Browsing by Author "Wakefield, Ronald R."

Now showing 1 - 12 of 12
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    Assessing the Finite-Time Performance of Local Search Algorithms
    Henderson, Darrall (Virginia Tech, 2001-05-13)
    Identifying a globally optimal solution for an intractable discrete optimization problem is often cost prohibitive. Therefore, solutions that are within a predetermined threshold are often acceptable in practice. This dissertation introduces the concept of B-acceptable solutions where B is a predetermined threshold for the objective function value. It is difficult to assess a priori the effectiveness of local search algorithms, which makes the process of choosing parameters to improve their performance difficult. This dissertation introduces the B-acceptable solution probability in terms of B-acceptable solutions as a finite-time performance measure for local search algorithms. The B-acceptable solution probability reflects how effectively an algorithm has performed to date and how effectively an algorithm can be expected to perform in the future. The B-acceptable solution probability is also used to obtain necessary asymptotic convergence (with probability one) conditions. Upper and lower bounds for the B-acceptable solution probability are presented. These expressions assume particularly simple forms when applied to specific local search strategies such as Monte Carlo search and threshold accepting. Moreover, these expressions provide guidelines on how to manage the execution of local search algorithm runs. Computational experiments are reported to estimate the probability of reaching a B-acceptable solution for a fixed number of iterations. Logistic regression is applied as a tool to estimate the probability of reaching a B-acceptable solution for values of B close to the objective function value of a globally optimal solution as well as to estimate this objective function value. Computational experiments are reported with logistic regression for pure local search, simulated annealing and threshold accepting applied to instances of the TSP with known optimal solutions.
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    Characterizing Virtual Prototype Constructability Programming for the Pictographic Instruction of Procedure
    Johnston, Brendan Ashley (Virginia Tech, 2012-10-08)
    The modern design-construction boundary is facing an unprecedented moment of evaluation. Global applications of building information modeling, including virtual prototyping, factory-based component procurement and industrialized site production are only a few of the forces that threaten to engulf the established façades of architecture, engineering and construction practice. Those professional identities that are unable or unwilling to reach deeply into this oncoming torrent of interoperability, integrated delivery, and infinite domains will be lost. It is even possible that the language of building culture will be washed away forever. Preparations should be made. This research proposes to strengthen available built-project communications. It does so by examining the natural architectonic relationships which exists at the most primitive level of production — about the assembly task. A work and its procedures are investigated through the programming interface of a Virtual Prototype (VP) modeling system. With visualized constructability as its goal, this study highlights the character of VP programming as it translates between design and production information with digital specificity. The results of that investigation fashion a test of a new production communications language with the potential to enrich and refresh the insulate expressions and hollow specification of traditional design communications.
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    A Common Taxonomy for Modeling Construction Operations
    Al-Masalha, Sami (Virginia Tech, 2004-08-02)
    The construction industry continues to strive for new ways to improve construction operations. This requires better understanding and analysis of these operations, which necessitates a way to systematically capture and analyze the diverse elements involved. The dynamic nature of construction is very difficult to describe using existing computer simulation and modeling systems. What is needed is rather a common construction language and a comprehensive modeling system that can be used to capture and analyze construction operations and potentially lead to improvements. A new taxonomy and its use for modeling construction operations are developed here. This taxonomy identifies a hierarchical representation of construction projects based on operational considerations. The hierarchy consists of seven levels: product, assemblies and subassemblies, components, operations, processes, physics, and control. The hierarchical levels were established by looking in the ways that construction field operations are being carried out. The new modeling system successfully accounts for the geometric and physical representations of not only the product but also the processes involved in shaping the product. Six major blocks of construction knowledge are described and information about the interaction processes required to model construction operations in a logical way is provided. An overview of the current state of modeling and simulation techniques that are used to develop and evaluate construction operations is presented. The advantages and limitations of physical-based modeling, 4D-CAD, and virtual modeling techniques as an integral part of the developed taxonomy are identified. The potential uses of robotics and automation opportunities in construction are described. Also, distribution of work between humans and tools and equipment based on their physical and information contributions are reviewed and analyzed. Classifications of construction work at different levels of detail are described to identify which operations can be usefully modeled and the appropriate level of the model. Two practical case studies are discussed that show the capabilities and potential uses of the developed taxonomy. The first case study describes the modeling process of the fabrication, assembly, and erection of steel structures. The second exploratory case study shows the potential use of the developed modeling in improving the heat recovery system generator's (HRSG) erection process. Also, prototype models and 3D models of the HRSG assemblies are developed. Both case studies validate with great confidence the use of the developed taxonomy as a direct support tool that captures the diverse elements and enhances the modeling and analysis to improve construction operations.
