How a process simulator and a rule-based system contribute to virtual reality applications for process safety

摘要

The VIRTHUALIS project aims to develop a number of virtual reality applications for improving safety in the process industries. The applications allow human factors experts to study how operators interact with plant, and provide a safe environment in which new safety actions can be tried and tested. Safety applications are built on the SafeVR technology platform, a distributed clientserver virtual reality system. This paper describes how two external modules - a process simulator and a rule-based system - are interfaced to the platform and the benefits they provide both separately and together. The two modules communicate with the platform’s server by exchanging messages, conforming to a simple syntax. pSimProxy provides a generic interface to an external process simulator, which in turn delivers the realistic plant behaviour. It handles bidirectional data exchange with and control of the external simulator. It can be configured at run time to use whichever available mechanisms are supported by the actual process simulator that models the plant being simulated. ClipsClient is an expert or rule-based system, based on NASA’s CLIPS expert system software that can make inferences about the information contained in the messages. It consists of a set of facts, a number of rules and an inference engine. It can be provided with a number of rules that monitor how operators are running the plant, and react in useful ways to these events. The simulator notifies the server of changes in process parameters through a message. The values may be displayed, for example as gauge readings, in the virtual environment. As operators control the plant, their actions, say opening a valve, are also reported by messages via the server to the process simulation. Messages can also be read by the rule-based system, allowing it to maintain its own representation of the plant. This in turn permits automated expert reasoning on the state of the plant and the actions of its operators which can cause further message to be sent to the server. The rule-based system is therefore, a powerful mechanism for rapidly reconfiguring the application and general rules can be written that only require new facts at run-time to change the behaviour of the entire virtual environment. The message syntaxes, the system architecture and the interfacing of the external modules are described along with examples showing their individual and joint benefits.