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Author: search.filters.author.Wang, WC

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    Model for evaluating networks under correlated uncertainty - NETCOR
    (2000-11-01)
    Wang, WC
    ;
    Demsetz, LA
    ;
    土木工程學系
    ;
    Department of Civil Engineering
    Construction activities are often influenced by factors such as weather, labor, and site conditions. When several activities are influenced by the same factor, their durations may be correlated. If many activities along a path are correlated, the variability of path duration will increase, possibly increasing the uncertainty of completing the project by a target date. This paper presents the simulation-based model NETCOR (NETworks under CORrelated uncertainty) to evaluate schedule networks when activity durations are correlated. Based on qualitative estimates of the sensitivity of each activity to each factor, uncertainty in an activity's duration distribution (grandparent) is distributed to several factor subdistributions (parents). Each subdistribution is broken down further into a family of distributions (children), with each child corresponding to a factor condition. Correlation is captured by sampling from the same-condition child distributions for a given iteration of the simulation. NETCOR integrates the effect due to each factor at the path level. Awareness of the factors to which a path is sensitive can provide management with a better sense of what to control on each path, particularly on large projects.
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    Application example for evaluating networks considering correlation
    (2000-11-01)
    Wang, WC
    ;
    Demsetz, LA
    ;
    土木工程學系
    ;
    Department of Civil Engineering
    Current approaches to network scheduling do not consider the correlation between activity durations. When activity durations are correlated, the variability of path and project durations may be increased. High variability in a project's duration increases the uncertainty of completing the project by a target date. The model NETCOR (NETworks under CORrelated uncertainty) has been developed to evaluate schedule networks when activity durations are correlated. The NETCOR model builds upon a factor-based procedure to indirectly elicit correlation. An activity duration model disaggregates the effect of uncertainty by factors from a duration distribution (grandparent) for each activity. Correlation is captured by a child-distribution approach that further breaks down the factor-subdistribution (:parent) based on the factor conditions. This paper demonstrates the practical application of NETCOR to a current construction project. Using the same inputs, the program evaluation and review technique and several simulation analyses that do not consider correlation also are evaluated. Comparison of the results shows the significance of considering correlation in scheduling analysis.
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    Chaotic behaviors of bistable laser diodes and its application in synchronization of optical communication
    (2001-10-01)
    Wang, WC
    ;
    Hwang, TM
    ;
    Juang, C
    ;
    Juang, J
    ;
    Liu, CY
    Period-doubling routes to chaos behavior in bistable laser diodes is examined numerically, An external sinusoidal electronic drive is injected to generate chaotic light output. Phase portrait, Poincare map, bifurcation diagram, and Lyapunov exponent are then calculated to assert the existence of chaos. Furthermore, according to Pecora and Carroll's theory, a drive-response system is constructed by using the bistable laser diodes to mask the sinusoidal electronic signal with chaotic light. Synchronization can be achieved for optical simplex and duplex transmissions using bistable laser diodes. The proposed synchronization scheme between two separate chaotic systems provides a key step toward optical chaotic communication.
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    SIM-UTILITY: Model for project ceiling price determination
    (2002-01-01)
    Wang, WC
    ;
    土木工程學系
    ;
    Department of Civil Engineering
    Before considering bids submitted by competing contractors for a public procurement project, the owner should determine a project ceiling price or cost estimate to use as a reference point for evaluating the bids. A high ceiling price conflicts with the owner's interests in minimizing costs. Meanwhile, a low ceiling price can jeopardize the project if all bids exceed the ceiling price. This paper proposes a model for determining a reasonable project ceiling price. The model, called SIM-UTILITY, is based on a utility theory and facilitated by a cost simulation approach. The utility theory is applied to reflect the owner's preferences regarding the determination criteria, while the simulation approach is used to generate more objective project cost data to support execution of the utility theory. The advantages of SIM-UTILITY are proven by its successful application to three construction projects in Taiwan. A computerized SIM-UTILITY is expected to be broadly applicable to public construction projects in Taiwan.
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    Simulation-facilitated model for assessing cost correlations
    (2002-09-01)
    Wang, WC
    ;
    土木工程學系
    ;
    Department of Civil Engineering
    Project cost becomes increasingly variable if many cost items for a construction project are correlated, and this can increase the uncertainty of completing a project within a target budget. This work presents a factor based computer simulation model (COSTCOR) for evaluating project costs given correlations among cost items. Uncertainty in the total cost distribution of an item (grandparent) is transferred to several factor cost distributions (parents) according to qualitative estimates of the sensitivity of each cost item to each factor Each cost distribution is then decomposed further into a family of distributions (children; costs given factor conditions), with each child corresponding to a factor condition. Correlations are retrieved by sampling from the child distributions with the same condition for a given iteration of the simulation. COSTCOR integrates the uncertainty effects caused by each factor at the project cost level, thus making it easier for management to determine what parts of the project need to be controlled.
