Discrete-Event Simulation-Based Virtual Reality Environments for Construction Operations: Technology Introduction

The next logical evolution of discrete-event simulation (DES) technology for construction is for simulations and animations to run concurrently and in a manner that allows interaction with the animation to affect the course of events in the simulation. This effectively enables the creation of virtual environments with logic based on DES models, something that recent research efforts have made possible. This paper introduces this technology with the help of a case study. In particular, the paper presents how interactivity can improve the process of model validation in simulation studies, which is a critical step in achieving model credibility. Via a complex earthmoving operation, a construction engineer can use real-time interactivity to create situations of interest and study the model’s response to those, and thus validate that the response is appropriate. These capabilities can significantly enhance the process of model validation, thereby adding to the value of DES for practical use in operations planning and design.     

Dynamic 3D Visualization of Articulated Construction Equipment

Dynamic three-dimensional (3D) animation can be of significant value in improving the verification validation, and communication of discrete-event simulation (DES) models of construction operations, which in turn can make the models more credible and thus useful in operations planning and decision making. This paper presents research that led to the design and implementation of practical 3D animation methods to visualize multiply-articulated construction equipment in 3D animations of simulated construction operations. Using principles of forward and inverse kinematics, the writers designed and implemented generic virtual pieces of articulated construction equipment that accept task-level instructions from external software processes. DES models can configure and instantiate specific pieces of such equipment and instruct them to perform construction tasks using simple parametric text statements that embody a construction work-like terminology. Once instructed to perform specific tasks (e.g., load soil), these “smart” pieces of equipment (e.g., backhoes) automatically decipher the sequence and amplitudes of the elemental motions their components (e.g., boom, stick) must undergo to accomplish those tasks. The animation methods are implemented in a software tool called KineMach that integrates as an add-on with the VITASCOPE visualization system.     

Iconic Animation for Activity-based Construction Simulation

This paper discusses the development of an animation tool for the activity-based construction (ABC) modeling and simulation system. The tool uses an activity-based network diagram, i.e., ABC simulation model, as the animation background image, and uses precreated two-dimensional (2D) iconic images for simulation entities (e.g., resources). The animation process displays the queuing status and dynamic movements of 2D iconic images on the background. It also distinguishes active and idle states of resources and activities. Dynamic reports are available for selected activities with graphs including the production rate and utilization of involved resources. From visualizing the change of status of a simulation process and dynamic interaction between simulation entities in the process, the user can better understand the dynamic nature of the construction process. Animation provides an avenue to demonstrate how dynamic operations are simulated. It also provides an effective tool for the user to verify a simulation model and to validate the obtained simulation results. Compared to other systems, the ABC animation does not require any extra effort in addition to the ABC simulation model constructed for simulation purposes. Therefore, the presented technology greatly reduces the time and cost for achieving animation. A variety of useful information can be observed through animation, and is illustrated using two construction examples.     

Constructing a Complex Precast Tilt-Up-Panel Structure Utilizing an Optimization Model, 3D CAD, and Animation

This paper presents the concept used to construct a complex residential tilt-up-panel structure utilizing three-dimensional (3D) modeling and animations. The residence comprises of 108 precast concrete panels of varying rectangular shapes with “dog legs” and window and door “cutouts” that look like an assembled jigsaw puzzle. The erection and installation procedure called for a maximum panel-to-panel joint tolerance of 1.27?cm (0.5?in.), often in 90° joints between panels. 3D animations were used to experiment with the construction process on the computer screen prior to construction in order to avoid potential costly on-site errors. In addition, the 3D animations were also used as a training tool for the contractors. This paper focuses on describing the methodology used to integrate a crane selection algorithm and optimization model with 3D modeling and animation for the selection, utilization, and location of cranes on construction sites. Analytical optimization processes were used to decrease the traveling time and distance of the selected crane, to improve the crane lifting sequence and to minimize the use of panel casting slabs.     

