"Virtual Reality Helps Convert Fluid Analysis Results into Solutions," ME Online Web Exclusive, July 22, 2003

for 7/22/03

Virtual Reality Helps Convert Fluid Analysis Results into Solutions

Even people who are familiar with interpreting analysis results can gain insights that make it possible to understand the root causes of observed problems and plan design changes in much less time.

by Kenneth M. Bryden, Ph.D.

Virtual reality is beginning to have a major impact on engineering design by streamlining the process of converting analysis results into design solutions.

Today, the use of fluid flow analysis to solve design problems is slowed by the fact that the person performing the analysis often is not an expert on the design issues involved, while the engineers and customers who know the design best often have difficulty interpreting fluid flow results.

Virtual reality can overcome this problem by creating a computer-generated world in which people who are not analysis experts can see the results in a context that they can easily understand. Even people who are familiar with interpreting analysis results can gain insights that make it possible to understand the root causes of observed problems and plan design changes in much less time.

Computational fluid dynamics (CFD) is a powerful tool that can be used to provide fluid velocity, temperature, and other relevant variables throughout the solution domain for problems with complex geometries and boundary conditions. As part of the analysis, a researcher may change the system geometry or the boundary conditions and view the effect on fluid flow patterns, temperatures, or the distributions of other variables.

The ability of CFD to provide such complete information in much less time than would be required to build a physical prototype has made it the tool of choice for solving a wide range of design problems in the aerospace, automotive, power generation, chemical processing, and many other industries.

The most powerful CFD tools, such as FLUENT from Fluent Inc. in Lebanon, N.H., have made it possible to analyze flow problems of greater and greater complexity within industrially relevant timescales. These flow problems include multiphase flows, complex combustion-related phenomena, intricate equipment geometries, and detailed, chemically reacting flows.

Frontiers in fluid flow and heat and mass transfer applications are regularly rolled back, and problems that were inconceivable just a few years ago are now being solved. The question being asked now is not "What is CFD and how can it be used?" but "Why isn't CFD being applied to various flow problems?" It is precisely for these reasons that the technical benefits to engineers and the financial benefits to managers are driving the phenomenal rise in the use of CFD, a trend that shows no sign of abating in the foreseeable future.

Top view flow through a reaction chamber.

But traditional CFD post-processing software requires the user to interact with an analytical layer focused on how to manipulate model geometry relative to a fixed user position. This layer discourages discovery, as the analyst relies on pre-knowledge to select views that show her/him what she/he expects to see.

For the most part, the results are presented in the form of isometric views incorporating 2-D section cuts and the analyst, who determines which section cuts are to be presented, is not often the best person to determine which ones are most important. Yet the expert in the design or process, who is best suited to explore the analysis results, is often locked out by a user interface that prevents him from exploring anything other than the specific views of the data that he is presented with.

This obstacle can be overcome through the virtual reality experience that provides a remarkably intuitive mindset for immersing oneself in complex data and understanding the information provided. Virtual reality creates a safe and productive working environment in which to experience worlds too complex, too dangerous, not yet in existence, or otherwise impossible or impractical to explore directly. Virtual reality enables a close inspection of a component or activity whether the model is 50 meters high, as with a power boiler, or 5 mm wide, as with a channel in an electronic heat sink. The ultimate goal is to shift the user's mindset to focus purely on the problem with as little distraction as possible.

True VR applications provide a first-person perspective in which the user is a visitor who moves around freely in a stationary virtual world. Simulator-style navigation in a virtual environment makes it easy for a visitor to explore and discover unexpected but critical details about model behavior. Similarly, analytical tools and menus in a true virtual reality application need to be immersed with the visitor in the environment to maintain his or her focus on the world and to avoid distractions from the problem at hand.

A key aim of true virtual reality is to engage the human capacity for complex evaluation. A realistic visual experience activates creative, intuitive capabilities--the "mind's eye." By creating a realistic experience from a computed simulation, and maintaining the visitor's focus within that experience, the fullest potential of human thought and skill can be brought to bear on the problem.

The choice of how real to make the virtual reality experience is up to the user. Advances in affordable computing power and hardware now make fully immersive stereo cost effective and practical for routine use in many circumstances. However, the benefits of virtual reality visualization can also be achieved on more modest installations. The more "real" a virtual world appears, the less distracted the visitor will be and the more discoveries he or she might make. VR environments can take many forms.