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    New formulations for interface problems in polar coordinates
    (2003)
    Li, ZL
    ;
    Wang, WC
    ;
    Chern, IL
    ;
    Lai, MC
    ;
    應用數學系
    In this paper, numerical methods are proposed for some interface problems in polar or Cartesian coordinates. The new methods are based on a formulation that transforms the interface problem with a nonsmooth or discontinuous solution into a problem with a smooth solution. The new formulation leads to a simple second order finite difference scheme for the partial differential equation and a new interpolation scheme for the normal derivative of the solution. In conjunction with the fast immersed interface method, a fast solver has been developed for the interface problems with a piecewise constant but a discontinuous coefficient using the new formulation in a polar coordinate system.
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    Contractor selection by the most advantageous tendering approach in Taiwan
    (2003-05-01)
    Yang, JB
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    Wang, WC
    ;
    土木工程學系
    ;
    Department of Civil Engineering
    Construction clients usually tender their projects by either the lowest bid tendering method or the A-plus-B method to find a bidder that provides the lowest cost or highest profit. However, choosing a contractor that provides assured quality by examining his construction proposals along with his bid price and bid duration will compensate for the uncertainty in the lowest bid system, while retaining the advantages of the A-plus-B method. This paper presents a novel tendering method (the Most Advantageous Tendering approach) using a practical example in Taiwan. The rationales for contractor selection of the Government Procurement Law in Taiwan are reviewed herein. Several valuable issues regarding contractor selection in this case study are also presented.
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    Automatic schedule integration for highway projects
    (2003-07-01)
    Dzeng, RJ
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    Wang, WC
    ;
    土木工程學系
    ;
    Department of Civil Engineering
    The construction of a highway/expressway, which involves a complex combination of roads, bridges, and tunnels, is generally separated into several projects. Various contractors thus execute different projects and often apply differing scheduling practices. Since all projects involved in highway construction must be completed for the highway to be useful, the management of the various projects should preferably be integrated. To assist project controllers in schedule integration, this study proposes algorithms based on standardized codes and network modules. A computer system was also designed to help contractors use these modules for scheduling, and ultimately to let project controllers combine these schedules electronically. A questionnaire survey and industry feedback revealed the potential benefits of using the proposed algorithms for generating and integrating schedules, respectively. Contractors' computation capabilities must be improved before the proposed scheduling algorithms can be fully implemented. (C) 2003 Elsevier Science B.V. All rights reserved.
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    Numerical methods for semiconductor heterostructures with band nonparabolicity
    (2003-09-01)
    Wang, WC
    ;
    Hwang, TM
    ;
    Lin, WW
    ;
    Liu, JL
    ;
    應用數學系
    This article presents numerical methods for computing bound state energies and associated wave functions of three-dimensional semiconductor heterostructures with special interest in the numerical treatment of the effect of band nonparabolicity. A nonuniform finite difference method is presented to approximate a model of a cylindrical-shaped semiconductor quantum dot embedded in another semiconductor matrix. A matrix reduction method is then proposed to dramatically reduce huge eigenvalue systems to relatively very small subsystems. Moreover, the nonparabolic band structure results in a cubic type of nonlinear eigenvalue problems for which a cubic Jacobi-Davidson method with an explicit nonequivalence deflation method are proposed to compute all the desired eigenpairs. Numerical results are given to illustrate the spectrum of energy levels and the corresponding wave functions in rather detail. (C) 2003 Elsevier B.V. All rights reserved.
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    Subcarrier multiplexing by chaotic multitone modulation
    (2003-10-01)
    Juang, C
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    Huang, ST
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    Liu, CY
    ;
    Wang, WC
    ;
    Hwang, TM
    Subcarrier multiplexing by chaotic multitone modulation is investigated. Optical chaotic light can be achieved by injecting multiple subcarriers into a self-pulsating laser diode. Synchronization between two identical chaotic systems (drive and response) can be implemented provided that the conditional Lyapunov exponents are all negative. By adding amplitude modulation (AM) signals to each subcarrier, the two systems become asymptotically synchronized. The AM signals in each subcarrier can be recovered by the introduction of a filtering process where the Lyapunov exponent of the synchronized error function matches the cutoff frequency of a first order low pass filter.