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    A Cross-Cultural Examination: Effects of Reward Systems and Cultures on Low Severity Risk-Taking Behavior in Construction
    Thongsamak, Sasima (Virginia Tech, 2007-09-04)
    The overall research objective was to identify the effects of reward systems (rewards and a penalty) on risk-taking behavior and performance (quality and time) of construction workers from different cultures (American, Asian, and Latin American cultures). This research used the sociotechnical system as the underlying, guiding scientific framework. The research found that Americans and Latin Americans had higher risk-taking behavior than Asians (p<0.01). No difference in risk-taking behavior was found between Americans and Latin Americans (p<0.05). Although culture may influence individuals' risk-taking behavior, the results from this study showed that risk-taking behavior could be altered and suppressed by providing individuals with the proper safety training, education, and safety equipment. Customized safety training for people from different cultures would be useful because the culture elements that contribute to high risk-taking behavior could be addressed. The results also showed that the effects of reward systems on risk-taking behavior were not statistically significant (p>0.1). One possibility that no difference was found may be because the tasks used in this study did not contain enough possibility for participants to take more risk. The effects of reward systems on risk-taking behavior may have been reduced by the low possibility of risky behavior. It is suspected that if the tasks contained more opportunities for participants to take risk, differences in risk-taking behavior would have been significant. The researcher concluded that risk perception is situation-specific and has an influence on the individual's risk-taking behavior on that particular situation but cannot be used to predict risk-taking behavior. Also, general locus of control and general self-efficacy cannot be used to predict risk-taking behaviors. These findings are consistent with many studies that explore locus of control (Iversen & Rundmo, 2002; Rolison & Scherman 2002; Crisp & Barber, 1995), and many researchers that suggested self-efficacy is situation specific (Murdock et al., 2005; Martin et al., 1995; Perraud, 2000; Slanger & Rudestam, 1997). This study also found no relationship between risk-taking behavior and productivity, for both time and quality.
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    Decision-Making Framework for the Selection and Design of Shading Devices
    Olbina, Svetlana (Virginia Tech, 2005-02-11)
    Most shading device systems installed in windows or glass walls are used only for protection from overheating and glare, neglecting other possible functions, such as increasing the daylight level in the space or collecting solar energy. The blinds are usually made of opaque or translucent materials, and if they are partially open/closed or completely closed, a direct view to the outside is blocked. A balance between a sufficient amount of daylight and protection from overheating of the space in summer is not often achieved due to inappropriate control of the blinds’ tilt angle. There is also a need for specific guidance for the selection and design of shading device systems in the windows. This research develops a general decision-making framework (DMF) that can be used by architects and manufacturers of shading devices. The general DMF is a guide for the user in analyzing shading device performance in the process of selection/design of the shading device. This research also develops a specific DMF to better understand and validate the general DMF. The specific DMF, based on illuminance and luminance, is used for an analysis of daylighting performance of shading devices to select the best possible existing system or new system among several alternatives. Architects or manufacturers of shading devices, as the users of the DMF, analyze various systems of blinds applied on a particular building and at a given location. The users of the DMF can apply either an experimental procedure or computer simulation that provides information about illuminance and luminance levels in the space. Based on the analysis of the results of the experiments or simulations, the user of the DMF decides which blinds to select. The specific DMF proposes a methodology for both the analysis of the daylighting performance and for the process for making a decision based on the results of the analysis. A case study is conducted in order to validate the DMF. Three types of shading devices are tested: an existing system, a patented system, and a new system, proposed by this research. The shading devices are installed in an office space located in Roanoke, Virginia. The software