Simplified Discrete-Event Simulation Approach for Construction Simulation

The methodology of discrete-event simulation provides a promising alternative solution to designing and analyzing dynamic, complicated, and interactive construction systems. In this paper, an attempt is made to extend the previous work of simplifying construction simulation by delving into the fundamental approaches for discrete-event simulation. A new simplified discrete-event simulation approach (SDESA) is presented through extracting the constructive features from the existing event/activity-based simulation methods; both the algorithm and the model structure of simulation are streamlined such that simulating construction systems is made as easy as applying the critical path method (CPM). Two applications based on real road construction projects in Hong Kong serve as case studies to illustrate the methodology of simulation modeling with SDESA and reveal the simplicity and effectiveness of SDESA in modeling complex construction systems and achieving the preset objectives of such modeling. They are a granular base-course construction system featuring both cyclic and linear processes and an asphalt paving construction system with complicated technological/logical constraints. As a general-purpose method for construction planning, SDESA enables practitioners to deal with what the CPM-based network analysis method fails to solve by offering discrete-event simulation capabilities. Furthermore, the SDESA can potentially be adapted to special-purpose simulation tools to tackle large and complicated construction systems of practical size that have yet to find convenient solutions with existing simulation methods.     

Materials Handling System Simulation in Precast Viaduct Construction: Modeling, Analysis, and Implementation

The interactive, complicated system environment of a construction site renders conventional site layout planning and scheduling techniques to be inadequate in coping with materials handling system design in construction. In this paper, we present a university-industry joint endeavor for improving the effectiveness of the materials handling system on a precast viaduct construction project in Hong Kong by implementing the simplified discrete-event simulation approach (SDESA) along with its computer platform resulting from recent research. How to apply the simulation methodology of SDESA is elaborated step by step. Particular emphasis is placed on procedures of establishing a simulation model, validation of the simulation model, design of simulation experiments, and analysis of simulation results. With process flowchart, site layout plan, and process animation produced in a view-centric simulation environment, it is straightforward to establish, validate, and communicate the operations simulation. The research team convinced the project director, as well as field managers, of the functionality and effectiveness of operations simulation. The knowledge derived from simulation added to experiences of site managers in materials handling system design. With the aid of simulation, even junior engineers would be capable and confident to draw up an actionable construction plan that would lead to enhancement of cost effectiveness and productivity in the field.     

General-Purpose Systems for Effective Construction Simulation

This paper examines the characteristics of discrete-event simulation systems in terms of their application breadth (general or special purpose), modeling paradigm (process interaction versus activity scanning), and flexibility (programmable or not). Several construction simulation systems are examined with primary emphasis on CYCLONE and STROBOSCOPE as representatives of the wide range of tools that are currently available. CYCLONE is a well-established, widely used, and simple system that is easy to learn and effective for modeling many simple construction operations. STROBOSCOPE is a programmable and extensible simulation system designed for modeling complex construction operations in detail and for the development of special-purpose simulation tools. The characteristics of these systems, as well as other recent developments, illustrate that an effective general-purpose simulation tool for construction is in essence one based on extended forms of activity cycle diagrams and the activity scanning modeling paradigm. As explained through several examples, these representations are indeed the most convenient and intuitive for construction simulation systems. Furthermore, the programmability of such a system is the principal factor that determines its power, flexibility, and ease of learning and use.     

Dynamic Three-Dimensional Visualization of Fluid Construction Materials

The presented work extends the state-of-the-art of visualizing discrete-event construction simulations in three dimensions (3D). Efficient methods are presented along with a tool, ParticleWorks, that can be used to animate simulated construction processes that involve unstructured, fluid construction materials as resources or byproducts. Common construction processes that involve such fluid materials include placing concrete, dumping dirt, shotcreting, sandblasting, dewatering, water distribution, and inserting slurry. The writers capitalize on a classical computer graphics concept called particle systems to design simple, simulation model-authorable, parametric-text methods that can describe arbitrary volumes of dynamic fluid construction materials in animated 3D virtual construction worlds. These methods can be used to instrument discrete-event simulation models (or other external authoring interfaces) to automatically generate dynamic visualizations of any modeled construction operations that commonly handle and process fluid construction materials.     

