Elsevier

Automation in Construction

Volume 68, August 2016, Pages 235-248
Automation in Construction

Two-way integration of 3D visualization and discrete event simulation for modeling mobile crane movement under dynamically changing site layout

https://doi.org/10.1016/j.autcon.2016.05.013Get rights and content

Highlights

  • A framework for modeling construction site tempo-spatial behaviours using distributed simulation

  • Decoupling of 3D visualization and Discrete Event Simulation (DES) components

  • Two-way communication and synchronization between visualization and DES components

  • Pathfinding mechanism to model mobile resource movement under dynamic site layout

  • A sample case study is presented to demonstrate the feasibility of the framework.

Abstract

Construction site layout changes dynamically depending on the progress of construction activities in ways that may constrain access routes and paths of mobile resources. Discrete event simulation is a useful tool for modeling time dependent activities and resource interactions but usually cannot depict spatial changes in a natural way. This paper describes a framework for integrating 3D visualization components with discrete event simulations to model the movement of mobile cranes on industrial construction projects and facilitate tempo-spatial planning of site layout. The paper focuses on the integration approach using distributed simulation standards and spatial analysis using a dedicated visualization component with pathfinding algorithm. The A* algorithm is used in conjunction with mesh generation mechanism for developing the proposed framework. The benefits of the proposed framework emerge from taking full advantage of the geometrical and special processing strengths of the visualization component through loose coupling with simulation components. The paper describes the main components of the framework and the two-way communication mechanism between them based on distributed simulation standards. It also presents a case example of a real world project to demonstrate the proposed framework and compare the outcome to a traditional solution that uses a probability distribution to model crane travel times.

Introduction

Construction activities affect the space of construction sites over time. Therefore, models of such activities should account for the dynamic interaction between resources and space over time. The use of discrete event simulation is effective in representing construction process logic, resource interactions and uncertainty in activity durations [1], [2] but usually unable to represent construction site space utilization in an intuitive way. By comparison, 3D visualization technologies have the ability to represent space and site layouts in a natural and intuitive way, understandable by various project parties. The integration of simulation and 3D visualization in a single framework has its benefits as indicated through several publications [3], [4], [5], [6]. However, challenges and limitations exist in previous integration approaches, which constrain full utilization of 3D modeling and visualization technologies [7], [8]. In particular, feeding back results of geometry and space analysis of construction sites into simulation models at different time intervals of project execution (i.e. active participation of visualization components in simulation) is very limited. Integrating these two modeling techniques (i.e. simulation and 3D) without compromising their strengths can provide a valuable tool for dynamic planning of site space and resource mobilization throughout a project's lifecycle.

The work described in this paper uses a distributed simulation framework to integrate time-related site space (tempo-spatial) changes with simulation modeling. The framework is utilized here to model resource mobilization behaviors related to a resource's need of a certain space at a certain scheduled project time in order to perform its scheduled event. The case of heavy lift mobile cranes on industrial construction site is used to demonstrate the structure and utility of the framework. In this case the tempo-spatial behavior of these expensive resources include the need to move from one lifting location to another during the progress of the project, which in turn requires finding the shortest, obstacle-free paths under a dynamically changing site, where additional parts of the final facility are added at different time intervals.

This paper discusses the background of dynamic site space modeling and Simulation Driven Visualization (SDV) mechanisms, going through the relevant construction research related to both topics. It also discusses search algorithms, with emphasis on the A* algorithm and its use for path finding. The paper then presents the implementation of the proposed framework in the case of heavy lift mobile cranes in a real construction project.

The high cost and long time for mobilization processes of heavy resources, such as cranes, have been the subjects of many construction related studies. A stand-alone simulation system does not have the ability to neither represent site spatial changes in an intuitive way nor plan ahead for various resources' routes based on tempo-spatial interactions of those resources and the dynamically changing site layout. Accelerating this process by ascertaining the shortest mobilization path and accurately estimating its duration, considering dynamically changing site layouts, are invaluable.

Equally important, the current state of the art in simulation driven visualization models has a number of characteristics that hinder its utilization for day-to-day decision-making. It does not meet the growing complexity of construction operations and the need to integrate heterogeneous simulation, computing algorithms, and data sources in these models. These characteristics include: 1) One way data flow as existing SDV mechanisms do not allow the simulation to receive back information from the visualization; limiting the user/decision maker from evaluating or adjusting various construction processes and site layout scenarios based on the visualization output. 2) Coupling between simulation and visualization engines. This leads to compromises on the strengths of both the simulation and visualization components and decreases their reusability in day-to-day construction operations. Running the two components in parallel increases the demand on computer hardware and limits the development of highly detailed simulation and visualization models. In addition, it hinders the utilization of specially developed software for handling graphics and visualization tasks. 3) Post-processing visualization as it does not allow the user/decision-maker to interact with the simulation.