Autodesk VIZ 4 is used to simulate daylighting performance. The output information, such as illuminance and luminance levels in the space, is used as a basis for making the decision about which type of blinds to apply. A new system of shading device, which has a triangular cross section and is made of clear plastic with a silver coating on one side, shows better performance than the existing shading device and the patented shading device, given the research limitations. By using the specific decision-making framework, a shading device manufacturer/designer is able to understand the shading device daylighting performance from his design-imposed criteria. Selection of the shading device, given the designer's daylighting objectives, is better achieved. Existing shading devices are also able to be analyzed from a building designer's perspective. This analysis is based on the designer-imposed daylighting criteria. The specific decision-making framework helps the designers of the buildings, together with the clients, select the most appropriate shading device based on daylighting performance. The decision-making framework is a model for development of decision-making software that will help designers of buildings, facades, and shading device systems in the selection/design of shading device systems in all phases of the design.
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    A Decision-Making Framework for Vegetated Roofing System Selection
    Grant, Elizabeth J. (Virginia Tech, 2007-10-30)
    Design frequently involves a series of trade-offs to obtain the "optimal" solution to a design problem. Green roofs have many different characteristics based on a variety of variables. Designers typically weigh the impacts of these characteristics in an implicit process based on intuition or past experience. But since vegetated roofing is a relatively complex and comparatively new technology to many practitioners, a rational, explicit method to help organize and rank the trade-offs made during the design process is useful. This research comprises the creation of a framework diagramming the decision process involved in the selection of vegetated roofing systems. Through a series of expert interviews and case studies, the available knowledge is captured and organized to determine the critical parameters affecting design decisions. A set of six case study projects in North America is analyzed and six critically important evaluative categories are identified: storm water management, energy consumption, acoustics, structure, compliance with regulatory guidelines and governmental incentives, and cost. These six factors are key decision-making parameters in the selection of vegetated roofing systems and they form the basis of this study. They are addressed in the context of a decision support system for green roof designers. A summation of the total importance of the advantages represented by each alternative is used to determine the most feasible green roof system for a particular project. The decision-making framework developed in this dissertation will ultimately be adaptable to digital processing and a computer-based design assistance tool.
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    Development of a Virtual Reality Excavator Simulator: a Mathematical Model of Excavator Digging and a Calculation Methodology
    Park, Borinara (Virginia Tech, 2002-10-31)
    Virtual Reality (VR) simulators have become popular because of two distinctive merits. One is the capability to transfer data and information to users in an intuitive way by means of 3-D high-quality graphics output and real input devices. The other is the capability to represent physical systems in mathematical models so that meaningful responses of the systems can be predicted. Previous efforts in VR excavating machine simulator development, however, showed a lack of balance between the fidelity of the model of the physics and the visual representation of the simulated equipment. In order to ensure that a VR construction excavator simulator provides convincing operating results to users, the focus of simulator development needs to be shifted to interaction of physically valid soil and the excavator machine. This research aims to contribute to the development of a VR construction excavator simulator system by proposing a mathematical model of excavator digging and a calculation methodology. The mathematical model of excavator digging provides physically meaningful soil-bucket interaction information to a simulator. The calculation methodology provides systematic and efficient computation methods to ensure the seamless integration of the excavator digging model with a VR simulator system as well as adequate system speed. As a result, the simulator is realized as an engineering process tool equipped with real-time interactivity.
