Photios G. Ioannou

General purpose simulation with stroboscope

Stroboscope is a programming language designed for the simulation of processes common to construction engineering. These processes are very complex and involve many different types of resources. As a result, Stroboscope is also an efficient and effective general purpose simulation system. The paper presents an overview of Stroboscope and illustrates how it can be used to model a complex example taken from classic simulation literature.

Graphical object-oriented discrete-event simulation system

Building graphical models and running simulations directly on the models provides an attractive way of performing simulation. Most existing network-based simulation systems use graphical models to represent real world systems; however, users have to create separate simulation input files (usually text) to run the simulation. Inconsistency and mistakes between the two representations of a model are common and difficult to detect. By using object-oriented programming, modeling elements of a simulation system can be designed as objects that combine both interactive graphics and discrete-event simulation fi,mctions. This integration provides n@ only the friendly user interface to build simulation models but also the desired direct simulation on graphical networks, COOPS is a new discrete-event simulation system that utilizes this integration concept. It is a PC-based general purpose discrete-event simulation system capable of modeling systems such as service and manufacturing systems, or construction operations. COOPS runs on computers with 386, 486 or better CPU on top of Microsoft Windows 3.0 or above. This paper presents the modeling concept of COOPS and the design that makes the integration possible.

Scalable simulation models for construction operations

Construction operations are often repetitive not only in terms of time (the same tasks are performed over and over) but also in terms of space (the same tasks are repeated at several places, such as different floors in a high-rise building). Thus, construction simulation models in general must be cyclic to represent temporal repetitions, but also scaleable to represent spatial repetitions. This paper presents the mechanisms for preprocessor replacement and automatic code generation that have been designed and implemented to facilitate the development of scaleable simulation models in STROBOSCOPE, a general-purpose discrete-event simulation system developed by the authors. A relatively complex simulation model for the vertical transportation of people serves as an example to illustrate how to develop a completely scaleable model for the operation of an elevator in a building with any number of floors.

Simulation of complex construction processes

Eight successively refined simulation models for the earthmoving operations involved in the construction of a dam provide the foundation for illustrating the ease and effectiveness of modeling complex construction processes by using STROBOSCOPE, a modern simulation system based on a programming language that follows the activity-scanning paradigm. This approach and the use of characterized resources in a stochastic environment make the typical engineering calculations for heavy equipment performance relatively easy to implement and significantly more realistic and accurate.

Below-Average Bidding Method

The low-bid method, typically used for competitive bidding in the United States, may result in a contract with a firm that submits either accidentally or deliberately an unrealistically low-bid price. Such an occurrence hurts both the owner and the contractor by promoting disputes, increased costs, and schedule delays. To address this problem, other countries have adopted bidding methods based on the average of the bids submitted. One such approach is the below-average method where the winning bid is closest to but below the average of all bids. A competitive bidding model for the below-average-bid method is presented and its merits relative to the average-bid method and the low-bid method are explored. The below-average-bid process is investigated analytically and through Monte Carlo simulation. The results of bidding models for the below-average, the average, and the low-bid methods are presented in four easy-to-use nomograms which allow contractors to determine the optimal lump-sum bid price for each method without the need for complicated analysis. A comparison of the three methods provides information and insights to help owners with the difficult choice of a suitable bidding method for the project at hand.

Scheduling system with focus on practical concerns in repetitive projects

The line of balance (LOB) method has long been used to model construction projects with repetitive units. Critics, however, indicate two major shortcomings of applying LOB in the construction industry: (1) it has not yet been adapted to numerical computation as readily as network methods; and (2) it relies on restrictive assumptions and therefore cannot treat the practical concerns concluded in this paper. To treat all the practical concerns and provide necessary calculation power, a new scheduling system is proposed: the Repetitive Scheduling Method (RSM) and its computerized implementation, Repetitive Project Planner (RP2). RSM includes necessary modelling elements (i.e. activity and relationship types) and a set of computational algorithm to calculate the start time of every activity as well as the minimum project duration. RP2 automatically calculates and generates RSM diagrams that are particularly useful in serving as a test‐bed for project managers to perform what‐if analyses for different crew utilization strategies. A real‐life pipeline project is used to demonstrate the application of RP2 and to compare that with the critical path method (CPM) and traditional LOB models.

Optimal scheduling of probabilistic repetitive projects using completed unit and genetic algorithms

In this paper we introduce the completed unit algorithm (CU-AL), a probabilistic scheduling methodology for repetitive projects. The algorithm has two main advantages, simplicity and short computational time, that facilitate and expedite its use in simulation modeling and optimization. An integration between CU-AL and genetic algorithm (GA) is established to optimize the problem of maximizing profit for repetitive projects with probabilistic activity durations. This integration between CU-AL and GA is explained in detail through an example project with 5 activities and 10 repetitive units. A simulation model for this project is developed in Stroboscope, an activity-based simulation system. The optimization is performed by ChaStrobeGA, a Stroboscope add-on using genetic algorithm to optimize the overall objective function of project profit. Discussion of the results provides insight into the tradeoff between maintaining and relaxing resource continuity constraints in order to maximize expected project profit.

MODELING AIRSIDE AIRPORT OPERATIONS USING GENERAL-PURPOSE, ACTIVITY-BASED, DISCRETE-EVENT SIMULATION TOOLS

The application of activity-based simulation techniques to model runway operations at airports is described. The simulation tool used, STROBOSCOPE, is a discrete-event simulation system and programming language based on the three-phase activity scanning simulation paradigm. The model developed can be used as a tool to estimate runway capacity, delays, and double runway occupancy instances.

Evaluation of General-Purpose Construction Simulation and Visualization tools for Modeling and Animating AirSide Airport Operations

This paper illustrates how simulation modeling and visualization can be of substantial help in studying airside airport operations, and can greatly contribute in planning and designing construction operations at airports in a way that has the least impact on airside operations. The characteristic that distinguishes the current work is the capability to model and animate airside airport operations with high fidelity using general purpose discrete event simulation and visualization tools typically used to model and animate construction operations. The focus of the presented work is on evaluating the capabilities of state-of-the-art construction simulation and visualization tools in being able to accurately model and animate airside airport operations. The paper presents the simulation model and 3D animation of the airside operations at Detroit Metropolitan Wayne County Airport (DTW) in Romulus, Michigan. It also presents simultaneous modeling and visualization of operations in two different domains (i.e. airside operations and construction). The solution to the problem is described in detail using a simulation model developed in STROBOSCOPE and a 3D animation created using VITASCOPE. The obtained results highlight and prove that general-purpose tools, even if originally designed for specific domains, can be effective in studying operations involving the interaction of entities in multiple domains such as construction and airport operations.

Sequence step algorithm for continuous resource utilization in probabilistic repetitive projects

The sequence step algorithm addresses for the first time the problem of scheduling repetitive projects with probabilistic activity durations while maintaining continuous resource utilization. This algorithm is based on generalized concepts that can be implemented in most general-purpose simulation systems. The algorithm is presented in detail and is applied to an example project with 7 activities and 4 repetitive units using a simulation model developed in stroboscope, an activity-based simulation system. Numerical and graphical results help explain the algorithm and provide insight into the underlying tradeoff problem between reducing the expected crew idle time and increasing the expected project duration