Modeling Time-Constraints in Construction Operations through Simulation

Construction operations often face time constraints that influence the execution of activities, which are not addressed enough when modeling through general discrete-event simulation. This paper describes a simulation-based methodology to handle the time constraints including the cyclical break, preemption, and overtime use. In consideration of the variable number of breaks or variable break duration for different activities, an algorithm to determine the execution of the time-constrained activities is proposed, in which the concepts of time cycle and time window are introduced. The proposed algorithm is incorporated with an activity scanning simulation strategy to develop a construction simulation for modeling the time-constrained construction operations. Some examples are presented to illustrate and validate the algorithm, and highlight the effectiveness of the developed construction simulation. The study provides an alternative to improve construction simulation in modeling of the time-constrained construction operations and is expected to assist researchers or practitioners at analyzing or planning construction operations.     

Research in Visualization Techniques for Field Construction

Field construction can be planned, monitored, and controlled at two distinct levels: (1)?the activity or schedule level; and (2)?the operation or process level. Graphical three-dimensional (3D) visualization can serve as an effective communication method at both levels. Many research efforts in visualizing construction are rooted in scheduling. They typically involve linking activity-based construction schedules and 3D computer-aided design (CAD) models of facilities to describe discretely evolving construction product visualizations (often referred to as four-dimensional CAD). The focus is on communicating what components are built where and when, with the intention of studying the optimal activity sequence, spatial, and temporal interferences. The construction processes or operations actually involved in building the components are usually implied. A second approach in visualizing construction is rooted in discrete-event simulation that, in addition to visualizing evolving construction products, also concerns the visualization of the operations and processes that are performed in building them. In addition to what is built where and when, the approach communicates who builds it and how by depicting the interaction between involved machines, resources, and materials. This paper introduces the two approaches and describes the differences in concept, form, and content between activity level and operations level construction visualization. An example of a structural steel framing operation is presented to elucidate the comparison. This work was originally published in the proceedings of the 2002 IEEE Winter Simulation Conference. This paper expands on the original work by describing recent advances in both activity and operations level construction visualization.     

Automated Collection of Mixer Truck Operations Data in Highly Dense Urban Areas

Our research has investigated the feasibility of directly sourcing autonomous operations data from a construction-vehicle positioning system, so as to enable productivity analysis and simulation modeling in the practical context of ready mixed concrete production and delivery. In this paper, we first review research efforts related to applying radio frequency identification tags and global positioning system for tracking construction resources and acquiring operations data in the field. We then describe the technical design and system components of an automated data collection (ADC) solution to accumulating concrete delivery operations data, which is extended from a construction-vehicle positioning system tailored for highly dense urban areas. We further elaborate on how our ADC system captures, transforms, and analyzes data of mixer truck operations. Truck-tracking experiment results based on field trials are presented to demonstrate the usefulness of data sourced from our ADC system with respect to: (1) analyzing truck-waiting time versus truck-unloading time on site; and (2) predicting truck’s plant-to-site travel time. In conclusion, the ADC solution resulting from this research not only allows sophisticated analysis of mixer truck resource utilization at concreting sites situated in highly dense urban areas, but also provides an accumulation of input data that will enable concrete plant operations simulation modeling.     

RISim: Resource-Interacted Simulation Modeling in Construction

Discrete-event simulation is an effective approach to analyze construction operations. However, it is usually time-consuming and knowledge demanding to develop a practical simulation model, and thus not cost-effective due to the uniqueness and relatively short life of construction projects. The capability of discrete-event simulation modeling has not been popularly recognized by site managers until recently. A clear and explicit solution is to simplify and speed up the model development cycle, so as to enable users without much knowledge of simulation technology to easily generate a model in a relatively short period of time. In this paper, a resource-interacted simulation (RISim) modeling approach is presented, which adopts a resource oriented methodology to promote an intuitive feel to simulation modeling. In RISim, an operation is modeled in two abstraction levels—namely, the resource level and process level. An operation is viewed as a collection of resources and their interactions. Complex resources and simple resources are used to respectively represent resources with or without their own processes. The operation logic is mainly represented with internal complex resource flows, which are integrated by simple resource flows between complex resources. Resource flows can be easily conceived by site managers, enabling them to build up the logic naturally and simply. A resource library is used to implement resource reusability. Finally, an example in concrete delivery operation illustrates the methodology of resource-interacted simulation modeling and its potential for “plug-in and simulate.”     