Flow in a mixing tank showing tightly packed starting points for animated streamlines beside a baffle.

Software designed especially for visualizing CFD results is critical to the VR experience. We have had excellent results with Acuitiv visualization software from Fuel-Tech Inc., which makes it possible to gain a quick, intuitive understanding of the critical flow, pressure, temperature, and species parameters that are driving a process in a matter of minutes. This intuitive understanding makes it possible to pinpoint flow characteristics in a fraction of the time required with traditional tools. The software harnesses the power of virtual reality to convert the flow domain into a computer-generated world in which users can immerse themselves and focus on the problem and the solution not the analysis process.

A basic but very effective virtual reality experience is routinely accomplished with an ordinary, non-stereo monitor and standard desktop or workstation system. The CPU and graphics card performance on these systems now support VR visualization, where previously "high-performance" machines were a necessity. Computing power growth pushes through new milestones with predictable regularity. The recent breakthroughs in affordable high-performance graphics enable exciting new ways of handling complex and massive datasets.

Other hardware specific to the VR industry can be added to augment the virtual reality experience. The addition of an emitter and a pair of stereoscopic glasses can enhance the sense of depth and realism of the VR world for under $300. A second cost-effective addition is a "3-D input device" like the SpaceBall or SpaceMouse (from 3Dconnexion). Such a device is common in the CAD industry and allows the user to translate, rotate, and twist a ball or puck-shaped component on the device in the same way he would like to move inside the virtual world.

Flow past a valve stem and seat.

The projection of the virtual environment onto a wall is a highly cost-effective augmentation, particularly as a means to collaborate with customers. Collaborative environments amplify the human power for group problem solving and also enhance communication. Group visualization sessions allow for enhanced design creativity and further risk management. Designers can communicate visually what they have discovered and recommended to upper management for final decision-making and to customers for a greater probability of project approval and sale. Bringing the plant manager, the seasoned veteran, or the lead operator into the VR environment pays large dividends both in initial product design and final customer buy-in for the project.

Projectors for wall displays can be for mono or stereovision and use LCD or DLP technology. Companies like MechDyne Corp. provide a wide range of turnkey systems that include the projectors and single or multiple screens in flexible configurations. Projection on multiple walls results in the creation of a "VR theater," of which the CAVE (FakeSpace Systems Inc.) is a commonly recognized example. Currently, the ultimate system is the six-sided, fully immersive VR environment in which several people can interact.

Collaborative systems are also available such that people can interact in multiple environments at remote locations. There are other more specialized devices that create VR environments. Head-mounted displays, boom-mounted devices, and VR 3 - binoculars are all means by which a single user can explore a virtual world.

A tangentially fired boiler showing animated streamlines colored by velocity and isosurfaces of constant temperature.

These all work in roughly the same way. As the device is moved, whether attached to the user's head or swung to a new location by controls, the user's first-person perspective on the virtual world changes accordingly. The VisionStation (elumens), the ImmersaDesk (FakeSpace), and other devices present multi-user opportunities in a "station" format for an enhanced virtual reality experience. Other SE/VR resources include Head Mounted Displays (HMDs), a Barco Baron stereo workbench, and access to an auditorium equipped for passive stereo-projection of one or multiple simulated environments on a 36-foot wide screen.

Companies that want to obtain the ultimate VR experience can work with facilities such as the one at Iowa State that provides a wide range of computing resources and a wide variety of interface devices such as the C6 (a 10-foot x 10-foot x 10-foot room with six display screens) and the C4-flex (a 12-foot x 12-foot x 9-foot room with four display screens that can also be configured as a 36-foot x 9-foot video display wall) where the user is immersed in real time stereo 3-D image projections and full surround audio.

Virtual reality-based engineering is emerging as a key technology to support scientific and industrial advancements in the 21st century. No other technology offers more potential for perfecting processes, improving products, reducing design-to-manufacturing cycle time, and reducing overall development costs. Without a powerful visualization tool, it is often difficult to recognize the existence of problems or inefficiencies. The virtual reality approach makes it possible to gain a quick, intuitive understanding of the critical flow, pressure, temperature, and species parameters that are driving a process in a matter of minutes. This intuitive understanding makes it possible to understand problem spots or optimize new designs in a fraction of the time required with traditional tools.

Kenneth M. Bryden, Ph.D. is an assistant professor in the Department of Mechanical Engineering at Iowa State University Ames, Iowa