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    Framework for active solar collection systems
    Hassan, Marwa M. (Virginia Tech, 2003-05-29)
    A framework that presents a new methodology for design-evaluation of active solar collection systems was developed. Although this methodology emphasizes the importance of detailed modeling for accurate prediction of building performance, it also presents a process through which the detailed modeling results can be reused in a simplified iterative procedure allowing the designer the flexibility of revising and improving the preliminary design. For demonstration purposes, the framework was used to design and evaluate two case studies located in Blacksburg (VA) and Minneapolis (MN). These locations were selected because they both represent a cold weather region; presenting a need for using solar energy for heating and hot water requirements. Moreover, the cold weather in Blacksburg is not as severe as in Minneapolis. Therefore, the two cases will result in different thermal loading structures enabling the framework validation process. The solar collection system supplying both case studies consisted of a low temperature flat plate solar collector and storage system. Thermal performance of the case study located in Blacksburg was conducted using detailed modeling evaluation techniques; while thermal performance of the case study located in Minneapolis was conducted using a simplified modeling evaluation technique. In the first case study, hourly evaluation of the thermal performance of the solar collection system was accomplished using finite element (FE) analysis, while hourly evaluation of the building thermal performance was made using Energy Plus software. The results of the finite element analysis were used to develop a statistical predictive design equation. The energy consumption for the second case study was calculated using the heating design day method and the energy collection for that case study was calculated using the predictive design equation developed from the first case study results. Results showed that, in the case of the building located in Blacksburg, the solar collection system can supply an average of 85% of the building's heating and hot water requirements through out the year. In the case of the building located in Minneapolis, the solar collection system can supply an average of 56% of the building's heating and hot water requirements through out the year given no night time window insulation and using similar insulation thicknesses for both cases.
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    Land Leveling Using Optimal Earthmoving Vehicle Routing
    McInvale, Howard D. (Virginia Tech, 2002-04-22)
    This thesis presents new solution approaches for land leveling, using optimal earthmoving vehicle routing. It addresses the Shortest Route Cut and Fill Problem (SRCFP) developed by Henderson, Vaughan, Wakefield and Jacobson [2000]. The SRCFP is a discrete optimization search problem, proven to be NP-hard. The SRCFP describes the process of reshaping terrain through a series of cuts and fills. This process is commonly done when leveling land for building homes, parking lots, etc. The model used to represent this natural system is a variation of the Traveling Salesman Problem. The model is designed to limit the time needed to operate expensive, earthmoving vehicles. The model finds a vehicle route that minimizes the total time required to travel between cut and fill locations while leveling the site. An optimal route is a route requiring the least amount of travel time for an individual earthmoving vehicle. This research addresses the SRCFP by evaluating minimum function values across an unknown response surface. The result is a cost estimating strategy that provides construction planners a strategy for contouring terrain as cheaply as possible. Other applications of this research include rapid runway repair, and robotic vehicle routing.
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    Modernizing bridge safety inspection with process improvement and digital assistance
    Mills, Thomas H.; Wakefield, Ronald R. (Virginia Center for Transportation Innovation and Research, 2004-01)
    This research effort was developed to record and analyze the Virginia Department of Transportation (VDOT) bridge/structure inspection processes as an aid to modernizing and automating these inspection processes through the use of mobile personal computer (PC) devices such as Palm/PPCs and other wearable computing devices. The research was conducted using an informal conversational interview process coupled with direct observations to match the perceived processes with actual processes. Once the interviews and observations were completed, workflows were mapped and analyzed for operational bottlenecks and process improvement opportunities. The results of the mappings and a comprehensive literature review were used to analyze the existing work processes. New process transformation maps were created and overlaid on current mappings to complete a transformation model. Redundancies were observed in the reporting function, and bottlenecks were identified within the inspection management and inspection functions. The research also indicates that the inspection process is readily transformable from one that relies on marking up paper reports in the field and then returning to the office for semi-manual reporting to one that is electronically assisted in areas of data capture, automated bridge inventory updates, and semi-automated report production. From this analysis a series of strategies and recommendations were made to assist VDOT in modernizing and transforming their current bridge inspection processes to more efficient digitally assisted processes.