Automated Generation of Operations Level Construction Animations in Outdoor Augmented Reality

Three-dimensional (3D) visualization is an effective tool for communicating, verifying, and validating the results of a simulated operation. Traditional visualization tools used for this purpose are typically based on the paradigm of virtual reality. Augmented reality (AR) is a relatively newer visualization paradigm whose engineering applications have been explored by a limited number of researchers. In this paper, the problem of generating smooth and continuous AR animations from the results of running discrete event simulation models and a general purpose methodology to overcome this challenge are discussed. The structure of an AR animation authoring language developed by the writers to create a logical link between a running simulation model and its corresponding 3D visualization in AR is described. In order to validate the functionality and effectiveness of the designed methods and animation language, an AR-based visualization application was developed and the designed algorithms were successfully tested using different simulation scenarios of varying visual and operational complexity.     

Animation Tools for Extraterrestrial Construction

This paper explores the idea of developing space‐construction animation “tools” to facilitate extraterrestrial design and construction activities. These tools would integrate engineering operations in space. However, in order to develop such tools, it is necessary to determine their functional requirements. This involves an assessment of existing technological trends as well as an understanding of the future needs of this technology. The need for improved forms of communication between parties involved in space design and construction suggests the need for a dynamic or animated representation of the construction processes. Computer animation offers a unified approach to modeling the spatial dynamics so crucial in the planning and controlling of construction activities, and evaluation of automation models. For remotely monitored processes, simply providing critical information in an easily—and quickly—understood format could aid the space‐construction manager in anticipating interference and other critical conditions. The use of animation during remotely monitored or remotely controlled construction processes in space could significantly assist construction equipment operators.     

Activity-Based Construction (ABC) Modeling and Simulation Method

This research presents the activity-based construction (ABC) modeling and simulation method. ABC modeling (ABC-Mod) uses one single element (e.g., activity) for modeling general construction processes instead of multiple elements as required by current simulation systems. ABC simulation (ABC-Sim) executes the ABC model by manipulating activities in three stages: (1) Select activity; (2) advance simulation; and (3) release simulation entities. ABC-Mod and ABC-Sim constitute a unique simulation method, generally addressed as ABC. In summary, ABC is a general-purpose modeling and simulation method with an emphasis on construction application. Compared with existing simulation systems, it has all of the major features required for modeling and simulating the dynamic and random behaviors of a construction process. It requires no more knowledge to use than the critical path method does. Therefore, ABC is a simulation method for construction engineers and it has a potentially wide range of application in the industry.     

Geographic Information System-Based Visual Simulation Methodology and Its Application in Concrete Dam Construction Processes

System simulation has proved to be an effective tool for planning and improving the performance of a construction process in many successful case studies. However, with the aid of a three dimensional (3D) visualization system, simulation technology will be engaged to its farthest-reaching potential. This paper presents a geographic information system (GIS)-based visual simulation method, in which system simulation techniques are integrated with visualization techniques. The GIS-based visual simulation system (GVSS) was developed by the authors. The GVSS is a simulation tool offering powerful planning, visualizing, and querying capabilities that facilitate the detection of logic errors in simulation models. The software also helps to understand the comprehensively complex modeled construction process, and is capable of organizing vast amounts of spatial and nonspatial data involved in simulation. A hydroelectric project, which will take place on the Yellow River in the northwest of China, is used as an example. An optimum equipment set scheme is determined by simulating a variety of scenarios taking place under different construction conditions. Likewise, other parameters, such as the construction sequence of dam blocks, the monthly intensity of the concrete process, and the construction appearance at the middle and end of each year, are obtained. Meanwhile, the complex processes of dam construction are demonstrated dynamically using 3D animation, which provides a powerful tool for quickly and comprehensively understanding the whole construction process. The GVSS has proven to be a helpful and useful tool for the design and management of concrete dams.     