The proposed framework is based on the High Level Architecture (HLA) standards for distributed simulation with a Pathfinding Mechanism Extension (PME) to model site spaces geometry and find the shortest safe routes based on changes in these spaces. The main challenges in applying the proposed framework and the solutions developed to overcome these challenges focus mainly on: 1) establishing two-way communication and synchronization between the simulation and visualization components, enabling space and path analysis inside the visualization component, and 2) decoupling the visualization component and the simulation to take full advantage of their strength independently and exclusively.

The work thus promotes the adoption of distributed simulation by wider construction researchers, demonstrating how open communication along with separate and independent execution of the components can enable simulation developers to embed variety of algorithms within visualization components taking full advantage of their 3D object models and processing engines.

Section snippets

Research background

Researchers have used various methods to model changes in site space with time (dynamic site layout planning). The following sections summarize those research efforts to demonstrate the novelty of the approach followed in this study.

Formulating mobile resource pathfinding problem as a search problem

Search in artificial intelligence refers to an object (agent) examining different possible sequences of actions that lead to states of known values, then choosing the best sequence based on the desired search criteria. The problem is to dynamically model changes in site space throughout the project execution to achieve the goal of finding the shortest obstacle-free path when moving a mobile resource from one location to another on the current site layout. A search algorithm takes this problem

Framework for resources' site tempo-spatial planning

During the construction, there are various objects with variant geometries occupying the site spaces. These objects can be; permanent structures (for example structural elements) or temporary site facilities occupying site space as the construction proceeds. All these objects cause changes in both; the site space geometry and mobile resources paths on site. Modeling a site's spatial data in an intuitive way inside simulation and then finding the heavy lift resources' shortest safe travel paths

Two-way communication between the simulation and visualization components and framework time management

As previously stated, a major contribution of this research to the body of knowledge is that it will provide a framework necessary to enable two-way communication between simulation models and visualization components. The framework communications are done through several layers. The visualization federates reflect the simulation's object classes attributes values as they are updated by the simulation federates. These reflections are communicated between the two federates through the RTI of the

Development of mobile resource pathfinding mechanism

The pathfinding mechanism is an integration of mesh generation mechanism and A* algorithm; used to determine the shortest and obstacle-free path and its expected mobilization time. It is also utilized by the visualization component to generate depiction of the site for each resource mobilization event. Fig. 4 explains the conceptual data exchange between the simulation and visualization components during the simulation run, together with the inputs and outputs of the pathfinding mechanism.

A sample case

The following example is extracted from running the framework to simulate and visualize heavy crane mobilizations on an industrial construction project. The project represents the construction of an upgrader for crude oil. The facility is located in the industrial development of Scotford, northeast of Ft. Saskatchewan, Alberta. The Scotford Upgrader has a rated processing capacity of 355 barrels per day (56,000 m3/d) [57]. It is built using preassembled modules manufactured off-site in a

Model output evaluation

As a simplified alternative to the proposed HSV framework, simulation of travel times can be modeled using different probabilistic distributions to stochastically represent the variation in resource's traveling distance. In order to verify the effectiveness of the proposed HSV framework, a sample output after a complete run of the framework was modeled using Generalized Extreme Value Distribution. The theoretical and empirical Cumulative Distribution Functions (CDFs) were compared at a range of

Limitations and future research

Identifying the optimal pathfinding algorithm is not the focus of this research; the scope is to demonstrate the benefits of integrating decoupled engines with a show case of path planning application. The Mesh Generation Mechanism and A* algorithm implemented in this framework have their limitations when searching for the mobile resources shortest paths. Alternative path finding algorithms can replace the A* algorithm in future work and can be evaluated for efficiency and impact on overall

Conclusion

This work presents enhancements for simulation-driven visualization. It proposed a solution to model mobile crane movements under tempo-spatial changes of construction site layout that result from either project progression or relocation of temporary facilities. The enhancement integrates discrete simulation capabilities with a 3D visualization component; exploiting their capabilities for time and resource representation and analysis. Two-way communication and integration between the two

Acknowledgment

The authors would like to acknowledge the contribution of the Natural Science and Engineering Research Council of Canada (NSERC) and collaborating construction companies for their funding of this research through the Collaborative Research and Development Grant number CRDPJ 335345-05.

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