PepsiAmericas used simulation animation to check the operation of a new pallet line at its plant in Austin, Indiana, before it was built. Using Rockwell Software Arena simulation software, PepsiAmericas created an initial design concept prior to installation. The company then used the Arena software to calculate the many variables that can occur in the process during production. The animation allowed engineers to view and manipulate the system under a variety of conditions. The team was able to run the model with different scenarios using production variables such as flow rates, product volume and conveyor speeds. With each scenario, the team could evaluate system efficiency based on the output from the Arena software.
“We find the most value for dynamic simulation in training,” says Alex Johnson of Invensys. “We can run what looks like a real plant for the operators, inject faults, speed ups, slow downs, and then do an instant replay to show them what went wrong.” It also works during startup. “If we can convince a client to use Sim-Sci dynamic simulations, we can dramatically shorten startup times,” Johnson says. “It’s a good way to discover that equipment isn’t hooked up correctly, because the process doesn’t respond the way it should. We often find valves that are plumbed or connected incorrectly.”
Honeywell's UniSim Operations can do this now, says Stevenson. “With UniSim Operations, a duplicate of the operator control console used in the plant can be interface to the dynamic simulation,” he explains. “The operator can interact with the dynamic simulation just as if it were the real plant, getting realistic process responses to control actions.”
Many of the more important processes are too slow to run in real time says Greg McMillan, principal consultant, Emerson Process Management. “Distillation columns take hours or days to line out, most chemical batches take hours to complete, and many biochemical reactor batches take days to weeks to complete,” he explains. “A cell culture bioreactor’s cycle time typically ranges from 10 to 20 days. My simulations of bioreactors embedded in a DCS to create a virtual plant can run 1000x real time so these batches take 15 to 30 minutes. The user can change parameters as the simulation progresses, and stop and restore runs in DeltaV SimulatePro to create a true interactive environment. Another powerful feature involves the fast playback—10,000x real time or more depending upon data density and data processing capability—of scenarios produced by models already running faster than real time.” Existing plant data can also be played back at high speeds for data analytics and diagnostics.
“Dynamic system simulation requires more sophisticated models, but yield much more information,” says Javier Gutierrez, product marketing manager, National Instruments. “Another vector to consider is how the simulation is going to be executed: offline, where the system is fed with all the inputs and all the results collected for analysis; and online, where the execution of the simulation is done in real time--similar to videogames. We found that real-time simulation is one of the most appealing for new areas, as it allows training operators and changing design parameters on the fly to quickly experiment with parameters.”
Samsung Techwin, Seoul, Korea, used LabVIEW dynamic simulation, to develop gas turbine engine controllers. “By mathematically modeling the gas turbine engine, we were able to calculate the engine performance parameters,” says Moon Sohk Chae, at Samsung’s Power System Research Center. “We then converted those results into actual physical signals that we input and output to the gas turbine engine controller. Through trial and error, we tested the engine controller hardware and algorithm, improving reliability, reducing debugging and calibration time, and helping us prevent unanticipated controller malfunctions.”
The simulator has a virtual engine simulator, gas turbine engine controller, control algorithm, and a simulation server for the operator interface. “Using the simulator server program, the user can perform such user interface tasks as temporary engine status modification, simulation setting modification, simulation start, pause, and exit, and ultimate engine status setting,” notes Moon Sohk Chae.
“One of the most interesting features of online simulation is the capability to easily replace the simulated system with the real one,” notes Gutierrez. In a simulation of a helicopter control system, engineers used LabVIEW to solve a problem with three interacting PID controllers. “Finding the right system gain is a real time-consuming problem,” says David Whatley, CompactRIO software group manager. What they did was to monitor the responses of a real helicopter, put the data into the simulator, created a model, and ran tests. The simulated control had ten times better response than the helicopter’s standard control system, and the final control algorithms in the simulator could be loaded directly into the helicopter controller. The video (www.controlglobal.com/0810_SimHeli.html) explains how this was done.
“Simulation for training has the greatest need for virtual world modeling,” says Buckbee. “In fact, multi-player role-playing scenarios are now being used to train operating teams for nuclear reactors. The ability to create scenarios and characters on top of a high-fidelity real-time model allows operators to train quickly and to practice for abnormal situations. Such simulations are already in use in many plants and industries. Static and dynamic models are used to predict the effect of changes. Many chemical companies have fairly complete process model simulations.”
Running Simulations against Live Data
Suppose you could do a “what if?” while you were running the plant. “What if we took pump P163 down for emergency maintenance, and routed the piping through valves V234 and V567? What would that do to the process?” If you could run such a simulation, it would tell you what the outcome might be before you made the physical change. This, of course, requires plugging all the current, real-time process conditions into a simulator and running it in “faster than real time” to see.