Clinical significance of natural killing activity in patients with advanced lymphoma

OBJECTIVE: (1) To determine which facial landmarks show the greatest movement during specific facial animations and (2) to determine the sensitivity of our instrument in using these landmarks to detect putatively abnormal facial movements. DESIGN: Movements of an array of skin-based landmarks on five healthy human subjects (2 men and 3 women; mean age, 27.6 years; range, 26 to 29 years) were observed during the execution of specific facial animations. To investigate the instrument sensitivity, we analyzed facial movements during maximal smile animations in six patients with different types of functional problems. In parallel, a panel was asked to view video recordings of the patients and to rate the degree of motor impairment. Comparisons were made between the panel scores and those of the measurement instrument. RESULTS: Specific regions of the face display movement that is representative of specific animations. During the smile animation, landmarks on the mid- and lower facial regions demonstrated the greatest movement. A similar pattern of movement was seen during the cheek puff animation, except that the infraorbital and chin regions demonstrated minimal movement. For the grimace and eye closure animations, the upper, mid-facial, and upper-lip regions exhibited the greatest movement. During eye opening, the upper and mid-facial regions, excluding the upper lip and cheek, moved the most, and during lip purse, markers on the mid- and lower face demonstrated the most movement. We used the smile-sensitive landmarks to evaluate individuals with functional impairment and found good agreement between instrument rankings based on the data from these landmarks and the panel rankings. CONCLUSION: The present method of three-dimensional tracking has the potential to detect and characterize a range of clinically significant functional deficits.     

Framework for Building Intelligent Simulation Models of Construction Operations

Modeling and analyzing construction operations using simulation techniques allows researchers to capture the uncertainty and randomness usually associated with these operations and can thus be an effective tool for analysis and improvement. However, the effort and knowledge required to build simulation models and experiment with them tend to limit the use of simulation in construction. A common recommendation for removing this obstacle found in the literature leans towards developing simulation tools that reduce model development and experimentation time on the construction engineer’s side by packaging most of the knowledge required into the tool itself. Such “intelligent” simulation modeling tools may significantly impact the way construction engineers use simulation techniques in day-to-day decision?making. This paper presents a framework that extends and formalizes this recommendation by providing the foundation for building intelligence into simulation objects. The proposed framework provides the structure necessary for building intelligence and autonomy into simulation objects and permits a further reduction in the knowledge required to experiment with simulation models. This approach also automates model modification, not only through changes in numeric parameters, but through topological model changes as well, which may assist the model user in making many decisions throughout the different phases of simulation experimentation.     

Methodology for Conducting Discrete-Event Simulation Studies in Construction Engineering and Management

This paper suggests the methodology to follow when conducting discrete-event simulation (DES) studies in construction engineering and management research. Emphasis is made on the steps that, due to the uniqueness of the construction environment, are particularly important yet are not discussed extensively in the general DES literature. Guidelines are provided to determine what aspects of a DES study demand a rigorous application of the theory depending on the purpose of the study. The paper concludes with the importance of properly understanding the probabilistic concepts upon which DES relies and on coupling this understanding with engineering judgment as a key for successful use of DES in construction research.     

Simulation-Based Identification of Possible Locations for Mobile Cranes on Construction Sites

Identifying spatial-conflict free locations of mobile cranes that could minimize delays associated with crane relocation can result in productivity and safety improvements on construction sites. Existing approaches for identifying possible crane locations are based on two-dimensional (2D) work envelopes created by reasoning about the lift capacities of a crane during operations. Since spatial conflicts related to crane operations typically occur in three dimensions and during any period of operation, representing possible crane locations based on such 2D work envelopes can result in identifying some locations as good when in fact they might result in conflicts and missing possible locations that might be feasible. This paper presents an approach that determines possible locations of mobile cranes based on discrete-event simulation of crane operations incorporating dynamic behaviors of cranes. This approach starts with identifying a search space for possible crane locations by reasoning about a reachability radius of a crane determined by crane characteristics and the weight of the load to be carried. Later, it reduces the search space through boom-line intersection tests. For the remaining locations, it checks for potential spatial conflicts between building components and cranes moving in three dimensions and across time. Validation studies show that the developed approach can accurately identify possible locations for mobile cranes that minimize the relocation of mobile cranes and avoid potential spatial conflicts.