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    A Virtual Construction Environment (VCE) for Macro Planning
    Waly, Ahmed Fathi (Virginia Tech, 2001-06-12)
    Macro Planning of construction projects is among the most challenging tasks faced by the project team. Decisions made during this process have a tremendous impact on the successful execution of the project from its early conceptual phases, through the project construction and completion. For a large majority of construction projects, the current planning practices remain manually based. General and project specific data are communicated among project participants through design drawings in a 2D paper-based format. Due to the interdependence between the different elements and the large amount of information that needs to be manually processed, the current manual implementation approach is very difficult to undertake, and imposes a heavy burden on the project team to carry out the planning process. Various research efforts have been undertaken in an attempt to capture current planning techniques and allow for the development of new innovative and automated ways in planning. The developed planning systems are characterized as responsive decision systems, relying mainly on programmed knowledge and heuristics for decision making, hence reducing or eliminating the role of the human planner. This research presents the framework for a new interactive planning environment called the Virtual Construction Environment (VCE) that supports the thinking process of the project team during the macro planning phase of design-build projects. Unlike previous responsive-type systems developed, the approach utilized in the VCE is supportive to the project team enabling them to be an active participant in the decision making process. The main purpose of the VCE is to assist the project team during decision making, by providing pertinent information necessary for making appropriate decisions in a structured format. This information may be organized, stored, and retrieved by the project team whenever needed during the virtual sessions. The VCE also provides the project team with appropriate tools to test different work execution and site layout planning scenarios early during project development. During the virtual sessions, the project team reconstructs the facility by bringing graphical elements together. The project team's movements and interactions are recorded to capture their thinking process on how to construct the facility (i.e. sequence of major assemblies). Other project participants can retrieve recorded decisions for further review or modification. The project team is also able to specify construction methods, and allocate resources required for the implementation of major assemblies. The VCE guides the project team to perform these interdependent planning functions interactively and concurrently. Using system graphical libraries, major equipment and temporary facilities can be superimposed and displayed as graphical objects for site layout planning. This enables the project team to visually check for space and accessibility conflicts during different virtual construction time intervals. In order to define required information in the VCE, the author has developed a MAcro Planning Information Classification (MAPIC) model under which information required for macro planning decision making could be classified and organized in a structured standardized format. The project team may then retrieve and utilize this information whenever needed during the virtual sessions. A prototype computer tool is developed to illustrate the framework of the VCE. The computer prototype is implemented using available commercial software tools.
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    VITASCOPE: Extensible and Scalable 3D Visualization of Simulated Construction Operations
    Kamat, Vineet Rajendra (Virginia Tech, 2003-04-14)
    In the domain of operations design and analysis, the ability to see a 3D animation of processes that have been simulated allows for three very important things: 1) The developer of a simulation model can ascertain that there are no errors in the coding (Verification); 2) The experts, field personnel, and decision makers can discover differences between the way they understand the operation and the way the model developer understands it (Validation); and 3) A model can be communicated effectively which, coupled with verification and validation, makes it "credible" and thus used in making decisions. In the case of simulated construction operations, the existent body of knowledge and understanding did not generally permit modeled processes to be accurately visualized in 3D. The purpose of this research was to remedy this situation and find methods of describing animated 3D worlds that show how construction operations modeled using Discrete-Event Simulation were/can be carried out, using simple text statements and references to 3D CAD drawings. The fundamental question the work addressed was how to achieve accurate, dynamic, smooth, and continuous 3D animation of arbitrarily-complex simulated construction processes, based on meager pieces of operational information that can only be communicated when discrete events occur in simulation runs. The end result of this effort is VITASCOPE, an acronym for VIsualizaTion of Simulated Construction OPErations. VITASCOPE is a simple, parametric-text animation description language that is meant to be written out by end-user programmable software such as discrete-event simulation tools. Sequential instructions written in this language allow a computer to create a 3D virtual world that is accurate in time, space, and appearance; and that shows people, machines, and materials interacting as they build constructed facilities.