Nazzal, Dima, Armacost, Robert, Feldheim, Mary, University of Central Florida
Abstract / Description
In a time of strained resources and dynamic environments, the importance of effective and efficient systems is critical. This dissertation was developed to address the need to use feedback from multiple stakeholder groups to define quality and assess an entity's efficiency at achieving such quality.A decision support model with applicability to diverse domains was introduced to outline the approach. Three phases, (1) quality model development, (2) input-output selection and (3) relative...
Show moreIn a time of strained resources and dynamic environments, the importance of effective and efficient systems is critical. This dissertation was developed to address the need to use feedback from multiple stakeholder groups to define quality and assess an entity's efficiency at achieving such quality.A decision support model with applicability to diverse domains was introduced to outline the approach. Three phases, (1) quality model development, (2) input-output selection and (3) relative efficiency assessment, captured the essence of the process which also delineates the approach per tool applied. This decision support model was adapted in higher education to assess academic departmental efficiency at achieving stakeholder-relative quality. Phase 1 was accomplished through a three round, Delphi-like study which involved user group refinement. Those results were compared to the criteria of an engineering accreditation body (ABET) to support the model's validity to capture quality in the College of Engineering (&) Computer Science, its departments and programs. In Phase 2 the Analytic Hierarchy Process (AHP) was applied to the validated model to quantify the perspective of students, administrators, faculty and employers (SAFE). Using the composite preferences for the collective group (n=74), the model was limited to the top 7 attributes which accounted for about 55% of total preferences. Data corresponding to the resulting variables, referred to as key performance indicators, was collected using various information sources and infused in the data envelopment analysis (DEA) methodology (Phase 3). This process revealed both efficient and inefficient departments while offering transparency of opportunities to maximize quality outputs. Findings validate the potential of the Delphi-like, analytic hierarchical, data envelopment analysis approach for administrative decision-making in higher education. However, the availability of more meaningful metrics and data is required to adapt the model for decision making purposes. Several recommendations were included to improve the usability of the decision support model and future research opportunities were identified to extend the analyses inherent and apply the model to alternative areas.
Show less
Date Issued
2013
Identifier
CFE0004921, ucf:49636
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004921